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Biomedical subjects

C B Harris

Publications and source records attributed to C B Harris.

9 recordsLinked to original sources
PubMed2006

Pyrroloquinoline quinone nutritional status alters lysine metabolism and modulates mitochondrial DNA content in the mouse and rat.

Pyrroloquinoline quinone (PQQ) added to purified diets devoid of PQQ improves indices of perinatal development in rats and mice. Herein, PQQ nutritional status and lysine metabolism are described, prompted by a report that PQQ functions as a vitamin-like enzymatic cofactor important in lysine metabolism (Nature 422 [2003] 832). Alternatively, we propose that PQQ influences lysine metabolism, but by mechanisms that more likely involve changes in mitochondrial content. PQQ deprivation in both rats and mice resulted in a decrease in mitochondrial content. In rats, alpha-aminoadipic acid (alphaAA), which is derived from alpha-aminoadipic semialdehyde (alphaAAS) and made from lysine in mitochondria, and the plasma levels of amino acids known to be oxidized in mitochondria (e.g., Thr, Ser, and Gly) were correlated with changes in the liver mitochondrial content of PQQ-deprived rats, but not PQQ-supplemented rats. In contrast, the levels of NAD dependent alpha-aminoadipate-delta-semialdehyde dehydrogenase (AASDH), a cytosolic enzyme important to alphaAA production from alphaAAS, was not influenced by PQQ dietary status. Moreover, the levels of U26 mRNA were not significantly changed even when diets differed markedly in PQQ and dietary lysine content. U26 mRNA levels were measured, because of U26's proposed, albeit questionable role as a PQQ-dependent enzyme involved in alphaAA formation.

2-Aminoadipic Acid↗
PubMed2002

Electron solvation in two dimensions.

Ultrafast two-photon photoemission has been used to study electron solvation at two-dimensional metal/polar-adsorbate interfaces. The molecular motion that causes the excess electron solvation is manifested as a dynamic shift in the electronic energy. Although the initially excited electron is delocalized in the plane of the interface, interactions with the adsorbate can lead to its localization. A method for determining the spatial extent of the localized electron in the plane of the interface has been developed. This spatial extent was measured to be on the order of a single adsorbate molecule.

Journal Article↗
PubMed2001

Femtosecond infrared study of the dynamics of solvation and solvent caging.

The ultrafast reaction dynamics following 295-nm photodissociation of Re2CO10 were studied experimentally with 300-fs time resolution in the reactive, strongly coordinating CCl4 solution and in the inert, weakly coordinating hexane solution. Density-functional theoretical (DFT) and ab initio calculations were used to further characterize the transient intermediates seen in the experiments. It was found that the quantum yield of the Re-Re bond dissociation is governed by geminate recombination on two time scales in CCl4, approximately 50 and approximately 500 ps. The recombination dynamics are discussed in terms of solvent caging in which the geminate Re(CO)5 pair has a low probability to escape the first solvent shell in the first few picoseconds after femtosecond photolysis. The other photofragmentation channel resulted in the equatorially solvated dirhenium nonacarbonyl eq-Re2(CO)9(solvent). Theoretical calculations indicated that a structural reorganization energy cost on the order of 6-7 kcal/mol might be required for the unsolvated nonacarbonyl to coordinate to a solvent molecule. These results suggest that for Re(CO)5 the solvent can be treated as a viscous continuum, whereas for the Re2(CO)9 the solvent is best described in molecular terms.

Journal Article↗
PubMed2001

Triplet organometallic reactivity under ambient conditions: an ultrafast UV pump/IR probe study.

The reactivity of triplet 16-electron organometallic species has been studied in room-temperature solution using femtosecond UV pump IR probe spectroscopy. Specifically, the Si-H bond-activation reaction of photogenerated triplet Fe(CO)(4) and triplet CpCo(CO) with triethylsilane has been characterized and compared to the known singlet species CpRh(CO). The intermediates observed were studied using density functional theory (DFT) as well as ab initio quantum chemical calculations. The triplet organometallics have a greater overall reactivity than singlet species due to a change in the Si-H activation mechanism, which is due to the fact that triplet intermediates coordinate weakly at best with the ethyl groups of triethylsilane. Consequently, the triplet species do not become trapped in alkyl-solvated intermediate states. The experimental results are compared to the theoretical calculations, which qualitatively reproduce the trends in the data.

Journal Article↗
PubMed2000

Femtosecond studies of electron dynamics at interfaces.

A delocalized electron at a metal-dielectric interface interacts with the adlayer and spatially localizes or self-traps on the femtosecond time scale into what is termed a small polaron. The dynamics can be studied by two-photon photoemission. Theoretical and experimental analyses reveal the interaction energy and the lattice vibrational mode that mediates electron localization. These results contribute to a fundamental understanding of electron behavior in weakly bonded solids and can lead to a better understanding of carrier dynamics in many different systems, including organic light-emitting diodes.

Absorptiometry, Photon↗
PubMed2000

Health advice and the traveller.

We studied advice given by travel agents, the experiences of recent travellers, and the hidden costs for travellers to Kenya. There was a wide range of advice given by United Kingdom travel agents, much of it at variance with advice given by other travel agents and much of it incorrect. Nevertheless travel agents have a responsibility to give advice because they are often the only point of contact for health advice.

Bacterial Infections↗
PubMed1997

Femtosecond dynamics of electrons on surfaces and at interfaces.

Two-photon photoemission is a promising new technique that has been developed for the study of electron dynamics at interfaces. A femtosecond laser is used to both create an excited electronic distribution at the surface and eject the distribution for subsequent energy analysis. Time- and momentum-resolved two-photon photoemission spectra as a function of layer thickness fully determine the conduction band dynamics at the interface. Earlier clean surface studies showed how excited electron lifetimes are affected by the crystal band structure and vacuum image potential. Recent studies of various insulator/metal interfaces show that the dynamics of excess electrons are largely determined by the electron affinity of the adsorbate. In general, electron dynamics at the interface are influenced by the substrate and adlayer band structures, dielectric screening, and polaron formation in the two-dimensional overlayer lattice.

Journal Article↗