Gap modes due to impurity pairs in ki

The pair modes due to Cl^?, Br^?, Na⁺W and Rb^v impurities in KI have been investigated using the Greens function technique. Group theory is used to put the final results as solutions of (2 × 2) determinants which could be tried by a hand calculator. Even a mass defect approximation reproduced the gap modes due to chlorine pairs, but in all cases a small change in the force constant, deduced from fitting single impurity gap modes, was used. The Raman active modes in all these cases were also computed.     

A macrocyclic piperazine linked extremely Zn selective fluorescent chemosensor with bio-imaging and for H2PO4 sensing

A new macrocyclic fluorescent chemosensor piperazine coupled diimine phenol (PCDP) which forms extremely selective Zn(II) complex and thus builds up the platform for H₂PO₄⁻ (DHP) sensing in mixed aqueous medium, has been designed and synthesized. The binding of PCDP with Zn²⁺ and its displacement by DHP have been supported by DFT studies. The blue fluorescence in the PCDP–Zn complex is useful for bio-imaging. The fluorescence enhancement of PCDP on association with Zn²⁺ ion is quenched sharply in the presence of intracellular DHP.     

On-line derivatization gas chromatography with furan chemical ionization tandem mass spectrometry for screening of amphetamines in urine

A simple alternative method with minimal sample pretreatment is investigated for screening of amphetamines in small volume (using only 20 microL) of urine sample. The method is sensitive and selective. The method uses gas chromatography (GC) direct sample introduction (DSI) for on-line derivatization (acylation) of amphetamines to improve sensitivity. Furan as chemical ionization (CI) reagent in conjunction with tandem mass spectrometry (MS/MS) is used to improve selectivity. Low background with sharp protonated molecular ion peaks of analytes is the evidence of improvement in sensitivity and selectivity. Blank urine samples spiked with known amounts of amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine, 3,4-methylenedioxymethamphetamine and 3,4-methylenedioxyethylamphetamine is analyzed. Selected ion monitoring of the characteristic product ions (m/z 119+136+150+163) using furan CI-MS/MS in positive ion mode is used for quantification. Limits of detection (LOD) between 0.4 and 1.0 ng mL(-1) and limits of quantitation (LOQ) between 1.0 and 2.0 ng mL(-1) are established. Linear response over the range of 1-1000 ng mL(-1) (r(2)>0.997) is observed for all analytes, except for methamphetamine (2.0-1000 ng mL(-1)). Good accuracy between 86 and 113% and precision ranging from 4 to 18% is obtained. The method is also tested on real samples of urine from suspected drug abusers. This method could be used for screening and determination of amphetamines in urine samples, however needs additional work for full validation.     

Enantioselective H-atom transfer reaction: a strategy to synthesize formaldehyde aldol products

[reaction: see text] Enantioselective radical alkylation of Baylis-Hillman adducts furnished aldol products in good yield and selectivity. The results illustrate that the selectivity in the hydrogen atom transfer is dependent on the size of the ester substituent, with smaller substituents providing better enantioselectivity.     

Selective adduct formation by furan chemical ionization reagent in gas chromatography ion trap mass spectrometry

The analytical potential of furan as a chemical ionization (CI) reagent was evaluated for selectivity with nine monosubstituted naphthalene compounds. The ion-molecule reactions of furan and tetrahydrofuran (THF) were compared with those of methane, methanol and acetonitrile (prominently producing [M + H](+) ion base peaks) with naphthalene compounds in chemical ionization mass spectrometry (CI-MS). Reactions with furan predominantly show M(+) and [M + 39](+) ions. Based on this phenomenon, investigations were carried out for some of the molecular factors such as proton affinity, substituent effects and the preferred site of [C(3)H(3)](+) ion attachment that influence reactivity in furan CI. High selectivity with different substituents is observed in the formation of [M + 39](+) adduct ion, suggesting its usefulness as selective ionization reagent liquid. The selectivity and sensitivity are illustrated in the analysis of mixture of amino acids. Furthermore, the structure determination and reaction mechanism study is characterized by collision-activated dissociation experiments in CI-MS/MS and CI-MS/MS/MS.     

Structural evidence for the radical scavenging mechanism of some aminothiol group of radioprotectants

Aminothiols constitute an important group of radioprotectants. The structures of a few well-known compounds belonging to the family of radioprotectants have been determined by single crystal x-ray diffraction methods. The sulphur and the amino nitrogen atoms are separated by two tetrahedral carbon atoms in these compounds. Thegauche conformation of the sulphur and the nitrogen atoms and the consequent non-bonded intramolecular S … N interaction observed in some of the crystal structures appear to favour the hypothesis that the protective mechanism of these compounds is by free radical scavenging.     

Oxidative C-H activation/C-C bond forming reactions: synthetic scope and mechanistic insights

This paper describes a new palladium-catalyzed method for C-H activation/carbon-carbon bond formation with hypervalent iodine arylating agents. This transformation has been applied to a variety of arene and benzylic substrates containing different directing groups (pyridines, quinolines, oxazolidinones, and amides) and proceeds with high levels of regiocontrol. Mechanistic experiments provide preliminary evidence in support of an unusual mechanism for this transformation involving a Pd(II)/Pd(IV) catalytic cycle.