Survival and recovery of yeast cells after simultaneous treatment of UV light radiation and heat

Cell survival, synergistic interaction, liquid-holding recovery (LHR) kinetics and inactivation forms after the simultaneous treatment with UV light (254 nm) and various high temperatures were studied in diploid yeast cells Saccharomyces cerevisiae. The synergistic interaction was observed within a certain temperature range in which there was a temperature that maximizes the synergistic effect. The LHR study revealed that both the extent and the rate of recovery greatly decreased with the increase in exposure temperature. A quantitative approach describing the LHR process as a decrease in the effective radiation dose was used to estimate the probability of recovery per unit time and the irreversible component of damage. Using the experimental data obtained and the mathematical model described, it was shown that the irreversible component, i.e. the fraction of cells incapable of recovery, increased with the exposure temperature, whereas the recovery constant, i.e. the probability of recovery per unit time, was independent of the exposure temperature. The increase in the irreversible component was accompanied by an increase in cell death without postirradiation division. It is concluded based on this that the synergistic interaction of UV light radiation and hyperthermia in yeast cells is not related to the impairment of the recovery process itself and that it may be attributed to an increased yield of the irreversible damage.     

Further chemical studies on the Antarctic nudibranch Austrodoris kerguelenensis: new terpenoid acylglycerols and revision of the previous stereochemistry

The diterpenoid acylglycerol fraction from an extract of the mantle of a new collection of the Antarctic dorid gastropod mollusc Austrodoris kerguelenensis has been chemically analysed. Two novel 2-monoacylglycerols 9 and 12, along with known 1,2-diacyl glyceryl esters 5 and 6, now reassigned as 7 and 8, have been isolated. The linkage of a diterpenoid moiety at C-2 of glycerol characterizes all the compounds. Because the R absolute stereochemistry at C-2 of glycerol has been established for the corresponding 1,3-glyceryl esters 1 and 2, derived from 7 and 8 by acyl-migration of the terpenoid moiety from C-2 to C-3, our finding implies that 1,2-derivatives from Antarctic nudibranchs have the same S stereochemistry as all 1,2-sn-diacylglycerols from the other dorids.     

Modulation of the reduction potentials of fullerene derivatives

The cyclic voltammetric (CV) study of a series of novel bisfulleropyrrolidines (3) and bisfulleropyrrolidinium ions (4) is reported. The eight possible stereoisomers of each series were systematically investigated under strictly aprotic conditions that allowed the observation of up to four and five subsequent reversible reductions in 3 and 4, respectively. Because of the stabilizing effect of positive charges, a significant enhancement of the electronegative properties was observed in 4. In fact, 4-trans-2 and 4-trans-1 result among the strongest reversible electron-accepting C(60) oligoadducts. Furthermore, the study evidenced that, in both 3 and 4, the CV pattern, and in particular the potential separation between the second and third reductions, changes significantly with the addition pattern. A sequential pi-electron model that simulates the effect of subsequent reductions of C(60) bis-adducts gives a good correlation (r > 0.96) with the cyclic voltammetry data when the molecules are divided in two sets dependent on the location of the addends in the same or in opposite hemispheres.     

Asymptotics of the discrete spectrum for a radial Schrödinger operator with nearly Coulomb potential

The radial Schrödinger equation with Coulomb potential perturbed on a compact set is considered. An asymptotic formula for the discrete spectrum is obtained. It follows from this formula that the quantum defect tends to a constant when the principal quantum number tends to infinity. An explicit expression of this constant through the perturbation is obtained.     

Influence of potassium on the properties of steam reforming catalysts

The influence of K₂O on the amounts of chemisorbed hydrogen on a Ni catalyst, the catalyst activity and its resistance to coking were measured. Introducing potassium into the commercial catalyst (not into the support) appeared to enhance its resistance to coking. The best catalytic characteristics was noticed for a system containing ~0.5 wt. % K₂O. The investigations show a good agreement between the resistance to coking obtained by the temperature-programmed reaction (TPReaction) method and by the traditional thermogravimetric method. This revised version was published online in August 2006 with corrections to the Cover Date.     

The chemo- enzymatic synthesis of labeled <Emphasis Type="SmallCaps">l</Emphasis>-amino acids and some of their derivatives

This review compiles the combined chemical and enzymatic synthesis of aromatic l-amino acids (l-phenylalanine, l-tyrosine, l-DOPA, l-tryptophan, and their derivatives and precursors) specifically labeled with carbon and hydrogen isotopes, which were elaborated in our research group by the past 20 years. These compounds could be then employed to characterize the mechanisms of enzymatic reactions via kinetic and solvent isotope effects methods.     

Signal enhancement in desorption nanoelectrospray ionization by custom‐made inlet with pressure regulation

The efficiency of desorption/ionization becomes more critical as the sampled surface area decreases. Desorption electrospray and desorption nanoelectrospray belong to ambient ionizations and enable direct surface analysis including mass spectrometric imaging. Lateral resolution in tens of micrometers was demonstrated for desorption nanoelectrospray previously, but sensitivity of the surface scan can be an issue. For desorption electrospray, the drag force in the source is driven by the flow of used gases and vacuum suction. Ion signal intensity can be improved by controlling the nebulizing gas flow rate or auxiliary pumping of a closed compartment in front of the mass spectrometer inlet. Because nanoelectrospray generates charged droplets without the assistance of a nebulizing gas, only vacuum suction drives the gas flow. In this study, the effect of pressure drop between the atmospheric and evacuated region of a mass spectrometer on the ion signal intensity was investigated for desorption nanoelectrospray. A modification of the commercial inlet was designed. An auxiliary pump was directly connected to an inner compartment of the modified mass spectrometer inlet through a needle valve that enabled the regulation of the reduced pressure. Adjustment of the pressure drop significantly increased signal intensity (more than one order of magnitude in some cases). To a lesser extent, the temperature of a heated capillary (an integral part of the inlet) also influenced the signal intensity. The applicability of desorption nanoelectrospray equipped with pressure regulation was demonstrated by the analysis of synthetic cathinones or a pill of paracetamol. Because pressure in the inlet depends on the diameters of orifices and the power of vacuum systems of mass spectrometers, the effect of the pressure regulation can be different for different instruments. Nevertheless, the presented results confirmed the importance of pressure drop‐driven transport for desorption nanoelectrospray efficiency and can encourage its new applications.     

Crucial Roles of Two Hydrated Mg2+ Ions in Reaction Catalysis of the Pistol Ribozyme

Pistol ribozymes constitute a new class of small self‐cleaving RNAs. Crystal structures have been solved, providing three‐dimensional snapshots along the reaction coordinate of pistol phosphodiester cleavage, corresponding to the pre‐catalytic state, a vanadate mimic of the transition state, and the product. The results led to the proposed underlying chemical mechanism. Importantly, a hydrated Mg²⁺ ion remains innersphere‐coordinated to N7 of G33 in all three states, and is consistent with its likely role as acid in general acid base catalysis (δ and β catalysis). Strikingly, the new structures shed light on a second hydrated Mg²⁺ ion that approaches the scissile phosphate from its binding site in the pre‐cleavage state to reach out for water‐mediated hydrogen bonding in the cyclophosphate product. The major role of the second Mg²⁺ ion appears to be the stabilization of product conformation. This study delivers a mechanistic understanding of ribozyme‐catalyzed backbone cleavage.