Search results for "Proton"
showing 10 items of 5886 documents
Formation rates and protonation constants of azo dyes in a sodium dodecylsulphate micellar solution.
1991
The effects of a sodium dodecylsulphate micellar solution on the coupling rates of several diazotizated arylamines with N-(1-naphthyl)-ethylenediamine and the shifts in the protonation constants of the corresponding azo dyes are quantitatively studied. Aniline, o-, m- and p-aminobenzoic acids, ethyl p-aminobenzoate and several sulphadrugs are used, and the relationships among the intensity of the effects and the molecular structure of the diazonium ions and the dyes are discussed. A single simplified procedure for the determination of all the substances at pH = 1.3 +/- 0.3, where coupling is quickly completed to directly produce the protonated form of the dyes, is established and applied to…
Spectroscopic behavior of metal–drug complexes. Infrared spectra of Cu(II) dimer complexes with acetazolamide (H2acm) and an analogue sulfonamide (B-…
1999
Abstract The infrared spectra of the drugs H2acm and B-H2ats, and their copper(II) dimer complexes with stoichiometries [Cu(acm)(NH3)2(OH2)]2·H2O and [Cu(B-ats)(NH3)2]2 are reported and discussed. The Raman spectra of H2acm and B-H2ats are also reported. An assignment of H2acm and B-H2ats modes in the complexes is proposed in comparison with the modes of the free ligands. The spectral modifications due to the deprotonation and coordination effects are analyzed. The ν(N–H) modes of the sulfonamido, carbonamido and Nring–H of the imine tautomer have been accurately assigned. Important information about the S–O and S–N vibrations has been obtained.
Complexes of tryptophan dipeptides with the R2Sn(IV)2+ ion (R=Me, Ph): Spectroscopic studies, solution properties and structural implications
1995
Tryptophan dipeptides such as L-tryptophyl-L-alanine (H 2 TrpAla), L-tryptophyl-L-tyrosine (H 2 TrpTyr), L-tryptophyl-L-tryptophan (H 2 TrpTrp), along with L-histidyl-L-tyrosine (H 2 HisTyr), were reacted with R 2 SnO (R=Me, Ph) yielding the corresponding complexes. The complexes have been characterized by IR and 119 Sn Mossbauer spectroscopy in the solid state and by 1 H and 13 C NMR in CD 3 OD solutions. Monomeric species were detected, with the tin atom arranged in a pentacoordinated trigonal-bipyramidal structure. The dipeptides are coordinated via the terminal amino group, deprotonated peptide nitrogen and terminal carboxylate group. No side-chain appears to be involved in bonding. Det…
On the behaviour of the (Z)-Phenylhydrazones of some 5-alkyl-3-benzoyl-1,2,4-oxadiazoles in solution and in the gas phase: kinetic and spectrometric …
2008
Abstract Rate constants, k A,R , for the rearrangement of the ( Z )-phenylhydrazones ( 1a – e ) of a series of 5-alkyl-3-benzoyl-1,2,4-oxadiazoles substituted at C(5) with linear alkyl chains of different length (from C 4 up to C 12 ) into the relevant 4-acylamino-2,5-diphenyl-1,2,3-triazoles ( 2a – e ) have been measured in dioxan/water in the base-catalyzed region (pS + 10.5–12.6). For each substrate log k A,R are linearly related to pS + . The significant decrease of the slopes of these straight lines (from 0.96 down to 0.78) upon increasing the length of the linear alkyl chain at C(5) and that of the reactivity (down to 14–26%) upon increasing the substrate concentration suggest a decr…
CO2 as a C1-organic building block: Electrocarboxylation of aromatic ketones. A quantitative study of the effect of the concentration of substrate an…
2006
The purpose of this work is to establish and discuss quantitative relationships between the selectivity in preparative scale electrolysis and intrinsic and operational parameters for the electrocarboxylation of aromatic ketones. For the investigated ketones, under appopriate experimental conditions the selectivity of the process is mainly determined by the competition between carboxylation and protonation, de-halogenation reactions (when an halogenated ketone is involved), and possibly dimerizations involving the electrogenerated radical anion. A simple model was proposed to account for these unwanted side paths which allows to predict the dependence of the selectivity as a function of the …
Encapsulation of secondary and tertiary ammonium salts by resorcinarenes and pyrogallarenes: the effect of size and charge concentration
2015
The binding of different categories of alkyl ammonium (secondary and tertiary mono- and di-ammonium) salts with resorcinarenes and a pyrogallarene through weak interactions was analysed in all phases. 1H NMR spectroscopy and electrospray ionisation mass spectrometry were utilized in analysing the complexes in solution and in the gas phase, respectively. The 1H NMR titration studies in methanol-d4 reveal that the association constants for the 1:1 complexes vary according to the electronic properties of the hosts as well as the size, geometric orientation and charge concentration of the guest cations with binding constants of up to 950 M−1 in some cases. Mass spectrometry reveals 1:1 monomeri…
Fast proton conduction in hydrogen bonded microheterogeneous systems: Bis(2-ethylhexyl)phosphoric acid/N-methyl formamide liquid mixtures
2009
Structural and dynamical properties of bis(2-ethylhexyl)phosphoric acid (HDEHP)/N-methyl formamide (NMF) liquid mixtures in the whole composition range have been investigated by Fourier Transform Infrared spectroscopy (FT-IR), X-rays Diffraction (XRD), and AC complex impedance spectroscopy. Driven by hydrogen bond interactions among HDEHP PO(4)H group and NMF CO and NH groups, and also by steric effects among the HDEHP alkyl chains, the system microstructure is mainly characterized by the coexistence of spatially separated hydrophilic and hydrophobic nanodomains showing local organization and short-range order. The evolution of this structural feature with system composition has been highli…
Advanced CPMAS-13C NMR techniques for molecular characterization of size-separated fractions from a soil humic acid
2006
A humic acid extracted from a volcanic soil was subjected to preparative high-performance size-exclusion chromatography (HPSEC) to reduce its molecular complexity and eleven different size fractions were obtained. Cross-polarization magic-angle spinning 13C NMR (CPMAS 13C NMR) analysis performed with variable contact-time (VCT) pulse sequences showed that the largest molecular-size fractions contained aromatic, alkyl, and carbohydrate-like components. The carbohydrate-like content and the alkyl chain length seemed to decrease with decreasing molecular size. Progressive reduction of aromatic carbon atoms was also observed with decreasing molecular size of the separated fractions. Mathematica…
An Au(iii)–amino alcohol complex for degradation of organophosphorus pesticides
2015
An Au(III)–amino alcohol complex has been used to cleave organophosphorous pesticides of the dithiophosphate family. P–S bond breaking was readily demonstrated by 1H NMR, 31P NMR and MS. Thiol fragment release was also demonstrated using 2,4-dinitrobenzenesulfonyl fluorescein ethyl ester as a fluorescent sensor.
Photo-fragmentation of alkyl phosphates in the gas-phase
2018
Abstract Alkyl phosphates are experiencing an ever increasing use due to the current arising of new applications. This implies their increasing presence in the environment so their stability and reactivity under high-energy photons, which are still unknown, need to be clarified. In this study, a mass spectrometric investigation of the ionization and fragmentation processes of four representative alkyl phosphates (dibutyl, tributyl, bis-2-ethylhexyl, and tris-2-ethylhexyl phosphate) induced by vacuum ultraviolet (VUV) radiation has been carried out. The experimental data show that fragmentation occurs through a stepwise cleavage of the bonds between the phosphate group and the alkyl chains l…