A reaction surface Hamiltonian treatment of the double proton transfer of formic acid dimer

The double proton transfer reaction of the isolated formic acid dimer has been investigated within the reaction surface Hamiltonian framework, using a newly calculated three‐dimensional ab initio potential energy surface. The symmetric (synchronous) proton movement, the asymmetric (asynchronous) proton movement and the relative motion of two formic acid molecules have been explicitly included in the calculation. The calculation gives a tunneling splitting of 0.004 cm-1, which is considerably smaller than a previous theoretical prediction (0.3 cm-1). An effective tunneling path has been calculated from the lowest vibrational eigenfunction of the reaction surface Hamiltonian, and the path deviates significantly from the minimum energy path on the potential energy surface. The new results are consistent with the conventional understanding of heavy-light-heavy mass combination reactions. The effective reaction path from this calculation reveals evidence of asymmetric proton movement. However, a synchronous double proton transfer is the major mode of reaction. Tunneling splittings for a few excited vibrational levels have also been calculated within the reaction surface Hamiltonian framework. Vibrational excitation of a large amplitude, heavy atom mode dramatically increases the tunneling splitting.application/pdfjournal articl

A theoretical study of multidimensional nuclear tunneling in malonaldehyde

Various aspects of the intramolecular proton transfer in malonaldehyde have been investigated theoretically within the reaction surface Hamiltonian framework, which was recently applied with a two‐dimensional surface to this molecule by Carrington and Miller. The present calculation, which involves a three‐dimensional reaction surface and a high level of ab initio accuracy, gives a tunneling splitting which is -50% smaller than experiment and a hydrogen/deuterium isotope effect that is within 40% of experiment with no adjustable parameter. The vibrational wave function has been analyzed to extract an effective curvilinear tunneling path on the hypersurface. The path calculations, and other analysis, clearly demonstrate the limitations of one‐dimensional models for polyatomic tunneling systems like malonaldehyde. In addition, tunneling splittings have been calculated for excited vibrational states of malonaldehyde, leading to new insight into the multidimensional character of proton transfer.application/pdfjournal articl

STRUCTURE AND INFRARED-SPECTROSCOPY OF THE C-11 MOLECULE

Linear, cyclic and three-dimensional structures of C-11 have been studied with ab initio methods. At the MP2/6-31G(d) level, a cyclic structure is clearly the ground state, about 5 kcal/mol below the lowest linear structure. The three-dimensional structure proposed by van Vechten and Keszler is less stable by at least 200 kcal/mol. Arguments are presented in favor of assignment of the 1804 and 1844 cm-1 matrix IR bands to cyclic C-11, and of the 1818 cm-1 band to cyclic C-10

Effect of predicted protein-truncating genetic variants on the human transcriptome

Expression, genetic variation, and tissues Human genomes show extensive genetic variation across individuals, but we have only just started documenting the effects of this variation on the regulation of gene expression. Furthermore, only a few tissues have been examined per genetic variant. In order to examine how genetic expression varies among tissues within individuals, the Genotype-Tissue Expression (GTEx) Consortium collected 1641 postmortem samples covering 54 body sites from 175 individuals. They identified quantitative genetic traits that affect gene expression and determined which of these exhibit tissue-specific expression patterns. Melé et al. measured how transcription varies among tissues, and Rivas et al. looked at how truncated protein variants affect expression across tissues. Science , this issue p. 648 , p. 660 , p. 666 ; see also p. 640 </jats:p