Structural elucidation of diglycosyl diacylglycerol and monoglycosyl diacylglycerol from Streptococcus pneumoniae by multiple-stage linear ion-trap mass spectrometry with electrospray ionization

The cell wall of the pathogenic bacterium Streptococcus pneumoniae contains glucopyranosyl diacylglycerol (GlcDAG) and galactoglucopyranosyldiacylglycerol (GalGlcDAG). The specific GlcDAG consisting of vaccenic acid substituent at sn-2 was recently identified as another glycolipid antigen family recognized by invariant natural killer T-cells. Here, we describe a linear ion-trap multiple-stage (MS(n) ) mass spectrometric approach towards structural analysis of GalGlcDAG and GlcDAG. Structural information derived from MS(n) (n?=?2, 3) on the [M?+?Li](+) adduct ions desorbed by electrospray ionization affords identification of the fatty acid substituents, assignment of the fatty acyl groups on the glycerol backbone, as well as the location of double bond along the fatty acyl chain. The identification of the fatty acyl groups and determination of their regio-specificity were confirmed by MS(n) (n?=?2, 3) on the [M?+?NH(4) ](+) ions. We establish the structures of GalGlcDAG and GlcDAG isolated from S. pneumoniae, in which the major species consists of a 16:1- or 18:1-fatty acid substituent mainly at sn-2, and the double bond of the fatty acid is located at ω-7 (n-7). More than one isomers were found for each mass in the family. This mass spectrometric approach provides a simple method to achieve structure identification of this important lipid family that would be very difficult to define using the traditional method.     

Shape factor analysis of beta transitions in Pm-149

Shape factor analysis of the beta transitions in¹⁴⁹Pm is carried out for the first time, employing an intermediate image beta ray spectrometer. The ambigous situation arising from the disagreement between reported values in end point energies and intensities of the beta transitions is clarified. An attempt was made to evaluate the NME, for the 780 keV beta transition, using Simms formalism.     

Halogen substituted amides

A CNDO calculation was carried out for N-methyl carbomyl chloride and N-chloroacetamide. The charges, bond orders, and dipolemoments of these molecules were calculated and the effect of chlorine substitution on amide group is discussed. The two highest filled M.O.s in both molecules are almost degenerate; they are a pi-orbital followed by the non-bonding oxygen lone pair orbital. In case of N-chloro acetamide the charges, bond orders and dipolemoments have been calculated for both cis and trans structures and the average dipolemoment calculated on the basis of infrared data and orbital calculation is reported.

     

Incoherent scattering functions of 145 keV gamma rays by K-shell electrons in Y,Ag and Au

The values of incoherent scattering functions are determined experimentally for 145 keV gamma rays in elements Au, Ag and Y at scattering angles 40°, 70° and 100°, using a x-ray gamma coincidence technique. The corresponding theoretical values are obtained from the tabulations of Hubbellet al, and computed from the models of Jauch and Rohrlich and Shimizuet al. A comparison between the theoretical and experimental results showed that the non-relativistic approach adopted in the theory of Shimizuet al is inapplicable to the present cases. A gross agreement is noticed between the present experimental results and the other theoretical values.     

Some studies on thallium oxalates

Two methods (the Horowitz-Metzger and the Dharwadkar-Karkhanavala) for calculating the apparent activation energies of different thallium(I) oxalates were compared. The Dharwadkar-Karkhanavala method gave consistent values.     

Electron impact induced cyclizations in 4-chioro-3-(N-aryliminomethyl) (2H) benzopyrans and benzothiopyrans

Intramolecular substitutions leading to cyclizations with the ejection of chlorine have been noticed during mass spectral fragmentation of 4-chloro-3-(N-aryliminomethyl) (2H) benzopyrans and benzothiopyrans. Very interesting ortho effects involving intramolecular substitutions have also been observed in 6-methyl-4-diloro-3-[N-(2-methoxyphenyliminomethyl)] (2H) benzopyran and 6-methyl-4-chloro-3-[N-(2-chlorophenyliminomethyl)]-(2H) benzopyran. The proposed fragmentation mechanisms have been supported by the accurate mass measurements and linked scan studies.     

Ortho effects in organic molecules on electron impact part 22. Competing oxygen transfers from the nitro group to sulphur and the olefinic double bond in 2-nitrophenyl styryl sulphides

Double oxygen migration to sulphur from the ortho-nitro group leading to eliminations of SO₂ and ^·SO₂H from the molecular ions and single oxygen transfer to the olefinic double bond in the side-chain giving rise to the most abundant ion at m/z 138 have been observed in 2-nitrophenyl styryl sulphides on electron impact. The proposed fragmentation mechanisms and the product ion structures were confirmed with the aid of high-resolution data, B/E linked scan and CID spectra.     

CNDO calculations of some thioamides—II

CNDO calculation is made for thioformamide, N-methylthioformamide (both in cis and trans forms) and N, N-dimethyl thioformamide. The charges, bond orders, dipolemoments and ionization potentials of molecules are discussed and comparison made with corresponding amides. The barrier to internal rotation about C-N bond for thioformamide and N-chloroacetamide is reported along with changes in the charges on atoms and dipolemoment of molecules with rotation. The trans form of N-methyl thioformamide is found to be more stable than cis isomer by 4.9 Kcal/mole.