A Novel Photoproduct of 2-Methoxycytosine in Phosphate Solution Under Far UV Irradiation

Theph0tolysis0f2-meth0xycytosineinph0sphate-buffersoluti0nunderl0wpressuremercurylamp(LPML,254nm)wasrep0rtedasearlyasl963byMoor"wh0foundthatthepresence0fin0rganic0rthoph0sphatealteredthec0urse0ftheph0toIysispr0cess0f2-methoxycytosineandpr0ducedannewc0mp0undI(Schemel).Pith2andShawjconfirmedtheresultofM00r.butthereactionmechanismhadnotbeenelucidated.Inparticular,theroleofph0sphateinthemechanismwasn0tclear.Inaprevi0uspaper'wefoundthatthephot0lysisyieldofnucteobases'nucle0sidesandnucleotides(N…     

Production of mixed halogenated congeners of the natural product heptachloro-1′-methyl-1,2′-bipyrrole (Q1) by photolysis in the presence of bromine

Halogenated 1′-methyl-1,2′-bipyrroles (MBPs) are a class of marine halogenated natural products that have been detected in biota from all over the world. However, structures and standards of many mixed chlorinated/brominated MBPs are not available. For this reason, the known 2,3,3′,4,4′,5,5′-heptachloro-1′-methyl-1,2′-bipyrrole (Q1 or MBP-79) was UV-irradiated in the presence of bromine with the goal of inducing a chlorine → bromine exchange. A few drops of bromine were added to a solution of Q1 and 10 mL of either CH₂Br₂, CH₂Cl₂, or CHCl₃. The experiments were performed both at room temperature and elevated temperature for 30 min. At least four out of five possible bromohexachloro-1′methyl-1,2′-bipyrroles (BrCl₆-MBPs), at least seven out of 13 possible Br₂Cl₅-MBPs, as well as traces of Br₃Cl₄-MBPs and Br₄Cl₃-MBPs were obtained in this way. Selective fragment ions in the GC/ECNI-MS spectra as well as electrophilic bromination of hexachloro-MBP solutions were used to verify the structures of the BrCl₆-MBP isomers. The BrCl₆-MBPs eluted from DB-5-like columns in the order of 4′-bromo-2,3,3′,4,5,5′-hexachloro-1′-methyl-1,2′-bipyrrole (Br-MBP-76), which co-eluted with 3′-bromo-2,3,4,4′,5,5′-hexachloro-1′-methyl-1,2′-bipyrrole (Br-MBP-78), followed by 2-bromo-3,3′,4,4′,5,5′-hexachloro-1′-methyl-1,2′-bipyrrole (Br-MBP-75), 3-bromo-2,3′,4,4′,5,5′-hexachloro-1′-methyl-1,2′-bipyrrole (Br-MBP-77), and 5′-bromo-2,3,3′,4,4′,5-hexachloro-1′-methyl-1,2′-bipyrrole (Br-MBP-74). These BrCl₆-MBPs were also detected in a sample of cetacean blubber from Australia, but the abundance pattern was different. While Br-MBP-76/Br-MBP-78 dominated in the cetacean, irradiation of Q1 (MBP-79) in the presence of bromine led to high proportions of Br-MBP-75. The suitability of the UV-induced Cl → Br exchange was confirmed by the Br-assisted UV-irradiation of pentachloroanisole (PCA). This experiment produced at least two bromotetrachloro- and three dibromotrichloroanisoles, the last eluting in each case being the most relevant. Thus, this method is most likely generally suited for the production of mixed-halogenated aromatic organohalogen compounds which are not readily obtainable by synthesis.     

2-苯基苯并噁唑的光解反应

聚对苯撑苯并二噁唑(PBO)纤维对光较为敏感,在紫外光照射下会发生降解.本文研究了该纤维的单体2-苯基苯并噁唑(PO)的初级光化学反应机理.当PO分子吸收一个光子而跃迁到第一激发态后,克服25.59kJ·mol-1能垒而越过过渡态,此时噁唑环打开,且两个苯环形成大约90°的二面角而得到产物,该产物可进一步与空气中的水发生次级反应.计算结果表明在第一激发态上噁唑开环反应很容易,但在基态势能面并没有发现噁唑的开环路径.分子中的原子(AIM)的计算结果与上述分析过程相吻合.     

亚磷酸二烷基酯及其汞化物的光解活泼自由基的ESR研究

本文用自旋捕捉技术和ESR方法,对亚磷酸二烷基酯(RO)₂P(O)H(R=C₂H₅,n-C₃H₇,i-C₃H₇,n-C₄H₉)及其汞化物(RO)₂ P(O)HgX(X=OAc,Cl,Br)的光解产物进行了研究。结果表明,亚磷酸二烷基酯的汞化物比亚磷酸二烷基酯更容易产生自由基(RO)₂p(O)。据此对汞化物中P-Hg的成键特征进行了讨论。     

对位取代苯磺酸钠在溶液及界面的光反应研究

用自旋捕捉－ＥＳＲ方法研究了对位取代苯磺酸在水溶液中光化学行为，结果表明ｐＨ的改变及半导体胶体的存在都能影响其光解过程，使产生的中间体发生变化，发生光解过程中产生的中间体之一是硫中心自由基ＳＯ＾－３，在一定的ｐＨ范围还有Ｃ中心自由基和氢自由基生成，在较低ｐＨ范围，初始反应速率与ｐＨ值呈指数关系。     

Bis(4,5-dimethoxy-2-nitrophenyl)ethylene glycol: a new and efficient photolabile protecting group for aldehydes and ketones

Synthesis of a new photolabile protecting group, bis(4,5-dimethoxy-2-nitrophenyl)ethylene glycol (4) from 4,5-dimethoxy-2-nitrobenzyl alcohol in three steps in good yields is described. The acetals and ketals of 4 are stable against acidic and basic reaction conditions and are cleaved smoothly on irradiation at 350 and 400 nm with regeneration of carbonyl compounds in high yields and efficiency.     

Photochemical synthesis of isomeric (E/Z)-3-alkylidene-3H-isobenzofuranones

The synthesis of isomeric (E/Z)-3-alkylidene-3H-isobenzofuranones by photoisomerization of 2-aroyl-2-methyl/benzylindan-1,3-diones in high yields is described.     

STUDY ON THE PHOTOLYSIS MECHANISM OF POLYESTER FROM SUCCINIC ACID AND N-β-HYDROXYETHYL 2,2,6,6-TETRAMETHYL,4-HYDROXY PIPERIDINE (TINUVIN-622)

The photolysis mechanism of polyester of succinic acid with N—β-hydroxyethyl 2,2,6,6-tetramethyl-4-hydroxy piperidine (Tinuvin-622) has been studied by instrumental analysis. The results show that Tinuvin-622 can be easily photolysed. Based on the results of IR, NMR, ESR, GPC, GC, MS, the photolysis mechanism of Tinuvin-622 has been proposed.     

A new caging phototrigger based on a 2-acetonaphthyl chromophore

Irradiation (λ ∼ 350 nm in an aqueous environment) of carboxylic acid esters derived from the reaction between carboxylic acids and 2-bromo-1-(naphthalene-2-yl)ethanone affords the parent carboxylic acid in good yield, making the 2-acetonaphthyl chromophore a good phototrigger for caging applications, including biomolecular caging.