Simulation Study on Translocation of Confined Chain Through Interacting Nanopore

The translocation of a confined polymer chain through an interacting nanopore has been studied using two-dimensional bond fluctuation model with Monte Carlo dynamics. For different pore-polymer interaction, the average escaping time〈Τesc〉of the polymer chain through the nanopore, increases roughly linearly with the chain length and the nanopore length, respectively. However, the large repulsive and attractive pore-polymer interaction adds the difficulty of the monomers of the chain entering and leaving the nanopore, respec-tively, leading to the nonmonotonical dependence of〈Τesc〉on the pore-polymer interaction. The detailed translocation dynamics of the chain through the interacting nanopore is inves-tigated too.     

高分子单链凝聚成与线团相互穿透的多链凝聚态

高分子单链凝聚态由于链内链结构单元间存在范德化吸引作用,高分子链呈打圈链构象,而多链凝聚态由于链内链单元间的吸引作用被与相互穿透的近邻链的单元间吸引作用所屏蔽,高分子链呈高斯链构象。本文简要介绍单链凝聚态试样的制备方法,单链单晶体、单链玻璃体、溶胀的单链高弹态拉伸等的实验观察,并提出从单链凝聚态到多链凝聚态的转变过程问题,即高分子线团的相互穿透过程,目前还缺少基础了解。     

聚环氧乙烷链的微观构象研究

研究了聚环氧乙烷链在三级旋转异构态模型中的微观构象及其三级相互作用对聚环氧乙烷链的持久矢量的影响．计算了聚环氧乙烷链在三级旋转异构态模型中的键段的先验几率．这种方法能计算重复单元极复杂的对称高分子链的先验几率,还能研究不对称高分子链的微观构象,同时导出了三级旋转异构态模型中的持久矢量计算公式．     

Effect of processes at the reactor surface on the low-pressure hydrogen f lame

The interaction of the low-pressure flame of a 2H₂-O₂ mixture with a quartz reactor surface was studied by the resonance fluorescence technique. The results confirmed the fundamental statement of N. N. Semenov’s theory concerning chain propagation in the gas and termination on the surface in the kinetic region of chain termination (quadratic decay in the heterogeneous negative chain interaction) and in the diffusion region (linear decay). The kinetic curves observed in the kinetic and diffusion chain termination regions on the wall were well matched using N. N. Semenov’s theory, taking into account the heterogeneous catalytic chain initiation and interaction processes occurring on the wall with a variable “rate constant.” The interaction of chains on the wall markedly retards ignition in the gas in the kinetic region and has almost no influence on chain propagation in the gas in the diffusion region of the heterogeneous chain termination. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1301–1308, August, 2006.     

Kinetics of hydrogen oxidation near the lower explosion limit

Kinetics of hydrogen oxidation near the lower explosion limit in the kinetic region of chain termination has been studied. Major effects, causing deviations of the reaction kinetics from calculations by the linear theory of branched chain processes, are shown to be (1) the inhibition of the reacting mixture by the products of interaction of active centers with vacuum grease or with impurities contained in it and (2) the heterogeneous negative interaction of reaction active centers. The kinetics of hydrogen oxidation in this region has been calculated with consideration of the heterogeneous negative chain interaction. A set of parameters has been obtained that make it possible to determine by the shape of the kinetic curves the sign and the value of nonlinear interaction of chains near the lower explosion limit. It has been shown that the experimental data are in good agreement with the calculations, provided the heterogeneous negative chain interaction is taken into consideration and the inhibiting effect of impurities is eliminated. The rate of heterogeneous generation of chains on a quartz surface treated with hydrofluoric or boric acid has been determined.     

Monte Carlo Simulation of Polymers Confined Between Two Surfaces in the Presence of Diluent

Structure and surface properties of polymers confined between two surfaces are studied in the presence of diluent by using an off‐lattice Monte Carlo method. When the diluent–chain interaction is weak, the density of diluent beads near the surface increases sharply with increasing the diluent–surface interaction while the chain bead density near the surface decreases gradually. The total bead density near the surface increases with increasing the diluent–surface interaction until it exceeds the total bulk density. This is mainly due to a large increase in the diluent bead density near the surface. Because of the increase of diluent at the surface, chains near the surface change their conformation, i.e., long tails become abundant while short trains and loops are relatively depleted. On the other hand, when the diluent–chain interaction becomes strong, the total bead density near the surface increases slightly, but it exceeds the total bulk density only when the diluent–surface interaction is strong enough, because the diluents approaching the surface induce chain beads to move to the surface due to strong interaction between the chain and diluent.     

Effect of chain compositions on interpolymer specific interaction in solutions

An interpolymer specific interaction of polymers with complementary proton donor units and proton acceptor units was studied with viscometry. In this study, poly(styrene-co-octyl acrylate-co-acrylic acid) as proton donating polymer (PDP) and poly(styrene-co-octyl acrylate-co-4-vinylpyridine) as proton accepting polymer (PAP) with different macromolecular chain compositions were prepared by emulsion copolymerization. Complexed solutions formed by PDP and PAP were studied with a novel interaction criterion k_a based on viscosity enhance factor. The effects of macromolecular chain compositions on the ability to interpolymer interaction and complex stoichiometry were discussed. The results showed that long chain alkyl acrylate units play an important role in the interpolymer specific interaction.     

CALCULATION OF CONFORMATIONAL ENTROPY AND FREE ENERGY OF POLYSILANE CHAIN

The conformational entropy S and free energy F were calculated by exact enumeration of polysilane chain up to 23segments with excluded volume (EV) and long-range van der Waals (VW) interaction. A nonlinear relation between S_(EV+VW)and chain length n was found though S_(EV) was found to vary linearly with n. We found that the second-order transitiontemperature of polysilane chain with VW interaction increases with the increase of chain length, while that of polysilanechain without VW interaction is chain length independent Moreover, the free energies F_(EV+VW) and FEv are both linearlyrelated with n, and F_(EV+VW) 相似文献   

Effect of Interaction upon Translocation of Confined Polymer Chain Through Nanopore

The effect of the interaction between nanopore and chain monomer on the translocation of a single polymer chain confined in a finite size square through an interacting nanopore to a large space has been studied by two-dimensional bond fluctuation model with Monte Carlo simulation. Results indicate that the free energy barrier before the successful translocation of the chain depends linearly on the chain length as well as the nanopore length for different pore-polymer interaction, and the attractive interaction reduces the free energy barrier, leading to the reduction of the average trapping time.     

含柔性间隔链段的芳香共聚酯热致性液晶高分子的结构研究

本文用富里叶红外光谱方法研究了一系列柔性间隔链段长度不等的芳香共聚酯热致性液晶高分子。测定了它们的变温光谱和偏振性质。并将谱带的变温行为与液晶转变相关联。结果表明,芳香共聚酯热致性液晶中液晶基元之间的相互作用很强而柔性间隔链之间的相互作用很弱。柔性间隔链段主要是伸直的反式构象。从一些谱带的二向色性估算了体系的有序度参数以及取向角。分子链的取向程度随柔性间隔链段长度的增加而减小。     

Photochemistry and photophysics of organomonosilane and oligosilanes: Updating their studies on conformation and intramolecular interactions

This review article deals with recent studies on photochemistry and photophysics of organosilicon monomer to oligomers (here, chain length of Si is mostly less than 10). Arylmonosilanes have been caught attention as the fluorescent and charge-transporting materials. Increasing in silicon chain length, an importance of conformation for silicon single chain in organooligosilane is significant. The conformation affects the spectroscopic, photochemical, and photophysical characteristics. This review is mainly focused on the properties of arylsilanes and α,ω-diaryloligosilanes in which three types of intramolecular interactions, the σ–σ interaction between silicon atoms in a chain unit, the π–π interaction between two aromatic groups, and the σ–π interaction between an aromatic group and a silicon chain unit are expected. As a result, intramolecular excimer/exciplex formation, charge-transfer (CT) complex formation, excitation energy or photoinduced electron transfers were observed by the steady-state and the time-resolved fluorescence (TR-FL) spectroscopy. For the better understanding, the recent conformational studies of single oligosilane chain are also reviewed.     

磺化SIS及其离聚物的稀溶液性质

嵌段共聚物;比浓粘度;特性粘液;磺化SIS及其离聚物的稀溶液性质     

Complexation induced by weak interaction between DNA and PEO-b-P4VP below the CMC of the polymer

The complexation between circular DNA and individual chains of PEO-b-P4VP with a relatively long PEO block and a short P4VP block is highly controllable when the interaction between DNA and the polymer is weak enough. When one circular DNA chain is taken into consideration, and the polymer concentration is far below its critical micelle concentration(CMC), polymer chains are absorbed by DNA chain due to the interaction between the negatively charged DNA chain and the slightly positively charged P4VP block chains. After the adsorption/complexation, the DNA chain is converted into a nanoring(type 1). In the nanoring, the DNA chain is sufficiently wrapped by the polymer and adopts a fully stretched conformation, so that the DNA compact ratio in the nanorings is close to 1. When the polymer concentration is close to but lower than the CMC, the free polymer chains in the solution are adsorbed not only by the DNA chain but also by the polymer chains that have already been adsorbed on the DNA chain. As a result, the circular DNA chain adsorbs more polymer chains, and thus the resultant nanoring(type 2) has a larger width. In the type 2 nanoring, the DNA chain is slightly compressed; the DNA compact ratio is only about 2-3. Therefore, complexation induced by the weak interaction between DNA and PEO-b-P4VP below the CMC can produce narrow-disperse and large nanorings with a perimeter of micrometers, which are difficult to prepare by existing methods.     

全伸展DNA链折叠过程中三种非线性作用的布朗动力学模拟

脱氧核糖核酸(DNA)单分子链从完全拉伸状态折叠到平衡状态的动力学过程是溶液中DNA单分子力学的重要特征之一.通过构建全参数化的珠子-弹簧分子链模型,并运用一种高效平衡的半隐式预测——校验积分算法,系统研究了体积排斥作用、有限伸长弹性作用和涨落流体动力学作用等三种非线性作用对稀溶液中DNA分子链折叠过程相对回旋半径和驰豫时间的影响程度和变化趋势.模拟结果发现:体积排斥作用不影响分子链的折叠驰豫时间,但能显著减小平衡时的相对回旋半径;流体动力学作用不影响分子链的相对回旋半径,但明显缩短折叠过程的驰豫时间;有限伸长弹性作用能明显减小短链的相对回旋半径,能显著延长长链的折叠驰豫时间.模拟数据进一步表明:完全伸展的DNA分子链在折叠过程中的相对回旋半径随时间平滑变化,且折叠驰豫时间随长度的标度指数对上述三种非线性作用都具有两种不同的长度依赖性.     

表面活性剂与高分子链混合体系的模拟

计算机模拟了高分子链对表面活性剂胶束形成过程的影响，以及高分子链构象性质随胶束化过程的变化.结果表明,当高分子链与表面活性剂之间的相互作用强度超过临界值后，高分子链的存在有利于表面活性剂胶束的形成.临界聚集浓度（CAC）与临界胶束浓度（CMC）的比值CAC/CMC随高分子链长的增大和相互吸引作用的增强而减小.在CAC之前，高分子链与表面活性剂分子只有动态的聚集；但在CAC之后，表面活性剂胶束随表面活性剂浓度X的增加而增大，并静态地吸附在高分子链上，形成表面活性剂/高分子聚集体.随着表面活性剂分子的加入，高分子链的均方末端距和平均非球形因子先保持恒定；从X略小于CAC开始， 和快速减小，至极小值后又逐渐增大.模拟结果支持高分子链包裹在胶束表面的实验模型.     

Effects of overlapping GB virus C/hepatitis G virus synthetic peptides on biomembrane models

The present study was undertaken to examine the physicochemical properties of three overlapping peptides belonging to the E2 envelope protein of Hepatitis G virus (GBV-C/HGV) and its interaction with phospholipid biomembrane models using biophysical techniques. We describe our findings concerning the surface activity and the interaction of the peptides with monolayers and liposomes composed of the zwitterionic phospholipids dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine (DMPC) and a mixture of DMPC with the anionic phospholipid dimyristoylphosphatidylglycerol. The results inform about the effect of the chain length on their interaction with biomembrane models. The longest chain peptide interacts in a higher extent with all the phospholipid studied as a result of a combination of hydrophobic and electrostatic forces.     

咪唑类离子液体与酪氨酸相互作用及机理的密度泛函理论研究

Ionic liquids (ILs) are thermally and chemically stable and have adjustable structures, which gives them the potential to be used as green, efficient biomolecular solvents. Given the critical role of ILs in dissolving biomolecules, the mechanism of interaction between them deserves further study. Herein, density functional theory (DFT) calculations, using the SMD implicit water solvent model, were employed to study the interaction and mechanism between a hydrophobic zwitterionic amino acid (Tyr) and a series of imidazolium ILs with different alkyl chain lengths and methylation sites. The contributions of hydrogen bonding (H-bonding), electrostatic effects, induction, and dispersion to the intermolecular interactions were determined by combining the symmetry-adapted perturbation theory (SAPT), the atoms in molecules (AIM) theory, and reduced density gradient (RDG) analysis. The results indicate that the H-bonding between the IL cation and Tyr is stronger than that between the IL anion and Tyr; however, the binding between either ion and Tyr is dominated by electrostatic effects. By contrast, the difference between the induction and dispersion forces is small when methylation occurs on the C2 site of the imidazolium cation; whereas, it is significantly large when methylation takes place on the N3 site. This is rationalized by the interaction patterns that vary based on the methylation site. H-bonding and π⁺-π stacking interactions between the imidazole and benzene rings are dominant during C2-methylation, while H-bonding and C_Alkyl-H…π interactions between the alkyl chain and benzene ring are dominant during N3-methylation. Increasing the side alkyl chain length has different effects on the interaction energy to cations with different methylation sites. During N3-methylation, when the side alkyl chain length increases from 4 to 12, there are significant van der Waals interactions between the Tyr benzene and the side alkyl chain. However, these van der Waals interactions are inapparent when methylation takes place on the C2 site. Finally, the synergetic effect of the H-bonding and the interaction between the benzene and the side alkyl chain for C2-methylation is greater than the H-bonding and the interaction between the imidazole and benzene rings for N3-methylation, when the side alkyl chain length n > 9. Therefore, the interaction strength and mechanism in these imidazolium-Tyr complexes can be regulated by changing the methylation site and the side alkyl chain length of the cation. Further study of ion-pair and Tyr reveals that the change tendency of the interaction energy of IL-Tyr systems is consistent with that of cation-Tyr cases, and the ion pair further stabilizes the binding with Tyr. These results illustrate the interaction mechanism of IL-Tyr systems and provide a novel strategy for the design and screening of functional ILs for amino acid extraction and separation in the future.     

Influence of the saturation chain and head group charge of phospholipids in the interaction of hepatitis G virus synthetic peptides

Using the Langmuir technique, we have studied the properties at the air/water interface and the interaction of the hepatitis G virus synthetic peptide E1(53-66) and its palmitoyl derivative with membrane phospholipids. These phospholipids had different characteristics referring to the net charge and saturation of the acyl chain. The palmitoyl derivative was more stable at the air/water interface and in the kinetic at constant area measurements showed higher incorporation to the monolayer. The interaction was higher for saturated phospholipids and those with a negative net charge. When the peptides were in the subphase, they produced changes in the miscibility of mixed monolayers composed of DPPC/DPPG or DOPC/DOPG. It can be deduced from the results obtained that electrostatic interactions play a major role, but when the peptide is derivatized with the palmitoyl chain, hydrophobic interactions are added to the former ones. The interaction is also influenced by the saturation of the acyl chain.     

MOLECULAR INTERACTIONS OF CARBOXYLATED URETHANE ACRYLATE IONOMERS IN LOW-POLARITY AND POLAR SOLVENTS

Carboxylated urethane acrylate ionomers that have a small number of ionic groups per chain were synthesized with varying the molecular weight of soft segment, the degree of ionization, and the sort of diisocyanate. The effect of intra-and intermolecular interactions on solution properties was studied by viscosity measurements in low-polarity and polar solvents. In a low-polarity solvent (1,4-dioxane), ionomers showed almost no intramolecular interaction at dilute concentration and a small degree of intermolecular interaction at high concentrations, resulting from a small number of ionic groups per chain. In a polar solvent (dimethylacetamide, DMAc), ionomers showed typical polyelectrolyte behavior, even though ionomers have a small number of ionic groups per chain. Intermolecular interaction caused by polyether soft segment, phenyl group, and hydrogen bond between urethane acrylate ionomer chains contributed to the increase of reduced viscosity at low concentration.     

COMPUTER SIMULATION OF POLYMER SOLUTION THERMODYNAMICS

The statistical counting method for the computer simulation of the ther-modynamic quantities of polymer solution has been reviewed. The calculating results fora single athermal chain confirm the theory of the renormalization group. The results forthe athermal solution are consistent with the scaling law of the osmotic pressure with theexponent 2.25. The results for a single chain with the segmental interaction are in a goodagreement with the exact results obtained by the direct counting method. The results forthe polymer solution show us that the Flory-Huggins parameter is strongly dependent onboth the polymer concentration and the interaction energy between segments. Monte carlo simulation; Polymer solution; Thermodynamic quantities;Translational entropy; Conformational entropy; Scaling law