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.     

THE CHEMILUMINESCENCE OF INDOLE DERIVATIVES IN DIMETHYL SULFOXIDE*

The chemiluminescent autoxidation of over fifty indoles has been measured in dimethyl sulfoxide (DMSO). The 3-alkylindole derivatives represent the brightest and most efficient members of this group. The chemiluminescence yield (per mole) of skatole is (1·5 ± 0·6) × 10^-3. The chemiluminescence spectrum of skatole is identical with the fluorescence spectrum of o-formamidoacetophenone in the same environment Similar results for 2,3-dimethylindole lead to the identification of the acylamide anion as the emitter in indole chemiluminescence. A peroxide ring cleavage excitation mechanism is proposed.     

INFLUENCE OF THE ENVIRONMENT ON THE EXCITATION WAVELENGTH DEPENDENCE OF THE FLUORESCENCE QUANTUM YIELD OF INDOLE

Abstract— The influence of excitation wavelength, pH, oxygen and solvents, upon fluorescence quantum yields, were measured for insole Indole in neutral aqueous solution exhibits the same wavelength dependence as tryptophan, which indicates that COO- absorption is not responsible for the effect. Parameters such as pH and oxygen influence only the absolute fluorescence quantum yields but not their relative variation with wavelength, indicating competition with fluorescence emission for S1 deactivation. without any influence upon deactivation of higher excited states. In contrast, solvents exhibit a specific influence upon the wavelength dependence; for indole, the decrease of fluorescence yield excited around 215 nm, compared with the yield in the first absorption band is about 40% in water, 10% in acetonitrile, 70% in n-hexane and cyclohexane, whereas no appreciable decrease occurs in methanol, ethanol or n-butanol. These observations, together with the Stokes shifts of the emission spectra, may be well correlated with Kosower's Z-values, expressing microscopic solvent-solute interactions.     

RESOLUTION OF OVERLAPPING BANDS IN THE NEAR-UV ABSORPTION SPECTRUM OF INDOLE DERIVATIVES

Abstract— The second derivative spectra of tryptophan in water and in ethylene glycol at 22°C have been integrated in order to obtain the corresponding primitive functions. The integration was carried out by making use of Tchebychev polynomials. The results show that the integrated primitive functions do not correspond to the original absorption spectra of tryptophan in various solvents, but they reflect only the contributions of the ¹L_b bands of the indolic chromophore. The identification of the electronic component, which generates the second derivative spectrum, was based on the solvent insensitivity of the derivative peaks. The comparison between the absorption spectra reported in this paper and those calculated for the ¹L_b←¹A electronic transition of indole confirmed the assumption that the derivation process eliminates the broad, although more intense, contributions coming from the ¹L_a←¹A electronic transition.     

EFFECTS OF INDOLE AND TRYPTOPHAN ON FURAN OXIDATION BY SINGLET OXYGEN IN MICELLAR SOLUTIONS

Abstract— The 1,3-diphenylisobenzofuran oxidation by singlet oxygen was investigated in aqueous dode-cyltrimethylammonium chloride micellar solutions using pyrene as photosensitizer. It was found that indole and tryptophan markedly enhanced the furan oxidation in micellar solutions. This enhancement effect strongly depended on the ethanol content in micellar solutions; enhancement effect below about 0.3 mol fraction of ethanol and inhibition effect above this mole fraction. In the former ethanol range, a quenching of pyrene fluorescence by indole or tryptophan and a difference spectrum of furan between micellar solutions in the presence and absence of indole or tryptophan appeared strongly, but they were weakened in the latter ethanol range. The interactions between indole or tryptophan and pyrene and/or furan might be responsible for the enhancement effect observed. Discussion was made in connection with the micelle structure.     

PHOTOSENSITIZED SPLITTING OF PYRIMIDINE DIMERS IN DNA BY INDOLE DERIVATIVES AND TRYPTOPHAN-CONTAINING PEPTIDES

Abstract —Indole derivatives, such as serotonin or the oligopeptide Lys-Trp-Lys, are able to photosensitize the splitting of thymine dimers in DNA. These indole derivatives have to be bound to DNA in order to efficiently photosensitize the splitting reaction. Serotonin may also induce the photosensitized formation of thymine-containing dimers in native DNA. In this case, an equilibrium is reached when 5 per cent of the total thymines are dimerized. In both cases (splitting and dimer formation), the formation of electron donor-acceptor complexes between either dimers or two adjacent thymine monomers, and excited indole rings, could be an intermediate step in the reactions. Thymine-dimer splitting would then result from an electron transfer reaction involving the indole ring as the electron donor. These results are discussed with respect to the mechanism of action of the photoreactivating enzyme.     

PHOTODEGRADATION OF THE IMIDAZOLE RING INDUCED BY INDOLE DERIVATIVES IN OXYGEN-FREE AQUEOUS SOLUTIONS

Abstract— An imidazole ring photodegradation induced by indole derivatives in oxygen-free aqueous solutions (Λ_exc= 254 nm) was demonstrated and studied in various systems at low concentration (0.2 m M ). The degradation rate was maximal in the indole-imidazole system and decreased when a substituent was present on either or both rings. The degradation rate also depended on pH (maximal at pH ˜ 6) and on imidazole concentration. Results obtained under N₂O atmosphere, in the presence and absence of 1 M t -butanol, indicate that the imidazole degradation is promoted by hydrated electrons photogenerated by the indole chromophore. Kinetic analysis of the data confirms this mechanism.     

THE FORMATION OF HYDRATED ELECTRONS FROM THE EXCITED STATE OF INDOLE DERIVATIVES

Abstract— –Hydrogen atoms can be observed in u.v. irradiated aqueous solutions of indole derivatives. These H' atoms are produced in a reaction between H⁺ and solvated electrons which are formed in the excited state of indole. Protons are also known to be good quenching agents for the fluorescence of indole. However the pH dependence and effect of oxygen on the yield of hydrogen atoms indicates clearly that although both fluorescence and electron ejection originate in the excited singlet state the fluorescence quenching by protons is not caused by a transfer of electronic charge from the excited ring to H⁺. The temperature dependencies of both fluorescence and electron ejection yield an abnormally large "activation energy". It is proposed that this temperature dependence is to a large extent determined by a process characteristic of water as a solvent.     

EFFECTS OF TEMPERATURE ON THE VISCOSITY OF NONIONIC MJCELLAR SOLUTION IN THE PRESENCE OF ADDED SALTS

ABSTRACT

The effects of temperature on the viscosity of nonionic surfactant, Triton X-100, in the presence of added salts are presented. It was found that the plots of logarithm of relative viscosity versus 1/T were obtained from the slopes of these plots. The activation free energies (ΔG?) of the viscous flow were obtained from the slopes of these plots. The activation enthalpies ( ΔH?) and the entropies ( ΔS?) for the viscous flow were calculated and the entropic contribution was found to be negligible. The ΔG? and ΔH? were highly dependent on the nature of the positive ions. The greater the effect on the energy of the sphere-to-rod transition, the more strongly ions are bound. The ΔG? is interpreted in terms of the energy required to activate the transition of micellar structure capable of being transformed into rod micelle.     

WAVELENGTH EFFECTS ON THE PHOTOCYCLOREVERSION QUANTUM YIELD OF SOME PHOTOCHROMIC ENDOPEROXIDES

Abstract— The photocycloreversion quantum yields Q of the endoperoxides of anthradichromene, benzodixanthene and dimethylhomoocoerdianthrone have been investigated in the 248 ≤γ≤ 405 nm wavelength range. Two types of wavelength dependencies can be distinguished phenomenologically. For the excitation of the S_n (n ≥ 3) states of dimethylhomöocoerdianthrone endoperoxide γ-independent Q-values have been observed throughout 365 ≥γ≥ 265 nm. The endoperoxides of anthradichromene and benzodixanthene in contrast exhibit a quite different and unusual dependence of Q on γ. For both compounds Q first increases with photon energy until a fairly sharp maximum in Q is reached at 302 nm. With further increasing energy Q falls off and approaches a wavelength independent plateau between 280 and 248 nm. The S₁-states of the endoperoxides investigated are inactive for photocycloreversion, which is generally found in endoperoxide photochemistry. The wavelength dependencies observed reveal that the photocycloreversion of endoperoxides deviates remarkably from the commonly accepted generalization that photochemical reactions in solution phase should only occur from the lowest excited singlet or triplet states.     

ON THE MECHANISM OF WAVELENGTH REGULATION IN VISUAL PIGMENTS

Abstract— The contributions of different factors that might be responsible for the 500 nm absorption maximum of bovine rhodopsin are evaluated in detail. These include: (1) electrostatic interactions between the chromophore and a charged amino acid on the apoprotein; (2) exciton interactions with aromatic amino acids; (3) twisting about single bonds which have considerable double bond character; (4) weak interactions between the Schiff base and a putative counter-ion. Analysis of these mechanisms in terms of theoretical and experimental results suggests that(2–4) are all capable of contributing to the protein induced spectral shifts. However, the "external point charge" model proposed previously, i.e. mechanism (1), appears to provide the crucial interaction. In this paper, the theoretical basis for this model is discussed in detail. The model is briefly evaluated in light of the amino-acid sequence of bovine rhodopsin and possible implications for other visual pigments are considered.     

溶液pH值对聚邻甲苯胺电化学性质的影响

本文报道了溶液pH值对聚邻甲本胺电化学性质的影响。研究结果表明,电化学合成的聚邻甲苯胺的循环伏安曲线、氧化电位、膜的颜色、充放电容量、紫外可见光谱以及氧化还原活性都受到溶液pH的影响。在低pH值的溶液中,随着扫描电位的变化,聚邻甲苯胺膜的颜色可逆地变化,而在pH4.13的溶液中进行扫描时,膜的颜色不变化,电化学活性也消失。     

EFFECTS OF SURFACTANTS ON THE TERMINAL VELOCITY OF PHENOL SOLUTION DROPS FALLING IN n-BUTYL ACETATE

ABSTRACT

Measurements of formation times and terminal velocities of aqueous phenol solution drops falling through a continuous phase of n-butyl acetate at 20°C are presented. The influence of two commercial surfactants, Medialan KF and Triton X-100 on the indicated parameters is also reported. A comparison is made between experimental results and predicted values from correlations available for terminal velocities and critical diameters, in the absence of surfactants.     

酸对脱乙酰甲壳质稀溶液粘度的影响

脱乙酰甲壳质是甲壳质衍生物中最重要,用途最为广泛的一种,属阳离子性聚电解质,可以溶于多种稀酸溶液中,本文从脱乙酰甲壳质在甲酸、乙酸和丁酸溶液中的粘度变化,研究其稀溶液性质。分別考察了脱乙酰甲壳质在8×10~(71)～3×10~(72)/1,酸浓度在5×10~(-1)～1×10~(-1)mol范围内溶液ηsp/c-c的关系。实验结果表明,作为脱乙酰甲壳质溶剂的酸,在溶液稀释时对溶液ηsp/c的影响,在不同的阶段可以是完全不同的。当溶液中可离解的酸还未能完全满足游离氨基成盐要求时,酸溶液的增加将导致溶液的ηsp/c的增加,而一旦游离氨都已成盐,过量酸的增加都会导致溶液粘度的下降。而在一般情况下,酸的酸性越强,酸的浓度越大,都会使溶液得到较低的粘度值。     

PHOTOSENSITIZED SPLITTING OF PYRIMIDINE DIMERS BY INDOLE DERIVATIVES AND BY TRYPTOPHAN-CONTAINING OLIGOPEPTIDES AND PROTEINS

Abstract— Indole derivatives including tryptophan can be used as photosensitizers of the splitting of pyrimidine dimers. The reaction can take place in frozen aqueous solutions as well as in fluid medium. Electron transfer from the indole ring to the dimer appears to be involved in the photosensitized reaction. Solvated electrons produced by flash photolysis in the presence of indoles or by pulse radiolysis are also able to split thymine dimers.
The splitting of pyrimidine dimers in DNA can be photosensitized by indole derivatives such as serotonin and by tryptophan-containing oligopeptides. Several methods including fluorescence and nuclear magnetic resonance have been used to show that the indole ring of these oligopeptides is able to stack with bases in nucleic acids. These stacked complexes are involved in the photosensitized reaction.
The splitting of pyrimidine dimers in DNA has also been photosensitized by the protein coded by gene 32 of phage T4 which binds strongly and cooperatively to single-stranded DNA. The mechanism of the splitting reaction as well as the possible use of this reaction to investigate the role of tryptophan residues in the binding of proteins to nucleic acids are discussed.     

CATALYTIC EFFECTS IN THE AMINOLYSIS REACTIONS OF ARYLSULPHONIC ACID DERIVATIVES IN NON-AQUEOUS MEDIA

Abstract

The catalytic effects of organic bases in reactions of arylamines with arylsulphonic acid derivatives, ArSO₂X (X = Cl, Br, OSO₂Ar) in aprotic media are characterised by the following regularities. 1. The activity of 3- and 4-substituted pyridines, N-alkyl- and N-phenylimidazoles is desribed by the common Bränsted relationship. Substituents in positions 2 and 2,6 of the pyridine molecule have a strong steric influence. Tertiary cyclic amines of quinuclidine type with the same basicity as pyridines and imidazoles have more higher activity than the latter. N-Oxides of pyridine which are 4–5 pK_a units less basic than the corresponding pyridines have the catalytic activity 100 times as much, as compared with them. 2. The intensity of the catalytic action of pyridines and their N-oxides alters insignificantly with changing the leaving group X in the substrate, somewhat increasing in the order Cl < Br≤OSO₂Ar. 3. The activity of pyridine bases increases with increasing the solvent solvating ability. The inhibiting influence of the X^? anione on the rate of catalytic reaction displays in media of high polarity (nitrobenzene, acetonitrile). These regularities are explained in terms of the nucleophilic mechanism of catalysis which is supported by isolating intermediate adducts of tertiary amines (in particular 4-N,N-dimethylaminopyridine) with arylsulphonic acid bromides and anhydrides and by studies of their reactivity towards arylamines in methylene chloride. Compounds of bifunctional nature (carboxylic acids) do not accelerate the reaction under consideration unlike a similar substitution process at the carbonyl C-atom. The cause of this seems to be a different geometry of transition states in substitution at the sulpho group S-atom and at the carbonyl carbon, respectively.     

液体样品中铬的价态和微量分析方法的研究进展

文章对液体样中铬的价态、微量铬的分离富集和分析方法进行综述,引用文献60篇。     

PHYTOCHROME INTERMEDIATES IN VIVO-I. EFFECTS OF TEMPERATURE, LIGHT INTENSITY, WAVELENGTH AND OXYGEN ON INTERMEDIATE ACCUMULATION

Abstract— Accumulation of weakly absorbing phytochrome intermediates has been demonstrated in Pisum epicotyl tissue under conditions of pigment cycling using a quasi-continuous measuring spectrophotometer. An action spectrum shows 690–700 nm to be the most efficient wavelength range in this process. Difference spectra for the decay of intermediates maintained by 690 nm light show that, if the experiment is done at 0°C, only P_fr is formed. At – 11°C, intermediates decaying to P_r can also be observed. At – 20°C, P_r is produced as well as a pigment with peak absorption at 710nm. Kinetic analysis of intermediate decay at – 11°C reveals that at least two intermediates are maintained by 690 nm light. The level of intermediate maintained by incandescent light at 0°C was 25% higher in air than in nitrogen.