Synthesis and characterization of isotopically enriched methylmercury (CH3201Hg+)

A simple procedure for the synthesis of an important standard, isotopically enriched methylmercury, which is not commercially available, has been established successfully. The isotopically enriched standard synthesized is utilized in conventional isotope dilution mass spectrometry (IDMS), as well as in speciated IDMS (SIDMS), for determination of the true concentration of methylmercury in environmental samples. The CH₃²⁰¹Hg⁺ standard has been synthesized from commercially available ²⁰¹HgO and tetramethyltin. The synthesis time required is 1 h at 60°C. The product is highly pure, yielding more than 90% as ²⁰¹Hg in CH₃²⁰¹Hg⁺. Hazardous dimethylmercury does not occur during this synthesis procedure. The product synthesized was analyzed using high‐performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (ICP‐MS) and ICP‐MS alone in order to determine its concentration, isotopic composition and purity. The stability of the product was also evaluated for over 6 months and found to be stable at 4°C in the dark. The isotopically enriched methylmercury synthesized can be used in SIDMS and IDMS analyses as a standard. Copyright © 2003 John Wiley & Sons, Ltd.     

HPTLC Determination of Swertiamarin and Amarogentin in Swertia Species from the Western Himalayas

JPC – Journal of Planar Chromatography – Modern TLC - A high-performance thin-layer chromatographic (HPTLC) method has been established for simple and rapid quantification of two...     

Simultaneous densitometric determination of artemisinin, artemisinic acid and arteannuin-B in Artemisia annua using reversed-phase thin layer chromatography

A rapid and simple RP-TLC method for simultaneous quantification of pharmacologically important sesquiterpene artemisinin (AM) together with its precursors arteannuin-B (AB) and artemisinic acid (AA) in the inflorescence part of Artemisia annua plant has been developed. The RP-TLC of sesquiterpenes was performed on RP-18 F254 S thin-layer chromatographic plates by developing in mobile phase, containing 0.2% TFA in water/ACN (35:65, v/v). The densitometric determination of AM, AB and AA was carried out after derivatization with anisaldehyde reagent at 426 nm in absorption-reflectance mode.     

Imido Derivatives of Titanium (IV)

Reactions of titanium(IV) isopropoxide with acetamide, benzamide, and nicotinamide in different stoichiometric ratios in anhydrous benzene yielded imido derivatives of type (PrⁱO)_4-nTi(NHOCR)_n where n = 1, 2, 3, and 4; R = CH₃, C₆H₅, and C₅H₄N. All these complexes are insoluble in common organic solvents suggesting their polymeric nature. All these derivatives, with the exception of three which have characteristic melting points, did not sublime at 250°C in vacuo nor did they appear to decompose appreciably below 300°C. I.R. spectra of these derivatives are discussed.     

Synthesis of 2- and 4-substituted 5,12-dihydroxy-6,11-dioxo-1-azanaphthacenes from 2-aminoquinizarine

The reaction of 2-aminoquinizarine with α,β-unsaturated carbonyl compounds in presence of 10N-hydrochloric acid gives 2- and 4-substituted 5,12-dihydroxy-6,11-dioxo-1-azanaphthacenes.     

Electronic,mechanical, phase transition,and thermo-physical properties of TMC (TM = V,Nb, and Ta): high pressure ab initio study

The structural, electronic, mechanical, phase transition, and thermo-physical properties of refractory carbides, viz. VC, NbC, and TaC have been computed in stable B1 and high pressure B2 phases by means of two different ab initio calculations using pseudo- and full-potential schemes. These materials have mixed covalent-, metallic-, and ionic-type bonding. The calculations of elastic constants show the mechanical stability of these materials in B1 phase only. The brittle nature and anisotropy is observed in these materials in B1 phase. Non-central forces are present in both the phases. Elastic wave velocities and Debye temperature have also been calculated. The present results on structural, phase transition, elastic, and other properties are in reasonably good agreement with the available experimental and theoretical data. The calculations in high pressure phase need experimental verification.     

Theoretical investigation of the alloxan–dialuric acid redox cycle

The redox cycle between alloxan, a mild oxidizing agent, and its reduction partner, dialuric acid, is investigated using density functional theory. It is found that the initial step is the one‐electron reduction of alloxan followed by protonation, yielding a stable neutral radical, AH^·. The radical can then accept another electron to form the dialuric acid anion. The formation of this anion is thermodynamically favored in both the gas phase and in solution. The radical may also undergo dimerization to alloxantin, followed by the transfer of a proton from one moiety to another, yielding alloxan and dialuric acid. This reduction is thermodynamically feasible in the gas phase, but not in aqueous solution. In the case of reduction of alloxan by glutathione at the physiological pH, computed redox potentials indicate that a two‐electron reduction is the favored course of reaction, yielding directly the dialuric acid anion, which then undergoes aerial oxidation to yield the superoxide radical. The redox cycling between alloxan and dialuric acid is responsible for the diabetogenic activity of alloxan, producing cytotoxic radicals on reoxidation of dialuric acid. © 2013 Wiley Periodicals, Inc.