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.

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.

Role of self-phase modulation in stimulated Raman scattering from more than one mode.

Stimulated Stokes spectra obtained with picosecond pulses in organic liquids often exhibit transient gain in more than one mode. A theory is developed here to describe the important effect of self-phase modulation on such multiple-component spectra. The nonlinear refractive index generated by a two-component Stokes field produces additional spectral components, which are separated by the frequency spacing between the two initial components. Calculations indicate that the new components are observable at considerably lower intensities than that necessary to produce noticeable phase modulation of the pulse envelope and may be an intrinsic part of the excitation process in molecules exhibiting Stokes gain in more than one mode. A comparison between the calculated spectra and experimentally obtained stimulated Raman spectra in methanol confirms the theoretical predictions, and the consequences of the theory with regard to the stimulated Raman spectra of large molecules are discussed.

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.

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.

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.

Generation of widely tunable nanosecond pulses in the vibrational infrared by stimulated Raman scattering from the cesium 6s-5d transition.

The first reported use of a pulsed rhodamine-dye laser to generate widely tunable nanosecond light pulses in the vibrational infrared by stimulated electronic Raman scattering is discussed. Narrow-band pulses of up to 120 microJ were generated from 3450 to 900 cm(-1) (2.9 to 11.1 microm), and broadband pulses up to 75 microJ were generated from 3390 to 1800 cm(-1) (2.9 to 5.5 microm) by scattering from the 6s-5d transition in cesium vapor. Cesium dimer effects on tuning-curve structure and efficiency are discussed.

Generation of tunable picosecond pulses in the vibrational infrared by stimulated electronic Raman scattering of rhodamine-dye-laser pulses from the 6s-5d cesium transition.

The first reported use of a rhodamine-dye laser to generate tunable high-power picosecond pulses in the vibrational infrared is described. By using stimulated electronic Raman scattering from the 6s-5d transition in a superheated cesium vapor, we have shifted I-psec pulses from an amplified rhodamine-dye laser (568-590nm) to 3040-2320 cm(-1) (3.3-4.3 microm). Somewhat longer pulses have been shifted to 1950 cm(-1) (5.1 microm). Peak infrared energies of 11 microJ, representing a quantum efficiency of 4.6%, were obtained at a 10-Hz repetition rate. Tuning to longer wavelengths with short pulses is limited by nonlinear processes but should be possible by further reductions of cesium dimer effects.

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.

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.