Variation of U-microdistribution in fossil Hipparion teeth as a complicating factor in dating studies

Five Upper Miocene fossil Hipparion molars were studied for U-distribution by Fission Track. U uptake has reached the whole mass of the teeth and no saturation fronts seem to occur in the interior layers. Mean U-concentration in dentine, cement and enamel was 157, 139 and 78 ppm, respectively. U_enamel/U_dentine 0.5 is considerably higher than 0.1 reported in the past for Upper-Quaternary mammoth teeth. These features are disadvantageous for ESR-dating in Hipparion enamel, although a long-lived signal (g=2.0018) is apparent. Leaching phenomena occur in the outer regions of these teeth. Inner enamel folding seems to have hindered a more uniform U-distribution in the teeth.     

THE QUANTUM EFFICIENCY FOR THE INTERPHOTOCONVERSION OF THE BLUE and PINK FORMS OF PURPLE MEMBRANE

When the cations bound to purple membrane are removed it turns blue, and when this blue membrane is irradiated its color changes to pink. Irradiation of pink membrane leads to the reformation of blue membrane. We have determined that the quantum efficiency for the formation of pink membrane from deionized blue membrane is 1.6 ± 0.6 ± 10 ⁴ at 0^oC, pH 5.0. We also found that the quantum efficiency for the back photoconversion, i.e. the formation of blue membrane from pink membrane, is 8.8 ± 1.6 ± 10^-3 at 0^oC, 55 times greater than that of the forward photoconversion reaction. The extinction coefficients of the pink membrane and blue membrane were determined to be 44 500 ± 670 cm^-1 M^-1 at 491 nm and 54 760 ± 830 cm^-1 M ^-1 at 603 nm, respectively, assuming light-adapted purple membrane is 63 000 cm^-1 M ^-1 at 568 nm. The quantum efficiency for forming pink membrane from blue membrane is much lower than that for forming the photointermediate of the blue membrane's photocycle. Their relationship is similar to that of light-adaptation and photocycle of the dark-adapted purple membrane.     

Oxidation and Reduction Processes During NO x Removal with Corona-Induced Nonthermal Plasma

In this paper, the NO-to-NO ₂ conversion in various gaseous mixtures is experimentally investigated. Streamer coronas are produced with a dc-superimposed high-frequency ac power supply (10–60 kHz). According to NO _x removal experiments in N ₂ +NO _x and N ₂ +O ₂ +NO _x gaseous mixtures, it is supposed that the reverse reaction NO ₂ +ONO+O ₂ may not only limit NO ₂ production in N ₂ +NO _x mixtures, but also increase the energy cost for NO removal. Oxygen could significantly suppress reduction reactions and enhance oxidation processes. The reduction reactions, such as N+NON ₂ +O, induce negligible NO removal provided the O ₂ concentration is larger than 3.6%. With adding H ₂ O into the reactor, the produced NO ₂ per unit removed NO can be significantly reduced due to NO ₂ oxidation. NH ₃ injection could also significantly decrease the produced NO ₂ via NH and NH ₂ - related reduction reactions. Almost 100% of NO ₂ can be removed in gaseous mixtures of N ₂ +O ₂ +H ₂ O+NO ₂ with negligible NO production.     

Topochemical investigations of peptide systems

The basic principles of the topochemical approach to the investigation of the structure-function relation in peptide systems are formulated. This approach makes use of the new possibility of transforming natural peptides, consisting in the modification of the molecule as a whole and utilization of the resultant analogs to elucidate the boundaries of the stereoelectronic complementarity of the biologically active peptide to the corresponding receptor. In particular, on the example of depsipeptide antibiotics and their topochemical analogs the fruitfulness of using such compounds as tools in elucidating the physicochemical basis of functioning of biological membranes is shown. The topochemical principle has also been applied in preparing specific competitive inhibitors of proteolytic enzymes, whose study may shed light on the nature of the forces binding the substrate to the contact site of the corresponding enzyme.