Frank Weinhold

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Collagen-like peptides of the type (Pro-Pro-Gly)(10) fold into stable triple helices. An electron-withdrawing substituent at the H(gamma)(3) ring position of the second proline residue stabilizes these triple helices. The aim of this study was to reveal the structural and energetic origins of this effect. The approach was to obtain experimental NMR data on(More)
Resonance weights derived from the Natural Resonance Theory Ž . NRT , introduced in the preceding paper are used to calculate ‘‘natural bond order,’’ ‘‘natural atomic valency,’’ and other atomic and bond indices reflecting the resonance composition of the wave function. These indices are found to give Ž significantly better agreement with observed(More)
The X[bond]H bond length in X[bond]H...Y hydrogen bonded complexes is controlled by a balance of two main factors acting in opposite directions. "X[bond]H bond lengthening" due to n(Y)-->sigma(H[bond]X) hyperconjugative interaction is balanced by "X[bond]H bond shortening" due to increase in the s-character and polarization of the X[bond]H. When(More)
We present ab initio calculations of the Fermi contact term and experimental correlations of six coupling constants, 3JHNH alpha, 1JC alpha H alpha, 2JC'H alpha, 1JC alpha N, 2JC alpha N and 1JC'N, in a peptide as functions of the backbone dihedral angles, phi and psi. Given estimates of experimental uncertainties, we find semiquantitative experimental(More)
Hydrogen bonding underlies the structure of water and all biochemical processes in aqueous medium. Analysis of modern ab initio wave functions in terms of natural bond orbitals (NBOs) strongly suggests the resonance-type "charge transfer" (CT) character of H-bonding, contrary to the widely held classical-electrostatic viewpoint that underlies current(More)
We sketch the basic principles of natural bond orbital (NBO) theory, including critical discussion of its relationship to alternative bonding concepts and selected illustrations of its application to a broad spectrum of chemical bonding motifs. Particular emphasis is placed on the close NBO connections to prequantal bonding, and electromerism concepts, as(More)
Ab initio and hybrid density functional techniques were employed to characterize a surprising new class of H-bonded complexes between ions of like charge. Representative H-bonded complexes of both anion-anion and cation-cation type exhibit appreciable kinetic stability and the characteristic theoretical, structural, and spectroscopic signatures of hydrogen(More)
We describe quantitative numerical applications of the natural Ž . resonance theory NRT to a variety of chemical bonding types, in order to demonstrate the generality and practicality of the method for a wide range of . chemical systems. Illustrative applications are presented for 1 benzene and . . polycyclic aromatics; 2 CO , formate, and related acyclic(More)
We describe principal features of the newly released version, NBO 6.0, of the natural bond orbital analysis program, that provides novel "link-free" interactivity with host electronic structure systems, improved search algorithms and labeling conventions for a broader range of chemical species, and new analysis options that significantly extend the range of(More)