Molecular beam surface ionization detection: II. Field reversal and surface ionization study of Na on Re with adsorbed oxygen

The desorption and surface ionization of Na on a polycrystalline Re surface with various amounts of adsorbed oxygen have been studied by field reversal, surface ionization and thermoelectronic emission methods. In this work the unique properties of the field reversal method are taken advantage of, i.e. that both neutral and ionic desorption rate constants can be determined simultaneously. Absolute ionization coefficients have been measured by field reversal and have been compared with values found by the “oxygen coverage” method and by static surface ionization. The application to beam flux density determinations is discussed. The simultaneous variation of the neutral and ionic desorption rate constants during oxygen adsorption and the temperature dependence of them have been studied. The Re surface in 2 × 10^?8 Torr of oxygen and at 1300–1500 K is shown to be very stable and to behave differently than in studies at higher temperatures. The very rapid change in both desorption rate constants at an effective work function Φ^e = 5.35 V is here correlated with the results of LEED experiments (Gorodetskii and Knysh) and is proposed to indicate a change from a stable Re oxide surface at low Φ^e (and oxygen coverage) to a different surface structure at higher Φ^e. Desorption energies have been determined at various values of Φ^e. The neutral desorption energy at low oxygen pressure is 2.70 ± 0.06 eV, which agress well with earlier, here corrected modulated beam results. The energy (Schottky) cycle for surface ionization is shown to be closed at low Φ^e, which has been difficult to show with other methods in any other case.     

The role of nucleobase carboradical and carbanion on DNA lesions: a theoretical study

DNA base release induced by H and OH radical addition to thymine and their corresponding electron adducts is studied at the DFT B3LYP/6-31+G(d,p) level in gas phase and in solution. H atom transfer after radical formation from C2' on the sugar to the C6 site on the base is shown to be prohibited for the radical species. Their corresponding electron adducts, albeit minor events in cellular systems, show excellent capabilities to proton transfer from C2' on the sugar to the C6 site on the base. The barriers for subsequent N-glycosidic bond dissociation range from 0.1 to 1.6 kcal mol(-1) at the B3LYP level and around 5 kcal mol(-1) using the BB1K functional, implying that these reactions can serve as a source to abasic sites. Analysis of bond dissociation energies show that all the reactions are exothermic, which is consistent with the changes in N-glycosidic bond lengths during the proton-transfer reactions. Bulk solvation plays a reverse influence on proton transfer and the bond rupture reactions. Molecular orbitals, NPA charges, and electron affinities are calculated to shed further light on the properties leading up to the intramolecular reactions.     

Theoretical study of the antioxidant properties of pyridoxine

Molecules acting as antioxidants capable of scavenging reactive oxygen species (ROS) are of utmost importance in the living cell. The antioxidative properties of pyridoxine (vitamin B6) have recently been discovered. In this study, we have analyzed the reactivity of pyridoxine toward the ROS (.-)OH, (.-)OOH, and (.-)O(2)- at the density functional theory level (functionals B3LYP and MPW1B95). Two reaction types have been studied as follows: addition to the aromatic ring atoms and hydrogen/proton abstraction. Our results show that (.-)OH is the most reactive species, while (.-)OOH displays low reactivity and (.-)O2(-) does not react at all with pyridoxine. The most exergonic reactions are those where (.-)H is removed from the CH(2)OH groups or the ring-bound OH group and range from -33 to -39 kcal/mol. The most exergonic addition reactions occur by attacking the carbon atoms bonded to nitrogen but with an energy gain of only 6 kcal/mol.     

Thermometric analysis of blood metabolites in ICU patients

Journal of Thermal Analysis and Calorimetry - Real-time monitoring of patient’s blood metabolites, such as glucose and lactate, could potentially improve surgery and recovery outcomes for...     

Correction to: Pyrroloquinoline quinone glucose dehydrogenase adopted in thermometric analysis for enhancement of glucose determination

Journal of Thermal Analysis and Calorimetry - The article Pyrroloquinoline quinone glucose dehydrogenase adopted in thermometric analysis for enhancement of glucose determination, written by...