G-quadruplex sequences exist in eukaryotic organisms and prokaryotes, and the investigation of the interactions between G-quadruplexes and small molecule ligands is important for gene therapy, biosensor fabrication, fluorescence imaging and so on. Here, we investigated the behaviour of methylene blue (MB), an electroactive molecule, in the presence of different intramolecular G-quadruplexes by an electrochemical method using a miniaturized electrochemical device based on its intrinsic electrochemical properties. Although the effects of MB on different intramolecular G-quadruplex structures are not obvious by circular dichroism spectroscopy, distinct differences in the binding affinities of MB with different intramolecular G-quadruplexes were quickly and easily observed by an electrochemical technique. At the same time, for the human telomerase G-rich sequence (HT), the diffusion current of MB changed sensitively under different ionic conditions due to the formation of different conformations of HT, which indicated that our electrochemical method has the potential to study the influence of metal ions on the conformations of the G-quadruplexes with simplicity, rapid response and low cost. From all these, a new stacking mechanism and rule were obtained, which were also validated by docking studies and isothermal titration calorimetry (ITC).

•An overview of the effects of combining cationic surfactants and aromatic anions across concentration regimes is provided.•Aggregation processes involving aromatic anions and cationic surfactants at concentrations below their cmc are discussed.•Linking concentration regimes provides a framework for translation of findings for reactive probes to organic synthesis.The use of aqueous solutions as solvents in synthetic chemistry is one of the pathways towards more sustainable chemical processes. To increase solubility of reactants in aqueous solutions, surfactants can be used. In particular as a result of detailed kinetic studies involving probe reactions, our current understanding of the reaction environment offered by micelles is good to excellent. However, this understanding does not always translate well to reactions on a synthetic scale because concentrations are typically very different from concentrations used in probe reactions. These high concentrations may lead to changes in aggregate morphologies, in particular where aromatic anions are used in combination with cationic surfactants. An overview of aggregation processes and aggregate morphologies across concentration scales is presented together with a discussion of the resulting effects on reactivity in solutions containing cationic surfactants and (reactive) aromatic anions.Download high-res image (111KB)Download full-size image

UV-visible titrations, 1H NMRD experiments and molecular docking studies show that emissive anthraquinone appended dimetallic lanthanide complexes bind to DNA. The strength of binding and the observed relaxivity behaviour depend on the nature of the substituted anthraquinone core.

The nature of the rate-retarding effects of anionic micelles of sodium dodecyl sulfate (SDS) on the water-catalyzed hydrolysis of a series of substituted 1-benzoyl-1,2,4-triazoles (1a–f) has been studied. We show that medium effects in the micellar Stern region of SDS can be reproduced by simple aqueous model solutions containing small-molecule mimics for the surfactant headgroups and tails, namely sodium methyl sulfate (NMS) and 1-propanol, in line with our previous kinetic studies for cationic surfactants (Buurma et al. J. Org. Chem. 2004, 69, 3899−3906). We have improved our mathematical description leading to the model solution, which has made the identification of appropriate model solutions more efficient. For the Stern region of SDS, the model solution consists of a mixture of 35.3 mol dm–3 H2O, corresponding to an effective water concentration of 37.0 mol dm–3, 3.5 mol dm–3 sodium methylsulfate (NMS) mimicking the SDS headgroups, and 1.8 mol dm–3 1-propanol mimicking the backfolding hydrophobic tails. This model solution quantitatively reproduces the rate-retarding effects of SDS micelles found for the hydrolytic probes 1a–f. In addition, the model solution accurately predicts the micropolarity of the micellar Stern region as reported by the ET(30) solvatochromic probe. The model solution also allows the separation of the individual contributions of local water concentration (water activity), polarity and hydrophobic interactions, ionic strength and ionic interactions, and local charge to the observed local medium effects. For all of our hydrolytic probes, the dominant rate-retarding effect is caused by interactions with the surfactant headgroups, whereas the local polarity as reported by the solvatochromic ET(30) probe and the Hammett ρ value for hydrolysis of 1a–f in the Stern region of SDS micelles is mainly the result of interactions with the hydrophobic surfactant tails. Our results indicate that both a mimic for the surfactant tails (NMS) and a mimic for the surfactant headgroups (1-propanol) are required in a model solution for the micellar pseudophase to reproduce all medium effects experienced by a variety of different probes.

The syntheses of two chromophore-appended dipicolylamine-derived ligands and their reactivity with pentacarbonylchlororhenium have been studied. The resultant complexes each possess the fac-Re(CO)3 core. The ligands L111-[bis(pyridine-2-ylmethyl)amino]methylpyrene and L22 2-[bis(pyridine-2-ylmethyl)amino]methylquinoxaline were isolated via a one-pot reductive amination in moderate yield. The corresponding rhenium complexes were isolated in good yields and characterised by 1H NMR, MS, IR and UV-Vis studies. X-Ray crystallographic data were obtained for fac-{Re(CO)3(L11)}(BF4), C34H26BF4N4O3Re: monoclinic, P2(1)/c, a = 18.327(2) Å, α = 90.00°, b = 14.1537(14) Å, β = 96.263(6)°, c = 23.511(3) Å, γ = 90.00°, 6062.4(11) Å3, Z = 8. The luminescence properties of the ligands and complexes were also investigated, with the emission attributed to the appended chromophore in each case. Isothermal titration calorimetry suggests that fac-{Re(CO)3(L11)}(BF4) self-aggregates cooperatively in aqueous solution, probably forming micelle-like aggregates with a cmc of 0.18 mM. Investigations into the DNA-binding properties of fac-{Re(CO)3(L11)}(BF4) were undertaken and revealed that fac-{Re(CO)3(L11)}(BF4) binding to fish sperm DNA (binding constant 1.5 ± 0.2 × 105 M−1, binding site size 3.2 ± 0.3 base pairs) is accompanied by changes in the UV-Vis spectrum as typically observed for pyrene-based intercalators while the calorimetrically determined binding enthalpy (−14 ± 2 kcal mol−1) also agrees favourably with values as typically found for intercalators.

UV-visible titrations, 1H NMRD experiments and molecular docking studies show that emissive anthraquinone appended dimetallic lanthanide complexes bind to DNA. The strength of binding and the observed relaxivity behaviour depend on the nature of the substituted anthraquinone core.