Physicochemical Studies on the Micellization of Cationic, Anionic, and Nonionic Surfactants in Water–Polar Organic Solvent Mixtures

The effect of cosolvent (ethane-1,2-diol and dimethyl sulfoxide) on the self-assembly of three surfactants, <i>N</i>,<i>N</i>,<i>N</i>-trimethyl-1-dodecanaminium bromide (DTAB), sodium [dodecanoyl­(methyl)­amino]­acetate (SDDS), and polyoxyethylene (20) sorbitan monolaurate (Tween-20) in aqueous solution have been investigated by conductometric, tensiometric, and viscometric techniques at 298 K. The main focus was on the effect of solvent on critical micelle concentration (cmc), free energy contribution to micellization (Δ<i>G</i>_m⁰), tail transfer Gibbs free energy (Δ<i>G</i>_trans⁰), Gibbs adsorption energy (Δ<i>G</i>_ads⁰), and some micellar interfacial parameters, for example, Gibbs surface excess (Γ_max), minimum area per surfactant molecule (<i>A</i>_min), surface pressure (Π_cmc), and p<i>C</i>₂₀(= −log­(<i>C</i>₂₀), where <i>C</i>₂₀ is the surfactant molar concentration required to reduce the surface tension of mixed solvent by 20 mN m^–1). With increasing concentration of cosolvent in the binary mixture, the cohesive force decreases, and surfactant molecules are more soluble in mixed solvent. As a result, micellization process becomes less favorable, and an increase in cmc was obtained. Steady state fluorescence spectroscopy was used to determine the aggregation number (<i>N</i>_agg) of the surfactants in organic solvent–water binary mixture and also the micropolarity of the mixed solvent. It was observed that <i>N</i>_agg decreased with the increase of organic solvent concentration. The micropolarity of the mixed solvent and packing parameter (<i>P</i>) were also determined

Synthesis, Characterization, X‑ray Crystal Structure, DFT Calculations, and Catalytic Properties of a Dioxidovanadium(V) Complex Derived from Oxamohydrazide and Pyridoxal: A Model Complex of Vanadate-Dependent Bromoperoxidase

A vanadium­(V) complex with the formula [Et₃NH]­[V^VO₂(sox-pydx)] with a new tridentate ligand 2-[2-[[3-hydroxy-5-(hydroxymethyl)-2-methylpyridin-4-yl]­methylene]­hydrazinyl]-2-oxoacetamide (soxH-pydxH), obtained by condensation of oxamohydrazide and pyridoxal (one of the forms of vitamin B₆), has been synthesized. The compound was characterized by various analytical and spectroscopic methods, and its structure was determined by single-crystal X-ray diffraction technique. Density functional theory (DFT) and time-dependent DFT calculations were used to understand the electronic structure of the complex and nature of the electronic transitions observed in UV–vis spectra. In the complex, vanadium­(V) is found to be pentacoordinated with two oxido ligands and a bianionic tridentate ONO-donor ligand. The vanadium center has square-pyramidal geometry with an axial oxido ligand, and the equatorial positions are occupied by another oxido ligand and a phenolato oxygen, an imine nitrogen, and a deprotonated amide oxygen of the hydrazone ligand. A DFT-optimized structure of the complex shows very similar metrical parameters as determined by X-ray crystallography. The O₄N coordination environment of vanadium and the hydrogen-bonding abilities of the pendant amide moiety have a strong resemblance with the vanadium center in bromoperoxidase enzyme. Bromination experiments using H₂O₂ as the oxidizing agent, with model substrate phenol red, and the vanadium complex as a catalyst show a remarkably high value of <i>k</i>_cat equal to 26340 h^–1. The vanadium compound also efficiently catalyzes bromination of phenol and salicylaldehyde as well as oxidation of benzene to phenol by H₂O₂