Biomedical subjects

Bodo Martin

Publications and source records attributed to Bodo Martin.

4 recordsLinked to original sources

PubMed2006

DFT models for copper(II) bispidine complexes: structures, stabilities, isomerism, spin distribution, and spectroscopy.

Various DFT and ab initio methods, including B3LYP, HF, SORCI, and LF-density functional theory (DFT), are used to compute the structures, relative stabilities, spin density distributions, and spectroscopic properties (electronic and EPR) of the two possible isomers of the copper(II) complexes with derivatives of a rigid tetradentate bispidine ligand with two pyridine and two tertiary amine donors, and a chloride ion. The description of the bonding (covalency of the copper-ligand interactions) and the distribution of the unpaired electron strongly depend on the DFT functional used, specifically on the nonlocal DF correlation and the HF exchange. Various methods may be used to optimize the DFT method. Unfortunately, it appears that there is no general method for the accurate computation of copper(II) complexes, and the choice of method depends on the type of ligands and the structural type of the chromophore. Also, it appears that the choice of method strongly depends on the problem to be solved. LF-DFT and spectroscopically oriented CI methods (SORCI), provided a large enough reference space is chosen, yield accurate spectroscopic parameters; EDA may lead to a good understanding of relative stabilities; accurate spin density distributions are obtained by modification of the nuclear charge on copper; solvation models are needed for the accurate prediction of isomer distributions.

Journal Article↗

PubMed2005

Coordination chemistry of a new rigid, hexadentate bispidine-based bis(amine)tetrakis(pyridine) ligand.

The hexadentate bispidine-based ligand 2,4-bis(2-pyridyl)-3,7-bis(2-methylenepyridine)-3,7-diazabicyclo[3.3.1]nonane-9-on-1,5-bis(carbonic acid methyl ester), L(6m), with four pyridine and two tertiary amine donors, based on a very rigid diazaadamantane-derived backbone, is coordinated to a range of metal ions. On the basis of experimental and computed structural data, the ligand is predicted to form very stable complexes. Force field calculations indicate that short metal-donor distances lead to a buildup of strain in the ligand; that is, the coordination of large metal ions is preferred. This is confirmed by experimentally determined stability constants, which indicate that, in general, stabilities comparable to those with macrocyclic ligands are obtained with the relative order Cu(2+) > Zn(2+) >> Ni(2+) < Co(2+), which is not the typical Irving-Williams behavior. The preference for large M-N distances also emerges from relatively high redox potentials (the higher oxidation states, that is, the smaller metal ions, are destabilized) and from relatively weak ligand fields (dd-transition, high-spin electronic ground states). The potentiometric titrations confirm the efficient encapsulation of the metal ions since only 1:1 complexes are observed, and, over a large pH range, ML is generally the only species present in solution.

Journal Article↗

PubMed2003

AM1* parameters for phosphorus, sulfur and chlorine.

An extension of the AM1 semiempirical molecular orbital technique, AM1*, is introduced. AM1* uses AM1 parameters and theory unchanged for the elements H, C, N, O and F. The elements P, S and Cl have been reparameterized using an additional set of d orbitals in the basis set and with two-center core-core parameters, rather than the Gaussian functions used to modify the core-core potential in AM1. Voityuk and Rösch's AM1(d) parameters have been adopted unchanged for AM1* with the exception that new core-core parameters are defined for Mo-P, Mo-S and Mo-Cl interactions. Thus, AM1* gives identical results to AM1 for compounds with only H, C, N, O, and F, AM1(d) for compounds containing Mo, H, C, N, O and F only, but differs for molybdenum compounds containing P, S or Cl. The performance and typical errors of AM1* are discussed.

Chlorine↗

PubMed2003

Local molecular properties and their use in predicting reactivity.

Expressions for the local electron affinity, electronegativity and hardness are derived in analogy to the local ionization energy introduced by Sjoberg, Murray and Politzer. The local polarizability is also defined based on an additive atomic orbital polarizability model that uses Rivail's variational technique. The characteristics of these local properties at molecular surfaces and their relevance to electrophilic aromatic substitution, to S(N)2 reactivity and to the nucleophilicity of enolate ions are discussed.

Bromine↗