A solid-state [2 + 2] photodimerization involving coordination of Ag(I) ions to 2-pyridyl groups

Abstract

Photoreactive Ag(I) complexes of p-toluenesulfonate ions with the unsymmetrical alkene trans-1-(4-acetoxyphenyl)-2-(2-pyridyl)ethylene 1 is reported. The crystal [Ag(p-tol)(1)₂]?(H₂O) (p-tol?=?p-toluenesulfonate) undergoes a [2?+?2] photocycloaddition reaction in quantitative yield to afford the head-to-tail (ht) photoproduct rctt-1,3-bis(2-pyridyl)-2,4-bis(4-acetoxyphenyl)cyclobutane 2 regioselectively. The aromatic rings of the olefin participate in face-to-face π–π interactions and adopt an anti-conformation to position the carbon–carbon double bonds (C?=?C) in a suitable orientation to undergo photoreaction between neighboring complexes.     

Synthesis and stereochemical assignment of DNA spore photoproduct analogues

Investigation of the DNA repair process performed by the spore photoproduct (SP) lyase repair enzyme is strongly hampered by the lack of defined substrates needed for detailed enzymatic studies. The problem is particularly severe because the repair enzyme belongs to the class of strongly oxygen-sensitive radical (S)-adenosylmethionine (SAM) enzymes, which are notoriously difficult to handle. We report the synthesis of the spore photoproduct analogues 1 a and 1 b, which have open backbones and are diastereoisomers. In order to solve the problem of stereochemical assignment, two further derivatives 2 a and 2 b with closed backbones were prepared. The key step of the synthesis of 2 a/b is a metathesis-based macrocyclization that strongly increases the conformational rigidity of the synthetic spore photoproduct derivatives. NOESY experiments of the cyclic isomers furnished a clear cross-peak pattern that allowed the unequivocal assignment of the stereochemistry. The results were transferred to the data for isomers 1 a and 1 b, which were subsequently used for enzymatic-repair studies. These studies were performed with the novel spore photoproduct lyase repair enzyme from Geobacillus stearothermophilus. The studies showed an accordance with a recent investigation performed by us with the spore photoproduct lyase from Bacillus subtilis, in that only the S isomer 1 a is recognized and repaired. The ability to prepare a defined functioning substrate now paves the way for detailed enzymatic studies of the SP-lyase lesion recognition and repair process.     

Crystal structures and repair studies reveal the identity and the base-pairing properties of the UV-induced spore photoproduct DNA lesion

UV light is one of the major causes of DNA damage. In spore DNA, due to an unusual packing of the genetic material, a special spore photoproduct lesion (SP lesion) is formed, which is repaired by the enzyme spore photoproduct lyase (Spl), a radical S-adenosylmethionine (SAM) enzyme. We report here the synthesis and DNA incorporation of a DNA SP lesion analogue lacking the phosphodiester backbone. The oligonucleotides were used for repair studies and they were cocrystallized with a polymerase enzyme as a template to clarify the configuration of the SP lesion and to provide information about the base-pairing properties of the lesion. The structural analysis together with repair studies allowed us to clarify the identity of the preferentially repaired lesion diastereoisomer.     

DNA光解酶模型研究的近期进展

用模型化合物来模拟DNA光解酶与底物的作用, 有助于认识DNA光复活作用机理. 评述了环丁烷型嘧啶二聚体光解酶和(6-4)光产物光解酶的模型研究进展, 并展望了该领域的发展前景．     

Theoretical Investigation on the Absence of Spore Photoproduct Analogue at Cytosine-Thymine Site

As a well known DNA photolesion product, the special UV induced pyrimidine dimmer called spore photoproduct （SP）, has aroused strong research interests. The SP formation was reported solely between two adjacent thymidine residues. It remains unclear in pervious experimental observations why there is an absence of the cytosine-derived SP-like photoprod- uct formation at the cytosine containing DNA strand, although the cytosine residue holds great similarity to thymine in terms of molecular structure. From a theoretical perspec- tive, we have explored this issue in this work by means of density functional theory at the B3LYP/6-311＋＋G（d,p） //B3LYP/6-31G（d,p） level for the DNA dinucleotide fragment, cy- tosine phosphate thymine （CpT）. Key factors blocking the formation of the SP-like product between two adjacent cytosine and thymidine residues are revealed. Instead of undergoing photochemical SP reaction, a photophysical deactivation pathway back to the ground state turns out to be favorable for the CpT dinucleotide fragment.     

胞嘧啶-胸腺嘧啶二核苷SP光损伤反应的理论研究

在DNA光损伤产物中,有一种特殊的UV诱导生成的嘧啶二聚体(SP)．尽管胞嘧啶C和胸腺嘧啶T在分子结构上非常相似,在实验中还没有发现DNA相邻的C和T之间形成类似的SP产物．用密度泛函理论,以DNA中的片段CpT为模型分子,在B3LYP/6-311++G(d,p)//B3LYP/6-31G(d,p)计算水平上从理论的角度揭示 了阻碍CpT生成SP类似物的关键因素． 与生成类似SP产物相比较,CpT更倾向于通过光物理失活途径回到基态反应物     

Electron transfer reaction of meso-phenyl-tetrabenzo-porphyrinato-zinc and dicyanobenzene at low temperature

The behavior of photon-gated spectral hole burning with meso-phenyl-tetrabenzoporphyrinato-zinc as electron donor and dicyanobenzene as electron acceptor dispersed in polymethylmethacrylate was investigated.The data of absorption spectrum of the photoproduct acquired through photon-gated hole burning process by high power density and long hole burning time at 20 K were given The mechanism of photomduced donor-acceptor electron transfer for the iarget system in photon-gated spectral hole burning was demonstrated.     

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。     

Simultaneous detection of ultraviolet B-induced DNA damage using capillary electrophoresis with laser-induced fluorescence

An immunoassay based on CE–LIF was developed for the simultaneous detection of cyclobutane pyrimidine dimers (CPDs) and pyrimidine 6-4 pyrimidone photoproducts (6-4PPs) in genomic DNA irradiated with UVB or natural sunlight. Human cells were first exposed to varying amounts of UVB or natural sunlight to induce DNA damage. Genomic DNA was extracted and incubated with anti-CPD and anti-6-4PP primary antibodies attached to secondary antibodies with a fluorescent quantum dot (QD) reporter that emitted either red or yellow fluorescence. CE was used to separate the unbound antibodies from those bound to the photoproducts, and LIF with appropriate optical filters was used to separate the fluorescence signals from each QD to individual photomultiplier tubes for simultaneous photoproduct detection. Using this strategy, photoproducts were detected from ∼6 ng (200 ng μL⁻¹) of DNA under a low UVB fluence of 65 J m⁻² for CPDs or 195 J m⁻² for 6-4PPs. This assay was also the first to demonstrate the detection of CPDs in human cells after only 15 min of irradiation under natural sunlight.