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Under the illumination of ethanol solutions of chlorophyll "alpha" and "beta" in the presence of duroquinone positive photopotential (PP) appears, the sign of which is not changed with an increase of pH. However, if duroquinone is used, which had been illuminated with white light in the absence of air, in ethanol, which results in an increase of concentration of its reduced forms, at neutral weakly alkaline pH the PP sign gets negative. This fact supports the assumption that the change of PP sign at the change of pH when parabenzoquinone is used as an oxidizer results from the change of the direction of electron transfer during photoreaction. During photoreaction of pheophytin incapable of photooxidation with duroquinone and disposed to photoreduction, PP at all pH is negative. 相似文献
34.
The values of absolute quantum yield phi of the formation of free ion-radicals during the illumination of alkohol solutions of chlorophyll alpha (Chl) and rho-benzoquinone (Q) at room temperature were obtained by the method of impulse photoconductance. With an increase of the dielectric constant epsilon of the solvent from approximately 6 to approximately 25 phi increases by two orders ( approximately 10(-3)--approximately 10(-1). That obtained relationship phi (epsilon) is explained by epsilon effect on the efficiency of dissociation of "solvent-shared" ion-radical pair Chls+. Os-. The comparison of experimental data and theoretically expected ones allowed the estimation of some parameters to be obtained which characterize the ion-radical pair: interionic distance (10 A), the dissociation velocity constant ( approximately 10(5)--10(8) s-1), the velocity constant of reverse electron transfer (10(8) s-1), the life time approximately 10(-8) s). 相似文献
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The effect of the dielectric constant epsilon of the solvent on the yield delta n of ion-radicals during photooxidation of chlorophy-l a with n-benzoquinone was studied by the method of impulse photoconductivity. It was shown that in the studied range of dielectric constant valve (epsilon congruent to 5-25) delta n monotonously increased with an increase of epsilon the relationship delta n (epsilon) being of clearly pronounced S-like character with a bend in the region of epsilon congruent to 10. A half-quantitative explanation of the data obtained is presented. 相似文献
38.
Iu V Chicherin V I Evstigneev V A Lebedinski? 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1977,(5):95-98
Experiments were conducted on guinea pigs and Papio hamadryas; it was shown that a reduction of the intensity of postvaccinal immunity occurred at various periods after a single vaccination. In inhalation method of immunization in guinea pigs it decreased in 6 months 135 times, in monkeys in one year--133 times. However, at the mentioned periods vaccination provided protection of 50% of the animals from infection with Past. pestis in a dose constitutin 20 to 25 aerosol LD50 for nonimmunized animals. Despite the more pronounced (57--640 times) reduction of the intensity of immunity than in the animals vaccinated by inhalation, in the subcutaneously vaccinated guinea pigs in subcutaneously infected with Past. pestis protection level remained high (resistance index in 3 and 6 months constituted 37.10(6) and 3-3-10(6), respectively). 相似文献
39.
(1)H NMR spectroscopy (500 MHz) has been used to quantify the complexation of the antibacterial antibiotic Norfloxacin (NOR) with DNA in the presence of Caffeine (CAF). Separate studies have been made for the self-association of NOR, its hetero-association with CAF and complexation with a model self-complementary DNA tetramer, 5'-d(TpGpCpA), in order to determine the equilibrium parameters (induced chemical shifts, association constants, enthalpy and entropy) of the two-component mixtures to aid the analysis of the three-component systems. Investigations of the self-association of NOR and its hetero-association with CAF show that the aggregation of NOR molecules and association with CAF in solution are driven by the stacking of aromatic chromophores. The complexation of NOR with d(TGCA) has been analysed in terms of intercalation with the double-stranded form and non-intercalative binding with the single-stranded form of DNA. Investigations of the competitive binding of NOR and CAF with DNA show that at physiological concentrations of NOR (muM) and CAF (mM) the dominant mechanism influencing the affinity of NOR with DNA is the displacement of bound NOR molecules from DNA due to CAF-DNA complexation (i.e. the protector action of Caffeine). 相似文献
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Buchelnikov AS Hernandez Santiago AA Gonzalez Flores M Vazquez Ramirez R Davies DB Evstigneev MP 《European biophysics journal : EBJ》2012,41(3):273-283
A general model of competitive binding in drug–interceptor–DNA systems has been developed in order to quantify both the interceptor
and protector mechanisms. The model involves full parameterization of the basic equations governing the mutual competition
between drugs binding to DNA and incorporates as partial cases various similar models existing in the literature. The generality
of the model results from strict accounting of the statistical effects of the binding of the drug and interceptor with DNA
according to the McGhee-von Hippel formalism, and to the strict treatment of hetero-association between the drug and interceptor,
which includes formation of all possible types of self- and hetero-complexes in solution. Indirect experimental evidence is
provided for the importance of the protector mechanism in drug–caffeine–DNA systems, which is sometimes ignored in the literature
because of the small magnitude of the CAF-DNA binding constant. 相似文献