Electronic structure and bonding in metal phthalocyanines (MetalϭFe, Co, Ni, Cu, Zn, Mg) is investigated in detail using a density functional method. The metal atoms are strongly bound to the phthalocyanine ring in each case, by as much as 10 eV. The calculated orbital energy levels and relative total energies of these D 4h structures indicate that Fe and Co phthalocyanines have 3 A 2g and 2 E g ground states, respectively, but that these states are changed upon interaction with strong-field axial ligands. The valence electronic structures of Fe and Co phthalocyanines differ significantly from those of the others. The HOMOs in Fe, Co, and Cu phthalocyanine are metal 3d-like, whereas in Ni and Zn phthalocyanines, the HOMO is localized on the phthalocyanine ring. The first ionization removes an electron from the phthalocyanine a 1u orbital in all cases, with very little sensitivity of the ionization energy to the identity of the metal. Whereas the first reduction in Fe and Co phthalocyanine occurs at the metal, it is the phthalocyanine that is reduced upon addition of an electron to the other systems. Fe, Ni, and Cu phthalocyanines have smaller HOMO-LUMO separations than do Zn and Co phthalocyanine. There is very little variation in atomic charges within the phthalocyanine from one metal to the next.

A systematic theoretical study of the electronic structure and bonding in metal meso-tetraphenyl porphines MTPP, MϭFe, Co, Ni, Cu, Zn has been carried out using a density functional theory method. The calculations provide a clear elucidation of the ground states for the MTPPs and for a series of ͓MTPP͔ x ions (xϭ2ϩ, 1ϩ, 1Ϫ, 2Ϫ, 3Ϫ, 4Ϫ͒, which aids in understanding a number of observed electronic properties. The calculation supports the experimental assignment of unligated FeTPP as 3 A 2g , which arises from the configuration (d xy) 2 (d z 2) 2 (d xz) 1 (d yz) 1. The calculated M-TPP binding energies, ionization potentials, and electron affinities are in good agreement with available experimental data. The influence of axial ligands and peripheral substitution by fluorine are in accord with the experimental observation that not only half-wave potentials (E 1/2) of electrode reactions, but also the site of oxidation/reduction, may be dependent on the porphyrin basicity and the type of axial ligand coordination.

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Orthologous proteins of species adapted to different temperatures exhibit differences in stability and function that are interpreted to reflect adaptive variation in structural "flexibility." However, quantifying flexibility and comparing flexibility across proteins has remained a challenge. To address this issue, we examined temperature effects on cytosolic malate dehydrogenase (cMDH) orthologs from differently thermally adapted congeners of five genera of marine molluscs whose field body temperatures span a range of ∼60 °C. We describe consistent patterns of convergent evolution in adaptation of function [temperature effects on of cofactor (NADH)] and structural stability (rate of heat denaturation of activity). To determine how these differences depend on flexibilities of overall structure and of regions known to be important in binding and catalysis, we performed molecular dynamics simulation (MDS) analyses. MDS analyses revealed a significant negative correlation between adaptation temperature and heat-induced increase of backbone atom movements [root mean square deviation (rmsd) of main-chain atoms]. Root mean square fluctuations (RMSFs) of movement by individual amino acid residues varied across the sequence in a qualitatively similar pattern among orthologs. Regions of sequence involved in ligand binding and catalysis-termed mobile regions 1 and 2 (MR1 and MR2), respectively-showed the largest values for RMSF. Heat-induced changes in RMSF values across the sequence and, importantly, in MR1 and MR2 were greatest in cold-adapted species. MDS methods are shown to provide powerful tools for examining adaptation of enzymes by providing a quantitative index of protein flexibility and identifying sequence regions where adaptive change in flexibility occurs.

The effect of oxidation on the electronic structure of the green fluorescent protein chromophore Electronic effect on protonated hydrogen-bonded imidazole trimer and corresponding derivatives cationized by alkali metals ( Li + , Na + , and K + ) J. Chem. Phys. 122, 054311 (2005); 10.1063/1.1839855Electronic structure and bonding in metal porphyrins, metal=Fe, Co, Ni, Cu, Zn