PHOTOLYSIS OF CYSTINE IN THE PRESENCE OF AROMATIC AMINO ACIDS

Se dan evidencias para explicar los distintos rendimientos cuánticos de fotólisis con lux u.v. para distintos residuos de cisteina en lisozima e insulina. En sistemas modelos de mezclas de aminoácidos, el aminoácido triptofano muestra un marcado aumento en el rendimiento cuántico en la fotólisis de la cisteina. La fotosensibilidad de los residuos de cisteina en la lisozima se interpretan usando la conformación terciaria de la enzima la cual provee una relación espacial entre los residuos de triptofano y cisteina.     

LASER FLASH PHOTOLYSIS OF INDOLE IN THE PRESENCE OF AMINO ACIDS

The laser flash photolysis of indole at 265 nm in the presence of glycine, proline and hydroxy proline was studied. The relative yields of c _aq, triplet state, and indole cation radical were determined in the absence and in the presence of the amino acids. The yields were determined as a function of laser intensity and the values at very low intensity were compared with the fluorescence quenching results. It was concluded that in these conditions the photoionization of indole occurs via the fluorescent state. From the curves of triplet yield vs laser intensity, the triplet quantum yield extrapolated at low laser intensity was obtained, φr = 0.55 φ 0.05, relative to the literature value of 0.15 for φ_eag. This gives φ_F+φ_eaq= 1.0 ± 0.1 at room temperature. When proline and hydroxy proline were used as singlet quenchers, the yield of In was greater than the yield of c_aq. This was considered as evidence that a fraction of the quenching processes leads to complete electron transfer from indole to the amino acids.     

PREPARATION OF N-ACYL DERIVATIVES OF AMINO ACIDS FROM ACYL CHLORIDES AND AMINO ACIDS IN THE PRESENCE OF CATIONIC SURFACTANTS. A VARIATION OF THE SCHOTTEN-BAUMANN METHOD OF BENZOYLATION OF AMINO ACIDS

A very efficient method for the preparation of N-acylamino acids from the corresponding acyl chloride and amino acid is described. Amino acids, potassium carbonate, acyl chloride, and a catalytic amount of cationic surfactants were mixed in tetrahydrofuran and refluxed without ever obtaining a clear reaction mixture. After hot filtration, the product was isolated from the hot tetrahydrofuran solution in very high or almost quantitative yields.     

FAR UV IRRADIATION OF DNA IN THE PRESENCE OF PROTEINS, AMINO ACIDS OR PEPTIDES

Abstract— The DNA of bacteriophage SP02c12 was subjected to 254 nm irradiation in solutions containing lysozyme or histone. In these solutions, the protein-DNA mass ratios and the ionic strengths of the solvents were varied to change the amount of protein associated with the DNA. Lysozyme-DNA binding constants were measured under the same conditions. The sensitivity of phage DNA to biological inactivation by UV increased as the amount of lysozyme bound per DNA strand increased. Although binding constants could not be measured for the DNA-histone interaction, this protein had a protective effect which was greater under conditions which cause enhanced binding. No crosslinking of either protein could be detected even at doses ten-fold greater than those giving a surviving fraction of 0.01.
Irradiation was also performed in the presence of various amino acids and short peptides. These were chosen to include amino acids which: (1) are positively charged, (2) absorb UV of this wavelength or (3) form UV-induced crosslinks to DNA. None of the amino acids tested affected sensitivity of the DNA to biological inactivation. Peptides containing a UV-absorbing amino acid and a positively charged amino acid enhanced sensitivity. For each of these peptides, a mixture of the constituent amino acids had the same effect as the peptide itself. Under the conditions used, no evidence for formation of DNA-amino acid crosslinks was found. The results indicate that proteins and peptides can sensitize DNA to UV inactivation by mechanisms other than covalent crosslink formation. Such mechanisms could include energy or electron transfer or alterations in the conformation of the DNA.     

PHOTOCHEMICAL ADDITION OF AMINO ACIDS AND PEPTIDES TO DNA

Abstract— The quantum yields for photochemical addition of twenty of the amino acids commonly occurring in proteins to denatured calf thymus DNA have been determined in deoxygenated phosphate buffer at λ 254 nM and pH 7 using a fluorescamine assay technique. Fifteen were found to be reactive, with cysteine, lysine, phenylalanine, tryptophan and tyrosine being the most reactive. Alanine, aspartic acid, glutamic acid, serine and threonine were unreactive. Analogous quantum yields for a series of eighteen peptides of the form glycyl X (X being one of the commonly occurring amino acids) were also determined, along with the corresponding quantum yields for L-alanyl-L-alanine, L-alanyl-L-tryptophan, L-seryl-L-seryl-L-serine, L-threonyl-L-threonyl-L-threonine, and L-cystine- bis -glycine. All of the peptides were found to be reactive. The modified amino acids N^ε-methyllysine, N^ε, N^ε, N^ε-trimethyllysine and N^ε-acetyllysine, all occurring in minor amounts in the histone group of chromosomal proteins, were also found to be reactive as was N^α-acetyllysine. The quantum yields for photoaddition of a selected group of amino acids and peptides to denatured DNA and native DNA are compared. In some cases higher quantum yields for photoaddition to denatured DNA are observed while in other cases the reverse is true. The effect of oxygen on the quantum yields for photoaddition of selected peptides to DNA was examined. While for most systems studied the amount of reaction in aerated systems was less than in deoxygenated systems, in the case of glycyl-L-phenylalanine the reverse was true.     

二元阴离子型丙烯酰胺共聚物在二价金属离子存在下相分离行为的研究

水溶性丙烯酰胺类共聚物 ,作为粘度改性剂 ,在工业上已得到广泛应用 .特别近年来 ,它们大量应用于石油工业强化采油技术 ,引起了人们很大的重视[1] .目前 ,这类用途的聚合物 ,主要在聚丙烯酰胺结构中 ,引入阴离子组分和不断增高产物分子量的方法 ,以提高聚合物溶液粘度和增粘效果 ,然而 ,在二价金属离子 (如Ｃａ2 + ,Ｍｇ2 + 等 )存在下 ,羧酸阴离子型丙烯酰胺类共聚物很容易络合发生沉淀 ,从而失去增粘作用[2 ] .同时这类聚合物中酰胺基不稳定 ,易发生水解反应转化为羧酸基 ,并随温度升高而加剧[3 ] ,因此在温度较高的应用条件下 ,二价金属…     

PHOTOCHEMICAL ADDITION OF AMINO ACIDS AND PEPTIDES TO POLYURIDYLIC ACID

Abstract— The quantum yields for photochemical addition of glycine and the L-amino acids commonly occurring in proteins (excluding proline) to polyuridylic acid have been determined in deoxygenated phosphate buffer at pH 7, using a fluorescamine assay technique. All twenty amino acids were found to be reactive, with cysteine, tryptophan, phenylalanine, tyrosine, arginine, lysine and methionine being the most reactive. The analogous quantum yields for a series of eighteen dipeptides of the form glycyl X (X being one of the commonly occurring amino acids, including proline), of L-alanyl-L-tryptophan, of the tripeptides L-seryl-L-seryl-L-serine and L-threonyl-L-threonyl-L-threonine, of the tetrapeptide L-cystine- bis -glycine, and of the lysine derivative N_α-acetyllysine were also measured. All were found to be reactive toward photoaddition to poly U.     

含有不同脂肪环胺侧基的聚丙烯酰胺保护的贵金属胶体制备的研究

<正> 近年来高分子保护金属胶体的研究在金属催化剂领域中受到人们的突出关注。自Hirai等人对聚乙烯吡咯烷酮保护的铂族金属胶体的系统研究工作发表之后,一项重要的研究进展是双金属胶体的制备成功。当前制备窄分布乃至单分散胶体的努力成为众多研究的集中目标,具有重要的理论意义和实际应用价值。Bradley等报道用金属蒸汽冷凝至含有高分子稳定剂的有机溶剂中制备得到2.0—5.0nm直径的金属胶体,Schmid等报道用水溶性三苯膦磺酸钠小分子配位体作为稳定剂制备得到直径为18.6±0.1nm的金胶体。Esumi等用在有机溶剂中热解乙酸钯的方法制备得到不同粒径的均一球形的钯金属胶体。     

PHOTO-CIDNP OF THE AMINO ACIDS

A photochemically induced dynamic nuclear polarisation (photo-CIDNP) study is presented of the amino acids that are polarisable with a flavin dye. These include derivatives of tryptophan, tyrosine, histidine, methylated lysines and methionine. The influence of pH, concentration and chemical modification on the magnitude of the CIDNP effect has been studied to obtain mechanistic information about the radical pair formation. The pH and concentration dependence of tyrosine and tryptophan polarisation could be accounted for quantitatively. The CIDNP evidence indicates that hydrogen-atom abstraction is important in generating radical pairs in the case of histidine and tyrosine, while electron transfer prevails in the case of tryptophan, the methylated lysines and methionine.     

模板交联壳聚糖对过渡金属离子吸附性能研究

以锌离子为模板,合成了戊二醛交联壳聚糖树脂,通过对过渡金属离子吸附性能的研究。结果表明,该法合成的树脂对Ｚｎ（Ⅱ）离子具有较强的“记忆”能力,且对同族的Ｃｄ（Ⅱ）Ｈｇ（Ⅱ）也有较高吸附量。在酸性下条件再生不会发生软化和溶解,重复作用性能良好。     

PHOTOCHEMICAL INACTIVATION OF SINGLE-STRANDED VIRAL DNA IN THE PRESENCE OF UROCANIC ACID*

Abstract— Urocanic acid (UA) has previously been shown to react photochemically in vitro with N,N-dimethylthymine. In this study, mixtures of UA and phage G4 single-stranded DNA have been irradiated with UV light (λ≥ 254 nm) and the DNA assayed for infectivity. At the concentrations of UA employed (typically 5.4 × 10^-3 M ) there is extensive absorption of the incident light by the UA. The DNA is inactivated at rates greater than that predicted from the calculated shielding by UA, indicating that photosensitization is occurring. Photosensitization is also indicated by the fact that at high UA concentrations the inactivation rate does not decrease to zero but approaches a residual value. Furthermore, the ability to photoreactivate DNA that has been photolyzed in the presence of UA is much reduced relative to that observed upon photolysis of the DNA alone. UA is therefore responsible for the production of UV-induced DNA lesions, which are resistant to photoreactivation.
A general analysis of the effects of photosensitization on the kinetics of UV inactivation is presented in an appendix.     

氨基酸在甲醇-水混合溶剂中粘度的研究

报导了在293.15及298.15 K下, 氨基乙酸和DL-氨基丙酸在甲醇-水混合溶剂中的密度及粘度数据; 计算了在无限稀释条件下, 这些体系中氨基酸的粘度B系数及偏摩尔体积。实验结果表明: 在甲醇-水的质量比值(W_B)分别约为0.15及0.25处, 两种氨基酸的B系数均出现极小值。讨论了氨基酸的引入对溶剂结构的影响; 并应用流动过渡状态理论计算了两种氨基酸在甲醇水溶液中的流动活化参数。     

PHOTOCHEMICAL EXCHANGE REACTIONS OF THYMINE, URACIL AND THEIR NUCLEOSIDES WITH SELECTED AMINO ACIDS

The photoinduced exchange reactions of thymine with lysine at basic pH, using 254 nm light, have been studied. Three products have been isolated, namely, 6-amino-2-(1-thyminyl)hexanoic acid ( Ia ), 2-amino-6-(1-thyminyl)hexanoic acid ( IIa ) and 1-amino-5-(1-thyminyl)pentane ( IIIa ). Compound IIIa was shown to be a secondary product, produced by photochemical decarboxylation of Ia . Photochemical reaction of thymine with glycine and alanine at basic pH led, respectively, to formation of 2-(1-thyminyl)acetic acid ( Ic ) and 2-(1-thyminyl)propionic acid ( Id ). Compounds Ic and Id underwent photolysis to produce the decarboxylated secondary products 1-methylthymine and 1-ethylthymine, respectively. Thymidine reacts photochemically with glycine and alanine to produce the same products.
Irradiation of DNA in the presence of lysine at basic pH led to the formation of the same products formed in the thymine-lysine system, namely Ia , IIa and IIIa .
Uracil was found to undergo analogous photochemical exchange reactions with lysine to form 6-amino-2-(1-uracilyl) hexanoic acid ( Ib ), and 2-amino-6-(1-uracilyl)hexanoic acid ( IIb ). Compound Ib was found to undergo photodecarboxylation to form 1-amino-5-(1-uracilyl)pentane ( IIIb ), analogous to the secondary photoreaction of Ia . Photoreaction of uracil with 1,5-diaminopentane (cadaverine) likewise led to formation of IIIb .     

镧系金属离子的水化能

一、水化能公式 离子水化能是重要的热化学数据,前人曾作过很多研究^[1-4]。     

KINETIC FORMALDEHYDE ANALYSIS OF DNA ULTRAVIOLET IRRADIATED IN THE PRESENCE OF SILVER IONS*

Abstract— DNA from Escherichia coli was irradiated at 254 nm in the presence of silver in order to preferentially enhance the rate of formation of pyrimidine-dimer damage over nondimer damage. The irradiated DNA was treated with formaldehyde in order to measure the unwinding velocity of the defects associated with the pyrimidine dimers. This velocity was found to be 0.18 base pairs/min per pyrimidine dimer, which is nearly 8 times less than that found for a double-strand break (1.37 base pairs/min) obtained by use of sheared DNA whose size was determined by electron microscopy. The rate of reaction of the DNA with formaldehyde varied linearly with the pyrimidine dimer concentration and showed no inflection due to clustering. Treatment of irradiated DNA with UV endonuclease enhanced the formaldehyde reaction by ? 7-fold, consistent with the conversion of a dimer into the faster-reacting defect associated with a single-strand break. These results indicate that the distribution of dimers in DNA is random and not clustered, and that previous interpretations of clustering were based on the false assumption that dimer and chain break defects unwind with similar velocities when treated with formaldehyde.     

金属离子负载修饰阳离子树脂在酯化反应中的研究

将催化精馏中常用作催化填料的强酸性阳离子交换树脂用金属离子负载修饰后，考察了树脂催化性能的改变及树脂结构对催化性能的影响。实验表明，经修饰后树脂的催化能力都高于原树脂，在不分水的情况下，合成乙酸乙酯时乙酸的转化率最高可达73％，具有很好的选择性，金属离子能与树脂的磺酸基团产生络合，提高了树指的催化性能，所形成的新酸中心不会被阳离子交换而失活。     

PHOTOELECTRIC EFFECTS IN A BIMOLECULAR LIPID MEMBRANE IN THE PRESENCE OF LIGHT SENSITIVE INORGANIC IONS

Abstract— A new membrane photoeffect of high quantum efficiency is reported. The presence of a number of inorganic ions in the bathing solution of a bimolecular lipid film of oxidized cholesterol causes a change in the measured e.m.f. from -100 to -40 mV (photo e.m.f. effect) and increase in the conductivity by a factor of 100–200 (photoconductive effect) when the ions are excited by light. A model system, based upon the classical Becquerel Effect phenomenon of electronic charge injection into the membrane from electronically excited ions, is suggested and experiments verifying this model are reported. An extension of this model is used to suggest a new mechanism of the visual receptor process in biological photoreceptor structures.