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Hydrotropes affect a several-fold increase of the solubility of sparingly soluble solutes under normal conditions. Their water-solubility can significantly enhance the solubility of organic solutes such as esters, alcohols, aldehydes, ketones, hydrocarbons, and fats. While the study of hydrotropes is pioneered by a biochemist, greater appreciation of their role and applicability has happened rather in chemistry and chemical engineering than in biology. Hydrotropes are widely used in drug solubilization, as extraction agents for fragrances, as agents to increase the rate of heterogeneous reactions, and for separation of close-boiling liquid mixtures through extractive distillation and liquid-liquid extraction. Applications of hydrotropy and its mechanism are discussed and the scope for future work is presented in this review.

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SynopsisDensities of solutions of several a-amino acids and peptides in 3 and 6m aqueous urea solvents have been determined at 298.15 K. These data have been used to evaluate the infinite-dilution apparent molar volumes of the solutes and the volume changes due to transfer

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Main factors responsible for the red to near infrared (NIR) absorption of the benzobis(1,2,5‐thiadiazole) (BBT) derivatives have been investigated using high level computational studies. These molecules with NIR emission are of importance due to the recent reports of possible role in NIR organic light emitting diodes (OLED) development. The electronic structure has been determined using closed‐shell/open‐shell DFT methods (B3LYP and BHandHLYP). The wavefunction stabilities of these BBT derivatives have been tested. We notice that using the BHandHLYP functional, the wave function becomes instable though large HOMO–LUMO gaps (HLG) are obtained. On the other hand a stable wavefunction is obtained using the B3LYP functional but the HLG is small. The B3LYP HLG is in good agreement with the available experimental data. Nevertheless results from both functionals indicate a possible LUMO occupation/biradicaloid character (BRC). We calculated the BRC for all the molecules using different methods and observed that these molecules have a large BRC which correlates well with excitation energies. Larger the BRC smaller the excitation energy. Charge transfer based on Mulliken charges of both ground and excited state are obtained from high level SAC/SAC‐CI studies. We carried out the VB studies of the unsubstituted BBT to predict the relative weights of the individual Lewis structures to the resonance picture. It is concluded that a more general description which include the zwitterionic and biradical structures are necessary for these molecules and not just simple donor–acceptor–donor (D–A–D) structures as suggested in the literature. Copyright © 2011 John Wiley & Sons, Ltd.

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Abstract. Simple, sensitive and selective methods are proposed for the spectrophotometric determination of drugs, viz., tetracycline HC1, nifurtimox, ethionamide, propranolol HC1 and isonicotinic acid hydrazide, based on their reactivity with N-bromosuccinimide (NBS). The method involves the addition of excess NBS of known concentration in the presence of 0.25 M HC1 and the unreacted NBS is determined by the measurement of the decrease in the absorbance of the dye celestine blue (2m,x 540 rim), which was found to be the most suitable of several dyes tested. This method was applied for the determination of drug contents in pharamaceutical formulations and enabled the determination of the drugs in microgram quantities (0.2 to 5 gg/ml). Standard deviations were typically ~<0.5mg per dose (RSD 0.1-1.0%). No interferences were observed from excipients and the validity of the method was tested against reference method. Recoveries were 99.8-101.1%.