DNA与非离子糖基表面活性剂相互作用的研究

用动态表面张力法、键合等温线、紫外光谱及荧光光谱等方法研究了不同链长烷基葡萄糖苷(APG)与DNA的相互作用．研究发现APG对DNA键合可分为两阶段,第一阶段：多苷依靠多羟基结构与DNA形成动力学稳定的复合物;第二阶段：随时间延长,单苷由于其较小的空间位阻而与DNA形成能量更低的热力学稳定复合物．由平衡渗析法得到的单苷与DNA相互作用键合等温线显示,APG与DNA键合为一非协同过程．证实了其非离子氢键吸附的本质,同时也支持了DNA对胶束及预胶束的缠绕模型．紫外光谱结果证明了在APG与DNA作用过程中疏水作用的重要性．以溴化乙锭为探针,荧光光谱法研究证明,随APG链长增加,DNA构象缩拢程度加大,但即使是C2APG也仅能使DNA构象部分缩拢,推测DNA仅是部分链段对APG胶束进行包裹,其它链段仍处于伸展状态．与阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)可使DNA构象强烈缩拢的事实相比,证明了静电作用在大分子与表面活性剂相互作用中的主导性．     

DNA与表面活性剂的相互作用（I）——基于相行为的宏观研究进展

综述了以相行为为基础的DNA与表面活性剂在水及有机溶剂中相互作用的研究进展及其相关研究方法。阐述了静电作用及疏水作用对相行为的影响。介绍了用光散射法及浊度法确定沉淀边界和用键合等温线及恒温滴定量热法考察DNA与表面活性剂相互作用的键合度及协同键合过程的能量变化，以及利用短链DNA与表面活性剂复合物在固体表面的吸附等温线来考察沉淀后复合物的构象变化。     

DNA与两性表面活性剂相互作用研究

本文综述了DNA与两性表面活性剂相互作用的研究进展，主要介绍了利用荧光显微镜、动静态光散射、相图及浊度等方法对DNA与两性表面活性剂相互作用的观察与形成复合物的表征。由于两性表面活性剂所具有的独特性质，可以实现在特定pH范围通过静电作用诱导DNA构象发生线圈状向小球状的不连续转变，并可通过调节溶液pH值、离子强度等实现对DNA-两性表面活性剂复合物的稳定性的调控。DNA与两性表面活性剂相互作用形成的复合物在非病毒基因载体研究方面具有潜在的应用价值。     

DNA与表面活性剂的相互作用(Ⅰ)--基于相行为的宏观研究进展

综述了以相行为为基础的DNA与表面活性剂在水及有机溶剂中相互作用的研究进展及其相关研究方法.阐述了静电作用及疏水作用对相行为的影响.介绍了用光散射法及浊度法确定沉淀边界和用键合等温线及恒温滴定量热法考察DNA与表面活性剂相互作用的键合度及协同键合过程的能量变化,以及利用短链DNA与表面活性剂复合物在固体表面的吸附等温线来考察沉淀后复合物的构象变化.     

表面活性剂@Weakley型稀土多酸复合催化剂对甲基橙的光催化降解活性

以光催化活性高的多酸阴离子CeW_(10)O_(36)~(9-)、不同结构阳离子表面活性剂为构筑基元,通过水/氯仿两相静电包埋技术制备了一系列表面活性剂@多酸复合物,并利用傅里叶红外光谱(FTIR)、热重分析(TGA)对复合物的组成及结构进行分析;以甲基橙为光催化降解底物分子、表面活性剂@多酸复合物为催化剂,考察不同表面活性剂、催化剂用量、甲基橙浓度、有机染料对光催化降解率的影响;不同表面活性剂@稀土多酸复合催化剂的光催化活性顺序为DTAB(十二烷基三甲基溴化铵)@CeW_(10)TTAB(十四烷基三甲基溴化铵)@CeW_(10)CTAB(十六烷基三甲基溴化铵)@CeW_(10)OTAB(十八烷基三甲基溴化铵)@CeW_(10)DODA(双十八烷基二甲基溴化铵)@CeW_(10)。     

DNA与表面活性剂相互作用研究(Ⅱ)--基于构象变化的分子水平研究

综述了DNA在稀溶液中与表面活性剂在分子水平上的相互作用的研究进展。介绍了DNA与表面活性剂的两阶段键合过程以及伴生的DNA由线圈向小球的构象变化及其理论解释。同时阐述了相关的对其微观构象变化的研究方法，如热变性实验、荧光光谱、荧光显微技术、动静态光散射等。对DNA与表面活性剂形成的复合物作为基因转染载体的前景及限制因素作了简要介绍。     

m-6-m型Gemini双季铵盐表面活性剂与DNA的相互作用

合成了5种m-6-m型Gemini双季铵盐表面活性剂,在对产物结构和表面活性进行分析的基础上,分别采用紫外分光光度法和荧光分光光度法考察了m-6-m型Gemini双季铵盐表面活性剂与DNA的相互作用.结果表明,m-6-m型Gemini表面活性剂的CMC随烷基疏水链的增长呈逐渐下降趋势.几种表面活性剂均没有使DNA的紫外吸收峰发生红移或蓝移现象,说明复合物无嵌插作用或氢键形成,表面活性剂与DNA作用后的吸光度随表面活性剂浓度的增大而增强,当表面活性剂的浓度相同时,吸光度随疏水链的增大而逐渐减弱.Gemini表面活性剂浓度增大导致荧光强度降低,表面活性剂与DNA作用时的猝灭为静态猝灭,随着疏水链长度的增长,荧光猝灭常数降低,表面活性剂与DNA之间的作用力减弱.     

聚电解质复合物溶解性研究

报道了聚电解质复合物的一种新的溶剂体系———离子表面活性剂剂的水溶液 ,研究了表面活性的用量及结构、温度、外加小分子电解质对复合物溶解性的影响 ,初步探讨了溶解机理 ,通过扫描电镜观察了复合物溶解后在溶液中的形态 .研究表明 ,当复合物与离子表面活性剂定量结合到一定程度时 ,就会使复合物发生溶解 .表面活性剂碳链长度的增加、温度的提高均会对复合物的溶解有不同程度的促进 .加入少量的无机电解质如氯化钠 ,会促进复合物的溶解 ,若氯化钠加入量过多 ,反而不利于复合物的溶解 .复合物的溶解机理被认为是表面活性剂的解离作用和疏水作用二者的协同 .     

液体环境单分子免疫球蛋白G的原子力显微镜高分辨成像

原子力显微镜技术( AFM)具有纳米级高分辨成像能力,是研究生物大分子结构和功能的重要工具之一。制备合适的样品是获取高分辨成像的关键要素。本研究结合DNA折纸技术,将抗原分子修饰在DNA折纸上,通过分子识别作用,抗体分子与抗原分子特异性结合,形成由DNA折纸和抗原抗体复合物构成的纳米结构。利用DNA折纸在云母表面上的吸附特点,使得抗体分子选择性地吸附在衬底表面上,由此获得了液体环境中的单个地高辛抗体免疫球蛋白G( IgG)分子的“Y”超微结构形貌。本方法简单、方便,为AFM在单分子水平上检测和表征生物分子结构和功能提供帮助。     

水溶性聚电解质—表面活性剂复合物的聚集行为

聚电解质在溶液中与相反电荷的表面活性剂通过解电作用与疏水作用可形成聚电解质－表面活性剂复合物，依据反应条件生成的复事物可以是水溶性也可以是非水溶性的。水溶性的聚电解质－表面活性剂复合物由于有许多工业应用，因此近几十上来水溶性聚电解质－表面活性剂复合物的形成和结构已爱到人们的广泛重视。本文对水溶性聚电解质－表面活性剂复合物的聚集过程、聚集结构作了简要概述，此外对荧光光谱在这一领域的应用进行了重点介绍     

DNA and surfactants in bulk and at interfaces

Recent investigations of the DNA interactions with cationic surfactants and catanionic mixtures are reviewed. Several techniques have been used such as fluorescence microscopy, dynamic light scattering, electron microscopy, and Monte Carlo simulations.

The conformational behaviour of large DNA molecules in the presence of cationic surfactant was followed by fluorescence microscopy and also by dynamic light scattering. These techniques were in good agreement and it was possible to observe a discrete transition from extended coils to collapsed globules and their coexistence for intermediate amphiphile concentrations. The dependence on the surfactant alkyl chain was also monitored by fluorescence microscopy and, as expected, lower concentrations of the more hydrophobic surfactant were required to induce DNA compaction, although an excess of positive charges was still required.

Monte Carlo simulations on the compaction of a medium size polyanion with shorter polycations were performed. The polyanion chain suffers a sudden collapse as a function of the concentration of condensing agent, and of the number of charges on the polycation molecules. Further increase in the concentration increases the degree of compaction. The compaction was found to be associated with the polycations promoting bridging between different sites of the polyanion. When the total charge of the polycations was lower than that of the polyanion, a significant translational motion of the compacting agent along the polyanion was observed, producing only a small-degree of intrachain segregation, which can explain the excess of positive charges necessary to compact DNA.

Dissociation of the DNA–cationic surfactant complexes and a concomitant release of DNA was achieved by addition of anionic surfactants. The unfolding of DNA molecules, previously compacted with cationic surfactant, was shown to be strongly dependent on the anionic surfactant chain length; lower amounts of a longer chain surfactant were needed to release DNA into solution. On the other hand, no dependence on the hydrophobicity of the compacting agent was observed. The structures of the aggregates formed by the two surfactants, after the interaction with DNA, were imaged by cryogenic transmission electron microscopy. It is possible to predict the structure of the aggregates formed by the surfactants, like vesicles, from the phase behaviour of the mixed surfactant systems.

Studies on the interactions between DNA and catanionic mixtures were also performed. It was observed that DNA does not interact with negatively charged vesicles, even though they carry positive amphiphiles; however, in the presence of positively charged vesicles, DNA molecules compact and adsorb on their surface.

Finally Monte Carlo simulations were performed on the adsorption of a polyelectrolyte on catanionic surfaces. It was observed that the mobile charges in the surface react to the presence of the polyelectrolyte enabling a strong degree of adsorption even though the membrane was globally neutral. Our observations indicate that the adsorption behaviour of the polyelectrolyte is influenced by the response given by the membrane to its presence and that the number of adsorbed beads increases drastically with the increase of flexibility of the polymer. Calculations involving polymers with three different intrinsic stiffnesses showed that the variation is non-monotonic. It was observed also that a smaller polyanion typically adsorbs more completely than the larger one, which indicates that the polarisation of the membrane becomes less facilitated as the degree of disruption increases.     

电解质和乙醇对DNA与Gemini表面活性剂相互作用的影响

应用荧光探针和zeta电位方法研究了电解质NaBr、NaCl、KCl和有机溶剂乙醇对DNA与Gemini表面活性剂相互作用的影响. DNA诱导的表面活性剂类胶束在较低浓度即可生成, 这一浓度称为临界聚集浓度(CAC). Gemini表面活性剂比具有相同烷烃链长的单体表面活性剂更易聚集, 对应的CAC较低. 实验结果表明, 盐(NaBr)浓度对DNA/表面活性剂体系的CAC影响不大, 阴、阳离子的种类则对该体系有不同程度的影响. 阴离子(Br-、Cl-)对体系的CAC有显著的影响, 但阳离子(Na+、K+)的差异对CAC影响不大. 极性溶剂乙醇对DNA与表面活性剂相互作用的影响比较复杂. 乙醇浓度较低时有利于表面活性剂的聚集, 使得CAC减小; 而浓度较高时, 则不利于表面活性剂聚集,从而使CAC变大. 乙醇可显著改变DNA/表面活性剂复合物的zeta电位.     

Condensation and decondensation of DNA by cationic surfactant, spermine, or cationic surfactant-cyclodextrin mixtures: macroscopic phase behavior, aggregate properties, and dissolution mechanisms

The macroscopic phase behavior and other physicochemical properties of dilute aqueous mixtures of DNA and the cationic surfactant hexadecyltrimethylammounium bromide (CTAB), DNA and the polyamine spermine, or DNA, CTAB, and (2-hydroxypropyl)-β-cyclodextrin (2HPβCD) were investigated. When DNA is mixed with CTAB we found, with increasing surfactant concentration, (1) free DNA coexisting with surfactant unimers, (2) free DNA coexisting with aggregates of condensed DNA and CTAB, (3) a miscibility gap where macroscopic phase separation is observed, and (4) positively overcharged aggregates of condensed DNA and CTAB. The presence of a clear solution beyond the miscibility gap cannot be ascribed to self-screening by the charges from the DNA and/or the surfactant; instead, hydrophobic interactions among the surfactants are instrumental for the observed behavior. It is difficult to judge whether the overcharged mixed aggregates represent an equilibrium situation or not. If the excess surfactant was not initially present, but added to a preformed precipitate, redissolution was, in consistency with previous reports, not observed; thus, kinetic effects have major influence on the behavior. Mixtures of DNA and spermine also displayed a miscibility gap; however, positively overcharged aggregates were not identified, and redissolution with excess spermine can be explained by electrostatics. When 2HPβCD was added to a DNA-CTAB precipitate, redissolution was observed, and when it was added to the overcharged aggregates, the behavior was essentially a reversal of that of the DNA-CTAB system. This is attributed to an effectively quantitative formation of 1:1 2HPβCD-surfactant inclusion complexes, which results in a gradual decrease in the concentration of effectively available surfactant with increasing 2HPβCD concentration.     

DNA‐Surfactant Interactions. Compaction,Condensation, Decompaction and Phase Separation

Recent investigations of the interaction between DNA and alkyltrimethylammonium bromides of various chain lengths are reviewed. Several techniques have been used such as phase map determinations, fluorescence microscopy, and electron microscopy. Dissociation of the DNA‐surfactant complexes, by the addition of anionic surfactant, has received special attention. Precipitation maps for DNA‐cationic surfactant systems were evaluated by turbidimetry for different salt concentrations, temperatures and surfactant chain lengths. Single‐stranded DNA molecules precipitate at lower surfactant concentrations than double‐helix ones. It was also observed that these systems precipitate for very low concentrations of both DNA and surfactant, and that the extension of the two‐phase region increases for longer chain surfactants; these observations correlate well with fluorescence microscopy results, monitoring the system at a single molecule level. Dissociation of the DNA‐cationic surfactant complexes and a concomitant release of DNA was achieved by addition of anionic surfactants. The unfolding of DNA molecules, previously compacted with cationic surfactant, was shown to be strongly dependent on the anionic surfactant chain length; lower amounts of a longer chain surfactant were needed to release DNA into solution. On the other hand, no dependence on the hydrophobicity of the compacting agent was observed. The structures of the aggregates formed by the two surfactants, after the interaction with DNA, were imaged by cryogenic transmission electron microscopy. It is possible to predict the structure of the aggregates formed by the surfactants, like vesicles, from the phase behaviour of the mixed surfactant systems. The compaction of a medium size polyanion with shorter polycations was furthermore studied by means of Monte Carlo simulations. The polyanion chain suffers a sudden collapse as a function of the condensing agent concentration and of the number of charges on the molecules. Further increase of the concentration gives an increase of the degree of compaction. The compaction was found to be associated with the polycations promoting bridging between different sites of the polyanion. When the total charge of the polycations was lower than that of the polyanion, a significant translational motion of the compacting agent along the polyanion was observed, producing only a small‐degree of intrachain segregation. However, complete charge neutralization was not a prerequisite to achieve compacted forms.     

Photoreversible DNA condensation using light-responsive surfactants

A means to control DNA compaction with light illumination has been developed using the interaction of DNA with a photoresponsive cationic surfactant. The surfactant undergoes a reversible photoisomerization upon exposure to visible (trans isomer, more hydrophobic) or UV (cis isomer, more hydrophilic) light. As a result, surfactant binding to DNA and the resulting DNA condensation can be tuned with light. Dynamic light scattering (DLS) measurements were used to follow lambda-DNA compaction from the elongated-coil to the compact globular form as a function of surfactant addition and light illumination. The results reveal that compaction occurs at a surfactant-to-DNA base pair ratio of approximately 7 under visible light, while no compaction is observed up to a ratio of 31 under UV light. Upon compaction, the measured diffusion coefficient increases from a value of 0.6 x 10(-8) cm2/s (elongated coil with an end-to-end distance of 1.27 microm) to a value of 1.7 x 10(-8) cm2/s (compact globule with a hydrodynamic radius of 120 nm). Moreover, the light-scattering results demonstrate that the compaction process is completely photoreversible. Fluorescence microscopy with T4-DNA was used to further confirm the light-scattering results, allowing single-molecule detection of the light-controlled coil-to-globule transition. These structural studies were combined with absorbance and fluorescence spectroscopy of crystal violet in order to elucidate the binding mechanism of the photosurfactant to DNA. The results indicate that both electrostatic and hydrophobic forces are important in the compaction process. Finally, a DNA-photosurfactant-water phase diagram was constructed to examine the effects of both DNA and surfactant concentration on DNA compaction. The results reveal that precipitation, which occurs during the latter stages of condensation, can also be reversibly controlled with light illumination. The combined results clearly show the ability to control the interaction between DNA and the complexing agent and, therefore, DNA condensation with light.     

表面活性剂中DNA构象变化的研究

以荧光探针法研究了表面活性剂与小牛胸腺DNA的相互作用，结果表明：阳离子表面活性剂主要通过静电引力和疏水方式与DNA作用；阴离子表面活性剂与DNA之间存在静电排斥力，两者之间的相互作用不太明显；而非离子表面活性剂与DNA的相互作用类似于有机溶剂对DNA的影响，即通过溶液的极性、粘度和介电常数来影响DNA的构象，表面活性剂使得DNA构象发生较大的变化，预示了它可能使DNA的生物功能发生较大的变化。     

Compaction and decompaction of DNA induced by the cationic surfactant CTAB

A multifaceted study on the interaction of the cationic surfactant CTAB with calf thymus DNA was carried out by using different techniques. The measurements were done at different molar ratios X = [CTAB]/[DNA]. Results show the conformational change that DNA suffers due to the interaction with surfactant molecules at low molar ratios: the condensation of the polynucleotide, from an extended coil state to a globular state. The effect observed at the higher molar ratios is worth noting: the decondensation of DNA, that is, the transition from a compact state to a more extended conformation. Experimental data obtained confirm that this latter state is not exactly the same as that found in the absence of the surfactant. Attractive interactions between different parts of the molecule by ion correlation effects are the driving force to produce both the compaction and decompaction events. Results also show the importance of choosing both a proper system for the study and the most seeming measuring technique to use. The study demonstrates that, in some cases, the use of several techniques is desirable in obtaining reliable and accurate results.     

New Ion‐Pair Based All‐Solid‐State Surfactant Sensitive Sensor for Potentiometric Determination of Cationic Surfactants

Cationic surfactants of different types were determined using a few potentiometric sensors based on ion‐pair complexes (dodecyldimethylbenzylammonium dodecylsulfate, dodecylmethylbenzylammonium dodecylbenzensulfonate, tetrahexadecylammonium dodecylsulfate and Hyamine (benzethonium dodecylsulfate)) as sensing materials. The response of the all‐solid state surfactant sensitive electrode based on a Teflonized graphite conducting substrate, coated with a PVC membrane containing sensing material, was investigated in the solutions of Hyamine and hexadecyltrimethylammonium ion in the concentration range from 1 μM to 10 mM. Potentiometric surfactant cation titration has been performed using sodium dodecylsulfate as titrant and an ion‐pair‐based surfactant sensitive electrode as a potentiometric indicator. Several commercial surfactant products have also been titrated and the results were compared with those obtained with two‐phase standard titration method.     

DNA compaction onto hydrophobic surfaces by different cationic surfactants

DNA compaction by alkyltrimethylammonium surfactants at hydrophobized silica surfaces and the effect of the counterion, as well as the hydrocarbon chain length, was investigated by in situ null-ellipsometry. In addition, DNA compaction in the presence of a gemini surfactant, hexyl-alpha,omega-bis(dodecyldimethylammonium bromide), was studied. The type of cationic amphiphile used was found not to have a pronounced effect on the mixed DNA-cationic surfactant adsorbed layer thickness, although the surface concentration excess for the mixed layers seemed to follow the same trend as that for DNA-free surfactant layers. Interestingly, it was also found that the stability of the mixed adsorbed layer largely depends on the cationic surfactant used.     

Facilitation effect of oligonucleotide on vesicle formation from single‐chained cationic surfactant—Dependences of oligonucleotide sequence and size and surfactant structure

The interaction between DNA and surfactant has both biological and technological significances. Recently, we reported for the first time that oligo d(C)₂₅ can induce single‐chained cationic surfactant molecules to aggregate into vesicles. In this article, we studied systematically the formation of vesicles from traditional single‐chained cationic surfactant molecules in the presence of a series of oligonucleotides and found that the facilitation efficiency of oligonucleotide on vesicle formation depends on its size and base composition. Oligo d(T)_n cannot induce vesicle formation, whereas the other oligonucleotides can. Moreover, the oligonucleotide with a bigger size or with a hairpin structure favors vesicle formation more, and the increases in the size of the head group and/or the length of the alkyl group of surfactant decrease the facilitation efficiency of oligonucleotide. Since so far, there is very limited report about the vesicle formation in DNA/single‐chained cationic surfactant solution, this study could be expected to increase the efficiency and applicability for DNA/amphiphile system. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 434–449, 2009