Photoinduced morphism of gemini surfactant aggregates

The photochemical behaviour of an azobenzene chromophore inserted in a gemini surfactant imparts photocontrol to the resulting amphiphile assemblies, including the collapse, upon irradiation, of the multi lamellar vesicles formed in aqueous solution.     

Destruction of perfluoroalkyl surfactant aggregates by beta-cyclodextrin

A water 1H NMRD and 19F NMR spectroscopy study has proved, for the first time, that perfluoroalkyl surfactant micelles can be completely destroyed upon addition of beta-cyclodextrin to form successively 1:1 and 2:1 (beta-CD:R(F)) inclusion complexes.     

Monte carlo simulations of self-assembled surfactant aggregates

Monte Carlo simulations provide some insight into the self-assembly of amphiphiles in aqueous environment. A rather simple solvent-free model, with only two adjustable parameters in the effective pair potential, allows one to describe the formation of micelles, stable curved membranes, and metastable vesicles. Characteristic features of the self-assembled aggregates, such as the distribution of the micelle size and the value of the curvature elastic constant for membranes, can be obtained from simulated data. The capability of the simple approach was demonstrated for a surfactant model with three spherical segments. The extension of the simulation to molecules with more segments and branched amphiphiles is straightforward.     

Interactions between nonionic surfactant aggregates and gelatin-rheological measurements

The interactions between nonionic surfactants such as polyoxyethylene cetyl ethers (C₁₆EO₂₀) and the polymer gelatin were investigated by rheological methods. Capillary viscosity measurements of diluted aqueous solutions confirmed the results of previous investigations [1]. C₁₆EO₂₀ caused an accelerated renaturation of the polypeptide gelatin.A strong variation of viscoelastic data was measured by vibration rheometry when gelatin was added to the lyotropic cubic liquid crystalline phases formed by the surfactant used. Loss module (E) and loss factor (tan ) increased with increasing content of the polymer indicating an obstruction of the coupling between the globular surfactant associates.     

Diffusion-influenced deactivation processes in the study of surfactant aggregates

This review follows the evolution of the theories for excited state deactivation by diffusion-influenced quenching in microheterogeneous media, and the application of methods on this basis for the study of surfactant aggregates. From the starting point of the simple model for fluorescence quenching in monodisperse small micelles, the theoretical treatment has taken up polydisperse systems, quenching in long rods and lamellae, various possibilities for exchange of reactants between aggregates, and deactivation in clusters of small micelles. The information that can be obtained by time-resolved excited state deactivation studies is different in different types of systems, and is illustrated with examples from experimental studies. Limitations and possibilities are discussed.     

Experimental study on methane solubilization by organic surfactant aggregates

Seeking to enhance coal mine safety, an experimental study of a kind of water-based explosion suppression medium for the absorption of mine gas was carried out. Using methane as the model gas, solubilizing experiments with different concentrations of anionic and nonionic surfactants were carried out using headspace gas chromatography for surfactants consisting of sodium fatty alcohol polyoxyethylene ether carboxylate (AEC), fatty acid methyl ester sulfonate (MES), fatty methyl ester ethoxylate (FMEE), hexyl d-glucoside (APG06), octyl beta-d-glucopyranoside (APG08) and n-decyl glucoside (APG10). By selecting individual surfactants, the study investigated the methane solubilization performance of water mist with binary anionic–nonionic surfactants. Furthermore, the release of methane in solution was also examined. The results show that the apparent solubility of methane in solution is linearly and positively correlated with the surfactant concentration. The methane solubilization is significantly improved by the addition of anionic–nonionic surfactants. The optimal solubilizing ratio of the anionic–nonionic surfactant varies with the solution compositions. For a fixed ratio, surfactant compositions exhibit the most distinct synergistic effect and the best performance for methane solubilization. The release of methane from mixed micelles composed of the compound solution is superior to that of a single surfactant. Through the analysis of the solubilization effect and the stability of different absorbents, it is concluded that the anionic–nonionic surfactant system shows much better capability than the other selected surfactants.     

钙离子对表面活性剂单层膜聚集结构的影响

采用分子动力学模拟研究了气液界面上钙离子对阴离子表面活性剂十二烷基苯磺酸钠单层膜聚集结构的影响.结果表明,单层膜结构与表面覆盖度及Ca2＋离子存在与否均有关系.Ca2＋离子能够压缩表面活性剂极性头使聚集结构排列更加紧密,均力势体现了Ca2＋离子与极性头之间的结合能力强弱,二者之间的相互作用与稳定的溶剂分离极小值有关,而Ca2＋离子需要克服一个溶剂能障才能与之发生相互作用,并引起极性头周围水分子结构的重排.模拟表明,分子动力学方法可以在分子水平上研究无机盐离子对表面活性剂单层膜水化结构的影响,解释无机盐离子在界面膜中的动力学行为.     

Mass spectrometry of nanodiamonds

Detonation nanodiamonds (NDs) were studied by time‐of‐flight mass spectrometry (TOF MS). The formation of singly charged carbon clusters, C, with groups of clusters at n = 1–35, n ∼160–400 and clusters with n ∼8000 was observed. On applying either high laser energy or ultrasound, the position and intensity of the maxima change and a new group of clusters at n ∼70–80 is formed. High carbon clusters consist of an even number of carbons while the percentage of odd‐numbered clusters is quite low (≤5–10%). On increasing the laser energy, the maximum of ionization (at n ∼200 carbons) is shifted towards the lower m/z values. It is suggested that this is mainly due to the disaggregation of the original NDs. However, the partial destruction of NDs is also possible. The carbon clusters (n ∼2–35) are partially hydrogenated and the average value of the hydrogenation was 10–30%. Trace impurities in NDs like Li, B, Fe, and others were detected at high laser energy. Several matrices for ionizing NDs were examined and NDs themselves can also be used as a matrix for the ionization of various organic compounds. When NDs were used as a matrix for gold nanoparticles, the formation of various gold carbides Au_mC_n was detected and their stoichiometry was determined. It was demonstrated that TOF MS can be used advantageously to analyze NDs, characterize their size distribution, aggregation, presence of trace impurities and surface chemistry. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterization of fluorescent surfactant aggregates by fluorimetric and viscosimetric techniques

Summary A combination of fluorimetric and viscosimetric methods was used to characterize N,N-dimethyl-N-2-(4-(t-butylphenoxy)ethoxy)ethyl-N-hexadecylammonium chloride (BDHC), a doubletailed surfactant with dissimilar tail groups.BDHC was observed to fluoresce at 315 nm when excited at 274 nm, a feature which could be utilized to determine its critical micelle concentration (CMC). A value of 3.98×10^–5 M was obtained and was observed to be slightly temperature dependent with aT _min of 25.35°C. Fluorescence quenching experiments using 4-nitroaniline as a quencher were performed in order to determine the aggregation number which was found to be 42.0. The hydrodynamic radius of 21.91 Å was obtained using data from viscosimetric experiments. These data, together with theTanford andEinstein-Stokes relationships, were used to determine the micellar structure (spherical) and the diffusion coefficient (D=0.97×10^–6 cm²/s), respectively. The G of micellization forBDHC was determined to be –34.9 kJ/mol.

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Charakterisierung fluoreszierender oberflächenaktiver Aggregate mittels Fluorimetrie und Viskosimetrie

Zusammenfassung Die Verbindung N,N-Dimethyl-N-2-(4-(t-butylphenoxy)ethoxy)ethyl-N-hexadecylammoniumchlorid (BDHC), eine oberflächenaktive Substanz mit zwei unterschiedlichen Seitenketten, wurde mittels einer Kombination von fluorimetrischen und viskosimetrischen Methoden charakterisiert. Anregung bei 274 nm ruft eine Fluoreszenz bei 315 nm hervor; diese Eigenschaft wurde zur Bestimmung der kritischen Micellenkonzentration (CMC) herangezogen. Es wurde ein geringfügig temperaturabhängiger Wert von 3.98×10^–5 M gefunden (T _min=25.35°C). Quenchexperimente mit 4-Nitroanilin ergaben eine Aggregationszahl von 42.0, viskosimetrische Untersuchungen einen hydrodynamischen Radius von 21.91 Å. Die erhaltenen Daten erlauben zusammen mit den Beziehungen nachTanford undEinstein-Stokes die Bestimmung der Micellenstruktur (sphärisch) und des Diffusionskoeffizienten (0.97×10^–6 cm²/s). Das G der Micellenbildung fürBDHC beträgt –34.9 kJ/mol.

     

Mass spectrometry of hexuronosyldiglycerides

Conclusions The fragmentation under electron impact of the molecular ions of synthetic methyl esters of 1,2-di-O-acyl-3-O-(2',3',4'-tri-O-acetyl--D-glucopyranuronosyl)-L-glycerides was studied. Mass spectrometry of such compounds gives extensive information on their structure.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 94–102, January, 1975.     

Mass spectrometry of hydroxystilbazoles

The mass spectral fragmentation of the six 2′-, 3′- and 4′ -hydroxy substituted 4- and 2-azastilbenes is discussed and fragmentation pathways, elucidation of which were assisted by accurate mass measurements and metastable transitions, are proposed. It has been found that the position of the hydroxystyryl group in the pyridine ring may be deduced on the basis of mass spectral fragmentation patterns.     

Mass spectrometry of methyltetrazoles

The mass spectra of tetrazole, all isomers of monomethyl- and dimethyltetrazole, several trifluoromethyl substituted tetrazoles, as well as deuterated analogs, were recorded. Loss of N₂ was the important fragmentation of the molecular ions of tetrazole and 2-methyl substituted tetrazoles; however, HN₂ loss was more important for 1-methyl substituted tetrazoles. The 1-methyl-tetrazoles showed molecular ion peaks while the 2-methyltetrazoles exhibited an unprecedented [M + 1] peak with no molecular ion.     

Mass spectrometry of proteins

Several of the present mass spectrometric techniques have sufficient mass range and sensitivity to be viable alternatives or valuable supplements to traditional methods in protein chemistry. The precision of the molecular masses determined by mass spectrometry allows highly specific protein and peptide characterization as well as identification and localization of post translational modifications. In this article the principles and practical performance of the key techniques are discussed and examples of applications given.