Interaction Mechanisms Between Anionic Surfactant Micelles and Different Metal Ions in Aqueous Solutions

In its using or eliminating processes, surfactant solutions usually exhibit different behaviors because of the different species or concentrations of the encountered metal ions. Interactions between anionic surfactant (SDS) micellar solutions and several familiar metal salt solutions (Al₂(SO₄)₃, FeCl₃, CaCl₂ and MgCl₂) were investigated. Precipitates were formed in all systems except SDS‐MgCl₂ visually. Stoichiometric analysis reveals that, in SDS‐Al₂(SO₄)₃ system, the precipitation phenomenon is mainly owing to the effect of adsorption‐charge neutralization between Al³⁺ ions and SDS micelles; in SDS‐FeCl₃ system, bridge connection effect of Fe(OH)²⁺ ions among SDS micelles becomes the dominant mechanism; while in SDS‐CaCl₂ system, all SDS micelles are decomposed and solubility product of Ca(DS)₂ crystal results in the precipitation. SEM photographs of the precipitates can serve as additional vivid proofs of the above conclusion.     

A Monomer‐Micelle Model for the Formation of Simple Taurocholate Micelles

A kinetic dialysis technique was used to validate a relationship between monomer taurocholate (TC) concentration and total TC concentration in TC solutions containing 0.15 M NaCl and 0.01 M buffer (pH = 7.4). Based on the experimental data and Mukerjee's equations, the number average degree and the weight average degree of TC aggregates were estimated to be nearly the same (～5), indicating that simple TC micelles were the only aggregates. Furthermore, the TC dimer concentration was quantified to be negligible. According to the validated relationship, aggregation number of 5 for simple TC micelles, and the definition of critical micelle concentration (CMC), a modified monomer‐micelle model was used for describing simple TC micelle formation. Moreover, the CMC value was estimated to be ～6.3 mM, which is consistent with the reported value of ～6.0 mM.     

水杨酸钠对阳离子Gemini表面活性剂水溶液中蠕虫状胶束形成和性质的影响

用稳态和震荡剪切实验研究了水杨酸钠(NaSal)对50 mmol·L^-1阳离子Gemini表面活性剂2-羟基-(三亚甲基-α,ω-双十二烷基三甲基溴化铵和三亚甲基-α,ω-双十二烷基三甲基溴化铵, 简写为12-3(OH)-12和12-3-12)水溶液中形成蠕虫状胶束及其性质的影响. 在无盐状态下, 50 mmol·L^-1的12-3(OH)-12或12-3-12在水溶液中仅形成球状或棒状胶束. NaSal可促进上述两体系胶束的生长, 生成蠕虫状胶束. 比较而言, 12- 3(OH)-12对NaSal更敏感, 可以在低盐浓度下生成蠕虫状胶束. 而且与12-3-12体系相比, 12-3(OH)-12生成了更长的蠕虫状胶束. 这些差别在于12-3(OH)-12体系中存在羟基连接链之间的氢键作用, 这增加了12- 3(OH)-12头基的亲水性, 促进了反离子的解离, 增大的胶束表面电荷密度更强烈地结合水杨酸根反离子, 减小了头基间的静电斥力, 反过来又增强了分子间氢键, 致使 12-3(OH)-12胶束迅速生长.     

生物相容性嵌段型聚电解质胶束在水溶液中的酶降解行为

采用激光光散射仪和原子力显微镜研究了生物相容性嵌段型聚电解质聚左旋乳酸-b-聚甲基丙烯酸二甲氨基乙酯(PLLA-b-PDMAEMA)胶束在水溶液中2个温度(室温25.0℃和人体温度36.8℃)和2个pH值(肿瘤pH=4.9和正常组织pH=7.4)条件下的酶降解行为. 酶降解过程中存在一个失活时间, 在此之前, 胶束的酶降解遵循逐个降解机理. 失活时间之后, 出现裂纹或是通道的胶束核为降低其在溶剂中的表面积, 从而降低体系自由能, 胶束之间发生了聚集. 升高温度后, 酶的活性提高, 初始降解速率加快. 由于pH=4.9时胶束壳层因静电斥力作用而较为伸展, 使得胶束降解更快.     

阳离子碳氟表面活性剂研究I: 水溶液中的胶束特性及生长

利用动态光散射(Dynamic Light Scattering, DLS)、瞬态电双折射(Transient Electric Birefringence, TEB)和粘度测定方法研究了部分氟代阳离子表面活性剂氟代-2-羟基十一烷基二乙羟基甲基氯化铵(diethanolheptadecafluoro-2-undecanol methylammonium chloride, C₈F₁₇CH₂CH(OH)CH₂NCH₃(C₂H₄OH)₂Cl, DEFUMACl)水溶液的胶束化特性. 结果表明: DEFUMACl的临界胶束浓度cmc为3.8 mmol•L^－1. 稀溶液中随着DEFUMACl浓度的增加或者无机盐NaCl的加入, DEFUMACl胶束由球形向棒状转变, 其转变浓度, 即第二临界胶束浓度(cmc_II)为0.2 mol•L^－1; 电导测定的反离子(Cl^－)结合度为0.72. 利用球形和棒状胶束模型确定的DEFUMACl胶束聚集数分别为45和335.     

直链醇对反胶束体系中木素过氧化物酶催化活性的影响

根据研究发现, 在有醇作助表面活性剂的CTAB反胶束中木素过氧化物酶(LiP)不能表现活力, 而在水介质中CTAB对LiP的催化活性影响又不是很大. 为了揭示其中醇的影响, 本工作就不同碳链长度的醇对LiP酶催化性能的影响进行了研究. 由于CTAB反胶束体系中醇浓度较高, 且碳原子数大于4的直链醇在水中的溶解度又很小, 为此采用了LiP可在其中显示催化活性的CTAB正胶束、AOT反胶束和Brij30反胶束作介质, 通过研究这些介质中不同链长的醇对LiP催化活力的影响, 来探讨CTAB反胶束中木素过氧化物酶(LiP)不能表现活力的原因. 结果表明, 不管表面活性剂聚集体的结构、电性质及反胶束大小如何, 只要醇的浓度超过500 mmol•L^－1 (丁醇≥1200 mmol•L^－1), LiP在上述原本可显示活力的介质中均无催化活性. 据此推测CTAB反胶束中木素过氧化物酶(LiP)不能表现活力的原因主要是由助表面活性剂醇造成的.     

Dimensions and Orientation of Triton X-100 Micelles in Aqueous Solutions,According to Turbidimetric Data

Russian Journal of Physical Chemistry A - The size and orientation of micelles of nonionic surfactant Triton X-100 in aqueous solutions is determined turbidimetrically. It is shown that micelles...     

Temperature Dependant Micellization of AOT in Aqueous Medium: Effect of the Nature of Counterions

The lithium, potassium, and ammonium salts of bis (2‐ethylhexyl) sulphosuccinic acid have been prepared from the sodium salt (AOT) by applying ion‐exchange technique. The critical micellization concentrations (cmc) of the surfactants with four different counterions have been determined at a temperature range of 10°C to 40°C using surface tension as well as electrical conductivity measurements. Observed data have been utilized to evaluate the ionization degree (counter ion association constant),α, and various thermodynamic parameters of micellization viz, free energy, enthalpy, entropy changes of micelle formation, and also the surface parameters (Γ_max, A_min) in aqueous media. The value of cmc decreases with hydrated ionic size of the counter ions (except K⁺) and follows the order NH₄ ⁺>Na⁺>Li⁺>K⁺. While large negative free energy change (ΔG⁰ _m) and the positive entropy change (ΔS⁰ _m) favor the micellization process thermodynamically, nature of their variation with counterion supports the involvement of counterion size factor in micellization process via a change in the hydrophilicity of surfactant head group.     

Effect of Temperature on the Binding and Distribution Characteristics of Thionine in Sodium Dodecylsulfate Micelles

The interaction between thionine (a cationic thiazine dye) and anionic surfactant sodium dodecylsulfate in aqueous solution at different temperatures has been studied spectrophotometrically. The absorption spectra were used to quantify the dye/surfactant binding constants and surfactant/water partition coefficients of the dye by applying mathematical models that consider partitioning of the dye between the micellar and aqueous pseudo-phases. The Benesi-Hildebrand equation was applied to calculate the binding constants of thionine to sodium dodecylsulfate micelles over a temperature range of 293 to 333 K. To evaluate the thermodynamic aspects of the interaction of thionine with sodium dodecylsulfate micelles, Gibbs energy, enthalpy and entropy changes were determined. The effect of temperature on the critical micelle concentration of sodium dodecylsulfate in the presence of thionine was also studied and discussed. The binding affinity of thionine to the sodium dodecylsulfate micelles significantly decreased with increasing temperature because of the thermal agitation.     

系列离子液体型Gemini咪唑表面活性剂在水溶液中的分子动力学模拟

利用分子动力学模拟方法研究了系列离子液体型Gemini咪唑表面活性剂在水溶液中的表面活性和胶束化能力. 模拟结果表明,压力张量法得到的表面张力模拟值偏小,需乘以修正系数矫正;分子动力学模拟得到的临界胶束浓度变化规律与实验相符,可以定性比较不同结构的离子液体型Gemini咪唑分子间的胶束化能力;温度的升高会加剧分子的热运动,不利于离子液体型Gemini咪唑表面活性剂在水溶液中形成胶束;此外,研究还发现联接基不同的离子液体型Gemini咪唑表面活性剂可能遵循不同的胶束化机理.S≤6时,单个分子自组装成胶球后发生聚合形成大胶团.随着咪唑上长烷烃链碳数的增加,[C_n-4-C_nim]胶束化能力提高;而随着联接链长度增加,[C₁₀-S-C₁₀im]胶束化能力降低;当S ＞6时,分子联接基弯曲并伸入其它分子烷烃链内部以减小头基分离力,从而形成稳定的胶束或胶团.随着联接基团亚甲基数的增加,头基斥力减小,附加疏水相互作用增强,[C₁₀-S-C₁₀im]胶束化能力提高.     

Study on the Absorption Properties of C_(60) in Micellar Aqueous Solutions and Mechanisms for Solubilisation

SincethesuccessfijlpreparationandmasssynthesisofC,,.tremendousinterestshavebeenevokedinitsunusualfull-carbonstructurelikefootballandphysicalandchemicalproperties,whichhavebeenstudiedcarefullyandsystematically.However,suchworksaremainlycarriedoutinorganicsolvents,especiallyinarenesolvents(benzeneortoluene),duetothewater-insolublenatureofC,o'In1992,Andersonetal.'firstobtainedthewater-solubleC,,successfullyviacyclodextrin(CD)enclosing,soastoopenanewwayforstudyingofC,,inaqueoussolutions.Afterth…     

核糖核酸酶A在丁酸十二铵-环己烷反胶束溶液中的催化动力学

研究了核糖核酸酶A(RNaseA)在丁酸十二铵(DAB)-环己烷反胶束溶液中催化水解胞苷2',3'-环单磷酸酯的动力学,数据符合Michaelis-Menten酶催化机理.以k_cat/K_m表示酶催化活性时,Rnase A在反胶束溶液中的催化活性是在水溶液中的14～30倍.无论是固定DAB浓度还是固定H₂O与DAB浓度之比,随增溶水量的增加,k_cat/K_m呈下降趋势.     

Gradient Structure‐Induced Temperature Responsiveness in Styrene/Methyl Methacrylate Gradient Copolymers Micelles

In this work, micelles are formed by gradient copolymer of styrene and methyl methacrylate in acetone–water mixture and their temperature responsiveness is investigated in a narrow range near room temperature. Three different kinds of structural transitions could be induced by temperature: unimers to micelle transition, shrinkage/stretching of micelles, and morphological transition from spherical micelles to vesicles. In addition, a model analysis on the interface of gradient copolymer micelle is made to better understand these phenomena. It is found that both position and composition of the interface could alter in response to the change in temperature. According to the experiments and model analysis, it is proposed that temperature responsiveness might be an intrinsic and universal property of gradient copolymer micelles, which only originates from the gradient structure.

     

The Interplay of Cholesterol and Ligand Binding in hTSPO from Classical Molecular Dynamics Simulations

The translocator protein (TSPO) is a 18kDa transmembrane protein, ubiquitously present in human mitochondria. It is overexpressed in tumor cells and at the sites of neuroinflammation, thus representing an important biomarker, as well as a promising drug target. In mammalian TSPO, there are cholesterol–binding motifs, as well as a binding cavity able to accommodate different chemical compounds. Given the lack of structural information for the human protein, we built a model of human (h) TSPO in the apo state and in complex with PK11195, a molecule routinely used in positron emission tomography (PET) for imaging of neuroinflammatory sites. To better understand the interactions of PK11195 and cholesterol with this pharmacologically relevant protein, we ran molecular dynamics simulations of the apo and holo proteins embedded in a model membrane. We found that: (i) PK11195 stabilizes hTSPO structural fold; (ii) PK11195 might enter in the binding site through transmembrane helices I and II of hTSPO; (iii) PK11195 reduces the frequency of cholesterol binding to the lower, N–terminal part of hTSPO in the inner membrane leaflet, while this impact is less pronounced for the upper, C–terminal part in the outer membrane leaflet, where the ligand binding site is located; (iv) very interestingly, cholesterol most frequently binds simultaneously to the so-called CRAC and CARC regions in TM V in the free form (residues L150–X–Y152–X(3)–R156 and R135–X(2)–Y138–X(2)–L141, respectively). However, when the protein is in complex with PK11195, cholesterol binds equally frequently to the CRAC–resembling motif that we observed in TM I (residues L17–X(2)–F20–X(3)–R24) and to CRAC in TM V. We expect that the CRAC–like motif in TM I will be of interest in future experimental investigations. Thus, our MD simulations provide insight into the structural features of hTSPO and the previously unknown interplay between PK11195 and cholesterol interactions with this pharmacologically relevant protein.     

Interactions of D-Maltose and Sucrose with Some Amino Acids in Aqueous Solutions

Calorimetric titrations have been performed at 298.15 K in aqueous solutions to derive the stability constants and thermodynamic parameters of the interactions of D-maltose and sucrose with some amino acids (glycine, DL-alanine, DL-leucine, and L-serine). The apparent molal volumes of the disaccharides in dilute aqueous solutions of the amino acids have been determined from density measurements at 298.15 K. In contrast to D-maltose, sucrose was found to associate with the amino acids and these associated species are preferentially entropy stabilized. These results are interpreted in terms of the influence of the nature of the solutes, their specific conformations, and hydration, on the ability of the disaccharides to form associated complexes with the amino acids.     

可聚硼酸酯表面活性剂的表面化学性质及与LAS相互作用

用表面张力法研究了可聚合硼酸酯表面活性剂(BES)水溶液不同温度下(288-313 K)的表面活性和热力学函数变化；考察了BES与十二烷基苯磺酸钠(LAS)在0.5 mol·L-1 NaCl溶液中的相互作用. 结果表明, 298 K时, BES临界胶束浓度cmc达到0.066 mmol·L-1, γcmc为29.2 mN·m-1；在所考察的温度范围内BES胶束形成自由能(ΔG0m)在-22.4 - -25.8 kJ·mol-1之间, 胶束形成是熵驱动过程. BES/LAS混合体系为具有较大负偏差的非理想体系, BES/LAS分子间平均相互作用参数βm=-3.48；当溶液体相中BES摩尔分数αBES＝0.5时, 混合胶束中BES摩尔分数X1m为0.46, |βm|达到最大, 而且此时混合溶液cmc为0.017 mmol·L-1, 达到最低, γcmc为27.8 mN·m-1.