AM1-SM2 and PM3-SM3 parameterized SCF solvation models for free energies in aqueous solution

1992 ◽  
Vol 6 (6) ◽  
pp. 629-666 ◽  
Author(s):  
Christopher J. Cramer ◽  
Donald G. Truhlar
Keyword(s):  
Aqueous Solution ◽  
Free Energies ◽  
Solvation Models

2-Deoxyribose Radicals in the Gas Phase and Aqueous Solution. Transient Intermediates of Hydrogen Atom Abstraction from 2-Deoxyribofuranose

2005 ◽  
Vol 70 (11) ◽  
pp. 1769-1786 ◽  
Author(s):  
Luc A. Vannier ◽  
Chunxiang Yao ◽  
František Tureček
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Atom ◽  
Gas Phase ◽  
Computational Study ◽  
Hydrogen Atom Abstraction ◽  
Oh Radical ◽  
Free Energies ◽  
Intramolecular Hydrogen ◽  
Solvation Free Energies ◽  
Transient Intermediates

A computational study at correlated levels of theory is reported to address the structures and energetics of transient radicals produced by hydrogen atom abstraction from C-1, C-2, C-3, C-4, C-5, O-1, O-3, and O-5 positions in 2-deoxyribofuranose in the gas phase and in aqueous solution. In general, the carbon-centered radicals are found to be thermodynamically and kinetically more stable than the oxygen-centered ones. The most stable gas-phase radical, 2-deoxyribofuranos-5-yl (5), is produced by H-atom abstraction from C-5 and stabilized by an intramolecular hydrogen bond between the O-5 hydroxy group and O-1. The order of radical stabilities is altered in aqueous solution due to different solvation free energies. These prefer conformers that lack intramolecular hydrogen bonds and expose O-H bonds to the solvent. Carbon-centered deoxyribose radicals can undergo competitive dissociations by loss of H atoms, OH radical, or by ring cleavages that all require threshold dissociation or transition state energies >100 kJ mol-1. This points to largely non-specific dissociations of 2-deoxyribose radicals when produced by exothermic hydrogen atom abstraction from the saccharide molecule. Oxygen-centered 2-deoxyribose radicals show only marginal thermodynamic and kinetic stability and are expected to readily fragment upon formation.

A QM/MM study combined with the theory of energy representation: Solvation free energies for anti/syn acetic acids in aqueous solution

2006 ◽  
Vol 419 (1-3) ◽  
pp. 240-244 ◽  
Author(s):  
Takumi Hori ◽  
Hideaki Takahashi ◽  
Masayoshi Nakano ◽  
Tomoshige Nitta ◽  
Weitao Yang
Keyword(s):  
Aqueous Solution ◽  
Free Energies ◽  
Solvation Free Energies ◽  
Acetic Acids

THEORETICAL CALCULATION OF pKb VALUES FOR ANILINES AND SULFONAMIDE DRUGS IN AQUEOUS SOLUTION

2012 ◽  
Vol 11 (02) ◽  
pp. 283-295 ◽  
Author(s):  
BAHRAM GHALAMI-CHOOBAR ◽  
ALI GHIAMI-SHOMAMI ◽  
PARIA NIKPARSA
Keyword(s):  
Gas Phase ◽  
Continuum Model ◽  
Correlation Equation ◽  
Polarizable Continuum Model ◽  
Free Energies ◽  
Pcm Model ◽  
Solvation Models ◽  
Polarizable Continuum ◽  
Better Than ◽  
Good Agreement

In this work, calculations of p K b values have been performed for aniline and its substituted derivatives and sulfonamide drugs by using Gaussian 98 software package. Gas-phase energies were calculated with HF /6-31 G ** and B3LYP /6-31 G ** levels of theory. Free energies of solvation have been computed using the polarizable continuum model (PCM), conductor-like polarizable continuum model (CPCM) and the integral equation formalism-polarizable continuum model (IEFPCM) at the same levels which have been used for geometry determination in the gas-phase. The results show that the calculated p K b values using the B3LYP /6-31 G ** are better than those using the corresponding HF /6-31 G **. At first, the correlation equation was found to determine the p K b values of the investigated anilines. Then, this correlation equation was used to calculate the p K b values of the sulfonamide drugs. The results obtained indicate that the PCM model is a suitable solvation model for calculating p K b values in comparison to the other solvation models. For the investigated compounds a good agreement between the experimental and the calculated p K b values was also observed.

scholarly journals Role of Dispersion Attraction in Differential Geometry Based Nonpolar Solvation Models

2015 ◽  
Vol 3 (1) ◽  
Author(s):  
Zhan Chen
Keyword(s):  
Differential Geometry ◽  
Electrostatic Interactions ◽  
Polar Component ◽  
Great Success ◽  
Free Energies ◽  
Dispersion Interactions ◽  
Solvation Models ◽  
Nonpolar Solvation ◽  
Solvation Analysis

AbstractDifferential geometry (DG) based solvation models have shown their great success in solvation analysis by avoiding the use of ad hoc surface definitions, coupling the polar and nonpolar free energies, and generating solvent-solute boundary in a physically self-consistent fashion. Parameter optimization is a key factor for their accuracy, predictive ability of solvation free energies, and other applications. Recently, a series of efforts have been made to improve the parameterization of these new implicit solvent models. In thiswork, we aim at studying the role of dispersion attraction in the parameterization of our DG based solvation models. To this end, we first investigate the necessity of van derWaals (vdW) dispersion interactions in the model and then carry out systematic parameterization for the model in the absence of electrostatic interactions. In particular, we explore how the changes in Lennard-Jones (L-J) potential expression, its decomposition scheme, and choices of some fixed parameter values affect the optimal values of other parameters as well as the overall modeling error. Our study on nonpolar solvation analysis offers insights into the parameterization of nonpolar components for the full DG based models by eliminating uncertainties from the electrostatic polar component. Therefore, it can be regarded as a step towards better parameterization for the full DG based model.

General parameterized SCF model for free energies of solvation in aqueous solution

1991 ◽  
Vol 113 (22) ◽  
pp. 8305-8311 ◽  
Author(s):  
Christopher J. Cramer ◽  
Donald G. Truhlar
Keyword(s):  
Aqueous Solution ◽  
Free Energies

scholarly journals Carbonyl Addition Reactions: Factors Affecting the Hydrate–Hemiacetal and Hemiacetal–Acetal Equilibrium Constants

1975 ◽  
Vol 53 (6) ◽  
pp. 898-906 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Aqueous Solution ◽  
Carbonyl Compounds ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Steric Effects ◽  
Addition Reactions ◽  
Free Energies ◽  
Electronic Effects ◽  
Factors Affecting ◽  
Analogous Formula

Equilibrium constants for hydrate–hemiacetal interconversion in aqueous solution at 25° have been measured for four fluorinated carbonyl compounds: compound, alcohol, K4 (M−1): CF3CHO, C2H5OH, 2.3; CF3COCH3, CH3OH, 1.0; CF3COPh, CH3OH, 3.5; CF3COCF3, CH3OH, 0.14. These values, combined with values from the literature, permit an examination of substituent effects upon the equilibrium constant for[Formula: see text]The free energy change for this process, corrected for symmetry and steric effects, follows the equation[Formula: see text]Thus electronic effects upon this equilibrium are generally small and in fact are often smaller than steric effects.This analysis permits and justifies the calculation of free energies of formation of [Formula: see text] compounds from the (more generally measurable) free energies of formation of the analogous [Formula: see text] compounds.

Acid Ionizations of Nitroalkanes in Aqueous Solution

1973 ◽  
Vol 51 (12) ◽  
pp. 1941-1944 ◽  
Author(s):  
Takeki Matsui ◽  
Loren G. Hepler
Keyword(s):  
Aqueous Solution ◽  
Carboxylic Acids ◽  
Equilibrium Constants ◽  
Free Energies ◽  
Methyl Substitution ◽  
Calorimetric Measurements ◽  
Acid Ionizations

Calorimetric measurements have led to ΔH0 values for ionization of nitromethane, nitroethane, 1-nitropropane, and 2-nitropropane in aqueous solution at 298°K. Combinations of these enthalpies with free energies from equilibrium constants for ionization have led to ΔS0 values for the ionization reactions. It is noted that the trend toward decreasing pK with methyl substitution in nitroalkanes is unusual compared to phenols and carboxylic acids. Similarly, correlations of ΔS0 with ΔG0 and ΔH0 are different for nitroalkanes than for other acids.

A group equivalents scheme for free energies of formation of organic compounds in aqueous solution

1992 ◽  
Vol 70 (4) ◽  
pp. 1042-1054 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Aqueous Solution ◽  
Organic Compounds ◽  
Group Contributions ◽  
Free Energies

Group contributions have been determined allowing the calculation of free energies of formation in aqueous solution for organic compounds containing carbon, hydrogen, and oxygen. The system works well for monofunctional compounds. The available literature data for 198 compounds can be accommodated using 79 parameters with an rms deviation of 0.74 kcal/mol.

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