非线型聚苯类大分子的研究进展

对支化及树枝状聚苯、环状聚苯、环状聚苯乙炔以及环蕃等几类以苯环为基本结构单元的非线型大分子的研究, 特别是合成作了综述。     

Conformational changes of the amyloid beta-peptide (1-40) adsorbed on solid surfaces

The conformational change of the 39-43 residues of the amyloid beta-peptide (Abeta) toward a beta-sheet enriched state promotes self-aggregation of the peptide molecules and constitutes the major peptide component of the amyloid plaques in Alzheimer patients. The crucial question behind the self-aggregation of Abeta is related to the different pathways the peptide may take after cleavage from the amyloid precursor proteins at cellular membranes. This work is aiming at determining the conformation of the Abeta (1-40) adsorbed on hydrophobic Teflon and hydrophilic silica particles, as model sorbent surfaces mimicking the apolar transmembrane environment and the polar, charged membrane surface, respectively. The mechanism by which the Abeta interacts with solid surfaces strongly depends on the hydrophobic/hydrophilic character of the particles. Hydrophobic and electrostatic interactions contribute differently in each case, causing a completely different conformational change of the adsorbed molecules on the two surfaces. When hydrophobic interactions between the peptide and the sorbent prevail, the adsorbed Abeta (1-40) mainly adopts an alpha-helix conformation due to H-bonding in the apolar part of the peptide that is oriented towards the surface. On the other hand, when the peptide adsorbs by electrostatic interactions beta-sheet formation is promoted due to intermolecular association between the apolar parts of the adsorbed peptide. Irrespective of the characteristics of the solid sorbent, crowding the surface results in intermolecular association between adsorbed molecules leading to a strong aggregation tendency of the Abeta (1-40). [Diagram: see text] CD spectra of Abeta (1-40) at pH 7: A) in solution ([Abeta]=0.2 mg.ml(-1)) freshly prepared (line) and after overnight incubation (symbols);B) on Teflon (Gamma=0.5 mg.m(-2)).     

Nanotechnology with soft materials.

Nature exploits self-organization of soft materials in many ways, to produce cell membranes, biopolymer fibers and viruses, to name just three. Mankind is now able to design materials at the nanoscale, whether through atom-by-atom or molecule-by-molecule methods (top-down) or through self-organization (bottom-up). The latter method encompasses soft nanotechnology. Self-organization of soft materials can be exploited to create a panoply of nanostructures for diverse applications. The richness of structures results from the weak ordering because of noncovalent interactions. Thus, thermal energy is important as it enables transitions between phases with differing degrees of order. The power of self-organization may be harnessed most usefully in a number of nanotechnology applications, which include the preparation of nanoparticles, the templating of nanostructures, nanomotor design, the exploitation of biomineralization, and the development of functionalized delivery vectors.     

氢甲酰化反应溶剂效应的量子化学研究

在B3LYP/6-31G(d, p)(Rh和P采用LANL2DZ + Polar)水平下,利用自洽反应场（SCRF）的Onsager模型,系统研究了C6H12、C6H6、THF、CH2Cl2、CH3OH和H2O（相对介电常数ε分别为2.02、2.25、7.58、8.93、32.63和78.39）六种溶剂对乙烯氢甲酰化反应中各驻点的结构和反应机理的影响.分别在上述溶剂中优化了反应物、产物、中间体和过渡态的结构,并计算了自由能和活化自由能.计算结果表明,不同溶剂对反应势能面上各驻点的结构和能量均有一定的影响,而且随着相对介电常数ε的增加,反应的活化自由能下降.水是以上六种溶剂中最佳的溶剂,这与大量的实验研究结果一致.     

Two‐ and Three‐Dimensional Molecular Organization of Schiff‐Base Derivatives

We have designed and synthesized a series of Schiff base derivatives, and studied their structural features in two‐dimensional (2D) and three‐dimensional (3D) states by combining scanning tunneling microscopy (STM) and X‐ray diffraction experiments. The Schiff‐base derivatives with short alkyl chains crystallize easily, which allows a detailed structural analysis by X‐ray diffraction. Due to the strong adsorbate–substrate interactions, those bases with long alkyl chains easily form 2D assemblies on highly oriented pyrolytic graphite (HOPG). The STM images indicate also that the introduction of two methoxy groups into the molecule can change the structure of these 2D assemblies as a result of the increased steric hindrances, for example: the Schiff‐base derivative, bearing both methoxy groups and C₁₆H₃₃ tails, forms 2D Moiré patterns, and an alignment of pairing Schiff‐base molecules may be easily resolved. Conversely, the Schiff base derivative, bearing solely C₁₆H₃₃ tails, forms 2D non‐Moiré patterns. It is demonstrated that the 3D structural features result from the compromise of intermolecular interactions of different molecular moieties. However, there is one more factor, which also governs the 2D structure: the adsorbate‐substrate interaction. The 3D crystal structure may thus help to understand many factors involved in the formation of 2D structures, and would be helpful for designing new molecular assemblies with tailoring functions.     

Role of the special pair in the charge-separating event in photosynthesis

We synthesized special-pair/electron-acceptor systems consisting of a complementary slipped cofacial dimer of imidazolyl-substituted zinc porphyrin, bearing pyromellitdiimide as the electron acceptor. In the case of the dimer, the first and second oxidation potentials were split into a total of four peaks in the differential pulse voltammetry measurement. Furthermore, the shift values of the first oxidation potentials obtained by changing the solvent polarity for the dimer were almost half of those observed for the monomer. These results indicate that the radical cation is delocalized over the whole pi system of the dimer. Time-resolved transient absorption measurements revealed that, relative to the corresponding monomer, the dimer accelerated the charge separation rate, but decelerated the charge recombination rate. The smaller reorganization energy of the slipped cofacial dimer relative to that of the monomeric system demonstrates the significance of the special-pair arrangement for efficient charge separation in photosynthesis.     

Self‐Assembly of Dialkyltin Moieties and Mercaptobenzoic Acid into Macrocyclic Complexes with Hydrophobic “Pseudo‐Cage” or Double‐Cavity Structures: Supramolecular Infrastructures Involving Intermolecular C?H⋅⋅⋅S Weak Hydrogen Bonds and π–π Interactions

Four novel organotin complexes of two types—[R₂Sn(o‐SC₆H₄CO₂)]₆ (R=Me, 1 ?H₂O; nBu, 2 ) and {[R₂Sn(m‐CO₂C₆H₄S)R₂Sn(m‐SC₆H₄CO₂)SnR₂]O}₂ (R=Me, 3 ; nBu, 4 )—have been prepared by treatment of o‐ or m‐mercaptobenzoic acid and the corresponding R₂SnCl₂ (R=Me, nBu) with sodium ethoxide in ethanol (95 %). All the complexes were characterized by elemental analysis, FT‐IR and NMR (¹H, ¹³C, ¹¹⁹Sn) spectroscopy, TGA, and X‐ray crystallography diffraction analysis. The molecular structure analyses reveal that both 1 and 2 are hexanuclear macrocycles with hydrophobic “pseudo‐cage” structures, while 3 and 4 are hexanuclear macrocycles with double‐cavity structures. Furthermore, the supramolecular structure analyses show that looser and more intriguing supramolecular infrastructures were also found in complexes 1 – 4 , which exist either as one‐dimensional chains of rings or as two‐dimensional networks assembled from the organometallic subunits through intermolecular C? H???S weak hydrogen bonds (WHBs) and π–π interactions.     

Dipyrrolyldiketone difluoroboron complexes: novel anion sensors with C-H...X- interactions

1,3-Dipyrrolyl-1,3-propanediones, synthesized from pyrroles and malonyl chloride, form BF2 complexes, which represent a new class of naked-eye sensors for halide and oxoanions. The association mode for the interactions of both the pyrrolyl NH and bridging CH protons with anions was confirmed by 1H NMR chemical shifts in CD2Cl2 and supported by theoretical studies. The binding constants (Ka) were estimated as 8.1x10(4), 2.0x10(3), 3.3x10(2), 1.3x10(4), and 80 M(-1) for F-, Cl-, Br-, H2PO4(-), and HSO4(-) by UV/Vis absorption spectral changes in CH2Cl2. Augmentation of Ka compared with dipyrrolylquinoxaline for H2PO4(-) is much larger than those for other anions. Contrary to other anions, F- quenches the emission almost completely, which was detected by the fluorescence spectrum as well as the naked-eye. In the case of the chloride anion complex, the formation of Cl(-)-bridged 1D networks, in which anion is associated with two BF2 complexes, is observed in the solid state.     

Design and self-assembly of ditopic and tetratopic cavitand complexes

The self-assembly of open ditopic and tetratopic cavitand complexes has been investigated by using monofunctionalized cavitand ligands and suitable metal precursors. In the case of ditopic complexes, self-assembly protocols, leading exclusively to the formation of both thermodynamically stable cis-Pt square-planar complexes 8 and 9 and the kinetically inert fac-Re octahedral complex 14, have been elaborated. The use of cis-[Pt(CH3)CN)2Cl2] as metal precursor led to the formation of monotopic trans-10 and ditopic trans-11 cavitand complexes, while cis-[Pt(dmso)2Cl2] afforded both cis-13 and trans-11 isomers. The self-assembly of tetratopic cavitand complexes has been achieved by using mononuclear [Pd(CH3CN)4(BF4)2] and dinuclear [M2(tppb)(OTf)4] (19: M = Pt; 20: M = Pd) metal precursors. Only the tetratopic dinuclear complexes 21 and 22 were stable. The ligand configuration with two phosphorus and two cavitand ligands at the metal centers is the most appropriate to build tetratopic cavitand complexes with sufficient kinetic stability.     

Topological polymer chemistry by dynamic selection from electrostatic polymer self-assembly

A collection of recent developments in topological polymer chemistry is presented. First, topological isomerism occurring on randomly coiled, flexible polymer molecules having cyclic and linear structures is discussed. Second, an electrostatic self-assembly and covalent fixation strategy has been developed for the synthesis of polymeric topological isomers. These isomers have double cyclic, manacle-, and theta-shaped constructions, and are prepared by using either linear or star telechelic polymer precursors having moderately strained cyclic ammonium salt groups, which carry multifunctional carboxylate counteranions. A technique of reversed-phase chromatography (RPC) is demonstrated as an effective means to separate polymers with different topologies, especially polymeric topological isomers. A further extension of topological polymer chemistry has been observed by dynamic selection from electrostatic polymer self-assembly to enable the effective formation of tadpole-shaped, cyclic-linear hybrid topologies.