Kinetics Study on Reaction of Atenolol with Singlet Oxygen by Directly Monitoring the 1O2 Phosphorescence

The pharmaceutically active compound atenolol, a kind of $\beta$-blockers, may result in adverse effects both for human health and ecosystems if it is excreted to the surface water resources. To effectively remove atenolol in the environment, both direct and indirect photodegradation, driven by sunlight play an important role. Among indirect photodegradation, singlet oxygen (¹O₂), as a pivotal reactive species, is likely to determine the fates of atenolol. Nevertheless, the kinetic information on the reaction of atenolol with singlet oxygen has not been well investigated and the reaction rate constant is still ambiguous. Herein, the reaction rate constant of atenolol with singlet oxygen is investigated directly through observing the decay of the ¹O₂ phosphorescence at 1270 nm. It is determined that the reaction rate constant between atenolol and ¹O₂ is 7.0×10⁵ (mol/L)$^{-1}\cdot$s^-1 in D₂O, 8.0×10⁶ (mol/L)$^{-1}\cdot$s^-1 in acetonitrile, and 8.4×10⁵ (mol/L)$^{-1}\cdot$s^-1 in EtOH, respectively. Furthermore, the solvent effects on the title reaction were also investigated. It is revealed that the solvents with strong polarity and weak hydrogen donating ability are suitable to achieve high rate constant values. These kinetics information on the reaction of atenolol with singlet oxygen may provide fundamental knowledge to the indirect photodegradation of $\beta$-blockers.     

Fluoroquinolone Antimicrobials: Singlet Oxygen, Superoxide and Phototoxicity

The fluoroquinolone antibacterial agents possess photo-sensitizing properties that lead to phototoxic responses in both human and animal subjects. The phototoxicity order reported in humans is: fleroxacin > lomefloxacin, pefloxacin > ciprofloxacin ? enoxacin, norfloxacin and ofloxacin. Studies both in vivo and in vitro have related this phototoxicity to the generation of reactive oxygen species including hydrogen peroxide and the hydroxyl radical. We determined the quantum yields of singlet oxygen generation (φ_Δ,) by detection of the singlet oxygen (¹O₂) luminescence at 1270 tun for several fluoroquinolones, naphthyridines and other structurally related compounds. All the fluoroquinolones examined have low φ_Δ values ranging from 0.06 to 0.09 in phosphate buffer at pD 7.5. We also determined the ¹O₂ quenching constants for these compounds and their values were on the order of 10⁶M^?1 s¹, except for lomefloxacin whose rate constant was 1.8 × 10⁷M^?1 s^?1. The φ_Δ values were significantly decreased in a solvent of lower polarity such as methanol (0.007 ≤φ_Δ≤ 0.02). The production of ¹O₂ by these antibiotics did not correlate with the order reported for their phototoxicity. We also measured the photogeneration (λ > 300 nm) of superoxide by these antibacterials in dimethylsulfoxide using electron paramagnetic resonance and the spin trap 5,5-dimethyl-l-pyrroiine N-oxide. Although there is not a one-to-one correspondence between the relative rates of superoxide generation and the phototoxicity ranking of the fluoroquinolones, the more phototoxic compounds tended to produce superoxide at a faster rate. Nevertheless, the magnitudes of the observed differences do not appear sufficient to explain the range of fluoroquinolone phototoxicity potencies in human and animal subjects in general and the high activity of fleroxacin and lomefloxacin in particular. For these latter drugs the photoinduced loss of the F₈ atom as fluoride and the concomitant generation of a highly reactive carbene at C-8 provide a more plausible mechanism for their potent phototoxic and photocarcinogenic properties.     

Photolysis of ozone in the ultraviolet region. Reactions of O(1D), O2(1Δg) and O≠2

Reactions of O(¹D) and O₂(¹Δ_g) with ozone have been observed time resolved by the detection of the product O³P) and their rate constants have been determined. It is found that vibrationally excited molecular oxygen, O^≠₂, also produces O(³P) in reaction with ozone. These observations are supported by the results of quantum yield determinations of the ozone decomposition in UV-photolysis.     

溶剂极性对微波辐射老化制备前驱体及CuO/ZnO/Al2O3催化剂结构的影响

在制备CuO/ZnO/Al2O3催化剂的老化过程中,采用微波辐射老化技术,着重研究了溶剂极性对前躯体物相组成,烧后CuO/ZnO/Al2O3催化剂结构及其在浆态床合成甲醇工艺中催化性能的影响。通过XRD、DTG、H2-TPR,FTIR、HR-TEM和XPS对前驱体及催化剂表征表明,沉淀母液在微波辐射条件下进行老化,溶剂的极性对前躯体物相组成及催化剂结构影响显著。随着溶剂极性的增大,Zn2+/Cu2+取代Cu2(CO3)(OH)2/Zn5(CO3)2(OH)6中Cu2+/Zn2+的取代反应增强,使得前躯体中(Cu,Zn)5(CO3)2(OH)6和(Cu,Zn)2(CO3)(OH)2物相的含量增多,结晶度提高,导致烧后CuO/ZnO/Al2O3催化剂中CuO-ZnO协同作用增强,且CuO晶粒减小,表面Cu含量增加,催化剂活性和稳定性提高。水溶剂的极性最大,制备的催化剂活性和稳定性最好,甲醇的时空收率(STY)和平均失活率分别为320 mg.g-1.h-1和0.11%.d-1。     

Oxidation of Chiral 1,4-Cyclohexadienes: A Comparison of Chemically and Photochemically Generated Singlet Oxygen1O2(1Δg)

Chiral alkyl-substituted 2,5-cyclohexadiene-l-carboxyIic acids la-c have been oxidized in water and in methanol with singlet oxygen, ¹O₂ (¹Δ_g), generated either photochemically or chemically from the catalytic system hydrogen peroxide/sodium molybdate. These methods were compared in terms of chemo-, regio- and diastereoselec-tivities and the chemical (k_T) and physical (k_q) quenching rate constants of ¹O₂ were determined. The ratio of the cis and trans isomers of the hydroperoxides 2a-c is not influenced by the source of ¹O₂ but, on the other hand, it depends slightly on the solvent and greatly on the steric hindrance of the substituents linked to the chiral carbon. The results may be interpreted on the basis of the successive formation of an exciplex and a perepoxide that evolves either by giving the final allylic hydroperoxide or by dissociating into the starting substrate and singlet or triplet oxygen.     

An organic-inorganic polymer with Dawson-type polyoxometalates as building blocks: synthesis, characterization and crystal structure of [{Pr(DMF)6} {Pr(DMF)7}(P2W18O62)] n

Abstrtact  An organic-inorganic polymer of [Pr(DMF)₆Pr(DMF)₇(P₂W₁₈O₆₂)] _n has been synthesized in acetonitrile-water (5 : 2, volume ratio) mixed solvent. Single-crystal X-ray structural analysis indicates that the title compound crystallizes in a monoclinic lattice, P2₁/C, with a = 1.8574(4), b=2.3907(5), c=2.4222(5) nm, β=99.48(3)°, Z = 4, ∨=10.609(4) nm³, D _c =3.501 Mg/m³, F(000)=9972, R₁=0.0654 and wR ₂= 0.1098. The result of crystal structure analysis reveals that Pr³⁺(1) complex ion is eight-coordinated with a distorted bicapped trigonal prismatic environment, which is combined with the heteropolyanion by terminal oxygen atom, whereas Pr³⁺(2) complex ion is also eight-coordinated with a distorted square antiprismatic environment, which is linked to the heteropolyanion by terminal oxygen atom. Adjacent structure units of [Pr(DMF)₆Pr(DMF)₇(P₂W₁₈O₆₂)] are bridged through W-O-Pr1-O-W links to form an unprecedented one-dimensional zigzag linear chain by alternate polyanions and cationic units in the polymer. Thermal analysis reveals that the framework of the title polyanion decomposes at 613.8°C.     

Possible production of O2(1Δg) and O2(1Σ+g) in the reaction of NO with O3

High-resolution spectra of the NO₂ continuum emission produced from the reaction NO + O₃ → NO₂ + O₂ have been investigated to detect any possible emission from O₂(¹Δ_g) at 1270 nm or O₂(¹Σ⁺_g) at 762 nm. The photolysis of O₃/O₂ mixtures at 253.7 nm, which produces both states of O₂ with known quantum efficiency, has been used as an internal standard. From the results it is concluded that less than 1/300 and 1/200 of the NO + O₃ reactive collissions result in production of O₂(¹Δ_g) or O₂(¹Σ⁺_g), respectively, at room temperature.     

[Pt2(P2O4H2)4]4-和[Pt2(P2O4CH4)4]4-基态和激发态性质的理论研究

采用从头计算MP2和CIS方法分别优化等电子双核d⁸配合物[Pt₂(P₂O₄H₂)₄]^4-和[Pt₂(P₂O₄CH₄)₄]^4-的基态和激发态结构。结果表明基态Pt-Pt距离分别为0.290 5和0.298 7 nm，与实验的0.292 5和0.298 0 nm符合。NBO计算的Pt-Pt键级以及Pt原子间伸缩振动说明Pt-Pt相互作用具有吸引本质。CIS计算揭示电子激发到Pt-Pt的σ(p_z)成键轨道使得相互作用增强。保持激发态几何，含时密度泛函理论(TD-DFT)计算的溶液发射分别为449和475 nm，与实验值512和510 nm接近。     

Eu(C10H9N2O4)(C10H8N2O4)(H2O)3]•0.5bipy•3H2O配合物的合成、晶体结构及荧光性质

在水-乙醇混合体系中, 以2-羰基丙酸水杨酰腙(C₁₀H₁₀N₂O₄)、2,2-联吡啶(C₁₀H₈N₂, 简写bipy)与Eu(NO₃)₃•4H₂O反应, 首次培养出黄色单晶[Eu(C₁₀H₉N₂O₄)(C₁₀H₈N₂O₄)(H₂O)₃]•0.5bipy•3H₂O. 该晶体属三斜晶系, 空间群为P-1, 晶胞参数a＝0.93392(16) nm, b＝1.3100(2) nm, c＝1.3895(2) nm, α＝97.205(3)°, β＝105.411(2)°, γ＝106.364(2)°, V＝15.35(2) nm³, Z＝2, μ＝2.118 mm^－1, D_c＝1.686 Mg/m³, F(000)＝786, R＝0.0116, wR＝0.0507, GOF＝0.995. 晶体测试结果表明, 该单晶结构为铕的9配位配合物, 两个2-羰基丙酸水杨酰腙分别以负一价和负二价酮式和三个水分子同时参与配位; 每个2-羰基丙酸水杨酰腙中的羧基氧、酰胺基中的羰基氧和C＝N中的氮与Eu^3＋配位, 形成两个共边的稳定五元环, 另三个配位原子则分别来自三个水分子中的氧原子, 该配合物在空间呈扭曲的单帽四方反棱柱, 而在不对称单位中还有游离的一个2,2-联吡啶分子和三个水分子, 这些游离分子与配位分子之间存在大量分子内和分子间氢键, 整个分子在空间呈三维网状结构. 发光性能测试表明该配合物具有很好的荧光性质.     

Influence of Solvent Polarity and Proticity on the Photochemical Properties of Norfloxacin

Abstract— The fluoroquinolone antibacterial norfloxacin (NF) is a moderate photosensitizer of singlet molecular oxygen (¹O₂). We have studied photosensitization by NF as a function of medium polarity and proticity in solvent mixtures. We have used 1,4-dioxane and propylene carbonate mixtures to keep proticity constant while modulating polarity, and water/D₂O and ethylene carbonate mixtures to alter proticity without large changes in polarity. The absorption spectrum of NF was little affected by solvent changes, as compared to the fluorescence spectrum that exhibited as much as a 50 nm blue-shift, e.g. 1,4-dioxane versus D₂O. The quantum yield of NF fluorescence saturated at an almost 10 times higher value (?0.14) when proticity was increased by added water, up to 0.2 mol fraction, to ethylene carbonate. Less pronounced, the increasing polarity in 1,4-dioxane/propylene carbonate mixtures affected the fluorescence yield much less. Norfloxacin produces ¹O₂ and is able to quench ¹O₂. The rate constant for ¹O₂ quenching is 4.5 × 107 M^?1 s^?1 in propylene carbonate but decreases ca four times in D₂O. The quantum yield of ¹O₂ photogeneration was also up to five times higher in solvents that were both protic and polar than vice versa. Our data show that NF is more photochemically active in an environment that is both protic and polar. This suggests the involvement of polar excited state(s) and possible proton/hydrogen transfer during photoexcitation. Similar processes may initiate the phototoxic response reported in some patients treated with the fluoroquinolone drugs. The phototoxicity of NF and other fluoroquinolone antibiotics may strongly depend on their localization in hydrophilic or hydrophobic cell/tissue regions.     

立方Nd2O3上过氧物种光诱导生成的18O同位素示踪考察

采用原位显微Raman光谱和¹⁸O同位素示踪技术,以325 nm激光为激发光源,对立方Nd₂O₃上过氧物种的光诱导生成过程进行了详细表征,进一步证实过氧源于分子氧对晶格氧的氧化反应. 结果还表明,325 nm激光在室温下即可诱导过氧的生成,在实验条件下,生成的过氧物种可与Nd₂O₃的晶格氧发生快速的氧交换反应,位于Nd₂O₃体相的晶格氧也可迁移至样品表层进而参与过氧的生成. 325 nm激光照射有助于促进晶格氧的迁移以及晶格氧与分子氧之间的氧交换反应.     

Photooxygenations par transfert d'electron sensibilisees par le dicyano-9,10 anthracene. Role du solvant et formation d'oxygene singulet.

Photooxygenation of naphtalenic compounds sensitized by electron acceptors like 9,10 dicyanoanthracene (DCA) is shown to proceed by two distinct ways depending on the solvent polarity. In a polar solvent superoxide ion (O₂^-.) as well as singlet oxygen (¹O₂★) are involved while in a non polar solvent only singlet oxygen is produced.     

PO43-掺杂Bi2O2CO3/Bi0的制备及其可见光催化性能

构建氧空位以及附着金属单质Bi(Bi⁰)是增强半导体材料光吸收性能、促进半导体光生载流子分离的有效方法。通过简单的共沉淀法及氢气热还原成功制备了PO₄^3-掺杂Bi₂O₂CO₃附着Bi⁰(Bi-P-BOC)的可见光催化剂,并对其在可见光下催化降解氧氟沙星(OFX)的性能及机理进行了研究。材料表征结果表明BOC随着PO₄^3-的均匀掺杂,可见光吸收能力增强,表面缺陷增多,比表面积增大。而随着氢气热还原,BOC表面形成 Bi⁰的同时也原位构建了大量的氧空位。可见光催化性能测试表明,Bi-P-BOC可以在180 min内降解约85%的OFX,降解速率为0.013 0 min^-1,是BOC降解速率的8倍。Bi-P-BOC光催化降解机理表明其具有更好的可见光吸收能力,Bi⁰以及氧空位的存在促进了光生载流子的分离,h+是其光催化降解过程中的主要的活性氧物种(ROS),此外,¹O₂和·O₂^-也对降解有一定贡献。     

C2O(X3Σ−): absolute reaction rates measured by laser induced fluoresence

Absolute rate constants are reported for reactions of C₂O($\text{X}\text{?}$³Σ^?) under pseudo-first-order decay conditions. C₂O is generated by laser photodissociation of C₃O₂ at 266 nm, and detected by dye-laser induced fluorescence on the $\text{A}\text{?}$³Π_i-$\text{X}\text{?}$³Σ^? transition. Rate constants of (433 ± 12), (3.30 ± 0.12) and (1.12 ± 0.05) × 10^?13 cm³ molecule^?1 s^?1 are reported for reactions with NO, O₂ and isobutene. The NO value is approximate due to an apparent dark reaction between NO and C₃O₂. Upper limits of 1 × 10^?14 cm³ molecule^?1 s^?1 are reported for reactions with H₂, CO₂, C₃H₂ and C₂H₄. The C₂O + C₃O₂ reaction does not follow pseudo-first-order decay kinetics. Two explanations are proposed to explain this observation. Results are compared with previous relative rate measurements and are discussed in terms of their relevance to combustion chemistry.     

EPR and Spectrophotometric Studies of Free Radicals (O2°−, °OH, BPD-MA°−) and Singlet Oxygen (1O2) Generated by Irradiation of Benzoporphyrin Derivative Monoacid Ring A

Abstract— Benzoporphyrin derivative monoacid ring A (BPD-MA), a chlorin-type molecule, is a new photosensitizer currently in phase II clinical trials for the treatment by pho-todynamic therapy of cancerous lesions, psoriasis and pathologic neovascularization. The photochemistry (type I and/or II) of BPD-MA has been studied in homogeneous solution and in aqueous dispersions of unilamellar liposomes of dipalmitoylphosphatidylcholine (DPPC) using electron paramagnetic resonance and spectrophotometric methods. When oxygen-saturated solutions of BPD-MA were illuminated with 690 nm light, singlet oxygen (¹O₂), superoxide anion radical (O₂^?), hydroxyl radical (OH) and hydrogen peroxide (H₂O₂) were formed. The BPD-MA generates ¹O₂ with a quantum yield of ca 0.81 in ethanolic solution. The quantum yield does not change upon incorporation of BPD-MA into liposomes of DPPC. The superoxide anion radical was generated by the BPD-MA anion radical (BPD-MA^?) via electron transfer to oxygen, and this process was significantly enhanced by the presence of electron donors. The rate of production of 0₂ was also dependent on the concentration of BPD-MA used (3-100 μM). The quantum yield of O₂^?was found to be 0.011 and 0.025 in aqueous solution and DPPC liposomes, respectively. Moreover, O₂^_upon dis-proportionation can generate H₂O₂ and ultimately the highly reactive OH via the Fenton reaction. In anaerobic homogeneous solution, BPD-MA^?was predominantly photoproduced via the self-electron transfer between the excited- and ground-state species. The presence of an electron donor significantly promotes the reduced form of BPD-MA. These findings suggest that the photodynamic action of BPD-MA may proceed via both type I and type II mechanisms.     

双核锌配位化合物[Zn(C15H8O7S)(DMSO)]2•H2O的合成和晶体结构及光致发光性能研究

以白杨素为先导化合物, 对其进行磺化, 磺化衍生物与锌络合, 在含水10%的二甲基亚砜(DMSO)溶液中重结晶, 得双核锌配位化合物[Zn(C₁₅H₈O₇S)(DMSO)]₂•H₂O. 采用IR, ¹H NMR, DSC-TGA, 元素分析和X射线单晶衍射法对标题化合物进行了表征和晶体结构测定. 标题化合物属正交晶系, 空间群Pbcn, Zn(II)的配位数为5, 配位原子均为氧原子, 每个五配位的锌都具有四方锥型的配位构型, 被2个配体5-羟基氧负离子-7-羟基黄酮-6-磺酸根的5-羟基氧负离子桥联, 形成了一个中心Zn₂O₂的菱形平面. 水溶性白杨素黄酮配体与Zn(II)通过氢键、π-π堆积和配位作用自组装形成了一个三维结构的超分子化合物. 差示扫描量热分析(DSC-TGA)结果表明,标题化合物配体骨架分解温度为518.26 ℃. 同时, 标题化合物固体具有较强的光致发光现象, 在λ_ex＝423 nm条件下可发出λ_em＝488 nm的黄色荧光, 并对其发光机制进行了探讨.     

INFLUENCE OF THE PEPTIDE BOND ON THE SINGLET MOLECULAR OXYGEN-MEDIATED (O2[g]) PHOTOOXIDATION OF HISTIDINE and METHIONINE DIPEPTIDES. A KINETIC STUDY

The dye-sensitized photooxidation of l -histidine (His) and l -methionine (Met) and their simplest dipeptides with glycine (Gly) (His-Gly, Gly-His, Gly-Met) and Met-methyl ester (Met-ME) mediated by singlet molecular oxygen (O₂[_g]) was studied. The overall rate constants in acetonitrile-H₂O (K_t) for O₂(¹_g) quenching were measured by time-resolved phosphorescence detection. In H₂O a competitive kinetic method was employed. In both solvents the reactive rate constants (K_t,) were determined to discriminate between the overall and physical contributions to the quenching. The kinetic and mechanistic aspects of the interaction are discussed. For His-Gly, the peptide bond has practically no effect on the kinetics of photooxidation. For Gly-His the overall rate constant is much higher than that for His and His-Gly, in both H₂O and acetonitrile-H₂O. The main contribution to k₁ (for Gly-His) is the physical quenching of O₂(¹_g)- In water the k_t/k_r ratio for free His and His-Gly is 1.0, reaching a value of 2.0 in the organic solvent-H₂O mixture. The rates of-NH₂ loss upon sensitized photooxidation in all cases parallel the trend of k_r values. The main results for the His series indicate that: (1) a polar environment favors autoprotection (i.e. an increase in the contribution of physical quenching) against photodynamic effects; (2) only the rate constant for reactive interaction with O₂[_g] does not depend on the location of the peptide bond involving His. For Met derivatives the k_t, values are higher in both solvents than that for free Met. Only for the free amino acid in H₂O is the interaction with O₂(¹_g) totally reactive. For Gly-Met and Met-ME the physical quenching prevails: k_t, is, in both solvents, about one order of magnitude higher than k_r. According to our results on -NH₂ loss and on the basis of previous investigations by others, the photooxidative products distribution in the Met series indicates that Gly-Met yields only dehydroMet, whereas Met and Met-ME produce a mixture of Met-sulfoxide and the Met-dehydro compound.     

The crystal structure of NaAs4O6Br

The crystal structure of NaAs₄O₆Br [a = 5.237(1), B = 8.043(1), C = 18.978(2) Å; space group Pmcn-D¹⁶_2h; Z = 4] was solved by a direct method strategy and was refined to an R value of 0.038 for 1515 intensities and 68 variables. The structure is characterized by neutrally charged and slightly waved As₂O₃ sheets arranged parallel to (001). These sheets are combined by the Na and Br atoms. The Na atom is coordinated to nine oxygen atoms and one bromine atom and the Br atom is coordinated to six arsenic atoms and one sodium atom. The compound NaAs₄O₆Br was synthesized by thermal treatment of NaBr and As₂O₃ in methanol solution [400(5) K, saturation vapor pressure].     

PO43-掺杂Bi2O2CO3/Bi0的制备及其可见光催化性能

构建氧空位以及附着金属单质Bi(Bi⁰)是增强半导体材料光吸收性能、促进半导体光生载流子分离的有效方法。通过简单的共沉淀法及氢气热还原成功制备了PO₄^3-掺杂Bi₂O₂CO₃附着Bi⁰(Bi-P-BOC)的可见光催化剂,并对其在可见光下催化降解氧氟沙星(OFX)的性能及机理进行了研究。材料表征结果表明BOC随着PO₄^3-的均匀掺杂,可见光吸收能力增强,表面缺陷增多,比表面积增大。而随着氢气热还原,BOC表面形成Bi⁰的同时也原位构建了大量的氧空位。可见光催化性能测试表明,Bi-P-BOC可以在180 min内降解约85%的OFX,降解速率为0.013 0 min^-1,是BOC降解速率的8倍。Bi-P-BOC光催化降解机理表明其具有更好的可见光吸收能力,Bi⁰以及氧空位的存在促进了光生载流子的分离,h⁺是其...     

On the formation and stability of O− and O−2 radicals in type a zeolites and demonstration of cation interactions

Electron spin resonance studies show tha O^? is formed as the major paramagnetic oxygen species in γ-irradiated Ca₆-A zeolite followed by oxygen adsorption. This is a new method to generate this highly reactive catalytic intermediate. O^?₂ is formed in addition to O^? if oxygen is adsorbed prior to irradiation. In Na₁₂-A zeolite O^? is also seen but it transforms to O^?₂ in several hours. Thus O^? appears to be more stable in divalent exchanged zeolites. By electron spin echo modulation spectrometry interactions fo O^?₂ with Li⁺ have been detected which suggests that oxygen species locations in zeolites can be delineated.