摘要:

Abstract—Recently, a new technique of1O2generation has been described by Midden and Wang. The sensitizer is immobilized on silica gel particles which are attached on one surface of a glass plate which is placed, sensitizer‐side down, above a solution leaving a small air space between the sensitizer and the solution. Applying the principle of the technique, i.e. generation of1O2in the gas phase above the solution, we first improved the long‐term stability of the dye (rose bengal) by using double stock transparent tape instead of rubber cement. Under these conditions, although the initial rate of production was higher in rubber cement, the rate of production reached a plateau after 30 min, whereas with double stick transparent tape, the rate of generation was linear up to 100 min. This result was explained by the fact that silica glass beads are embedded in the cement which could lead to the bleaching reaction of the dye. Different reactions have been investigated, the bleaching of N,N‐dimethyl‐4‐nitrosoaniline (RNO) in the presence of imidazole, destruction of anthracenedipropionic acid, formation of a stable nitroxide from a sterically hindered secondary amine and the influence of pH on the nitroxide yield. The yield was measured to be 5 × 1012molecules of singlet oxygen produced per second per cm2from the surface of the plate using the RNO bleaching reaction. This method of generating1O2also seems promising for studying the killing of mammalian cells by1O2as the sole dama

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1987.tb08398.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract—The solution of chlorophyll a in hexane with more than 70% of chlorophyll molecules in the form of the dihydrate (CHl‐a.2H2O)nis investigated at room temperature by picosecond absorption technique. The transient difference spectra and the kinetic dependences of the absorption changes are measured for several excitation and probe wavelengths. Creation of a new state with blue‐shifted absorption band is observed in the system after excitation. A model of the behaviour of the system after excitation is proposed and checked by comparison of the computer‐simulated spectral and time dependences with the experimental data. According to the model, about 30% of excited molecules are in the state with the 0.046 eV shift of the absorption band in comparison with the ground state absorption. The lifetime of this state has 170‐ps component. The rest of the excited molecules are in the first excited state with the decay time component

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1987.tb08399.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract—By irradiating psoralen (the parent linear furocoumarin) in thin solid film two new fluorescent photodimers. compounds I and II, have been isolated and characterized. Unlike previously isolated dimers of furocoumarins which showed a ‘pyrone‐pyrone’ structure involving in the C4‐cycloaddition the 3,4‐double bond of the furocoumarinic moiety, the new dimers show respectively a ‘furan‐furan’ and a ‘furan‐pyrone’ structure, involving therefore the 4′,5′‐double bond. By analogy with the photocycloaddition reactions between furocoumarins and pyrimidine bases of DNA, in this case too the 4′,5′‐double bond of the furocoumarin can be involved. The experimental conditions, however, in which irradiation is

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1987.tb08400.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract—The absorption spectra of the un‐ionized and ionized forms of 4‐heptadecyl‐7‐hydroxycoumarin (HHC) in aqueous self‐assembled surfactant solution have been investigated. From a comparison with the absorption spectra of 7‐hydroxycoumarin, 7‐hydroxy‐4‐methylcoumarin (MHC) and HHC in neat organic solvents and organic solvent/water mixtures it is shown that the 7‐hydroxycoumarin chromophore of HHC in self‐assembled surfactant solution resides, on average, in an interfacial microenvironment which has a lower effective dielectric constant than that of the bulk aqueous solution. The absorption spectrum of the ionized form of HHC in aggregates of self‐assembled surfactant molecules with cationic quaternary ammonium headgroups is found to be consistent with there being specific molecular interaction between the anionic chromophore and the quaternary ammonium headgroup. pH titrations performed with MHC in pure water and in four molar aqueous solutions of sodium chloride and tetra‐methylammonium chloride indicate that the acid‐base dissociation of HHC in charged micelles and vesicles should not be substantially influenced by any interfacial salt‐effects, and that the acid‐base dissociation of HHC in cationic micelles and vesicles with quaternary ammonium headgroups should not be markedly affected by the specific molecular interaction that exists. Estimates of the electrostatic surface potentials of a number of self‐assembled surfactant aggregates are made by utilising the acid‐base dissociation of HHC and assuming that the nonionic micelles ofn‐dodecyl octaoxyethylene glycol monoether (C12E8) can serve as a reference state of zero surface potential. The validity of this assumption in relation to both micel

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1987.tb08401.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract—The phenolic antitumor drug 2N‐methyl‐9‐hydroxyellipticine (NMHE) has been found to undergo oxidative activation upon irradiation with near‐UV light at 365 nm (UVA) in aqueous medium. In the presence of leucine used as biological nucleophile, UVA‐induced activation of NMHE results in covalent binding as shown by the generation of the corresponding adduct isobutyl‐oxazolopyridocarbazole (IB‐OPC). The reaction involves as the initial step the one‐electron transfer from the drug to molecular oxygen yielding superoxide anion (O2‐) whereas the generation of IB‐OPC may proceed either through a free radical reaction or a Michael addition reaction. The UVA light‐induced production of IB‐OPC is markedly increased by superoxide dismutase (SOD) and by the singlet oxygen quencher diazabicyclooctane (DABCO) but not affected by β‐carotene. It is concluded that UVA induces the oxidation of NMHE through an oxidasic process which may result in the covalent binding of the drug to biological nucleophiles. This finding leads to further investigation of the photodynamic a

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1987.tb08402.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract—The time resolved fluorescence decay of horse liver alcohol dehydrogenase was measured using a frequency doubled picosecond dye laser and time‐correlated single‐photon counting detection. A flow‐cell technique is described which eliminates the photodegradation artifacts which commonly occur with laser excitation. A procedure is introduced which uses fluorescence quenching to reveal minor fluorescence lifetime components. The decay of the unquenched tryptophanyl fluorescence could be described by a double exponential decay law, but experiments conducted in the presence of iodide ion showed that the fluorescence decay must be more complex than this. A model is presented in which the fluorescence decay consists of three exponential components, only two of which are susceptible to quenching by iodide ion. Several possibilities are presented for the origin of this minor decay component, the most reasonable of which is that it arises from conformational heterogeneity in the solvent‐exposed tryptophany

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1987.tb08403.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract—Molecular mechanism of fluorescence quenching of flavins in flavodoxin fromDesulfovibrio vulgaris, strain Miyazaki, and riboflavin binding protein from egg white has been investigated by means of picosecond laser photolysis technique. In the case of flavodoxin, a transient absorption band characteristic of the non‐fluorescent exciplex formed by electron transfer from indole to excited flavins in model systems has been observed around 600 nm at the delay time of 33 ps from exciting ps pulse pulse width, 25 ps). In the case of riboflavin binding protein, the transient absorption spectra were different from those of flavin‐indole exciplex and rather similar to the spectra of the model system of flavin‐phenol. These results suggest that tryptophan residue exists near the isoalloxazine nucleus in flavodoxin, and in riboflavin binding protein, tyrosine residue exists near the flavin. Direct measurements of the ultrafast process of the electron transfer in flavoproteins as developed here could provide useful information for elucidating protein dynamics, associated with redox reaction, in the picosecond time

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1987.tb08404.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract—The fluorescence properties of lumazine, 1‐methyl‐lumazine (1‐ML) and 3‐methyl‐lumazine (3‐ML) in aqueous solution are pH dependent. Emissions with the following maxima were attributed to the four ionic species of lumazine: dianion (483 nm), monoanion (467 nm), neutral (380 nm) and monocation (505 nm). Neutral lumazine emitted, besides, a fluorescence at 481 nm with a large Stokes shift (10 000 cm‐1). As a similar emission is observed with 3‐ML but not with 1‐ML, we suggest as emitting species the N(8)‐H‐phototautomer resulting from the N(l) to N(8) proton transfer in the excited state. At pH 10, the fluorescence quantum yield of 3‐ML, Qf= 0.24 ± 0.02 was higher than that of 1‐ML, Qf= 0.015 ± 0.002. At this pH, lumazine is a mixture of N(l)‐deprotonated and N(3)‐deprotonated monoanions, the emitting properties being principally due to the N(l)‐deprotonated species, Qf= 0.24 ± 0.02. The evaluation of the ionization constants in the excited state are discussed in relation to the tauto

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1987.tb08405.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract—Pyrenebutylmethylphosphonofiuoridate or pyrenepropylmethylphosphonofluoridate reacts with the serine 195 residue of α‐chymotrypsin to yield a stoichiometric fluorescent derivative. The fluorescence decay of the modified enzyme was studied using a frequency‐doubled, synchronously pumped picosecond rhodamine‐6G laser excitation source with time‐correlated single‐photon‐counting detection. Upon excitation above 330 nm, it could only be described adequately by a triple exponential decaying function. The exact reason for complexity of the emission has not yet been understood. Heterogeneous labeling seems irrelevant. The presence of different enzyme conformations on the single‐photon‐counting time‐scale seems more plausible. The enzyme conformations where the pyrene label is situated close to the side groups of certain residues such as tryptophan and lysine show a much shorter fluorescence decay time resulting in non‐exponential fluorescence behaviour. Dynamic fluorescence quenching experiments indicate that the pyrene label is located in a more polar region of the enzyme characterized by a negative charge. It seems that the pyrene group is too large to fit well in the hydrophobic pocket of the enzyme but is bent more towards the entrance of the cavity which is characterized by a higher polarity. Upon excitation at 296 nm, the excitation energy is transferred from the tryptophan chromophores to

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1987.tb08406.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract—Laser flash photolysis studies of the production of the triplet state of the xanthene dye, rose bengal (RB), have been carried out. The reactions of this state with oxygen to form singlet oxygen and the superoxide anion radical have been observed and yields measured. Quenching of RB(T1) by oxygen leads to approximately 75% singlet oxygen and 20% superoxide. The reactivity of these species‐RB(T1), O2(1Δg) and O2‐—with four nucleotides and DNA have been determined. Only guanine residues showed any noticeable reaction at neutral pH. At higher pH guanine rate constants increased. The consequences to biological photodynamic processes are d

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1987.tb08407.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY