Co-C bond dissociation energy and reaction volume change of 2',5'-dideoxyadenosylcobalamin studied by laser-induced time-resolved photoacoustic calorimetry

Time resolved photoacoustic calorimetry (PAC) was applied to a study of the photolysis of a coenzyme B(12) analog 2',5'-dideoxyadenosylcobalamin, which lacks an -OH group at the 2' position of ribofuranose ring. In aqueous solution, we report for the first time the quantum yield Phi(d) (0.25+/-0.02), Co-C bond dissociation energy (BDE; 31.8+/-2.5 kcal mol(-1)) and reaction volume change deltaV(R) (6.5+/-0.5 ml mol(-1)) due to conformation changes of the corrin ring and its side chains accompanying the cleavage of the Co-C bond. These values for the analog are very similar to those for the natural cofactor. Based our results and previous studies, a possible explanation for the similarity in their structure and properties versus the large difference in their enzymatic activity is discussed.     

铬系乙烯齐聚和聚合催化剂

综述了近年来国内外铬系催化剂的最新研究进展。介绍了该类催化剂齐聚和合的性能研究和应用，讨论了该催化剂长期引起争议的活性中心，活性价态，以及反应机理，并同时预测了铬系催化剂在工业和纳米技术方面的发展趋势。     

Reverse of regioselectivity in intramolecular nucleophilic substitution of pi-allyl palladium species. Highly selective formation of vinylic cyclopropanes via the Pd(0)-catalyzed coupling-cyclization reaction of organic iodides with 2-(2', 3'-Dienyl)malonates

Vinylic cyclopropanes were formed highly selectively via the Pd(PPh(3))(4)-catalyzed insertion-intramolecular nucleophilic substitution reaction of aryl or 1-alkenyl iodides with 2-(2', 3'-dienyl)malonates. The regioselectivity observed here is different from what was reported by Cazes et al.     

电感耦合等离子体原子发射光谱法测定工业废水中铅、镉、铬和砷

采用电感耦合等离子体原子发射光谱(ICP-AES)法同时测定工业废水中铅、镉、铬和砷。对仪器的工作参数和被测元素的分析谱线进行了优化和选择。方法的检出限依次为0.008,0.002,0.007,0.015 mg.L-1。在质量浓度为0.489 mg.L-1(Pb),0.086 6 mg.L-1(Cd),0.231 mg.L-1(Cr)及0.395 mg.L-1(As)的水平上按试验方法测定8次,作了精密度试验,测得相对标准偏差值依次为1.71%,1.22%,0.95%及1.40%。在两个废水样品的基础上作了加标回收试验,所得结果在95.4%~104.6%之间。     

纳秒强激光场中苯电离产生高价离子的研究

用25 ns脉冲Nd-YAG 532 nm的激光，在1010～1011 W•cm－2的光场强度下，利用飞行时间质谱对He、 N2、Ar载气条件下苯的激光电离过程进行了研究.发现当利用氩作为载气时，除观察到C2＋、C2H2+、C3H3+、C6H6+离子外，还观察到很强的Cq＋(q=1～3)高价离子.这些离子都有很高的平动能， C2＋的最可几平动能为12.9 eV， C3＋为37.5 eV.通过改变载气种类和压力及在不同光场强度条件下的实验，可以认为这些高价离子来源于含苯团簇的库仑爆炸过程.     

外加盐作用形成的正负离子表面活性剂双水相

癸基三乙基溴化铵-癸基磺酸钠（C10NE-C10SO3）等摩尔混合均相体系（即使在表面活性剂总浓度高达0.2 mol•L－1时仍然可形成稳定的均相溶液）在外加盐NaF、Na2SO4和Na3PO4的作用下可自发分离成两个水相（双水相）.研究了该类双水相体系的形成、相行为及其对牛血清蛋白（BSA）的分配，并与普通的正负离子表面活性剂混合双水相体系进行了比较.结果表明，该类双水相体系克服了普通的正负离子表面活性剂混合双水相体系的一些不足，具有一些独特的优点.该类双水相体系的相行为可以通过外加盐进行调控,通过外加盐的种类来调控和优化BSA的分配行为.图1表2参8     

树枝形聚合物修饰的双8-羟基喹啉光物理研究

研究了树枝形聚合物修饰的双8-羟基喹啉衍生物(Gn-QMQ, n=1~3)在二氯甲烷和乙腈中的荧光猝灭过程和荧光衰减过程. 随着代数n的增加, 猝灭速率常数减小, 核心双8-羟基喹啉基团荧光寿命增长, 非辐射失活速率常数减小. 研究结果表明, 随着代数的增加, 树枝形骨架对核心基团的位点分离作用增大, 在乙腈中树枝形骨架趋于紧密构象, 具有更强的位点分离作用.     

Cinnamolid‐3β‐ol hemihydrate and 3β‐hydroxycinnamolide acetate,two drimanolide‐class sesquiterpene lactones from Warburgia ugandensis

3β‐Hydr­oxy‐7‐drimen‐12,11‐olide hemihydrate, C₁₅H₂₂O₃·0.5H₂O, (I), has two sesquiterpene mol­ecules and one water mol­ecule in the asymmetric unit. The OH groups of both mol­ecules and both H atoms of the water mol­ecule are involved in near‐linear inter­molecular hydrogen bonds, having O⋯O distances in the range 2.632 (3)–2.791 (2) Å. 3β‐Acet­oxy‐7‐drimen‐12,11‐olide, C₁₇H₂₄O₄, (II), has its ring system in very nearly the same conformation as the two mol­ecules of (I).     

Chemical basis of DNA sugar-phosphate cleavage by low-energy electrons

DNA damage by low-energy electrons (LEE) was examined using a novel system in which thin solid films of oligonucleotide tetramers (CGTA and GCAT) were irradiated with monoenergetic electrons (10 eV) under ultrahigh vacuum. The products of irradiation were examined by HPLC. These analyses permitted the quantitation of 16 nonmodified nucleobase, nucleoside, and nucleotide fragments of each tetramer resulting from the cleavage of phosphodiester and N-glycosidic bonds. The distribution of nonmodified products suggests a mechanism of damage involving initial electron attachment to nucleobase moieties, followed by electron transfer to the sugar-phosphate backbone, and subsequent dissociation of the phosphodiester bond. Moreover, virtually all the nonmodified fragments contained a terminal phosphate group at the site of cleavage. These results demonstrate that the phosphodiester bond breaks by a distinct pathway in which the negative charge localizes on the phosphodiester bond giving rise to nonmodified fragments with an intact phosphate group. Conversely, the radical must localize on the sugar moiety to give as yet unidentified modifications. In summary, the reaction of LEE with simple tetramers involved dissociative electron attachment leading to phosphodiester bond cleavage and the formation of nonmodified fragments.     

7-(对甲酰基苯偶氮)-8-羟基喹啉-5-磺酸的合成及其双波长分光光度法测定镓

7－（对甲酰基苯偶氮）－8－羟基喹啉－5－磺酸是一新显色剂。该试剂在微碱性介质中（pH＝7．5）与镓形成黄色络合物。络合物λmax＝392nm，摩尔吸光系数ε392＝2．24×104L·mol-1·cm-1。同时在500nm呈现负峰，用双峰观波长法测定镓ε392～500＝6．89×104L·mol-1·cm－1，灵敏度是单波长法的三倍多．线性范围0～2．0×10－5mol／L。用拟定的方法测定了掺硅的GaAS材料及岩石中的镓，加入回收率为106％～110％；方法的相对标准偏差小于1．6％。