摘要:

Abstract—The absorption, fluorescence, and phosphorescence of a series of estrogens is reported. The behavior of estrogens without a keto‐group is compared with that of the isolated phenylic, phenolic and naphtholic chromophores. In the latter two, attachment to the steroidal frame is inconsequential as regards their luminescent behavior. In all keto‐estrogens with the exception of equilenin there is a very strong transfer of excitation energy from the A ring chromophore to the keto group. The fluorescence of 6‐keto‐estradiol, which has a conjugated aromatic carbonyl chromophore, is apparently due to the rigidity of the steroid frame and exhibits a rather perculiar excitation

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06582.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—Initial quantum yields for the formation of all four uracil dimers,anti h, t(I);anti h, h(II);syn h, h(III) and syn h, t (IV), have been quantitatively determined in aqueous degassed and air‐saturated solutions as well as in degassed and air‐saturated solutions of micellar sodium dodecyl sulfate (NaLS) and hexadecyltrimethylammonium bromide (CTAB). In aqueous solutions the order of dimer yields isIV>III>II>I. Percentages of dimerIIIdecreases from 18‐9 per cent in water to 2–7 per cent in micellar CTAB and to 6.0 per cent in micellar NaLS, but those for dimersIandIIincrease in the micellar

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06583.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—The quantum yield for inactivation of aqueous trypsin fits the expression φf=Σrfrφ‘r, where fr, is the fraction of incident light absorbed by residues of typerand the φ’rare constants. The values φ‘trp= 0.012, φtyr= 0.005 and φ’eys= 0.10, obtained at pH 3 in the wavelength range 240–290 nm, are attributed to independent events by comparing with quantum yields of the initial photochemical products and permanent residue destruction. The proposed inactivating processes are photoionization of one essential tryptophyl residue, photolysis of one essential cystyl residue, and splitting of an essential cystyl residue induced by light absorption in a nearby tyrosyl residue. The initial photochemical process from pH 3–7 identified by flash photolysis is the ejection of electrons from approximately two tryptophyl residues, leading to the formation of the disulfide bridge electron adduct and the hydrated electron. It is proposed that one photoionized tryptophyl residue is permanently disrupted and the other is restored through a back reaction that leads to a damaged, active enzyme form. An enhanced inactivation quantum yield at flash photolysis light intensities is attributed to a biphotonic process. A model based on one‐photon photoionization of tryptophan from a short‐lived precursor of the fluorescent state and the biphotonic photoionization of tryptophan via the triplet state is consistent with

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06584.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—Irradiation (Λ>240 nm) of thymine in aqueous solution in the presence of glutathione produces primarily 5‐S‐glutathione‐5, 6‐dihydropyrimidine and 5‐S, S‐glutathione‐5, 6‐dihydro‐pyrimidine. These adducts are obtained in better yields when the irradiations (Λ>280 nm) are carried out in the presence of triplet‐state sensitizers. Reduction of 5‐S, S‐glutathione‐5, 6‐dihydropyrimidine with zinc dust in acetic acid yields the corresponding 5, 6‐dihydropyrimidine. When thymine‐glutathione adducts are heated in 6NHCl for 2h, 5‐S‐cysteine‐5, 6‐dihydrothymine and 5‐S, S‐cysteine‐5, 6‐dihydrothymine are formed. Under these conditions, uracil‐glutathione adducts are less stable and are con

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06585.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—In addition to the monomer‐like fluorescence, a long‐wavelength emission (Λmaxem= 410 nm) has been detected in the dinucleoside 5′‐5′ pyrophosphate (CppC) at room temperature. This emission looks very similar to that previously reported for the acidic forms of Poly C (Poly C. Poly C+and Poly I. Poly C. Poly C+). Only the monomer‐like emission (Λmaxem= 330 nm) can be detected in neutral Poly C, acidic CppC, and the neutral or protonated forms of the dinucleoside phosphate CpC.A correlation between the room temperature fluorescence of oligo and polycytidylic acids and their photochemical behaviour is found. Irradiation of all the polymeric samples at both neutral and acid pH results in the formation of minor photoproducts. They have been characterized by their absorbance (in the range 300–400 nm) and their fluorescence spectra. The same product is obtained in all cases where the monomer‐like fluorescence only is detected. Distinct products are formed in neutral CppC and in the acidic Poly C forms.The results are discussed with respect to the conformation of the oligo and polycytidylic acids and possible relationships between the 410–420 nm emission and adduct formation. An excimer is proposed as a common, intermediate excited state in both radiative deactivation and adduct formation in neutral CppC and th

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06586.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—Nanosecond laser photolysis was used to determine the rate constants of quenching (including chemical reactions) of the triplet states of eosin and thionine, at pH 7, by imidazole, l‐histidine, l‐methionine, l‐phenylalanine, l‐tryptophan, 3‐indole‐acetic acid, cytidine, guanosine, α‐chymotrypsin, lysozyme, allylthiourea, thiourea,p‐nitrosodimethylaniline, I‐N3‐and Fe(CN)64‐. The quenching rate constants for thionine were found to be up to three orders of magnitude higher than those for eosin. The mechanism of photosensitized oxygenations (free radical vs singlet oxygen) is discussed on the basi

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06587.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—The irradiation of horse and sperm‐whale Fe 3 * or Fe 2* myoglobins with visible light showed that axial ligands that render the heme diamagnetic (e.g. O2, CO or CN‐) endow the hemoproteins with a marked photosensitivity. In contrast, high‐spin myoglobins are unaffected by visible light. These findings appear to be of general validity for all hemo‐proteins and are in agreement with the involvment of the triplet state of the heme as the reactive intermediate. In all cases, the overall photoprocess occurs within a very narrow spatial range, leading to specific modification of these photooxidizable side chains adjacent to the chromophore. Therefore, this technique can be used to probe the environment of the prosthetic group in hemoproteins. In particular, our data suggest that, in horse myoglobin, histidines‐93 and ‐64 represent the heme‐linked and the distal imidazole groups, respectively; moreover, the thioether function of methionine‐131 must be nearer the heme in horse than in sperm‐whale myoglobin. The selectivity of the photoreaction can be further enhanced by a suitable choice of the sixth ligand, and/or by controlling the pH of the irradiated solution. For example, for both proteins, irradiation of the cyanide derivative results in specific photooxidation of the proximal histidine, whereas irradiation of horse CO‐ferromyoglobin at pH values below 6 causes specific photooxidation of methionine‐131. Consequently, this photooxidative procedure can also be utilized to monitor conformational changes upon binding of the heme with different ligands, as well as to achieve the selective modification of amino acid residues, which are usually buried insi

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06588.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractFluorescence and fluorescence polarization spectra of chlorophyll a dissolved in ethanol,n‐propanol, EM (ethanol‐methanol, 4:1) and EPE (ether,n‐pentane, ethanol, 5:5:2) were measured at 77 K. An emission band (‘shoulder’) between the two usual fluorescence bands appears in such spectra of dilute solutions (concentration ˜ 10‐5M) of chlorophyll a (except in EPE). The position, intensity and half‐width of this band were calculated using a computer. The correlation between electronic transitions of chlorophyll a and these emission band

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06589.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—The first phases of the fluorescence transient elicited by illumination of dark‐adapted algae or isolated chloroplasts (biphasic rise φ***v‐ φI‐P) have previously been shown to be controlled by two quenchers:Q, the primary acceptor of Photosystem 2 interacting with the secondary acceptor poolA; andR, a non‐photochemical quencher which goes into a non‐quenching state as A is reduced.The dependence of the kinetics of φ decay after illumination upon the redox state ofAwas studied. It is suggested that some of the centres are in a disconnected state, where electron transfer betweenQandAis hindered, the amount of such centres being correlated to the reduction state ofA. The implications of this hypothesis on the problem of the variation of theQ‐A‘equilibrium constant’ under different experimental conditions, and on Murata's ‘weak light effect’ are discussed.The effect of 3‐(3,4 dichlorophenyl)‐1,1 dimethylurea (DCMU) onRis shown to depend upon the redox state ofA. A DCMU‐induced shift of the midpoint potential ofRmay account for this dependence.Evidence is given suggesting that the transient reduction ofAwhich occurs in algae during the φI‐φPrise is controlled by an induction process on

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06590.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06591.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY