Hugh M. Huffman

Bio: Hugh M. Huffman is an academic researcher from Stanford University. The author has contributed to research in topics: Heat capacity & Vapor pressure. The author has an hindex of 26, co-authored 57 publications receiving 2081 citations.

Development and Testing of the OPLS All-Atom Force Field on Conformational Energetics and Properties of Organic Liquids

Abstract: The parametrization and testing of the OPLS all-atom force field for organic molecules and peptides are described. Parameters for both torsional and nonbonded energetics have been derived, while the bond stretching and angle bending parameters have been adopted mostly from the AMBER all-atom force field. The torsional parameters were determined by fitting to rotational energy profiles obtained from ab initio molecular orbital calculations at the RHF/6-31G*//RHF/6-31G* level for more than 50 organic molecules and ions. The quality of the fits was high with average errors for conformational energies of less than 0.2 kcal/mol. The force-field results for molecular structures are also demonstrated to closely match the ab initio predictions. The nonbonded parameters were developed in conjunction with Monte Carlo statistical mechanics simulations by computing thermodynamic and structural properties for 34 pure organic liquids including alkanes, alkenes, alcohols, ethers, acetals, thiols, sulfides, disulfides, a...

A biomolecular force field based on the free enthalpy of hydration and solvation: the GROMOS force-field parameter sets 53A5 and 53A6.

Abstract: Successive parameterizations of the GROMOS force field have been used successfully to simulate biomolecular systems over a long period of time. The continuing expansion of computational power with time makes it possible to compute ever more properties for an increasing variety of molecular systems with greater precision. This has led to recurrent parameterizations of the GROMOS force field all aimed at achieving better agreement with experimental data. Here we report the results of the latest, extensive reparameterization of the GROMOS force field. In contrast to the parameterization of other biomolecular force fields, this parameterization of the GROMOS force field is based primarily on reproducing the free enthalpies of hydration and apolar solvation for a range of compounds. This approach was chosen because the relative free enthalpy of solvation between polar and apolar environments is a key property in many biomolecular processes of interest, such as protein folding, biomolecular association, membrane formation, and transport over membranes. The newest parameter sets, 53A5 and 53A6, were optimized by first fitting to reproduce the thermodynamic properties of pure liquids of a range of small polar molecules and the solvation free enthalpies of amino acid analogs in cyclohexane (53A5). The partial charges were then adjusted to reproduce the hydration free enthalpies in water (53A6). Both parameter sets are fully documented, and the differences between these and previous parameter sets are discussed.

Electron spin resonance studies of transient alkyl radicals

Abstract: Electron spin resonance methods have been used to observe alkyl radicals in liquid hydrocarbon systems during irradiation with 2.8‐MeV electrons. These investigations provide detailed structural, radiation chemical, and kinetic information about a large number of radicals.In general, in these studies the ESR lines are found to be narrow; considerable fine structure is observable, permitting positive assignment of the radical species. Accurate hyperfine constants are reported for 21 alkyl and cycloalkyl radicals (including several deuterated species), vinyl, 1‐methylvinyl, 3‐butenyl, allyl, and cyclohexadienyl radicals, and hydrogen and deuterium atoms. Except for cyclopropyl radical, all the alkyl and cycloalkyl radicals have α coupling constants in the range 21–23 G. The β coupling constants in cases where they have been rotationally averaged isotropically are found to decrease with increasing substitution of alkyl groups on the α carbon atom. In general the values for primary, secondary, and tertiary ra...

Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals

Abstract: VOLUME I Introduction The Incentive Physical-Chemical Properties Experimental Methods Quantitative Structure-Property Relationships (QSPRs) Mass Balance Models of Chemical Fate Data Sources and Presentation Illustrative QSPR Plots and Fate Calculations References Aliphatic and Cyclic Hydrocarbons Lists of Chemicals and Data Compilations Summary Tables and QSPR plots References Mononuclear Aromatic Hydrocarbons Lists of Chemicals and Data Compilations Summary Tables and QSPR plots References Polynuclear Aromatic Hydrocarbons (PAHs) and Related Aromatic Hydrocarbons Lists of Chemicals and Data Compilations Summary Tables and QSPR plots References VOLUME II * Halogenated Aliphatic Hydrocarbons Chlorobenzenes and Other Halogenated Mononuclear Aromatics Polychlorinated Biphenyls (PCBs) Chlorinated Dibenzop-dioxins Chlorinated Dibenzofurans VOLUME III * Ethers Alcohols Aldehydes and Ketones Carboxylic Acids Phenolic Compounds Esters VOLUME IV Nitrogen and Sulfur Compounds Lists of Chemicals and Data Compilations Summary Tables References Herbicides Lists of Chemicals and Data Compilations Summary Tables References Insecticides Lists of Chemicals and Data Compilations Summary Tables References Fungicides Lists of Chemicals and Data Compilations Summary Tables References APPENDICES List of Symbols and Abbreviations Alphabetical Index CAS Registry Index Molecular Formula Index * Each chapter contains lists of chemicals and data compilations, summary tables, QSPR plots, and references