摘要:

Abstract—Millisecond time‐resolved emission spectroscopy was used to probe the phosphorescence kinetics of the α‐β‐enone 6β, 19‐epoxycholest‐4‐en‐3‐one (1) as a function of concentration in several paraffinic and hydroxylic glasses at 77 K. Only in methylcyclohexane/methylcyclopentane glass at low concentration (10−4M) does the phosphorescence decay exponentially. It is interpreted as emission from the3n* state. Upon increasing the concentration a second emission grows which is characterized by a longer lifetime, a decreased fine structure and a hypsochromically shiftedS0→1nπ* excitation spectrum. This phosphorescence is ascribed to3ππ* emission of aggregates of 1. In hydroxylic glasses the phosphorescence decay is multiexponential, even at 10−4Mconcentration; from emission band shapes and lifetimes it follows that both3nπ* and3ππ* type emissions are present, the latter increasing with the alcohol concentration in the solvent. The two types of phosphorescence have different excitation spectra: that of the structureless and long‐lived3ππ* emission is shifted to the blue in theS0→1nπ* region and to the red in theS0→1ππ* region. This emission is ascribed to complexes of 1 with the alcoholic solvent. The results of time‐resolved measurements of the circular polarization of the luminescence are consistent with the assignments given above and indicate that in the H‐bonded and possibly also in the free species3ππ* and3n

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb03652.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—Urocanic Acid (UCA) exists in mammalian skin primarily as the trans isomer and is photoisomerized to cis UCA upon UVB absorption. Our previous studies indicated that the photoiaomerization of UCA is the initiating event in UVB‐induced suppression of cell‐mediated immunity (tUCA → cUCA → immune suppression). The purpose of this study was to verify the role of UCA in UV‐induced immune suppression of contact hypersensitivity (CHS) in BALB/c mice. Since UCA is a metabolite of the amino acid L‐histidine, we reasoned that increased dietary levels of histidine should raise skin tUCA levels. If skin tUCA is the UVB photoreceptor for immune suppression, this increase should enhance UV‐induced suppression of CHS. HPLC analysis of skin from BALB/c mice given a histidine‐rich diet (10%) showed that the total amount of UCA is significantly higher in these animals than in mice fed a normal diet. Further, levels of suppression of CHS of 3% and 49% in control fad mice, induced by 4.8 and 7.2 kJ/m2 UVB were significantly increased to 21% and 71% respectively in histidine‐fed animals at these same UVB doses. These findings provide additional support for the UCA model for immune suppression, and provide the first evidence that UV‐induced immune suppression can be enhanced by a dietary c

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb03653.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—The anaerobic photoreduction of riboflavin, flavin mononucleotide, N(3)‐carboxymethylriboflavin, N(3)‐methyl‐lumiflavin, and lumiflavin by EDTA was studied in aqueous solution over the pH range 2.5–10. The electrostatic effects of the electron donor‐acceptor pair produce a secondary effect on the reactivity, and this effect can be predicted from the product of the charges (ZDx ZA). The trianonic and tetraanonic species of EDTA have nitrogens which are free from intramolecular hydrogen bonding, and these species are potentially the most reactive. However, in some pH regions the electrostatic effect can become the dominant factor when both the electron donor and acceptor become negatively charged. The excited states of flavins are susceptible to charge effects whether the charge is localized on the side chain or involves the isoalloxazine

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb03654.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—A model is suggested for tryptophan fluorescence quenching by acrylamide based on the prediction that acrylamide can absorb a photon from the excited indole moiety and then dissipate the optical energy into a sink of fast exchanging conformations. Semiempirical electronic structure calculations of the indole‐acrylamide pair indicate little actual intermolecular orbital mixing a1 van der Waals contact distances. However, the two lowest singlet transitions of the molecular pair, assigned to the acrylamide {π*}←n(O) line and to the indole1Lb←1A1line, respectively, vary significantly in energies and in transition and excited state moments with the geometry of interaction between the two entities. The distribution of optimal quenching coordinations depends separately on the benzene and pyrrole portions and has a distinctly non‐spherical shape at these

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb03655.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—Species differences in red blood cell susceptibility to the photohemolytic agents chlorpromazine, menadione and tetracycline were examined in mouse, rat, dog, and human blood. Menadione and tetracycline (25 μM) hemolyzed mouse but not dog, rat, or human red blood cells (RBC) when irradiated with UV light but not in the dark. Chlorpromazine (25 μM) produced a photohemolytic response in all four species with mouse and rat RBC lysing fastest followed by human then dog cells. Investigations into the nature of these species differences suggested that the size of mouse RBC may contribute to its high sensitivity to photohemolytic agents. An investigation of the effect of UV light on key antioxidant enzymes revealed species differences in enzyme inactivation. These data suggest that mouse RBC may be particularly vulnerable to phototoxic agents, especially those compounds which produce active oxygen species and, therefore, may prove more useful than human RBC as a model for predicting phototoxic potential of some chemical entit

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb03656.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—α‐Terthienyl photosensitizes single strand breaks in pBR322 DNA. Almost identical results were observed under oxygen and under argon. In the presence of oxygen, this DNA nicking was enhanced by histidine and was not affected by superoxide dismutase, catalase, or the antioxidant BHT. Although chemical damage to DNA treated with α‐terthienyl plus near‐UV was clearly demonstratedin vitro, transformation inE. coliwith this damaged pBR322 DNA still took place. Likewise,Haemophilus influenzaeDNA transforming activity was not significantly decreased by photosensitization with α

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb03657.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—Spectral properties of several diporphyrin ethers were assessed in different solvents and after accumulation by leukemia L1210 cellsin vitro. To facilitate studies in a variety of solvents, both tetramethylesters of the diporphyrin ethers and free acids were employed. For comparison, studies on the corresponding porphyrin monomers were also carried out. The joining of two porphyrins by an ether linkage had several consequences. We observed a blue shift in the Soret band of the ethers, but not of the corresponding simple porphyrins, in protic solvents. This phenomenon is likely related to ether aggregation under conditions which promote H‐bonding. The presence of an ether linkage was associated with enhanced fluorescence at 630–640 nm and decreased fluorescence lifetimes and yields, especially in protic solvents. The ether linkage was unaffected by intracellular enzymes, but porphyrin esters were readily hydrolyzed upon accumulation by L1210 cells. The joining of two hematoporphyrin molecules by an ether linkage promoted dye accumulation by L1210 cells. In contrast, accumulation of mesoporphyrin and protoporphyrin was thereby ret

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb03658.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—A group of polycarboxylic diporphyrins, two dichlorins and a porphyrin‐chlorin dimer, with rings linked by methylene groups, were examined to help identify structures which can mediate photodynamic tumor eradicationin vivo. Among the features sought were short persistence of normal tissue photosensitization and substantial absorbance at wavelengths longer than 630 nm. Both objectives were achieved, with pertinent structure‐activity relationships partly characterized. The relative hydrophobicity of the different sensitizers was an important determinant of their accumulation in cell culture, but not ofin vivoeffectiveness. These compounds showed affinity for protein and high‐density lipoprotein components of serum. Their distribution may be mediated by a different mechanism than that which occurs with more hydrophobic sensitizers like hematoporphyrin derivative which have greater affinity for low‐density lipoproteins and less for protein components of serum, as compared with the products examined in t

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb03659.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—The lipophilic photosensitizing dye merocyanine 540 (MC540) is being studied intensively as an antitumor and antiviral agent. Since plasma membranes are believed to be the principal cellular targets of MC540‐mediated photodamage, we have studied membrane damage in a well characterized test system, the human erythrocyte ghost. When irradiated with white light, MC540‐sensitized ghosts accumulated lipid hydroperoxides (LOOHs derived from phospholipids and cholesterol) at a rate dependent on initial dye concentration. Neither desferrioxamine nor butylated hydroxytoluene inhibited LOOH formation, suggesting that Type I (iron‐mediated free radical) chemistry is not important. By contrast, azide inhibited the reaction in a dose‐dependent fashion, implicating a Type II (singlet oxygen,1O2) mechanism. Stern‐Volmer analysis of the data gave a1O2quenching constant ∼50 times lower than that determined for an extramembranous target, lactate dehydrogenase (the latter value agreeing with literature values). This suggests that1O2reacts primarily at its membrane sites of origin and that azide has limited access to these sites. Using [14C]cholesterol‐labeled membranes and HPLC with radiodetection, we identified 3β‐hydroxy‐5α‐cholest‐6‐ene‐5‐hydroperoxide as the major cholesterol photoproduct, thereby confirming1O2intermediacy. Irradiation of MC540‐sensitized membranes in the presence of added iron and ascorbate resulted in a large burst of lipid peroxidation, as shown by thiobarbituric acid reactivity and appearance of 7‐hydroperoxycholesterol and 7‐hydroxycholesterol as major oxidation products. Amplification of MC540‐initiated lipid peroxidation by iron/ ascorbate (attributed to light‐independent reduction of nascent photoperoxides, with ensuing free radical chain reactions) could prove useful in au

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb03660.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—The action spectra and quantum yields for singlet oxygen (1O2) generation by merocyanine 540 (MC540) in liposomes and isolated erythrocyte membranes were obtained using electron spin resonance techniques. Oxygen consumption was measured by spin label oximetry in the presence of histidine for fully‐saturated dimyristoylphosphatidylcholine vesicles, mono‐unsaturated 1‐palmitoyl‐2‐oleoylphosphatidylcholine vesicles and erythrocyte membranes. The quantum yield for the photogeneration of1O2by membrane‐bound MC540 in aqueous buffer was determined to be 0.065 ± 0.005, which is approx. 1/10 of the value determined for Rose Bengal under similar conditions. Using unilamellar liposomes and isolated erythrocyte membranes containing MC540 at different monomer/dimer ratios, we have observed that the action spectra of1O2generation closely overlap the absorption spectra of the monomeric dye in these systems. It is likely that factors which affect the monomer‐dimer equilibrium of MC540 will influence the production of1O2. These findings have important implications for the phototherapeutic e

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb03661.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY