摘要:

Abstract—The rates for conversion of pre‐vitamin D3(pre‐D) to vitamin D, (D) and of D to pre‐D in the cholesteric liquid‐crystalline and isotropic phases of a 60/26/14 (wt/wt/wt) mixture of cholesteryl oleate/cholesteryl nonanoate/cholesteryl chloride and in hydrocarbon solvents (hexane and 2,2,4‐tri‐methylpentane) have been measured. The rate constants for the forward and reverse reactions in the cholesteric mixture are greater than those measured in the hydrocarbon solvent. The pre‐D D rate in the liquid‐crystalline phase is independent of whether pre‐D is generatedin situfrom 7‐dehydrocholes‐terol or from lumisterol3. Eyring plots of data from the cholesteric mixture show no perceptible differences between the liquid‐crystalline and isotropic phases: ΔH=83.85 3.0 kJ/mol and ΔS=‐64.3 9.7 J/mol‐degree for pre‐D D; ΔH=104.22.7 kJ/mol and ΔS = ‐13.7 8.4 J/ mol‐degree for D pre‐D. It is concluded that macro‐solvent order does not play an important role in the rates and equilibria for the pre‐D D intcrconversion. Solvent‐solute spatial interactions may be responsible for the

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb02592.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—A detailed study has been made of the luminescence spectra of 3‐β‐d‐ribofuranosyl‐7‐amino‐pyrazolo(4,3‐d)pyrimidine (formycin A), 3‐propyl‐7‐aminopyrazolo(4,3‐d)pyrimidine (7APP), and their various N‐methyl derivatives, at room temperature and in methanol‐water glasses at 77 K. Comparisons of the foregoing, together with the observed dependence of the emission spectra of formycin and 7APP on excitation wavelength, demonstrated that these consist of two tautomeric species, N(1)H and N(2)H, both of which emit at 300 and 77 K. The two tautomers may be distinguished by the location of the emission maxima, especially for phosphorescence, and quantum yields for emission.Comparisons of the emission spectra of the protonated forms of 7APP and its N‐methyl derivatives showed that the fluorescence of the cations of 7APP and its N,‐ and N2‐methyl derivatives originates from the forms protonated on N(4). By contrast, the forms protonated on N(6) contribute appreciably to the phosphorescence at 77 K. On the basis of the emission spectra at 77 K, it is concluded that the major tautomeric form of the formycin cation is N(1)H,N(4)H+, but there is also some contribution by the form N(2)H,N(4)H+.In acid medium at room temperature, there is photodissociation of a proton from the pyrazole ring of the formycin cation. This leads to formation in the state S! of the tautomeric species N(4)H, which does not exist in the ground state. This conclusion, similar to that previously reported for the analogous isomeric 4‐aminopyrazolo(3,4‐d)pyrimidines, is derived from a comparison of the fluorescence spectra of the cations of formycin and N4‐methylformycin, which exhibit two bands at 375 and 440 nm, the latter corresponding to the emission of the neutral form of N,i‐methylformycin. The proposed mechanism of phototautomerization is suppor

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb02593.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—A variety of polynucleotides containing 5‐iodouracil residues were irradiated in aqueous solution with wavelengths between 240 and 313 nm. From the rate of deiodination the photochemical cross sections (aB) were determined as a function of the irradiation wavelength (A). The expression was used to relate the observed values ofBto the intrinsic quantum yield, φINT, and to the absorption cross sections, and for the iodinated and noniodinated residues, respectively. φINTis the probability an excited iodouracil residue will deiodinate, while the parameterbis a measure of the number of noniodinated bases which contribute their excitation energy to the deiodination process. For IdUrd and poly(5‐iodouridylic acid), the average values of φINTcalculated from the experimentalBvalues were 0.0202 and 0.0188, respectively, for irradiation in air. In native, denatured, and depurinated DNA in which IdUrd was substituted for 10% of the Thd, the average φINTvalues were 0.0069, 0.0088, and 0.0153, respectively, indicating an enhancement in φINTupon decreasing the order of the polynucleotide. In contrast, the average values ofbbor the same set of compounds were found to be4, 2 and 0.4, respectively, indicating a decrease inbwith decreasing polynucleotide order, i.e. a loss of base stacking decreases the extent of energy transfer. A value ofb= 4 for native DNA is assumed to mean that the extent of energy transfer in native DNA is limited to four base donors per iodouracil residue serving as an e

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb02594.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—Ultraviolet light flashes induced voltage transients across bilayer lipid membranes when aromatic amino acids were adsorbed to one side of the membrane. These photo‐effects varied with the chromophore structure, the aqueous solution salt concentration, pH and oxygen partial pressure. These photo‐effects are attributed to the migration of electrically charged photochemical intermediates in the membrane, and provide a new method for studying the effects of UV light on memb

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb02595.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—The kinetic properties of O2(1Δg) have been examined in unilamellar vesicle dispersions composed of didodecyldimethylammonium bromide, di‐n‐octadecyl phosphate and egg lecithin. Light absorbing sensitizers 2‐acetonaphthone, methylene blue and a methylene blue derivative of enhanced water‐solubility were used. The rate parameters for singlet oxygen were monitored by observing the time profile of the bleaching of the reactive substrates diphenylisobenzofuran and anthracene dipropionate. The natural lifetime of O2(1Δg) in D2O‐based suspensions was shown to be 46/JS in good agreement with that found earlier for D2O alone and D2O‐based micelle systems. The bimolecular rate constants for reaction with diphenylisobenzofuran and dimethylindole (both lipid‐bound) and histidine (water‐bound) were also in close conformity with the values found earlier in micellar media. Kinetic spectrophotometry has been shown to be a useful technique for examining rate parameters in these

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb02596.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—3‐Carbethoxypsoralen (3‐CPs) has been tested in the photochemotherapy of psoriasis. It only forms monoadducts with DNA and is being considered as a non‐carcinogenic alternative to 8‐MOP which itself forms DNA crosslinks that arc difficult to repair. Using laser flash photolysis or pulse radiolysis, the triplet state of 3‐CPs, a possible intermediate in photosensitization, has been generated in several solvents: ethanol, water and benzene. The triplet lifetime, extinction coefficient and quantum efficiency of formation have been measured. Triplet reactivities towards (i) the solvents used, (ii) 3‐CPs, (iii) oxygen, (iv) tryptophan and (v) tyrosine, leading, respectively, to photoadditions with water, ethanol and 3‐CPs, to1O2, semioxidized tryptophan and semioxidized tyrosine, (vi) thymine and (vii) uracil have been investigated. The dark binding of 3‐CPs to DNA has been studied by comparing the reactivity of eaq‐with free 3‐CPs, free DNA and the 3‐CPs DNA complex. Some photophysical and photochemical properties of 4′,5′di‐hydro‐3‐carbethoxypsoralen(DH–3‐CPs), model of the main fluorescent photo‐product of 3‐CPs, have also been investigated. Biological consequences of the photochemical properties of 3‐CPs andDH–3‐CPs have be

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb02597.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—Action spectra for photoreactivation (enhancement of colony forming ability) and photorepair (monomerization of pyrimidine dimers in DNA) were obtained for ICR 2A frog cells over the334–577 lira range. These spectra were very similar with peaks at 435 nm and little effectiveness at wav

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb02598.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—Enhanced reactivation of UV‐ and y‐irradiated herpes virus was investigated by the plaque assay onCV–1 monkey kidney monolayer cells irradiated with UV light or X‐rays. Both UV‐ and X‐irradiatedCV–1 cells showed enhancement of survival of UV‐irradiated virus, while little or no enhancement was detected for y‐irradiated virus assayed on UV‐ or X‐irradiated cells. The enhanced reactivation of UV‐irradiated virus was greater when virus infection was delayed 24 or 48 h, than for infection immediately following the irradiation of cells. It is demonstrable that the UV‐ or X‐irradiatedCV–1 cells are able to enhance the repair of UV damaged herpes virus DNA

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb02599.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—Using toluidine blue, a potent photosensitizer with a1O2dominated mechanism in yeast cell inactivation, it was found that addition of ascorbate to the sensitizer‐cell mixture during illumination enhanced the inactivation. The enhancement required the presence of oxygen in the reaction mixture. The same enhancement was observed with methylene blue and thionine but not with xanthenes (Rose Bengal and eosin Y). The consumption of O2and ascorbate seemed coupled in the enhancement. From the observation that the presence of ascorbate for a very short time (1 s) in the reaction mixture was enough to exhibit the same enhancement, it was concluded that the ascorbate enhancement processes are probably initiated in bulk medium, not intracellularly. The ascorbate enhancement may be a combined consequence of the high electron‐accepting property of triplet toluidine blue and the strong tendency of ascorbate to act as an electron donor. The role of oxygen was not specified whether it was directly involved in the photoinactivation of cells. Addition of N J appeared to suppress the photoinacti‐vation only in the higher fluence region where ascorbate had been consumed. Thus the ascorbate enhancement seems to occur under low fluence conditions and may probably be independent of the singlet oxygen me

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb02600.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—Mouse cells (3T3 line) and human fibroblasts are equally sensitive to UV light. At fluences of 2.0–2.5 J/m2mouse cells excise only 20% of the pyrimidine dimers as compared to 80% excised by human fibroblasts. This fluence allows 37% survival in both cases. Hence, mouse cells are more resistant to the same burden of unexcised dimers. The reason for this increased tolerance to dimers does not seem to be due to a recombinational mechanism, as judged by the fact that only ca. 5% of the dimers are transferred from parental to daughter strands. The transfer of dimers was measured by theMicrococcus luteusUV endonuclease assay, irradiating cells at Gi to avoid artifacts arising from introduction of dimers in nascent strands. The possibility of other mechanisms being involved in the process of tolerance to DNA lesions is discus

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb02601.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY