S. Lifson

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEnergy functions for peptides and proteins. I. Derivation of a consistent force field including the hydrogen bond from amide crystalsA. T. Hagler, E. Huler, and S. LifsonCite this: J. Am. Chem. Soc. 1974, 96, 17, 5319–5327Publication Date (Print):August 1, 1974Publication History Published online1 May 2002Published inissue 1 August 1974https://pubs.acs.org/doi/10.1021/ja00824a004https://doi.org/10.1021/ja00824a004research-articleACS PublicationsRequest reuse permissionsArticle Views1599Altmetric-Citations578LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

An inductive method for a systematic selection of energy functions of interatomic interactions in large families of molecules is suggested and is applied to the family of cycloalkane and n-alkane molecules. Equilibrium conformations, vibrational frequencies, and excess enthalpies, including strain energies and vibrational enthalpies, are all derived from the same set of energy functions. The energy-function parameters are optimized by a least-squares algorithm to give the best possible agreement with a large amount and variety of observed data. Analytical derivatives of the various calculated quantities with respect to the energy parameters help to facilitate the computational procedures. The resulting agreement with experiment is used as a measure of success of the energy functions with optimized parameters, referred to as “consistent force field” (CFF). Different CFF's are compared and selected according to their relative success. Energy functions commonly used in conformational analysis are examined in preliminary consistent-force-field calculations and are found inadequate. Considerable imporvement is obtained when Coulomb interactions between residual atomic charges are included, and when interactions between atoms bonded to a common atom are represented by a Urey–Bradley-type force field, while Lennard-Jones potentials are used for nonbonded interactions between atoms separated by more than one atom. Vibrational frequencies as well as vibrational molecular enthalpies are derived for all cycloalkanes C5 through C12. The spectroscopic force constants are derived from the CFF as functions of molecular conformations. Agreement with available spectroscopic assignments of frequencies is reasonably good. A few improvements are suggested for cyclopentane assignments. The path and moment of inertia of pseudorotation in cyclopentane are calculated. Cyclodecane frequency assignments, based on the derived conformational C2h symmetry, are suggested for the first time. Calculated excess enthalpies of C5H10 and medium cycloalkanes agree well with observed values. Contributions of vibration–translation–rotation are shown to amount to a significant part of the excess enthalpy.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTConsistent force field studies of intermolecular forces in hydrogen-bonded crystals. 1. Carboxylic acids, amides, and the C:O.cntdot..cntdot..cntdot.H- hydrogen bondsS. Lifson, A. T. Hagler, and P. DauberCite this: J. Am. Chem. Soc. 1979, 101, 18, 5111–5121Publication Date (Print):August 1, 1979Publication History Published online1 May 2002Published inissue 1 August 1979https://doi.org/10.1021/ja00512a001RIGHTS & PERMISSIONSArticle Views1430Altmetric-Citations444LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTConsistent force field studies of intermolecular forces in hydrogen-bonded crystals. 2. A benchmark for the objective comparison of alternative force fieldsA. T. Hagler, S. Lifson, and P. DauberCite this: J. Am. Chem. Soc. 1979, 101, 18, 5122–5130Publication Date (Print):August 1, 1979Publication History Published online1 May 2002Published inissue 1 August 1979https://pubs.acs.org/doi/10.1021/ja00512a002https://doi.org/10.1021/ja00512a002research-articleACS PublicationsRequest reuse permissionsArticle Views870Altmetric-Citations371LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Abstract ( 1 ) The electrostatic internal energy of a solution of rodlike, ionized polymolecules is calculated by an integration which makes use of the molecular potentials evaluated previously. ( 2 ) The electrostatic free energy is calculated by a charging process for which the reference state is a discharged solution of the same concentration as that of the charged solution. ( 3 ) A series of graphs is presented for the numerical evaluation of the internal and free energies of salt‐free polyelectrolyte solutions as a function of concentration, degree of ionization, and temperature. ( 4 ) The osmotic pressure of stretched polyelectrolytes is calculated from the free energy expression. The calculated osmotic coefficients are practically independent of molecular weight and polyelectrolyte concentration, and are determined by the degree of ionization. A comparison with the measurements of Kern on salt‐free polyacrylic acid at higher degrees of ionization (for which the macromolecules are stretched) gives a very satisfactory agreement. ( 5 ) An expression for the light scattering by polyelectrolyte solutions is derived from the equation for osmotic pressure and discussed briefly.