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The potentiometric titration (PT) method has been applied for the first time to investigate the stability of l-ascorbic acid (H2Asc) and to determine its degradation products in aqueous solutions. The presented electrochemical procedures can be considered to be a fast, simple and inexpensive way to control the stability of H2Asc in a regular analytical practice as well as in the chemical and pharmaceutical industries. Experimental data as well as modeling suggest that the enolic form of 2,3-diketogulonic acid predominates in a solution as the main product of dehydroascorbate degradation. Furthermore, the PT results supported by conductometric measurements and electrospray ionization mass spectrometry data enable us to propose the putative mechanism of the H2Asc decomposition. Moreover, it has been proven that among different types of investigated electrolytes (KNO3, KClO4 and KSCN), the thiocyanate ions (SCN−) reveal the stabilizing effect against the degradation of H2Asc. Thus, the presence of SCN− in the H2Asc solution is proposed as an alternative way for some organic solvents earlier used. Finally, a new paraffin-protection-layer procedure has been recommended for studying as well as storage of the solutions comprising components sensitive to external factors (e.g. O2, CO2) and to evaporation. [ABSTRACT FROM AUTHOR]

Three complementary experimental techniques: isothermal titration calorimetry, differential scanning calorimetry and conductometric titration, have successfully been applied to describe the process of sodium dodecyl sulphate (SDS) micellization in the presence of pH buffering substances, namely 2-(N-morpholino)ethanesulfonic acid, piperazine-N,N'-bis(2-ethanesulfonic acid), 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid and 3-(N-morpholino)propanesulfonic acid, commonly used in biological experiments as well as in calorimetric studies. The measurements were taken in aqueous solutions (pH 6.5), at 298.15 K. The influence of the buffer components as well as the composition of the system under study on the critical micelle concentration, the molar standard enthalpy for micelle formation (Δ H) and the molar heat capacity that corresponds to the thermal midpoint ( T) of micelle transition has been discussed. It has been shown that the dependence of SDS stability on the kind of buffer may be helpful for the precise interpretation of the molecular recognition processes. [ABSTRACT FROM AUTHOR]

The potentiometric and conductometric titration methods have been used to characterize the stability of series of VO(IV)-, Co(II)- and Ni(II)-oxydiacetato complexes in DMSO-water solutions containing 0-50 % ( v/ v) DMSO. The influence of DMSO as a co-solvent on the stability of the complexes as well as the oxydiacetic acid was evaluated. Furthermore, the reactivity of the complexes towards superoxide free radicals was assessed by employing the nitro blue tetrazolium (NBT) assay. The biological properties of the complexes were investigated in relation to their cytoprotective activity against the oxidative damage generated exogenously by using hydrogen peroxide in the Human Dermal Fibroblasts adult (HDFa) cell line as well as to their antimicrobial activity against the bacteria ( Bacillus subtilis, Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis). The relationship between physicochemical and biological properties of the complexes was discussed. [ABSTRACT FROM AUTHOR]

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Analgesic efficacy was determined by the hot plate method for a group of 17 new pyrazine and 3 non-pyrazine CH and NH acids. The biological data were quantitatively related to the hydrophobicity of the compounds, expressed by fragmental constant, and to the orbital energy of the highest occupied molecular orbital, calculated quantumchemically. It has been found that the higher the electron donating properties, the more active is the agent, provided that its hydrophobicity allows it to reach its site of action. The results obtained support the charge transfer model for the biological interaction of analgesic agents. [ABSTRACT FROM AUTHOR]