Biomedical subjects

Malcolm I Heggie

Publications and source records attributed to Malcolm I Heggie.

4 recordsLinked to original sources

PubMed2006

Pattern formation on carbon nanotube surfaces.

Calculations of fluorine binding and migration on carbon nanotube surfaces show that fluorine forms varying surface superlattices at increasing temperatures. The ordering transition is controlled by the surface migration barrier for fluorine atoms to pass through next neighbor sites on the nanotube, explaining the transition from semi-ionic low coverage to covalent high coverage fluorination observed experimentally for gas phase fluorination between 200 and 250 degrees C. The effect of solvents on fluorine binding and surface diffusion is explored.

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PubMed2005

Analysis of polyaddition levels in i-Sc3NC80.

Using the density functional method, the stabilities of highly hydrogenated and fluorinated [80]fullerenes, both empty and containing the Sc3N molecule, have been calculated. Addition of 44 atoms to i-Sc3NC80 is predicted to be most favorable due to the formation of six octahedrally located benzenoid rings, while addition of up to 52 atoms (consistent with preliminary fluorination data) gives a structure stabilized by the presence of four benzenoid rings. The most stable isomers at this addition level have been determined and the relative stabilities of a number of C80H52, C80F52, and i-Sc3NC80H52 species calculated. The hydrogenation of the i-Sc3NC80 has been computed to be more difficult than the corresponding partner, C80. From the geometrical point of view, the Sc3N molecule is planar in the parent [80]fullerene but is calculated to be pyramidal in some of the hydrogenated/fluorinated derivatives. Moreover, in these it has fixed locations due to orbital interactions arising from deformation of the cage and the presence of localized double bonds.

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PubMed2004

Open-cage fullerene derivatives with 15-membered-ring orifices.

The addition reaction of the N-MEM-ketolactam derivative of [60]fullerene with phenyl, p-Br-phenyl, and p-MeO-phenyl hydrazines proceeds regioselectively, affording three open-cage fullerene derivatives bearing a 15-membered-ring orifice on the fullerene cage. Both experimental data and theoretical calculations were utilized for the structure determination of the new [60]fullerene adducts.

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PubMed2003

Wigner defects bridge the graphite gap.

We present findings on the structure, energies and behaviour of defects in irradiated graphitic carbon materials. Defect production due to high-energy nuclear radiations experienced in graphite moderators is generally associated with undesirable changes in internal energy, microstructure and physical properties--the so-called Wigner effect. On the flip side, the controlled introduction and ability to handle such defects in the electron beam is considered a desirable way to engineer the properties of carbon nanostructures. In both cases, the atomic-level details of structure and interaction are only just beginning to be understood. Here, using a model system of crystalline graphite, we show from first-principles calculations, new details in the behaviour of vacancy and interstitial defects. We identify a prominent barrier-state to energy release, reveal a surprising ability of vacancy defects to bridge the widely spaced atomic layers, and discuss physical property and microstructure changes during irradiation, including interactions with dislocations.

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