表面活性剂在水溶液中性质的质子核磁共振研究

综述了质子核磁共振的几种方法在表面活性剂水溶液研究中的应用.自从上世纪六十年代以来的许多研究表明核磁共振的各种技术是研究表面活性剂溶液的有效手段.它可以提供表面活性剂在水溶液中的cmc、胶束的结构、尺寸、水化、加溶性质和位置，不同表面活性剂胶束之间的相互作用，以及胶束与生物分子和高聚物的相互作用.化学位移已经成为惯常方法，弛豫测量提供动态信息，自扩散系数测量是研究胶束尺寸的很好手段.近来由于核磁共振技术的不断发展，用于研究生物大分子的2D NOESY和HOESY也逐渐应用到研究表面活性剂聚集结构中.由此可以得到有关表面活性剂在水溶液中行为的分子水平信息，是其它谱学方法所不能及的.     

模板技术制备单块介孔分子筛

模板技术与溶胶 -凝胶过程结合是合成介孔分子筛的有效方法 .模板通常采用表面活性剂在一定条件下自组装形成超分子结构 ,在不同条件下 ,此超分子结构具有不同聚集形态 ,合成出的介孔分子筛也具有不同的孔道排列方式 [1～ 4 ] .溶胶 -凝胶过程是通过硅源体的水解缩合并缓慢蒸发除去溶剂实现的 .此过程及产物受体系的 p H值影响很大 .在碱性体系中制备的介孔材料通常为粉末状 ,不利于实际应用 ,因此人们更加重视合成具有规则外形的介孔材料[5] .目前报道大多是在酸性体系中制备不同形状的介孔材料 [6～ 12 ] .有关合成单块介孔分子筛的报道…     

Mesoscopic simulation of self-assembly in surfactant oligomers by dissipative particle dynamics

Self-assembling properties of surfactant oligomers in an aqueous medium is simulated by dissipative particle dynamics (DPD). The critical micellar concentration (CMC) of dimeric (oligomerization = 2) and trimeric (oligomerization = 3) surfactant is much lower than their single-chain counterpart. All surfactants form spherical micelles at the concentration not far above their CMC. The transition from spherical to cylindrical micelles exhibits with increasing surfactant concentration. Lamellar micelles will appear with further increasing the surfactant concentration. For dimeric and trimeric surfactants, cylindrical micelles transform into extremely long “wormlike” or “threadlike” micelles before the transition to lamellar micelles. These results are in qualitative agreement with laboratory experiment. Average aggregation numbers (AN) of micelles increase with a power law of AN  c when the surfactant concentration c CMC. The self-diffusion coefficients will drop with a power law of D  c⁻ when wormlike micelles are formed.     

BINDING OF IONIC SURFACTANTS ON OPPOSITELY CHARGED POLYELECTROLYTES OBSERVED BY FLUORESCENCE METHODS

Our recent studies concerning the binding of ionic surfactants on oppositely charged polyelectrolytes observedwith fluorescence techniques are reviewed. The cationic surfactants cetyltrimethylammonium bromide (CTAB),dodecyltrimethylammonium chloride (DTAC), and nonionic surfactant octaethylene glycol monododecyl ether (C_(12)E_8) wereallowed to bind on anionic poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) and its pyrene and/or naphthalenelabeled copolymers. The relative excimer emission intensity I_E/I_M of a cationic probe l-pyrenemethylamine hydrochloride(PyMeA·HCl) and the non-radiative energy transfer (NRET) I_(Py)/I_(Np) of naphthalene to pyrene for labeled polyelectrolyteswere chosen to monitor the binding process and the conformation change of surfactant-bound polyelectrolytes. The 1:1aggregation of polyelectrolyte-CTAB with respect to the charge was found as long as the CTAB concentration was slightlyhigher than its critical aggregation concentration (CAC). The intermolecular NRET indicated that the CTAB-boundpolyelectrolytes aggregated together through the hydrophobic interaction between the CTAB tails. However, neither 1:1polyelectrolyte-DTAC aggregation nor intermolecular aggregation of DTAC-bound polyelectrolyte was observed owing to itsweaker hydrophobicity of 12 carbon atoms in the tail, which is shorter than that of CTAB. As known from the fluorescenceresults, nonionic surfactant C_(12)E_8 did not bind on the anionic polyelectrolytes, but the presence of PAMPS promoted themicelle formation for C_(12)E_8 at the CAC slightly below its critical micelle concentration (CMC). The solid complex of dansyllabeled AMPS copolymer-surfactant exhibited a decrease in local polarity with increasing charge density of thepolyelectrolyte or with alkane tail length of the surfactant. SAXS suggested a lamella structure for the AMPS copolymer-surfactant solid complexes with a long period of 3.87 nm for CTAB and 3.04 nm for DTAC, respectively.     

HDEHP和HEHEHP界面性质及添加剂对界面性质的影响

测定了HDEHP、HEHEHP、TOPO、TBP、SDS和CTMAB的煤油溶液与硫酸盐水溶液所构成的液-液体系的界面张力,考察了水相pH对界面张力的影响,求得这些化合物的界面吸附常数,计算出饱和吸附时界面吸附分子的截面积,提出了用Cmin计算活性剂分配比的方法,研究了向HDEHP或HEHEHP体系中添加TOPO(或TBP)、SDS、CTMAB时界面张力的变化及其对萃取速率的影响。界面化学反应控制的萃取金属阳离子过程的速率将因添加剂占据界面和(或)形成界面负电层而降低,因添加剂与萃取剂形成界面活性较强的分子缔合物对金属的萃取而提高。     

有机电解质在胶束催化聚苯乙烯氯甲基化反应中的作用

在实施聚苯乙烯氯甲基化反应的胶束催化体系中加入四丁基溴化铵 ((Bu)₄NBr, TBAB), 研究了有机电解质TBAB对胶束催化反应的影响规律. 实验结果表明, 在非离子表面活性剂NP-10及阴离子表面活性剂SDS的胶束催化体系中, TBAB的加入使聚苯乙烯氯甲基化反应的速率明显增大, 前者尤为突出；而在阳离子表面活性剂CTAB的胶束催化体系中, TBAB的加入几乎对反应速率无促进作用. 这种结果一方面归因于加入电解质TBAB会降低SDS的临界胶束浓度, 从而增强对聚苯乙烯四氯化碳溶液的增溶能力；更主要的原因是TBAB的丁基与表面活性剂碳氢链间的疏水相互作用会使季铵离子(Bu)₄N⁺嵌入SDS的胶束之中, 结合到NP-10的胶束表面, 使SDS胶束的阴离子头基对亲核取代反应(控制步骤)的禁阻作用得以减缓, 使NP-10的胶束表面携带了正电荷, 显著促进亲核取代反应的进行, 而对于CTAB的胶束, 由于静电排斥作用, 季铵离子(Bu)₄N⁺不能接近CTAB的胶束, 故TBAB的加入对聚苯乙烯氯甲基化反应不产生作用.     

New Methylene Blue (NMB) Encapsulated in Mesoporous AlMCM‐41 Material and Its Application for Amperometric Determination of Ascorbic Acid in Real Samples

New methylene blue (NMB) dye incorporated into AlMCM‐41 surfactant‐free and hybrid surfactant‐AlMCM‐41 mesophase. UV‐vis evidence shows that new methylene blue dye protonated in both cases of zeolites. New methylene blue is electroactive in zeolites and their electrochemical activity has been studied by cyclic voltammetry and compared to that of NMB in aqueous solutions. New methylene blue molecules are not released to the solution during CV measurements and are accessible to H₃O⁺ ions. The presence of surfactant affects the kinetics of the redox process through proton ions diffusion. The midpoint potentials (E_m) values show that new methylene blue dye incorporated into AlMCM‐41 can be reduced easily with respect to solution new methylene blue. New methylene blue interacting with surfactant polar heads and residual Br^? ions as a results, it shows a couple of peaks in high potential with respect to new methylene blue solution. The electrode made with methylene blue‐AlMCM‐41 without surfactant was used for the mediated oxidation of ascorbic acid. The anodic peak current observed in cyclic voltammetry was linearly dependent on the ascorbic acid concentration. The calibration plot was linear over the ascorbic acid concentration range 1.0×10^?5 to 5.0×10^?4 M. The detection limit of the method is 1.0×10^?5 M, low enough for trace ascorbic acid determination in various real samples.     

Radical deoxygenation of alcohols and intermolecular carbon-carbon bond formation with surfactant-type radical chain carriers in water

An efficient and mild method is developed for radical deoxygenation of alcohols and formation of carbon-carbon bonds in water without adding additives such as surfactants. The reaction was applied to synthesis of 2′,3′-didehydro-2′,3′-dideoxynucleosides that are potent anti-HIV agents. The reaction afforded environmentally benign reaction conditions.     

Decreased surfactant activity coefficients in polymer-surfactant mixtures

The SDS unimer concentration in a series of mixed anionic/non-ionic surfactant solutions comprising sodium dodecylsulphate (SDS) and sugar-based dodecyl bis-N-methyl gluconamides (C₁₂BNMG) have been studied using an anionic surfactant selective electrode, both in the presence and absence of the polyampholyte gelatin. The activity of the SDS has been calculated at the critical micelle concentration (CMC) in the gelatin-free studies and at CMC(1) in the gelatin studies. From the known solution composition, the activity coefficients can be calculated; these show deviations from unity around a solution mole fraction (_SDS) of 0.95 SDS in both cases. The deviation is significantly greater in the presence of gelatin, to an extent that the SDS activity versus _SDS curve exhibits a maximum and a minimum in the region _SDS=0.8–1.0, consistent with the possibility of coexisting micelle types, in agreement with our earlier NMR study (Griffiths et al. (1998) J Chem Soc Chem Comm 1:53).