离子型表面活性剂在水溶液中的分子构型

本文利用表面活性剂分子中内在的荧光探针及外加荧光探针,研究了离子型表面活性剂分子在水溶液中的构型,烷基三苯基鱗盐及N-烷基吡啶盐对芘的单体荧光猝灭服从Stern-Volmer方程,是扩散控制的碰撞猝灭,但不同链长的猝灭剂的荧光猝灭行为呈反常状态,即链越长,猝灭速率常数越大,在十六烷基三甲基铵(CTMAB)水溶液中观察到了芘的激基缔合物荧光,同时观察到了CTMAB对芘的荧光猝灭的阻碍(阳离子猝灭剂)和促进(阴离子猝灭剂)作用,提出离子型表面活性剂在水溶液中呈绕曲状的分子构型,且是一种动态构型。     

芘荧光探针法研究C60-胶束水溶液体系的微环境性质

首次运用芘荧光探针法考察了Ｃ６０－胶束水溶液体系的微环境性质,发现Ｃ６０的介入可以改变非离子表面活性剂所形成胶束的结构而破坏胶束的有序情,从而使胶束的体积变大。Ｃ６０能显著猝灭芘单分子的荧光,而几乎不会破坏芘单体与其激基二聚体的平衡,表明Ｃ６０主要是同芘单分子之间发生ＣＴ作用。同时Ｃ６０对芘单分子荧光的猝灭在有机体系中主要呈现静态猝灭而在胶束体系中则主要呈现动态猝灭。     

稳态荧光猝灭法确定胶束聚集数的研究

选用芘作为荧光探针, 二苯酮作为猝灭剂, 以稳态荧光猝灭法测定了十二烷基硫酸钠、十二烷基磺酸钠和十六烷基三甲基演化铵的胶束聚集致, 并对其测定胶束聚集数方法的有效范围进行了讨论. 实验结果表明, 选择的探针-猝灭剂体系适用于稳态荧光猝灭法确定阴离子和阳离子表面活性剂的胶束浓度和聚集数.     

一类新的表面活性剂——长链烷基三苯基鏻——Ⅵ.稳态荧光猝灭法测定十二烷基三苯基溴化鏻胶束的平均簇集数

研究了十二烷基三苯基溴化鏻(C_(12)PBr)胶束中N,N-二甲基苯胺(DMA)和二苯甲酮(DPK)对芘的荧光猝灭,发现DMA的猝灭行为不符合Stern-Volmer动态猝灭和Turro静态猝灭模型;DPK的猝灭行为不符合Stern-Volmer猝灭模型,但遵从Turro静态猝灭模型。根据DPK的静态猝灭性质测得C_(12)PBr胶束的平均簇集数为15士2,并相应地得到C_(12)PBr的临界胶束浓度为(1.77±0.09)×10~(-3)mol/L,后者与文献值一致。     

烷基苄基铵对芘的荧光猝灭行为研究

广义的荧光猝灭系指所有能使荧光强度降低的物理和化学过程,但通常涉及的主要有动态猝灭和静态猝灭,二者均遵从Stern-Volmer方程,但由于猝灭作用本质不同,它们在荧光寿命变化、温度效应及吸收光谱等方面表现出差异可资区别.本文通过稳态荧光强度变化和荧光衰减速率的比较研究了具有不同烷基链长的十四烷基苄基二甲基氯化铵(Zeph)和苄基三甲基溴化铵(TMBA)对芘的荧光猝灭,并基于电导实验结果以及猝灭剂全反式构象从理论上计算了Zeph和TMBA的猝灭速率常数,讨论了荧光猝灭的性质和长链分子的构型。     

敏化光解 盐的研究——蒽、芘、 电子转移荧光猝灭

本文采用稳态和瞬态光谱方法研究了四种二苯基碘 盐(Ph~2I^+X^-)对蒽、芘、 的激发态的猝灭作用, 通过Stern-Volmer方程确定了它们的光致电子转移速度常数。结果表明Ph~2I^+AsF^-~6对荧光猝灭是最有效的, 猝灭过程是扩散控制的。比较荧光强度和荧光寿命测定得到的猝灭常数, 表明猝灭是动态过程, 敏化剂与 盐间没有基态复合物生成。     

敏化光解 盐的研究——蒽、芘、 电子转移荧光猝灭

本文采用稳态和瞬态光谱方法研究了四种二苯基碘 盐(Ph~2I^+X^-)对蒽、芘、 的激发态的猝灭作用, 通过Stern-Volmer方程确定了它们的光致电子转移速度常数。结果表明Ph~2I^+AsF^-~6对荧光猝灭是最有效的, 猝灭过程是扩散控制的。比较荧光强度和荧光寿命测定得到的猝灭常数, 表明猝灭是动态过程, 敏化剂与 盐间没有基态复合物生成。     

敏化光解螉盐的研究——蒽、芘、苝电子转移荧光猝灭

本文采用稳态和瞬态光谱方法研究了四种二苯基碘鎓盐(Ph_2I~+X~-)对蒽、芘、苝的激发态的猝灭作用,通过Stern-Volmer方程确定了它们的光致电子转移速度常数,结果表明Ph_2I~+AsF_6~-对荧光猝灭是最有效的,猝灭过程是扩散控制的。比较荧光强度和荧光寿命测定得到的猝灭常数,表明猝灭是动态过程,敏化剂与鎓盐间没有基态复合物生成。     

芘在玻璃基片表面的单层组装及其对有机铜盐的选择性传感

将多环芳烃芘经含三乙基四胺结构的连接臂化学单层组装于玻璃基质表面, 制备了一种荧光薄膜材料. 荧光测量结果表明, 醋酸铜、酒石酸铜、柠檬酸铜等有机铜盐可以显著猝灭薄膜荧光, 而且猝灭过程可逆; 硫酸铜、氯化铜、硝酸铜等无机铜盐对薄膜荧光影响不大; 醋酸锌、醋酸铅、醋酸钴、醋酸镍等其它醋酸盐对有机铜盐的检测影响轻微. 荧光寿命测定表明, 醋酸铜对上述薄膜荧光的猝灭遵循静态猝灭机制.     

十二烷基磺酸钠增强的吡啶锉 对芘的荧光猝灭

水溶液中三种吡啶 盐(吡啶盐酸盐, HP+;N-苄基吡啶,BP^+; 苄基紫精, BV^2^+)对芘的荧光猝灭因十二烷基磺酸钠(SLS)的引入而增强, 且猝灭常数对SLS浓度的敏感性BV^2^+>BP^+>HP^+, 电导实验表明体系中无簇集体形成。认为SLS与吡啶 的静电作用及表面活性剂分子中烷基链的绕曲是导致猝灭增强的原因。     

Characterization of micelle formation of dodecyldimethyl-N-2-phenoxyethylammonium bromide in aqueous solution

Aggregation behavior of dodecyldimethyl-N-2-phenoxyethylammonium bromide commonly called domiphen bromide (DB) was studied in aqueous solution. The Krafft temperature of the surfactant was measured. The surfactant has been shown to form micellar structures in a wide concentration range. The critical micelle concentration was determined by surface tension, conductivity, and fluorescence methods. The conductivity data were also employed to determine the degree of surfactant counterion dissociation. The changes in Gibb's free energy, enthalpy, and entropy of the micellization process were determined at different temperature. The steady-state fluorescence quenching measurements with pyrene and N-phenyl-1-naphthylamine as fluorescence probes were performed to obtain micellar aggregation number. The results were compared with those of dodecyltrimethylammonium bromide (DTAB) surfactant. The micelle formation is energetically more favored in DB compared to that in DTAB. The 1H-NMR spectra were used to show that the 2-phenoxyethyl group, which folds back onto the micellar surface facilitates aggregate formation in DB.     

Fluorescence probes study on the mixed cationic-anionic surfactant solutions

Pyrene andp-N,N-dimethylaminostyrylphenylmalononitrile are used as the fluorescence probes to study the micro environment and observe the excimer formation of pyrene in sodium alkylcarboxylate and alkyltrimethyl ammonium bromide mixed solutions. The micro polarity, micro-dielectric constants and micro viscosity of the self-organized assemblies in the mixed cationi-anionic surfactant solution were compared before and after sonication, which may form different organized assemblies (micelle or vesicle). The micelle and vesicles have almost the same polarity for the probing molecules whereas the microviscosity differs. The variation of fluorescence quenching curves also shows the different effect of the change of assembly forms (micelles to vesicles). Thus some novel physicochemical properties about the micro environment of the cationic-anionic surfactant assemblies were found from this report.     

Quenching and dequenching of pyrene fluorescence by nucleotide monophosphates in cationic micelles

The fluorescence behavior of pyrene solubilized in the hexadecyltrimethylammonium bromide aqueous micellar solution in the presence of adenosine 5'-monophosphate (AMP) and uridine 5'-monophosphate (UMP) was investigated. AMP and UMP were found to influence oppositely the fluorescence of micellized pyrene. UMP acts as quencher, while AMP acts as dequencher. Both effects saturate at high nucleotide concentration (about 40 mM). Dequenching of micellized pyrene fluorescence is induced also by addition of disodium hydrogen orthophosphate (Na 2HPO 4), while loading with sodium bromide (NaBr) quenches the fluorescence. Furthermore, in absence of micelles, pyrene fluorescence depends on the UMP, according to the Stern-Volmer relation, but is unaffected by AMP. Dynamic light scattering experiments showed that the size and shape of aggregates is not affected by different types of nucleotide loaded into the solution; thus, we conclude that the opposite photophysical effect exploited by AMP and UMP are uncorrelated to any change in micellar microstructure. The whole fluorescence data set was successfully accounted for by assuming that the anionic nucleotides compete with the surfactant counterion (bromide) for the surface of the micelle. Accordingly, substitution of bromide with the more effective quencher UMP results in a strong decrease of the pyrene fluorescence, while the substitution of bromide with the nonquencher AMP results in an increase in the pyrene fluorescence.     

Unusually efficient quenching of the fluoroscence of an energy transfer-based optical sensor for oxygen

A two-fluorophore system consisting of pyrene as donor and perylene as energy acceptor undergoes efficient energy transfer when pyrene is electronically excited. The excitation wavelength was that of pyrene and fluorescence was monitored at the emission wavelength of perylene. The fluorescence of pyrene is strongly quenched by oxygen, but that of perylene is not. The two-fluorophore system, in contrast, is very strongly quenched, with a 4-fold increase in the Stern-Volmer quenching constant as compared to the quenching of pyrene, as a result of the effect of oxygen on the formation of the donor-acceptor exciplex, and quenching by oxygen. The results are used to design a fluorescence-based optical oxygen sensor which offers a sensitivity greatly exceeding that of existing oxygen probes.     

Anomalous association and fluorophore influence on the position of dimethylaniline in micelles: fluorescence quenching of 1,8-acridinedione

Fluorescence quenching of 9,10-dimethyl-3, 4,6,7,9,10-hexahydro-1,8(2H,5H) acridinedione (ADD) dye by N,N-dimethylaniline (DMA) in SDS and CTAB were studied by steady state fluorescence and time resolved techniques. The Stern-Volmer plots for the quenching of ADD by DMA is found to be linear and the Stern-Volmer constant K(SV) depends on the micellar concentration. The fluorescence quenching analysis reveals the binding of DMA with the micelles. The perturbation of the probe on the position of DMA molecule in micelle is inferred in the present investigation. The ADD fluorophore drives the DMA molecule into the non-polar region (core) of the micelle whereas other fluorophores like pyrene and rhodamine6G do not affect the position of DMA. In this report, the importance of the nature of fluorophores in determining the position and association of the quencher molecules in the aggregated systems is being discussed.     

Spectrochemical evaluation of pyridinium chloride as a possible selective fluorescence quenching agent of polycyclic aromatic hydrocarbons in water and neat acetonitrile

Pyridinium chloride (PC) is examined as a selective, fluorescence quenching agent for alternant as opposed to nonalternant polycyclic aromatic hydrocarbons (PAHs) in two polar solvents - water and acetonitrile. Nine alternant and 13 nonalternant PAHs were dissolved in water and acetonitrile and a total of 0.2 M of pyridinium chloride was added. The resulting change in fluorescence intensity was observed and reported as the Stern-Volmer quenching constant. Results show that PC is a selective quencher in both polar solvents. It selectively quenches the fluorescence emission intensity of alternant PAHs while leaving the nonalternant PAH fluorescence emission virtually unchanged. These results agree with the selective quenching behavior seen for PC surfactant analogs, cetylpyridinium chloride (CPC) and dodecylpyridinium chloride (DDPC). Furthermore, these results illustrate that the presence of a surfactant or micelle is not a requirement for selective quenching. The selective quencher PC is applicable to situations where a surfactant is not desirable or soluble.     

MOLECULAR CONFORMATION OF IONIC SURFACTANTS IN AQUEOUS SOLUTION

The molecular conformation of ionic surfactant in aqueous solution is investigated withfluorescent probes which are intrinsic insurfactant molecules or externally introduced. Quench-lng or pyrene monomer fluorescence by alkyltriphenylphosphonium or N-alkylpyridiniumobeys Stern-Voimer equation, being diffusi6n-controlled dynamic quenching, but the behaviorof quenching with different lengths of alkyl chain is "abnormal", i.e. the longer the chain,the greater the quenching rate constant. The pyrene excimer fluorescence is observed in theaqueous solution of cetyltrimethylammonium bromide (CTMAB), and the inhibition (for cationicquenchers) and promotion (for anionic quenchers) effects of CTMAB on the quenching ofpyrene fluorescence are also observed. The self-coiling conformation of ionic surfactantmolecules in aqueous solution is proposed to be responsible for these observations and theconformation to be dynamic.     

Pyrene solubilization capacity in octaethylene glycol monododecyl ether (C12E8) micelles

We used fluorescence quenching, vibronic band ratios and excimer fluorescence techniques to quantify the statistics of pyrene solubilization in nonionic octaethylene glycol monododecyl ether (C₁₂E₈) micelles. Using a two-phase model (aqueous and micellar pseudophases) to interpret fluorescence results, we found that all three of these experimental methods provide consistent information about pyrene partitioning between aqueous and micellar pseudophases. From dynamic quenching experiments we determined the pyrene partition coefficient and the average number of pyrene molecules solubilized per micelle over a range of surfactant concentrations. The pyrene partition coefficient increases with increasing surfactant concentration. We confirmed the partitioning results by excimer fluorescence measurements. Quenching results indicate that pyrene is accessible to Cu²⁺ quenchers even in the limit of high surfactant concentration where solubilized pyrene is in the infinite dilution limit in the micellar pseudophase. This suggests that solubilized pyrene resides in the micellar palisade layer. We determined the maximum number of pyrene solubilizates allowed per micelle (micellar solubilization capacity) by applying a three-phase model to fluorescence experiments conducted in the presence of solid phase pyrene. The estimated maximum capacity is 6 pyrene molecules per micelle. The three phase partitioning model successfully predicted the excimer fluorescence in the presence of solid pyrene.     

The unusual micelle micropolarity of partially fluorinated gemini surfactants sensed by pyrene fluorescence

New gemini surfactants having two fluorocarbon chains were prepared by refluxing partially fluorinated alkyl bromide with N,N,N',N'-tetramethyl-1,6-diaminohexane in acetonitrile. The partially fluorinated gemini surfactants containing a six-methylene spacer chain are easily soluble in water. The critical micelle concentrations (cmc's) were determined by various fluorescent probe methods. The hydrophobicity of a CF2 group was estimated to be 1.5 times that of a CH2 group according to the cmc values. The micelle micropolarity of a fluorocarbon gemini sensed by pyrene fluorescence was unusually high, suggesting an apparent iceberg-like environment in the location of pyrene. The significantly small micelle aggregation numbers of fluorinated gemini surfactants were ascertained by the pyrene fluorescence quenching method. The micelle ionization degree estimated by fluorescence quenching of 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ) gave tendencies similar to those of the corresponding hydrocarbon geminis.     

Self-assembly of tetradecyltrimethylammonium bromide in glycerol aqueous mixtures: A thermodynamic and structural study

In this paper, we have studied the effect of glycerol on the micelle formation of tetradecyltrimethylammonium bromide. Changes in both the critical micelle concentration and the degree of counterion binding of the surfactant upon the addition of glycerol across a temperature range (20-40 degrees C) were examined by using the conductance method. The equilibrium model of micelle formation was applied to obtain the thermodynamic parameters of micellization. An enthalpy-entropy compensation effect was observed in all the solvent systems, but whereas the micellization of the surfactant in the medium with 20% glycerol occurs under the same structural conditions as in pure water, in glycerol rich mixtures the results suggest that the lower aggregation in these media is due to the minor cohesive energy of the solvent system in relation to water. It was also observed that the micellar aggregation number, as obtained by the static quenching method, decreases with the glycerol content. This fact was attributed to an increase in the surface area per headgroup of the surfactant as a consequence of an enhanced solvation, probably induced by the incorporation of some glycerol molecules in the micellar solvation layer. Although the pyrene 1:3 ratio index does not indicate significant changes in the micropolarity at the micelle-bulk interface, the data of fluorescence anisotropy of coumarin 6 and fluorescein are compatible with the formation of a more compact solvation layer.