Photophysical characteristics and density functional theory calculations of indole 2-carboxylic acid in the presence of mercurous ions

Many photo-physical studies have been reported for the detection of Hg²⁺ ions. Here we present the effect of Hg ₂ ²⁺ ions on the absorption and fluorescence of indole-2-carboxylic acid (I2C). Experimental evidence, supported by density functional theory B3LYP/LANL2DZ/PCM, for the formation of a I2C-Hg ₂ ²⁺ complex, is reported for the first time. It was observed that I2C forms a ground-state complex with Hg ₂ ²⁺ ions in a ratio of 3:1. The possibility of I2C to be used as a selective novel chemical sensor for the spectrophotometric detection of mercurous ions is described.     

A validated liquid chromatographic method for estimation of solasodine in various Solanum species and market formulations

This paper describes an improved liquid chromatographic (LC) method involving a prechromatographic derivatization step for the estimation of solasodine from berries of various Solanum species, market samples of Solanum xanthocarpum herb, extract, and its market formulations. Solasodine has heterocyclic nitrogen but has no conjugated double bonds in its structure. However, in all reported LC methods, detection was made in the ultraviolet range of 200-213 nm. In the present study, a prechromatographic derivatization of solasodine was done by forming an ion-pair complex of the heterocyclic nitrogen using the acidic dye methyl orange and acetate buffer of pH 4.7. Detection could be made in the visible range at 530 nm in this method. The method was validated and successfully applied to determine solasodine content in various plant samples and polyherbal formulations. The relative standard deviation was found to be 0.025% for system precision, and 0.8% for the linearity of the method, and the correlation coefficient was 0.999. Plant samples and market formulations were analyzed and found to contain solasodine in the range of 0.113-0.227% (w/w) on a fresh weight basis in berries; 0.3-1.278% (w/w) and 0.412% (w/w) on a dry weight basis in S. xanthocarpum herb powder and extract, respectively; and 0.245-0.525% (w/w) on dry weight basis in formulations containing S. xanthocarpum herb powder. No matrix interference was encountered. The method was found to be accurate, with a mean recovery of 100.5 +/- 0.83%. The method has good reproducibility and was found to be suitable for estimation of solasodine.     

Thermal studies of furosemide–caffeine binary system that forms a cocrystal

Thermal techniques, differential scanning calorimetry (DSC), and hot stage microscopy (HSM) have been used to study the interactions between furosemide and caffeine that are known to form a 1:1 cocrystal. This system has been used as an example to study the probable mechanism of cocrystal formation when the individual components, which are polymorphic, are heated. The study indicates that the phase transition of the low temperature stable polymorph of furosemide initiates cocrystal formation. This result suggests increased mass transfer rate can trigger cocrystal formation. The binary phase diagram (composition–temperature plots) of furosemide–cocrystal–caffeine system was determined from the DSC curves. The results imply that the cocrystal forms eutectic with caffeine but not with furosemide. This study has thus exemplified the use of DSC in understanding binary phase system where the two components form a cocrystal.     

Photo-induced Synthesis and Characterization of Poly（methyl methacrylate） Grafted Sodium Salt of Partially Carboxymethylated Guar Gum

Photo-induced graft copolymerization of methyl methacrylate（MMA） onto sodium salt of partially carboxymethylated guar gum（Na-PCMGG, DS = 0.291） was carried out in an aqueous medium using ceric ammonium nitrate（CAN） as photoinitiator to synthesize a novel graft copolymer, Na-PCMGG-g-PMMA, which may find its potential application as a metal adsorbent. The influences of synthesis variables such as concentrations of photoinitiator（CAN）, nitric acid and monomer（MMA） as well as reaction time, temperature and amount of substrate on the grafting yields were studied and the reaction conditions for optimum photo-grafting were evaluated. At optimum concentration, the maximum values of the grafting yields achieved were G = 271.61% and GE = 63.89%. The experimental results were found to be in very good agreement with the proposed kinetic scheme. The photo-graft copolymerization of MMA onto Na-PCMGG（ DS = 0.291） was also carried out in the presence and absence of ultraviolet radiation for studying the efficiency of the photoinitiator. The influence of carboxymethyl groups introduced onto the guar gum molecules with regard to its behavior towards ultra-violet radiation induced grafting with MMA was also investigated. Photo-grafting process was confirmed and the products were characterized with the help of the spectroscopic（1H-NMR and FTIR） and SEM techniques.     

Determination of selenium(IV) and tellurium(IV) by differential pulse polarography

Differential pulse polarographic methods for the determination of selenium(IV) and tellurium(IV) in nitric acid medium are described. The peak current is maximal when 0.25M nitric acid medium is used, the DPP peaks for Se(IV) and Te(IV) being at -0.54 and -0.8 V vs. Ag/AgCl respectively. The peak current is a linear function of selenium concentration over three ranges, 5.1 x 10(-6)-1.3 x 10(-5), 1.27 x 10(-5)-1.27 x 10(-4) and 1.27 x 10(-4)-7.60 x 10(-4)M Se(IV), with different slopes. The plot for Te(IV) is linear over the range 0.78 x 10(-6)-9.40 x 10(-5)M.     

Measurement techniques for mercury species in ambient air

This review critically evaluates the measurement methodologies most commonly employed for the analysis of the various forms of mercury (Hg) in air. Emphasis is given to the three most common forms of mercury in air [i.e. gaseous elemental mercury (GEM, Hg⁰), reactive gaseous mercury (RGM), and particle-bound mercury (Hg_p)]. Moreover, we also briefly describe methods dealing with gas-phase analysis of organic mercury species (e.g., mostly methyl mercury), as they are also reported to be present in air on rare occasions. To begin with, we describe the approaches to sampling airborne mercury species and associated sample-treatment strategies. We evaluate both conventional and emerging alternative detection techniques for different mercury forms with respect to their applicability in airborne mercury analysis. We also discuss the artifacts and the biases associated with analysis of different mercury species. Finally, the review summarizes current methodological developments for the determination of mercury in air and highlights future prospects for improvements.     

Three component tandem reactions involving protected 2-amino indoles, disubstituted propargyl alcohols, and I2/ICl: iodo-reactant controlled synthesis of dihydro-α-carbolines and α-carbolines via iodo-cyclization/iodo-cycloelimination

Two simple, highly efficient three component tandem reactions for the synthesis of diversified N^aN^b di-carbamate-4,9-dihydro-3-iodo-α-carbolines and N^a-carbamate-3-iodo-α-carbolines have been described. The strategy involves one-pot condensation of bis-carbamate protected 2-amino indoles with disubstituted propargyl alcohols and I₂/ICl. The salient feature of the reaction involves iodocyclo-elimination of N^b-linked carbamate under mild condition in the final step.