Minute but appreciable amounts of D-amino acids were detected in normal human plasma. The content was significantly higher in an elderly population (age 76 +/- 6 years, mean +/- SD, n = 41) than in a younger group (age 42 +/- 4 years, n = 26), i.e. 6.9 +/- 4.8 nmol/ml (mean +/- SD, range 0-18.8 nmol/ml) and 2.5 +/- 1.8 nmol/ml (range 0-6.3 nmol/ml) for the elderly and the younger groups, respectively. Elevation of plasma D-amino acid level was observed in a group of patients with renal disease (3.6-52.6 nmol/ml), in proportion to the serum level of creatinine (n = 50, r = 0.726, P less than 0.001), beta 2-microglobulin (n = 34, r = 0.551, P less than 0.005), and to glomerular filtration rate (n = 39, r = 0.556, P less than 0.001).

Abstract:We report the activation energy, ΔE a , for the quantum yield in thermally assisted photoelectron emission (TAPE) under 210-nm-wavelength light irradiation, and the associated X-ray photoelectron spectroscopy (XPS) results. Samples were cleaned only in acetone and scratched in air, water, methanol, ethanol, acetone, benzene, and cyclohexane. Glow curves, describing the temperature dependence of photoelectron emission (PE) quantum yield (emitted electrons/photon), Y, were obtained. A simple method of determining ΔE a using Y, called Y GC , at seven temperatures up to 353 °C , for the same Y glow curve, was proposed. The ΔE a obtained using this method was almost the same as that obtained from Y for seven stationary temperatures (Y ST ). For scratched samples, the TAPE was measured over two cycles of temperature increase and subsequent decrease (Up1, Down1 and Up2, Down2 scans) in the 25-339 °C range, and ΔE a was obtained from Y GC . The Arrhenius plot was approximated by a straight line, although a convex swelling peak appeared in the Up1 scan. ΔE aUp1 was in the 0.212-0.035 eV range, depending on the environment in which scratching was performed; ΔE aUp1 for water was much higher than that for acetone. This was explained in terms of the mode of the acid-base interaction between the liquid molecules and the hydroxyl group of Fe-OH. The values of ΔE aDown1 , ΔE aUp2 , and ΔE aDown2 were in the 0.038-0.012 eV range. The total count of electrons emitted during the Up1 and Up2 scans was found to decrease with increasing ΔE aUp1 and ΔE aUp2 , respectively. ΔE aUp2 was found to increase with increasing presence of the FeO component in the analyzed Fe oxides. The convex swelling peak was attributed to the removal of carbon materials from the scratched surface and the effect of the increased electron density of the surface hydroxyl group of FeOH under the light irradiation.

The influence of temperature and surface overlayer on the photoelectron emission from scratched real iron surfaces was investigated using thermally assisted photoelectron emission (TAPE) and X‐ray photoelectron spectroscopy (XPS) measurements. The scratching was conducted with a diamond cutter in seven atmospheres. The intensity of TAPE as a function of temperature, called glow curve, was measured in the range 25–339 °C using a Geiger counter under ultraviolet irradiation at 210 nm. The temperature was scanned in two cycles (Up1 and Down1, and Up2 and Down2). The XPS measurements were carried out at 25 °C and after TAPE measurements at 200 and 339 °C. The photoelectron emission intensity at 40 °C in the Up1 scan increased in the order of air < water ≈ methanol ≈ cyclohexane < ethanol < benzene < acetone, and then each glow curve exhibited a gradual increase with temperature through a broad peak. It was found that the dependence of the emission intensity in the Up1 scan on the oxygen component ratio, ZO = O2−/(OH− + O2−) and the percentage of the Fe metal and FeOOH components of the Fe3p spectra for the atmospheres greatly differed. Additionally, the glow curve in the Up1 scan was completely different from that in the other scans. It was proposed that the photoelectron emission in the Up1 scan originates from not only the base metal but also the surface overlayer having trapped electrons and is strongly influenced by the acid–base interaction of the surface hydroxyl groups with the liquids molecules. Copyright © 2016 John Wiley & Sons, Ltd.

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