The experimental and theoretical methods of determination gas-phase basicities, proton affinities protonation entropies are presented in a tutorial form. Particularities limitations these when applied to polyfunctional molecules emphasized. Structural effects during the process their consequences on corresponding thermochemistry reviewed classified. role nature basic site (protonation non-bonded electron pairs or pi-electron systems) substituent (electrostatic resonance) first examined....

The complexes [L(5)Fe(II)Cl]BPh(4) and [L(5)Fe(II)(H(2)O)](BPh(4))(2) (L(5) = N,N,N'-tris(2-pyridylmethyl)-N'-methyl-ethane-1,2-diamine) have been isolated. Bernal et al. (Bernal, J.; J. Chem. Soc., Dalton Trans. 1995, 3667-3675) prepared this ligand the corresponding complex [L(5)Fe(II)Cl]PF(6). We obtained structural data of by X-ray diffraction. It crystallizes in orthorhombic space group P2(1)2(1)2(1) with a 17.645(7) Å, b 16.077(6) c 13.934(5) V 3953(3) Å(3), Z 4. presents Fe(II)-N bond...

A gas chromatography-mass spectrometry method is presented which allows the simultaneous determination of plasma concentrations selective serotonin reuptake inhibitors citalopram, paroxetine, sertraline, and their pharmacologically active N-demethylated metabolites (desmethylcitalopram, didesmethylcitalopram, desmethylsertraline) after derivatization with reagent N-methyl-bis(trifluoroacetamide). No interferences from endogenous compounds are observed following extraction samples six...

Nonheme FeIII-hydroperoxo and FeIII-peroxo complexes with aminopyridyl-type ligands have been prepared characterized by UV/Vis, EPR, mass Resonance Raman (RR) spectroscopy. The FeIII(OOH) species are low-spin exhibit a deep purple color due to the ligand-to-metal charge transfer (LMCT) band centered at ca. 550 nm. RR spectra of display two bands 620 800 cm−1 that assigned respective Fe−O O−O stretching modes on basis characteristic H/D 16O/18O frequency shifts. Upon deprotonation, FeIII(O2)...

The importance of protein glycosylation in the interaction pathogenic bacteria with their host is becoming increasingly clear. Neisseria meningitidis, etiological agent cerebrospinal meningitis, crosses cellular barriers after adhering to cells through type IV pili. Pilin genes (pgl) are responsible for PilE, major subunit pili, 2,4-diacetamido-2,4,6-trideoxyhexose residue. Nearly half clinical isolates, however, display an insertion pglBCD operon, which anticipated lead a different,...

The various protonated forms of phenol (1), catechol (2), resorcinol (3), and hydroquinone (4) were explored by ab initio quantum chemical calculations at the MP2/6-31G(d) B3LYP/6-31G(d) levels. Proton affinities (PA) 1–4 calculated combined G2(MP2,SVP) method, their gas-phase basicities estimated after calculation change in entropy on protonation. These theoretical data compared with corresponding experimental values determined a high-pressure mass spectrometer. This comparison confirmed...

The present article is the second part of a general overview gas-phase protonation thermochemistry polyfunctional molecules. first review (Mass Spectrom. Rev., 2007, 26:775-835) was devoted to description physico-chemical concepts and methods determination, both experimental theoretical, basicity. Several clues concerning structural energetic aspects isolated species have been emphasized. In article, specific examples are examined. field investigation limited molecules containing "saturated"...

Acid–base thermochemistry of isolated amino acids containing oxygen or sulfur in their side chain (serine, threonine, cysteine and methionine) have been examined by quantum chemical computations. Density functional theory (DFT) was used, with B3LYP, B97-D M06-2X functionals using the 6-31+G(d,p) basis set for geometry optimizations larger 6-311++G(3df,2p) energy Composite methods CBS-QB3, G3B3, G4MP2 G4 were applied to large sets neutral, protonated deprotonated conformers. Conformational...

Rate constants have been determined for proton transfer reactions of the type [MH]+ + B ⇆ M [BH]+, where is ketene, methylketene, and formaldimine a reference base. A quantitative relationship between rate constant free energy (or enthalpy) reaction allows determination gas-phase basicity, GB, affinity, PA) M. This thermokinetic method gives results comparable to that obtained from equilibrium measurements. The values derived follow: GB(ketene) = 788 ± 3 kJ/mol, PA(ketene) 817 kJ/mol;...

Three new complexes, [Fe(LN4H2)Cl2]+, [Fe(LN4H2)(Cat)]+, and [Fe(LN4H2)(DBC)]+, were synthesized by using the tetradentate macrocyclic ligand LN4H2 (where LN4H2, Cat, DBC stand for 2,11-diaza[3,3](2,6) pyridinophane, catecholate, 3,5-di-tert-butylcatecholate, respectively). The structure of [Fe(LN4H2)Cl2]+ was determined X-ray diffraction. It crystallizes in monoclinic space group C2/c with a = 9.613(1), b 11.589(1), c 14.063(2) Å, β=110.20(2)°, V 1541.9(3) Å3, Z 4. These complexes found to...

Protonated 4-bromophenol and 4-bromoanisole produced by methane chemical ionization are found to easily be dehalogenated upon high (8 keV) or low (20−30 eV) energy collisional activation giving essentially phenol anisole radical cations, respectively. Under similar conditions, protonated unsubstituted is also readily demethylated generating the ion but not cyclohexadienone ions. Other nonconventional isomers of ionized only detected MS/MS/MS experiments performed on [M−CO]•+ ions from...

The thermokinetic method is applied to a set of six amino acids (glycine, alanine, proline, serine, lysine, histidine) and 30 their di-and tri-peptides for which experimental proton transfer rate constants were available. comparison between the presently determined gas-phase basicities, GBs, with values obtained from equilibrium constant determination generally good (a mean deviation ∼3 kJ mol −1 observed). Derived affinities are discussed. basicities peptides provided by present study...

Abstract A microcanonical analysis of the extended kinetic method is performed using statistical rate calculations based on orbiting transition state theory. The model systems simulate polydentate bases M which exhibit losses entropy upon protonation up to 35 kJ mol −1 K . It shown that correlations natural logarithm ratio constants vs proton affinity reference bases, at several effective temperatures, lead correct and base interest. systematic underestimate latter quantity (by 5–15%),...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRole of ion-neutral complexes during acid-catalyzed dehydration ethanol in the gas phaseGuy Bouchoux and Yannik HoppilliardCite this: J. Am. Chem. Soc. 1990, 112, 25, 9110–9115Publication Date (Print):December 1, 1990Publication History Published online1 May 2002Published inissue 1 December 1990https://pubs.acs.org/doi/10.1021/ja00181a012https://doi.org/10.1021/ja00181a012research-articleACS PublicationsRequest reuse permissionsArticle...

The goal of this work was to obtain a detailed insight on the gas-phase protonation energetic adenosine using both mass spectrometric experiments and quantum chemical calculations. experimental approach used extended kinetic method with nanoelectrospray ionization collision-induced dissociation tandem spectrometry. This provides values for proton affinity, PA(adenosine) = 979 ± 1 kJ·mol−1, "protonation entropy", ΔpS°(adenosine) S°(adenosineH+) − S°(adenosine) −5 5 J·mol−1·K−1. corresponding...

Structural characterization of molecular species by mass spectrometry supposes the knowledge type ions generated and mechanism which they dissociate. In this context, a need for rationalization electrospray ionization(+)(−) spectra small molecules has been recently expressed. Similarly, at other end scale, efforts are currently made to interpret major fragmentation processes protonated deprotonated peptides their reduced forms produced in electron capture or transfer experiments. Most...

This article constitutes the fourth part of a general review gas-phase protonation thermochemistry polyfunctional molecules (Part 1: Theory and methods, Mass Spectrom Rev 2007, 26:775–835, Part 2: Saturated basic sites, 2012, 31:353–390, 3: Amino acids, 31:391–435). is devoted to carbonyl containing molecules. After short reminder methods determination basicity underlying physicochemical concepts, specific examples are examined under two major chapters. In first one, aliphatic unsaturated...

Some nonheme hydroperoxoiron(III) species have been recently characterized by several groups. The reported examples were obtained adding H2O2 in excess to an FeII complex with a neutral polypyridine ligand. We show here that on deprotonation, the purple low-spin [L5FeIIIOOH]2+ [L5 = N-methyl-N,N′,N′-tris(2-pyridylmethyl)ethane-1,2-diamine] gives blue high-spin which we as η2-peroxoiron(III) [L5FeIIIO2]+. It seems such auxiliary ligand, hydroperoxo group is acidic contrast its basicity when...

The proton affinity ( PA) and protonation entropy, Δ p S°, of glycine (Gly), 1, aspartic acid (Asp), 2, asparagine (Asn), 3, histidine (His), 4, lysine (Lys), 5, glutamic (Glu), 6, glutamine (Gln), 7, have been reinvestigated by the extended kinetic method, using “isothermal point” method orthogonal distance regression technique. values α-amino acids bearing a basic residue PA = 926.8, 965.2, 996.0, 993.9, 981.8 988.1 kJ mol −1 for 2–7, respectively) show significant deviation from tabulated...