Narrow Results

The antioxidative activities of 12 medicinal plants and the compounds isolated from them were investigated using the thiocyanate method to evaluate inhibitory effects on lipid peroxidation in the linoleic acid system. The peroxide levels gradually increased during incubation in the presence of linoleic acid over 3 days, and most of the plants inhibited lipid peroxidation. In particular, of the plants tested, Cudrania tricuspidata, Zanthoxylum piperitum, Houttuynia cordata and Ulmus parvifolia reduced lipid peroxidation more effectively as lipid peroxidation progressed, resulting in inhibition of about 80% relative to the control value by the 3rd day of incubation. In addition, the polyphenols isolated from the plants also showed marked and dose-dependent inhibitory effects on lipid peroxidation. The compounds with the strongest activities were 3,4-dihydroxylbenzoic acid, quercetin, the quercetin glycosides quercetin-3-O-β-D-galactoside, quercetin-3-O-α-L-rhamnoside, quercetin-3-O-β-D-glucoside and quercetin-3-O-rutinose, catechin, gallic acid, methyl gallate and rosamultin isolated from Zanthoxylum piperitum, Houttuynia cordata, Rosa rugosa and Cedrela sinensis. Moreover, quercetin glycosides showed stronger activity than quercetin, suggesting that glycosylation increases the antioxidative activity of quercetin. Our results indicate that the medicinal plants and their polyphenols show promise as therapeutic agents for various disorders involving free radical reactions.

The single crystal X-ray structure of [Co(TPP)(BzNH₂)₂](SCN), compound 2, where TPP = 5,10,15,20-tetraphenylporphyrin dianion and BzNH₂ = benzylamine, reveals that the SCN^- ion is hydrogen-bonded to one of the coordinated amino group hydrogen atoms via its sulfur atom. Furthermore, the N–H⋯SCN interaction is balanced by a stronger N–H⋯NCS hydrogen bonding interaction for the trans BzNH₂ ligand as a result of the multiple hydrogen bond accepting character of the thiocyanate ion. Analysis of the crystal packing shows that these two hydrogen bonds play a major role in fixing unusual orientations for the axial ligands relative to the porphyrin ring in this system. This, in turn, leads to the formation of a nonplanar porphyrin core conformation that is a mixture of ruffle- and saddle-type distortions. The intricate hydrogen bonding between the cations and anions in 2 results in an unusually long mean Co–N_amine coordination distance of 2.033(4) Å, some 0.05 Å longer than previously observed for other bis(primary amine) complexes of Co(III) porphyrins with comparable porphyrin ligands. Density functional theory (DFT) calculations at the B3LYP/LACVP* level of theory have been used to gauge the perturbation of the electronic structure of the [Co(TPP)(BzNH₂)₂]⁺ cation caused by the N–H⋯SCN and N–H⋯NCS hydrogen-bonded SCN^- ions. The calculations show that partial mixing of the anion MOs with those of the porphyrin cation lead to changes in the electron populations of the 3d orbitals of up to 0.42 e as well as more nearly tetragonal electronic symmetry for the Co(III) ion as a result of adjustments of the relative energies of the MOs with predominantly 3d character.

Metalloporphyrin-based ion-selective electrodes for flow-injection potentiometric determination of thiocyanate are described. The detection system is based on a coated glassy carbon electrode membrane sensor incorporating 5,10,15,20-tetraphenyl-21H,23H-porphine manganese(III) chloride as the active ingredient. The influences of the membrane composition, pH, and the effects of flow-injection parameters on the response of the system were investigated. At the optimized flow-injection potentiometric conditions, the sensor exhibited a Nernstian slope of -58.0 mV per decade of thiocyanate activity over the range 4.2 × 10^-7–7.6 × 10^-2M, where 50 μL of each sample solution was injected into the carrier solution. The detection limit of thiocyanate in the FIP mode was 4.2 × 10^-7M. The selectivity of the flow-injection potentiometric system with respect to several common inorganic and organic anions was superior to that of the batch mode using the same sensor and similar operating conditions. The sensor was applied to the determination of thiocyanate in urine samples.

Electrochemical oxidation of thiocyanate in sulphuric acid medium at 0-2°C was studied using cyclic voltammetry. The electro oxidation produces trithiocyante, SCN₃^- as the relatively stable, reducible species. The SCN₃^- is produced only up to a limited potential range at low concentration of thiocyanate. The potential range of SCN₃^- formation increases with increase in concentration of thiocyanate and it is exclusively produced in the potential range of 0.450 - 1.40 V with 1.0M thiocyanate.