Joseph J. BelBruno

A prediction of chromium(III) accumulation in humans from chromium dietary supplements.

It has been proposed that 90% of Americans diets are deficient in the trace essential mineral chromium. Several chromium(III) dietary supplements are currently available to alleviate this deficiency. We show here that the same pharmacokinetic models that have been used to quantitate absorption of chromium(III) in humans predict that ingested chromium(III) will accumulate and be retained in human tissues for extended periods. Calculations were carried out with the popular supplement chromium picolinate as an example, but may be applied to any chromium(III) complex. Results from these calculations were compared to clinical data obtained from chromium(III) absorption/retention studies in humans. The models predict that chromium(III) can accumulate in human tissues to reach the levels at which DNA damage has been observed in animals and in vitro. The use of chromium supplements for extended periods or in excess dosages should be reevaluated in terms of these established models because the possible long‐term biological effects of chromium accumulation in humans are poorly understood.—Stearns, D. M., BelBruno, J. J., Wetterhahn, K. E. A prediction of chromium(III) accumulation in humans from chromium dietary supplements. FASEB J. 9, 1650‐1657 (1995)

ZnnSm+ cluster production by laser ablation

Abstract Laser ablation of ZnS or mixtures of elemental zinc and sulfur was used to produce clusters. Mass spectrometric detection was used to identify the products. Regardless of the composition of the ablation sample, mass spectra were dominated by mixed cluster ions. The mass peak corresponding to Zn 13 S 13 + was present in an abundance much greater than its neighbor ions, indicating that the geometry of this particular cluster confers a special stability. The mass spectra of the analogous ZnO clusters did not exhibit magic numbers. Structure calculations were employed to provide a preliminary estimate of the possible geometries of this cluster.

The structure of AlnNn (n=2–4) clusters: a DFT study

Abstract The geometry, harmonic vibrational frequencies and stability of the structural isomers of small aluminum nitride clusters have been investigated using density functional theory. The lowest energy structures are cyclic. The cyclic structures have Dnh symmetry. The caged structure for Al4N4 lies higher in energy than the planar cumulenic monocyclic ring. The Al–N bond dominates the structures for many isomers so that one preferred dissociation channel is loss of the AlN monomer. The properties of the aluminum nitride clusters are similar to those of the BN clusters even though the aluminum atoms have a significantly larger atomic radius.

The structure and energetics of carbon-nitrogen clusters

The structures and energies of clusters of carbon and nitrogen with up to 12 atoms have been investigated by density functional theory using the hybrid B3LYP functional and the cc-pVTZ basis set. This is the first systematic study of these clusters. Geometries are reported for the lowest energy states at this level of theory. Linear structures tend to be the global minima for clusters containing one or two nitrogen atoms, and patterns in the electronic structure of these clusters are reported. More complex branched structures lie close in energy to the linear conformations and, for clusters greater than six atoms and containing three or more nitrogen atoms, these branched structures are the minimum energy conformers. Comparisons are made with pure carbon and silicon-carbon clusters.

The structure of small gallium nitride clusters

The geometry, vibrational frequencies and stability of the structural isomers of small gallium nitride clusters (n = 2–4) have been investigated using density functional theory. The lowest energy structures are cyclic. The ground electronic state of the cyclic forms for n > 2 is the singlet state. All of the cyclic structures have Dnh symmetry. The caged structures for Ga4N4 lie higher in energy than the planar cumulenic monocyclic ring. The Ga-N bond dominates the structures for many isomers, so that one dissociation channel is loss of a GaN monomer. However, unlike the corresponding boron and aluminum clusters, dissociation into larger fragments is energetically favored. The structural properties of the gallium nitride clusters are similar to those of the analogous AIN (and BN) clusters.

The structure of C60 and endohedral C60 on the Si{100} surface

The possible structures of C60 on the Si{1 0 0} surface in the four dimer position over the dimer trench have been investigated using ab initio total energy minimisations. Four possible structures have been found. The fullerenes bond to the silicon surface by breaking carbon–carbon double bonds. One electron from the broken bond is contributed to the carbon–silicon bond. The second electron is involved in forming a new π-bond within the fullerene cage. The carbon–silicon bond is primarily covalent with some charge transfer. Some discussion of endohedral fullerenes is also given.

Detection of AuF by emission spectroscopy in a hollow cathode discharge

Abstract The emission spectrum of AuF, produced in a hollow cathode discharge, is recorded over the wavelength range from 350 to 650 nm. By comparison with density functional theory calculations, including relativistic corrections, and using the known spectrum and DFT calculations for the low-lying electronic states of CuF, the three AuF bands are assigned to vibrational transitions involving the lowest energy 1 Σ + and 1 Π excited states. Spectral assignments differ from those previously reported.

A selective molecularly imprinted polymer‐carbon nanotube sensor for cotinine sensing

Conductive composite films comprised of single‐walled carbon nanotubes coated with molecularly imprinted poly‐4‐vinylphenol are produced and characterized using ultraviolet and infrared spectroscopies, confirming the successful molecular imprinting of the film with cotinine. The electrical resistance of the imprinted film changes significantly upon binding cotinine, by more than 30 kΩ, while the unimprinted film in comparison elicits little response. Additionally, once the cotinine template desorbs from the film, the resistance of the imprinted film returns to a value close to the pre‐adsorption baseline. Scanning electron microscopy is used to study the morphology of the film compared with the unimprinted control, and gas chromatography quantitatively confirms that the imprinted film selectively detects cotinine while discriminating against the structurally similar alkaloid, nicotine. Copyright

Structures and energies of CnS+ (1 ≤ n ≤ 16) and CnS− (9 ≤ n ≤ 16) clusters

Abstract The structures and energies of ionic clusters of carbon and sulfur with up to 17 atoms have been investigated by density functional theory using the hybrid B3LYP functional and double-ζ plus polarization basis sets. Geometries are reported for the ground states of all isomeric clusters containing a single sulfur atom. Generally, linear structures, with a terminal sulfur atom, are the energetically favored clusters.

Investigation of Semiconductors by Nanoindentation

Si and InSb were subject to depth sensing multicycling nanoindentation. T he load-depth curves exhibited hysteresis loops which are explained in terms of pres sur induced phase transformations. In order to study the impact of crystal distortions on phase trans formation, the specimens were subject to boron implantation (ion energy 180keV) of different implanta tion doses (10 14 to 10 ions/cm) and indented without annealing. In InSb, the hysteresis loops disappea red after implantation of 10 ions/cm, and for Si with its stronger bonds a dose of 3*10 /cm is required for the same effect. In GaAs the contact pressure is not high enough to cause phase transitions. Characteristic pile-up patterns for the crystal symmetry are observe d inst ad.