新型含硫化合物的荧光光谱及其光解机理

本工作合成了硫代α-萘甲酸-s-苯酯和硫代苯甲酸-s-苯并噻唑酯,对其光化学和光物理行为进行了研究。由于萘基和苯并噻唑基的引入,有效地增加了该类化合物的最大吸收光谱范围,并在受光激发后,可观察到有荧光发射。工作中发现,硫代α-萘甲酸-s-苯酯荧光发射强度会随光照时间的增加而加强,这是因该化合物光解时生成了有高荧光量子产率的α,α'-联萘;但在硫代苯甲酸-s-苯并噻唑酯的光解中观察不到上述现象,文章对所得结果进行了讨论。     

ESR STUDIES OF CHLOROPHYLL ONE-ELECTRON PHOTOCHEMISTRY: KINETICS AND MECHANISM OF REVERSIBLE HYDROQUINONE OXIDATION IN SOLUTION*

Abstract— ESR studies have been made of the kinetics of semiquinone radical formation and disappearance resulting from the reversible photosensitization by chlorophyll of hydroquinone oxidation in a pyridine-water solvent. The rate of radical decay was found to be second order with respect to the radical concentration, with a rate constant of 6.7 × 10⁵ l./mole sec at -30°C and an activation energy of 6900 cal/mole. The rate of radical formation was recombination-limited and, through the use of β-carotene as a quencher, the rate constant was determined to be 8.81 × 10⁵ l./mole sec at -30°C. The effect of light intensity and hydroquinone concentration on the rate of semiquinone radical formation and on the steady state radical concentration was also investigated and possible mechanisms to explain the results are discussed.     

THE USE OF SPECIFIC RADIOIMMUNOASSAYS TO DETERMINE ACTION SPECTRA FOR THE PHOTOLYSIS OF (6-4) PHOTOPRODUCTS

Abstract. A radioimmunoassay (RIA) was developed which specifically detects a photoproduct produced by the near-UV photolysis of pyrimidine(6-4)pyrimidone photoproducts. This assay was used in conjunction with a previously characterized RIA which specifically detects (6-4) photoproducts to determine the relative efficiency of wavelengths between 265 and 435 nm for photolysing these lesions. The rate of loss of antibody-binding sites associated with (6-4) photoproducts correlates with the production of those associated with its photolysis product. Action spectra for both the loss of (6-4) photoproducts and the induction of the photolysis product parallel the absorption spectrum of the (6-4) photoproduct.     

KINETICS OF RHODOPSIN PHOTOLYSIS INTERMEDIATES IN RETINAL ROD DISK MEMBRANES—I. TEMPERATURE DEPENDENCE OF LUMIRHODOPSIN AND METARHODOPSIN I KINETICS

Abstract— Kinetic measurements have been carried out on rhodopsin photolysis intermediates in retinal rod membrane suspensions on a millisecond time scale over a wide spectral range at 10, 20 and 36°C. To adequately account for the data we find that a three exponential fit is required at most wavelengths and temperatures investigated. The fastest component at 380, 420, 480, 515 and 540 nm is due to the lumirhodopsin → metarhodopsin I transition. The slowest process is not isochromic with the larger amplitude process found on the metarhodopsin I → metarhodopsin II time scale. The properties of the larger amplitude slow component are identical with the classical metarhodopsin I → metarhodopsin II process. Effects of various experimental conditions are discussed. It is shown that scattered light, in particular, can significantly affect the measured kinetics. For example, sonication, low salt and refractive index matching reduce light scattering and increase the contribution of the lumirhodopsin → metarhodopsin I reaction to the absorption transients. Care must also be taken in the analysis because the isosbestic wavelengths in the spectral transients are highly temperature dependent. For example, the lumirhodopsin–metarhodopsin I isosbestic is 490–500 nm at 10°C, 480–490 nm at 20°C and to the blue of 470 nm at 36°C. Activation energies of 77.8, 130.9 and 101.3 kJ/mol were found for the lumirhodopsin → metarhodopsin I, the metarhodopsin I → metarhodopsin II and the slow millisecond processes, respectively. All three processes contribute to the signals at lower temperatures. The amplitude of the slowest component decreases as the temperature is raised, and at physiological temperature its amplitude is essentially negligible compared to the metarhodopsin I → metarhodopsin II reaction. The lumirhodopsin → metarhodopsin I reaction makes a large contribution to the amplitude of the signals at most wavelengths observed from 380–540 nm, especially at physiological temperatures. At physiological temperatures the decay rates of lumirhodopsin and metarhodopsin I are within a factor of three of each other. Thus, lumirhodopsin decay may be much more important for visual transduction than suggested by low temperature studies. In contrast to reports of several other laboratories we have no evidence for kinetic complexity in the metarhodopsin I → metarhodopsin II reaction.     

OXIDATIVE DEGRADATION OF BILIVERDIN AND BILIRUBIN ESTERS IN PRESENCE OF SILVER NITRATE

Treatment of biliverdin IXα dimethyl ester(2)with silver nitratein alkaline solution gave two violin-like tripyrrione carbaldehydes, one de-graded at C15-C16, other at C4-C5.Biliverdin IXα(1), bilirubin IXα(3)and its dimethyl ester(4)gave the same results.     

水杨醛缩对甲苯胺的吸收光谱和失活动力学研究

利用纳秒级的闪光光解方法研究了水杨醛缩对甲苯胺的瞬态吸收光谱。根据瞬态吸收光谱和动力学数据,该化合物的基本光产物被认为是一个两性离子。实验结果表明,光产物的性质与溶剂的性质和浓度有关。对该化合物的光致变色机理也进行了讨论。     

FLASH PHOTOLYSIS OF BOVINE SERUM ALBUMIN: IDENTIFICATION AND DECAY KINETICS OF TRANSIENT INTERMEDIATES

Abstract. Using the method of flash photolysis, the triplet of the single indole side chain of human serum albumin was detected at room temperature. In a nitrogen saturated solution, this species was found to decay exponentially for over a factor of ten with a lifetime τ 0.5 ms. Analogous experiments, reported here, with bovine serum albumin yield a non-exponential decay which may be decomposed into two components. The yield of the longer lived triplet, with an average τ of ∼6 ms, is significantly enhanced by addition of a 20 fold excess of sodium dodecyl sulfate or 1 M Br^-. The yield of the shorter lived triplet, τ 0.4 ms, is unaffected by these treatments as was previously observed for the single indole in HSA. Thus, the short lived triplet may be assigned to the indole in BSA which is homologous to the one in HSA. The longer lived triplet may be assigned to the remaining indole of BSA. On the bases of wavelength dependence studies, two additional transients may be identified; the electron adduct of the disulfide bond, λ; 420 with a τ 30 ms, and the neutral indole radical,λ; 520 nm with τ ls. These results suggest that the triplet, because of its long τ, will be a valuable intrinsic reporter group for the study of the structure and dynamics of proteins in solution at room temperature.     

FLASH PHOTOLYSIS STUDIES OF PROTEINS AND INDOLE DERIVATIVES IN SOLUTION

Abstract— Transients obtained upon flash photolysis of a number of proteins in aqueous solution appear to derive from electron ejection from tryptophyl residue side chains. These decay by a second order process. Oxygen is an effective quencher for the protein transients but is less so for the flash-induced signals obtained from simple indole derivatives. Experiments using other quenchers indicate that the signals are not due to an indole triplet state, but that the triplet state may be a precursor of the flash-induced metastabie species. Compounds which bind to the active site of chymotrypsin were found to exert only non-specific effects on the flash-induced signals.     

酞花菁及金属酞菁化物紫外光解的ESR研究

在较强的紫外辐射作用下,即使较为稳定的酞菁化合物也可能发生光解。水文用自旋捕捉与ESR技术相结合的方法检出了在光解中生成的氮中心自由基。     

卟啉衍生物的ESR与光化动力学研究

本文测定了2,4-二(α-亚氨基乙酸乙基)次卟啉Ⅸ和2,4-二(α-巯乙基)次卟啉Ⅸ的g因子、ΔH_(pp)、线型及自旋浓度;它们的ESR信号强度对微波功率的饱和效应及对温度的响应;同时测定了在不同温度下UV-辐照的ESR相对强度。发现它们的ESR由两种顺磁中心所贡献;卟啉环中的未偶非定域电子与环上的磁性核相互作用产生的超精细结构和卟啉与氧有关的自由基。与氧有关的自由基的ESR信号强度对微波功率的饱和效应与各化合物析出的等电点pH值有关;对温度的响应情况比较复杂;光化反应对与氧有关的自由基呈现零级动力学行为,整个反应受三态氧向激发态卟啉“活动范围”的扩散所控制。     

BIPHASIC ENERGY CONVERSION KINETICS AND ABSORBANCE DIFFERENCE SPECTRA OF PHOTOSYSTEM II OF CHLOROPLASTS. EVIDENCE FOR TWO DIFFERENT PHOTOSYSTEM II REACTION CENTERS

Abstract— The continuous illumination induced kinetics of photochemical energy conversion at system II have been measured with isolated and 3-(3, 4-dichlorophenyl)-l, l-dimethylurea (DCMU) poisoned chloroplasts by means of absorbance difference spectroscopy in the UV and by the area growth over the fluorescence induction curve at room temperature. An optimal set of conditions was found in order to isolate absorbance changes caused by the reduction of the primary electron acceptor Q of PS II by suppressing other electron transfer processes. The light induced kinetics of Q- accumulation in the absorbance change measurements were found to be biphasic and strictly correlated with the kinetics of the area growth measured under the same conditions. From the resolution of the biphasic kinetics at different wavelengths in the UV region of the spectrum, it was found that both kinetic components in the system II photochemistry involve the reduction of a plastoquinone molecule to its plastosemiquinone anion. From the two kinetic components one was fast and non-exponential and the other relatively slow with an exponential time course. The initial rate difference in the kinetics of the two components was by a factor of approximately 3. A difference by a factor of about three was also found in the flash saturation curves of the two kinetic components.
The results are explained by the hypothesis that in higher plant chloroplasts there are system II reaction centers embedded in a large pigment matrix with statistical energy transfer, and system II reaction centers embedded in separate, in terms of excitation energy transfer, units. The effective absorption cross section per reaction center for the centers in the statistical pigment bed is approximately 3 times larger than that of the reaction centers in the separate system II units. The two types of system II reaction centers have different yields of excitation trapping and charge stabilization properties.     

ELECTROCHEMICAL GENERATION OF SOLUTION LUMINESCENCE—III.: EFFECT OF OXYGEN ON QUANTUM YIELD AND KINETICS OF LUMINOL

Abstract -The growth and decay of light emission were examined for luminol as a funtion of oxygen concentration in aqueous alkaline solutions during and after the application of a controlled potential, square-wave electrochemical pulse. The results indicate that, in the rise portion of the light, the rate of electrochemical oxidation of luminol governs the light emission rate; while in the decay portion, the rate is first order and is independent of oxygen concentration. Quantum yields based on integration of the total light emitted also appear to be independent of oxygen above a threshold value. These results are consistent with evidence that the emitting state is an excited singlet.     

硝酸钕和钐的水合物在水中溶解热的测定

本文用补偿式数字量热计测定了六水、四水硝酸钕和六水、五水硝酸钐298.15K时在水中的溶解热,求得了它们的标准生成热、相应的标准脱水焓和晶格能。     

SPIN-TRAPPING AND ESR STUDIES OF THE DIRECT PHOTOLYSIS OF AROMATIC AMINO ACIDS, DIPEPTIDES, TRIPEPTIDES AND POLYPEPTIDES IN AQUEOUS SOLUTIONS—I. PHENYLALANINE AND RELATED COMPOUNDS

Abstract— The direct UV photolysis of l -Phe and peptides containing l -Phe in aqueous solutions has been investigated at room temperature. The short-lived free radicals formed during photolysis were spin-trapped by t -nitrosobutane and identified by electron spin resonance. During the photolysis of l -Phe the decarboxylation and the deamination radicals were spin-trapped. For N-formyl and N-acetyl- l -Phe the decarboxylation radicals were observed. For dipeptides containing Phe the decarboxylation radicals were observed and in some cases the deamination radicals from the N-terminal residue were found. For the tripeptides Gly- l -Phe- l -Ala and Gly-Gly- l -Phe, the C-terminal decarboxylation radical was spin trapped; for l -Phe-Gly-Gly only the deamination radical of the N-terminal residue could be detected. However, for Gly- l -Phe-Gly, five different radicals were identified. The results of the spin-trapping experiments of the 260 nm photolysis of RNase-S-peptide, containing 20 amino acid residues, was interpreted in terms of a chain scission between the alpha carbon of the Phe residue and the adjacent carbonyl group.     

硝酸钕水合物热分解机理及脱水过程动力学的研究

本文采用TG-DTG法研究了Nd(NO)·nHO(n=6,5,4)的热分解行为,并通过IR对反应物、中间产物和最终产物进行了鉴别。发现中间产物有低水合物、无水盐和碱式盐,最终产物是氧化钕。另外,还进行了上述样品某些脱水过程的动力学研究,借助不同升温速率下的TG-DTG曲线,应用Kissinger法计算了它们脱水的表观活化能值,并利用DSC求出了它们的脱水焓值。     

ELECTROCHEMICAL GENERATION OF SOLUTION LUMINESCENCE—II: LUMINOL AND PHTHALHYDRAZIDE

Abstract— The electrochemical techniques of voltage-scan, chronopotentiometry, chrono-amperometry, coulometry and square-wave pulse have been applied to the electro-oxidation of luminol and phthalhydrazide in an attempt to elucidate the mechanism and species responsible for electroluminescence in the presence of oxygen and base. The rate of electro-oxidation has been shown to be diffusion controlled with no evidence of a reverse reduction wave. Monitoring of light intensity decays after a potential-pulse has given a first order rate of 1.63 times 10³ sec^-1 at 25". A heat of activation of 2.89 + 0.12 kcal/mole was determined for the reaction from the temperature dependence of the rate. A general reaction sequence for the electroluminescent pathway is proposed.     

PHOTODECOMPOSITION OF CATECHOLAMINES. PHOTOPRODUCTS, QUANTUM YIELDS AND ACTION SPECTRUM OF ADRENALINE

The photochemical decomposition of several catecholamines in aqueous solution was investigated. The respective aminochromes were found to be products of adrenaline and isoprenaline. Irradiation of adrenochrome and N-isopropylnoradrenochrome produced their respective 5, 6-dihydroxyindoles in addition to the ultimate formation of melanine. No trihydroxyindoles could be detected amongst the photoproducts of catecholamines. The action spectrum of adrenaline suggested that the catecholamine itself, in excited state, initiated the first step in the transformation process. The quantum yields for the decomposition were determined for several catecholamines: N-alkyl compounds. decompose more rapidly under influence of light (λ 254 nm) than those with an unsubstituted amino group. In determining the quantum yields the use of corrections for the inner filter effect could be avoided.     

FLASH PHOTOLYSIS STUDY OF ALIPHATIC AMINO ACIDS AND PEPTIDES IN AQUEOUS SOLUTION*

Abstract— The intermediates produced in the photolysis of oxygen-free aqueous solutions of a number of aliphatic amino acids and peptides were observed spectrophotometrically using the fast-reaction technique of flash photolysis. Included among the compounds examined are the N-acetyl derivatives of glycine, alanine, sarcosine, glutamic acid and glycylglycine; the esters and amides of these N-acetyl compounds; diketopiperazines; the amino acids glycine, alanine and β-alanine; and finally the oligopeptides di-, tri- and tetraglycine. The direct optical excitation of these compounds was found to lead primarily to a photo-induced decarboxylation reaction:
The transient spectra of the radicals produced have been identified. The quantum yields of these processes were found to be directly proportional to the p K _a of the carboxyl groups of the corresponding ground-state molecules, and hence to the concentration of the non-ionized carboxylic acids. The φ's of these processes for the ionized acids were close to zero. The dependence of φ upon pH is correlated to the absorption spectra of these compounds. The quantum yields of the corresponding esters were lower but independent of pH. No intermediates were observed from excitation of the amine derivatives. Other photolytic reactions are suggested. The photo-decarboxylation of alanine and diglycine were found to be monophotonic, while that of N-acetyl alanine, N-acetyl diglycine, and tetraglycine were found to be biphotonic. A triplet excited state precursor is indicated for the latter group of compounds. These and other results are discussed.