Design, synthesis and stimuli responsive gelation of novel stigmasterol-amino acid conjugates

An efficient synthesis of three novel stigmasterol-amino acid (glycine, L-leucine and L-phenylalanine) conjugates as stimuli responsive gelators is reported. The gelation properties of the prepared compounds were investigated in a variety of organic as well as aqueous solvents. The most striking finding of our investigation was that the hydrochloride salts of the prepared conjugates acted as gelators, whereas the neutral conjugates were either non-gelators or formed only a weak gel in anisole. The hydrochloride salts of stigmasteryl glycinate and L-leucinate form gels in n-alcohols (n=4-10) and in ethane-1,2-diol, and that of stigmasteryl L-phenylalaninate forms gels in aromatic solvents and in tetrachloromethane. These unique properties of the gelators were explored to prepare stimuli responsive, "acid-base" triggered reversible sol-gel transitions. The gelators and their gels were characterized by liquid and solid-state NMR as well as FT-IR. The morphology of their corresponding xerogels was investigated by SEM.     

Sequential injection determination of orthophosphate as ion associate of 12-molybdophosphate with Astra Phloxine

A simple and fast reaction between 12-molybdophosphate heteropoly anion and the polymethine dye Astra Phloxine was used for the development of a new SIA method for the determination of orthophosphate. The suggested method has higher sensitivity and a broader calibration range than existing SIA methods. It can be used to detect phosphate in the range from 0.2 to 10 μmol L⁻¹ with a detection limit of 0.1 μmol L⁻¹ and an acceptable throughput of 20 samples h⁻¹. The comparably low molybdate (5.6 mmol L⁻¹) and dye (0.1 mmol L⁻¹) concentrations led to an improvement in the stability of the base line. Inter-day reproducibility was better than 5%, while the intra-day RSD was in the range 0.8-3.5%. The method was used for the analysis of natural water samples and phosphorus-containing chemicals having a low content of orthophosphate.