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C F Matta

Publications and source records attributed to C F Matta.

4 recordsLinked to original sources
PubMed2001

Bonding to titanium.

The recent synthesis of a crystalline compound containing Ti bonded to cyclopentadienyl and a substituted dienyl fragment prompted the question of whether Ti-C contacts that were found to be shorter than other such bonded contacts in the same molecule should be considered as short nonbonded contacts or "nonclassical metal-to-saturated-carbon atom interactions", fitting the description of agostic interactions. This question has a unique answer within the framework of the quantum theory of atoms in molecules (QTAIM). QTAIM uses the measurable electron density to assign a molecular structure and the physics of an open system to determine the nature of the bonded interactions. All of the classical bonding descriptors, when recast in terms of the topologies of the electron density and the pair density, are faithfully recovered when QTAIM is applied to the hydrocarbon framework of the Ti complex, thereby justifying its application to the analysis of the Ti-C interactions. No bond paths are found to link the Ti to the carbons exhibiting the "short contacts", and the topology of the density gives no indication of an incipient change in structure that would result in their formation.

Journal Article↗
PubMed2001

Twisted amides: synthesis and structure of 1,6-dipivaloyl-3,4,7,8- tetramethyl-2,5-dithioglycoluril.

[structure: see text] The 1,6-dipivaloyl derivative of 3,4,7,8-tetramethyl-2,5-dithioglycoluril (6) was prepared and the crystal structure determined by X-ray diffraction; 6 is a twisted amide in which severe ring strain and nonbonded interactions compel both pivaloyl groups to twist dramatically out of the ring plane. The amide oxygen atoms point in opposite directions with respect to the mean plane through the glycoluril core, and the bridgehead methyl groups are forced out of the symmetric syn geometry (eta = 30.5 degrees ). The structure of 7, a rearrangement product generated during synthesis of 6, was also determined by single-crystal X-ray diffraction.

Journal Article↗
PubMed2000

An atoms-in-molecules study of the genetically-encoded amino acids: I. Effects of conformation and of tautomerization on geometric, atomic, and bond properties.

The theory of Atoms-In-Molecules (AIM) is a partitioning of the real space of a molecule into disjoint atomic constituents as determined by the topology of the electron density, rho(r). This theory identifies an atom in a molecule with a quantum mechanical open system and, consequently, all of the atom's properties are unambiguously defined. AIM recovers the basic empirical cornerstone of chemistry: that atoms and functional groups possess characteristic and additive properties that in many cases exhibit a remarkable transferability between different molecules. As a result, the theory enables the theoretical synthesis of a large molecule and the prediction of its properties by joining fragments that are predetermined as open systems. The present article is the first of a series (in preparation) that explore this possibility for polypeptides by determining the transferability of the building blocks: the amino acid residues. Transferability of group properties requires transferability of the electron density rho(r), which in turn requires the transferability of the geometric parameters. This article demonstrates that these parameters are conformation-insensitive for a representative amino acid, leucine, and that the atomic and bond properties exhibit a corresponding transferability. The effects of hydrogen bonding are determined and a set of geometrical conditions for the occurrence of such bonding is identified. The effects of transforming neutral leucine into its zwitter-ionic form on its atomic and bond properties are shown to be localized primarily to the sites of ionization.

Amino Acids↗