Heterogeneous Wide Range <Emphasis Type="Italic">pH</Emphasis>-sensing Materials Allowing Ratiometric Fluorescence Detection Based on Structurally Rigid Analogs of 2,6-distyrylpyridine

The new sensing materials based on the microsized silica gel powder with non-covalently immobilized structurally rigid analogs of 2,6-distyrylpyrydine ((3E,5E)-3,5-dibenzylidene-8-phenyl-1,2,3,5,6,7-hexahydrodicyclopenta[b,e]pyridines) were developed and tested. Most of the investigated compositions demonstrate linear ratiometric fluorescence response on pH in the physiologically important interval (pH 6–9). The compound with the greatest number of protolytic centers within the studied series demonstrated the widest pH sensitivity range, however in this case the analytical signal was the lowest. The prospects for the practical application of the investigated materials in the fiber optics sensing devices were outlined.     

Elementary reaction step model of the N‐nitrosation of ammonia

This contribution develops a comprehensive kinetic model of the N-nitrosation reaction mechanism, consisting almost entirely of elementary reaction steps and applies it to study the nitrosation of ammonia. The reaction mechanism features 26 species and 22 reactions, with 8 parallel reaction pathways for ammonia nitrosation and a side pathway for nitrous acid decomposition. We compiled forward and reverse rate constants for each of the reactions, either from the literature sources or by correlation with known rate and equilibrium constants. The concentration of each reaction species with respect to time can be obtained for any set of initial concentrations by invoking a simultaneous solution to the system of ordinary differential equations describing the reaction mechanism. The model successfully predicts previous experimental results for ammonia nitrosation, with and without the addition of the catalyst thiocyanate. The effect of pH on the rate and mechanism of ammonia nitrosation was studied with the model. For uncatalyzed nitrosation, the results indicate that between pH 6.0 and 1.5 the reaction proceeds predominantly via reaction with N₂O₃, whereas ON⁺ nitrosation becomes the preferred pathway below pH 1.5. ONSCN is the dominant nitrosating agent across the entire pH range studied when the nucleophile thiocyanate was added in appreciable quantities. However, with the weak nucleophile Cl⁻, nitrosation by N₂O₃ and ON⁺ governed the reaction kinetics at high and low pH, respectively. We demonstrate that nitrosating agent formation is rapid and does not limit the rate of ammonia nitrosation; however, nitrosating agent formation could become the rate-limiting step for the nitrosation of highly reactive substrates. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 645–656, 2007     

Water soluble complexes of methyl β-cyclodextrin and sulconazole nitrate

Complexation between methyl β-cyclodextrin (Me βCD) and sulconazole nitrate (SULC) was realized both under freeze drying and ultrasonication conditions. The process was carried out in solution and in solid state. In solution, the complexation was evaluated using solubility studies, nuclear magnetic resonance spectroscopy (¹H-NMR) and UV–Vis absorption studies. In the solid state, differential scanning calorimetry (DSC), and X-ray diffraction studies were used. Solubility studies indicate the existence of inclusion complexes between SULC and Me βCD. ¹H-NMR data showed that the inclusion complexes have different structures, according with the method we used for synthesis: for the freeze dried method the complex is obtained by complexation of dichlorobenzene ring of SULC into inner cavity of CD while for ultrasonication method the complex is obtained by complexation of imidazole graph of SULC into the CD molecule. DSC and X-ray studies bring supplementary information concerning the formation of complex Me βCD–SULC. As a result of the inclusion process into Me βCD, the solubility of SULC increase significant, being 10 times more comparative with the pure drug. We anticipate that these modifications will have a significant impact on the biological effects of the drug, making the SULC–Me βCD complex an appropriate candidate for a new drug delivery system.