Hyaluronate depolymerization following thermal decomposition of oxytetracycline

Depolymerization of sodium hyaluronate (HA) by tetracyclines was investigated. Reduction in HA molecular weight was followed by size exclusion chromatography with a low angle laser light scattering detector. On mixing with oxytetracycline hydrochloride (OTC) solution and incubating at 37 degrees C, HA was gradually depolymerized. OTC, a representative antibiotic, is known as a photosensitizer, and phototoxic side effects relevant to radicals have been reported. However, HA depolymerization required no irradiation. As time passed, OTC solution incubated at 37 degrees C got colored reddish brown, even in the dark. With reversed-phase HPLC separation, several peaks derived from decomposed OTC appeared. One of the peaks had an absorbance in the visible range. A quantitative correlation between the discoloration and the HA depolymerization rate was obtained. On the other hand, when samples were incubated below 25 degrees C, change of color was slight, and practically no HA depolymerization was observed after up to 4 h. Oxygen depletion by nitrogen saturation or addition of mannitol also prevented the depolymerization. Under anaerobic conditions, the color of the solution did not change, whereas it turned red under aerobic conditions in the presence of mannitol. The mannitol did not inhibit the OTC decomposition, but it preserved HA from damage. On the basis of the known decomposition of OTC and the results of HPLC separation, anhydrooxytetracycline can be proposed as the derivative causing HA depolymerization.     

Time-resolved detection of melanin free radicals quenching reactive oxygen species

Melanin, a ubiquitous, heterogeneous biological polymer composed of many different monomers, contains a population of stationary, intrinsic semiquinone-like radicals. Additional extrinsic semiquinone-like radicals are reversibly photogenerated with visible or UV irradiation. The free radical chemistry of melanin is complex and not well characterized, especially the photochemistry of melanin in the presence of oxygen. To determine directly how melanin reacts in the presence of oxygen, time-resolved electron paramagnetic resonance (TREPR) spectroscopy was used to examine melanin free radical chemistry in human retinal pigment epithelium (RPE) cells under aerobic and anaerobic conditions. A TREPR difference spectrum was used to explore the nature of melanin chemistry in the presence of oxygen. The position and symmetrical line shape of the TREPR three-dimensional difference spectrum shows that when reactive oxygen species (ROS) are scavenged, only one of the two or more chemically different melanin free radical species participates in ROS scavenging. This protective melanin radical species exists in both the extrinsic and intrinsic populations of melanin free radicals, allowing melanin to protect the RPE from toxic species in both the light and dark.     

Molecular mechanism of naproxen photosensitization in red blood cells

Red blood cell lysis photosensitized by naproxen was investigated. The photohemolysis rate was enhanced by deuterium oxide and inhibited by butylated hydroxyanisole, reduced glutathione, sodium azide and superoxide dismutase. Photohemolysis was also observed under anaerobic conditions. In the absence of red cells the irradiation of deaerated solutions underwent a decarboxylation process via intermediate radicals, while under aerobic conditions photo-oxidation leading to the photoproduct 6-methoxy-2-acetonaphthone occurred. A molecular mechanism involving free radicals and singlet oxygen as important intermediates and consistent with the overall results is proposed.     

Novel Visible and Ultraviolet Light Photogeneration of Hydroxyl Radicals by 2-Methyl-4-nitro-quinoline-N-oxide (MNO) and 4, 4'-Dinitro-(2, 2') bipyridinyl-N, N'-dioxide (DBD)

Chemicals that upon absorption of light generate hydroxyl radicals (·OH), free of other damaging species under physiological conditions, are useful tools for the study of the biological effects of ·OH radical and for its utilization for analytical purposes. We report the novel property of 2-methyl-4-nitro-quinoline- N -oxide (MNO) and 4, 4'-dinitro-(2, 2') bipyridinyl-N, N'-dioxide (DBD) to act as photogenerators of ·OH with UV and visible light. Upon irradiation with 360–400 nm light MNO and DBD generate free radicals that convert coumarin carboxylic acid (CCA) to fluorescent 7-OH-CCA; the ·OH radical scavengers dimethylsulfoxide (DMSO) and ethanol eliminate the induction of 7-OH-CCA fluorescence. Upon 400 nm illumination in the presence of MNO, supercoiled plasmid DNA is converted to circular and strand break-age is significantly reduced in the presence of DMSO and completely absent in the absence of MNO. The conversion of CCA to 7-OH-CCA and of supercoiled plasmid to circular DNA are also observed in the absence of oxygen. Taken together, these data indicate that MNO and DBD constitute novel ·OH-generating compounds. Because currently known ·OH-photogenerating compounds require UV illumination (< 360 nm) that also damages DNA and cells directly, the property of MNO to generate ·OH upon 400 nm illumination is advantageous when studies on cells, DNA and other biomolecules are conducted.     

Study on DNA damage induced by CdSe quantum dots using nucleic acid molecular “light switches” as probe

The calf thymus DNA (ctDNA) damage induced by water-soluble CdSe quantum dots (QDs) was investigated using nucleic acid molecular “light switches” as probe. It was found that little ctDNA was damaged by CdSe QDs without UV irradiation. However, under UV irradiation, ctDNA was nicked by CdSe QDs very clearly. The mechanism of ctDNA damage was also discussed. The results strongly suggested that the ctDNA damage caused by CdSe QDs was not due to photo-induced liberation of Cd²⁺, but due to the production of free radicals and reactive oxygen species.     

Visible-light-sensitive photocatalytic reaction on chromium-containing mesoporous silica: selective partial oxidation of propane with molecular oxygen

The photocatalytic reactivities of chromium-containing mesoporous silica molecular sieves (Cr-HMS) under visible light irradiation have been investigated. Cr-HMS involves tetrahedral chromium oxide (Cr-oxide) moieties which are highly dispersed and incorporated in the framework of molecular sieve with two terminal Cr=O groups. In the presence of propane with molecular oxygen, a partial oxidation proceeded under visible light irradiation to produce acetone and acrolein, with high selectivity, while a complete oxidation proceeded under UV light irradiation mainly to produce CO₂. The charge-transfer excited state of the tetrahedral Cr-oxide moieties plays a significant role in the photocatalytic reactions.     

Formation of free radicals in photoirradiated cellulose. VI. Effect of lignin

The effect of lignin on free-radical formation in photoirradiated pulp was studied by means of electron spin resonance spectroscopy. Samples were irradiated with light of wavelength longer than 3400 Å as well as longer than 2537 Å. Radical formation in aspen lignin was observed before and after irradiation with light of wavelength longer than 3400 Å. Upon irradiation, free radicals were formed in a pulp sample with 0% lignin content only when oxygen was present. On irradiation with light longer than 2537 Å, in the presence of nitrogen, oxygen, and under vacuum, free-radical formation was found in all cases. The largest concentration of radicals was obtained under vacuum, the smallest in oxygen. It is evident that cellulose was protected from radiation by the presence of lignin. Increased aspen lignin content in pulp led to a decrease in the relative signal intensity of ESR spectrum, that is, a decrease of the yield of free radicals in the cellulose fraction in pulp. Irradiation with light in the presence of oxygen caused significant yellowing of the pulp sample, and these photooxidation and discoloration reactions occurred primarily on the surface of the sample irradiated.     

Photooxidation Mechanism of Levomepromazine in Different Solvents

Unwanted photoinduced responses are well‐known adverse effects of most promazine drugs, including levomepromazine (LPZ, Levoprome^® or Nozinan^®). This drug is indicated in psychiatry primarily for the treatment of schizophrenia and other schizoaffective disorders. Levomepromazine's particular sedative properties make it especially fit for use in psychiatric intensive care. Nevertheless, it is photolabile under UV‐A and UV‐B light in aerobic conditions resulting in the formation of its sulfoxide. The LPZ photochemistry in acetonitrile (MeCN) is completely different from that in methanol (MeOH) and phosphate buffer solutions (PBS, pH = 7.4). The major photoproduct in PBS and MeOH under aerobic conditions is levomepromazine sulfoxide (LPZSO), although the amount is considerably higher in the aqueous environment. The corresponding main photoproduct in MeCN could not be characterized. The destruction quantum yields of LPZ in PBS, MeOH and MeCN are 0.13, 0.02 and <10^?3, respectively. It is further demonstrated that LPZSO does not form by the reaction of singlet oxygen with ground‐state LPZ. This oxidation product is actually produced by the reaction of the cation radical of LPZ (LPZ·⁺) with molecular oxygen. This cation radical in turn, is produced by an electron transfer process between the ³LPZ* and ground‐state molecular oxygen.     

MOLECULAR MECHANISM OF DRUG PHOTOSENSITIZATION–II. PHOTOHEMOLYSIS SENSITIZED BY KETOPROFEN

Red blood cell lysis photosensitized by ketoprofen (KPF) was investigated. The photohemolysis was inhibited by butylated hydroxyanisole, reduced glutathione, superoxide dismutase and mannitol, and was unaffected by sodium azide; the presence of oxygen markedly enhanced the lysis. Photohemolysis was also observed under anaerobic conditions. Ketoprofen, irradiated in aqueous buffer solution at pH 7.4, underwent a decarboxylation process via intermediate radicals, leading to the compounds (3-benzoylphenyl)ethane, (3-benzoylphenyl)ethyl hydroperoxide, (3-benzoylphenyl)ethanol and (3-benzoylphenyl)ethanone under aerobic conditions and only to the compound (3-benzoylphenyl)ethane under anaerobic conditions. The four photoproducts showed lytic activity, particularly high for the alcohol and hydroperoxide. The overall results suggest for KPF-photosensitized hemolysis a molecular mechanism involving free radicals, superoxide anion and sensitizer photodegradation products.     

High Pressure Liquid Chromatographic Determination of Promethazine Hydrochloride in the Presence of its Thermal and Photolytic Degradation Products: A Stability Indicating Assay

Abstract

A stability indicating method has been developed for the quantitation of promethazine hydrochloride in the presence of its photolytic and thermal degradation products. Following a basic extraction with acetonitrile, promethazine is separated from its internal standard, promazine, and vehicle components by direct high performance liquid chromatography using ultraviolet detection (249 nm) and a stainless steel column 25 cm in length, 0.46 cm i.d. packed with octa-decyl silica 5μ in diameter. A linear relationship was obtained between peak height ratio (promethazine/promazine) and promethazine hydrochloride in water over the range 30–600 g/ml. The percent coefficient of variation of the assay is 0.8% and the recovery of promethazine hydrochloride from aqueous solutions is 99.7%. The photolytic degradation of promethazine hydrochloride does not follow simple first order kinetics. Potassium iodide and p-benzoquinone had a significant effect on the degradation rate of promethazine during the first 30 minutes of the photolytic degradation reaction. However, after one hour there is no apparent quenching effect on the photolytic degradation rate of promethazine hydrochloride in the presence of these quenchers.     

Molecular mechanism of drug photosensitization. Part 3. Photohemolysis sensitized by diflunisal.

The lysis of red blood cells photosensitized by diflunisal (DFN) was investigated. Photohemolysis is inhibited by butylated hydroxyanisole and reduced glutathione, but is unaffected by mannitol and enhanced by sodium azide; the presence of oxygen markedly reduces the lysis which is accelerated in anaerobic conditions. These results contrast with those expected for a photodynamic mechanism. High lytic activity is observed for pre-irradiated solutions, mainly under anaerobic conditions. Direct irradiation of DFN in buffer solution at pH 7.4 leads to the formation, under anaerobic conditions, of compound 2'-(2',4'-difluoro-3'-carboxy-[1',1'-biphenyl]-4'-oxy)-4'- fluoro-4-hydroxy-[1,1'-biphenyl]-3-carboxylic acid (PhP), whereas under aerobic conditions formation of PhP is accompanied by unidentified photo-oxidation products; only compound PhP displays strong lytic activity. The overall results for DFN-photosensitized hemolysis suggest a mechanism involving a concerted action of free radicals, superoxide anion, singlet oxygen and sensitizer photoproducts.     

Visible light-induced photoepoxidation of propene by molecular oxygen over chromia-silica catalysts

Highly dispersed chromate species on silica catalyse the selective epoxidation of propene to propene oxide (PO) by molecular oxygen under visible light irradiation with the same quantum yield as that under UV light irradiation.     

PHOTOSENSITIZATION BY 2-CHLORO-3, 11-TRIDECADIENE-5, 7, 9-TRIYN-1-OL: DAMAGE TO ERYTHROCYTE MEMBRANES, Escherichia coli, AND DNA

The natural product 2-chloro-3,11-tridecadiene-5,7,9-triyn-1-ol (1) photosensitized the inactivation of Escherichia coli in the presence of near-ultraviolet light (320-400 nm; NUV) under both aerobic and anaerobic conditions. A series of E. coli strains differing in DNA repair capabilities and catalase proficiency exhibited indistinguishable inactivation kinetics following treatment with the chemical plus NUV. The presence of carotenoids did afford some protection to E. coli against inactivation under aerobic conditions, consistent with the involvement of singlet oxygen. The photosensitized hemolysis of human erythrocytes occurred more rapidly in the absence than in the presence of oxygen. Aerobically, the onset of hemolysis was partially inhibited by NaN3 and by 2,6-di-t-butyl-4-methylphenol (BHT) but not by superoxide dismutase (SOD). The aerobic lipid peroxidation observed in the membranes of erythrocyte ghosts was completely inhibited by BHT, and partially by NaN3, but not by SOD. These results suggest that either lipid peroxidation of the membrane is not the main cause of photohemolysis or that BHT has insufficient access to intact erythrocyte lipids to protect them. Aerobically, crosslinking of membrane proteins was also observed; it was not affected by SOD, but was partially inhibited by BHT and NaN3. The anaerobic photosensitized hemolysis of erythrocytes was more rapid; a radical mechanism was suggested since BHT inhibited the hemolysis to a greater extent than under aerobic conditions. Neither lipid peroxidation nor protein crosslinking was observed under conditions believed to be anaerobic. A light-dependent electron transfer to cytochrome c was obtained under argon but not under oxygen. Although induced mutations were not observed in the experiments with E. coli, 1 was capable of damaging both supercoiled pBR322 and Haemophilus influenzae transforming DNA in a manner that seemed to be equivalent under aerobic and anaerobic conditions. In conclusion, 1 can behave as typical photodynamic molecule under aerobic conditions but, in contrast to most photodynamic molecules, it is also phototoxic under anaerobic conditions. The extent to which the radical reactions detected under anaerobic reactions compete with the photodynamic processes when oxygen is present is not known.     

Mechanism of visible light phototoxicity on Porphyromonas gingivalis and Fusobacterium nucleatum

Phototoxicity of visible light laser on the porphyrin-producing bacteria, Porphyromonas gingivalis, in the absence of photosensitizers and under aerobic conditions was shown in previous studies. Recently, we found that the noncoherent visible light sources at wavelengths of 400-500 nm, commonly used in restorative dentistry, induced a phototoxic effect on P. gingivalis, as well as on Fusobacterium nucleatum, and to a lesser extent on the Streptococci sp. To elucidate the mechanism of this phototoxic effect, P. gingivalis and F. nucleatum were exposed to light (1) under aerobic and anaerobic environments and (2) in the presence of scavengers of reactive oxygen species (ROS). Phototoxic effect was not observed when the bacteria were exposed to light under anaerobic conditions. Dimethyl thiourea, a hydroxyl radical scavenger, was effective in reducing phototoxicity (P 相似文献   

SOME RELATIONSHIPS BETWEEN ULTRAVIOLET LIGHT AND HEME-PROTEIN-INDUCED PEROXIDATIVE LIPID BREAKDOWN IN LIPOSOMES, AS REFLECTED BY FLUORESCENCE CHANGES: THE EFFECT OF NEGATIVE SURFACE CHARGE

Abstract— The water soluble, photolabile nitrene precursor,azidonaphthalene–2,7-disulfonic acid (ANDS) was encapsulated in small unilamellar, isoelectric (egg PC) or negatively charged (egg PC + dihexadecylphosphate) liposomes. The individual and combined effects of heme-proteins and UV irradiation on the fluorescence of these vesicles under aerobic conditions were studied. Consistent with the catalytic action of heme-proteins on lipid peroxidation and peroxide decomposition, addition of cytochrome c (positively charged) or catalase (negatively charged) to the vesicles elicited immediate formation of a fluorescence band at 470 nm, characteristic of Schiff bases that form from aldehyde byproducts of decomposing hydroperoxides. Ultraviolet irradiation of liposomes for 5 min caused no significant changes in the fluorescence spectrum, in spite of the radiolysis of ANDS inside the vesicles with consequent formation of nitrene radicals. When isoelectric vesicles were irradiated with UV light in the presence of cytochrome c or catalase, Schiff base formation was further increased by2–3 fold, which effect was not observed in the absence of internal ANDS, or in the presence of negative surface charge on the vesicles. These findings suggest that (a) UV irradiation, by itself, cannot trigger lipid decomposition even when it is assisted by photoproduced nitrene radicals, (b) there is a ternary synergism between UV light, heme-proteins and nitrene radicals in promoting peroxidative lipid breakdown, and (c) negative surface charge inhibits the above synergism, which effect is unlikely to be due to electrostatic interaction between the vesicles and the protein or the ANDS.     

Degradation of hyaluronic acid at the metal surface

 When the viscosity of hyaluronic acid (HA) solution was measured with a rotational visco-meter, depolymerization occurred only by leaving the sample in the cup of the viscometer, while the solution in a glass test tube at the same temperature, 37 °C, was practically stable during the entire period of investigation. As the parts where the sample solution had contact with the viscometer are stainless steel, the participation of metal ions in the depolymerization was suspected. Therefore, experiments were carried out with stainless-steel beads in the HA solution. The results show that the molecular weight of HA decreased on exposure to the beads under aerobic conditions. The addition of 10 beads to 2 ml of a 0.1% HA solution prepared with 0.2 M NaCl reduced the molecular weight to about 75% of the initial value after 4 h. The degradation rate was proportional to the surface area of the beads. However, no dissolution of metal ion was detected, and therefore, this reaction was thought to proceed at the surface of the metal. Received: 26 September 1997 Accepted: 27 November 1997     

Chemical and photochemical electron transfer of new helianthrone derivatives: aspects of their photodynamic activity

Helianthrones 2-4 are a new class of synthetic photosensitizers, which have a molecular skeleton related to that of hypericin. We established that irradiation of heliantrones with visible light leads to the formation of semiquinone radicals and reactive oxygen species. The structures of the paramagnetic anion species produced by electron transfer were calculated on the density functional level and investigated by cyclovoltammetry, UV/vis, and EPR/ENDOR spectroscopy. As with hypericin, the pi system of the helianthrones was found to be considerably deviated from planarity, and, upon electron transfer, deprotonation in the bay region occurs. The structure of the semiquinone radicals was found to be identical in THF, DMF, and aqueous buffered solutions regardless of the means by which reduction was achieved. Semiquinone radicals can be formed via self-electron transfer between the excited state and the ground state or via electron transfer from an electron donor to the excited state of helianthrone. Therefore, the presence of an electron donor significantly enhanced the photogeneration of semiquinone and superoxide radical. The kinetic studies showed that no significant photochemical destruction of helianthrones occurred upon irradiation. Generation of superoxide and singlet oxygen upon irradiation of helianthrones was established by spin trapping techniques. This shows that both type I and type II mechanisms are of importance for the photodynamic action of these compounds.     

TiO2膜电极光电催化降解苯甲酸的机理研究

利用自制纳米TiO2薄膜作电极, 对苯甲酸光电催化降解过程进行了系统研究. 同时利用扫描电镜(SEM)、X射线衍射图谱(XRD)和光电流-电压响应谱分析光催化剂的微观性质和光电性能. 选取较高的pH 10.5, 以利于苯甲酸降解中间产物的检测(GC/MS). 通过对比光电催化与单一的TiO2光催化体系中苯甲酸的降解动力学、总有机碳(TOC)的去除率、降解产物的生成(GC/MS)及活性自由基物种的产生(ESR), 提出光电催化降解苯甲酸的具体反应路径和氧化机理. 羟基化的苯甲酸在羟基自由基与活性氧自由基的共同作用下, 经由含六个碳原子的二酸(顺式己二烯二酸), 被进一步氧化成小分子酸和CO2.     

光敏聚合中链端基的活性作用

本文用2,2-二甲氧基2-苯基苯乙酮(DMPA)作引发剂,在氧气存在条件下,进行MMA本体聚合,得到的聚合物具有一种异常的双峰分子量分布(MWD)。其中,高分子量峰仅在氧气条件下才产生,并且与DMPA和氧的浓度、光照时间以及添加剂有关,所得结果指出,由于聚合物PMMA链端基上活性的苄基过氧化物光裂解的结果,形成新的高分子自由基,又发生再次聚合,这导致生成更高分子量的聚合物,同时在MWD图上出现高分子量峰。     

壳聚糖在水溶液中的辐射降解反应

研究了壳聚糖在CH3COOH/NaCl缓冲溶液均相体系下的辐射降解反应,给出了H2O2、异丙醇、pH、样品初始分子量等因素对壳聚糖降解的影响,探讨了实验条件下溶液中不同自由基对壳聚糖降解的作用,并对辐照前后壳聚糖的结构进行了表征.结果表明,酸性条件下,壳聚糖的降解主要由.H和.OH自由基共同作用引起,加入H2O2或者通入N2O都能够略微提高.OH自由基浓度,对壳聚糖的降解有促进作用.加入异丙醇后,由于同时降低了.H和.OH自由基浓度,导致壳聚糖降解缓慢.当溶液的pH接近中性后,对壳聚糖的降解起主要作用的为.OH自由基,加入H2O2或者通入N2O都会增加.OH自由基的浓度,从而明显提高壳聚糖的降解速率.此外,研究发现低分子量的壳聚糖具有较快的降解速率.样品的UV、FTIR分析表明,辐照后除在壳聚糖分子链端生成羰基外,壳聚糖主链结构未见变化,脱乙酰度也没有显著改变,显示出辐射降解是一种有效的控制壳聚糖分子量方法.