The effects of nanometer-sized tridecameric aluminum polycation (nano-Al13) on lactate dehydrogenase (LDH) activity have been investigated using differential pulse voltammetry (DPV) at the molecular level. The effects of nano-Al13 on LDH activity at different temperature and pH values were investigated. The results showed that these factors had quite different influences. The characteristic parameters of Michaelis constant Km and maximum velocity vmax were evaluated by monitoring the DPV reduction current of NAD+ (β-nicotinamide adenine dinucleotide) and compared with the other known inhibitors of LDH. The proposed method might be hypothesized to be a simple and convenient approach to evaluate the toxic and biological effects of nanoparticles on the environment.

Theoretical modeling and analyzing of reversible electrode reaction coupled with Langmuir adsorption is presented using cyclic reciprocal derivative chronopotentiometry (CRDCP) with symmetrical programmed current applied, in which the finite difference method was firstly used to solve the boundary value problem corresponding to the electrode processes. The algorithm described in this paper is available to solve analogous difference equations with nonlinear boundary conditions. Distinct features of dt/dE–E curves for typical models of electrode processes are obtained. If the adsorption coefficients of the electroactive species are of different orders of magnitude, the predominant peak splitting of the dt/dE–E curves can be observed, corresponding to the adsorption peaks and diffusion peaks. The sequence of the diffusion and adsorption peaks can indicate the strong adsorption of either reactant or product.

The structures of core-links Al13 (C-Al13) and flat-Al13 (F-Al13) complexes in aqueous solution have been investigated using density functional theory (DFT) at the level of B3LYP/6-31G(d). The present work focuses on the following three aspects: (1) C-Al139+ was optimized with the consideration of solvent effect and the 27Al NMR chemical shifts using Hartree Fock GIAO and B3LYP GIAO methods were computed respectively; (2) the optimization of F-Al1315+ was also performed and the 27Al NMR chemical shifts were obtained using the same methods as above; (3) the structural parameters of a series of typical aluminum species (Al3+, AlOH2+, AlF2+, Al24+, Al66+, K-Al137+, C-Al139+ and F-Al1315+) were compared.

In this article we investigate the effect of monovalent cations (Li+, Na+, K+, Cs+) on self-assembly of thiol-modified double-stranded DNA (ds-DNA) and single-stranded DNA (ss-DNA) on gold electrodes. Electrochemical characteristics (surface coverage, ion penetration and charge transfer) of ds-DNA and ss-DNA self-assembled monolayers (SAMs) formed with different monovalent cations are inspected based on six important interfacial parameters including surface coverage (Γm), interfacial capacitance (C), phase angle (Φ1 Hz), ion transfer resistance (Rit*), current density difference (Δj) and charge transfer resistance (Rct) from chronocoulometry (CC), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Three sections are included: (1) Investigation of the relationships of parameters (Γm, C, Φ1 Hz, Rit*, Δj and Rct) for ds-DNA-SAMs and ss-DNA-SAMs with cation types and concentrations; (2) confirmation and explanation of our experimental results combined with our recently proposed simple DNA model and literature reports; (3) exploration of the mechanism for the orders of monovalent cations (Li+, Na+, K+, Cs+) on availing the adsorption of ds-DNA and ss-DNA molecules on gold based on their physicochemical parameters (ion size, solvation free energy and enthalpy, ion-water bond length and water exchange rate) and possible binding modes with DNA molecules. This work might provide a useful reference for understanding interactional mechanism of cations with DNA molecules.

Density functional theory (DFT) calculation is carried out to investigate the structures, 19F and 27Al NMR chemical shifts of aqueous Al−F complexes and their water-exchange reactions. The following investigations are performed in this paper: (1) the microscopic properties of typical aqueous Al−F complexes are obtained at the level of B3LYP/6-311+G**. Al—OH2 bond lengths increase with F− replacing inner-sphere H2O progressively, indicating labilizing effect of F− ligand. The Al−OH2 distance trans to fluoride is longer than other Al—OH2 distance, accounting for trans effect of F− ligand. 19F and 27Al NMR chemical shifts are calculated using GIAO method at the HF/6-311+G** level relative to F(H2O)6− and Al(H2O)63+ references, respectively. The results are consistent with available experimental values; (2) the dissociative (D) activated mechanism is observed by modeling water-exchange reaction for [Al(H2O)6-iFi](3−i)+ (i = 1−4). The activation energy barriers are found to decrease with increasing F− substitution, which is in line with experimental rate constants (kex). The log kex of AlF3(H2O)30 and AlF4(H2O)2− are predicted by three ways. The results indicate that the correlation between log kex and Al—O bond length as well as the given transmission coefficient allows experimental rate constants to be predicted, whereas the correlation between log kex and activation free energy is poor; (3) the environmental significance of this work is elucidated by the extension toward three fields, that is, polyaluminum system, monomer Al-organic system and other metal ions system with high charge-to-radius ratio.

The structures and water-exchange reactions of aqueous aluminum-oxalate complexes are investigated using density functional theory. The present work includes (1) The structures of Al(C2O4)(H2O)4+ and Al(C2O4)2(H2O)2– were optimized at the level of B3LYP/6-311+G(d,p). The geometries obtained suggest that the Al—OH2 bond lengths trans to C2O42- ligand in Al(C2O4)(H2O)4+ are much longer than the Al—OH2 bond lengths cis to C2O42-. For Al(C2O4)2(H2O)2–, the close energies between cis and trans isomers imply the coexistence in aqueous solution. The 27Al NMR and 13C NMR chemical shifts computed with the consideration of sufficient solvent effect using HF GIAO method and 6-311+G(d,p) basis set are in agreement with the experimental values available, indicating the appropriateness of the applied models; (2) The water-exchange reactions of Al(III)–oxalate complexes were simulated at the same computational level. The results show that water exchange proceeds via dissociative pathway and the activation energy barriers are sensitive to the solvent effect. The energy barriers obtained indicate that the coordinated H2O cis to C2O42- in Al(C2O4)(H2O)4+ is more labile than trans H2O. The water-exchange rate constants (kex) of trans- and cis-Al(C2O4)2(H2O)2– were estimated by four methods and their respective characteristics were explored; (3) The significance of the study on the aqueous aluminum-oxalate complexes to environmental chemistry is discussed. The influences of ubiquitous organic ligands in environment on aluminum chemistry behavior can be elucidated by extending this study to a series of Al(III)–organic system.

This paper examines the effect of five major pretreatments on the surface coverage Γm of dodecanethiol self-assembled monolayer on polycrystalline gold electrode (C12SH-SAMs-Au). It is based on the electrochemical reductive desorption in the alkaline solution by cyclic voltammetry (CV). The five different pretreatment methods include: aqua regia pretreatment, reductive annealed pretreatment, UV/O3 pretreatment, piranha reagents pretreatment and simple polishing pretreatment, and then all above pretreatments following the same procedure of electrochemistry cleaning. The experimental results show that the surface coverage Γm for C12SH-SAMs-Au by the five pretreatment methods are: aqua regia pretreatment (8.0 × 10−10 mol cm−2) ∼ reductive annealed pretreatment (7.8 × 10−10 mol cm−2) > UV/O3 pretreatment (5.0 × 10−10 mol cm−2) ∼ piranha reagents pretreatment (4.1 × 10−10 mol cm−2) ∼ simple polishing pretreatment (4.0 × 10−10 mol cm−2). This indicates that Au surfaces pretreated by aqua regia and reductive annealing can achieve the best results, and the Γm values obtained are consistent with the theoretical coverage values (Γm ≈ 8.0 × 10−10 mol cm−2); however, the Γm values for other three pretreatment methods (UV/O3, piranha reagents and simple polishing) are not satisfactory, obtaining only almost half of the theoretical Γm value. Thus, we recommend aqua regia and reductive annealed pretreatments as the best methods for self-assembling the alkyl thiol monolayer (CnSH-SAMs-Au), whereas UV/O3, piranha reagents and simple polishing pretreatments are not recommended.

In this article we studied the permeable characteristics of thiol-modified double-stranded DNA (ds-DNA) self-assembled monolayers (SAMs) on a gold substrate assembled under different NaCl concentrations by electrochemical methods. It was based on the inspection of five important parameters including interfacial capacitance (C), phase angle (Φ1Hz), ions transfer resistance (Rit*), current density difference (Δj) and electron transfer rate (ket) through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Three sections were included: (1) Investigation of the relationships of C, Φ1Hz, Rit*, Δj and ket with NaCl concentrations and comparison with the reports from literature. Experimental results showed that ds-DNA-SAMs were permeable films. (2) Construction of a simple model for exploring the permeable characteristics of ds-DNA-SAMs on gold. (3) Confirmation of the simple model by chronocoulometry (CC) and application of the model to explain the permeable mechanism. This study was significant for exploring the mechanism of electron transfer through the interior of ds-DNA duplex helix.

The interaction of monomeric aluminium and chloride ion in aqueous solution is investigated by density functional theory (DFT) calculations. The computational results show that it is difficult for Cl− to enter the inner-coordination shell of aluminium complexes by replacing the bound water molecules, independent of pH and the concentration of Cl−. However, pH and the concentration of Cl− might influence the conformations, bond lengths and natural charge populations of monomeric aluminium complexes to a given extent. Based on the computed Gibbs energies, pKa values of various hydrolysis species in the presence and absence of Cl− are evaluated, respectively. It is concluded that pKa increases with the introduction of Cl−.

The mechanisms for the substitution of an aqua ligand with F− in monomeric Al complexes were studied with density functional theory (DFT). Typical mechanisms are modeled to determine the preferred substitution pathway according to the activation energy barriers. The present computational results are in favor of interchange associative (Ia) mechanism for the substitution of F− into Al(H2O)63+, whereas interchange dissociative (Id) mechanism is preferred for the substitution into Al(H2O)5(OH)2+, which is in agreement with the previous experimental findings. This implies the mechanistic changeover from Ia to Id induced by the spectator hydroxyl ligand. Like the water-exchange reaction, the substitution rate is accelerated by OH− ligand. The difference of the computational and experimental activation enthalpy values is interpreted as the DFT errors in energy and the deviation of transmission coefficient from unity.

This paper proposed a simple hexagonal model to explore the specific structural characteristics of thiol-modified single-stranded DNA (ss-DNA) self-assembled monolayers (SAMs) on gold substrate. The calibrated gyration diameter d′gd′g (d′g=rdgd′g=rdg) was used to quantify the size of ss-DNA molecules on gold by introducing a calibrating factor r, where dg was ss-DNA gyration diameter in solution. Based on the model, the interfacial parameters of ss-DNA-SAMs on gold assembled under different ionic strength were obtained theoretically. The ss-DNA-SAMs were assembled on gold under different concentrations of CNaCl and six important electrochemical parameters were used to validate the model experimentally, which include surface coverage (Γm), interfacial capacitance (C), phase angle (Ф1 Hz), ions transfer resistance (Rit*), current density difference (Δj) and charge transfer resistance (Rct) from chronocoulometry (CC), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Three main aspects were included in this paper: (1) construction of a simple hexagonal model to describe the specific structural characteristics of ss-DNA-SAMs on gold; (2) calculation of the calibrating factor r by CC experiments and several important conclusions from the simple model; and (3) confirmation of the simple model by our experimental results and literature reports. The simple model may provide an important reference for optimizing the design of DNA sensor.

In this article we investigated the effect of solvents (CCl4, CH3CN, DMF, ethanol, ethanol–H2O and H2O) on self-assembly of Thioctic acid (TA) and Mercaptohexanol (MCH) on gold by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Electrochemical characteristics of TA and MCH self-assembled monolayers (SAMs) formed in different solvents were evaluated by inspecting the ions permeability (interfacial capacitance C and phase angle Ф1 Hz) and electron transfer capability (current density difference Δi and charge transfer resistance Rct). Experimental results indicated that the ability of solvents availing the ordering of SAMs was: for TA, CCl4 > ethanol > CH3CN > ethanol–H2O > DMF; for MCH, H2O > ethanol–H2O ≈ CCl4 > ethanol ≈ CH3CN > DMF. Through relating the C, Ф1 Hz, Δi and Rct of SAMs (TA and MCH) with parameters of solvent (polarity ETN, solubility parameter δ and octanol/water partition coefficients logPow), it was found that solvents with bigger logPow (smaller ETN and δ) availed the ordering of TA-SAMs but the effect of solvents on MCH self-assembly was complex and MCH-SAMs formed in H2O (the biggest ETN, δ and the smallest logPow) and CCl4 (the smallest ETN, δ and the biggest logPow) were more ordered than in other solvents.

Theoretical modeling and analyzing of electrode process in the presence of adsorptive reactants is presented using cyclic reciprocal derivative chronopotentiometry (CRDCP) with symmetrical programmed current applied. Electrode process proposed based on the assumption of the electrolysis sequence of diffusion and adsorbed electroactive species is described as “on first, off last” and denoted as Onfol model. The numerical simulated (dt/dE)–E waves obtained from the analytical potential-time expressions of the Onfol model present peaks during both “diffusion processes” and “adsorption processes”. Influences of maximum surface excess, adsorbed monolayer thickness, adsorption coefficient and current steps on CRDCP characteristic parameters are discussed. CRDCP behavior allows us to distinguish the form of the electroactive species contributing to the system current and electrolysis sequence can therefore be determined.

In this article we systematically investigated self-assembly of short-chain thiols of thioctic acid (TA) and mercaptohexanol (MCH) on gold under potential control, Edc (−0.4, +0.4 and +0.7 V) and compared the results obtained with open circuit potential (EOCP). Effect of Edc on thiol self-asembly was inspected based on the changes in electrochemical parameters including interfacial capacitance (C), phase angle (Φ1Hz), current density difference (Δi), charge transfer resistance (Rct) through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Experimental results showed that Edc could not obtain stable short-chain self-assembled monolayers (SAMs) (TA and MCH) in a short time. Both TA and MCH had slow self-assembly dynamics and needed a long time (> 24 h) to achieve adsorption equilibrium. Furthermore, the negative potential Edc (−0.4 V) did not facilitate the ordering of SAMs. The ordering of TA-SAMs was found to be the best when assembled under Edc (+0.4 V), whereas that of MCH-SAMs was almost the same when assembled under either EOCP or Edc (+0.4, +0.7 V). We considered that permeation of ions and water molecules perhaps dominated the slow self-assembly dynamics of short-chain thiols (TA and MCH) under Edc and mutual interaction between adjacent chains of thiols played an important role in the ordering of SAMs.

In this paper, a sensitive electrochemical approach for monitoring the effect of nano-Al2O3 on lactate dehydrogenase (LDH) activity is established. It is based on the determination of reduction current of NAD+ involved in enzyme promoting catalytic reaction of “” by differential pulse voltammetry (DPV). Various influencing factors including nano-type, nano-size, and adsorbed pollutant organics have been investigated. The experimental results show that the proposed electrochemical method is useful in monitoring and evaluating the toxic effects of nanoparticles, which might be suitable to the environmental pollutant's toxicity analysis.

Raman frequency calculations of Al(H2O)63+ and Al(OH)4- species in different models were carried out with density functional theory (DFT). Gas-phase model (GP), polarizable continuum model (PCM), supermolecule model (SM) and supermolecule-polarizable continuum model (SM-PCM) were considered and frequencies over the wavenumber range from 0 to 1000 cm−1 were discussed. The calculated frequencies of the two species in SM-PCM model are in fair agreement with the observed frequencies in aqueous solution and the average deviation is 6 cm−1. Based on the results of Al(H2O)63+ and Al(OH)4-, the DFT method and the SM-PCM model were used to study the Al–O Raman bands for some other monomeric and dimeric aluminiums. The monomeric aluminiums Al(OH)2+, Al(OH)2+ and Al(OH)63- as well as the dimer Al2O(OH)62- were included. As a result, we predict the main Al–O skeleton vibrations of Al(OH)(H2O)52+ at 685 cm−1, trans  -Al(OH)2(H2O)4+ at 542 cm−1, Al(OH)63- at 510 cm−1 and Al2O(OH)62- at 510 and 699 cm−1 respectively in Raman spectra of aqueous solution. It can also be concluded that the calculated frequencies of Al2O(OH)62- are close to the experimental values and the existence of Al(OH)63- in aluminate solution cannot be ruled out.

A simple and sensitive indirect determination method for sulfide in water samples by anodic stripping voltammetry (ASV) using mercury-film electrode (MFE) has been developed, which is based on the determination of residual cadmium ion after reaction of Cd2+ with S2−. The linear range is adjustable depending on Cd2+ concentration, for example, the determination of S2− can be achieved in the range of 1.5–7.0 × 10−6 mol L−1 by selecting 3.0 × 10−6 mol L−1 Cd2+. The detection limit is 1.3 × 10−8 mol L−1 under optimum conditions, and the relative standard deviation (RSD, n = 10) for 2.0 × 10−6 mol L−1 S2− is 0.7%. Compared with other methods, this method has the following prominent advantages: with low detection limit, easy to operate and less interference. The proposed method has been successfully applied to the determination of S2− in synthetic wastewater, lake water, beverage, spring water and real wastewater samples.

The water exchange reactions on the gibbsite surface have been investigated by density functional calculations (B3LYP/6-31G(d) level) combining the supermolecular model and PCM model in this paper, and the water exchange rate constants on the gibbsite surface have also been predicted. In the proposed reaction pathways, the clusters Al6(OH)18(H2O)60 and Al6(OH)12(H2O)126+ are used as the models of gibbsite surface and protonated gibbsite surface respectively to examine the effect of protonation of gibbsite surface on the water exchange rate constants. The activation energy barriers ΔEs≠(aq) for Al6(OH)18(H2O)60 and Al6(OH)12(H2O)126+ are 28.6 and 27.2 kJ mol−1, respectively. The reaction energies ΔEs(aq) for Al6(OH)18(H2O)60 and Al6(OH)12(H2O)126+ are 2.9 and 14.4 kJ·mol−1, respectively, indicating that hexacoordinate aluminum in the gibbsite surface is more stable. The log kTST for Al6(OH)18(H2O)60 and Al6(OH)12(H2O)126+ are 6.5 and 7.5 respectively, and the log kex calculated by the given transmission coefficient for Al6(OH)18(H2O)60 and Al6(OH)12(H2O)126+ are 2.4 and 3.4 respectively, indicating that the protonation of gibbsite surface promotes the water exchange reaction of gibbsite surface and accelerates the dissolution rate of gibbsite. The relationship between the calculated free energy and experimental rate constants was explored, and according to this relationship, the log kex for Al6(OH)18(H2O)60 and Al6(OH)12(H2O)126+ are 2.5 and 3.1 respectively, close to the corresponding values calculated by the given transmission coefficient. The water exchange rate constant of gibbsite surface is close to those of K−MAl12(M = Al, Ga, and Ge) polyoxocations, but deviates from that of Al(H2O)63+, implying that the same reactions with similar structure have similar water exchange rate constants.

Cyclic reciprocal derivative chronopotentiometry (CRDCP) with successive symmetrical programmed currents applied has been extended to describe irreversible electrode reactions where Henry adsorption occurs at the electrode/solution interface. The numerical simulated (dt/dE)–E curves are sensitive to electrode reactions coupled with adsorption processes. Effects of parameters on (dt/dE)–E curves presented in this work involve adsorption constants (KOx and KRed) and kinetic parameters (ks0 and α). Characteristic parameters of (dt/dE)–E curves depend on the adsorption strength markedly and afford effective criteria to determine different cases. The characteristic behavior of (dt/dE)–E curves with successive currents applied give distinct descriptions between two limiting cases – the “surface nature” and “diffusion character”. Comparisons are made with reversible charge transfer reaction with Henry adsorption and uncomplicated, irreversible electrode reaction.

Reaction pathways, solvent effects and energy barriers have been investigated for the dimerization of the deprotonated aquo ion of Al(III) in aqueous solution by performing supramolecule density functional theory calculations. Two competing reaction pathways were investigated, sharing a common first step and third step, i.e. the formation of the aggregate II of two aluminium monomers and the doubly bridged dimer. One pathway involves a nucleophilic attack to undercoordinated metal center in the first step and then the loss of a coordinated water molecule. Another pathway involves a water exchange reaction in the first step and then the formation of the hydroxo bridge. The calculated results indicate that both pathways I and II are possible in aqueous solution. The direct participation of the solvent water molecule facilitates the dimerization, but the extremely large solvent shifts of the energy barriers for each reaction are attributed mainly to the bulk effect. The computed activation energies for the water exchange reactions are in good agreement with the available experimental values, namely, the calculated value 37.5 kJ mol−1 compared to the experimental value 36.4 (±5) kJ mol−1. In agreement with experimental observations in aqueous solution, the calculated results favor the transformation of singly-bridged to doubly-bridged aluminium ion, which is helpful to understand the complicated hydrolytic polymerizaiton of Al(III).

Supermolecule density functional calculations were performed on the hydrolysis of aluminum(III) and prediction of pKa in aqueous solution. The optimization results showed that the most stable structures for the first, second and third hydrolysis products were hexacoordinate, hexacoordinate and pentacoordinate, respectively. The different coordination geometries could easily transform into each other due to the small energy gaps (within 2.5 kcal mol−1). The calculated value of 4.6 for the first hydrolysis constant agreed well with the experimental value of 5.0. The results from the different thermodynamic cycles have been compared, which revealed that the cycle involving the solvation of H2O and H3O+ could reasonably predict the first hydrolysis constant, while the other cycle involving the solvation of H+ acquired a fairly good correlation of the hydrolysis reaction free energies and the experimental pKa.

The water exchange reaction of the polyoxocation GeO4Al12(OH)24(H2O)128+ (K-GeAl12) in aqueous solution has been simulated by means of supermolecule density functional calculations. In the proposed dissociative pathway, the leaving water molecule in the first coordination sphere is dissociated from its coordinated aluminium, and via a transition state enters into the second coordination sphere. Our calculated results indicate that the polyoxocation K-GeAl12 exchanges water in a dissociative way with a barrier height of 37.0 kJ mol−1, and that the gas-phase model is not suitable to simulate the water exchange reaction of K-GeAl12 because of the proton-transfer reaction. The calculated results on the transmission coefficients of the water exchange reactions of K-MAl12 imply that the water exchange reactions of aluminium species with similar structures have close transmission coefficients, but the different charges of aluminium species have an important influence on the transmission coefficients, which may be the reason why K-MAl12 polyoxocations with different reactivity have nearly the same water exchange rate constants.

Reaction pathways, solvent effects and energy barriers have been investigated for the dehydration processes of aquated Al(OH)2+ species in aqueous solution by density functional calculations using a supermolecule model. The dehydration processes from Al(H2O)4(OH)2+ to Al(H2O)2(OH)2+ involve the water exchange on cis-Al(H2O)4(OH)2+ and dehydration of the following intermediate pentacoordinate Al(H2O)3(OH)2+. The calculated results indicate that cis-Al(H2O)4(OH)2+ exchanges water in a dissociative way with an activation energy of 27.7 kJ mol−1. Loss of coordinated water from hexacoordinate and pentacoordinate Al(OH)2+ is unfavourable by 22.1 and 6.6 kJ mol−1, respectively, which supports the presence of the stable hexacoordinate Al(H2O)4(OH)2+ in aqueous solution. Our results also indicate that both the explicit water molecules and bulk water molecules have great influences on the energy barriers, and they can not be neglected.

This paper reports the electrochemical behavior of lactate dehydrogenase (LDH) immobilized in the silica sol–gel film on gold electrode after adding nanometre-sized tridecameric aluminium polycation (nano-Al13, also called nanopolynuclear Al13) as a promoter. A pair of surface controlled quasi-reversible cyclic voltammetry peaks with the formal potential (E0′) of 154 mV (vs.SCE) was found in the presence of nano-Al13. A potential application of the nano-Al13-LDH electrode for the determination of resorcinol and p-xylene was also investigated. The experimental results showed that both resorcinol and p-xylene inhibited LDH activity, and the calibration ranges were 5.0 × 10−6–3.0 × 10−4 mol L−1 for resorcinol and 1.0 × 10−6–1.0 × 10−5 mol L−1 for p-xylene, respectively. The nano-Al13-LDH electrode can be anticipated to be applied to environmental toxic assessments.

Assessment of the accuracy of methods including 29 DFT methods and 2 ab initio wave function theory (WFT) methods for predicting 27Al nuclear magnetic resonance shielding tensors of aquated Al(III) species was carried out. Among all of the tested methods, HF and MP2 methods give the best performance for the calculations of chemical shifts. Among all of the DFT methods with GIAO calculations, O3LYP and MPWKCIS1K are the most accurate models for calculations of chemical shifts, followed in order by BHandHLYP, B98, B97−1, mPW1PW91, PBE1PBE, and MPW1KCIS. Among all of the DFT methods with CSGT calculations, VSXC is the best method for the prediction of chemical shifts, followed in order by TPSSh, B97−2, O3LYP, TPSS, TPSS1KCIS, MPWKCIS1K, BHandHLYP, B97−1, and B98. The popular B3LYP method overestimates largely the chemical shifts with both GIAO and CSGT methods. The calculated results indicate that the predictions of 27Al chemical shifts on the base of the model that includes both explicit solvent effect and bulk solvent effect are most accurate for aquated Al(III) species.

Through extensive and systematic reviewing of literatures, this paper presents some thoughts on the existence of ion and water channels in highly dense and well-ordered CH3-terminated alkanethiol self-assembled monolayers (CnSH-SAMs) on gold: (1) based on the combinational effect of “the van der Waals interaction between the neighbor hydrocarbon chains”, “the framework size of CnSH molecule” and “the surface lattice structure of CnSH-SAMs on gold”, a simple ideal model of the close-packed CnSH-SAMs is proposed for the first time. The channel with an appropriate diameter of about 3 Å (∼3 Å) existing in SAMs on Au is deduced, which is found large enough for ions and water molecules to permeate; (2) through summarizing the literature reports for various experiments (e.g. scan microscopy techniques and electrochemical methods, etc.), the existence of the ion and water channels (∼3 Å) in close-packed CnSH-SAMs is verified; (3) furthermore, the effect of the ions and water molecules permeation on the studies of the SAMs’ electron tunneling process is discussed. This simple ideal model of the close-packed CnSH-SAMs established by us may clarify the controversies about the permeation mechanism of ions and water molecules in CnSH-SAMs.

This paper reports the preparation of dodecanethiol self-assembled monolayers (C12SH-SAMs) on polycrystalline gold electrodes in a magnetic field. The qualities of C12SH-SAMs were characterized by both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that highly dense and well-ordered SAMs could form in a relatively short time (3 h), indicating that the rate of SAMs formation increased under an external magnetic field compared with the natural self-assembly process. Moreover, the results of CV and EIS measurements also suggested that the presence of a magnetic field had influenced the qualities of the SAMs; the stronger magnetic intensity can help to obtain much denser and well-ordered SAMs.

Supermolecule density functional calculations suggest the dissociative (D) mechanism for the water exchange of aquated Al(III) species in aqueous solution and the calculated results agree well with experimental data.

This paper reports the study of the solvent (tetrachloromethane, toluene, tetrahydrofuran, acetone, N,N-dimethylformamide, acetonitrile, ethanol, ethanol–water mixture (1:1, v:v) and neat dodecanethiol liquid) effect on the quality of self-assembled monolayers of dodecanethiol (C12SH-SAMs) on polycrystalline gold. The quality of the C12SH-SAMs was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and the results show that highly dense and well-ordered C12SH-SAMs can be prepared from ethanol–water mixture and neat dodecanethiol liquid. The property parameters of the solvents, such as polarity, solubility parameter, molecular diameter, octanol–water partition coefficients and viscosity were correlated with their ability to influence the quality of the C12SH-SAMs.

We present a novel method for the study of the aggregation of protein induced by metal ion aluminum(III) using resonance Rayleigh scattering (RRS) technique. In neutral Tris–HCl medium, the effect of this aggregation of protein results in the enhancement of RRS intensity and the relationship between the enhancement of the RRS signal and the Al concentration is nonlinear. On this basis, we established a new method for the determination of the critical induced-aggregation concentrations (CCIAC) of metal ion Al(III) inducing the protein aggregation. Our results show that many factors, such as, pH value, anions, salts, temperature and solvents have obvious effects. We also studied the extent of aggregation and structural changes using ultra-violet spectrometry, protein intrinsic fluorescence and circular dichroism to further understand the exact mechanisms of the aggregation characteristics of proteins induced by metal ion Al(III) at the molecular level, to help us to develop effective methods to investigate the toxicity of metal ion Al, and to provide theoretical and quantitative evidences for the development of appropriate treatments for neurodementia such as Parkinson's disease, Alzheimer's disease and dementia related to dialysis.

A novel method for recognition and indirect determination of AlIII by using biological molecules has been established based on the quenching of RRS intensity. In the weak acidic medium, the reaction of ethyl violet (EV) and DNA would result in great enhancement of RRS intensity. However, the presence of AlIII would lead to the decrease of the RRS intensity owing to the competition coordination of Al with DNA. The decreased intensity of RRS is directly proportional to the concentration of AlIII in the range of (0.1–2.5) × 10−6 and (0.30–4.5) × 10−5 M, respectively. The method has high sensitivity and its detection limit (3σ) is 3.6 × 10−8 M. The characteristics of RRS spectra of the system, the optimum conditions of the reaction, and the reaction mechanism have been investigated. The method can recognize AlIII selectively owing to its strong binding to the phosphate backbone of DNA, and has been applied to the determination of AlIII concentration in synthetic biological samples with satisfactory results. Therefore, the proposed method is promising as an effective means for selective recognition and sensitive determination in situ of AlIII. Furthermore, this study would contribute to further understanding of the biological significance of Al neurotoxicity.

The promotion effect of titania nanoparticles (nano-TiO2) on the direct electron transfer between lactate dehydrogenase (LDH) and the silica sol–gel modified gold electrode was investigated by adding nano-TiO2 (50 nm) in the modification process. This nano-TiO2–LDH electrode showed a pair of quasi-reversible cyclic voltammetry peaks with the formal potential of 70 mV (vs. SCE). Compared to the previous result of LDH modified electrode with only an irreversible cathodic peak, an anodic peak appeared and the cathodic peak potential shifted to the positive direction on this nano-TiO2–LDH electrode, which demonstrated that the direct electrochemistry of LDH was enhanced by nano-TiO2. We supposed that the direct electrochemistry of LDH may be due to the redox reaction of some electroactive amino acids in the LDH molecule. The surface morphologies of electrodes characterized by SEM indicated that LDH was successfully immobilized on the sol–gel matrix and also had some interactions with nano-TiO2. This electrode can be used as a biosensor for the determination of lactic acid. The calibration range of lactic acid was from 1.0 to 20 μmol L−1 and the detection limit was 0.4 μmol L−1. Meanwhile, the small Kmapp value (2.2 μmol L−1) suggested that LDH possessed high enzymatic activity and good affinity to lactic acid owing to the promotion effect of nano-TiO2.

Theoretical expressions and mathematical analysis in cyclic reciprocal derivative chronopotentiometry (CRDCP) are presented for totally irreversible electrode processes corresponding to the application of symmetrical and unsymmetrical programmed currents. For two successive unsymmetrical programmed currents, the effect of the currents ratio b (b = |I2(t)/I1(t)|) on the (dt/dE)–E curves is discussed. The electrochemical behavior of totally irreversible electrode processes has been studied corresponding to the application of the unique unsymmetrical programmed Φm(I0) proposed recently. CRDCP characteristic parameters obtained for totally irreversible electrode processes are different from those of reversible electrode processes. Therefore, a comparison of CRDCP between both mechanisms is presented. Based on the mathematical derivation, alternative methods for kinetic measuring are described. It is prospected that CRDCP is convenient and applicable for studying the reversibility of the electrode processes in form of CRDCP characteristic parameters.

The direct electrochemistry of lactate dehydrogenase (LDH) immobilized in silica sol–gel film on gold electrode was investigated, and an obvious cathodic peak at about −200 mV (versus SCE) was found for the first time. The LDH-modified electrode showed a surface controlled irreversible electrode process involving a one electron transfer reaction with the charge-transfer coefficient (α) of 0.79 and the apparent heterogeneous electron transfer rate constant (Ks) of 3.2 s−1. The activated voltammetric response and decreased charge-transfer resistance of Ru(NH3)62+/3+ on the LDH-modified electrode provided further evidence. The surface morphologies of silica sol–gel and the LDH embedded in silica sol–gel film were characterized by SEM. A potential application of the LDH-modified electrode as a biosensor for determination of lactic acid was also investigated. The calibration range of lactic acid was from 2.0 × 10−6 to 3.0 × 10−5 mol L−1 and the detection limit was 8.0 × 10−7 mol L−1 at a signal-to-noise ratio of 3. Finally, the effect of environmental pollutant resorcinol on the direct electrochemical behavior of LDH was studied. The experimental results of voltammetry indicated that the conformation of LDH molecule was altered by the interaction between LDH and resorcinol. The modified electrode can be applied as a biomarker to study the pollution effect in the environment.

The existence of dimethylselenium (DMSe) and dimethyldiselenium (DMDSe) in some environmental samples can cause serious interference on Se(IV) determination by hydride generation atomic fluorescence spectrometry (HG-AFS) due to their contribution on HG-response. A flow injection separation and preconcentration system coupled to HG-AFS was therefore developed by on-line coprecipitation in a knotted reactor (KR) for eliminating interference subjected from organoselenium. The sample, spiked with lanthanum nitrate, was merged with an ammonium buffer solution (pH 8.8), which promoted coprecipitation of Se(IV) and quantitative collection by 150 cm PTFE KR. DMSe and DMDSe, however, were unretained and expelled from the KR. An air flow was introduced to remove the residual solution from the KR, then a 1.2 mol l−1 HCl was pumped to dissolve the precipitates and merge with KBH4 solution for HG-AFS detection. The interference of DMSe and DMDSe on the Se(IV) determination by conventional HG-AFS and its elimination by the developed separation and preconcentration system were evaluated. With optimal experimental conditions and with a sample consumption of 12.0 ml, an enhancement factor of 18 was obtained at a sample frequency of 24 h−1. The limit of detection was 0.014 μg l−1 and the precision (R.S.D.) for 11 replicate measurements of 1.0 μg l−1 Se(IV) was 2.5%. The developed method was successfully applied to the determination of inorganic selenium species in a variety of natural water samples.

A novel and reliable high-performance liquid chromatographic method for trace short-chain organic acids measurement in wheat root exudates under aluminum stress has been optimized and validated. The chromatographic separation of the short-chain organic acids (citric, oxalic, malonic, succinic, tartaric, malic, and acetic acids) was achieved with Bio-rad Aminex HPX-87H cation exchange resin column. These seven organic acids were identified and quantified in 25 min. Well-shaped peaks were obtained for trace organic acids using dilute sulfuric acid as mobile phase. Under optimum conditions, Bio-rad Aminex HPX-87H column showed distinct advantages of the ability to well separate different short-chain organic acids (especially for tartaric and malic acids, as well as malonic and acetic acids) in wheat root exudates under aluminum stress, and offered accurate and precise results for the analysis of these organic acids. This HPLC method can efficiently eliminate the aluminum’s interference and is quite suitable to the trace detection of trace organic acids in wheat root exudates under aluminum stress.

In this paper, the theoretical study of cyclic reciprocal derivative chronopotentiometry (CRDCP) for totally reversible electrode processes with symmetrical and unsymmetrical programmed currents is presented. The main viewpoints are: (1) for symmetrical programmed current, the amplitudes of the successive currents are the same, i.e. I(t) = (−1)i+1I0, whereas the transition times of each current step, τi, have different values. The properties of the dt/dE–E curves corresponding to each current cycle also differ a lot. (2) For unsymmetrical programmed current proposed in this work for the first time, the applied current successively reversed at each transition time steps to different amplitude. The use of this unique programmed current is advantageous versus symmetrical programmed current since the transition times obtained are equal to each other anticipatively, and the dt/dE–E curves also coincide with each other for the successive cycles. In this case, the results obtained in CRDCP are almost similar to those of cyclic voltammetry (CV). The characteristic parameters obtained in the dt/dE–E curves in both cases are quantitatively related to the species concentrations adjacent to the electrode surface and afford simple diagnosis criteria to characterize the reversibility of electrode processes. Properties of reversible electrode processes have also been further studied through the use of more than one current cycle.

The direct voltammetry of catalase (CAT) immobilized in silica sol–gel film in the presence of cysteine on gold electrode was investigated. The CAT electrode showed a pair of well-defined and quasi-reversible cyclic voltammetry peaks. It can be used as an electrochemical biosensor for the determination of hydrogen peroxide. The calibration range of H2O2 was from 1 to 30 μmol L−1 and the detection limit was 0.4 μmol L−1 at a signal-to-noise ratio of 3. The interaction of CAT and aluminum ion was also investigated based on the CAT-modified electrode. The electrochemical activity of the CAT-modified electrode was increased with the addition of Al3+. The experimental results of voltammetry and fluorescence spectroscopy indicated that the conformation of CAT molecule was altered by the formation of Al–CAT complex with Al3+, which may influence the activity of CAT.

The interaction of superoxide dismutase (SOD) with aluminum (Al) ions was investigated by cyclic voltammetry, fluorescence spectroscopy and synchronous fluorescence spectroscopy. The electrochemical activity of the SOD enzyme electrode was inhibited irreversibly by the addition of Al. Meanwhile, the static fluorescence quenching mechanism further revealed the existing of molecular complex of SOD with Al3+. The association constant was obtained from Lineweaver-Burk plot. The experimental results of voltammetry and fluorescence spectroscopy indicated that the conformation of SOD molecule was altered by the formation of Al–SOD complex. It may influence the activity of SOD enzyme since the optimum action of SOD depends upon a particular configuration of electrostatic charges in the enzyme molecule.

A novel non-chromatographic approach for direct speciation of mercury, based on the selective retention inorganic mercury and methylmercury on the inner wall of a knotted reactor by using ammonium diethyl dithiophosphate and dithizone as complexing agents respectively, was developed for flow injection on-line sorption preconcentration coupled with chemical vapor generation non-dispersive atomic fluorescence spectrometry. With the sample pH kept at 2.0, the preconcentration of inorganic mercury on the inner walls of the knotted reactor was carried out based on the exclusive retention of Hg–DDP complex in the presence of methylmercury via on-line merging the sample solution with ammonium diethyl dithiophosphate solution, and selective preconcentration methylmercury was achieved with dithizone instead of ammonium diethyl dithiophosphate. A 15% (v/v) HCl was introduced to elute the retained mercury species and merge with KBH4 solution for atomic fluorescence spectrometry detection. Under the optimal experimental conditions, the sample throughputs of inorganic mercury and methylmercury were 30 and 20 h− 1 with the enhancement factors of 13 and 24. The detection limits were found to be 3.6 ng l− 1 for Hg2+ and 2.0 ng l− 1 for CH3Hg+. The precisions (RSD) for the 11 replicate measurements of each 0.2 μg l− 1 of Hg2+ and CH3Hg+ were 2.2% and 2.8%, respectively. The developed method was validated by the analysis of certified reference materials (simulated natural water, rice flour and pork) and by recovery measurements on spiked samples, and was applied to the determination of inorganic mercury and methylmercury in biological and environmental water samples.

A novel method for the determination of trace amounts of Al(III) based on resonance Rayleigh scattering (RRS) has been developed. In the presence of some surfactants, Al(III) can react with morin and form an Al(III)–morin–surfactant complex, which results in the enhancement of RRS intensity and the appearance of the corresponding RRS spectral characteristics. Their maximum scatter peaks are at 476 nm for the cetyltrimethylammonium bromide (CTAB) system, 489 nm for the cetylpyridinium chloride (CPC) system, 474 nm for the Triton X-100 system, and 473 nm for the Tween-20 system. The enhanced RRS intensity is directly proportional to the concentration of Al(III). The detection limits are in the range of (0.50–1.2)×10−7 mol l−1 depending on the surfactant. The characteristics of RRS spectra of the complexes, the optimum conditions of these reactions and the influencing factors have been investigated. The method has high selectivity, and was successfully applied to the determination of Al(III) in natural and biological samples. Furthermore, according to different complexation capacity of Al(III)–morin–CTAB system under two pH conditions, speciation analysis of Al(III) in natural waters was explored. The labile monomeric Al fraction (mainly inorganic Al, Ali) is determined at acidic pH and the total monomeric Al fraction (Ala) is determined at alkaline pH. The results are in agreement with those obtained by Driscoll’s 8-hydroxyquinoline extraction-ion exchange method.

A third-generation biosensor for superoxide anion (O2−) was developed based on superoxide dismutase (SOD) immobilized by thin silica–PVA sol–gel film on gold electrode surface. A rapid and direct electron transfer of SOD in the thin sol–gel film at the gold electrode was realized without any mediators or promoters. The characterization of the SOD electrodes showed a quasi-reversible electrochemical redox behavior with a formal potential of (versus SCE) in 50 mmol l−1 phosphate buffer solution (PBS), pH 7.0. The heterogeneous electron transfer rate constant was evaluated to be about 2.1 s−1. The anodic and cathodic transfer coefficients are 0.6 and 0.4, respectively. Based on biomolecular recognition for specific reactivity of SOD toward O2−, the SOD electrode was applied to a sensitive and selective measurement of O2− with the low operation potential (−0.15 V versus SCE) in phosphate buffer solution, pH 7.0. The amperometric response was proportional to O2− concentration in the range of 0.2–1.6 μmol l−1 and the detection limit was 0.1 μmol l−1 at a signal-to-noise ration of 3. The preparation of SOD electrode is easy and simple. The uniform porous structure of the silica–PVA sol–gel matrix results in a fast response rate of immobilized SOD and is very efficient for stabilizing the enzyme activity.

In weakly acidic buffer medium, the interaction of amikacin with calf thymus DNA, yeast RNA and denatured DNA has been investigated by using resonance Rayleigh scattering (RRS) technique. The result shows that calf thymus DNA is capable of enhancing the RRS intensity of the amikacin, while yeast RNA and denatured DNA have very little enhancement effect. Based on the characteristics, a sensitive assay for detecting double-stranded DNA in the presence of denatured DNA and yeast RNA has been developed. The enhancement of the RRS signal is directly proportional to the concentration of double-stranded DNA in the range 0.02–12.0 μg ml−1 for calf thymus DNA and its detection limit (3σ) is 2.5 ng ml−1. The method shows a wide linear range and high sensitivity, and almost no interference can be observed from RNA, denatured DNA, amino acid and most of the metal ions. The trace amounts of nucleic acid in synthetic samples and practical samples are determined with satisfactory results. Therefore, the proposed method is promising for as an effect means for recognition in vivo and determination in situ of double-stranded DNA.

The electrochemical behavior of maltol on a glassy carbon (GC) electrode was investigated. The results were applied to differential pulse voltammetric determination of maltol in beverages pretreated by ultrafiltration. Under the optimum experimental conditions, the linear range is 1×10−5 to 6×10−4 mol l−1 maltol and the relative standard deviation for 0.4 mmol l−1 maltol is 0.6% (n=9). The detection limit was 5 μmol l−1. Furthermore, silica sol–gel film on GC electrode could be used as suitable selective membrane, which integrated selective membrane on the electrode and substituted for the pretreatment of ultrafiltration. Under the above conditions, maltol was determined by semi-differential linear sweep voltammetry at a silica sol–gel modified GC electrode in the concentration range of 5×10−6 to 5×10−4 mol l−1. The detection limit was 2 μmol l−1 and the relative standard deviation for 0.1 mmol l−1 maltol was 0.7% (n=7). The proposed method is of sensitivity, simplicity, rapidness and no contamination. It had been applied to the direct determination of maltol in beverages such as grape wines, drinks and beers without any pretreatment. The results obtained with the present method were satisfactory with those obtained by spectrophotometry. It could be used as a simple and practical method for the determination of the flavor enhancer maltol in beverages.

The determination of trace levels of aluminum by high performance liquid chromatography (HPLC) with spectrophotometric detection using quercetin, a bioactive substance as a pre-column reagent, is developed in this paper. The Al–quercetin chelate was separated on a reversed-phase ODS column with a mobile phase consisting of 70% water (pH 1.0 with perchloric acid) and 30% methanol, and detected at its maximum of 415 nm. The response was linear over the 1.0×10−7 to 8.0×10−5 M concentration range with a detection limit of 5.0×10−8 M and a relative standard deviation of 1.0% at the 5×10−6 M level. The analysis was free from common ions except iron, which could be successfully screened by 1,10-phenanthroline. This method has been employed to the determination of Al in environmental and biological samples. Moreover, direct speciation of labile monomeric Al, the toxic form of Al, in natural water by the present technique was explored. The coordination ratio of Al complex with quercetin was also elucidated by HPLC combined with molar ratio method. Only a 1:1 complex was formed. Because quercetin exists in body, a preliminary thinking of in vivo determination of Al is provided in this study.

Resonance Rayleigh scattering (RRS) of the thionine (TH)–nucleic acids system and its analytical application have been studied. In pH 2.2 acidic buffer medium, some nucleic acids can react with TH to form TH–nucleic acids complex. This results in a great enhancement of RRS and the appearance of new RRS spectra. The RRS spectral characteristics of TH–ctDNA system, the affecting factors and the optimum conditions of the reaction have been investigated. The enhancement of the RRS signal is directly proportional to the concentration of nucleic acids in the range 0–10.0 μg/ml for calf thymus DNA and 0–15.0 μg/ml for yeast RNA, and its detection limits (3σ) are 3.5 ng/ml for calf thymus DNA and 4.9 ng/ml for yeast RNA, respectively. The method shows a wide linear range and high sensitivity, and was applied to the determination of trace amounts of nucleic acid in synthetic samples and practical samples with satisfactory results. The bind properties for the interactions of TH with ctDNA were investigated using a Scatchard plot based on the measurement of the enhanced RRS data at 340 nm, and the binding number and intrinsic binding constant are 4.9 and 2.6×105 mol/dm3, respectively.

The electrochemical behavior of alizarin red S (1,2-dihydroxyanthraquinone sulfonate, ARS) immobilized on electrochemically pretreated glassy carbon (GC) electrode by silica sol–gel process was investigated. The central quinone functionalities of the ARS molecule underwent quasi-reversible redox reaction. Oxidation of the dihydroxyl functionalities gave unstable products which underwent further follow-up chemical transformation to give new electroactive species. The results were applied to develop a reagentless sensor for the indirect determination of aluminum (Al) ions. Various experimental parameters, which influenced the properties of the modified electrode, were optimized. Under the optimum experimental conditions, the linear response range for Al3+ ions employing differential pulse voltammetry was 1.4×10−7 to and the relative standard deviation for Al3+ was 2.7% (n=7). The detection limit was . The modified electrode, as a reagentless sensor, is stable and portable. This method has been applied to determine Al in water samples.

An on-line solid-phase extraction (SPE) technique, linked to spectrophotometry, has been developed to overcome the problem of high matrix concentration, which is thought to interfere with the determination of low levels of aluminum (Al) in environmental samples. Tiron modified resin was prepared and used as a SPE absorbent, which can quantitatively adsorb Al(III) at pH 4–6 with an adsorption capacity of 5.6 mg g−1 resin. The main advantages of this novel method are: (1) a much higher sensitivity has been obtained by SPE technology; and (2) a large amount of Na+, K+, Ca2+ and Mg2+ can be removed and the interference of Fe(III), Mn(II) and F− can be efficiently eliminated by eluting with 0.25 mol l−1 NaOH. It is a highly selective and sensitive method for simple and quick determination of dissolved Al in soil extracts and ground waters, particularly suitable for the analysis of complex environmental samples.

A comparison between the effects of aluminum and cupric ions on the dopachrome (DC) conversion and the cooperation effect of the both ions in the DOPA oxidation to melanin pathway has been studied by UV–Vis spectrophotometric method. Both aluminum and cupric ions catalyze the DC conversion reaction, which is an important step in the melanin synthesis pathway. However, cupric ions catalyze the conversion of DC to yield 5,6-dihydroxyindole-2-carboxylic acid (DHICA) but the product of DC conversion catalyzed by aluminum is 5,6-dihydroxyindole (DHI). DOPA oxidation catalyzed by aluminum and cupric ions is studied in the presence of hydrogen peroxide. The results from our experiments provide evidence that aluminum can markedly increase the oxidative stress of copper-mediated the melanin formation and influence the properties of the melanin by means of changing the ratio of DHICA/DHI in the acidic environment (pH 5.5).

The effect of aluminum ions on the kinetics and mode of the conversion of dopachrome (DC) in acidic environment has been studied using UV-Vis spectrophotometric and cyclic voltammetric methods. The DC conversion step is an important reaction in melanogenesis. Aluminum ions catalyze greatly the decarboxylative transformation of DC to give 5,6-dihydroxyindole (DHI) rather than 5,6-dihydroxyindole-2-carboxylic acid (DHICA) at pH 5.5, which enhance the ratio of formation DHI/DHICA in melanin synthesis pathway. The kinetics of DC conversion catalyzed by aluminum ions is dependent on the concentration of DC and aluminum ions. These results provide evidence that aluminum ions could play a role in the synthesis of melanin pathway in acidic condition through catalyzing the DC decarboxylative transformation to yield DHI and influence the melanin structure and properties.

The biological effects of aluminium have received much attention in recent years. Speciation of Al is of basic relevance as it concerns its reactivity and bioavailability. A differential pulse voltammetry (DPV) procedure is proposed for speciation analysis of AlIII in natural waters and biological fluids using six catechols (L-dopa, dopamine, epinephrine, norepinephrine, caffeic acid and o-benzenediol) as electroactive ligands. The decrease of the DPV anodic peak current for each catechol ligand is linear with the increase of Al concentration. This speciation analysis idea is based on the measurement of the complexation capacity, namely, different affinities of AlIII for catechols and organic ligands under two pH conditions. The labile monomeric Al fraction (mainly inorganic aluminium) is determined at pH 4.6, while the total monomeric Al fraction is determined at pH 8.5. The principle for AlIII speciation analysis by an electrochemical method is discussed. This sensitive and simple fractionation method is successfully applied to the speciation analysis of Al in natural waters and the results agree well with those of Driscoll’s method. The speciation analysis of Al in biological fluids is also explored and the results are compared with those obtained by ultrafiltration and dialysis. Compared with other speciation protocols the electrochemical method possesses some remarkable advantages: rapidity, high sensitivity, cheap instrumentation and a simple operation procedure.

A differential pulse voltammetric (DPV) procedure is proposed for the speciation of aluminium in natural waters using Pyrocatechol Violet chemically modified electrodes (PCV-CMEs). This novel speciation idea is based on the selective determination of different AlIII forms under two pH conditions. The labile monomeric Al fraction (mainly inorganic Al) is analysed at pH 4.8 (0.20 mol dm−3 NaOAc–HOAc) and the total monomeric Al fraction is analysed at pH 8.5 (0.20 mol dm−3 NH3·H2O–NH4Cl). The difference is thought to be caused by the weak competition ability of PCV to sequester AlIII from AlIII–natural organic matter complexes. This sensitive and simple speciation method has been applied successfully to aluminium speciation in natural waters sampled from different regions of China. Five fractions are measured directly or indirectly: (i) labile monomeric Al; (ii) total monomeric Al; (iii) acid reactive Al; (iv) non-labile monomeric Al; and (v) acid soluble Al. The results are in satisfactory agreement with those obtained by Driscoll’s 8-hydroxyquinoline extraction–ion exchange method.

The speciation of aluminum (Al) is a critical issue when evaluating the environmental and biological significance of elevated Al concentrations in soil solutions caused by acidic precipitation. Numerous studies have revealed that, with increased concentrations of silica acid in soil, the activity of Al species in soil solutions is greatly modified by SiO42−. However, thus far there has been little thorough theoretical modeling of this subject. This paper reports a computer simulation of the distribution of Al speciation in soil solutions in equilibrium with the mineral phase imogolite based on a chemical equilibrium calculation. The unique characteristic associated with imogolite reported by previous researchers can be explained theoretically by the proposed model. The dissolved silica has a remarkable influence on Al speciation: increasing concentrations of silica acid may effectively inhibit the formation of polymeric alumino-hydroxo species, and, furthermore, detoxify Al toxicity to plants.

It was demonstrated that the decrease of the differential pulse voltammetric (DPV) anodic peak current of dopamine (3,4-dihydroxyphenylethylamine, DA) was linear with the increase of aluminum (Al) concentration. Under optimum experimental conditions (pH 4.6, 1.2×10−3 M DA, and 0.04 M NaAc–HAc buffer solution), the linear range is 4.0×10−7–8.0×10−5 M, the detection limit is 1.4×10−7 M, and the relative standard deviation for 4×10−5 M AlIII is 3.5% (n=8). Many foreign species, especially some low-molecule-weight biological molecules, were chosen for interference testing. The proposed method was applied to the determination of Al in biological samples such as synthetic renal dialysate, Ringer’s solution, human blood, cerebrospinal fluid of a patient, and urine of a diabetic patient. The corresponding recoveries were generally between 95 and 105%. The basic principle of the method was determined by examining Al complexed with DA. This results in the blockage of the electroactive sites on DA, followed eventually by the reduction of the electrochemical response of DA. This result was verified by examining the behavior of DA, both in the presence and absence of Al, using electrochemical, UV–Vis, Raman, and 13C NMR spectroscopic methods.

The differential pulse voltammetric (DPV) indirect determination of aluminium using L-dopa under alkaline conditions on a glassy carbon working electrode was studied. The proposed method relies on the linear decrease of the DPV anodic peak current of L-dopa with increase in the concentration of aluminium added. Under the optimum experimental conditions (pH 8.5, 0.08 M NH4Cl–NH3·H2O buffer solution, and 4 × 10−4 M L-dopa), the linear range is 2–18 × 10−7 M Al III. The detection limit is 7.6 × 10−8 M and the relative standard deviation for 8 × 10−7 M Al III is 3.5% (n = 8). A number of foreign species were examined as potential interferents. The method was applied to the determination of aluminium in drinking waters, synthetic renal dialysate, sodium chloride injection, sucrafate, hydrothorax, blood, urine and hair samples. The physiological significance is discussed.

The determination of trace levels of aluminum in natural waters with rubeanic acid (RA) by adsorption chronopotentiometry is developed in this paper. Optimum experimental conditions include an accumulation potential of −0.40 V, accumulation time of 60 s, and a RA concentration of 6×10−6 M in 0.2 M NaAc–HAc buffer solution (pH 4.6). The response is linear over the 1×10−8∼4×10−7 M concentration range. The detection limit is 5.6×10−9 M and the relative S.D. (at the 3×10−7 M level) is 2.6%. Possible interferences are evaluated. The method has been applied to the determination of trace levels of Al in various real samples. Direct determination of toxic forms of Al in surface waters by this technique is also explored.

In the study of the vapor deposition of metal atoms onto long-chain alkanethiol self-assembled monolayers (CnSH-SAMs, n>10) on Au(111) substrate, metal atoms with different diameters can penetrate selectively into the CnSH-SAMs or not, which looks like the “size exclusion effect”. In this paper, we proposed a new mechanism for the metal atoms penetration by establishing a simple ideal penetration model of the long-chain CnSH-SAMs with defect-free structure on Au(111). The intrinsic and regular–distributed channels with ∼ 3 Å diameters (which are decided by the framework size of the three-aggregate of the CnSH molecules) were deduced. This new penetration mechanism can explain reasonably the selective penetration of metal atoms into the long-chain CnSH-SAMs on Au(111): When the driving force is applied, the metal atoms with diameter smaller than 3 Å will overcome the van der Waals interaction among the neighboring hydrocarbon chains and penetrate into the CnSH-SAMs through the ∼ 3 Å channels reaching to the surface of Au(111), while the metal atoms with large diameter (> 3 Å) can not penetrate.

Density functional theory (DFT) calculations were performed on the structures and water-exchange reactions of aqueous Al(III)–salicylate complexes. Based on the four models (gas phase (GP); polarizable continuum model (PCM), which estimates the bulk solvent effect; supermolecule model (SM), which considers the explicit solvent effect, and supermolecule–polarizable continuum model (SM–PCM), which accounts for both types of solvent effects), we systematically conducted this study by examining three different properties of the complexes. (1) The microscopic properties of the aqueous Al(III)–salicylate complexes were studied by optimizing their various structures (including the possible 1:1 mono- and bidentate complexes, cis and trans isomers of the 1:2 bidentate complexes and 1:3 bidentate complexes) at the B3LYP/6-311+G(d, p) level. (2) The 27Al and 13C NMR chemical shifts were calculated using the GIAO method at the HF/6-311+G(d, p) level. The calculation results show that the values obtained with the SM–PCM models are in good agreement with the experimental data available in the literature, indicating that the models we employed are appropriate for Al(III)–salicylate complexes. (3) The water-exchange reactions of 1:1 mono- and bidentate Al(III)–salicylate complexes were simulated using supermolecule models at the B3LYP/6-311+G(d, p) level. The logarithm of the water-exchange rate constant (log kex) of the 1:1 bidentate complex predicted using the “log kex–dAl–OH2” correlation is 4.0, which is in good agreement with the experimental value of 3.7, whereas the calculated range of log kex of the 1:1 monodentate complexes is 1.3–1.9. By effectively combining the results for the thermodynamic static structures with the simulations of the kinetic water-exchange reactions, this work promotes further understanding of the configurations and formation mechanism of Al(III)–salicylate complexes.

Reaction pathways, solvent effects and energy barriers have been investigated for the water exchange of the polyoxocation GaO4Al12(OH)24(H2O)127+ (K–GaAl12) in aqueous solution by means of supermolecule density functional theory calculations. In the proposed reaction pathway, the supermolecular reactant K–GaAl1215H2O first loses a water ligand to form an intermediate with a five-coordinated aluminum atom, and then the incoming water molecule in the second coordination sphere attacks the intermediate with a five-coordinated aluminum atom to produce the reaction product. Our calculated results indicate that the water exchange of K–GaAl12 proceeds via a dissociative mechanism, and that the reverse reaction of Step II is the most favorable dissociative pathway, with a barrier height of 31.3 kJ mol−1. The calculated transition-state rate for the favorable dissociative pathway is much larger than the experimental rate constant, but is close to the data calculated for Al30 by molecular dynamics. The transmission coefficient was also predicted on the basis of both the calculated transition-state rate and the experimental rate. Our calculated results also indicate that both the explicit solvent effect and the bulk solvent effect have obvious effects on the barrier heights of the water exchange reaction of K–GaAl12. By comparison, the water exchange mechanism for K–GaAl12 was found to be more similar to that for mineral surfaces than that for monomeric aluminum species.

The formation mechanism of Al30O8(OH)56(H2O)2618+ (Al30) has been investigated by the density functional theory based on the supermolecule model and kinetic analysis on the 27Al nuclear magnetic resonance (NMR) experimental results in monitoring Al30 synthesis process. The theoretical chemistry calculations on the four possible schemes show that δ-Na–Al13 is the reasonable intermediate followed by the substitution of Na with Al to form δ-Al14, and Na+ plays an important role in stabilizing the intermediate (δ-Na–Al13) in the transformation. The kinetic analysis on the 27Al NMR experimental data indicates that ε-Al13 decomposes and isomerizes in the formation of Al30, while Al monomers facilitate the decomposition of ε-Al13 and so the isomerization of ε-isomers to δ-isomers effectively. The favorable formation mechanism of Al30 includes three steps: (1) ε-Al13 decomposes and rearranges into the isomer δ-Al13; (2) Na+ reacts with δ-Al13 to stabilize the intermediate δ-Na–Al13, followed by Al monomers replacing Na to form δ-Al14; (3) δ-Al14 reacts with the Al monomers in the solution to finally form Al30. Both Al monomers and Na+ are important in the transformation. Al monomers are the basic building units and helpful to the isomerization while Na+ can well stabilize the isomer δ-Al13 to yield intermediate δ-Na–Al13. The results also show that other isomers of ε-Al13 (β-Al13 and α-Al13) form in the formation of Al30, and their calculated 27Al NMR tetrahedral resonance shifts are consistent with the experimental 27Al NMR tetrahedral signals in the preparation process of Al30.

In this paper, the structure of the Al30O8(OH)56(H2O)2618+(Al30) polyoxocation in aqueous solution is investigated, including an exploration of its water-exchange reaction using a supramolecular model. Thirty-one solvent water molecules were explicitly included in the supramolecular model to approximate the influence of the solvent. The calculated results indicated that both the gas-phase and the supramolecular models could correctly reproduce the structure of the Al30 polyoxocation, but the supramolecular model described the structure more accurately. Using the supramolecular model, we calculated the 27Al NMR chemical shifts of various aluminum atoms using HF and GIAO methods, and they compared well to the chemical shifts determined experimentally. The water-exchange reaction of the Al30 polyoxocation could not be simulated with the gas phase model because of a proton-transfer reaction that is induced by the highly positive charge of the Al30 polyoxocation. However, the inclusion of an explicit second solvation sphere lowered the acidity of the coordinated water molecules and allowed simulation of the water exchange reaction.

Supermolecule density functional calculations were performed on the hydrolysis of aluminum(III) and prediction of pKa in aqueous solution. The optimization results showed that the most stable structures for the first, second and third hydrolysis products were hexacoordinate, hexacoordinate and pentacoordinate, respectively. The different coordination geometries could easily transform into each other due to the small energy gaps (within 2.5 kcal mol−1). The calculated value of 4.6 for the first hydrolysis constant agreed well with the experimental value of 5.0. The results from the different thermodynamic cycles have been compared, which revealed that the cycle involving the solvation of H2O and H3O+ could reasonably predict the first hydrolysis constant, while the other cycle involving the solvation of H+ acquired a fairly good correlation of the hydrolysis reaction free energies and the experimental pKa.

The water exchange reaction of the polyoxocation GeO4Al12(OH)24(H2O)128+ (K-GeAl12) in aqueous solution has been simulated by means of supermolecule density functional calculations. In the proposed dissociative pathway, the leaving water molecule in the first coordination sphere is dissociated from its coordinated aluminium, and via a transition state enters into the second coordination sphere. Our calculated results indicate that the polyoxocation K-GeAl12 exchanges water in a dissociative way with a barrier height of 37.0 kJ mol−1, and that the gas-phase model is not suitable to simulate the water exchange reaction of K-GeAl12 because of the proton-transfer reaction. The calculated results on the transmission coefficients of the water exchange reactions of K-MAl12 imply that the water exchange reactions of aluminium species with similar structures have close transmission coefficients, but the different charges of aluminium species have an important influence on the transmission coefficients, which may be the reason why K-MAl12 polyoxocations with different reactivity have nearly the same water exchange rate constants.

Reaction pathways, solvent effects and energy barriers have been investigated for the dimerization of the deprotonated aquo ion of Al(III) in aqueous solution by performing supramolecule density functional theory calculations. Two competing reaction pathways were investigated, sharing a common first step and third step, i.e. the formation of the aggregate II of two aluminium monomers and the doubly bridged dimer. One pathway involves a nucleophilic attack to undercoordinated metal center in the first step and then the loss of a coordinated water molecule. Another pathway involves a water exchange reaction in the first step and then the formation of the hydroxo bridge. The calculated results indicate that both pathways I and II are possible in aqueous solution. The direct participation of the solvent water molecule facilitates the dimerization, but the extremely large solvent shifts of the energy barriers for each reaction are attributed mainly to the bulk effect. The computed activation energies for the water exchange reactions are in good agreement with the available experimental values, namely, the calculated value 37.5 kJ mol−1 compared to the experimental value 36.4 (±5) kJ mol−1. In agreement with experimental observations in aqueous solution, the calculated results favor the transformation of singly-bridged to doubly-bridged aluminium ion, which is helpful to understand the complicated hydrolytic polymerizaiton of Al(III).

The interaction of monomeric aluminium and chloride ion in aqueous solution is investigated by density functional theory (DFT) calculations. The computational results show that it is difficult for Cl− to enter the inner-coordination shell of aluminium complexes by replacing the bound water molecules, independent of pH and the concentration of Cl−. However, pH and the concentration of Cl− might influence the conformations, bond lengths and natural charge populations of monomeric aluminium complexes to a given extent. Based on the computed Gibbs energies, pKa values of various hydrolysis species in the presence and absence of Cl− are evaluated, respectively. It is concluded that pKa increases with the introduction of Cl−.

The structures of core-links Al13 (C-Al13) and flat-Al13 (F-Al13) complexes in aqueous solution have been investigated using density functional theory (DFT) at the level of B3LYP/6-31G(d). The present work focuses on the following three aspects: (1) C-Al139+ was optimized with the consideration of solvent effect and the 27Al NMR chemical shifts using Hartree Fock GIAO and B3LYP GIAO methods were computed respectively; (2) the optimization of F-Al1315+ was also performed and the 27Al NMR chemical shifts were obtained using the same methods as above; (3) the structural parameters of a series of typical aluminum species (Al3+, AlOH2+, AlF2+, Al24+, Al66+, K-Al137+, C-Al139+ and F-Al1315+) were compared.

Supermolecule density functional calculations suggest the dissociative (D) mechanism for the water exchange of aquated Al(III) species in aqueous solution and the calculated results agree well with experimental data.

A simple and sensitive indirect determination method for sulfide in water samples by anodic stripping voltammetry (ASV) using mercury-film electrode (MFE) has been developed, which is based on the determination of residual cadmium ion after reaction of Cd2+ with S2−. The linear range is adjustable depending on Cd2+ concentration, for example, the determination of S2− can be achieved in the range of 1.5–7.0 × 10−6 mol L−1 by selecting 3.0 × 10−6 mol L−1 Cd2+. The detection limit is 1.3 × 10−8 mol L−1 under optimum conditions, and the relative standard deviation (RSD, n = 10) for 2.0 × 10−6 mol L−1 S2− is 0.7%. Compared with other methods, this method has the following prominent advantages: with low detection limit, easy to operate and less interference. The proposed method has been successfully applied to the determination of S2− in synthetic wastewater, lake water, beverage, spring water and real wastewater samples.

The mechanisms for the substitution of an aqua ligand with F− in monomeric Al complexes were studied with density functional theory (DFT). Typical mechanisms are modeled to determine the preferred substitution pathway according to the activation energy barriers. The present computational results are in favor of interchange associative (Ia) mechanism for the substitution of F− into Al(H2O)63+, whereas interchange dissociative (Id) mechanism is preferred for the substitution into Al(H2O)5(OH)2+, which is in agreement with the previous experimental findings. This implies the mechanistic changeover from Ia to Id induced by the spectator hydroxyl ligand. Like the water-exchange reaction, the substitution rate is accelerated by OH− ligand. The difference of the computational and experimental activation enthalpy values is interpreted as the DFT errors in energy and the deviation of transmission coefficient from unity.

Reaction pathways, solvent effects and energy barriers have been investigated for the dehydration processes of aquated Al(OH)2+ species in aqueous solution by density functional calculations using a supermolecule model. The dehydration processes from Al(H2O)4(OH)2+ to Al(H2O)2(OH)2+ involve the water exchange on cis-Al(H2O)4(OH)2+ and dehydration of the following intermediate pentacoordinate Al(H2O)3(OH)2+. The calculated results indicate that cis-Al(H2O)4(OH)2+ exchanges water in a dissociative way with an activation energy of 27.7 kJ mol−1. Loss of coordinated water from hexacoordinate and pentacoordinate Al(OH)2+ is unfavourable by 22.1 and 6.6 kJ mol−1, respectively, which supports the presence of the stable hexacoordinate Al(H2O)4(OH)2+ in aqueous solution. Our results also indicate that both the explicit water molecules and bulk water molecules have great influences on the energy barriers, and they can not be neglected.