Selective Determination of Total Capsaicinoids in Plant Material Using Poly(Gallic Acid)‐modified Electrode

Novel voltammetric approach for the selective determination of total capsaicinoids has been developed using glassy carbon electrode modified with multi‐walled carbon nanotubes and poly(gallic acid) (PGA/MWNT/GCE). The modified electrode provides significant improvements in the capsaicinoids voltammetric characteristics in comparison to GCE and MWNT/GCE. The electrooxidation of capsaicinoids is irreversible adsorption‐controlled process with the anodic transfer coefficient of 0.49–0.53 and heterogeneous electron transfer rate constant of 1300–2400 s^?1. The analytical ranges of 0.010–1.0 and 1.0–50 μM for capsaicin, 0.025–0.75 and 0.75–75 μM for dihydrocapsaicin and 0.025–5.0 and 5.0–75 μM for nonivamide with the detection limits of 2.9, 5.9 and 6.1 nM, respectively, have been obtained using differential pulse voltammetry (DPV). The selectivity of the capsaicinoids quantification in the presence of ascorbic acid, α‐tocopherol and carotenoids is shown. The method has been tested on the samples of red hot pepper spices and Capsicum annuum L. tinctures. The results correspond to the chromatographic data.     

Theoretical study of solvent effects on the thermodynamics of iron(III) [tetrakis(pentafluorophenyl)]porphyrin chloride dissociation

A quasichemical method that combines ab initio treatment of explicit solvent with dielectric continuum models has been used to study the origin of a strong effect of methanol on the extent of iron(III) [tetrakis(pentafluorophenyl)]porphyrin chloride dissociation in acetonitrile-methanol solutions. It is shown that the dissociation is energetically more favorable in methanol than in acetonitrile primarily because of the strong specific interactions between the chloride anion and the solvent methanol molecules in its first solvation shell. These interactions are weaker in acetonitrile. The final estimate for the difference in the dissociation free energies in methanol and acetonitrile is -23 kJ/mol, in a good agreement with the experimental value of -21 kJ/mol. Energy decomposition analysis of chloride-solvent interactions suggests that stronger chloride-methanol binding is a result of the contribution of charge delocalization effects to the chloride-methanol interactions.     

Preparation of novel heterogeneous catalysts by adsorption of a cationic tetrapyrrole on to bentonite: equilibrium, kinetics, and thermodynamics

Abstract  

Adsorption of an octacationic tetrapyrrole, octakis(2-trimethylammoniumethylsulfanyl)porphyrazinatocobalt octaiodide (QCoPz), from aqueous solutions on to negatively charged bentonite was investigated. Effects of temperature, dye concentration, solid concentration, and contact time on adsorption were determined. Zeta potential and ion-release measurements were also used as supporting experiments. Experimental data were analyzed using four adsorption kinetic models; a pseudo second-order kinetic model resulted in better correlation with experimental results than the others. Experimental equilibrium data were analyzed by non-linear regression using five adsorption isotherm models with two, three, or four terms. Free energies, enthalpies, and entropies for the adsorption process were determined. The results indicated that adsorption of QCoPz on bentonite was exothermic and spontaneous in nature. FT-IR spectroscopy of the composite and its desorptive behavior were also investigated to identify the mechanism of adsorption. The novel QCoPz–bentonite composites obtained are likely to be used in “green chemistry” and in a wide range of optical and/or catalytic applications, especially those crucially important in the petroleum and pulp/paper industries for waste water cleaning (destruction of mercaptans, sulfides, phenol, and halogenated aromatics, etc.) and removal of bad odor.