2 research outputs found
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 [dodecanoylÂ(methyl)Âamino]Âacetate (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><sub>m</sub><sup>0</sup>), tail transfer Gibbs free energy (Δ<i>G</i><sub>trans</sub><sup>0</sup>), Gibbs adsorption energy (Δ<i>G</i><sub>ads</sub><sup>0</sup>), and some micellar
interfacial parameters, for example, Gibbs surface excess (Γ<sub>max</sub>), minimum area per surfactant molecule (<i>A</i><sub>min</sub>), surface pressure (Î <sub>cmc</sub>), and p<i>C</i><sub>20</sub>(= −logÂ(<i>C</i><sub>20</sub>), where <i>C</i><sub>20</sub> is the surfactant molar
concentration required to reduce the surface tension of mixed solvent
by 20 mN m<sup>–1</sup>). 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><sub>agg</sub>) of the surfactants
in organic solvent–water binary mixture and also the micropolarity
of the mixed solvent. It was observed that <i>N</i><sub>agg</sub> 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 vanadiumÂ(V) complex with the formula
[Et<sub>3</sub>NH]Â[V<sup>V</sup>O<sub>2</sub>(sox-pydx)] with a new
tridentate ligand 2-[2-[[3-hydroxy-5-(hydroxymethyl)-2-methylpyridin-4-yl]Âmethylene]Âhydrazinyl]-2-oxoacetamide
(soxH-pydxH), obtained by condensation of oxamohydrazide and pyridoxal
(one of the forms of vitamin B<sub>6</sub>), 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, vanadiumÂ(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 O<sub>4</sub>N 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 H<sub>2</sub>O<sub>2</sub> 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><sub>cat</sub> equal to 26340 h<sup>–1</sup>. The vanadium compound also efficiently catalyzes bromination of
phenol and salicylaldehyde as well as oxidation of benzene to phenol
by H<sub>2</sub>O<sub>2</sub>