尾链含对硝基苯醚基团的阳离子Gemini表面活性剂的胶束化热力学

利用等温滴定微量量热法和电导法研究了具有不同疏水链长并且疏水链尾部含有对硝基苯醚基团的Gemini表面活性剂胶束化过程的热力学, 分别利用相分离模型和质量作用模型对观察焓与浓度的关系曲线进行拟合, 获得了胶束化过程的热力学参数. 两种模型获得的胶束化焓一致, 均为较大负值, 而吉布斯自由能却相差较大. 用相分离模型得到的胶束化过程的热容变化均为负值, 并随链长增加绝对值增大, 胶束化过程总的热容变化主要来自非极性的烷基链去水合产生的热容变化, 证明处于疏水链末端的对硝基苯醚基团在表面活性剂形成胶束后依然与水相接触. 质量作用模型获得的胶束聚集数随疏水链长增加逐渐下降, 这是由具有长疏水链的表面活性剂形成预胶束所导致.     

自由能微扰法研究系列烷基芳基磺酸盐的胶束化焓-熵补偿现象

为了研究不同结构的表面活性剂分子在水溶液中的胶束化焓-熵补偿现象, 采用自由能微扰(FEP)法计算了系列烷基芳基磺酸盐的溶剂化自由能, 并根据胶团化过程的质量作用模型讨论了相关热力学性质. 结果表明: 自由能微扰法得到的溶剂化自由能大小与用传统热力学表面张力法测定的吉布斯自由能相近, 能够用于比较不同结构的烷基芳基磺酸盐间胶束化能力; 烷基芳基磺酸盐在水溶液中的胶束化过程是自发进行的, 且存在焓-熵补偿现象, 补偿温度范围均在(302±2) K; 随着分子结构中芳环向长烷基链中间位置移动, 胶束化能力和胶束的稳定性均下降; 而随着芳环上短烷基链或长烷基链碳数的增加, 形成胶束的能力与稳定性均提高.     

Gemini表面活性剂烷烃尾链在吸附和聚集过程中的疏水协同效应(英文)

以表面张力法测定了系列Gemini表面活性剂m-6-m以及对应单体表面活性剂CmTABr的临界胶束浓度(cmc)和降低水表面张力20mN·m-1需要的浓度(pC20).比较这些参数表明m-6-m胶束化和在界面吸附的能力均强于CmTABr,这被归结为Gemini表面活性剂烷烃尾链间的疏水协同效应.与不对称Gemini表面活性剂12-6-m比较,对称的Gemini结构更有利于表面活性剂的聚集和吸附.     

十二烷基聚氧乙烯(n)醚与牛血清白蛋白的团簇化热力学模型

用表面张力和稳态荧光猝灭技术研究非离子表面活性剂十二烷基聚氧乙烯(n)醚(AEO_n)与牛血清白蛋白(BSA)的团簇化体系,根据质量作用定律建立AEO_n与BSA的团簇化热力学模型.从ΔH°>0,ΔS°>0及ΔG°＜0可以推知,AEO_n束缚胶束与BSA形成软物质团簇是熵驱动的超分子自组装过程,其间的超分子作用力以疏水作用为主.团簇化过程的(ΔG°)_clu与表面活性剂自由胶束化过程的(ΔG°)_mic皆小于零,且c₁＜cmc,可以圆满解释在团簇化体系中表面活性剂形成束缚胶束并与大分子经超分子自组装形成软团簇在先,而表面活性剂分子自组装形成自由胶束在后的实验事实.     

乙二醇对烷基三甲基溴化铵胶团化行为的影响

利用电导法研究了烷基三甲基溴化铵表面活性剂(CnTAB,n=12,14,16),即十二烷基三甲基溴化铵(DTAB),十四烷基三甲基溴化铵(TTAB)和十六烷基三甲基溴化铵(CTAB),在混合极性溶剂乙二醇/水(体积分数0～40%)中的胶团化行为。考察了温度对胶团形成的影响,应用相分离模型估算了三个表面活性剂的胶团热力学参数。结果表明临界胶团浓度(cmc)和反离子解离度(α)都随乙二醇组分的增加而增大。在乙二醇/水混合溶剂中胶团形成的标准吉布斯自由能相差很小,混合焓都是负值,而混合熵都为正值,说明焓-熵补偿效应在胶团形成中起主导作用。     

系列烷基芳基磺酸盐在水溶液中胶束化的焓-熵补偿现象

以表面张力法研究了系列烷基芳基磺酸盐在水溶液中胶束化的热力学性质,并考察了温度与分子结构对胶束化的影响.结果表明,烷基芳基磺酸盐在水溶液中胶束化是一个自发过程,主要来自熵驱动;随着温度升高,先有利于胶束化而后又不利于胶束化,且熵变对吉布斯自由能变的贡献有下降趋势,而焓变的贡献有增大趋势;胶束化存在焓-熵补偿现象,补偿温度Tc均在(306±2)K,基本不随烷基芳基磺酸盐的分子结构的改变而变化;随着芳环上短烷基链或长烷基链碳数的增加,胶束化能力和胶束的稳定性均提高,而随着芳环向长烷基链中间位置移动,胶束化能力和胶束的稳定性均下降.     

表面活性剂对污泥脱水性能影响的机理研究:Gemini表面活性剂与聚电解质相互作用的分子动力学模拟

表面活性剂可以与污泥表面的胞外聚合物(EPS)吸附形成胶束,释放出自由水和结合水,从而达到改善污泥脱水性能的目的.本文采用粗粒化的分子动力学模拟方法,研究了Gemini表面活性剂与EPS形成复合物的过程和结构.聚电解质链的亲疏水性对吸附过程有显著影响,亲水聚电解质链与Gemini表面活性剂吸附的主要驱动力为静电吸引,Gemini表面活性剂头基吸附在链上,尾链朝向溶剂;疏水聚电解质链与Gemini表面活性剂吸附过程由静电作用与疏水作用共同促进,Gemini表面活性剂以平行于聚电解质链的构型存在.Gemini表面活性剂联结基团长度对吸附过程的影响甚微;聚电解质链的电荷密度对亲水聚电解质链的吸附产生协同作用,对疏水聚电解质链的吸附不产生作用.     

含对苯氧基联接链的羧酸盐Gemini表面活性剂合成及胶团化特性

合成了含对苯氧基联接链的羧酸盐Gemini表面活性剂,研究了其胶团化特性.结果表明,该羧酸盐Gemini表面活性剂具有很低的cmc值,给出了cmc-T(温度)以及lncmc-(m+1)(烷烃链长)的回归方程.计算了胶团化的热力学函数变化,证实胶团化过程来自熵驱动,并表现出焓/熵补偿现象,在所考察的系列中,以(m+1)=11的胶团最为稳定.     

Gemini型CO_2/N_2开关表面活性剂的制备及性能研究

以CO_2/N_2为开关,在CO_2的作用下连接基1,6-己二醇硫酸酯钠盐与N,N-二甲基烷基胺发生相互作用,制备出不同链长的Gemini型CO_2/N_2开关表面活性剂,鼓泡通入N_2后会使该类表面活性剂的表面活性消失,重复通入CO_2和N_24次,能可逆地控制Gemini表面活性剂表面活性的有无.测量了3种不同疏水链碳数(14,16和18)的Gemini型CO_2/N_2开关表面活性剂水溶液的表面性能,实验结果显示随着表面活性剂疏水链长的增加,临界胶束浓度(ccmc)和气液界面最大吸附量(Γmax)逐渐减小,表面活性剂在界面的单分子面积(Amin)和效率因子(pc20)值逐渐增大,表面压(πcmc)受疏水链长影响较小,表现出较高的表面活性.以CO_2和N_2为开关还可控制表面活性剂起泡性能,循环4次,对起泡能力没有影响.     

双酯基型Gemini表面活性剂的合成及其性能

以1,4-环己二醇、氯乙酰氯、长链叔胺(RN(CH_3)_2,R=10、12、14、16)为原料,合成了一系列不同长度烷基链的双酯基型Gemini表面活性剂(分别命名为C10-EG-10、C12-EG-C12、C14-EG-C14、C16-EG-C16),用FTIR、NMR(~1H、~(13)C)对中间体及产物进行了表征,并研究了表面活性剂的表面性能及抑菌能力。结果表明:在298.15K时,采用铂金环法测定了合成的4种不同长度烷基链Gemini表面活性剂的临界胶束浓度,C10-EG-C10、C12-EG-C12、C14-EG-C14、C16-EG-C16的CMC值分别为5.495、1.096、0.186、0.045 mmol·L~(-1),与传统单链季铵盐表面活性剂相比,合成的Gemini表面活性剂具有较低的CMC值。胶束化热力学参数结果表明在形成胶束过程中是自发放热的。对合成的4种表面活性剂进行了乳化性能、起泡性能和抑菌测试,C14-EG-C14表面活性剂具有很好的乳化能力;C16-EG-C16 Gemini表面活性剂具有良好的稳泡能力;C10-EG-C10表面活性剂具有良好的抑菌能力。     

N-酰基-L-丝氨酸钠表面活性剂的合成和胶束化热力学性质

以L-丝氨酸和长链酰氯为原料,合成了3种不同碳链长度（n=8,12,14）的N-酰基-L-丝氨酸。 并以1H NMR、ESI-MS和元素分析对3种目标产物进行了表征。 采用表面张力法研究了N-酰基-L-丝氨酸钠在298、308、318和328 K时水溶液中的聚集行为,确定了临界胶束浓度（cmc）、临界胶束浓度下的最低表面张力（γcmc）、表面饱和吸附量Γmax。 由cmc和温度的关系,应用相分离模型计算了胶束化热力学参数ΔGom、ΔHom和ΔSom。 结果表明,ΔGom＜0,ΔHom的绝对值比-TΔSom绝对值小的多,说明胶束化过程为熵驱动过程,随着温度的升高,胶束化过程是熵-焓补偿的过程。     

十六烷基二苯醚二磺酸钠表面化学性质及胶团化作用

用滴体积法通过表面张力的测定, 系统地研究了十六烷基二苯醚二磺酸钠(C₁₆-MADS)在不同温度(298.0～318.0 K)和不同NaCl浓度(0～0.50 mol•L^-1)下的表面活性. 结果表明, 温度升高使C₁₆-MADS溶液的临界胶束浓度(cmc)略有增大, 表面极限吸附量(Γ_∞)降低. cmc随NaCl浓度的增大从1.45×10^-4 mol•L^-1降至4.10×10^-5 mol•L^-1, 但最低表面张力(γ_cmc)基本不受影响. 在298.0 K与303.0 K时, NaCl浓度的增大, Γ_∞增大; 在308.0、313.0与318.0 K时, NaCl浓度的增大, 出现了Γ_∞从2.27 μmol•m^-2降低至1.41 μmol•m^-2的“反常”现象. 胶团形成自由能(ΔG_m⁰)随温度和NaCl浓度增加负值增大(－63.98～－76.20 kJ•mol^-1), 胶团的形成主要是熵驱动过程.     

Thermodynamic and structural characterization of zwitterionic micelles of the membrane protein solubilizing amidosulfobetaine surfactants ASB-14 and ASB-16

Surface tension and isothermal titration calorimetry (ITC) were used to determine the critical micelle concentration (cmc) of the zwitterionic amidosulfobetaine surfactants ASB-14 and ASB-16 (linear-alkylamidopropyldimethylammoniopropanosulfonates) at 25 °C. The cmc and the heat of micellization were determined from 15 to 75 °C by ITC for both surfactants. The increase in temperature caused significant changes in the enthalpy and in the entropy of micellization, with small changes in the standard Gibbs energy (ΔG(mic)), which is consistent to an enthalpy?entropy compensation with a compensatory temperature of 311 K (ASB-14) and 314 K (ASB-16). In the studied temperature range, the heat capacity of micellization (ΔC(p)(mic)) was essentially constant. The experimental ΔC(p)(mic) was lower than that expected if only hydrophobic interactions were considered, suggesting that polar interactions at the head groups are of significant importance in the thermodynamics of micelle formation by these surfactants. Indeed, a NMR NOESY spectrum showed NOEs that are improbable to occur within the same monomer, resulting from interactions at the polar head groups involving more than one monomer. The ITC and NMR results indicate a tilt in the polar headgroup favoring the polar interactions. We have also observed COSY correlations typical of dipolar interactions that could be recovered with the partial alignment of the molecule in solution, which results in an anisotropic tumbling. The anisotropy suggested an ellipsoidal shape of the micelles, which results in a positive magnetic susceptibility, and ultimately in orientation induced by the magnetic field. Such an ellipsoidal shape was confirmed from results obtained by SAXS experiments that revealed aggregation numbers of 108 and 168 for ASB-14 and ASB-16 micelles, respectively. This study characterizes an interesting micelle system that can be used in the study of membrane proteins by solution NMR spectroscopy.     

Studies on the Effect of Organic Solvents and Temperature on the Micellar Solution of Pentamethylene-1,5-bis(tetradecyldimethylammonium bromide) Gemini Surfactant

Effects of three organic solvents, viz. methyl cellosolve, acetonitrile, and formamide, on the micellization process of Gemini surfactant pentamethylene-1,5-bis(tetradecyldimethylammonium bromide) aqueous solutions, with the volume percentages of the organic solvents up to 50%, have been investigated conductometrically. The studies were made at different temperatures and the data were used to find out different micellization parameters. From the study, it was observed that, although an increment in the amount of the organic solvents delays the micellization, the increase in the critical micelle concentration (cmc) is comparatively less below 20%(v/v) showing the predominance of water character in the bulk phase at lower compositions of the organic solvents. Applying equilibrium model for micelle formation, various thermodynamic parameters were also calculated from the temperature dependence of the cmc values and the results show that the micellization process becomes less spontaneous as the volume % of the organic solvent increases in the system due to the action of water-organic solvent mixed media as better solvent than pure water (solvophobic effect) for the studied Gemini molecules.     

Thermodynamic characterization of 3-[(3-cholamidopropyl)-dimethylammonium]-1-propanesulfonate (CHAPS) micellization using isothermal titration calorimetry: temperature, salt, and pH dependence

A systematic investigation of the micellization process of a biocompatible zwitterionic surfactant 3-[(3-cholamidopropyl)-dimethylammonium]-1-propanesulfonate (CHAPS) has been carried out by isothermal titration calorimetry (ITC) at temperatures between 278.15 K and 328.15 K in water, aqueous NaCl (0.1, 0.5, and 1 M), and buffer solutions (pH = 3.0, 6.8, and 7.8). The effect of different cations and anions on the micellization of CHAPS surfactant has been also examined in LiCl, CsCl, NaBr, and NaI solutions at 308.15 K. It turned out that the critical micelle concentration, cmc, is only slightly shifted toward lower values in salt solutions, whereas in buffer media it remains similar to its value in water. From the results obtained, it could be assumed that CHAPS behaves as a weakly charged cationic surfactant in salt solutions and as a nonionic surfactant in water and buffer medium. Conventional surfactants alike, CHAPS micellization is endothermic at low and exothermic at high temperatures, but the estimated enthalpy of micellization, ΔHM0, is considerably lower in comparison with that obtained for ionic surfactants in water and NaCl solutions. The standard Gibbs free energy, ΔGM0, and entropy, ΔSM0, of micellization were estimated by fitting the model equation based on the mass action model to the experimental data. The aggregation numbers of CHAPS surfactant around cmc, obtained by the fitting procedure also, are considerably low (nagg ≈ 5 ± 1). Furthermore, some predictions about the hydration of the micelle interior based on the correlation between heat capacity change, Δcp,M0, and changes in solvent-accessible surface upon micelle formation were made. CHAPS molecules are believed to stay in contact with water upon aggregation, which is somehow similar to the micellization process of short alkyl chain cationic surfactants.     

pH-responsive surface activity and solubilization with novel pyrrolidone-based Gemini surfactants

A new series of pH-responsive Gemini surfactants with 2-pyrrolidone head groups, N,N'-dialkyl-N,N'-di(ethyl-2-pyrrolidone)ethylenediamine (Di-C(n)P, where n = 6, 8 10, 12), were synthesized and characterized by (1)H NMR, (13)C NMR, ESI-MS, and elemental analysis. The surface activity and micellization behavior at acidic, neutral, and basic conditions were characterized by equilibrium surface tension and fluorescence techniques. It was found that the surface activity of Di-C(n)P depends on the pH of aqueous solutions due to the protonation state of surfactant molecules when pH was varied. The new compounds have lower cmc and γ(cmc) in comparison with that of m-2-m type conventional cationic Gemini surfactants and gluconamide-type nonionic Gemini surfactants. Fluorescence data confirm that micelles are formed when the concentration is above the cmc. Since micellization is of fundamental importance in surfactant applications such as solubilization, microemulsion, and related technologies, the significant difference in cmc at different pH of this new Gemini surfactant is employed to solubilize cyclohexane. The preliminary result indeed shows that the solubilization capacity of Di-C(n)P can be tuned by pH.     

Conductometry and Thermodynamics Study of Metal Dodecyl Sulfates in Aqueous Solution

The aggregation behavior of metal dodecyl sulfates (MDS), [Na¹⁺, Mg²⁺, Mn²⁺, Co²⁺, and Ni²⁺] in water has been studied by electrical conductivity (at 293.15–333.15 K) and surface tension methods (at 303.15 K). Critical micelle concentrations (CMCs), degree of counterion dissociation (β) evaluated from conductivity data. Using law of mass action model, the thermodynamic parameters viz. Gibbs energy (ΔG_m ⁰), enthalpy (ΔH_m ⁰), and entropy (ΔS_m ⁰) were evaluated. The enthalpy of micellization decreases strongly with increasing temperature. ΔG is always negative (thermodynamically favored process) and slightly temperature and counterion dependent. Gibbs energy and entropy exploit micellization as thermodynamic favorable process. The electrostatic repulsions between ionic head groups, which prevent the aggregation, are progressively screened as the ionic character decreases with the size of the counterion. The plots of differential conductivity, (dk/dc) _T,P , versus the total surfactant concentration enables us to determine the CMC values more precisely than the conventional method. Surfactants with strong condense counterion are adapted to rodlike micelle better than to a spherical micelle. The data are explained in terms of molecular characteristics of surfactants viz. degree of dissociation, polar head group size and counterion.     

Thermodynamic properties of micellization of Sulfobetaine-type Zwitterionic Gemini Surfactants in aqueous solutions--a free energy perturbation study

In this article, the validity and accuracy of the free energy perturbation (FEP) model used in a previous article for ionic liquid-type Gemini imidazolium surfactants (ILGISs) is further evaluated by using it to model the Enthalpy-entropy compensation of Sulfobetaine-type Zwitterionic Gemini Surfactants (SZGSs), with different carbon atoms of the hydrophobic group or the spacer chain length, in aqueous solutions. In the FEP model, the Gibbs free energy contributions to the driving force for micelle formation are computed using hydration data obtained from molecular dynamics simulations. According to the pseudo-phase separation model, the thermodynamic properties of micellization in aqueous solutions for SZGS were discussed. The results show that the micellization of SZGS in aqueous solutions is a spontaneous and entropy-driven process. It is linearly Enthalpy-entropy compensated and different from the micelle formation of ILGIS but similar to anionic surfactants. The compensation temperature was found to be (302±3)K which was lower than ILGIS. As the temperature rises, the micellization is easy initially but then becomes difficult with the unusual changes of enthalpy values from positive to negative. The contribution of entropy change to the micellization tends to decrease but the contribution of enthalpy change tends to increase. In particular, as the number carbon atoms in the alkyl chains and spacer chains are increased, the thermodynamic favorability and stability of the micelles both increase.     

Effect of head group size, temperature and counterion specificity on cationic micelles

The critical micelle concentration (cmc) and ionisation degree (α), of micelles of cetyltrimethylammonium bromide (CTABr), cetyltrimethylammonium chloride (CTACl), cetyltripropylammonium bromide (CTPABr) and cetyltripropylammonium chloride (CTPACl) have been measured over a narrow temperature range at 2 degree intervals using electrical conductivity. CTPACl and CTPABr are very soluble in water and were measured in the temperature range 275.15-323.15K. The Krafft temperatures for CTABr and for CTACl are 293.15K and 284.15K, respectively and established a lower temperature limit for our studies on these two surfactants. The cmc vs temperature curves have a smooth minimum near room temperature and α linearly increases with temperature. The changes of cmc and α with temperature are smaller than those associated with the modification of head group size or counterion nature. Using these results, basic thermodynamic quantities associated with the phenomena of micellization have been evaluated. Thermodynamic properties of the surfactant solutions were discussed in terms of temperature dependence of the free energy, enthalpy and entropy of micellization. A close similarity between the effects of change in temperature on protein folding and micellization process appears from the data.     

新型Gemini咪唑表面活性剂的合成及表面性能

以2,2-双(溴甲基)-1,3-丙二醇为连接基合成了新型的连接基为枝状的Gemini咪唑表面活性剂2,4-二(溴化-3-烷基咪唑)-1,3-丙二醇([Cn-P-Cnim]Br2,n=10,12,14).产物经核磁共振氢谱(1H NMR)、红外(IR)光谱和元素分析等进行了分析,证明所得产物即为目标产物.通过表面张力法和电导法测量其表面活性并计算胶束形成热力学参数(ΔG m—0,ΔH m—0,ΔS m—0).结果表明,25℃时3种表面活性剂均具有很高的表面活性,胶束的形成是自发的熵驱动过程.