摘要:

Abstract—Photolysis of naphthalene on the surface of SiO2under an atmosphere of air produces phthalic acid as the only major photoproduct, accounting for 49%o of the consumed naphthalene. Photolysis on Al2O3also produces phthalic acid, in 31% yield. Photolysis of 1 ‐methylnaphthalene on SiO2proceeds under similar conditions to produce 2‐acetylbenzoic acid (35%) as the major photoproduct with the production of a small amount of I‐naphthaldchyde (6%). 1‐Cyanonaphthalene does not photooxidize under similar conditions. The presence of oxygen is necessary for the photodecomposition of naphthalene and 1‐methylnaphthalene to proceed. Superoxide formed from the photolysis of naphthalene at the SiO2/air interface is readily observed by electron paramagnetic resonance spectroscopy. In the absence of naphthalene no superoxide is observed. A mechanism involving electron transfer from the S1state of the naphthalene to O2is proposed on the basis of these observations and related literatur

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb09541.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract—Irradiation of 1‐phenyl‐1,3,5‐hexatriynes with various olefins in methylene chloride yields [2 + 2] type 1:1 photoadducts. The photoreaction proceeds through a triplet excited state and shows site selectivity and regioselectivity. Olefins with electron‐withdrawing substituents, such as dimethyl fumarate, fumaronitrile, acrylonitrile, methyl acrylatc, and styrene, are more reactive than electron‐rich olefins, suggesting that the triplet excited states of 1‐phenyl‐1,3,5‐hexatriynes have a nucleophilic

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb09542.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract—Irradiation of thin films consisting of 4,5′,8‐trimethylpsoralen (TMP), adenosine and small amounts of alcohols led to TMP‐alcohol photoadducts in addition to TMP‐adenosine photoadducts. Four TMP‐ethanol and two TMP‐methanol adducts have been separated and characterized. Covalent bonds were formed between the 4‐carbon of TMP and the α‐carbon to the hydroxy group in the alcohols. The TMP‐alcohol photoadducts were formed only in the TMP film containing small amounts of alcohol and adenosine. Furthermore, no photoadduct of TMP and ribose was detected upon photolysis of a TMP‐ribose film, suggesting that the adenine moiety plays a specific role in the reaction. The interaction of adenosine with psoralens in a dry film may be related to the DNA sequence selectivity observed for the photoreaction

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb09543.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract—Proteins exist in a predominately aqueous solvent environment. Hydration of the protein surface significantly affects many aspects of the protein's structure and function; these effects may be related to the molecular dynamics of the protein. We have examined the influence of hydration on the internal dynamics of hen egg white lysozyme using room‐temperature phosphorescence from the intrinsic tryptophan residues. Powders of lyophilized lysozyme were hydrated in a phosphorimeter using a flow system that allowed for continuous manipulation of relative humidity over the range 0–92%; this system allowed us to directly compare intensity differences that result from changes in hydration. Lysozyme phosphorescence intensity decreased as a function of hydration over the entire relative humidity range; the decrease was not linear but appeared to occur in distinct phases. The phosphorescence intensity decays were multiexponential over the hydration range studied, and hydration had the largest influence on the long lifetime component. These data suggest that the protein exists in multiple, static conformations in the dry state and that water binding to polar (as opposed to charged) sites on the protein surface induces local and/or global softening of the protein stru

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb09544.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract—The Basu theory of the solvent effect on the absorption spectra of dye molecules in nonpolar solvent is reexamined. The term due to the transition dipole moment of a solute molecule was found to be irrelevant in the formula of the spectral shift and only the term due to the electronic polarizability was necessary for the spectral shifts of large dye molecule

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb09545.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract—It is shown for a series of tyrosine‐derivatives and tyrosine‐containing peptides that the amide group in combination with electron‐withdrawing substituents quenches the fluorescence of the phenol moiety. The ammonium group has the strongest electron‐withdrawing effect and thus the largest influence on the quenching rate. The peptide group itself does not quench the fluorescence. In a series of peptides with an increasing number of alanines the decreasing quenching efficiency or the peptide group due to the greater distance of the ammonium group is demonstrated. In tyrosine‐containing di‐ and tripeptides a linear correlation between the13C‐NMR chemical shift δ of the C2atom of various aliphatic amino acids and the fluorescence‐quenching constant confirms the hypothesis that electron‐withdrawing and donating groups are modulating the fluorescence‐quenching efficiency of the peptide group. In small peptides the fluorescence lifetime of tyrosine is characteristic for the neighboring amino acids. Using model substances the redox properties of a peptide group and the phenol ring were studied electrochemically. The highest occupied molecular orbital of the tyrosine (1.4 Vvssaturated calomel electrode [SCE]) and the lowest unoccupied molecular orbital of the peptide group (‐3.12 VvsSCE) have appropriate energies for a photoinduced electron transfer reaction. For solute‐quenching experiments quencher molecules can

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb09546.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract—The hydrophobic interactions of bulky polycyclic aromatic hydrocarbons with nucleic acid bases and the formation of noncovalent complexes with DNA are important in the expressions of the mutagenic and carcinogenic potentials of this class of compounds. The fluorescence of the polycyclic aromatic residues can be employed as a probe of these interactions. In this work, the interactions of the (+)‐transstereoisomer of the tetraol 7,8,9,10‐tetrahydroxytetrahydrobenzo[a]pyrene (BPT), a hydrolysis product of a highly mutagenic and carcinogenic diol epoxide derivative of benzo[a]pyrene, were studied with 2′‐deoxynucleosides in aqueous solution by fluorescence and UV spectroscopic techniques. Ground‐state complexes between BPT and the purine derivatives 2′‐deoxyguanosine (dG), 2′‐deoxyadenosine (dA), and 2′‐deoxyinosine (dI) are formed with association constants in the range of ∼40–130M−1Complex formation with the pyrimidine derivatives 2′‐deoxythymidine (dT), 2′‐deoxycytidine (dC), and 2′‐deoxyuridine (dU) is significantly weaker. Whereas dG is a strong quencher of the fluorescence of BPT by both static and dynamic mechanisms (dynamic quenching rate constant kdyn= [2.5 ± 0.41 × 109M1s1, which is close to the estimated diffusion‐controlled value of ∼ 5 × 109M− 1s−1), both dA and dI are weak quenchers and form fluorescenceemitting complexes with BPT. The pyrimidine derivatives dC, dU, and dT are efficient dynamic fluorescence quenchers (Kdyn∼ [1.5–3.0] × 109M−1s−1), with a small static quenching component due to complex formation evident only in the case of dT. None of the four nucleosidcs dG, dA, dC and dT are dynamic quenchers of BPT in the triplet excited state; the observed lower yields of triplets are attributed to the quenching of single excited states of BPT by 2′‐deoxynucleosides without passing through the triplet manifold of BPT. Possible fluorescence quenching mechanisms involving photoinduced electron transfer are discussed. The strong quenching of the fluorescence of BPT by dG, dC and dT accounts for the low

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb09547.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract—Different classes of tryptophan residues in sarcoplasmic reticulum calcium‐ATPase were investigated with respect to their exposure to quenchers and sensitivity to high‐affinity calcium binding to the ATPase. The charged quenchers, iodide and cesium, produced only slight quenching of ATPase fluorescence, whereas noncharged acrylamide and notably oxygen produced significant quenching. This finding gives support to the proposed location of most of the tryptophan residues of the ATPase in transmembrane domains of this protein (MacLennanet al., 1985,Nature316r, 696–700). Among the different quenchers tested, oxygen quenching alone was sensitive to calcium binding to the ATPase, indicating that oxygen quenched tryptophan residues located in regions of the ATPase molecule which undergo conformational changes upon calcium binding. Time‐resolved oxygen quenching data were analyzed with a recently described model that takes into account the existence of two different classes of emitters in the ATPase (Ferreira and Verjovski‐Almeida,1991,J. Lumin.48, 430–434): a short‐lived blue‐shifted exponential component plus a long‐lived red‐shifted continuous lifetime distribution. Oxygen quenching of the single‐exponential lifetime component was found to be insensitive to calcium, whereas quenching of the distributed lifetime component was significantly (ca25%) enhanced by calcium binding. The different sensitivities of the two tryptophan classes to calcium binding to the ATPase are interpreted in terms of the proposed location of tryptophan residues in relation to the calcium transport sites

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb09548.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract—Biophysical and photobiological properties of a group of bacteriochlorins were compared with efficacy of these products for photodynamic therapy of murine tumors. Predictive factors for selective photosensitizationin vivoinclude affinity binding to lipoproteins greater than albumin, extinction coefficient at the wavelength of irradiation and tumor/skin distribution. Efficacy was correlated with circulating plasma levels of the different sensitizers but not with the photodynamic therapy response in cell cultur

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb09549.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract—Photodynamic therapy (PDT) of cancer is a modality that relies upon the irradiation of tumors with visible light following selective uptake of a photosensitizer by the tumor tissue. There is considerable emphasis to define new photosensitizers suitable for PDT of cancer. In this study we evaluated six phthalocyanines (Pc) for their photodynamic effects utilizing rat hepatic microsomes and human erythrocyte ghosts as model membrane sources. Of the newly synthesized Pc, two showed significant destruction of cytochrome P‐450 and monooxygenase activities, and enhancement of lipid peroxidation, when added to microsomal suspension followed by irradiation with ∼ 675 nm light. These two Pc named SiPc IV (HOSiPcOSi[CH3]2[CH2]3N[CH3]2) and SiPc V (HOSiPcOSi[CH3]2[CH2]3N[CH3]31I) showed dose‐dependent photodestruction of cytochrome P‐450 and monooxygenase activities in liver microsomes, and photoenhancement of lipid peroxidation, lipid hydroperoxide formation and lipid fluorescence in rnicrosomes and erythrocyte ghosts. Compared to chloroaluminum phthalocyanine tetrasulfonate, SiPc IV and SiPc V produced far more pronounced photodynamic effects. Sodium azide, histidine, and 2,5‐dimethylfuran, the quenchers of singlet oxygen, afforded highly significant protection against SiPc IV‐ and SiPc V‐mediated photodynamic effects. However, to a lesser extent, the quenchers of superoxide anion, hydrogen peroxide and hydroxyl radical also showed some protective effects. These results suggest that SiPc IV and SiPc V may be promising photosensitizers for th

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1993.tb09550.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY