Co-reporter:Zhi Zhang, Yueping Guan, Tingting Xia, Jiao Du, Tao Li, Zongying Sun, Chen Guo
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2017 Volume 520(Volume 520) pp:
Publication Date(Web):5 May 2017
DOI:10.1016/j.colsurfa.2017.01.071
•A simulation system was established to evaluate the influence of exposed MNPs.•Both the body and surface of exposed MNPs had associations with the CL signal.•Treatment methods played a big role in the effect of exposed MNPs on CL signal.•Exposed Fe3O4 MNPs were successfully applied in the detection of hCG.To a certain extent, uneven coating of nanoparticles may lead to exposure of their contents. In this work, a simulation system was established and exposed Fe3O4 magnetic nanoparticles (MNPs) were used to investigate the influence of the exposed case in a chemiluminescence immunoassay. Some factors such as the concentration of MNPs, coexistence of horseradish peroxidase (HRP), different particle sizes, and various treatment methods were investigated. It was confirmed that both the bodies of nanoparticles and metallic oxides on the exposed surface have associations with the detection signal. This conclusion may provide a new way to explain the deviation emerged in a chemiluminescence immunoassay. In addition, an exposed Fe3O4 MNPs based chemiluminescence immunoassay was developed to detect human chorionic gonadotropin (hCG). Carboxyl-functionalized MNPs were modified with anti-α-hCG antibody, and further used as solid-phase supports for sandwich-type immunoassay. The detection limit for hCG under optimal conditions was as low as 1.184 ng/mL with a linear response range of 2–100 ng/mL and a correlation coefficient of 0.989. The proposed method could be used for the determination of hCG in serum samples, which demonstrated their application potential in rapid and cost-effective detection of biological samples.Download high-res image (130KB)Download full-size image
Co-reporter:Xinwei Zhao;Yueping Guan;Changfu Xia;Tingting Xia;Xiaolin Qiu;Chuhang Wang
Journal of Applied Polymer Science 2016 Volume 133( Issue 10) pp:
Publication Date(Web):
DOI:10.1002/app.43005
ABSTRACT
Micrometer-sized superparamagnetic poly(styrene–glycidyl methacrylate)/Fe3O4 spheres were synthesized by two-stage dispersion polymerization with modified hydrophobic Fe3O4 nanoparticles, styrene (St), and glycidyl methacrylate (GMA). The morphology and properties of the magnetic Fe3O4–P (St-GMA) microspheres were examined by scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, thermogravimetric analysis, and attenuated total reflectance. The average size of the obtained magnetic microspheres was 1.50 μm in diameter with a narrow size distribution, and the saturation magnetization of the magnetic microspheres was 8.23 emu/g. The magnetic Fe3O4–P (St-GMA) microspheres with immobilized iminodiacetic acid–Cu2+ groups were used to investigate the adsorption capacity and selectivity of the model proteins, bovine hemoglobin (BHb) and bovine serum albumin (BSA). We found that the adsorption capacity of BHb was as high as 190.66 mg/g of microspheres, which was 3.20 times greater than that of BSA, which was only 59.64 mg/g of microspheres as determined by high-performance liquid chromatography. With a rather low nonspecific adsorption, these microspheres have great potential for protein separation and purification applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43005.
Co-reporter:Shi-Kai Wang, Feng Wang, Yi-Ru Hu, Amanda R. Stiles, Chen Guo, and Chun-Zhao Liu
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 1) pp:109
Publication Date(Web):December 16, 2013
DOI:10.1021/am404764n
Magnetic flocculant was synthesized for the highly efficient recovery of microalgal cells. The highest flocculation was achieved using the magnetic flocculant synthesized with iron oxide and 0.1 mg/mL cationic polyacrylamide (CPAM). This resulted in a recovery efficiency of more than 95% within 10 min using a dosage of 25 mg/L for Botryococcus braunii and 120 mg/L for Chlorella ellipsoidea. For both species, the adsorption isotherm data fit the Freundlich model better than the Langmuir model, indicating that the adsorption process was a heterogeneous multilayer. The maximum adsorption capacity was 114.8 and 21.4 mg dry cells/mg-particles at pH 7 for B. braunii and C. ellipsoidea, respectively. The primary flocculation mechanism was bridging, which was assisted by the electrostatic interactions between the microalgal cells and the magnetic flocculant under acidic conditions. These results provide new opportunities and challenges for understanding and improving the harvesting of microalgae using magnetic separation.Keywords: Botryococcus braunii; cationic polyacrylamide; Chlorella ellipsoidea; magnetic flocculant; microalgae harvesting;
Co-reporter:Mingzhu Yang, Yueping Guan, Yu Yang, Tingting Xia, Wubin Xiong, Chen Guo
Materials Letters 2014 Volume 137() pp:113-116
Publication Date(Web):15 December 2014
DOI:10.1016/j.matlet.2014.08.135
•The catalytic activity of DMNPs is independent on the surface properties of MNPs.•DMNPs were successfully applied in the detection of MP.•The method based on DMNPs is more sensitive than the method based on WMNPs.The peroxidase-like activity of dissolved Fe3O4 magnetic nanoparticles (MNPs) was determined and compared with whole Fe3O4 MNPs in this study. We detected the peroxidase-like activity of Fe3O4 MNPs through the catalytic reaction between Fe3O4 MNPs and TMB. Due to the high catalytic activity of ferric ions and ferrous ions released from Fe3O4 MNPs after dissolution, dissolved Fe3O4 MNPs showed much better peroxidase-like activity than whole Fe3O4 MNPs. In addition, we used the peroxidase-like activity of Fe3O4 MNPs in the diagnosis of mycoplasma pneumonia infection in which Fe3O4 MNPs was used as substitution of horseradish peroxidase. Both Fe3O4 MNPs modified with amino groups (MNPs-NH2) and Fe3O4 MNPs modified with polyethyleneimine (MNPs-PEI) were successfully used in the indirect immunoassay for the detection of mycoplasma pneumoniae. And the results of dissolved Fe3O4 MNPs were more sensitive and specific than that of whole Fe3O4 MNPs.
Co-reporter:Mingzhu Yang, Yueping Guan, Yu Yang, Li Xie, Tingting Xia, Wubin Xiong, Chen Guo
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2014 Volume 443() pp:280-285
Publication Date(Web):20 February 2014
DOI:10.1016/j.colsurfa.2013.11.026
•The peroxidase-like activity of DMNPs is higher than WMNPs.•DMNPs demonstrated the same change trend as standard ferric ion solutions.•DMNPs were successfully applied in the detection of GP73.•The method based on DMNPs is more sensitive than the method based on WMNPs.The peroxidase-like activity of dissolved Fe3O4 magnetic nanoparticles was reported in this work. The chromogenic results of dissolved magnetic nanoparticles demonstrated almost the same change trend as standard ferric ion solutions. And the chromogenic reactions of dissolved Fe3O4 magnetic nanoparticles were more sensitive than that of whole Fe3O4 magnetic nanoparticles. The chromogenic reaction of dissolved Fe3O4 magnetic nanoparticles was utilized to replace the chromogenic reaction of horseradish peroxidase in traditional enzyme-linked immunosorbent assay and applied in the immunoassay of hepatocellular carcinoma biomarker GP73. The method based on the chromogenic reaction of dissolved Fe3O4 magnetic nanoparticles achieved a detection limit of 250 ng/mL, which was more sensitive than the method based on the peroxidase-like activity of whole Fe3O4 magnetic nanoparticles. The immunological detection method based on dissolved Fe3O4 magnetic nanoparticles proved to be simple, sensitive, specific and low-cost in this paper.
Co-reporter:Ning Wang, Yueping Guan, Liangrong Yang, Lianwei Jia, Xuetuan Wei, Huizhou Liu, Chen Guo
Journal of Colloid and Interface Science 2013 Volume 395() pp:50-57
Publication Date(Web):1 April 2013
DOI:10.1016/j.jcis.2012.11.062
A stable drug carrier has been prepared by covalently coating magnetic nanoparticles (MNPs) with PEO–PPO–PEO block copolymer Pluronic P85. The particles were characterized by TEM, XRD, DLS, VSM, FTIR, and TGA. A typical product has a 15 nm magnetite core and a 100 nm hydrodynamic diameter with a narrow size distribution and is superparamagnetic with large saturation magnetization (57.102 emu/g) at room temperature. The covalently-coated Pluronic-MNPs (MagPluronics) were proven to be stable in different conditions, such as aqueous solution, 0.2 M PBS solution, and pH 13.5 solution, which would be significant for biological applications. Furthermore, MagPluronics also possess temperature-responsive property acquired from the Pluronic copolymer layer on their surface, which can cause conformational change of Pluronics and improve load and delivery efficiency of the particles. The temperature-controlled loading and releasing of hydrophobic model drug curcumin were tested with these particles. A loading efficiency of 81.3% and a sustained release of more than 4 days were achieved in simulated human body condition. It indicates that the covalently-coated MagPluronics are stable carriers with good drug-loading capacity and controlled-release property.Graphical abstractHighlights► The magnetic nanoparticles are covalently coated by Pluronic P85 as drug carriers. ► The synthesis route of the drug carriers is easy and green. ► The drug carriers are superparamagnetic, water-disperse, and temperature-responsive. ► The drug carriers greatly improve the solubility and bioavailability of curcumin. ► The drug carriers are more stable, biocompatible, and suitable for drug delivery.
Co-reporter:Mingzhu Yang, Yueping Guan, Yu Yang, Tingting Xia, Wubin Xiong, Ning Wang, Chen Guo
Journal of Colloid and Interface Science 2013 Volume 405() pp:291-295
Publication Date(Web):1 September 2013
DOI:10.1016/j.jcis.2013.04.045
•Surface modification does not affect the peroxidase-like activity of MNPs.•Modified MNPs display much better thermal stability and pH tolerance than HRP.•Modified MNPs were successfully applied in the detection of hCG.•Modified MNPs were separation carriers and detection indicator in the immunoassay.Amino-functionalized Fe3O4 magnetic nanoparticles with high peroxidase-like activity (MNPs–NH2) are reported in this work. The peroxidase-like activity is approximately the same as naked Fe3O4 magnetic nanoparticles (MNPs). MNPs–NH2 displayed much better thermal stability and pH tolerance than horseradish peroxidase (HRP). The optimal pH and temperature are approximately pH 4 and 40 °C, respectively. We showed that the MNPs–NH2 were successfully applied in a double-antibody sandwich “enzyme”-linked immunosorbent assay to replace of HRP, in which MNPs–NH2 were not only separation carriers, but also detection indicator.Graphical abstract
Co-reporter:Lianwei Jia, Chen Guo, Junfeng Xiang, Ning Wang, Liangrong Yang, Yalin Tang, and Huizhou Liu
Langmuir 2012 Volume 28(Issue 3) pp:1725-1732
Publication Date(Web):December 20, 2011
DOI:10.1021/la203693c
Interaction between PEO–PPO–PEO copolymers and a hexapeptide, growth hormone releasing peptide-6 (GHRP-6), was investigated by NMR to study the potential use of the copolymers in peptide drug delivery. 1H NMR and nuclear Overhauser effect spectroscopy (NOESY) measurements determined that PO methyl protons interacted with methyl protons of the Ala moiety, aromatic protons of the Trp moiety, and some of the Phe aromatic protons. The Lys moiety and part of the Phe moiety entered the hydrophilic EO environment via hydrogen bonding. PEO–PPO–PEO copolymers and the peptide formed a complex in 1:1 stoichiometry. Binding constants between copolymers and GHRP-6 were determined, and it was indicated that the copolymers containing more EO and PO units will lead to greater affinity with the peptide. Isothermal titration calorimetry (ITC) measurements confirmed the results of NMR experiments. This study indicates that PEO–PPO–PEO copolymers have great potential in delivering peptide drugs.
Co-reporter:Lianwei Jia, Chen Guo, Liangrong Yang, Junfeng Xiang, Yalin Tang, and Huizhou Liu
The Journal of Physical Chemistry B 2011 Volume 115(Issue 10) pp:2228-2233
Publication Date(Web):February 20, 2011
DOI:10.1021/jp111418z
In order to investigate the effect of PEO−PPO−PEO copolymers on the glutathione (GSH)/glutathione-S-transferase (GST) detoxification system, interaction between the copolymers and GSH is studied by NMR measurements. Selective rotating-frame nuclear Overhauser effect (ROE) experiment confirms that glutamyl (Glu) α-H of GSH has spatial contact with EO methylene protons. Spin−lattice relaxation times of GSH Glu α-H show a decrease when PEO−PPO−PEO copolymers are added, and the decrease is greater with copolymers possessing more EO units. Other protons of GSH show little change in the presence of the copolymers. The addition of GSH promotes the dehydration of PEO−PPO−PEO copolymers. This results from the breaking of hydrogen bonds between water and the polymers and the forming of hydrogen bonds between Glu α-carboxylate protons and oxygen atoms of EO units. The dissociation constant between GSH and P85 copolymer is determined by spin−lattice relaxation measurements, which shows the binding is of low affinity and the two molecules are in fast dissociation kinetics. This study suggests that GSH transporting or utilizing systems may be affected by treatment of PEO−PPO−PEO copolymers.
Co-reporter:Hongshuai Gao, Chen Guo, Jianmin Xing, Junmei Zhao and Huizhou Liu
Green Chemistry 2010 vol. 12(Issue 7) pp:1220-1224
Publication Date(Web):27 May 2010
DOI:10.1039/C002108C
The Brønsted acidic ionic liquids 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM][HSO4]) and N-butylpyridinium hydrogen sulfate ([C4Py][HSO4]) were used as extractant and catalyst for desulfurization of diesel. The results show that [BMIM][HSO4] is better as extractant and catalyst than [C4Py][HSO4] during the desulfurization process. The sulfur removal of dibenzothiophene (DBT) in n-octane was 99.6% in 90 min under the conditions of Vmodel oil/VIL = 2:1 and H2O2/DBT molar ratio at 5 (O/S = 5), at room temperature. The sulfur removal of four sulfur compounds by extraction and catalytic oxidation process followed the order of DBT > benzothiophene (BT) > thiophene (TS) > 4,6-dimethyldibenzothiophene (4,6-DMDBT). Moreover, the [BMIM][HSO4] can be recycled for at least 6 times with a little decrease in the desulfurization activity. The sulfur removal of diesel fuel containing sulfur content of 97 ppm is 85.5%, which was much better than desulfurization performance by simple extraction with IL (11.0%). In this extraction and oxidative desulfurization process, DBT was oxidized to corresponding sulfone by H2O2 with Brønsted acidic IL [BMIM][HSO4] which served as not only extractant but also catalyst.
Co-reporter:Lianwei Jia, Chen Guo, Liangrong Yang, Junfeng Xiang, Yalin Tang, Chunzhao Liu, Huizhou Liu
Journal of Colloid and Interface Science 2010 Volume 345(Issue 2) pp:332-337
Publication Date(Web):15 May 2010
DOI:10.1016/j.jcis.2010.01.060
The micellization mechanism of PEO–PPO–PEO block copolymer in aqueous solutions was studied by two-dimensional correlation FTIR spectroscopy. The 1400–1000 cm−1 region was investigated, involving the stretching vibrations of ether band, C–H wagging vibrations of EO methylene groups and C–H symmetric deformation vibrations of PO methyl groups. In the 2D correlated spectra, the hydrous and anhydrous state of the ether band, PO methyl groups, and the two conformations of EO methylene groups were observed. Molecules with different PO lengths and increasing molecular weight were investigated to determine the sequence of association of the separate groups. During temperature-induced micellization, the following changes were detected: firstly, EO methylene groups changed from a gauche state to a trans state; secondly, conformational transitions led to the dehydration of hydrated methyl groups; next, the hydrogen bonding between C–O band and water diminished; and finally, dehydrated groups approached to form hydrophobic cores, resulting in micelle formation. From this variation in the sequence of group associations, it is concluded that aggregates of unimers first formed, then hydrophobic cores formed through the hydrophobic interaction from dehydrated PPO blocks, and proper micelles eventually evolved. The temperature-induced conformational changes are suggested the reason for micellization.New insight into the sequence of group associations in PEO–PPO–PEO copolymers was obtained during temperature-induced micellization, using 2D FITR spectroscopy.
Co-reporter:Liangrong Yang, Chen Guo, Lianwei Jia, Keng Xie, Qinghui Shou and Huizhou Liu
Industrial & Engineering Chemistry Research 2010 Volume 49(Issue 18) pp:8518-8525
Publication Date(Web):August 4, 2010
DOI:10.1021/ie100587e
A novel kind of biocompatible pH- and temperature-responsive magnetic nanoparticle consisting of iron oxide nanoparticles coated with pH-responsive chitosan oligosaccharide and temperature-responsive poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) block copolymer was developed. The particles were characterized by TEM, DLS, VSM, FTIR spectroscopy, and TGA. The results indicated that the self-aggregation of the prepared nanoparticles was not only caused by the thermoinduced self-assembly of the immobilized block copolymers, but also affected by the pH-induced charge property change of the particle surface. The self-assembled behaviors can be readily reversed by adjusting the pH or temperature value. Thus, the attractive properties of reversible and controllable dual-responsive self-assembly might endow the biocompatible magnetic nanoparticles with potential applications in biomedical fields such as DNA delivery, drug targeting, and tissue engineering.
Co-reporter:Feng Wang;Hui-Zhou Liu;Chun-Zhao Liu
Journal of Chemical Technology and Biotechnology 2008 Volume 83( Issue 1) pp:97-104
Publication Date(Web):
DOI:10.1002/jctb.1793
Abstract
BACKGROUND: Immobilized enzymes provide many advantages over free enzymes including repeated or continuous reuse, easy separation of the product from reaction media, easy recovery of the enzyme, and improvement in enzyme stability. In order to improve catalytic activity of laccase and increase its industrial application, there is great interest in developing novel technologies on laccase immobilization.
RESULTS: Magnetic Cu2+-chelated particles, prepared by cerium-initiated graft polymerization of tentacle-type polymer chains with iminodiacetic acid (IDA) as chelating ligand, were employed for Pycnoporus sanguineus laccase immobilization. The particles showed an obvious high adsorption capacity of laccase (94.1 mg g−1 support) with an activity recovery of 68.0% after immobilization. The laccase exhibited improved stability in reaction conditions over a broad temperature range between 45 °C and 70 °C and an optimal pH value of 3.0 after being adsorbed on the magnetic metal-chelated particles. The value of the Michaelis constant (Km) of the immobilized laccase (1.597 mmol L−1) was higher than that of the free one (0.761 mmol L−1), whereas the maximum velocity (Vmax) was lower for the adsorbed laccase. Storage stability and temperature endurance of the immobilized laccase were found to increase greatly, and the immobilized laccase retained 87.8% of its initial activity after 10 successive batch reactions.
CONCLUSION: The immobilized laccase not only can be operated magnetically, but also exhibits remarkably improved catalytic capacity and stability properties for various parameters, such as pH, temperature, reuse, and storage time, which can provide economic advantages for large-scale biotechnological applications of laccase. Copyright © 2007 Society of Chemical Industry
Co-reporter:Shu Chen, Bin Yang, Chen Guo, Jun-He Ma, Liang-Rong Yang, Xiangfeng Liang, Chao Hua and Hui-Zhou Liu
The Journal of Physical Chemistry B 2008 Volume 112(Issue 49) pp:15659-15665
Publication Date(Web):November 14, 2008
DOI:10.1021/jp8019039
A novel method has been developed to prepare vesicles from aqueous solutions of poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) triblock copolymer, by adding anionic surfactant sodium dodecyl sulfate (SDS) and inorganic salt NaF. As determined by TEM and dynamic light scattering (DLS) measurements, the average diameter of vesicles is about 800 nm having 50 nm outer shell thickness. Identifying hydrophobic interactions between the block copolymers and the microenvironments around the vesicles using FTIR, 1H NMR, and fluorescence spectroscopy techniques revealed the vesicle formation mechanism. The spontaneously formed vesicles were further cross-linked by converting the terminal hydroxyl groups of block copolymers into aldehydes, and then chemically bridging the polymer chains by the reaction between aldehydes and diamine compounds. The cross-linked vesicles are proved much more stable than free vesicles even at higher dilutions. The obtained vesicles with good stability and biocompatibility are promising candidates for widespread applications.
Co-reporter:Junhe Ma, Chen Guo, Yalin Tang, Junfeng Xiang, Shu Chen, Jing Wang, Huizhou Liu
Journal of Colloid and Interface Science 2007 Volume 312(Issue 2) pp:390-396
Publication Date(Web):15 August 2007
DOI:10.1016/j.jcis.2007.03.013
1H nuclear magnetic resonance (NMR) spectroscopy has been applied to study the temperature and concentration-induced micellization of a poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) triblock copolymer, Pluronic P105, in D2O solutions in the temperature range from 5 to 45 °C and the concentration range from 0.01 to 15% (w/v). The intrinsic probes, the chemical shift, and the half-height width of the PO CH3 signal are very sensitive to the local environment and can be used to characterize the temperature and concentration-dependent aggregation process. When the temperature approaches the critical micellization temperature or the polymer concentration reaches the critical micellization concentration, the chemical shift of the PO CH3 signal moves toward lower ppm values and the half-height width of the PO CH3 signal shows a sudden increase. It indicates that the methyl groups are experiencing a progressively less polar environment and transferring from water to the hydrophobic micellar core. The hydrodynamic radius of the unimers and the micelles are determined as be 1.8 and 5.0 nm by means of pulsed-field gradient spin-echo (PGSE) NMR. They were independent of temperature and concentration. The drastic shortening of spin–lattice relaxation time T1T1 for the PO CH3/CH2 protons in the transition region suggested that the PPO blocks are located in a “liquid-like” micellar core, whereas the exponential increase of T1T1 for the PEO CH2 protons implied that the PEO blocks are still keeping in contact with surrounding water. Thermodynamics analysis according to a closed association model shows that the micellization process is entropy-driven and has an endothermic micellization enthalpy.(a) Overall 1H NMR spetra of 1% Pluronic P105 in D2O solution recorded at 5 °C; (b) Stack plot of PO CH3 signal in 1H NMR spectra at various temperatures.
Co-reporter:Shu Chen;Guo-Hua Hu;Hui-Zhou Liu
Colloid and Polymer Science 2007 Volume 285( Issue 14) pp:1543-1552
Publication Date(Web):2007 November
DOI:10.1007/s00396-007-1721-x
Dissipative particle dynamics (DPD) was used to simulate the formation and stabilization of gold nanoparticles in poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) block copolymer micelles. Primary gold clusters that were experimentally observed in the early stage of gold nanoparticle formation were modeled as gold bead in DPD simulation. It showed that gold beads were wrapped by the block copolymer and aggregated into spherical particles inside the micelles and forming stable Pluronic–gold colloids with two-layer structures. Increasing Pluronic concentration, molecular weight, and PPO block length led to the formation of more uniform and more stable gold nanoparticles. Density profiles of water beads suggested that the micelles, especially the hydrophobicity of the micellar cores, played an important role in stabilizing gold nanoparticles. Dynamic process indicated that the formation of gold nanoparticles was controlled by the competition between aggregation of primary gold clusters and the stabilization by micelles of block copolymers.. The DPD simulation results of gold–copolymer–water system agree well with previous experiments, while more structure information on microscopic level could be provided.
Co-reporter:Junhe Ma, Chen Guo, Yalin Tang, Jing Wang, Lily Zheng, Xiangfeng Liang, Shu Chen, Huizhou Liu
Journal of Colloid and Interface Science 2006 Volume 299(Issue 2) pp:953-961
Publication Date(Web):15 July 2006
DOI:10.1016/j.jcis.2006.02.021
1H and 13C nuclear magnetic resonance (NMR) spectra of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymers in D2O solutions have been systematically investigated. The detailed assignments of various 1H and 13C NMR signals are presented. The hyperfine structure of PO CH2 protons was clearly assigned, the arising reason of this hyperfine structure was attributed to the influence of the chiral center of CHCH3 groups and the direct coupling between the PO CH2 and CH3 protons. The external standard 2,2-dimethyl-2-silapentane-5-sulfonate sodium salt (DSS) was firstly applied in this system. Accurate chemical shift values referenced to the external standard DSS were obtained. 1H NMR chemical shift of PO CH2 and CH3 signals shows a larger decrease in ppm values than that of EO CH2 signal with the increase of PPO/PEO ratio or temperature indicating that PO segments exist in a more hydrophobic microenvironment. A new resonance signal assigned to the PO CH2 protons appeared when the temperature is above the CMT, which is attributed to the breakdown of the intra-molecular (CH)⋯O hydrogen bond between the PO CH2 protons and the ester oxygens. The breakdown of this intra-molecular hydrogen bond may result in a decrease of gauche conformers of the PPO chain. The increase of 13C NMR chemical shift of block copolymers validates this conformational change assumption. It can be inferred that the amount of gauche conformers decreases whereas that of trans conformers increases in both PO and EO chains when elevating the PPO/PEO ratio or temperature. The observed 13C NMR chemical shifts of PO segments show a bigger increase than those of EO segments, supporting the formation of a nonpolar microenvironment around PO segments.(a) One-dimensional original 1H NMR spectrum of 1% (w/v) Pluronic P105 at 20 °C in D2O solution. (b) EO CH2 and PO CH2 region (3.4–3.82 ppm3.4–3.82 ppm). (c) PO CH3 region (1.09–1.22 ppm1.09–1.22 ppm).
Co-reporter:Yangyang Jiang, Chen Guo, Hansong Xia, Iram Mahmood, Chunzhao Liu, Huizhou Liu
Journal of Molecular Catalysis B: Enzymatic (June 2009) Volume 58(Issues 1–4) pp:103-109
Publication Date(Web):1 June 2009
DOI:10.1016/j.molcatb.2008.12.001
Candida rugosa lipase was immobilized on magnetic nanoparticles supported ionic liquids having different cation chain length (C1, C4 and C8) and anions (Cl−, BF4− and PF6−). Magnetic nanoparticles supported ionic liquids were obtained by covalent bonding of ionic liquids–silane on magnetic silica nanoparticles. The particles are superparamagnetic with diameter of about 55 nm. Large amount of lipase (63.89 mg/(100 mg carrier)) was loaded on the support through ionic adsorption. Activity of the immobilized lipase was examined by the catalysis of esterification between oleic acid and butanol. The activity of bound lipase was 118.3% compared to that of the native lipase. Immobilized lipase maintained 60% of its initial activity even when the temperature was up to 80 °C. In addition, immobilized lipase retained 60% of its initial activity after 8 repeated batches reaction, while no activity was detected after 6 cycles for the free enzyme.
Co-reporter:Feng Wang, Chen Guo, Hui-Zhou Liu, Chun-Zhao Liu
Journal of Molecular Catalysis B: Enzymatic (3 September 2007) Volume 48(Issues 1–2) pp:1-7
Publication Date(Web):3 September 2007
DOI:10.1016/j.molcatb.2007.05.003
Magnetic Cu2+-chelated particles, prepared by cerium initiated graft polymerization of tentacle-type polymer chains with iminodiacetic acid (IDA) as chelating ligand, were employed for glucoamylase immobilization. The particles had an obvious high adsorption capacity of glucoamylase with a great activity recovery of 84.0% after immobilization. The immobilized glucoamylase exhibited improved stability in reaction conditions over a wide pH region (pH 3.5–6.0) and a broad temperature range (45–75 °C). The value of the Michaelis constant (Km) of the immobilized glucoamylase (1.77 mg/ml) was higher than that of the free one (1.07 mg/ml), whereas the maximum velocity (Vmax) was lower for the adsorbed glucoamylase. Storage stability and temperature endurance of the immobilized glucoamylase were found to increase greatly, and the immobilized glucoamylase retained 75.7% of its initial activity after 30 successive batch reactions. The magnetic Cu2+-chelated particles also exhibited excellent reusability, indicating the advantage of the magnetic metal-chelated particles in biocatalytic applications.
