原位核磁共振技术考察L-缬氨酸导引下合成花状纳米结构聚苯胺形成机理的研究

利用~1H-NMR原位追踪在L-缬氨酸存在下合成花状纳米聚苯胺的形成过程中发现此结构的形成经历3个阶段:首先在苯胺与缬氨酸构成的类胶束结构内聚合成吩嗪类寡聚物;其次通过p-p重叠作用及胶束融合过程成为片状聚集体;最终通过与缬氨酸形成氢键组装成花瓣状纳米聚苯胺.通过改变反应条件,对比形成过程中核磁共振图谱及产物形貌的变化发现花状纳米聚苯胺的形成有如下特征:反应初期L-缬氨酸作为缓冲试剂可以避免苯胺的骤然质子化,有利于生成具有吩嗪结构的寡聚物;反应前苯胺单体与缬氨酸形成稳定的反应环境保证寡聚物始终在其内聚集生长,有效避免了外部环境的影响.     

A Near-Infrared Dye That Undergoes Multiple Interconversions through Acid–Base Equilibrium and Reversible Redox Processes

A near-infrared (NIR) polymethine dye ( 1 ), consisting of a cyclohepta[1,2-b;4,3-b′]dithiophene and two phenol moieties, was synthesized. This dye exhibited pH-responsive changes in its photophysical properties due to a two-step acid–base equilibrium that produced a protonated cation ( 1H⁺ ) and an anion ( 1⁻ ). While 1H⁺ showed an intense fluorescence in the red region of the visible spectrum, 1⁻ exhibited a strong absorption in the NIR region. The tropylium ion character in 1H⁺ induces high pK_a1 and pK_a2 values for 1 . Moreover, a stable radical ( 1^. ) was prepared, which showed a NIR absorption band with a maximum at circa 1600 nm. The cyclic voltammogram of 1^. revealed a two-step reversible redox process that produced 1⁻ and the cation 1⁺ , which is different from 1H⁺ . These redox processes accompany drastic electrochromic changes in the vis–NIR region. Overall, 1 is susceptible to multiple interconversions between five forms, due to the multifaceted character of the cycloheptadithiophene skeleton.     

Carbocation-π interaction: the 1,1-dimethylallyl cation and benzene

Computational studies of the interaction of 1,1-dimethylallyl cation with benzene reveal that its potential energy surface has a rich complexity. The lowest energy π-complex, which involves binding of both ends of the cation to the benzene ring, is calculated to be 4.5 kcal mol⁻¹ lower in energy than its related σ-complex. The results provide further support for the idea that π complexation of carbocations is stronger over the periphery of aromatic systems, and offer insight into why biological reactions involving this type of carbocation do not lead via σ-complex formation to electrophilic substitution of the aromatic rings in proteins.     

Stacked 1,3,5-tris[(2,5-dimethylphenyl)ethynyl]benzenes: dimer and conjugated microporous polymer

A new [2.2]paracyclophane compound consisting of two 1,3,5-tris[(2,5-dimethylphenyl)ethynyl]benzenes stacked in proximity to each other. The compound exhibited a unique absorption band (cyclophane band) and an emission from the phane state, both of which were derived from the π-π stacking of the poorly extended conjugation systems of 1,3,5-tris[(2,5-dimethylphenyl)ethynyl]benzene. In addition, a conjugated microporous polymer (CMP) that comprises pseudo-para-substituted [2.2]paracyclophane was prepared. The obtained CMP is regarded as a polymer, in which 1,3,5-tris[(2,5-dimethylphenyl)ethynyl]benzenes are infinitely stacked to form a network structure. The CMP exhibited a type I nitrogen gas sorption profile and an H4-like hysteresis loop, and possessed the slit-like mesopores with a BET surface area of 501 m² g⁻¹.     

Anion-controlled networks of intermolecular interactions in the crystal structure of 9-aminoacridinium salts

A series of salts, with the 9-aminoacridinium cation (9-AA) and aromatic carboxylic acid: benzoate (1), ortho-phthalate (2), and salicylate (3) anions have been synthesized and characterized using X-ray diffraction. In the crystal packing, the ions are linked via N-H?O, O-H?O, and C-H?O hydrogen bonds. Analysis of the hydrogen bonds in the crystal lattices of the title compounds shows that the cations and anions form tetramers. The ions in these tetramers are linked via N(amino)-H?O(carboxy) hydrogen bonds forming R₂²(8) (1 and 3) or R₂⁴(15) (2) hydrogen bond ring motifs. The cations interact through π-π interactions in the ABBA (1), AB (2) or ABA (3) arrangement to form columns (1 and 2) or chains (3).     

基于1-(1′，3′-苯并噁唑-2′-甲基)苯并咪唑的钴(Ⅱ)配合物：晶体结构、弱相互作用和荧光发射光谱

配体1-(1′,3′-苯并恶唑-2′-甲基)苯并咪唑(L)是通过苯并咪唑与2-(氯甲基)-1,3-苯并恶唑烷基化制备而来。配体L与CoCl2.2H2O反应得到了配合物[CoCl2L2](1)。配合物1通过π-π堆积作用和C-H…Cl氢键形成了三维超分子框架结构。测定了L和1的荧光发射光谱。     

Adsorption of nonpolar benzene derivatives on single-walled carbon nanotubes

The adsorption of benzene, toluene, and chlorobenzene on single-walled carbon nanotubes (SWCNTs) with and without acid oxidation was conducted to investigate the influences of derivative groups on benzene rings and functional groups from SWCNTs on adsorption by SWCNTs. The SWCNTs of high purity were chosen and moderate acid oxidation was performed so that the surface physical properties remained unchanged after acid oxidation and the influences of acid oxidation on adsorption were only contributed from the modification of the surface chemistry of SWCNTs. The oxygen-containing surface groups introduced by acid oxidation obstructed the interactions between functional groups of nonpolar benzene derivatives and C-rings of SWCNTs significantly. The dispersive interaction between the partially positive H⁺ of the methyl group and the oxygen-containing surface groups slightly increased the adsorption of toluene on oxidized SWCNTs at high solution pH. The thermodynamic of adsorption was also studied at different temperatures.     

CH/pi hydrogen bonds determine the selectivity of the Src homology 2 domain to tyrosine phosphotyrosyl peptides: an ab initio fragment molecular orbital study

The CH/pi hydrogen bond is a weak molecular force occurring between CH groups (soft acids) and pi-systems (soft bases), and has been recognized to be important in the interaction of proteins with their specific ligands. For instance, it is well known that Src homology-2 protein (SH2) recognizes its specific pTyr peptide in two key regions, pTyr-binding region and specificity-determining region, by the use of attractive molecular forces, including the CH/pi hydrogen bond. We hypothesized that the CH/pi hydrogen bond plays a key role in determining the selectivity of SH2 proteins, and studied this issue by the ab initio fragment molecular orbital (FMO) method. The FMO calculations were carried out, at the HF/6-31G* and MP2/6-31G* level, for SH2 domains of Src, Grb2, P85alpha(N), Syk, and SAP, in complex with corresponding pTyr peptides. CH/pi hydrogen bonds have in fact been found to be important in stabilizing the structure of the complexes. We conclude that the CH/pi hydrogen bond plays an indispensable role in the recognition of SH2 domains with their specific pTyr peptides, thus playing a vital role in the signal transduction system.     

Synthesis and Structure of a Zinc（Ⅱ） Complex： [Zn（Pybta）·Cl2]n

The title compound, [Zn（Pybta）Cl2]n （Pybta = 1-（2-pyridylmethyl）benzontriazole）, has a zigzag chain structure. It crystallizes in the monoclinic system, space group P21/c with a = 9.0103（11）, b = 17.0276（18）, c = 9.2288（11）A,β = 101.309（6）°, Mr= 346.51, V= 1388.4（3）A^3, Z= 4, De= 1.658 g/cm^3, F（000） = 696,/a = 2.143 mm^-1, the final R = 0.0492 and wR = 0.1236 for 2545 observed reflections with I 〉 2σ（I）. The Zn atom is four-coordinated by two N and two Cl atoms, forming a slightly distorted tetrahedral geometry. Each zigzag chain links its adjacent symmetryrelated equivalents via multiple π-π interactions, which are not frequently observed in the previously reported architectures.     

Proton Transfer Isomerization of Pyrazole in the Ground State： σ vs π Mechanism and Water Assisting Effect

The proton transfer isomerization of pyrazole and the water assisting effect by looping 1 to 4 water molecules on the singlet state potential energy surface have been investigated by using hybrid density functional theory method （B3PW91） with a 6-311＋＋G^＊＊ basis set. Two mechanisms were proposed to explain the mono- and multi-water assisting effects, respectively. The reactants and products of all groups have been characterized on their potential energy surfaces. For the isomerizafion of monomolecule pyrazole, the isomeriz＇ation energy barrier is 46.4 kcal·mol^-1. For the monohydration assisting mechanism, the reactant complex is connected to the product complex via two saddle points. The corresponding isomerization barriers are 46.7and 23.0 kcal·mol^-1, respectively. As to the multihydration assisting mechanism, the isomerization barriers are 12.0, 10.9 and 13.14 kcal·mol^-1 accordingly, when the number of water molecules is 2, 3 and 4, respectively. The multihydration assisting isomerization can occur in water-dominated environments, for example, in the organism, and thereby is crucial to energy transference. The deproton and dehydrogen energies of monomolecule pyrazole and various hydrated pyrazoles were calculated and then found much bigger than the isomerization barriers of their relative complexes, suggesting the impossibility of deprotonation or dehydrogenation. The isomerization of pyrazole is a proton-coupling-electron-migration process, but two different mechanisms are noticed, viz. σ- and π-type mechanisms. The π-bond of pyrazole participates in isomerization in the π-type mechanism, whereas only o-electron takes part in isomerization in the σ-type mechanism.