三氯乙酸酯与二级胺反应的研究

三氯乙酸酯与二级胺反应,在不同条件下得到不同的产物。当三氯乙酸酯与环状二级胺反应时,碳碳键断裂并生成胺基甲酸酯;而与链状二级胺反应时则发生碳氧键断裂并生成叔胺。     

HNCO与CX（X=F，Cl，Br）自由基反应机理的密度泛函理论研究

用量子化学密度泛函理论的B3LYP方法,在6-31+G~*水平上按BERNY能量梯度解 析全参数优化了HNCO与CX（X=F,Cl,Br）反应势能面上各驻点的几何构型,通过 振动频率分析确认了中间体和过渡态,内禀反应坐标（IRC）对反应物、中间体、 过渡态和产物的相关性予以证实,对各驻点进行了零点能校正（ZPE）在此基础上 计算了反应能垒。研究结果表明,与HNCO和其它小分子自由基反应不同,HNCO与 CX自由基反应首先发生分子间H原子迁移,随后N与CX的C（1）原子相互靠近成键并 生成较稳定的中间体,再发生N-C（2）键的断裂,完成N向C（1）上的迁移并进一 步解离为产物。反应按反应物→TS1→IM→TS2→产物通道进行。反应为放热反应。     

混合三烃基卤化锡二苯基环己基碘化锡和甲基二环己基氯化锡与巯基乙酸在有机胺存在下的反应产物及生物活性研究

在有机胺的存在下,Ph2CySnI和McCy2SnCl与HSCH2COOH反应,得到了非锡碳键断裂的五配位阴离子型有机锡化合物和锡碳键断裂的有机锡聚合物两类产物.对于有机胺作为缚酸剂,有机锡卤化物与有机酸反应机理的研究进行了深入探讨.通过IR 1H NMR,13C NMR,元素分析对反应产物进行了表征,确定了反应产物的结构.测定了反应产物体外对人类肺癌肿瘤细胞(A-549)、结肠癌肿瘤细胞(HCT-8)和肝癌肿瘤细胞(Bel-7402)的抑制活性,结果表明该类化合物具有很强的体外抗肿瘤活性.     

聚苯乙烯热降解机理的理论研究

采用密度泛函理论B3LYP/6-311G（d）方法,对聚苯乙烯（PS）热降解反应机理进行了研究。PS热降解的主要产物是苯乙烯,其次是甲苯、α-甲基苯乙烯、乙苯和二聚体等芳烃化合物。PS热降解反应主要包括主链C-C键均裂、β-断裂、氢转移和自由基终止等反应。针对以上各类反应进行了路径设计和理论计算分析,对参与反应的分子的几何结构进行了优化和频率计算,获得了各热降解路径的标准动力学和热力学参数。计算结果表明,苯乙烯主要由自由基的链端β-断裂反应形成;二聚体主要由分子内1,3氢转移的反应形成;α-甲基苯乙烯由分子内的1,2氢转移后进行β-断裂形成;甲苯由苯甲基自由基夺取主链上的氢原子形成;乙苯由苯乙基自由基夺取氢原子形成。动力学分析表明,苯乙烯形成所需要的能垒低于其他产物形成所需要的能垒,故苯乙烯为主要的热降解产物;这与相关实验结果基本一致。     

金属钠—硫磺法合成聚苯硫醚

以金属钠和硫磺为原料,六磷胺作溶剂合成了聚苯硫醚。本工作表明,反应分为两个阶段,首先硫八元环断裂生成了由硫化钠和六磷胺组成的中间产物,中间产物再与对二氯苯反应生成聚苯硫醚。本工作还对钠与溶剂的反应及反应中微量水的影响作了研究。     

全氟烷基磺酸酯C-O键断裂的同面SN2反应

用密度泛函理论研究了CF3SO3CF2CF3 F^-的碳氧键断裂反应的机理。首先，用DFT方法优化了反应物、中间体、过渡态、产物的平衡构型，分析了碳氧键断裂反应的势能面变化，发现在SN2反应机理中，除了S-O断裂SN2反应外，引起C-O键断裂的同面进攻也是一个可能的反应途径。理论计算表明，最终反应的产物是受热力学控制的，S-O键的断裂绝对地优于C-O的断裂。因此，C-O断裂的同面机理虽然是可能的，但却难以被实验观察到，本文还讨论了端基-CF3在同面SN2反应中的邻位效应，以及基组对这个效应的影响。     

双[1,3-二(三甲硅基)环戊二烯基]四羰基二铁的反应性

题示化合物分子中的铁铁键被钠汞齐还原断裂, 生成相应的单核铁负离子, 后者分别与PhCOCl, PhCH~2Cl,ClCH~2COOC~2H~5, Ph~3SnCl 及Ph~2SnCl~2进行亲核取代反应,生成在铁原子上引入相应取代基的产物。题示化合物分别与卤素和二氯化汞反应, 生成铁铁键断裂的铁卤化物和铁氯汞化物。用X-射线测定了题示化合物与Ph~3SnCl反应生成产物的晶体和分子结构。     

涉及碳-碳键断裂的克莱森-施密特缩合反应

研究了Ba(OH)_2促进的β-二酮与芳香醛的克莱森-施密特反应,反应产物可能为单烯烃或双烯烃化合物.单烯烃的生成涉及碳-碳键的断裂,双烯烃产物是姜黄素的三元环类似物.     

四氢萘(C_(10)H_(12))热解反应动力学研究

本文在385—485℃、压力约100atm条件下对四氢萘热解反应动力学进行研究。热解产物的定性鉴定表明,四氢萘主要发生脱氢反应生成萘和异构化反应生成甲基茚满。由a-C_B-C键断裂生成丁基苯反应则较少。反应产物中还有少量茚满、甲苯、乙苯等,它们分别来自甲基茚满和正丁基苯的进一步裂解。本文对复杂的四氢萘热解反应作了定量处理,进行了较详细的动力学研究,求得了相应的速率常数、活化能和指前因子。在实验结果基础上,借助热化动力学计算,参考一些文献结果,提出了四氢萘热解反应机理。由该机理出发所得的各产物速率方程与实验结果基本吻合。     

四氢萘(C10H12)热解反应动力学研究

本文在385—485 ℃、压力约100 atm条件下对四氢萘热解反应动力学进行研究。热解产物的定性鉴定表明, 四氢萘主要发生脱氢反应生成萘和异构化反应生成甲基茚满。由α-C_B-C键断裂生成丁基苯反应则较少。反应产物中还有少量茚满、甲苯、乙苯等, 它们分别来自甲基茚满和正丁基苯的进一步裂解。本文对复杂的四氢萘热解反应作了定量处理, 进行了较详细的动力学研究,求得了相应的速率常数、活化能和指前因子。在实验结果基础上, 借助热化动力学计算, 参考一些文献结果, 提出了四氢萘热解反应机理。由该机理出发所得的各产物速率方程与实验结果基本吻合。     

Characterization of bleomycin cleavage sites in strongly bound hairpin DNAs

The first complete, systematic study of DNA degradation by bleomycin under conditions analogous to those likely in a therapeutic setting has been carried out. Hairpin DNAs selected for their ability to bind strongly to BLM A(5) were used to determine the relationship between high-affinity DNA binding sites and the cleavage efficiency and selectivity of BLM A(5) and deglycoBLM A(5) on these DNAs. Of the 10 hairpin DNAs examined, 8 contained at least one 5'-GC-3' or 5'-GT-3' cleavage site, which have traditionally been associated with strong cleavage by Fe·BLM. In the hairpin DNAs, these included the strongest cleavage sites for BLM A(5) and were generally among those for deglycoBLM A(5). However, numerous additional cleavages were noted, many at sequences not usually associated with (deglyco)BLM-mediated cleavage. The remaining DNAs lacked the preferred (5'-GC-3' or 5'-GT-3') BLM cleavage sequences; however, strong cleavage was nonetheless observed at a number of unusual cleavage sites. The most prominent cleavage sequences were 5'-AT-3', 5'-AA-3', 5'-GA-3', and 5'-TT-3'; treatment with Fe(II)·BLM A(5) or Fe(II)·deglycoBLM A(5) resulted in strong cleavage at these sequences. Additionally, in contrast with BLM A(5), which produced cleavage within the randomized and flanking invariant regions, deglycoBLM A(5) showed a preference for cleavage in the randomized region of the DNAs. Previous reports have established that deglycoBLM exhibits decreased DNA cleavage efficiency relative to BLM. This was also generally observed when comparing cleavage efficiencies for the strongly bound hairpin DNAs. However, some cleavage bands produced by Fe·deglycoBLM A(5) were stronger in intensity than those produced by BLM A(5) at concentrations optimal for both compounds. To investigate the chemistry of DNA degradation, selected hairpin DNAs were treated with n-butylamine following cleavage with Fe(II)·BLM A(5) or Fe(II)·deglycoBLM A(5) to explore the alkali labile pathway of DNA degradation by BLM. While all 10 DNAs showed evidence of alkali labile products, five DNA hairpins afforded some products formed solely via the alkali labile pathway.     

Determination of Alkylphenols Originated from Alkylphenol Ethoxylates by Cleavage Treatment Combined with GC-MS

A chemical cleavage technique was developed for the determination of alkylphenol ethoxylates (APEOs) in environmental samples involving the conversion of APEOs to alkylphenols (APs). Aluminum triiodide (AlI₃) and trimethylsilyl iodide were selected as cleavage reagents and the former was found to be highly reactive and suitable. With AlI₃ as cleavage reagent, nonylphenol ethoxylates (NPEOs) and octylphenol ethoxylates (OPEOs) were equivalently converted to the corresponding origins—nonylphenol (NP) and octylphenol (OP), which were detected by gas chromatography—mass spectrometry (GC-MS). The cleavage process was completed under refluxing condition. Water and methanol influenced the cleavage reaction significantly and should be removed prior to the cleavage reaction. The analytical approach was applied for the estimation of APEOs contents in wastewater by normalizing to APs and presented satisfactory recovery and reproducibility. This cleavage technique provides a common and reliable means to assess the environmental significance of samples contaminated by APEOs based on the presence of APs.     

DNA cleavage promoted by diethylenetriaminepentaacetic acid （DTPA） derivatives

DTPA and its two derivatives were synthesized and used as catalysts in DNA cleavage.Under physiological conditions,a series of experiments have been done.The effects of DNA cleavage with three ligands were studied under different concentrations, cleavage time,and pH values.The results strongly suggested that the plasmid DNA(pUC 19) can be cleaved efficiently by CITC-DTPA. For the cleavage reaction catalyzed by CITC-DTPA,FormⅠDNA could convert to FormⅡmostly,and the DNA-cleavage mechanism involved an oxid...     

Mass spectrometry in structural and stereochemical problems—CCXLIV : The influence of substituents and stereochemistry on the mass spectral fragmentation of progesterone

The complete high resolution mass spectra of progesterone (Δ⁴-pregnene-3,20-dione) and twenty-nine stereoisomers and alkyl substituted analogs have been analyzed with the aid of the recently developed computer program INTSUM. Progesterone analogs with “normal” configuration at the six chiral skeletal carbon atoms give rise to abundant ions corresponding to cleavage of the 1–2 and 3–4 bonds (ketene elimination), to cleavage of the 6–7 and 9–10 bonds (ring B cleavage), and to cleavage of the 13–17 and 15–16 bonds (partial ring D cleavage); these reactions are frequently followed by elimination of alkyl radicals. Alkyl groups at C-6 and C-10 exert a pronounced influence on the formation and fragmentation of the [M-ketene] ions. Reversal of configuration at C-10 increases the importance of ring B cleavage, whereas reversal at C-17 favors the partial cleavage of ring D. The fragmentation of 17-alkylprogesterones differs significantly from the general pattern, with acetyl loss (cleavage of the 17–20 bond) and partial ring D cleavage as the predominating reactions. Loss of ring D by cleavage of the 13–17 and 14–15 bonds is not an important reaction of progesterones. Direct interaction of the two ketonic functions was not observed.     

Real-time monitoring of double-stranded DNA cleavage using molecular beacons

Traditional methods to assay enzymatic cleavage of DNA are discontinuous, time-consuming and laborious. Here, we report a new approach for real-time monitoring of double-stranded DNA cleavage by restriction endonuclease based on nucleic acid ligation using molecular beacon. Upon cleavage of DNA, the cleavage product can be ligated by DNA ligase, which results in a fluorescence enhancement of the molecular beacon. This method permits real-time monitoring of DNA cleavage and makes it easy to characterize the activity of restriction endonuclease and to study the cleavage reaction kinetics.     

Specificity of immobilized porcine pepsin in H/D exchange compatible conditions

Statistical analysis of data from 39 proteins (13 766 amino acid residues) digested with immobilized porcine pepsin under conditions compatible with hydrogen/deuterium (H/D) exchange (<1 degrees C, <30 s) was performed to examine pepsin cleavage specificity. The cleavage of pepsin was most influenced by the amino acid residue at position P1. Phe and Leu are favored residues each with a cleavage probability greater than 40%. His, Lys, Arg, or Pro residues prohibit cleavage when found at the P1 position. Pro also cannot be at position P2 (cleavage probability <0.3%). Occupation of the P3 position by His, Lys, or Arg, or occupation of the P2' position by Pro, also leads to very little cleavage (cleavage probability <1.7%). The average cleavage probability over the entire data set was 13.6%, which is slightly lower than the value previously obtained by Powers et al. (14.8%). This is due, in part, to the larger protein sizes used in the current study. While the specificity of pepsin was similar to that previously observed, higher selectivity was observed in the present study due to less experimental variation in the conditions used to generate our database.     

Synthesis of well-defined telechelic trans-1,4-polyisoprene by oxidative cleavage

Synthesis of telechelic trans-1,4-polyisoprenes(TPI: trans-structure 95%) was evaluated based on two different methods of oxidative cleavage(indirect cleavage: first epoxidation of TPI, then the selective cleavage of epoxidized units in epoxidized trans-1,4-polyisoprene(ETPI) and direct cleavage of isoprene units in TPI). The influence of solvents and the ratio of oxidative agents was investigated by 1H-NMR and 13C-NMR. A series of well-defined telechelic TPI with double terminated functional groups and less side reaction(molecular weight distribution range: 1.96?2.26) were synthesized by indirect cleavage in chloroform. Telechelic TPI showed similar crystallization behavior with TPI and interesting cold crystallization behavior characterized by DSC.     

Evaluation of gaseous hydrogen fluoride as a convenient reagent for parallel cleavage from the solid support

We have tested the limits of gaseous hydrogen fluoride as an agent for parallel detachment of organic molecules from the solid support. Peptides were chosen as relatively sensitive models for this reaction. Acid-catalyzed amide bond hydrolysis, side chain modification (tryptophan and other unnatural amino acids) by the protecting group residues as well as dehydration of serine and asparagine was followed. The technique of cleavage of side chain protection prior to the resin cleavage has given satisfactory results. Two-step deprotection and cleavage from benzhydrylamine resin by TFA and HF was compared to the deprotection and cleavage by TFA from Knorr resin.     

结合丝组二肽的树状多肽对λDNA的切割

以Fmoc手工固相合成法合成了以多聚赖氨酸为骨架, 表面结合丝组二肽的四分支和二分支树状多肽, 以高效液相色谱提纯, 电喷雾电离质谱表征, 并通过凝胶电泳法研究了其对λDNA的切割活性.     

Ether Cleavage with Organo-Alkali-Metal Compounds and Alkali Metals

Reactions with organo-alkali-metal compounds are mostly carried out in ether-type solvents. It has long been known that ether cleavage takes place at the same time. The mechanism of the cleavage, in particular the fact that dialkyl ethers can be decomposed by a variety of mechanisms acting simultaneously, has only become clear in the most recent investigations. The observation that even with purely aliphatic ethers a considerable amount of Wittig ether rearrangement can occur is remarkable. Unusual secondary reactions can also occur by means of which alkyl- and aryllithium compounds in ether or tetrahydrofuran yield new organolithium compounds—sometimes with rearrangement. The reactions of alkyl aryl ethers with alkali metals are also varied and five different mechanisms for them have been discussed in the literature. It is interesting, for example, that the cleavage of anisole can be directed simply by changing the solvent so that in one case only cleavage of the aryl-oxygen bond occurs and in the other almost 100% cleavage of the alkyl-oxygen bond results. The formation of biphenyl as a by-product upon cleavage of the alkyl-oxygen bond in anisole was also puzzling. This was later shown to occur not through the dimerization of phenyl radicals but via 2-methoxybiphenyl. The number of cleavage mechanisms reduces to two if one assumes two different σ^*-radical anions as being intermediates in the kinetically controlled reaction. Comparison of the reactivity of thioethers and ethers reveals not only gradual but also fundamental differences—the cleavage of the thioethers is thermodynamically controlled.