Thermodynamic investigation on M–Te–O (M = Sc, Y) system

The standard Gibbs energy of formation of M₂TeO₆ and M₆TeO₁₂ (where M = Sc, Y), was determined from its vapor pressure measurements by employing thermogravimetry-based transpiration technique. This technique was validated by measuring the vapor pressure of well-studied substances such as TeO₂(s) and CdCl₂(s). The temperature dependence of the vapor pressure of TeO₂(g) over the mixtures M₆TeO₁₂ + M₂O₃ (where M = Sc, Y), generated by the incongruent vaporization reaction, M₆TeO₁₂(s) → 3M₂O₃(s) + TeO₂(g) + ½O₂(g) were measured in the temperature range 1,413–1,473 K and 1,623–1,743 K for Sc₆TeO₁₂(s) and Y₆TeO₁₂(s), respectively. Similarly, the vapor pressure of TeO₂(g) over the mixtures M₂TeO₆(s) + M₆TeO₁₂(s) generated by the vaporization reaction, 3M₂TeO₆(s) → M₆TeO₁₂(s) + 2TeO₂(g) + O₂(g) was measured in the temperature range (1,223–1,293 K) and (1,333–1,423 K) for Sc₂TeO₆(s) and Y₂TeO₆(s), respectively. From the vapor pressure measurements, the standard Gibbs energy of formation of M₆TeO₁₂ and M₂TeO₆ were derived.     

Thermal analysis of interaction between 2-PAM chloride and various excipients in some binary mixtures by TGA and DSC

Pralidoxime chloride known as 2-PAM chloride is used as antidote for nerve agent’s poisoning. This study was undertaken to establish the compatibility of 2-PAM chloride with a number of commonly used excipients by using thermoanalytical technique viz., differential scanning calorimetry (DSC) and thermogravimetry/differential thermogravimetry (TG/DTG) used in pharmaceutical formulation. The TG and DSC both results demonstrated that polyvinyl alcohol, polyacrylamide, microcrestline cellulose, hydroxypropyl cellulose, cellulose acetate, ethyl cellulose found to be compatible with 2-PAM chloride and chosen for the preparation of antidote against chemical warfare agents.     

Solvent-Free Esterification of Carboxylic Acids and Alcohols in the Presence of Silphos [PCl3-n(SiO2)n] as a Heterogeneous Phosphine Reagent

An efficient solvent-free method for the preparation of esters from various aromatic and aliphatic acids with primary, secondary, and tertiary alcohols using a heterogeneous phosphine reagent, silphos [PCl_3-n(SiO₂)_n], in good yields is reported.     

Synthesis of Novel Spiro[indol-2,2′-pyrroles] Using Isocyanide-Based Multicomponent Reaction

An efficient and facile method for the synthesis of novel spiro[indole-2,2′-pyrroles] from N-methyl-3-isatin imines, t-butyl isocyanide, and dialkyl acetylenedicarboxylate has been achieved by [3 + 2] cyclo addition reaction. All the products were purified by column chromatography as yellow solids and confirmed with ¹H NMR, ¹³C NMR, fast atom bombardment, mass, and infrared. Compound 11 was further confirmed with x-ray analysis.     

Raman spectroscopic characterization of urine of normal and oral cancer subjects

Urine is considered as one of the diagnostically important bio fluids, as it has many metabolites. The distribution and the physiochemical properties of the metabolites may vary during any altered metabolic and pathological conditions. Raman spectroscopy was employed in the characterization of the metabolites of human urine of normal subjects and oral cancer patients in the finger print region (500–1800 cm⁻¹). Principal component analysis‐based linear discriminant analysis was performed to discriminate cancer patients from normal subjects. The discriminant analysis classifies the cancer patients from normal subjects with a sensitivity and specificity of 98.6% and 87.1%, respectively, with an overall accuracy of 93.7%. Copyright © 2014 John Wiley & Sons, Ltd.     

pH‐controlled reaction divergence of decarboxylation versus fragmentation in reactions of dihydroxyfumarate with glyoxylate and formaldehyde: parallels to biological pathways

The reactions of dihydroxyfumarate with glyoxylate and formaldehyde exhibit a unique pH‐controlled mechanistic divergence leading to different product suites by two distinct pathways. The divergent reactions proceed via a central intermediate (2,3‐dihydroxy‐oxalosuccinate, 3 , in the reaction with glyoxylate and 2‐hydroxy‐2‐hydroxymethyl‐3‐oxosuccinate, 14 , in the reaction with formaldehyde). At pH 7–8, products ( 7 , 8 , and 15 ) exclusively from a decarboxylation of the intermediate are observed, while at pH 13–14, products ( 9 , 10 , and 16 ) solely derived from a hydroxide‐promoted fragmentation of the intermediate are formed. The decarboxylative and fragmentation pathways are mutually exclusive and do not appear to coexist under the range of pH (7–14) conditions investigated. Herein, we employ a combination of quantitative ¹³C NMR measurements and density functional theory calculations to provide a rationale for this pH‐driven reaction divergence. These rationalizations also hold true for the reactions of dihydroxyfumarate produced in situ by the catalytic cyanide‐mediated dimerization of glyoxylate. In addition, the non‐enzymatic decarboxylation and fragmentation transformations of these central intermediates ( 3 and 14 ) appear to have intriguing parallels to the enzymatic reactions of oxalosuccinate and formation of glyceric acid derivatives in extant metabolism – the high and low pH mimicking the precise control exerted by the enzymes over reaction pathways. Copyright © 2016 John Wiley & Sons, Ltd.     

A Plausible Simultaneous Synthesis of Amino Acids and Simple Peptides on the Primordial Earth

Following his seminal work in 1953, Stanley Miller conducted an experiment in 1958 to study the polymerization of amino acids under simulated early Earth conditions. In the experiment, Miller sparked a gas mixture of CH₄, NH₃, and H₂O, while intermittently adding the plausible prebiotic condensing reagent cyanamide. For unknown reasons, an analysis of the samples was not reported. We analyzed the archived samples for amino acids, dipeptides, and diketopiperazines by liquid chromatography, ion mobility spectrometry, and mass spectrometry. A dozen amino acids, 10 glycine‐containing dipeptides, and 3 glycine‐containing diketopiperazines were detected. Miller’s experiment was repeated and similar polymerization products were observed. Aqueous heating experiments indicate that Strecker synthesis intermediates play a key role in facilitating polymerization. These results highlight the potential importance of condensing reagents in generating diversity within the prebiotic chemical inventory.     

Synthesis of SnO2 nanostructures by ultrasonic-assisted sol–gel method

Fluorine doped SnO₂ nanostructures were grown using ultrasonic assisted sol–gel method. The gel was obtained by dissolving stannous chloride in methanol with ammonium fluoride as dopant followed by irradiation with ultrasonic vibrations. Obtained samples were characterized by structural, morphological and optical studies. All the peaks in the X-ray diffractograms are identified and indexed as tetragonal cassiterite structure. Negative slope of Williamson–Hall plots indicates compressive strain. Particle size of SnO₂ nanostructures is decreases with increases in concentration of fluorine doping. Atomic force microscopy, scanning electron microscopy and transmission electron microscopy studies confirm the formation of ring like porous structures and then hollow tube like growth with increase in the fluorine concentration. Peaks in Raman spectra also indicate strong confinement in SnO₂ particles. Distinct peaks in the PL spectra make the structure suitable for photovoltaic applications.     

Synthesis of Peptide Cysteine Dimedone Using Fmoc-Cys(Dmd)-OH: Glutathione Cysteine Dimedone as a Probe in Investigating the Sulfenic Acid Mediated Oxidation of Glutathione

Dimedone is the most widely used chemical probe for detection of cysteine sulfenic acid in peptides and proteins. The reaction of dimedone with cysteine sulfenic acid results in the formation of unique cysteine dimedone motif containing thioether bridge. Based on the structure of cysteine dimedone residue in polypeptide, a new building block of Fmoc-Cys(Dmd)-OH was developed for solid phase synthesis of peptide cysteine dimedone. Mass spectrometric sequencing of synthetic peptides have confirmed successful incorporation of cysteine dimedone in peptide chain using HBTU/HOBt as a coupling agent. The new method permits synthesis of peptides containing both cysteine thiol and cysteine dimedone in the same sequence which was difficult to achieve by conventional methods. The synthetic peptide of glutathione cysteine dimedone was used as a standard in probing the air-mediated oxidation of thiol to disulfide form of glutathione. The co-elution of standard peptide and reaction mixture of oxidation of glutathione in presence of dimedone using RP-HPLC have confirmed the formation of glutathione cysteine sulfenic as an intermediate in the air-mediated oxidation of glutathione. The synthetic peptides of cysteine dimedone may find application in the field of redox proteomics and generation of antibodies against modified cysteine residue.     

Cu(OAc)2 entrapped on ethylene glycol-modified melamine–formaldehyde polymer as an efficient heterogeneous catalyst for Suzuki–Miyaura coupling reactions

Research on Chemical Intermediates - This work is described as an environmental friendly approach for Cu(OAc)2 entrapped on ethylene glycol-modified melamine–formaldehyde-based polymeric...