Measurement of the first ionization potential of astatine by laser ionization spectroscopy.

The radioactive element astatine exists only in trace amounts in nature. Its properties can therefore only be explored by study of the minute quantities of artificially produced isotopes or by performing theoretical calculations. One of the most important properties influencing the chemical behaviour is the energy required to remove one electron from the valence shell, referred to as the ionization potential. Here we use laser spectroscopy to probe the optical spectrum of astatine near the ionization threshold. The observed series of Rydberg states enabled the first determination of the ionization potential of the astatine atom, 9.31751(8) eV. New ab initio calculations are performed to support the experimental result. The measured value serves as a benchmark for quantum chemistry calculations of the properties of astatine as well as for the theoretical prediction of the ionization potential of superheavy element 117, the heaviest homologue of astatine.

Variations of lacrimal fluid peroxidase activity in female and male rats.

Previous research from this laboratory showed that human lacrimal fluid peroxidase has cyclic variations during the menstrual cycle, correlated with plasma levels of 17beta-oestradiol. In the present investigation, variations of enzyme activity and total protein content during the oestrous cycle of young adult female rats are analysed. Effects from circadian rhythm and a gender-related influence are also examined. In female rats, as in women, lacrimal fluid peroxidase activity shows cyclic variations; in fact, it significantly (p < 0.05) changes during the different phases of the oestrous cycle. In contrast, in males such variations do not occur. Thus, we suggest that gender seems to exert a significant influence on the secretion of this specific tear protein, probably by a direct effect of oestrogens.

Effect of oral contraceptives on lacrimal fluid peroxidase activity in women.

Lacrimal fluid peroxidase has been supposed to be involved in the protection against oxidative damage to the ocular surface. Our recent findings showed the existence of significant cyclic variations in lacrimal fluid peroxidase activity that were positively correlated with those of 17beta-estradiol plasma levels throughout the menstrual cycle of fertile women. In the present study lacrimal fluid peroxidase activity of 8 healthy normocyclic women using low-dose oral contraceptives during the monthly cycle was determined. Data showed that low-dose oral contraceptives caused a decrease in lacrimal fluid peroxidase activity and a lack of its cyclic pattern with respect to the enzyme activity of 8 untreated age-matched women. Moreover, this result suggests that lacrimal fluid peroxidase activity could be regulated by estrogen.