电化学氧化赖氨酸应用于改变碳表面荷电状态

电化学氧化赖氨酸应用于改变碳表面荷电状态;表面改性;玻碳;赖氨酸单层膜;循环伏安;静电排斥作用     

含有4,4′-双(甲基丙烯酰胺基)偶氮苯水凝胶的合成及其在结肠位药物释放的动物实验

合成了不同链长的甲基丙烯酸酯、甲基丙烯酰胺及丙烯酸与 4 ,4′ 双 (甲基丙烯酰胺基 )偶氮苯交联共聚的功能凝胶 .三维网络结构通过压缩弹性模量、有效交联密度及聚合物与溶剂间的相互作用参数进行了表征 .主要研究了这类凝胶在pH2 2和pH7 4的缓冲溶液的平衡溶胀特性及其偶氮交联基团在体内的降解行为 ,并讨论了其降解机制 .凝胶在胃部的性能稳定 ,既不发生溶胀 ,亦不发生降解 ;但在盲肠内偶氮交联基因可发生降解 .其降解率与凝胶的平衡溶胀程度有一个很好的关联 :交联程度、疏水基侧链的长度及含量对凝胶溶胀行为的影响结果与这些因素对偶氮交联基团体内降解的影响结果完全一致 .通过调节这些因素不仅可以控制凝胶的溶胀程度 ,而且可以控制偶氮交联基团在体内的降解行为 .     

Study of the mesomorphic behaviour through the structure modification of azo and acetylene pyridinium and imidazolium-based ionic liquid crystals

ABSTRACT

In this work, 14 pyridinium and imidazolium-based ionic liquid crystal (ILC) with azo (N=N) and acetylene (C≡C) as linking group were synthesised in high yields and completely characterised. The structure of the molecules were planned in order to allow a complete investigation on how modifications such as presence and position of charges, linking group, number of alkoxy chains and their length affect the thermal stability and liquid crystalline behaviour. All compounds were thoroughly investigated using polarised optical microscopy (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) measurements and thermogravimetric analysis (TGA). While the presence of charges favoured a liquid crystalline behaviour, especially SmA (and SmA₂) phase, a decrease of thermal stability was noticed. A strong dependence of the charge position and a preference for monolayer or bilayer molecular organisation was observed. On the other hand, it was demonstrated that the addition of a second alkoxy chain promoted layer distortions in some molecules, resulting in the formation of Smà and Cub phases. Also a direct comparison between the N=N and C≡C linking groups was realised, along with further comparison with literature data. The structure–properties are investigated in detail.     

Covalent Adaptable Networks with Tunable Exchange Rates Based on Reversible Thiol–yne Cross‐Linking

The design of covalent adaptable networks (CANs) relies on the ability to trigger the rearrangement of bonds within a polymer network. Simple activated alkynes are now used as versatile reversible cross‐linkers for thiols. The click‐like thiol–yne cross‐linking reaction readily enables network synthesis from polythiols through a double Michael addition with a reversible and tunable second addition step. The resulting thioacetal cross‐linking moieties are robust but dynamic linkages. A series of different activated alkynes have been synthesized and systematically probed for their ability to produce dynamic thioacetal linkages, both in kinetic studies of small molecule models, as well as in stress relaxation and creep measurements on thiol–yne‐based CANs. The results are further rationalized by DFT calculations, showing that the bond exchange rates can be significantly influenced by the choice of the activated alkyne cross‐linker.     

Effect of quantum partial charges on the structure and dynamics of water in single-walled carbon nanotubes

In this work, using quantum partial charges, computed from 6-31G(**)B3LYP density functional theory, in molecular dynamics simulations, we found that water inside (6,6) and (10,0) single-walled carbon nanotubes with similar diameters but with different chiralities has remarkably different structural and dynamical properties. Density functional calculations indicate that tubes with different chiralities have significantly different partial charges at the ends of tubes. The partial charges at the ends of a (10,0) tube are around 4.5 times higher than those of a (6,6) tube. Molecular dynamics simulations with the partial charges show different water dipole orientations. In the (10,0) tube, dipole vectors of water molecules at the end of the tube point towards the water reservoir resulting in the formation of an L defect in the center region. This is not observed in the (6,6) tube where dipole vectors of all the water molecules inside the tube point towards either the top or the bottom water reservoir. The water diffusion coefficient is found to increase in the presence of the partial charges. Water in the partially charged (10,0) tube has a lower diffusion coefficient compared to that of in the partially charged (6,6) tube.     

Network structures of polyhedral oligomeric silsesquioxane based nanocomposites: a Monte Carlo study

The network structures of polyhedral oligomeric silsesquioxane based nanocomposites are studied by continuous-space Monte Carlo simulations. The nanoporous network contains intercubic pores and mesopores which can be clearly identified in this work. In terms of degree of cross linking and pore size distribution (PSD), effects of linker length, tether rigidity, and number of reactive tethers are examined. It is found that the extent of cross linking as well as the intercubic pore size of the network increases as linker length increases which are consistent with experimental findings. However, the mesopores appear to shift to a smaller radii regime for networks with longer linkers. Networks with rigid tethers contain lots of free linkers, thus, low cross linking density and narrow PSD are observed. On the other hand, reduction of the reactive tethers shows an insignificant effect on the degree of cross linking of the system. The fact that the intercubic pore size increases as the number of reactive tethers decreases causes the nanobuilding blocks to possess larger free volumes and distribute themselves more evenly throughout the system. As a result, it reduces the possibility of forming large mesopores.     

Induced asymmetries in the heteroaggregation of oppositely charged colloidal particles

Heterocoagulation of cationic and carboxylated polystyrene latexes is studied for a wide range of salt concentrations by static light scattering. The weak character of the surface groups providing the charges allows variation of the relative charge of the systems. Two situations are studied: both latexes with similar surface charges and with very different ones. In both cases at low ionic concentration pure heteroaggregation takes place, whereas diffusive aggregation is observed at high kappa, above the critical coagulation concentration (C.C.C.) of both latexes. The overall rate of aggregation describes a minimum at intermediate salt concentrations when both latexes bear similar charges. The heterocoagulation rate constant decreases continuously to reach the diffusive value at high salt. An interesting behavior is observed when the latexes have very different charge. The heterocoagulation kinetic constant becomes diffusive above the C.C.C. of the less charged latex.     

The interphase between mercury and acetone+ nitromethane mixtures with KPF6 as a supporting electrolyte

Differential capacity and interfacial tension measurements were carried out on mercury for acetone+nitromethane mixtures with KPF₆ as a supporting electrolyte. On the basis of Gibbs adsorption equation and Guggenheim's model of the surface phase the composition of the surface layer was estimated for different acetone contents and different charges on the mercury electrode. The results obtained indicate that the positive acetone adsorption is marked at negative charges with maximum at σ_m=?0.07 C m^?2, but is practically non-existent at zero and positive charges.     

Studies on Hydrogen Bonding Network Structures of Konjac Glucomannan

In this paper, the hydrogen bonding network models of konjac glucomannan （KGM） are predicted in the approach of molecular dynamics （MD）. These models have been proved by experiments whose results are consistent with those from simulation. The results show that the hydrogen bonding network structures of KGM are stable and the key linking points of hydrogen bonding network are at the O（6） and O（2） positions on KGM ring. Moreover, acety has significant influence on hydrogen bonding network and hydrogen bonding network structures are more stable after deacetylation.     

Bio-inspired motifs via tandem assembly of polypeptides for mineralization of stable CaCO3 structures

A macromolecular-assembly of polypeptides constructs a network of anionic and cationic charges vital for recognizing and coassembling Ca(2+) and CO(3)(2-) ions to mineralize and stabilize different mineral forms of CaCO(3) with core-shell or solid morphologies in an aqueous solution.     

Preparation and properties of copolymer resin based on polybenzimidazole and bisoxazoline

Reaction between the NH groups in polybenzimidazole (PBI) and bisoxazoline compounds (1,3‐phenylene bisoxazoline, 1,3‐PBO) resulted in the successful preparation of novel network polymers. Adjusting the amount of the bisoxazoline compound, which is a cross‐linking agent for the preparation of network polymers, and obtaining dynamic mechanical measurements, electrical resistivity measurements, thermomechanical measurements, and tensile tests allowed the determination of the heat resistance and mechanical strength of these novel network polymers. Examination of the elementary reaction of PBI and the1,3‐PBO curing reaction by using model compounds revealed that the NH group in the PBI structure reacted with the oxazoline group of 1,3‐PBO. Comparison of noncross‐linked PBI with the PBI network polymers obtained through cross‐linking reaction with bisoxazoline compounds demonstrated improvements in heat resistance and mechanical strength of the PBI‐bisoxazoline network polymers.     

Electrooxidation of Glucose at Nanoporous Gold Surfaces: Structure Dependent Electrocatalysis and Its Application to Amperometric Detection

Electrooxidation of glucose is investigated at nanoporous gold (NPG) with controlled surface structures by applying different deposition charges during the formation of Ag? Au layers. As the deposition charge increases, the NPG surfaces exhibit smaller ligament/pore structures and the electrocatalytic oxidation of glucose becomes more effective. Voltammetric responses of NPG suggest that the electrocatalytic oxidation arises from the enrichment of (110) or (100) surface orientation of gold with higher deposition charges. The electrooxidation of glucose is retained at NPG surfaces with higher deposition charges in the presence of Cl^?, which suggests possible applications to the amperometric glucose detection in biological samples.     

Coulombic Basis for Relative Hydrogen-Bonding Basicities and Conformational Energies of Tertiary Amine Oxides and Phosphine Oxides

The structures, energies, and natural atomic charges of 2-dimethylaminophenol oxide, 2-Me₂N-(O)C₆H₄OH, and 2-dimethylphosphinylphenol, 2-Me₂P(O)C₆H₄OH, in three different conformations were computed at the ab initio MP2/6-31G* level. Computed natural charges indicate distributions of electron density in amine oxides and phosphine oxides that are quite different from what is normally assumed on the basis of the formal charges in the usual representations of these compounds. The charges on nitrogen and phosphorus in these compounds are typically computed to be approximately zero on nitrogen and +2 on phosphorus, and the oxygen is considerably more negative in the phosphine oxide than in the amino oxide. Electronegativity differences thus play a larger role and formal charges a smaller one in determining atomic charges in these compounds than is generally believed. Despite the more negative oxygen in phosphine oxides, amine oxides are computed to be considerably more basic when participating in hydrogen bonding. Calculations treating the computed natural charges on these six conformations as point charges for classical approximations of the coulombic energies support the idea that the quantum mechanically computed relative energies are largely determined by coulombic interactions.     

On the origin of the thermostabilization of proteins induced by sodium phosphate

The B1 domain of protein L shows a linear rise in thermostability with increasing concentrations of sodium phosphate. Equal behavior is observed for a set of mutant proteins where surface lysines are mutated to noncharged residues, but the mutant's thermostabilities show different sensitivities to phosphate, encoded in the varying slopes observed (mi). The melting temperature in the absence of the cosolute also correlates linearly with mi. The stabilizing effect of the phosphate ion reaches a saturation point, which has been experimentally determined for protein L (1610 mM phosphate). These results indicate that the phosphate-induced stabilization is an inherent property of the protein, encoded in the amino acid sequence. Changes in stability upon mutation are attributed to a redistribution of the overall network of solvated surface charges. Stabilization by phosphate is understood in terms of interactions with the protein surface, reducing the unfavorable contacts between like charges, maximizing the number of accessible conformations of the surface-charged side chains, and optimizing solvation.     

Designed layer assembly: a three-dimensional framework with 74% extra-framework volume by connection of infinite two-dimensional sheets

A coordination polymer with 74% extra-framework volume is prepared by predictable linking of the honeycomb network to generate a framework-structured solid designed with two distinct connecting ligands.     

计算分子中原子净电荷的新方法及芳烃亲电取代反应定位效应的定量处理

本文提出一种简捷计算分子中原子净电荷的新方法。用这种方法计算了２３种一元取代苯的原子净电荷。计算所得苯环上碳原子净电荷与其￣（１３）Ｃ－ＮＭＲ化学位移有良好的线性关系。利用苯环上碳原子净电荷及立体参数作为输入参数，应用人工神经网络方法预报２４种一元取代苯硝化反应的邻、间、对位产物产率，结果良好。     

Comparison between the behaviour of native and denatured DNA at mercury and gold electrodes by capacity measurements and cyclic voltammetry

The effect of the double-layer structure on the adsorption of DNA has been studied by comparing its behaviour at Hg and Au interfaces. Some features of the adsorbing behaviour are studied by the use of combined cyclic voltammetry and capacity measurement. The results illustrate the common characteristics at both interfaces as regards the lowering of the capacity in the vicinity of the pzc, although the kinetics of the process is different on the two metals. The adsorption behaviour at larger values of the charge cannot be compared directly because on Hg this is masked by a reduction at negative charges which does not occur in the accessible range on Au, while an oxidation occurs at positive charges on Au.     

Assessing the role of polarization in docking

We describe a strategy for including ligand and protein polarization in docking that is based on the conversion of induced dipoles to induced charges. Induced charges have a distinct advantage in that they are readily implemented into a number of different computer programs, including many docking programs and hybrid QM/MM programs; induced charges are also more readily interpreted. In this study, the ligand was treated quantum mechanically to avoid parametrization issues and was polarized by the target protein, which was treated as a set of point charges. The induced dipole at a given target atom, due to polarization by the ligand and neighboring residues, was reformulated as induced charges at the given atom and its bonded neighbors, and these were allowed to repolarize the ligand in an iterative manner. The final set of polarized charges was evaluated in docking using AutoDock 4.0 on 12 protein-ligand systems against the default empirical Gasteiger charges, and against nonpolarized and partially polarized potential-derived charges. One advantage of AutoDock is that the best rmsd structure can be identified not only from the lowest energy pose but also from the largest cluster of poses. Inclusion of polarization does not always lead to the lowest energy pose having a lower rmsd, because docking is designed by necessity to be rapid rather than accurate. However, whenever an improvement in methodology, corresponding to a more thorough treatment of polarization, resulted in an increased cluster size, then there was also a corresponding decrease in the rmsd. The options for implementing polarization within a purely classical docking framework are discussed.     

Chitosan Cross-Linked Films for Drug Delivery Application

This work evaluated such a cross-linked chitosan based controlled release device to be later used for sustained drug release. Cross linking was required to control chitosan swelling/deswelling rate. Hexamethylene 1,6-Bis (aminocarboxysulfonate), a bisulfite blocked diisocyanate obtained by the reaction of 1,6 Hexamethylene Diisocyanate and Sodium bisulfite, was used as cross linking agent. Two films formulations were tested: 30 and 50% cross-linked, and they were prepared by solvent evaporation technique. Chitosan cross-linked films were characterized for cross linkage by FTIR, for hydrophilicity by Contact Angle and for swelling behavior by Gravimetric method. Cross linking reaction was confirmed by FTIR. Moreover, cross linking increased the hydrophilic character of cross-linked films and suppressed swelling. However, 30% cross-linked film swollen less than the 50% one, while 50% cross-linked film swollen less than chitosan film itself. This behavior was attributed to the hydrophilic character of the cross linking agent and to the polymeric network formation by cross linking.