Polarizability as a landmark property for fullerene chemistry and materials science

The review summarizes data on dipole polarizability of fullerenes and their derivatives, covering the most widespread classes of fullerene-containing molecules (fullerenes, fullerene exohedral derivatives, fullerene dimers, endofullerenes, fullerene ions, and derivatives with ionic bonds).

A comparative study of O2, CO and CN binding to heme IX protein models

Parametrization of a molecular-mechanics program to include terms specific for five- and six-coordinate transition metal complexes results in computer-simulated structures of heme complexes. The principal new feature peculiar to five and six coordination is a term that measures the effect of electron-pair repulsion modified by the ligand electronegativity and takes into account the different structural possibilities. The model system takes into account the structural differences of the fixing centre in the haemoglobin subunits. The customary proximal histidine is added. The prosthetic group heme IX is wholly considered in our model. The calculations show clearly that certain conformations are much more favourable that others for fixing O2. From the O2 binding in haemoglobin, myoglobin and simple Fe porphyrin models it is concluded that the bent O2 ligand is best viewed as bound superoxide O2-. Axial ligands are practically free-rotating. A small modification of the model in both crystal and protein matrix affects the orientation of the ligands in experimental systems.

A theoretical model of the photoabsorption spectra of carbon buckyonions

A theoretical model has been developed to predict the photoabsorption spectra of spherical carbon buckyonions in the region dominated by the pi-plasmon feature. This model makes use of the microscopic electronic structure of the system, which is provided by an effective Huckel one-electron model. The important screening effects are treated within the random phase approximation, whose form is an extension to the dynamic case of the one derived in a previous work for the static polarizabilities of these species. A systematic analysis as a function of the buckyonion size is performed. We compare the spectra obtained in this way with those derived from a different representation of the electron motion, namely a two-dimensional spherical electron gas, and from a classical dielectric model.

Valence Topological Charge-Transfer Indices for Dipole Moments

New valence topological charge-transfer indices are applied to the calculation of dipole moments. The algebraic and vector semisum charge-transfer indices are defined. The combination of the charge-transfer indices allows the estimation of the dipole moments. The model is generalized for molecules with heteroatoms. The ability of the indices for the description of the molecular charge distribution is established by comparing them with the dipole moments of a homologous series of phenyl alcohols. Linear and non-linear correlation models are obtained. The new charge-transfer indices improve the multivariable non-linear regression equations for the dipole moment. When comparing with previous results, the variance decreases 92%. No superposition of the corresponding G_k–J_k and – pairs is observed. This diminishes the risk of co-linearity. Inclusion of the oxygen atom in the π-electron system is beneficial for the description of the dipole moment, owing to either the role of the additional p orbitals provided by the heteroatom or the role of steric factors in the π-electron conjugation. Linear and non-linear correlations between the fractal dimension and various descriptors point not only to a homogeneous molecular structure but also to the ability to predict and tailor drug properties.