铝酸钠溶液中超声诱致自由基的检测

文首次应用自由基捕获方法和电子顺磁共振技术(EPR),检测铝酸钠溶液在超声波空化作用下产生的羟自由基.本实验利用DMPO捕获羟自由基而生成寿命较长的DMPO-OH这一特性,分析了超声输出功率、超声处理时间等对DMPO-OH的自旋共振谱图中对称振动峰强弱的影响.实验结果表明:当超声输出功率达到或超过空化阈值,过饱和中等浓度铝酸钠溶液中水分子可裂解为羟自由基和氢原子自由基;同时自由基的产量与超声输出功率、超声作用时间以及溶液浓度有关.     

喹喔啉氮氧自由基-Zn(Ⅱ)配合物的合成、结构和磁性质

采用喹喔啉基取代的氮氧自由基NITQ与锌(Ⅱ)离子进行配位,得到了1个单核的双自旋配合物[Zn(acac)₂(NITQ)₂]·2CH₂Cl₂(其中acac=乙酰丙酮阴离子,NITQ=2-(2'-喹喔啉基)-4,4,5,5-四甲基咪唑啉-3-氧化-1-氧基自由基)。 X射线单晶衍射分析结果表明,两个NITQ自由基作为单齿配体分别与Zn(acac)₂配位,形成八面体构型的双自旋配合物。 变温磁化率研究表明,NITQ自由基间存在铁磁相互作用,其居里常数C=0.7242 cm³·K/mol,外斯常数θ=0.5958 K。     

微量热法和荧光显微法研究CdTe量子点敏化的纳米TiO2对大肠杆菌的抗菌活性及细胞损伤机制

通过水热合成法和自组装方法分别合成了CdTe(QDs)量子点与CdTe(QDs)敏化的纳米TiO₂复合物,并将CdTe(QDs)/TiO₂与TiO₂均配成浓度为1×10^-2 mol/L的悬浮液. 取一小环大肠杆菌(E. coli)的营养肉汤培养基至5 mL LB培养基中,则E. coli的浓度配成大约1×10⁶ cell/mL的悬浮液以作备用. 在37.0 ℃条件下,利用LKB-2277生物活性检测仪并采用停流法进行检测,研究了CdTe(QDs)/TiO₂对E. coli的抗菌行为. 通过测定和分析产热功率-时间曲线,获得细胞生长速率常数(k)、最大产热功率(P_m)、传代时间(t_G)以及抑制率(I)等热动力学常数. 结果表明：在0～4.0×10^-5 mol·L^-1浓度范围内,生长速率常数(k)和抑制率(I)均与浓度成一定的线性关系. 生长速率常数(k)和最大产热功率(P_m)随着CdTe(QDs)/TiO₂的浓度增加而下降,而传代时间(t_G)和抑制率(I)随着CdTe(QDs)/TiO₂ 的浓度增加而增加;其中,CdTe(QDs)/TiO₂的生长速率常数斜率(0.0001)小于TiO₂的生长速率常数斜率(0.0005),可以初步判断CdTe(QDs)/TiO₂对E. coli的代谢影响较TiO₂要大. TiO₂和CdTe(QDs)/TiO₂对E. coli代谢活性均有一定的抑制作用. 在相同浓度时,CdTe(QDs)/TiO₂的抑制率斜率(0.84)大于TiO₂的抑制率斜率(0.26),进一步说明了CdTe(QDs)/TiO₂相比TiO₂具有对E. coli 更强的细菌抑制作用;结合Hadama荧光显微方法,进一步佐证了CdTe(QDs)/TiO₂相对于TiO₂表面结构的改变可能是导致其抗菌效果较好的主要原因之一. 从而为深入揭示纳米材料影响微生物生长代谢过程的热动力学规律和细胞损伤机制提供理论支撑.     

乙醇-苯乙烯体系的辐解及α-羟乙基自由基反应动力学

γ射线辐照乙醇, 通过苯乙烯抑制其辐解产物的研究, 证明在乙醇介质中α-羟乙基自由基只进行重合反应, 而无歧化反应; 苯乙烯可与α-羟乙基自由基反应, 其竞争反应为Sl+CH_3 CHOH→P 2CH_3CHOH→(CH_3CHOH)_2求得动力学方程为G'=G_0 k_6/2(k_7) 1/2 (G'/Dk')[Sl] G_0为纯乙醇γ射线辐照时2、3-丁二醇的产额, G_0=2.1, k_6/(k7)~(1/2)=0.53. 假定k_7为扩散反应速率常数, 则α-羟乙基自由基与丰乙烯加成反应的速率常数为k_6=4.0×10~4 L·mol~(-1)·s~(-1).     

乙醇-苯乙烯体系的辐解及α-羟乙基自由基反应动力学

γ射线辐照乙醇,通过苯乙烯抑制其辐解产物的研究,证明在乙醇介质中α-羟乙基自由基只进行重合反应,而无歧化反应;苯乙烯可与α-羟乙基自由基反应,其竞争反应为Sl+CH_3 CHOH→P 2CH_3CHOH→(CH_3CHOH)_2求得动力学方程为G'=G_0 k_6/2(k_7) 1/2 (G'/Dk')[Sl] G_0为纯乙醇γ射线辐照时2、3-丁二醇的产额,G_0=2.1,k_6/(k7)~(1/2)=0.53.假定k_7为扩散反应速率常数,则α-羟乙基自由基与丰乙烯加成反应的速率常数为k_6=4.0×10~4 L.mol~(-1).s~(-1).     

臭氧提高纳米TiO2光催化活性的ESR分析

以5,5-二甲基-1-吡咯啉-N-氧化物(DMPO)为自由基捕获剂,分别以去离子水和二甲基亚砜(DMSO)为溶剂,利用电子自旋共振(ESR)方法对UV、O₃、TiO₂/O₃、TiO₂/UV/O₂、UV/O₃和TiO₂/UV/O₃这6种体系中形成的羟基自由基(·OH)和超氧阴离子自由基(·O₂^-)进行了检测,同时考察了反应时间、催化剂投量以及体系溶解氧对TiO₂/UV/O₃体系形成·OH和·O₂^-的影响.结果显示,在纳米TiO₂光催化体系中加入臭氧,能显著增加反应体系中·OH和·O₂^-自由基的生成量,6种体系中DMPO-·OH和DMPO-·O₂^-加合物的ESR波谱峰信号强度分别为:TiO₂/UV/O₃>TiO₂/UV/O₂>UV/O₃>UV>TiO₂/O₃>O₃和TiO₂/UV/O₃≈TiO₂/UV/O₂>TiO₂/O₃>UV>UV/O₃>O₃,在TiO₂/UV/O₃体系中成功监测到·O₃^-自由基的存在.     

Nd2O3/TiO2光催化剂的光生羟基自由基和光活性

以硝酸钕和钛酸四正丁酯作为前驱体,采用溶胶-凝胶法制备了Nd₂O₃/TiO₂纳米光催化剂,并通过XRD和BET等手段进行了表征.以对苯二甲酸作为探针分子,结合化学荧光技术研究了光催化剂表面羟基自由基的生成;并以甲基橙为光催化降解反应模型化合物,考察了光催化剂的活性.测定了甲基橙在TiO₂和Nd₂O₃/TiO₂(1.0%)光催化剂上的吸附常数.结果表明:Nd₂O₃掺杂使TiO₂的粒径减小,比表面积增大;羟基自由基的生成速率越大,催化剂的催化活性越高.Nd₂O₃掺杂有利于反应底物在催化剂表面的吸附,Nd₂O₃的最佳掺入量为Nd/Ti(摩尔比)=1.0%.     

超氧化物歧化酶对TiO2光催化损伤DNA的影响

以小牛胸腺DNA为对象, 在超氧化物歧化酶(superoxide dismutase, SOD)存在下, 研究了纳米二氧化钛(TiO₂)光催化对DNA损伤特性及SOD对TiO₂光催化损伤DNA的影响. 采用凝胶电泳和高效液相色谱(HPLC)分析法, 探讨了DNA的损伤程度. 运用生物标准样8-羟基脱氧鸟苷(8-hydroxy-2 -deoxyguanosine, 8-OHdG)为内标物并通过高效液相色谱-电喷雾离子化串联质谱联用技术(HPLC-ESI-MS/MS)对DNA损伤产物进行了跟踪分析, 采用过氧化物酶催化分光光度法及顺磁共振技术(ESR)跟踪测定TiO₂光催化DNA损伤过程中H₂O₂和氧化物种的变化, 探讨了DNA氧化损伤机理. 结果表明, 在实验条件下紫外光照(UV, λ＝200～275 nm), Dark/TiO₂和UV/TiO₂体系中, DNA氧化损伤程度为UV/TiO₂＞UV＞Dark/TiO₂. 光催化260 min DNA损伤99%, 反应动力学常数K＝7.82×10^－3 min^－1. 抗氧化剂SOD具有清除光催化体系中超氧自由基( )的能力, 可以抑制DNA的损伤, 反应动力学常数K＝2.27×10^－3 min^－1. 8-OHdG为DNA损伤中鸟嘌呤氧化的特异产物, UV及光催化体系对DNA损伤主要涉及 及羟基自由基(•OH)历程, 光催化体系对DNA损伤伴随有深度氧化(矿化)过程, 实验条件下12 h DNA矿化75.06%.     

通过扫描光电化学显微镜研究超分子光敏剂-二氧化钛薄膜系统的光诱导电子转移（英文）

在基于TiO₂的光阳极上枝接电荷转移通道仍然是太阳能到化学转换技术的一个迫切瓶颈。尽管进行了大量的尝试,但TiO₂作为有前途的光阳极材料仍然受到电荷传输动力学迟缓的影响。因此,一种组装策略涉及将金属卟啉基光敏剂分子(MP)轴向配位嫁接到表面改性的TiO₂纳米棒(TiO₂NRs)光阳极上,形成复合MP/TiO₂ NRs光电极。正如预期的那样,与单独的TiO₂NR和MPA/TiO₂NRs光电极相比,所得到的独特的MPB/TiO₂ NRs光电极具有明显提高的光电流密度。采用扫描光电化学显微镜(SPECM)和强度调制光电流光谱(IMPS)系统地评估了MP/TiO₂ NRs光电极的连续光激发电子转移(PET)动力学信息。通过数据拟合发现,在光照条件下,MPB/TiO₂ NRs的光电子转移速率(k_eff)常数比纯TiO₂ NRs高2.6倍...     

CF3CH2CH3+OH的反应机理及动力学性质的理论研究

采用密度泛函理论BB1K/6-31+G(d,p)计算了反应CF₃CH₂CH₃+OH各反应通道上驻点的稳定结构和振动频率, 并分别在BMC-CCSD, MC-QCISD和G3(MP2)水平上进行了单点能校正. 运用变分过渡态理论, 在BMC-CCSD//BB1K, MC-QCISD//BB1K, G3(MP2)//BB1K以及BB1K水平上计算了各反应通道的速率常数, 讨论了-CH₂和-CH₃基团上H提取通道对总反应的贡献, 并与已有实验和理论结果进行了对比. 计算结果表明, BMC-CCSD水平上的速率常数与实验测量值符合得很好, 进而给出了该水平上反应在200~1000 K温度范围内速率常数k(cm³?molecule^-1?s^-1)的三参数表达式: k=1.90×10^-21T^3.21exp(-292.62/T).     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS—II. SPIN TRAPPING OF PHOTOLYSIS PRODUCTS FROM SULFANILAMIDE AND 4-AMINOBENZOIC ACID USING 5,5-DIMETHYL-1-PYRROLINE-1-OXIDE

Abstract— The photodecomposition of sulfanilamide, 4-aminobenzoic acid and related analogs in aqueous solution has been studied with the aid of spin traps 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) and CH₃NO₂ as well as by direct electron spin resonance techniques. The NH₂ radical was trapped by DMPO during the photolysis of aqueous solutions of sulfanilamide with a Xe arc lamp. Studies with [¹⁵N¹]-sulfanilamide indicated that the NH₂ radical was generated by homolytic fission of the sulfur-nitrogen bond. Under the same conditions DMPO trapped the H and SO⁻₃ radicals during photolysis of sulfanic acid. Direct photolysis of sulfanilamide, sulfanilic acid and Na₂SO₃ in the absence of any spin trap yielded the SO⁻³ radical. Photolysis of 4-aminobenzoic acid at pH 7 gave the H radical which was trapped by DMPO. At low pH values OH and C₆H₄COOH radicals were generated during the photolysis of 4-aminobenzoic acid. No e⁻_aq were trapped by CH₃NO₂ when acid (pH 4) and neutral aqueous solutions of sulfanilamide or 4-aminobenzoic acid were photoirradiated. The mechanism of formation of known photoproducts from the free radicals generated by sulfanilamide and 4-aminobenzoic acid during irradiation are discussed. The free radicals generated by these agents may play an important role in their phototoxic and photoallergic effects.     

Photocatalytic bleaching of p-nitrosodimethylaniline in TiO2 aqueous suspensions: A kinetic treatment involving some primary events photoinduced on the particle surface

The photocatalytic bleaching of p-nitrosodimethylaniline (P) has been investigated in aqueous suspensions of TiO₂. It was found that both charge carriers (hole and electron) were reactive to P to result in a bleaching. The roles of O₂ and several hole scavengers (HCOO⁻, EDTA, I⁻) have also been examined. A reaction mechanism has been proposed with consideration of several primary processes photoinduced on TiO₂ surface. The results of the kinetic analysis fit fairly well to those of the experiments. The rate constant (k^h_p) of the reaction between P and the adsorbed hydroxyl radical was estimated to be in the order 10¹⁰ M⁻¹ s⁻¹, which is in good agreement with that obtained from the homogeneous reaction of P with free OH radicals. Of particular interest is the pH dependence of the photobleaching rate. Around both pK_a of P and pH_ZPC of TiO₂, the photobleaching of P was steeply enhanced. This can be reasonably attributed to the mutual interaction (repulsion versus attraction) between P and TiO₂ particles in different pH ranges.     

A SPIN TRAPPING STUDY OF THE PHOTOCHEMISTRY OF 5,5-DIMETHYL-1-PYRROLINE N-OXIDE (DMPO)

The photochemistry of 5,5-dimethyl-l-pyrroline N -oxide (DMPO) has been studied in benzene, cyclohexane and aqueous buffer solutions (pH 7.4) by means of electron paramagnetic resonance (EPR) and the spin trapping technique. Ultraviolet irradiation of DMPO in aqueous buffer with unfiltered UV radiation from a Xe arc lamp results in photoionization of the spin trap and the generation of the DMPO cation radical, DMPO⁺. The aqueous electron, e_aq⁻, was trapped by DMPO and detected as the DMPO/H adduct. The DMPO⁺- reacted with the water to yield the DMPO/OH adduct. Ultraviolet irradiation of DMPO in nitrogen-saturated benzene gave an unidentified carbon-centered DMPO adduct that was replaced by hydroperoxyl and alkoxyl adducts of DMPO when oxygen was present. Experiments employing ¹⁷O₂ gas indicated that the oxygen in the DMPO alkoxyl adduct was derived from molecular oxygen. However, UV irradiation of DMPO in cyclohexane yielded the cyclohexyl and cyclohexyloxyl adducts of DMPO in nitrogen-saturated and air-saturated solutions, respectively. These observations suggest that in aprotic solvents UV irradiation of DMPO generates a carbon-centered radical (R⁻), derived from the trap itself, which in benzene reacts with oxygen to yield an alkoxyl radical (RO⁻), possibly via a peroxyl radical (ROO⁻) intermediate. In cyclohexane R⁻ abstracts a hydrogen atom from the solvent to yield the cyclohexyl radical in the absence of oxygen and the cyclohexyloxyl radical in the presence of oxygen. These findings indicate that when DMPO is used as a spin trap in studies employing short-wavelength UV radiation (λ < 300 nm) the photochemistry of DMPO cannot be ignored.     

乙酸钠、草酸钠、酒石酸钾在三氧化钨-水体系中光生自由基的研究

当分散在溶液中的TiO₂、znO、CdS、WO₃等多相体系受到光照时,固态的半导体物质吸收光子后会产生电子-空穴对,它们在半导体界面上与周围介质反应,可能以各种方式进行电荷转移而形成不同的活泼中间体,引起人们对发生在半导体粉末上的光化学过程的关注。     

PHOTOREDUCTION OF IRON(III)PORPHYRINS

Abstract— Ferrideuteroporphyrin in benzene, water or micelle solutions containing primary or secondary alcohols as well as in pure or basic 2-propanol solutions is clearly reduced to the ferrous state by continuous light irradiation in the Soret region. Quantum yields range between 4 × 10⁻⁴ and 3 × 10⁻² depending on the solvents used and on the coordination state of the ferric porphyrin. As inferred from laser pulse photolysis experiments, the primary chemical step appears to be the homolytic cleavage of the bond between the ferric ion and a coordinated alcoholate anion leading to the ferrous porphyrin and the alkoxy radical. This cleavage is found to occur within less than 50 ns. The alkoxy radical rearranges leading to the α-hydroxyalkyl radical which reacts with excess ferric porphyrin leading to further reduction. The reaction rate constant for the reaction of α-hydroxyisopropyl radicals is found to be k = (2.1 ± 0.3) × 10⁸ M ⁻¹ s⁻¹ in pure 2-propanol. As expected, this rate is greatly increased in basic 2-propanol where α-hydroxyisopropyl radicals deprotonate.     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS—X. A SPIN-TRAPPING AND DIRECT ELECTRON SPIN RESONANCE STUDY OF THE PHOTOCHEMICAL PATHWAYS OF DAUNOMYCIN AND ADRIAMYCIN

Abstract— Irradiation of daunomycin (or adriamycin) and the spin trap 5,5-dimethyl-l-pyrroline-1-oxide (DMPO) at 490 nm in the presence or in the absence of air generated the hydroxyl radical adduct (DMPO-OH). The observed DMPO-OH signal was not affected by the addition of hydroxyl radical scavengers (ethanol, formate), suggesting that direct trapping of the hydroxyl radical was not involved. The DMPO-OH signal was insensitive to superoxide dismutase and catalase, which ruled out the possibility of superoxide or H₂O₂ involvement. These findings demonstrate that daunomycin (or adriamycin) does not generate hydroxyl radicals or superoxide radical anions when subjected to 490-nm excitation. However, when daunomycin (or adriamycin) was irradiated at 310 nm DMPO adducts derived from two carbon-centered radicals, superoxide and the hydroxyl radical were detected. The superoxide adduct of DMPO was abolished by the addition of SOD, providing unequivocal evidence for the generation of the superoxide anion radical. The daunomycin semiquinone radical, observed upon 310-nm irradiation of daunomycin in the absence of DMPO, appears to be the precursor of the superoxide radical anion. One of the carbon-centered radicals trapped by DMPO exhibited a unique set of hyperfine parameters and was identified as an acyl radical. This suggests that the known photochemical deacylation of daunomycin occurs via a homolytic cleavage mechanism. The free radicals generated photolytically from adriamycin and daunomycin may be involved in the etiology of the skin ulceration and inflammation caused by these drugs. A knowledge of the dependence of these photogenerated radicals on the wavelength of excitation may be important in the development of adriamycin and daunomycin for photodynamic therapy.     

Radiation induced decomposition of tryptophan in the presence of oxygen

Tryptophan decomposition in oxygenated aqueous solutions in neutral media was investigated by gamma and pulsed electron irradiation. By using pulse radiolysis it was found that 27% of tryptophan OH-adducts eliminate water. Tryptophan neutral radical, Trp, thus formed reacts rapidly with O^-•₂, k(Trp^•+O^-•₂) = (4.5±0.7) × 10⁹M^-1s^-1. The remaining tryptophan OH-adducts react with oxygen to give peroxy radicals which may eliminate O^-•₂, produce _N-formylkynurenine and disproportionate yielding organic peroxides. Peroxy radicals derived from tryptophan H-adducts regenerate tryptophan by the elimination of HO^•₂, and recombine with TrpH(OH)OO^• radicals producing organic peroxides.     

CHLOROPHYLL PHOTOSENSITIZED ELECTRON TRANSFER IN PHOSPHOLIPID BILAYER VESICLE SYSTEMS: SECONDARY OXIDATION OF REDUCED VIOLOGEN ACCEPTORS BY Ru(NH3)63+

Abstract— The kinetics of the oxidation of a homologous series of 4,4'-di(n-alkyl)-bipyridinium (viologen) radicals by Ru(NH₃)₆³⁺ in vesicle suspensions was studied using laser flash photolysis. The viologen radicals were produced photochemically in the bilayer membrane phase of the vesicles by electron transfer from the triplet state of chlorophyll-α. At high concentrations of Ru(NH₃)₆³⁺, the rate of oxidation of the viologen radicals in the aqueous phase was limited by the rate at which the radicals diffused from the membrane to the aqueous phase. The exit rate constant decreased from 2 × 10⁵ s⁻¹ for the methyl viologen radical to 4 × 10³ s⁻¹ for the pentyl viologen radical. Both the exit rate constants and the calculated values for the equilibrium association constants of the viologen radicals were unexpectedly insensitive to the length of their alkyl substituents. This, as well as other data, suggests that the radicals that diffused into the aqueous phase tended to remain associated with the membrane-water interface.     

First steps in radiation-induced hydrogel synthesis: radical formation and oligomerization in dilute aqueous N-isopropylacrylamide solutions

The reactions of hydroxyl radical, hydrogen atom and hydrated electron intermediates of water radiolysis with N-isopropylacrylamide (NIPAAm) were studied by pulse radiolysis in dilute aqueous solutions. OH, H and e_aq⁻ react with NIPAAm with rate coefficient of (6.9±1.2)×10⁹, (6.6±1)×10⁹, and (1.0±0.2)×10¹⁰ mol⁻¹ dm³ s⁻¹. In OH and H radical addition to the double bond mainly -carboxyalkyl type radicals form, (OHCH₂CH^√C(N-i-C₃H₇)O and CH₃CH^√C(N-i-C₃H₇)O). In reaction of e_aq⁻ oxygen atom centered radical anion is produced (CH₂CHC^√(N-i-C₃H₇)O⁻), the anion undergoes reversible protonation with pK_a=8.7. There is also an irreversible protonation on the β-carbon atom that produces the same radical as forms in H atom reaction (CH₃CH^√C(N-i-C₃H₇)O). The -carboxyalkyl type radicals at low NIPAAm concentration (0.1–1 mmol dm⁻³) mainly disappear in self-termination reactions, 2k_t,m=8.4×10⁸ mol⁻¹ dm³ s⁻¹. At higher concentrations the decay curves reflect the competition of the self-termination and radical addition to monomer (propagation). The termination rate coefficient of oligomer radicals containing a few monomer units is 2k_t≈2×10⁸ mol⁻¹ dm³ s¹.     

ESR investigation into the effects of heat treatment and crystal structure on radicals produced over irradiated TiO2 powder

Electron spin resonance measurements were carried out at 77 K under irradiation for anatase TiO₂ powders treated by heating at various temperatures in the air. For the untreated powder photoproduced holes were trapped at the surface forming Ti⁴⁺O⁻Ti⁴⁺OH⁻ radicals, while, for the heated powder, they were trapped as Ti⁴⁺O²⁻Ti⁴⁺O⁻ radicals at the surface. Photoproduced electrons were trapped as Ti³⁺ at the desorption of surface hydroxyl groups and the change in the surface accompanied by the crystalline growth. No photoproduced radicals were detected for rutile TiO₂ powder, which may explain the low photocatalytic activity of this crystalline structure.