TiO2表面羟基及其性质

TiO₂材料表面含有丰富的羟基基团，研究表面羟基的分布和性质对理解TiO₂的吸附和光催化作用本质有非常重要的意义。本文简要总结了国内外近年来关于TiO₂表明羧基的研究进展，如不同晶相结构TiO₂的表面羟基状态及不同晶面上羧基的种类、表面吸附水对羟基分布的影响、表面羟基的光电化学性质以及其在光催化反应中的作用等。最后对TiO₂表面羧基研究中存在的问题进行了分析。     

锌/NaOH水溶液还原芳酮及芳醛的便捷且环境友好的方法

本文报道在氢氧化钠水溶液中，用锌粉把含有羟基或氨基取代基团的9，10－蒽醌和邻（或对）羟基（或氨基）芳醛酮还原为亚甲基衍生物。本还原方法避免了Wolff-Kishner-Huang Minlon 反应中NH₂-NH₂的污染和Clemmensen反应中Hg污染，具有操作方便、产率高、不使用有机溶剂的特点。根据使用DFT理论的计算结果，提出这类还原反应的机理。     

纳米三氧化钨修饰碳纳米管载铂催化剂对甲醇氧化的电催化性能

采用表面修饰技术将碳纳米管(CNT)表面羧基化, 通过羧基将钨离子基团修饰到碳纳米管的外表面, 再通过高温焙烧处理将钨离子基团氧化成WO₃, 成功合成了纳米WO₃/CNT复合物, 进一步还原Pt 的前驱体而得到Pt-WO₃/CNT复合催化剂. 采用X射线粉末衍射(XRD)和透射电镜(TEM)对样品的形貌和晶型结构进行了表征, 结果表明, Pt纳米粒子为面心立方晶体结构, 均匀地分布在WO₃修饰的碳纳米管表面. 采用循环伏安(CV)和计时电流法研究了在酸性溶液中Pt-WO₃/CNT催化剂对甲醇的电催化氧化活性, 结果表明WO₃修饰的碳纳米管载铂催化剂比用混酸处理的碳纳米管载铂催化剂对甲醇呈现出更高的电催化氧化活性和更好的稳定性.     

介孔SiO2气凝胶的常压干燥制备研究

以廉价的水玻璃为硅源，用乙醇(EtOH) / 三甲基氯硅烷(TMCS) / 庚烷(Heptane)溶液对湿凝胶进行改性，采用一种新的常压干燥工艺合成了SiO₂气凝胶。通过TMCS与乙醇、湿凝胶孔隙水及Si-OH基团之间的反应，使湿凝胶的溶剂交换和表面改性得以在一步完成。所合成的SiO₂气凝胶为轻质透明的块状固体，密度为0.128～0.136 g·cm^-3，孔隙率93.8%～94.2%。利用FTIR、SEM、TEM和BET吸附对气凝胶的微观结构、形貌和性质进行了研究。结果表明，气凝胶为海绵状结构，粒子直径和孔径分布均匀，比表面积559～618 m²·g^-1，表面带有较多的Si-CH₃基团，呈现出明显的疏水性。     

表面富锡MCM-41分子筛的表面金属有机化学制备及其对苯酚羟基化催化反应性能研究

采用SnBu₄在MCM-41表面的接枝反应和后续处理制备出了一种只在表面含锡的MCM-41型介孔分子筛。通过与采用纳米SnO₂和MCM-41机械混合法、SnCl₄浸渍法、水热合成法等制备的具有相当硅锡比(Si/Sn≈100)的SnMCM-41分子筛进行结构和对苯酚羟基化反应催化性能的比较发现， 由该法所得分子筛的水热稳定性明显提高，并在苯酚羟基化反应中表现出优良的催化活性、选择性和过氧化氢利用率。本文还详细考察了该催化剂对苯酚羟基化反应的最佳反应条件。     

一个新的二茂铁-钴四核双螺旋配合物的合成，结构和电化学性质研究

利用1，1′-双羧酸二茂铁为配体设计合成了一个新的二茂铁-钴四核双螺旋配合物并研究了其电化学性能。该配合物具有一个垂直于其螺旋轴的C₂对称性，四个金属中心形成一个边长为5.4?菱形结构。二茂铁配体的两个羧基以顺式结构与两个金属中心配位。电化学研究表明作为桥联基团的金属钴配位中心能够有效传递二茂铁基团间的氧化还原性能。     

2-氨基对苯二甲酸根及2-咪唑烷酮构筑的镉(Ⅱ)配位聚合物的合成、晶体结构及荧光性质

以一种尿素的衍生物2-咪唑烷酮为溶剂,采用脲热法合成了一个新的配位聚合物[Cd(NH₂bdc)(e-urea)]_n(1)(H₂NH₂bdc为2-氨基对苯二甲酸,e-urea为2-咪唑烷酮),并对其结构和荧光性质进行了研究。单晶结构分析结果表明,标题化合物的中心镉(Ⅱ)离子分别与2-氨基对苯二甲酸根配体的羧基氧原子和溶剂氧原子配位形成七配位的变形五角双锥结构。相邻的中心镉(Ⅱ)离子通过溶剂氧原子和配体羧基基团的连接,形成无限的一维链。这些一维的链进一步通过2-氨基对苯二甲酸根配体的连接最终形成了具有一维孔道的三维框架结构。研究表明,该化合物在室温下能发出较强的蓝色荧光。     

树状聚酰胺-胺桥联受阻酚类抗氧化剂的合成及清除DPPH·活性研究

以系列1.0、2.0代树状聚酰胺-胺(PAMAM)为桥联基,3-(3,5-二叔丁基-4-羟基苯基)丙酰氯为抗氧化基团,通过酰胺化缩合反应合成了系列树状桥联受阻酚类抗氧化剂。红外光谱和核磁共振氢谱证实了系列树状聚酰胺-胺桥联受阻酚类抗氧化剂的化学结构。采用EPR技术研究系列树状聚酰胺-胺桥联受阻酚类抗氧化剂清除DPPH·的能力,结果表明,系列树状聚酰胺-胺桥联受阻酚类抗氧化剂具有良好清除DPPH·活性,且随着清除时间的延长、桥联基长度和代数的增加,其清除活性增强。     

功能化ZnxCd1-xS纳米晶的制备及其光学性能的研究

以氯化锌、氯化镉和硫化钠为原料，采用巯基乙醇为表面修饰剂，H₂O/DMF为溶剂，制得未团聚且分散均匀的纳米晶溶液，同时得到表面富含羟基基团不同锌镉组成的复合Zn_xCd_1-xS纳米晶。利用FTIR、EDS、UV-Vis、XRD、荧光光谱(PL)考察了复合纳米晶结构和光学性能的关系，并利用紫外灯摄像技术对Zn_xCd_1-xS纳米晶的光致发光性能进行     

两个基于4-咪唑羧酸配体超分子配位聚合物的合成、结构和性质

以含4-咪唑和羧酸基团的双功能基团4-咪唑基苯甲酸(HL₁)为配体,用水热法合成了2个超分子化合物[Cd(L₁)(HL₁)I] (1)和[Co₂(L₁)₄(H₂O)₈] (2),并进行了元素分析、红外、热重、粉末衍射及X-射线单晶衍射等表征。晶体结构解析结果表明:配合物1属于单斜晶系,P2₁/c空间群,L₁-配体连接Cd(Ⅱ)离子成一维链,这些一维链通过氢键连接成三重贯穿的α-Po结构的超分子聚合物;配合物2不对称结构单元中,存在3种不同的金属Co(Ⅱ)中心单核分子,这些相互独立的分子单元通过丰富的氢键连接成三维的聚合物。同时,对配合物1室温下的固体荧光性质和配合物2对气体的吸附性能进行了研究。     

聚酰胺-胺型树形分子模板法制备Pt纳米簇

利用紫外-可见吸收光谱和红外光谱对Pt2＋与G5.5-COOCH3聚酰胺-胺型树形分子的络合机理进行了研究, 结果表明Pt2＋与G5.5-COOCH3 PAMAM的最外层叔胺基发生络合作用, 但两者之间达到络合平衡需要较长时间, 且平衡时间随Pt2＋与树形分子物质的量比增大而增长; Pt2＋与G5.5-COOCH3树形分子的最大络合数为50～55; 采用硼氢化钠还原法原位制备了G5.5-COOCH3 PAMAM包裹、平均粒径小于2 nm、多晶的球形Pt纳米簇, 并研究了Pt2＋与PAMAM物质的量比对Pt纳米簇形貌的影响, 实验结果表明, Pt2＋与PAMAM物质的量比为10时, 生成尺寸较小分布较窄的内型Pt纳米簇/树形分子复合材料, 而物质的量比为50时, 会生成部分尺寸较大、分布较宽的外型Pt纳米簇/树形分子纳米复合材料.     

Formation of columnar liquid crystals on the basis of unconventional triazine-based dendrimers by the C3-symmetric approach

Two series of unconventional triazine-based dendrimers with C(2) symmetry and C(3) symmetry were prepared. The newly prepared C(3)-symmetrical dendrimers were characterized by (1)H and (13)C NMR spectroscopy, mass spectrometry, and elemental analysis. Differential scanning calorimetry, polarizing microscopy, and powder XRD showed that the C(3)-symmetrical dendrimers display columnar liquid-crystalline phases during thermal treatment, but the C(2)-symmetrical dendrimers were not observed to behave correspondingly. The molecular conformations of C(3)- and C(2)-symmetrical dendrimers were obtained by computer simulation with the MM2 model of the CaChe program in the gas phase. The simulation results reasonably explain the different mesogenicities of C(3)- and C(2)-symmetric dendrimers. This new strategy should be applicable to other types of unconventional dendrimers with rigid frameworks for displaying columnar liquid-crystalline behavior.     

Efficient halogen-lithium exchange reactions to functionalize poly(alkyl aryl ether) dendrimers

Poly(alkyl aryl ether) dendrimers were functionalized with bromophenyl groups at their peripheries, so as to have 3, 6, 12, and 24 groups in the zero, first, second, and third generation dendrimers, respectively. The new bromophenyl functionalized dendrimers were assessed for their reactivities in C-heteroatom and C-C bond forming reactions. For this purpose, the bromophenyl functionalized dendrimers were converted quantitatively to their polylithiated derivatives, using n-BuLi in benzene. The polylithiated dendrimers were reacted either with D₂O or with CO₂, so as to afford the corresponding deuterated and carboxylic acid functionalized dendrimers, respectively. The carboxylic acid functionalized dendrimers were modified further to the methyl esters during their characterization.     

Electrostatic layer-by-layer deposition of photoactive dendrimers with triviologen-like cores on their surfaces. Synthesis and electrochemical and photocurrent generation measurements

The stepwise assembly of Fréchet-type dendrimers with naphthalene peripheral groups and positively charged viologen-like cores on quartz and ITO surfaces utilizing the layer-by-layer approach was investigated. We were able to deposit only the (+6) charged dendrimers series on ITO. The number of assembled dendrimers was found to increase as we go to higher-generation dendrimers. This dendrimer generation effect was evident from the UV-vis and electrochemical measurements of the assembled dendrimers. The half-wave potentials (E1/2) of the dendrimers shift to less negative values as the dendrimer generation increases in acetonitrile and to more negative values when assembled on ITO. Anodic photocurrent generation was seen upon light irradiation of the second- and third-generation dendrimers, NB1V3+6 and NB2V3+6, assembled on ITO but not for the zero-generation one, NV3+6. This observation was attributed to a fast charge recombination process in NV3+6 when compared to that of NB1V3+6 and NB2V3+6 dendrimers.     

Photoswitchable flexible and shape-persistent dendrimers: comparison of the interplay between a photochromic azobenzene core and dendrimer structure

Two analogous classes of dendrimers with a single azobenzene moiety at the core have been prepared. Flexible benzyl aryl ether dendrimers 1a-e were obtained in good yields by direct alkylation of diphenolic azobenzene 3 with benzyl aryl ether dendrons [G-n]-Br (n = 0-4). In rigid dendrimers 2a-e, the azobenzene configurational switch was linked to phenylacetylene dendrons through acetylenic linkages to maintain the shape-persistent nature of these dendrimers. A comparison of these two different classes of dendrimers with azobenzene cores reveals a difference in the properties of the photochromic moiety upon dendritic incorporation as well as a significant difference in the photomodulation of dendrimer properties. The E --> Z photoisomerization quantum yield decreased markedly with increasing generation for dendrimers 1a-e but only slightly for dendrimers 2a-e. However, increasing generation did not significantly alter thermal isomerization kinetics or activation barriers. The hydrodynamic volumes of azobenzene-containing dendrimers 2b-e were significantly modulated when the azobenzene unit is subjected to irradiation, while those of dendrimers 1b-e were only slightly affected.     

Peptide dendrimer enzyme models for ester hydrolysis and aldolization prepared by convergent thioether ligation

Peptide dendrimers with multiple histidines or N-terminal prolines efficiently catalyze ester hydrolysis or aldol reactions in aqueous medium. Part of the catalytic proficiency of these dendritic enzyme models stems from multivalency effects observed in G2, G3 and G4 dendrimers displaying multiple catalytic groups in their branches. To study multivalency in higher generation systems, G4, G5 and G6 peptide dendrimers were prepared by a convergent assembly. Thus, peptide dendrimers bearing four or eight chloroacetyl groups at their N-termini underwent multiple thioether ligation with G2 and G3 peptide dendrimers with a cysteine residue at their focal point, to give G4, G5 and G6 dendrimers containing up to 341 amino acids, including multiple histidines or N-terminal prolines. While the efficiency of the esterase catalysts was comparable to that of their lower generation analogs, a remarkable reactivity increase was observed in G5 and G6 aldolase dendrimers.     

Molecular batteries: ferrocenylsilylation of dendrons, dendritic cores, and dendrimers: new convergent and divergent routes to ferrocenyl dendrimers with stable redox activity

The ferrocenylsilylation of the phenol triallyl dendron 2, of the phenol nonaallyl dendron 4, and of the 9-, 27-, 81-, and 243-allyl dendrimers 7-10 (monitored by the disappearance of the signals of the olefinic protons in 1H NMR spectra) has been achieved using ferrocenyldimethylsilane 1 and Karstedt's catalyst in diethyl ether at 40 degrees C, yielding the corresponding ferrocenyl dendrons and dendrimers. An alternative convergent synthesis of the nonaferrocenyl dendron 5 was carried out by reaction of the triferrocenyl dendron 2 with a protected triododendron followed by deprotection. Reaction of the nonaferrocenyl dendron 5 with hexakis(bromomethyl)benzene gave the 54-ferrocenyl dendron 6. All the ferrocenyl dendron and dendrimers produce a chemically and electrochemically reversible ferrocenyl oxidation wave at seemingly the same potential. Stable platinum electrodes modified with the high ferrocenyl dendrimers were fabricated. The soluble orange-red ferrocenyl dendrimers can also be oxidized in CH2Cl2 by [NO][PF6] to the insoluble deep blue polyferrocenium dendrimers. For instance, the 243-ferrocenium dendrimer has been characterized by its Mossbauer spectrum, which is of the same type as that of ferrocenium itself. The ferrocenium dendrimers can be reduced without any decomposition back to the ferrocenyl dendrimer, indicating that these multielectronic redoxstable dendrimers behave as molecular batteries.     

Comparison of PAMAM-Au and PPI-Au nanocomposites and their catalytic activity for reduction of 4-nitrophenol

Dendrimer-Au nanocomposites are prepared in aqueous solutions using poly(amidoammine)dendrimers (PAMAM) (generation 2, 3, and 5) and poly(propyleneimine)dendrimers (PPI)(generation 2, 3, and 4) by wet chemical NaBH(4) method. The Au nanoparticles thus obtained are 2-4 nm in diameter for both dendrimers and no generation dependence on the particle size is observed, whereas the generations of the dendrimers are increased as stabilization of Au-nanoparticles is achieved with lower dendrimer concentrations. Studies of the reduction reaction of 4-nitrophenol using these nanocomposites show that the rate constants for the PAMAM dendrimers (generations 2 and 3) are higher than those for the PPI dendrimers (generations 2 and 3), while a distinct difference in the rate constants is not seen for the PAMAM dendrimer (generation 5) or the PPI dendrimer (generation 4). In addition, the rate constants for the reduction of 4-nitrophenol involving all the dendrimers decrease with increases in dendrimer concentrations.     

Synthesis of Novel Amphiphilic Poly （ester-amine） Dendrimers and Their Recognition of Hg2＋ at the Air／Water Interface

Two novel amphiphilic poly(ester-amine)dendrimers were synthesized and characterized by 1H NMR,13C NMR and IR spectra.Their properties of Langmuir film were investigated at the air/water interface.The relationship between the surface pressure and area isotherms of the dendrimers was found to be dependent on the nature of subphases,Interaction between HgCl2 and the dendrimers was observed,indicating that the amphiphilic dendrimers could act as a sensor for Hg^2 .     

Dendritic chelating agents. 1. Cu(II) binding to ethylene diamine core poly(amidoamine) dendrimers in aqueous solutions

This paper describes an investigation of the uptake of Cu(II) by poly(amidoamine) (PAMAM) dendrimers with an ethylenediamine (EDA) core in aqueous solutions. We use bench scale measurements of proton and metal ion binding to assess the effects of (i) metal ion-dendrimer loading, (ii) dendrimer generation/terminal group chemistry, and (iii) solution pH on the extent of binding of Cu(II) in aqueous solutions of EDA core PAMAM dendrimers with primary amine, succinamic acid, glycidol, and acetamide terminal groups. We employ extended X-ray absorption fine structure (EXAFS) spectroscopy to probe the structures of Cu(II) complexes with Gx-NH2 EDA core PAMAM dendrimers in aqueous solutions at pH 7.0. The overall results of the proton and metal ion binding measurements suggest that the uptake of Cu(II) by EDA core PAMAM dendrimers involves both the dendrimer tertiary amine and terminal groups. However, the extents of protonation of these groups control the ability of the dendrimers to bind Cu(II). Analysis of the EXAFS spectra suggests that Cu(II) forms octahedral complexes involving the tertiary amine groups of Gx-NH2 EDA core PAMAM dendrimers at pH 7.0. The central Cu(II) metal ion of each of these complexes appears to be coordinated to 2-4 dendrimer tertiary amine groups located in the equatorial plane and 2 axial water molecules. Finally, we combine the results of our experiments with literature data to formulate and evaluate a phenomenological model of Cu(II) uptake by Gx-NH2 PAMAM dendrimers in aqueous solutions. At low metal ion-dendrimer loadings, the model provides a good fit of the measured extent of binding of Cu(II) in aqueous solutions of G4-NH2 and G5-NH2 PAMAM dendrimers at pH 7.0.