scholarly journals Diol Mediated Tautomerization of Glycine: a DFT Study

2019 ◽  
Vol 16 (1) ◽  
pp. 33-39
Author(s):  
Francis Suh ◽  
Vanessa Rivera ◽  
Ruben Parra
Keyword(s):  
Activation Energy ◽  
Aqueous Solution ◽  
Hydrogen Bonds ◽  
Proton Transfer ◽  
Gas Phase ◽  
Activation Energies ◽  
Dft Study ◽  
Hydroxyl Groups ◽  
Neutral Process ◽  
Product Forms

The tautomerization of glycine via a triple proton transfer was investigated both in the gas phase and in aqueous solution using the B3LYP/6-31+G(d,p) level of theory. Fully optimized complexes of the neutral and zwitterion forms of glycine with 1,3-propanediol were used for the reactant and product forms, respectively. The hydroxyl groups in the diol are conveniently oriented for glycine tautomerization through a concerted triple proton transfer facilitated by a network of three hydrogen bonds: N-H…O-H…O-H…O=C. The activation energy for the zwitterion à neutral process increases in solution. Also, the diol-glycine complex favors the neutral over the zwitterion form in a vacuum, but the opposite is true in solution. For comparative purposes, the tautomerization of glycine via a three-proton transfer mediated by two molecules of water was also examined. The results are qualitatively similar, albeit with activation energies that are smaller to those found in the corresponding diol-mediated tautomerization. KEYWORDS: Glycine; zwitterion, diol-mediated tautomerization; water-mediated tautomerization

scholarly journals Hydrothermal synthesis and structure of a new layered zincophosphate intercalated with 3-methylaminopropylamine cations

2005 ◽  
Vol 70 (4) ◽  
pp. 625-634 ◽  
Author(s):  
Nevenka Rajic ◽  
Natasa Zabukovec-Logar ◽  
Djordje Stojakovic ◽  
Sanja Sajic ◽  
Amalija Golobic ◽  
...  
Keyword(s):  
Activation Energy ◽  
Hydrothermal Synthesis ◽  
Hydrogen Bonds ◽  
Negative Charge ◽  
Membered Ring ◽  
Hydroxyl Groups ◽  
Hydrothermal Crystallization ◽  
Structure Directing Agent

A novel layered zincophosphate (ZnPO?MPA) was prepared by hydrothermal crystallization using 3-methylaminopropylamine (MPA) as a structure-directing agent. The structure consists of macroanion [Zn2P3O8(OH)3]2- layers which are built up of 4-membered ring channels. The channels (of about 3.7 ? diameter) arise through the connection of the neighbouring rings by two oxygen bridges. The negative charge of the layers is compensated by diprotonated MPA molecules which are stacked parallel to the ring channels. ZnPO?MPA is stable up to 300 ?C. At higher temperatures MPA decomposition begins followed by a dehydration, which occurs through condensation of the framework hydroxyl groups. The activation energy of the MPA decomposition is high due to the fact that the layers and MPA cations are held together by strong hydrogen bonds.

Preparation and performance characterization of novel PVA blended with fluorinated polyimide membrane for gas separation

2020 ◽  
pp. 095400832095970
Author(s):  
Yunwu Yu ◽  
Peng Lin ◽  
Ye Zhao ◽  
Changwei Liu ◽  
Changwei Xu ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Bonds ◽  
Gas Separation ◽  
Amic Acid ◽  
Gas Permeation ◽  
Separation Performance ◽  
Hydroxyl Groups ◽  
Operating Pressure ◽  
Polyimide Membrane ◽  
Fluorinated Polyimide

Fluorinated polyimide and PVA blending membranes were prepared by aqueous solution casting. We chose a poly (amic acid) ammonium salt (PAAS) in aqueous solution based on a novel green strategy as the PI precursor. The blending membranes were characterized by ATR-FTIR, DSC, TGA and gas permeation measurement. The ATR-FTIR analysis revealed that the imidization reaction of 6FPI based on aqueous precursor was completed at 180°C and hydrogen bonds formed between PVA and 6FPI. 6FPI showed good compatibility with PVA segment in blending membranes without obvious separated phase structure. The blending membranes showed high separation properties, for blending with 6FPI the gas separation performance stability was improved due to the hydrogen bonds between hydroxyl groups of PVA and carbonyl groups of 6FPI, and the rigid structure of 6FPI. At high operating pressure 10 bar, the CO2 permeability and CO2/N2 selectivity remained rather high. Using water as the solvent in the PAAS synthesis and membrane preparation is more environmentally friendly and less costly.

SN2 reactions in the gas phase. Transition states for the reaction: Cl− + RBr = ClR + Br−, where R = CH3, C2H5, and iso-C3H7, from abinitio calculations and comparison with experiment. Solvent effects

1989 ◽  
Vol 67 (8) ◽  
pp. 1262-1267 ◽  
Author(s):  
Kimihiko Hirao ◽  
Paul Kebarle
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Aqueous Solution ◽  
Transition State ◽  
Gas Phase ◽  
Closed Shell ◽  
Basis Set ◽  
Phase Reaction ◽  
Ion Molecule Reactions ◽  
Abinitio Calculations

The geometries and the energies of the reactants, transition state, and products for the gas phase reaction: Cl− + CH3Br = ClCH3 + Br−, were obtained from abinitio calculations using a closed shell SCF method with a MINI basis set developed by Huzinaga etal. The energy changes predicted by the calculations are found in good agreement with the experimental data. The energies and geometries of the reactants and the transition state for the gas phase reactions: Cl− + RBr = ClR + Br−, where R = C2H5 and iso-C3H7, were also obtained. The resulting activation energies follow the same trend as the experimental data: Me < Et < iso-Pr; however, the predicted increase of activation energy is considerably larger. The energies and geometries for the reactants, transition state, and products of the gas phase ion-dihydrate reaction: Cl−(H2O)2 + CH3Br → H2O(ClCH3Br)−H2O → Br−(H2O)2 + CH3Cl were obtained as well. These data provide an interesting comparison with experimental results in aqueous solution. The reaction coordinate of the ion-dihydrate reaction is very much closer to that for aqueous solution than to that for the gas phase. Keywords: nucleophilic substitution reactions, ion–molecule reactions, activation energy.

Theoretical studies of the 2- and 4-hydroxybenzoic acid with competing hydrogen bonds in the gas phase and aqueous solution

1993 ◽  
Vol 97 (18) ◽  
pp. 4628-4642 ◽  
Author(s):  
Peter I. Nagy ◽  
William J. Dunn ◽  
Giuliano Alagona ◽  
Caterina Ghio
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Bonds ◽  
Gas Phase ◽  
Hydroxybenzoic Acid ◽  
Theoretical Studies
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