Andrographolide: Solving Chemical Instability and Poor Solubility by Means of Cocrystals

The bioactive agent andrographolide was screened with pharmaceutically acceptable coformers to discover a novel solid form that will solve the chemical instability and poor solubility problems of this herbal medicine. Liquid‐assisted grinding of andrographolide with GRAS (generally regarded as safe) coformers in a fixed stoichiometry resulted in cocrystals with vanillin (1:1), vanillic acid (1:1), salicylic acid (1:1), resorcinol (1:1), and guaiacol (1:1). All the crystalline products were characterized by thermal, spectroscopic, and diffraction methods. Interestingly, even though the cocrystals are isostructural, their physicochemical properties are quite different. The andrographolide–salicylic acid cocrystal completely inhibited the chemical transformation of andrographolide to its inactive sulfate metabolite, and moreover, the cocrystal exhibited a dissolution rate that was three times faster and a drug release that was two times higher than pure andrographolide.     

Liquid chromatography tandem mass spectrometry method for the quantification of rimonabant, a CB1 receptor antagonist, in human plasma

A sensitive high-performance liquid chromatography-tandem mass spectrometry method was developed and validated for the quantification of rimonabant in human plasma. Following liquid-liquid extraction, the analytes were separated using an isocratic mobile phase on a reverse-phase column and analyzed by MS/MS in the multiple reaction monitoring mode using the respective (M+H)+ ions, m/z 463-363 for rimonabant and m/z 408-235 for the internal standard. The assay exhibited a linear dynamic range of 0.1-100 ng/mL for rimonabant in human plasma. The lower limit of quantification was 0.1 ng/mL with a relative standard deviation of less than 6%. With dilution integrity up to 10-fold, the upper limit of quantification was extendable up to 1000 ng/mL. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.0 min for each sample made it possible to analyze more than 250 human plasma samples per day. The validated method was successfully used to analyze human plasma samples for application in pharmacokinetic studies.     

COSMO-RS Based Predictions for the Extraction of Lignin from Lignocellulosic Biomass Using Ionic Liquids: Effect of Cation and Anion Combination

A total of 34 cations belonging to 6 classes and 34 anions resulting in 1156 possible combinations are screened using the quantum chemical based COSMO-RS (COnductor-like Screening MOdel for Real Solvents) model. The Hildebrand solubility parameter (?? _H) is calculated using the predicted infinite dilution activity coefficient (?? ^??) of lignin in ionic liquids at 303.15 K. Initial benchmarking is performed by predicting the Hildebrand solubility parameter of lignin in ionic liquids. Comparison with literature values involving 12 ILs gives the average root mean square deviation (RMS) as 10.15?%. Except for anions based on hexafluorophosphate [PF₆], bis(oxalato(2)borate) [BOB], tetracyanoborate [B(CN)₄] and bis(trifluoromethylsulfonyl)amide [BTA], all the cation?Canion combinations have calculated solubility parameters equal to that of lignin at 303.15 K, indicating high solubilities for lignin.     

Effect of gamma irradiation on transport of charge carriers in Cu nanowires

In this paper, we report the effect of gamma ray photons on the electrical conductivity of 100 nm Cu nanowires prepared by the technique of electrodeposition using track-etched membranes. Different fluences of photons have been used to observe the effect and in each case of post-irradiation, electrical conductivity is found to increase in a linear manner with increase in applied potential difference; however the rate of increase of conductivity is different in different cases of radiation fluence. Grain boundary scattering is of significance for the post-irradiation parabolic nature of the I–V characteristics (IVC), which are of a linear pattern following Ohm’s law before irradiation. Increase or decrease in the number of charge carriers during their transport through the nanowires is the result of two competitive processes—specular and diffusive scattering of charge carriers (electrons) from grain boundaries, which are itself a region of high resistance rather than inter-grain regions. The results have been discussed in light of the Mayadas and Shatzkes (MS) model with a slight modification for irradiated nanowires.