Origin of informational polymers: The concurrent roles of formamide and phosphates

Formamide chemistry provides a unitary system by gathering all of the precursors needed to synthesise pregenetic informational polymers in a single milieu. This is not observed with HCN chemistry. With common catalysts, formamide affords all of the precursor nucleobases, photochemically condenses into acyclonucleosides, favours transphosphorylation and enhances micellar aggregation of surfactants. Also, formamide provides a set of physicochemical conditions that thermodynamically favour the polymeric state of nucleotides over the monomers. In the origin-of-informational-polymers scenario, formamide acts in every step, the least characterised being the set of its reactions with phosphates. On this matter, we report two complementary sets of results: 1) the synthesis of prebiotic precursors from formamide, which are catalysed by soluble and mineral phosphates-we observed the formation of rich mixtures that include uracil, 9H-purine, cytosine, dihydrouracil, hypoxanthine, adenosine, urea, parabanic acid, the amino acid N-formylglycine and the peptide-condensing agent carbodiimide; and 2) the protection of ribo- and deoxyribophosphoester bonds by phosphates. The relevance of these effects with respect to the origin of informational polymers is discussed.     

Synthesis and degradation of nucleobases and nucleic acids by formamide in the presence of montmorillonites

We describe the role of formamide, a product of the hydrolysis of hydrogen cyanide, as precursor of several components of nucleic acids under prebiotic conditions. When formamide is heated in the presence of montmorillonites, the efficient one-pot synthesis of purine, adenine, cytosine, and uracil is obtained. Along with these nucleobases, several components of the inosine pathway are obtained: 5-aminoimidazole-4-carboxamide, 5-formamidoimidazole-4-carboxamide and hypoxanthine. This almost complete catalogue of nucleic acid precursors is accompanied by N(9)-formylpurine, which, containing a masked glycosidic bond in its formyl moiety, is a plausible precursor of purine acyclonucleosides. In addition, montmorillonites differentially affect the rate of degradation of nucleobases when embedded in 2'-deoxyoligonucleotides; namely, montmorillonites protect adenine and guanine from the degradative action of formamide, while thymine degradation is enhanced. The oligonucleotide backbone reactivity to formamide is also affected; this shows that the interaction with montmorillonites modifies the rate of abstraction of the Halpha and Hbeta protons on the sugar moieties.     

甲酰胺系钛溶胶性能对TiO2材料微结构的影响

稳定的甲酰胺系溶胶的制备是乳液模板法制备高度有序多孔陶瓷材料的前提和基础。系统考察了水含量rw对甲酰胺系钛溶胶性能的影响,同时研究了溶胶性能对TiO2材料的孔径及比表面积等微观结构的影响。结果发现溶胶的粒径随rw和放置时间的增加而增大,黏度随rw的增大而增大。rw越大,制备出的TiO2材料的比表面积越小,而孔径(约8 nm)并不随rw的变化而变化。该研究为多孔TiO2材料的微结构控制提供了实验基础。     

Hypersensitive radical probes and the mechanisms of cytochrome P450-catalyzed hydroxylation reactions

The title probes are precursors to kinetically calibrated, aryl-substituted cyclopropylcarbinyl radicals that rearrange with picosecond lifetimes. Applications in studies of cytochrome P450-catalyzed hydroxylation reactions are reviewed. Initially confusing results regarding lifetimes of radicals in the hydroxylation reactions were resolved when second-generation probes that distinguish between radicals and cations were employed. The results indicate that two electrophilic oxidizing species are involved in P450-catalyzed hydroxylations, an iron-oxo species that inserts oxygen and a hydroperoxo-iron species that inserts OH(+). The cationic rearrangement products are ascribed to reactions of the protonated alcohol products formed from the latter.     

Mn(III)-catalyzed radical reactions of 1,3-dicarbonyl compounds and cyclopropanols with vinyl azides for divergent synthesis of azaheterocycles

Mn(III)-catalyzed formal [3+2]- and [3+3]-annulations have been developed using readily available vinyl azides with 1,3-dicarbonyl compounds and cyclopropanols. Vinyl azides were successfully applied as a three-atom unit including one nitrogen to prepare various azaheterocycles via Mn(III)-catalyzed radical reactions.     

成型TiO_2负载型纳米碳纤维催化材料的制备与表征

采用成型TiO2为载体,以甲烷为碳源,镍铜双金属催化剂,改变反应温度以及碳氢比(CH4/H2摩尔比),生长纳米碳纤维(CNF),制备出结构化复合纳米碳纤维催化材料-生长在成型TiO2上的纳米碳纤维材料(CNF/TiO2).扫描电镜(SEM)和物理吸附仪(BET)表征结果表明,CNF粗细均匀、直径～70 nm,而且与其他传统催化剂载体(活性炭)相比几乎没有微孔.并以CNF/TiO2为载体,采用浸渍法负载金属钯,制备出结构化纳米碳纤维负载型钯催化剂(Pd/CNF/TiO2),以苯乙烯加氢为模型反应进行活性评价,结果表明,其催化活性明显优于成型活性炭负载型Pd催化荆.结构化纳米碳纤维具有比表面适中,且不含微孔,是一种优良的催化剂载体,可望用于受内扩散制约的气液固三相催化反应.     

紫外-可见光谱确定甲酰胺/AEO3/正辛烷非水微乳微观结构研究

研究了以甲酰胺为极性相,正辛烷为油相,以脂肪醇聚氧乙烯(3)醚(AEO3)为表面活性剂形成的非水微乳液相行为。以甲基蓝(MB)和甲基橙(MO)为探针,利用探针在溶液、胶束、反胶束等不同极性环境下吸收峰位置的变化,通过紫外-可见光吸收光谱研究了该非水微乳液相区的微观结构,确定了该体系可以形成以甲酰胺为分散相,正辛烷为连续相的油连续型微乳液。     

非水微乳体系相图研究

研究了以甲醇或甲酰胺为极性相,正辛烷为油相,添加不同HLB值的表面活性剂形成的非水微乳体系的三元相图.结果表明,具有适当HLB值的表面活性剂可与正辛烷、甲醇或甲酰胺形成单相区,亲水性强的表面活性剂不利于形成单相微乳体系;在m(表面活性剂):m(正辛烷)=1∶4,甲醇(甲酰胺)增溶量为最大增溶量的50％时,各微乳液相点的粒径在20～60 nm.     

纳米TiO2薄膜光催化降解罗丹明B的研究

本文采用sol-gel法制备了TiO2溶胶,以载玻片作为底材,用提拉法镀膜,经高温热处理后得到了TiO2纳米晶薄膜。采用XRD、SFM研究了薄膜的物相及其结构特征,UV-vis研究了薄膜的光吸收特性,以罗丹明B溶液作为目标反应物,研究了溶胶的浓度、pH值以及热处理气氛对TiO2薄膜光催化性能的影响。     

Nucleoside Analogues: Synthesis from Strained Rings

Nucleoside analogues are widely employed as bioactive compounds against cancer and viral infections. Consequently, it is important to develop efficient synthetic methods to access them with high efficiency and structural diversity. Herein, we present a full account of our work on the synthesis of nucleoside analogues via annulations of donor acceptor aminocyclopropanes and aminocyclobutanes. Thymine- and uracil-derived diester cyclopropanes were accessed from the corresponding nucleobases via vinylation and rhodium-catalyzed cyclopropanation, and were then used in (3+2) annulations with aldehydes, ketones and enol ethers. The obtained analogues could be transformed into important hydroxymethyl derivatives. Thymine and fluoro-uracil-derived diester cyclobutanes obtained from the nucleobases via vinylation and (2+2) cycloaddition could also be used in a (4+2) annulation with aldehydes. Finally, purine-derived diester cyclopropanes could be accessed using the condensation of nucleobases with chloromethyl ethylidene malonates, but annulation reactions with this class of substrates were not successful.     

二丁氨基锌酞菁的合成与性质

以4-硝基邻苯二甲腈、二正丁胺、亚氨基二丙酸为原料,合成2（3）-（N,N-二丙酸氨基）-9（10）,16（17）,23（24）-（N,N-二-丁氨基）锌酞菁（FPC）.通过IR谱、UV-Vis谱、元素分析和1H NMR谱表征其结构,比较了产物在TiO2薄膜和N,N-二甲基甲酰胺（DMF）溶液中的UV-Vis谱.结果证明,所合成的化合物FPC在DMF中具有良好的溶解性,且在一定浓度范围内不发生集聚现象.FPC的UV-Vis谱发生明显红移,能级与纳米TiO2薄膜匹配,适用于制备太阳能电池.     

聚对苯撑乙烯类共聚物／TiO2复合材料光物理性能的研究

两种经过化学修饰的PPV（聚对苯撑乙烯）类共轭高分子共聚物分别与纳米TiO2复合，作为有机／无机复合材料进行研究。这两 人聚物在乙醇、二氯甲烷溶液中分别与以Sol-Gel法、反胶束法制得的TiO2共混得到均匀分散的体系而不出现相分离，用共聚物与TiO2的复合液可以在石英基底上制成均匀的复合膜，结果表明，高聚物／TiO2复合物的光物理特性与单纯的高聚物相比呈现明显的差异；不同粒径的纳米TiO2以复合物性能的影响不同；中间苯环的聚代基对共聚物的性质影响明显，共轭高分子与纳米TiO2复合涂膜后其发光性能明显改善，有作为发光器件的应用前景。     

攀钢铁水罐用后高铝残砖分析

利用化学分析、X射线衍射仪、电子探针以及热力学等方法对攀钢铁水罐用后高铝残砖进行了分析.结果表明:残砖几乎没有挂渣层.舍钒钛渣由于表面张力小,黏度低,在高铝砖中的渗透很深;渣中的V2O5、TiO2、MnO、FeO等与高铝砖中组分反应生成的固溶体和化合物(如尖晶石、刚玉、钙长石等)中均发现固溶有V2O5;变质层的形成导致了致密化热震剥落;而较高的气孔率也是高铝砖损毁严重的另一重要原因.     

纳米TiO_2薄膜的结构及紫外可见光谱研究

本文以钛酸丁酯[Ti(OC4H9)4]、盐酸和去离子水为原料,采用溶胶-凝胶法和旋转涂膜工艺,在玻璃基片上制备透明的TiO2纳米薄膜。通过XRD测试表明:经500°C退火得到的薄膜上TiO2为锐钛矿晶相而粉末为锐钛矿、金红石和板钛矿的混合晶相。通过对膜进行紫外可见光谱分析,探讨了影响TiO2纳米膜厚度和禁带宽度的各种因素。实验结果表明:溶胶的陈化时间、膜的热处理温度、涂膜层数等都将直接影响二氧化钛薄膜的紫外可见光谱和禁带宽。     

在可见光照射下金属离子改性二氧化钛水溶胶对甲基橙的降解

以钛酸四丁酯为前驱物,采用沉淀胶化法制备了TiO2水溶胶,比较了制备方法对TiO2水溶胶性能的影响,并用TiO2水溶胶制备薄膜.采用金属离子Fe3+[1]、Co2+和Ni2+对TiO2水溶胶进行改性,分析离子改性TiO2水溶胶的光吸收性能,发现金属离子与TiO2水溶胶形成了配位化合物.研究了金属离子改性对TiO2水溶胶...     

尿素/甲酰胺增塑PVA的性能研究

采用流延成膜法制备了以尿素/甲酰胺为复配增塑剂改性的聚乙烯醇(PVA)改性薄膜。采用FTIR研究了复配增塑剂尿素/甲酰胺和PVA之间的相互作用,采用XRD、DSC、TGA和拉伸性能测定对改性后的PVA膜性能进行了测试表征。结果表明,尿素/甲酰胺能与PVA形成氢键作用,破坏PVA的结晶结构,降低PVA膜的结晶度。尿素/甲酰胺的加入降低了PVA的熔点,提高了PVA的热分解温度。改性后的PVA膜的拉伸强度降低,断裂伸长率提高。     

掺入SiO_2对TiO_2热催化剂的影响

以ZrO_2为载体,掺入SiO_2的TiO_2作为活性成分,制备负载型催化剂,考察掺入SiO_2对TiO_2热催化剂的影响。结果表明,掺入SiO_2后生成Ti—O—Si,使TiO_2和ZrO_2载体结合的更为牢固。SiO_2能有效抑制TiO_2从锐钛矿转变成金红石,同时抑制锐钛矿型的生成。掺入SiO_2物质的量分数达到15%时,900℃焙烧仍能得到100%的锐钛矿。TiO_2-SiO_2在ZrO_2表面形成薄层,并出现龟裂,可能是因为掺入SiO_2所致。     

Pd-Fe/TiO2催化硝基苯和醇羰基化合成苯氨基甲酸酯

以Pd-Fe/TiO2为催化剂,硝基苯与醇或酚进行羰基化反应合成苯氨基甲酸酯,考察了反应条件和不同反应底物对羰基化反应的影响.结果发现Pd-Fe/TiO2催化剂对羰基化反应具有较好的催化活性,在硝基苯20mmol,醇或酚21mmol,Pd和Fe负载量分别为0.3％和0.1％,催化剂用量96mg,乙腈20mL,CO压力0...     

Control of the β-Hydride Elimination Making Palladium-Catalyzed Coupling Reactions more Diversified

Pd(II)-catalyzed coupling reactions were developed using β-heteroatom elimination and protonolysis reaction to quench the carbon–palladium bond in the presence of halide ions or nitrogen ligands (pyridine, bipyridine, phenanthroline, etc.) for regenerating the divalent palladium species. Halide ions or nitrogen ligands are necessary for the catalytic cycle and high yield of the reactions. For Pd(0)-catalyzed reactions, control of β-hydride elimination is also a challenge for making coupling reactions more diversified. Different kinds of ligands were used to make the coupling reaction suitable for aliphatic compounds. Recently, examples using chloride ion or bathophenanthroline for this purpose were also developed.     

具有光催化活性的透明亲水性自清洁涂料的制备

以钛酸丁酯前躯体在低温条件下,采用溶胶-凝胶法低温制备透明纳米TiO2/SiO2复合薄膜,红外光谱、XRD、SEM、接触角测定仪分析表明:TiO2/SiO2溶胶中TiO2和SiO2既独立成相,也存在TiO2和SiO2的复合物;生成的TiO2的晶型为锐钛型;TiO2的平均粒径为18 nm;TiO2/SiO2复合薄膜与水的接触角为4.2°;通过光催化和户外试验,表明自制的自清洁涂料具有良好的耐沾污性能。