Search results for " ionization"
showing 10 items of 621 documents
Study on the synthesis of novel 5-substituted 2-[2-(pyridyl)ethenyl]-1,3,4-oxadiazoles and their acid–base interactions
2014
Abstract A series of novel 5-substituted 2-[2-(pyridyl)ethenyl]-1,3,4-oxadiazoles were efficiently synthesized by cyclocondensation of the appropriate 3-(pyridyl)acrylohydrazides with triethyl orthoesters in the presence of glacial acetic acid. The products were identified by means of spectroscopic methods and their pKA ionization constants were determined. The influence of substituents on the basicity of the pyridine system has been discussed. Graphical Abstract
Rapid characterization of alkylpolyphosphonates by CZE with indirect photometric and mass spectrometric detection.
2006
Methods for the rapid characterization of industrial alkylpolyphosphonates (APPs) by infusion MS and CZE with indirect photometric (IPD) and MS detection are described. Technical-grade APPs, including alkylaminepolyphosphonates with 3-5 phosphonate groups and different hydrocarbon skeletons, hydroxyethyl-amino-bis(methylenephosphonic acid), hydroxyethylidene-diphosphonic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid, were examined. A 10 mM solution of adenosine triphosphate disodium salt at pH 2.2 was used as BGE. The nominal compounds of the industrial APPs and their impurities were well resolved in less than 15 min. The peaks were identified by using extracted ion electropherograms…
On the determination of underivatised fatty alcohol ethoxylates by electrospray ionisation–mass spectrometry
2006
Abstract The oligomers of fatty alcohol ethoxylates (FAEs) exhibit large sensitivity differences in mass spectrometry with electrospray ionisation (ESI–MS) and atmospheric pressure chemical ionization (APCI). Standards of the oligomers from m = 1 to 7 ethylene oxide units (EOs) and linear alkyl chains from n = 10 to 18 carbon atoms were infused to examine the relative sensitivities or response factors in several media. The response factors of the [M + H]+ and [M + Na]+ peaks in 9:1 acetonitrile/water and methanol/water media containing acid buffers increased following irregular patterns when n and m increased. In methanol/water the response factors depended on the parity of m, being larger …
Cu2+ Coordination Properties of a 2-Pyridine Heptaamine Tripod: Characterization and Binding Mechanism
2009
The synthesis, protonation, and Cu(2+) coordination chemistry of a tripodal heptaamine ligand (L(1)) functionalized with 2-pyridine fragments at the ends of its three branches are reported. L(1) presents six relatively high protonation constants followed by much more reduced constant that as indicated by the UV-vis and NMR data, occur on the pyridine fragments. p[H]-metric, ESI/MS(+), EPR and UV-vis data show that L(1) is able to form mono-, di-, and trinuclear Cu(2+) complexes. Slippage movements and molecular reorganizations have been observed to occur as a function of p[H] in the 1:1 Cu(2+) complexes. The kinetic studies showed that the complex formation is fast and proceeds through a di…
d-Glucose as a multivalent chiral scaffold for combinatorial chemistry
2002
Due to their high density of functional groups and their availability in a variety of diastereomeric forms, monosaccharides are considered attractive scaffolds for combinatorial chemistry that allow the attachment and defined spatial alignment of up to five different pharmacophoric groups. For their application in combinatorial syntheses on solid phase, a set of selectively removable hydroxy protecting groups in combination with a cleavable anchor is required. Herein, we report on the construction and use of a versatile multivalent glucose building block for parallel synthesis on the solid phase.
A newin vitroapproach for the simultaneous determination of phase I and phase II enzymatic activities of human hepatocyte preparations
2007
Primary hepatocytes are still the best qualified in vitro system to anticipate drug metabolism in man. Recent advances in hepatocytes cryopreservation have notably increased their use not only for drug metabolism studies, but also for other applications such as cell transplantation. Evaluation of the drug-metabolizing competence of each hepatocytes preparation is needed. To date, the metabolic characterization of hepatocytes preparations relies on the assessment of phase I activities and the role of phase II enzymes receives little attention. A novel approach for the rapid assessment of the metabolic functionality of hepatocytes has been developed. A five-probe cocktail was used to simultan…
Intramolecularly Coordinated Bis(crown ether)-Substituted Organotin Halides as Ditopic Salt Receptors
2013
The synthesis of the bis(crown ether)-substituted organostannanes X2Sn(CH2-[16]-crown-5)2 (3, X = I; 4, X = Br; 5, X = Cl; 6, X = F) and X2Sn(CH2-[13]-crown-4)2 (10, X = I; 11, X = Br; 12, X = F) is reported. The compounds have been characterized by 1H, 13C, 19F, and 119Sn NMR spectroscopy, elemental analyses, and electrospray ionization mass spectrometry (ESI-MS). Single-crystal X-ray diffraction analyses reveal a distorted-octahedral cis,cis,trans configuration of the tin atoms in compounds 4–6 and 10–12 as a result of intramolecular O→Sn coordination. The ability of the host molecules to form mono- and ditopic complexes with various halide salts in different solvents, including water, ha…
Investigation of polymers in the mass spectrometer, 7. Pyrolysis-gas chromatography-mass spectrometry of low molecular and high polymeric sulfanilami…
1975
A number of low molecular, monomeric and polymeric sulfanilamide derivatives, which have found interest as possibly selective antitumour agents, were investigated by pyrolysis-gas chromatography (GC)-mass spectrometry (MS). Thermal degradation mechanisms were studied using also direct polymer pyrolysis in the ion source of the mass spectrometer. Thermal degradation products as well as low molecular weight sulfanilamides and related model compounds were characterized in their fragmentation behaviour by low and high resolution electron impact and field desorption mass spectrometry. Thermal fragments of structural significance were found, and a differentiation of the low and high molecular sul…
Analysis of odour and taste problems in high-density polyethene
1998
Abstract The compounds that cause off-flavours in plastics, have been recognized mainly as carbonyl compounds (aldehydes, ketones and esters). They occur in low concentrations, and due to their low-threshold odour concentrations, their typical odours were identified. Most of these off-flavour compounds are volatile. Chemical analysis of smelling compounds requires a very sensitive method with a high-resolution capability. The analysis of volatile organic compounds (VOCs) in high density polyethene (HD-PE) granules and waters in which the granules have been shaken for 4 h, were carried out by gas chromatography–mass spectrometry–sniffing system (GC–MS–SNIFF) and by gas chromatography–fourier…
Concentration-dependent switch between chain association and dissociation of oppositely charged weak polyelectrolytes in solution
2019
Abstract Joint solutions of oppositely charged weak polyelectrolytes are considerably less studied than their strong counterparts; as a result, their thermodynamic understanding is still unsatisfactory. This shortcoming hampers the development of a general picture about the physical properties of these mixtures, which further hampers their use to design new materials. To close this gap, we investigate the ternary system ethanol/polyacid/polybase (polyacid: methacrylic acid containing copolymer; polybase: N,N-dimethylaminoethyl methacrylate containing terpolymer) with respect to its demixing and viscometric behavior. Complete homogeneity can only be reached if the total polymer concentration…