Protonation site for anilines in aqueous media

Pankratov, A. N.; Uchaeva, I. M.

doi:10.2298/jsc0202111p

Cited by 6 publications

(8 citation statements)

References 1 publication

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“…Unlike the case for p-aminobenzoic acid, protonation of the carbonyl O atom at the carboxylic acid is not resonantly stabilized, and the amine is calculated to be the favored gas-phase protonation site. 47 An intramolecular HB cannot be formed between these two functional groups, making MABAH + an excellent model for investigating the intrinsic competition between the hydration of a protonated amine and neutral carboxylic acid. These results provide insight into how water interacts with both charged and neutral functional groups.…”

Section: ■ Introductionmentioning

confidence: 99%

Hydration of Gaseous m-Aminobenzoic Acid: Ionic vs Neutral Hydrogen Bonding and Water Bridges

2014

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Hydration of a protonated amine and a neutral carboxylic acid were investigated for protonated m-aminobenzoic acid (MABAH(+)) with up to 15 water molecules attached using infrared photodissociation spectroscopy, laser-induced dissociation kinetics, and computational chemistry. A free COO-H stretch in the spectra of MABAH(+)·(H2O)1-5 indicates that water does not bind to the carboxylic acid H atom. This band is absent in the spectrum of MABAH(+) with six or more water molecules attached, and there is a hydrogen-bonded (HB) COO-H stretch indicating that water hydrogen bonds to the carboxylic acid H atom for these larger clusters. Photodissociation kinetic data for MABAH(+)·(H2O)6 indicate that greater than 74 ± 13% of the ion population consists of the HB COO-H isomer, consistent with this isomer being ≥0.5 kJ mol(-1) lower in energy than isomers where the carboxylic acid H atom does not donate a hydrogen bond. Calculations at the B3LYP/6-31+G** and MP2/6-31+G**//B3LYP/6-31+G** levels of theory indicate that this energy difference is 3-5 kJ mol(-1), in agreement with the experimental results. Lower effective ion heating rates, either by attenuation of the laser power or irradiation of the ions at a lower frequency, result in more time for interconversion between the free and HB COO-H isomers. These data suggest that the barrier to dissociation for the free COO-H isomer is less than that for the HB COO-H isomer but greater than the barrier for interconversion between the two isomers. These results show the competition between hydration of a primary protonated amine vs that of a neutral carboxylic acid and the effect of water bridging between the two functional groups, which provide valuable insight into the hydration of protonated amino acids and establish rigorous benchmarks for theoretical modeling of water-biomolecule interactions.

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Section: ■ Introductionmentioning

confidence: 99%

Hydration of Gaseous m-Aminobenzoic Acid: Ionic vs Neutral Hydrogen Bonding and Water Bridges

2014

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“…The latter fact was confirmed by quantum-chemical calculations with the explicit inclusion of water medium [5][6][7]; for this purpose, we studied clusters containing molecular systems IA and IB and 197 water molecules. The more water molecules are included in the cluster (up to 729 in a cubic cell with the edge of 28.00 Å, which corresponds to the density of liquid water [8]), the more adequately is the water medium taken into account.…”

Section: Resultsmentioning

confidence: 65%

Structure of Sulfophthalexons, Chelating Analytical Reagents

Pankratov

2005

J Anal Chem

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A research are related to the synthesis, investigation, and analytical application of phthalexons was developed at Saratov State Pedagogical Institute under the direction of Prof. Cherkasov [1]. Phthalexons are compounds of the triphenylmethane series whose molecules involve iminodiacetate fragments. A specific feature of the structure of sulfophthalexons is that they can exist both as inner complex salts (zwitterions) (A) and as the form with the closed heterocycle (B).The aim of this work was to solve the problem of revealing the structure of sulfophthalexon molecules using quantum-chemical methods. The compounds under study were phthalexon S ( I ), ortho -chlorophthalexon S ( II ), ortho -bromorophthalexon S ( III ), orthocresolphthalexon S (Xylenol Orange) ( IV ), para-xylenolphthalexon S ( V ), thymolphthalexon S (Methylthymol Blue) ( VI ), and meta -cresolphthalexon S ( VII ). EXPERIMENTALCalculations were performed by the PM3 method [2] using the HyperChem program (HyperChem (TM), HyperCube Inc., 1115 NW 4th Street, Gainesville, Florida 32601, USA) with full geometry optimization (Polak-Ribiere procedure [3]). In quantum-chemical calculations, the gradient norm was no higher than 0.02 kcal mol -1 Å -1 for isolated phthalexon molecules and 1 kcal mol -1 Å -1 for supermolecular systems containing water. For clusters involving 197 water molecules, the minimum distance between the molecules of water and the dissolved compound was 1.7 Å. C Y OH CH 2 N(CH 2 COOH) 2 X X (HOOCCH 2 ) 2 NCH 2 HO Y Z Z SO 3 + -C Y OH CH 2 N(CH 2 COOH) 2 X X (HOOCCH 2 ) 2 NCH 2 HO Y Z Z SO 2 O A B ARTICLESAbstract -On the basis of quantum-chemical calculations, it is demonstrated that, for isolated sulfophthalexon molecules, the heterocyclic form is thermodynamically more stable than the open zwitterionic form. On the contrary, the latter is predominant in aqueous solutions.

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“…The results presented in Table 4 show that as in the case considered in [23][24][25][26][27], the density distribution of water molecules in the cell approaches that of water in the liquid state, even if we neglect the fact that part of the cell volume is occupied by the molecular system I -IV . Table 1.…”

Section: Resultsmentioning

confidence: 89%

Tautomerism and Regioselectivity of the Protonation of 2-Pyrrolidone. Stereoselectivity of Complexation between Palladium(II), Chloride Ion, and 2-Pyrrolidone

2005

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Palladium(II) complexes with organic ligands are promising as medicines [1] that interact with functional groups of biological systems to give the corresponding coordination entities [2]. In the study of reactions of the palladium ion with bioligands, its interactions with inorganic compounds contained in an organism's fluids should also be considered. It is not improbable that inorganic ligands (H 2 O , Cl -, etc.) competing with biologically active substances for the metal ion can reduce its toxicity. On the other hand, coordination of inorganic ligands by the metal cation can diminish the efficiency of palladium-based medicines; for this reason, mixed-ligand complexes of palladium(II), in which the opposite trends are more or less counterbalanced, are acceptable as medicines.It is expedient to use the chloride ion as an inorganic ligand since it is contained in biological fluids. For instance, blood plasma is simulated by 0.86% (0.147 mol/l) NaCl, while the gastric juice is simulated by 0.1 M HCl [3].2-Pyrrolidone (2-pyrrolidinone, pyrrolidine-2-one, 2-oxopyrrolidine, and γ -butyrolactam) is a promising ligand for the formation of biologically active complexes with platinum metal cations [4]; 2-pyrrolidone can exhibit lactam-lactim tautomerism [5,6]. In sufficiently acidic media, protonation of 2-pyrrolidone (which is possible both at the N and O atoms) can compete with its coordination by metal cations. In[7], dichlorobis(pyrrolin-2-ol)palladium [Pd ( C 4 H 7 NO ) 4 Cl 2 ] was synthesized by the reaction of palladium(II) chloride with 2-pyrrolidone in aqueous acetone and its crystal and molecular structures were determined by X-ray diffraction analysis [8]. The structure consists of an electrically neutral complex and two 2-pyrrolidone molecules attached to it by intermolecular éç ··· é hydrogen bonds [8]. The most important features of the complexation is the lactim (pyrroline-2-ol) structure of the organic ligand, N-coordination, and the cis -structure of dichlorobis(pyrroline-2-ol)palladium [8].Usually, complexation reactions yield trans -isomeric products [9, 10]. However, it is cis -isomers that are of interest as potential antitumor preparations. For this reason, it is important to explain the stereoselectivity of complexation.The goal of this study was to calculate, by quantumchemical methods, the tautomerism and regioselectivity of the protonation of 2-pyrrolidone in the gas phase and an aqueous solution and to justify the stereoselectivity of the complexation between palladium(II), chloride ion, and pyrroline-2-ol. EXPERIMENTALQuantum-chemical calculations for the gas phase were performed by the AM1 [11] and PM3 methods Abstract -According to the AM1, PM3, HF/6-31G(d,p), and MP2/6-31G(d,p)//HF/6-31G(d,p) calculations, it is the lactam tautomer of 2-pyrrolidone that is thermodynamically most stable in both the gas phase and an aqueous solution. Analysis of the PM3 data with consideration of the medium showed that the tautomeric equilibrium of 2-pyrrolidone (pyrroline-2-ol) in aqueous solution is shift...

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Protonation site for anilines in aqueous media

Cited by 6 publications

References 1 publication

Hydration of Gaseous m-Aminobenzoic Acid: Ionic vs Neutral Hydrogen Bonding and Water Bridges

Hydration of Gaseous m-Aminobenzoic Acid: Ionic vs Neutral Hydrogen Bonding and Water Bridges

Structure of Sulfophthalexons, Chelating Analytical Reagents

Tautomerism and Regioselectivity of the Protonation of 2-Pyrrolidone. Stereoselectivity of Complexation between Palladium(II), Chloride Ion, and 2-Pyrrolidone

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