D. H. W. den Boer

Ab initio calculations on first-row transition metal porphyrins. Part 1. Geometrical details, charge distributions and the effects of additional charge

Abstract Ab initio calculations were done on eight first-row transition-metal porphyrins and dihydrogen porphyrin. The metal ions situated in the centre of the porphyrins were: chromium(III), manganese(III), iron(III), cobalt(III), cobalt(II), nickel(II), copper(II) and zinc(II). A chlorine counter ion was included in order to keep the molecules containing metal(III) ions neutral. The optimal geometries and charge distributions were calculated with the restricted Hartree-Fock routines and distributed multipole analysis routines present in gamess-uk . The metal atoms, the nitrogen atoms and the chlorine atoms were described using the SV-3-21G basis set and the carbon and hydrogen atoms with STO3G. The effect of additional charge on the molecules was estimated by removing one electron from the HOMO or adding one to the LUMO of each compound. The porphyrin charge distributions assume the shape of concentric rings of alternating sign. They provide the molecules with the ability to preserve a remarkably high charge on the central metal ion. This enables the occurrence of stable metal ions in an apolar environment that are still accessible because of the planar geometry of the porphyrin moieties.

Bond length alternation in pentalene

According to lcao-mo calculations lower π-electron and total electron energy values result if the molecular symmetry group for pentalene is taken to be C2h instead of D2h . Though a considerable reduction in π-electron energy is obtained, the gain in total electron energy is much smaller. Nevertheless it may be stated that in the ground state the twofold axes C2 x and C2 y are not present.

Bond length alternation in heptalene

Using LCAO-MO theory it is shown that the heptalene molecule possesses only a centre of symmetry instead of two mutually perpendicular twofold axes in the molecular plane. Charges and free valence numbers indicate that the 1-position should be the most reactive.

Ab initio calculations on first-row transition metal porphyrins Part 2. Ground state spin multiplicities, calculated ionisation potentials and electron affinities and their relation to catalytic activity

Abstract This article continues the discussion of ab initio calculations on chromium(III)-chloro-, manganese(III)-chloro-, iron(III)-chloro-, cobalt(III)-chloro-, cobalt(II)-, nickel(II)-, copper(II)- and zinc(II)-porphyrin. Restricted Hartree Fock (RHF) and Singles and Doubles Configuration Interaction (SDCI) results were obtained with the quantum chemical program system GAMESS-UK. The SDCI calculations were used to confirm the high spin multiplicities found with RHF for the electronic ground states of the metal porphyrins. The metal, nitrogen and chlorine atoms were described with the Split Valence 3-21G basis set; the carbon and hydrogen atoms with STO3G. The largest SDCI calculation dealt with 14.6 million Configuration State Functions. The electron distribution of singly charged porphyrins (cations and anions) show that the Highest Occupied Molecular Orbitals (HOMOs) of each porphyrin are delocalised, doubly occupied orbitals from the porphyrin ring moiety. The HOMOs donate the first electron, even though there are singly occupied orbitals present in the system. Acceptance of the first electron takes place in an orbital dominated by metal Atomic Orbital components. The partially occupied d-like orbitals present in the porphyrins take little part in this process and tend to preserve their identities. The energy differences of the charged porphyrins may give an indication of their ionisation potentials and electron affinities. A relation is apparent between the spin multiplicity of the ground states of the porphyrins discussed here and the activity of the porphyrin in the catalytic decomposition of cyclohexyl peroxide: all porphyrins with a quartet or higher spin ground state may be found among the active catalysts.

Valency-bond studies of some conjugated hydrocarbons—II Pentalene, and some preliminary results on heptalene

Valency-bond studies of the still unknown molecule pentalene C8H6 in which the molecular symmetry may be either D2h or C2h show that a more stable molecule (lower ground state energy) is found for the lower symmetry, and that marked alternation of bond lengths occurs. The corresponding Penney-Dirac bond orders have been determined. Preliminary results for heptalene forecast a similar conclusion.

A Comparison Between the Intermediary Amino Acid Metabolism of the Rat, The cat and a Blowfly Larva (Calliphora Erythrocephala, Meig

AbstractGrowing rats, a growing cat and larvae of Calliphora erythrocephala (the latter aseptically reared from the egg) were fed with N15-labelled ammonia, the Calliphoro larvae also with N15-glutamic acid. The greater part of the amino acids were isolated and their atom percentage excess N15 was determined by means of a mass spectrometer.The amino acids generally considered as the most metabolically active (glutamic cid, aspartic acid and alanine) were found to be highest labelled. The high N15 value for alanine in the cat and Calliphora (equal to or even higher than in glutamic acid) is remarkable.Calliphora proved to have a greater number of inert amino acids (which do not take up-N15 H2) than mammals. In the latter only lysine and threonine are inert, in Calliphora lysine, threonine, arginine, histidine and phenylalanine.Probably proline in Calliphora is synthesized in another way than in mammals.