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91.
92.
Jenö Tomasz Sandor Bottka Janos Ludwig Istvan Pelczer 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):597-600
Abstract The title compounds were synthesized by converting cyclic AMP with a sulfonyl chloride to the symmetrical anhydride or with diphenyl phosphorochloridate to the mixed anhydride, then aminolyzing the anhydrides without isolation. The synthesis preferentially gave Sp-amides. Characteristic differences were observed in the behavior of the unsubstituted amide and the dimethylamide under hydrolysis conditions. 相似文献
93.
94.
Dr. Basem Kanawati Dr. Istvan Gebefügi Dr. Dominique Peyron Prof. Philippe Cayot Prof. Régis D. Gougeon Dr. Philippe Schmitt‐Kopplin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(41):13059-13067
A new method for efficient ionization of sugars in the negative‐ion mode of electrospray mass spectrometry is presented. Instead of using strongly hydrophobic dopants such as dichloromethane or chloroform, efficient ionization of sugars has been achieved by using aqueous HCl solution for the first time. This methodology makes it possible to use hydrophilic dopants, which are more appropriate for chromatographic separation techniques with efficient sugar ionization and detection in mass spectrometry. The interaction between chloride anions and monosaccharides (glucose and galactose) was studied by DFT in the gas phase and by implementing the polarizable continuum model (PCM) for calculations in solution at the high B3LYP/6‐31+G(d,p)//B3LYP/6‐311+G(2d,p) level of theory. In all optimized geometries of identified [M+Cl]? anions, a non‐covalent interaction exists. Differences were revealed between monodentate and bidentate complex anions, with the latter having noticeably higher binding energies. The calculated affinity of glucose and galactose toward the chloride anion in the gas phase and their chloride anion binding energies in solution are in excellent agreement with glucose and galactose [M+Cl]? experimental intensity profiles that are represented as a function of the chloride ion concentration. Density functional calculations of gas‐phase affinities toward chloride anion were also performed for the studied disaccharides sucrose and gentiobiose. All calculations are in excellent agreement with the experimental data. An example is introduced wherein HCl was used to effectively ionize sugars and form chlorinated adduct anions to detect sugars and glycosylated metabolites (anthocyanins) in real biological systems (Vitis vinifera grape extracts and wines), whereas they would not have been easily detectable under standard infusion electrospray mass spectrometry conditions as deprotonated species. 相似文献
95.
C Yohannan Panicker Hema Tresa Varghese Annamma John Daizy Philip Krisztina Istvan Gabor Keresztury 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(2):281-287
FT-IR, FT-Raman and FT-SERS spectra of 4-aminosalicylic acid sodium salt dihydrate (4ASAS) have been recorded and analysed. The vibrational bands due to NH2, OH, carboxyl group, and the benzene ring are identified. The CX ipb(17a, 17b), CC ipb(6,18a) and CH ipb (3,14a, 14b) bands are more enhanced in SERS. Broadening of the inplane carboxyl bend indicates interaction with the silver surface. Further the vC=O, v(C-O)c and v(C-O)h are intense in the SERS spectrum. The rocking and wagging modes of NH2 also show up in SERS. The molecule (O, N donor ligand) is thought to adsorb through the carboxyl oxygen atom with the benzene ring in a 'perpendicular side on orientation' with respect to the silver surface. 相似文献
96.
Papp L Palcsu L Major Z Rinyu L Tóth I 《Isotopes in environmental and health studies》2012,48(4):494-511
This paper describes the procedure followed for noble gas measurements for litres, millilitres and microlitres of water samples in our laboratory, including sample preparation, mass spectrometric measurement procedure, and the complete calibrations. The preparation line extracts dissolved gases from water samples of volumes of 0.2?μ l to 3?l and it separates them as noble and other chemically active gases. Our compact system handles the following measurements: (i) determination of tritium concentration of environmental water samples by the (3)He ingrowth method; (ii) noble gas measurements from surface water and groundwater; and (iii) noble gas measurements from fluid inclusions of solid geological archives (e.g. speleothems). As a result, the tritium measurements have a detection limit of 0.012 TU, and the expectation value (between 1 and 20 TU) is within 0.2 % of the real concentrations with a standard deviation of 2.4 %. The reproducibility of noble gas measurements for water samples of 20-40?ml allows us to determine solubility temperatures by an uncertainty better than 0.5?°C. Moreover, noble gas measurements for tiny water amounts (in the microlitre range) show that the results of the performed calibration measurements for most noble gas isotopes occur with a deviation of less than 2 %. Theoretically, these precisions for noble gas concentrations obtained from measurements of waters samples of a few microlitres allow us to determine noble gas temperatures by an uncertainty of less than 1?°C. Here, we present the first noble gas measurements of tiny amounts of artificial water samples prepared under laboratory conditions. 相似文献
97.
98.
Oral delivery remains a challenge for a number of drug candidates with low absorption profile (poor membrane permeability, lack of stability, solubility issues or susceptibility to enzymatic degradation) and various methodologies have been investigated to overcome it. The approach presented here consists of associating, by ion-pairing, a hydrophilic, ionizable model drug to a series of synthetic counter-ionic entities with a controlled degree of lipophilicity in order to enhance its penetration of biomembranes and offer some protection against in situ degradation, while preserving its biologically active chemical structure. We report herein the synthesis of a series of positively charged potential penetration enhancers designed from d-glucose, 2-aminododecanoic acid, and additional lipophilic amino acids, and converted afterward into quaternary ammoniums in an optimized, innovative one-step reaction. Each liposaccharide derivative synthesized was fully characterized and their ability to generate micelles in solution was assessed by isothermal titration calorimetry. 相似文献
99.
The consistency of different splitting schemes has mostly been studied for bounded operators by means
of the traditional Taylor series expansion. In this paper second order of consistency is proved for the symmetrically weighted
sequential (SWS) splitting and the Marchuk-Strang (MS) splitting for unbounded generators of strongly continuous semigroups. 相似文献
100.
Seyrek E Hierrezuelo J Sadeghpour A Szilagyi I Borkovec M 《Physical chemistry chemical physics : PCCP》2011,13(28):12716-12719
Highly charged polyelectrolytes adsorbed on oppositely charged colloidal particles are investigated by electrophoresis and dynamic light scattering. The dependence of the adsorbed amount and of the hydrodynamic layer thickness on the molecular mass and the salt level is analyzed. The adsorbed amount increases with increasing salt level and decreases with increasing molecular mass. The hydrodynamic layer thickness is independent of the molecular mass at low salt levels, but increases with the molecular mass as a power law with an exponent 0.10 ± 0.01 at high salt. The same behavior was observed for different polyelectrolytes and substrates and therefore is suspected to be generic. Due to semi-quantitative agreement with computer simulations carried out by Kong and Muthukumar in 1998, the observed behavior is interpreted with conformational changes of single adsorbed polyelectrolyte chains. 相似文献