Triplet Photoreactivity of the Diaryl Ketone Tiaprofenic Acid and Its Decarboxylated Photoproduct. Photobiological Implications

The 2-benzoylthiophene chromophore of the photosensitizing drug tiaprofenic acid and of its decarboxylated derivative is characterized by a unusually high energy gap between the T₁ (π,π*) and T₂ (n,π*) excited states, which makes this a unique system to study the intrinsic photo-reactivity of the two states. Weak fluorescence and phosporescence emission were detected at room temperature. Tiaprofenic acid undergoes photodecarboxylation from the triplet manifold as the main reaction. The photoprocess is temperature dependent with activation energy of 7–10 kcal/mol, close to the energy gap between T₁ and T₂. The decarboxylated product abstracts hydrogen in type I reactions. The involvement of T₂ in the above processes is proposed. Moreover the decarboxylated derivative exhibits reactivity toward phenols, consistent with a participation of the T₁ state as electron acceptor. The observed photoprocesses can account for biological photosensitization reactions, like membrane damage and protein modification.     

Photoreactivity of 3-thujopsanone

The photoreactivity in the liquid phase of the polysubstituted cyclohexanones 3-thujopsanones results from a primary process of Norrish I type, but is modified by the opening of the cyclopropyl ring. Quantum yields are higher than for less substituted cycloalkanones. In aprotic solvents, only hydrocarbons are formed either with the loss of a C₂H₂O group leading to the main photoproduct 4 or with decarbonylation of the ketone leading to a new cyclopropyl chain. In alcohol solvent, two isomeric compounds with an oxygenated heterocycle are obtained from the addition of solvent to a carbene intermediate.     

Photoreactivity of ETS-10

Irradiation of H-ETS-10 in the presence of adsorbed methanol or ethene causes photoreduction of Ti(IV) to Ti(III); photoreduction does not occur for Na, K-ETS-10, but a photoinduced polymerization of ethene is observed.     

Unveiling Latent Photoreactivity of Imines

Unlike carbonyl compounds, it has long been common understanding that excited imines show virtually no photoreactivity, and hence their properties and potential utility in chemical science remain largely unexplored. Now, a strategy is presented for eliciting latent photoreactivity of imines based on the introduction of a donor–acceptor (D‐A) structure to extend the lifetime of their photoexcited states. A series of spectroscopic analyses and density functional theory calculations reveal unique photophysical properties of the D‐A‐type imines. Furthermore, the reactivity of the D‐A‐type imines is demonstrated by using them as a photoredox catalyst for atom‐transfer radical addition. These findings illuminate a previously neglected chemical space in the field of photochemistry, which will be exploited by taking advantage of the inherent structural modularity of imines.     

Rendering Photoreactivity to Ceria: The Role of Defects

The photoreactivity of ceria, a photochemically inert oxide with a large band gap, can be increased to competitive values by introducing defects. This previously unexplained phenomenon has been investigated by monitoring the UV‐induced decomposition of N₂O on well‐defined single crystals of ceria by using infrared reflection‐absorption spectroscopy (IRRAS). The IRRAS data, in conjunction with theory, provide direct evidence that reducing the ceria(110) surface yields high photoreactivity. No such effects are seen on the (111) surface. The low‐temperature photodecomposition of N₂O occurs at surface O vacancies on the (110) surface, where the electron‐rich cerium cations with a significantly lowered coordination number cause a local lowering of the huge band gap (ca. 6 eV). The quantum efficiency of strongly reduced ceria(110) surfaces in the photodecomposition of N₂O amounts to 0.03 %, and is thus comparable to that reported for the photooxidation of CO on rutile TiO₂(110).     

Synthesis of {100} Facet Dominant Anatase TiO2 Nanobelts and the Origin of Facet‐Dependent Photoreactivity

Sword‐like anatase TiO₂ nanobelts exposed with 78 % clean {100} facets were synthesized and the facet‐dependent photoreactivity of anatase TiO₂ was investigated. By quantitative comparison with the reference {001} facets, the {100} facets possessed about ten‐times higher active sites density than that on {001} facets, resulting in higher photoreaction efficiency. After the active sites density normalization, the {100} and {001} facets exhibited distinct wavelength‐dependent photocatalytic performance, attributed to the anisotropic electronic structures in TiO₂ crystals.     

Chemistry of the diazeniumdiolates. 3. Photoreactivity

We have found O(2)-substituted diazeniumdiolates, compounds of structure R(2)N-N(O)=NOR' that are under development for various possible pharmaceutical uses, to be rather photosensitive. With R = ethyl and R' = methyl, benzyl, or 2-nitrobenzyl, the observed product distributions suggest that two primary pathways are operative. A minor pathway involves the extrusion of nitrous oxide (N(2)O) with simultaneous generation of R(2)N(*) and R'O(*), which may then form amines, aldehydes, and alcohols. The major reaction pathway is an interesting photochemical cleavage of the N=N bond to form a nitrosamine (R(2)NN=O) and an oxygen-substituted nitrene (R'ON). The intermediacy of the O-nitrene was inferred from the production of abundant oxime, via rearrangement of the O-nitrene to a C-nitroso compound (R'ON --> O=NR'), and subsequent tautomerization to the more stable oxime. Involvement of the O-nitrene was confirmed by trapping with 2,3-dimethyl-2-butene to form the aziridine and with oxygen to generate the nitrate ester. 2-Nitro substitution on the benzyl derivative had surprisingly little effect on the reaction course. For each compound examined, minor amounts of nitric oxide (NO), presumably produced by secondary photolysis of the nitrosamine, were observed. Time-resolved infrared experiments provided additional support for the above reaction pathways and confirmed that the nitrosamine is a primary photoproduct. We have also found that the relative contributions of the reaction pathways can be altered in certain derivatives. For example, when R' = 2,4-dinitrophenyl, the contribution of the nitrosamine/O-nitrene-forming pathway was diminished. Pharmacological implications of these results are discussed.     

The Role of Singlet Oxygen in Photoreactivity and Phototoxicity of Curcumin

Curcumin is a plant-derived yellow-orange compound widely used as a spice, dye and food additive. It is also believed to have therapeutic effects against different disorders. On the other hand, there are data showing its phototoxicity against bacteria, fungi and various mammalian cells. Since the mechanism of its phototoxic action is not fully understood, we investigated here the phototoxic potential of curcumin in liposomal model membranes and in HaCaT cells. First, detection of singlet oxygen (¹O₂) luminescence proved that curcumin generates ¹O₂ upon blue light irradiation in organic solvent and in liposomes. Then, HPLC-EC(Hg) measurements revealed that liposomal and cellular cholesterol is oxidized by ¹O₂ photogenerated by curcumin. Enrichment of liposome membranes with curcumin significantly increased the oxygen photo-consumption rate compared to the control liposomes as determined by EPR oximetry. Cytotoxicity measurements, mitochondrial membrane potential analyses and protein hydroperoxides detection confirmed strong phototoxic effects of curcumin in irradiated HaCaT cells. These data show that since curcumin is advertised as a valuable dietary supplement, or a component of cosmetics for topical use, caution should be recommended especially when skin is exposed to light.     

共轭亚油酸的结构、生理功能及来源

综述了共轭亚油酸的结构、生理功能及来源,并详细介绍了共轭亚油酸的合成.     

Induction of Wavelength-Dependent Photochemistry in Bilirubins by Serum Albumin

Summary.  Quantum yields for Z⇄E photoisomerization of the natural bi-chromophore bilirubin IXα in ammoniacal methanol solution were found to vary with excitation wavelength, whereas no variation (within experimental error) was observed for xanthobilirubic acid and for symmetrically substituted bilirubins (bilirubin IIIα, bilirubin XIIIα, and mesobilirubin XIIIα) in the same solvent. The quantum yield for Z⇄E photoisomerization of xanthobilirubic acid bound to human serum albumin was also invariant with excitation wavelength. In contrast, quantum yields for Z⇄E photoisomerization of the symmetrically-substituted bilirubins did show marked excitation wavelength dependency when they were bound to human serum albumin. These results show that quantum yields for Z⇄E photoisomerization of bilirubins are markedly sensitive to protein binding and to the nature of pyrrole ring β-substituents. They also demonstrate that wavelength-dependent photochemistry is characteristic of bilirubins with non-identical pyrromethenone chromophores, as expected from exciton coupling theory, and that complexation with albumin induces wavelength-dependent photochemistry in symmetrically substituted bilirubins. Received January 13, 1998. Accepted January 27, 1998     

In Vitro Evaluation of the Photoreactivity and Phototoxicity of Natural Polyphenol Antioxidants

Polyphenols are a large family of natural compounds widely used in cosmetic products due to their antioxidant and anti-inflammatory beneficial properties and their ability to prevent UV radiation-induced oxidative stress. Since these compounds present chromophores and are applied directly to the skin, they can react with sunlight and exert phototoxic effects. The available scientific information on the phototoxic potential of these natural compounds is scarce, and thus the aim of this study was to evaluate the photoreactivity and phototoxicity of five phenolic antioxidants with documented use in cosmetic products. A standard ROS assay was validated and applied to screen the photoreactivity of the natural phenolic antioxidants caffeic acid, ferulic acid, p-coumaric acid, 3,4-dihydroxyphenylacetic acid (DOPAC), and rutin. The phototoxicity potential was determined by using a human keratinocyte cell line (HaCaT), based on the 3T3 Neutral Red Uptake phototoxicity test. Although all studied phenolic antioxidants absorbed UV/Vis radiation in the range of 290 to 700 nm, only DOPAC was able to generate singlet oxygen. The generation of reactive oxygen species is an early-stage chemical reaction as part of the phototoxicity mechanism. Yet, none of the studied compounds decreased the viability of keratinocytes after irradiation, leading to the conclusion that they do not have phototoxic potential. The data obtained with this work suggests that these compounds are safe when incorporated in cosmetic products.     

Photoreactivity of triazolopyridinones, including the drug trazodone, in aqueous solution

Irradiation of triazolo[4,3-a]pyridin-3-ones at 310 nm has been investigated in water/acetonitrile (7%). Cis-cisoid-fused cyclobutanes are generally obtained. Cage products are found starting from derivatives bearing (piperazin-1-yl)aryl moiety under dilute conditions (10⁻³ M). Two different routes appear to be involved in the formation of the observed photoproducts. A plausible mechanistic explanation is reported.     

三种不同晶型二氧化钛的制备及光催化性能研究

分别以Ti(SO₄)₂和TiCl₄为原料,通过水热pH值的控制,批量制备了片状的锐钛矿(AT)、棒状的金红石(RT)和菱形的板钛矿型(BT)TiO₂.其中,AT具有最小的晶粒尺寸(约10nm),其次为RT(30—50nm),而BT具有最大的晶粒尺寸(50—70nm).固体漫反射显示出AT、BT和RT对光响应的阀值分别为375nm、385nm和415nm.其中,AT在紫外区显示出最强的光吸收能力.以阴离子活性染料X3B为目标分子的光催化降解实验结果显示,3种催化剂的光活性次序为AT>RT>BT,这与它们对X3B的吸附能力一致.文章对这产生TiO₂光活性差异的原因进行了讨论.     

焙烧的P-25 TiO2微结构特性和光催化活性

光催化氧化能把有机污染物完全转化为二氧化碳和水,被认是有广泛应用前景的水处理方法[1,2]．但是,这一方法真正在污水处理中实际应用,有许多问题仍待解决,其中光催化剂的活性和稳定性需要进一步改善．研究最多的光催化剂是TiO2,影响其催化活性的因素很多[3,4],本工作用XRD、TEM、BET研究了烧结的P－25TiO2微结构特征,并用苯酚光催化降解作探针反应,得到了很有意义的相关信息．1材料和方法1．1催化剂商品P－25TiO2是从Degussa公司购买．样品分别经不同温度和时间焙烧,具体条件见表1．1．2催化剂表征XRD用于测定样品品相…     

Excitation Wavelength-Dependent Fluorescence of a Lanthanide Organic Metal Halide Cluster for Anti-Counterfeiting Applications

The achievement of significant photoluminescence (PL) in lanthanide ions (Ln³⁺) has primarily relied on host sensitization, where energy is transferred from the excited host material to the Ln³⁺ ions. However, this luminous mechanism involves only one optical antenna, namely the host material, which limits the accessibility of excitation wavelength-dependent (Ex-De) PL. Consequently, the wider application of Ln³⁺ ions in light-emitting devices is hindered. In this study, we present an organic–inorganic compound, (DMA)₄LnCl₇ (DMA⁺=[CH₃NH₂CH₃]⁺, Ln³⁺=Ce³⁺, Tb³⁺), which serves as an independent host lattice material for efficient Ex-De emission by doping it with trivalent antimony (Sb³⁺). The pristine (DMA)₄LnCl₇ compounds exhibit high luminescence, maintaining the characteristic sharp emission bands of Ln³⁺ and demonstrating a high PL quantum yield of 90–100 %. Upon Sb³⁺ doping, the compound exhibits noticeable Ex-De emission with switchable colors. Through a detailed spectral study, we observe that the prominent energy transfer process observed in traditional host-sensitized systems is absent in these materials. Instead, they exhibit two independent emission centers from Ln³⁺ and Sb³⁺, each displaying distinct features in luminous color and radiative lifetime. These findings open up new possibilities for designing Ex-De emitters based on Ln³⁺ ions.     

Photoreactivity of the nonsteroidal anti-inflammatory 2-arylpropionic acids with photosensitizing side effects.

The photoreactivity of the nonsteroidal anti-inflammatory 2-arylpropionic acids benoxaprofen, carprofen, naproxen, ketoprofen, tiaprofenic acid, and suprofen is reviewed with special emphasis on fundamental photophysical and photochemical properties. The absorption and emission properties of the excited states of these drugs as well as their main photodegradation routes are summarized. The photochemical mechanisms are discussed on the basis of product studies and detection of short-lived intermediates by means of laser flash photolysis. After dealing with the unimolecular processes, attention is focused on the photosensitized reactions of key biomolecules, such as lipids, proteins or nucleic acids. Finally, a short section on the photobiological effects on simple biological models is also included. Although some earlier citations are included, the literature coverage is in general limited to the last decade.     

Photoreactivity of UV-b damage in bacteriophage phi X174 DNA

Abstract— The fraction of biological damage in isolated single-strand and double-strand forms of bac-teriophage DNA resulting from pyrimidine dimers following exposure to germicidal UV (254 nm) and UV-B (280-320. nm) radiation has been compared. Radiation from a Westinghouse FS-40 sunlamp filtered through a cellulose acetate sheet was used as the UV-B radiation source. Biological damage from pyrimidine dimers was determined by measuring the survival of the viral DNA with and without photoreactivation, an enzymatic process specific for repair of pyrimidine dimers. The same fraction of biological damage in the single strand and double–strand forms of φX174 DNA is repairable by photo-reactivation following exposures to germicidal UV and UV-B radiation.