模型化研究药物小分子阻滞细胞周期

基于扩散动力学与细胞信号传导动力学,研究药物小分子对细胞周期的阻滞特性.理论模型考虑药物小分子穿越细胞膜输运的动力学特性,以及进入细胞内的药物分子对细胞周期的阻滞效应.研究发现,穿越细胞膜内层进入细胞内的药物分子,将会在很大程度上决定药物分子对相关的靶向基因、蛋白的阻滞功效.细胞膜对药物分子的输运特性,是影响药物分子阻滞细胞周期的关键因素.另外,药物分子的降解程度,将会改变药物分子与靶向基因、蛋白作用时间,进而改变对相关细胞生长增殖的抑制效应.通过对模型中各参数的敏感度分析,我们确认了药物分子穿越细胞膜、进入细胞内过程的多种因素对细胞周期的抑制效应.本文理论结果符合模拟、实验观测,进一步深刻揭示了药物小分子阻滞细胞周期的物理机制,可为设计确切的疗法药物提供必要的参考和新方案.     

多纳米粒子穿越磷脂膜

本文采用耗散粒子动力学模拟方法研究了多纳米粒子与溶液中的磷脂膜相互作用. 模拟中选择纳米颗粒的形状分别为球状和柱状,并且在动力学过程中给它们设置了不同的初始速度. 根据纳米粒子穿膜在动力学过程中体现出不同的特性,分别定义了几种粒子穿越磷脂的模式,并且基于粒子之间的相互作用强度和粒子初始速度,描绘了穿膜模式的详细相图. 本文还进一步研究了体系能量、迴旋半径等参数在不同穿越模式中的动力学过程. 研究结果有助于人们理解纳米颗粒穿膜在生命活动过程中的作用.     

多纳米粒子穿越磷脂膜（英文）

本文采用耗散粒子动力学模拟方法研究了多纳米粒子与溶液中的磷脂膜相互作用.模拟中选择纳米颗粒的形状分别为球状和柱状,并且在动力学过程中给它们设置了不同的初始速度.根据纳米粒子穿膜在动力学过程中体现出不同的特性,分别定义了几种粒子穿越磷脂的模式,并且基于粒子之间的相互作用强度和粒子初始速度,描绘了穿膜模式的详细相图.本文还进一步研究了体系能量、迴旋半径等参数在不同穿越模式中的动力学过程.研究结果有助于人们理解纳米颗粒穿膜在生命活动过程中的作用.     

磷酸钾缓冲溶液与模型细胞膜相互作用的和频光谱

利用和频光谱技术详细研究了磷酸钾缓冲溶液与带负电荷的生物仿生膜(d₅₄-DMPG磷脂双层膜)相互作用的实时过程．通过监控CD₂、CD₃、磷脂分子头部的磷酸根以及羰基官能团的光谱信号随加入磷酸钾缓冲溶液的实时变化,获得了磷脂双层膜分子结构的动力学变化．结果表明K⁺能够结合到细胞膜上,并且很快地引起了CD₂、CD₃、磷脂头部磷酸根以及羰基官能团信号的变化．根据各官能团的和频信号响应,磷酸钾缓冲溶液很可能是通过在双层膜中形成环形气孔来与磷脂双层膜发生作用．该结果可以很好地解释磷酸钾缓冲溶液环境下的离子协助蛋白质的跨膜过程．     

Co膜中多次超快瞬态反射突变现象研究

飞秒激光泵浦瞬态热反射技术是研究金属薄膜超快动力学的有效手段,这种技术具有两大突出特点：首先,可以揭示飞秒激光激发的微观电、声子的传输过程是一个非平衡热输运过程。其次,反射率瞬态变化实验中电子运动的超短时间分辨可以用来研究热过程中电子的非平衡相互作用情况。利用磁控溅射真空镀膜技术,在玻璃衬底和硅衬底上蒸镀了不同厚度的Co单层膜,Cr,Co双层膜以及Ag,Co双层膜。利用飞秒激光瞬态反射技术研究了Co膜及其双层膜的瞬态反射率响应。结果表明,在同一厚度的Co膜样品上,施加不同的泵浦光功率时,Co膜内电子的加热时间与泵浦光功率的大小无关,均为0.1344 ps。而对于不同厚度的Co膜,电子的热化时间与薄膜厚度直接相关。此外,发现与以往研究结果不同的是,在泵浦光功率足够大时,玻璃衬底上的Co膜在飞秒激光脉冲泵浦下会出现两次或三次瞬态反射率下降现象,Co膜厚度决定了Co膜内瞬态反射率突变的次数,即Co膜内电子的超快动力学变化次数。     

磷脂在膜结构间的交换:温度和离子强度的影响

磷脂跨膜交换对生物膜功能与药学研究有重要意义.石英电子微天平及耗散系数测量仪被用于研究囊泡与支撑膜间磷脂的交换行为.研究表明:首先,在磷脂跨膜输运过程中,热力学环境和离子强度对支撑膜表面吸附囊泡的形变程度影响较小,囊泡与支撑膜的总接触面积直接取决于囊泡的吸附数量;其次,交换过程中膜结构间最大总接触面积随着温度的升高和离子强度的降低而增大,温度和离子引起的囊泡吸附速率和跨膜交换速率的变化在其中发挥着关键调节作用.本研究有助于加深对磷脂在生理条件下跨膜输运过程的理解,并为基于脂质体的药物载运体系研究提供参考.     

拉曼光谱研究人参皂苷Rb1与DPPC双层膜的作用

为深入了解人参皂苷的分子药理学特性,阐明人参皂苷与细胞膜的作用机制,利用拉曼光谱从分子水平研究了不同浓度人参皂苷Rb1与DPPC(二棕榈酰磷脂酸胆碱)双层膜的作用.结果表明,人参皂苷Rb1没有改变DPPC的极性头部O-C-C-N+的稳定构象,极性头仍然平行于膜表面.并且,拉曼峰值比I1096/I1126/1096/I1062和I2848/I288/0随着药物浓度的增加而相应的变大,说明Rbl增加了烃链的无序度,增强了双层膜的流动性.由此推测该药物与DPPC的作用可能由于皂苷分子内及分子间的氢键与磷脂双层膜的极性头部相作用而停留在膜的表面.     

共轭聚合物中均匀无序对极化子输运动力学的影响

基于扩展的Su-Schrieffer-Heeger紧束缚模型和非绝热动力学方法, 研究了共轭聚合物材料中均匀无序效应对极化子输运动力学的影响. 研究发现: 极化子的动力学输运过程由外加电场和均匀无序效应共同决定; 在大部分电场范围下, 均匀无序效应对极化子输运的影响不太明显, 几乎可以忽略; 但在弱电场下, 均匀无序效应不利于极化子输运. 与高斯型无序效应下极化子的输运过程相比, 具有均匀无序的薄膜形貌更有利于极化子输运.     

多聚赖氨酸诱导的负电性磷脂巨囊泡形变

利用荧光显微技术表征了多聚赖氨酸诱导的负电性磷脂巨囊泡的动力学响应行为.研究发现,多聚赖氨酸可吸附至二油酰磷脂酰胆碱和二油酰磷脂酸混合磷脂巨囊泡的表面,诱导其发生粘连、出"绳"及破裂现象.分析认为,在低盐环境中,膜形变由多聚赖氨酸吸附于二油酰磷脂酸富集区引起的膜两叶应力不对称,以及静电相互作用等因素产生.研究结果对基于聚合物-巨囊泡体系的药物输运控释、细胞形变、微控反应和基因治疗等方面的研究提供有价值的支持.     

不同类型细胞穿膜肽二级结构特征研究

细胞穿膜肽是一类能以受体依赖或非受体依赖方式介导胞吞作用的小分子短肽,能够携带不同分子穿过细胞膜,这一特性使细胞穿膜肽成为一种有效的运输载体,为药物靶向治疗提供了新希望.本文从生物信息角度针对不同长度区间、运输不同类型分子细胞穿膜肽之间的异同二级结构特征进行了系统研究,同时进一步对不同穿膜方式对应的细胞穿膜肽二级结构特征进行了对比研究,结果表明不同类型细胞穿膜肽之间在二级结构组成上具有不同程度差异特征,为今后揭示细胞穿膜肽相关分子结构机制奠定可靠的理论基础.     

Diffusion of gases across lipid membranes with OmpA channel: a molecular dynamics study

Molecular transport across biological membranes occurs in a range of important chemical and biological processes. The biological membrane can usually be modelled as a phospholipid bilayer, but to correctly represent biological transport, the embedded transmembrane proteins must also be included. In previous molecular simulation studies on transport of small gas molecules in dipalmitoylphosphatidylcholine (DPPC) bilayer membrane, a coarse-grained model was used to provide direct insight into collective phenomena in biological membranes. Coarse graining allowed investigation of longer time and length scales by reducing the degrees of freedom and employing suitable potentials. In this work, membranes that include transmembrane proteins are modelled. This allows one to compare the molecular transport across a lipid membrane with and without the assistance of transmembrane channels. Outer membrane protein A (OmpA) – a porin from Escherichia coli with a small pore size – was chosen in this study because its detailed structure is known, it has high stability and is known to form a nonspecific diffusion channel that permits the penetration of various solutes. In this work the pore characteristics and interaction between lipid and protein were investigated and transport of water and other small gas molecules within the channel were studied. The MD simulation results obtained are compared with previous simulation results and available experimental data. The results obtained from this study will lead to better understanding of protein functionality and advance the development of biochips and drug delivery systems.     

NMR studies of carrier-mediated transport across lipid bilayer membranes

Two theoretical models are presented which show how the various kinetic steps involved in transport across lipid bilayer membranes affect NMR spectral lineshapes and relaxation times. The first model applies whenever the transported material moves across the membrane by restricted diffusion. The second model applies when the motion can be described as a jump between membrane interfaces. Both carrier-mediated and carrier-independent cases are treated. Special attention is given to the effects of relaxation in the membrane and to morphology. Exact analytical solutions for the simplest one-dimensional geometry are presented. More complicated morphologies are best treated numerically.     

Regulation of the intermittent release of giant unilamellar vesicles under osmotic pressure

Osmotic pressure can break the fluid balance between intracellular and extracellular solutions. In hypo-osmotic solution, water molecules, which transfer into the cell and burst, are driven by the concentration difference of solute across the semi-permeable membrane. The complicated dynamic processes of intermittent bursts have been previously observed. However, the underlying physical mechanism has yet to be thoroughly explored and analyzed. Here, the intermittent release of inclusion in giant unilamellar vesicles was investigated quantitatively, applying the combination of experimental and theoretical methods in the hypo-osmotic medium. Experimentally, we adopted a highly sensitive electron multiplying charge-coupled device to acquire intermittent dynamic images. Notably, the component of the vesicle phospholipids affected the stretch velocity, and the prepared solution of vesicles adjusted the release time. Theoretically, we chose equations and numerical simulations to quantify the dynamic process in phases and explored the influences of physical parameters such as bilayer permeability and solution viscosity on the process. It was concluded that the time taken to achieve the balance of giant unilamellar vesicles was highly dependent on the molecular structure of the lipid. The pore lifetime was strongly related to the internal solution environment of giant unilamellar vesicles. The vesicles prepared in viscous solution were able to visualize long-lived pores. Furthermore, the line tension was measured quantitatively by the release velocity of inclusion, which was of the same order of magnitude as the theoretical simulation. In all, the experimental values well matched the theoretical values. Our investigation clarified the physical regulatory mechanism of intermittent pore formation and inclusion release, which provides an important reference for the development of novel technologies such as gene therapy based on transmembrane transport as well as controlled drug delivery based on liposomes.     

Construction of a molecular model of a fragment of a lipid membrane in the gel and liquid crystalline states

A model of a lipid membrane in the liquid crystalline and gel states is constructed. The model of the membrane in the liquid crystalline state adequately reproduces the geometric parameters of the membrane, lipid packing, and the mobility parameters of molecules. The model of the membrane in the gel state of the bilayer reproduces the geometric parameters of the real membrane and lipid packing. New methods for calculation of the mobility parameters of phospholipid molecules in the plane of the bilayer are presented.     

Fluorescence Correlation Spectroscopy (FCS) Analysis of Human Red Blood Cell System

Recent studies have revealed the importance of the lipid micro domain for signal transduction in cell membrane. To analyze the biophysical properties of the lipid micro domain at the single molecule level, we measured the diffusion of fluorescence probe in human red blood cell (RBC) membrane using fluorescence correlation spectroscopy (FCS). The value of diffusion constant of octadecyl rhodamine B chloride (R18), D = 4.7 × 10⁻⁹cm²/s, is close to that of phospholipid molecules in membrane. This indicates that the probed RBC with R18 could be a convenient model for analyzing membrane property under natural conditions. Using this model, we investigated how amyloid beta peptide (A-beta) interacts with plasma membrane. This paper demonstrates that A-beta was inserted into the phospholipid bilayer of the RBC membrane and predicts the existence of the micro domain, lipid raft, on this membrane by the heterologous insertion of A-beta.     

Electroporation of cells and tissues

Electrical pulses that cause the transmembrane voltage of fluid lipid bilayer membranes to reach at least U_m≈0.2 V, usually 0.5-1 V, are hypothesized to create primary membrane “pores” with a minimum radius of -1 nm. Transport of small ions such as Na⁺ and Cl^- through a dynamic pore population discharges the membrane even while an external pulse tends to increase U_m, leading to dramatic electrical behavior. Molecular transport through primary pores and pores enlarged by secondary processes provides the basis for transporting molecules into and out of biological cells. Cell electroporation in vitro is used mainly for transfection by DNA introduction, but many other interventions are possible, including microbial killing. Ex vivo electroporation provides manipulation of cells that are reintroduced into the body to provide therapy. In vivo electroporation of tissues enhances molecular transport through tissues and into their constitutive cells. Tissue electroporation, by longer, large pulses, is involved in electrocution injury. Tissue electroporation by shorter, smaller pulses is under investigation for biomedical engineering applications of medical therapy aimed at cancer treatment, gene therapy, and transdermal drug delivery. The latter involves a complex barrier containing both high electrical resistance, multilamellar lipid bilayer membranes and a tough, electrically invisible protein matrix     

Pathway of membrane fusion with two tension-dependent energy barriers

Fusion of bilayer membranes is studied via dissipative particle dynamics (DPD) simulations. A new set of DPD parameters is introduced which leads to an energy barrier for flips of lipid molecules between adhering membranes. A large number of fusion events is monitored for a vesicle in contact with a planar membrane. Several time scales of the fusion process are found to depend exponentially on the membrane tension. This implies an energy barrier of about 10k(B)T for intermembrane flips and a second size-dependent barrier for the nucleation of a small hemifused membrane patch.     

The New Fluorescent Membrane Probe Ahba: A Comparative Study with the Largely Used Laurdan

Lipid bilayers have been largely used as model systems for biological membranes. Hence, their structures, and alterations caused on them by biological active molecules, have been the subject of many studies. Accordingly, fluorescent probes incorporated into lipid bilayers have been extensively used for characterizing lipid bilayer fluidity and/or polarity. However, for the proper analysis of the alterations undergone by a membrane, a comprehensive knowledge of the fluorescent properties of the probe is fundamental. Therefore, the present work compares fluorescent properties of a relative new fluorescent membrane probe, 2-amino-N-hexadecyl-benzamide (Ahba), with the largely used probe 6-dodecanoyl-N,N-dimethyl-2-naphthylamine (Laurdan), using both static and time resolved fluorescence. Both Ahba and Laurdan have the fluorescent moiety close to the bilayer surface; Ahba has a rather small fluorescent moiety, which was shown to be very sensitive to the bilayer surface pH. The main goal was to point out the fluorescent properties of each probe that are most sensitive to structural alterations on a lipid bilayer. The two probes were incorporated into bilayers of the well-studied zwitterionic lipid dimyristoyl phosphatidylcholine (DMPC), which exhibits a gel-fluid transition around 23 °C. The system was monitored between 5 and 50 °C, hence allowing the study of the two different lipid structures, the gel and fluid bilayer phases, and the transition between them. As it is known, the fluorescent emission spectrum of Laurdan is highly sensitive to the bilayer gel-fluid transition, whereas the Ahba fluorescence spectrum was found to be insensitive to changes in bilayer structure and polarity, which are known to happen at the gel-fluid transition. However, both probes monitor the bilayer gel-fluid transition through fluorescence anisotropy measurements. With time-resolved fluorescence, it was possible to show that bilayer structural variations can be monitored by Laurdan excited state lifetimes changes, whereas Ahba lifetimes were found to be insensitive to bilayer structural modifications. Through anisotropy time decay measurements, both probes could monitor structural bilayer changes, but the limiting anisotropy was found to be a better parameter than the rotational correlation time. It is interesting to have in mind that the relatively small fluorophore of Ahba (o-Abz) could possibly be bound to a phospholipid hydrocarbon chain, not disturbing much the bilayer packing and being a sensitive probe for the bilayer core.     

Photochemical kinetics for holographic grating formation in phenanthrenequinone doped poly (methyl methacrylate) photopolymer

The photochemical kinetics of phenanthrenequinone (PQ) doped poly (methyl methacrylate) photopolymer in holographic recording was studied theoretically and experimentally. The diffusion of PQ molecules during holographic recording was negligible because of its small diffusion coefficient at room temperature. A photochemical reaction kinetics model of PQ/PMMA was established. The analytical expressions for the temporal variations of transmittance and diffraction efficiency were derived. By fitting the experimental curves, some parameters related with the polymer components were obtained by the proposed model, which can be used to analyze the photochemical process and will be helpful to the optimization of material preparation.