Biomedical subjects

Matthew D Wodrich

Publications and source records attributed to Matthew D Wodrich.

3 recordsLinked to original sources

PubMed2006

Systematic errors in computed alkane energies using B3LYP and other popular DFT functionals.

[structure: see text] Energies computed by B3LYP and other popular DFT functionals are flawed by systematic errors, which can become considerable for larger molecules. These errors, predominately due to inadequacies in assessing longer-range nonbonded attractive effects (dispersion), are illustrated by the isodesmic stabilization energies of n-alkanes (based on methane and ethane, which have no stabilizing 1,3-alkyl group interactions). Newer functionals, designed to describe weak interactions, give somewhat better agreement with experiment, but are not fully satisfactory.

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PubMed2006

New additivity schemes for hydrocarbon energies.

[structure: see text] A new isodesmic additivity scheme based on the energetic relationships among the simplest hydrocarbon molecules reproduces the experimental heats of formation for a broad range of unstrained hydrocarbons with remarkable accuracy. The stabilizations of radicals, double, and triple CC bonds by alkyl substituents (hyperconjugation), as well as the stabilization by 1,3-alkyl group interactions at the same carbon (branching), support conventional interpretations. Statistical data fitting can also be achieved by using only four adjustable parameters.

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PubMed2005

Evidence for d orbital aromaticity in square planar coinage metal clusters.

Quantitative evidence for the existence of aromaticity involving the d orbitals of transition metals is provided for the first time. The doubly bridged square planar (D(4)(h)()) coinage metal clusters (M(4)Li(2), M = Cu (1), Ag (2), and Au (3)) are characterized as aromatic by their substantial nucleus independent chemical shifts (NICS) values in the centers (-14.5, -14.1, and -18.6, respectively). Nevertheless, the participation of p orbitals in the bonding (and cyclic electron delocalization) of 1-3 is negligible. Instead, these clusters benefit strongly from the delocalization of d and to some extent s orbitals. The same conclusion applies to Tsipis and Tsipis' H-bridged D(4)(h)() Cu(4)H(4) ring (4). Canonical MO-NICS analysis of structures 1-3 shows the total diatropic d orbital contributions to the total NICS to be substantial, although the individual contributions of the five sets of filled d orbitals vary. The d orbital aromaticity of Cu(4)Li(2) also is indicated by its atomization energy, 243.2 kcal/mol, which is larger than Boldyrev's doubly (sigma and pi) aromatic Al(4)Li(2) (215.9 kcal/mol).

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