Micelle characterisation

Several experimental techniques are available for the investigation of miceUar systems, capable of elucidating different aspects of the miceUisation process, as well as the micellar structure and morphology. In a first approach, these techniques can be categorised in three subclasses microscopy, scattering and spectroscopic techniques. Extensive reviews on the various experimental methods suitable for block copolymer micelle characterisation have been provided [6-8]. Therefore, in this section, our aim is to briefly outline the different methods used and the information they provide, along with some of their main advantages and limitations [1,2,71]. 

For an a-helical fraction fH = 0,5 30% methanol, 20% ethanol, 15% i-propanol or 10% trifluoroethanol are necessary. Trifluoroethanol like perfluorinated alcohols, e.g. hexafluoroisopropanol is characterised on the hand by a strong acidic proton at the OG-group due to the —1-effect of the fluor atoms. On the other hand fluorocarbons are more hydrophobic than the hydrocarbons which is mainly due to the larger surface of the F compared with H. For this reason the critical micelle concentration of perfluorinated detergents is much lower than that of the corresponding hydrocarbon compounds. It was found that C4F7-derivatives act as detergents... 

Between 5 and 23 minutes, a continuous evolution is observed, characterised by the increase of the intensity at low q and by the q"1 slope in a log-log plot that is the signature of ID objects (figure 3). This corresponds to the transformation of the shape of the micelles from spherical to cylindrical and their continuous growth in length up to few tens of nanometers. The increase of turbidity in solution is related to the growth of the micelles, and coincides with the beginning of the condensation of silica. 

Pancreatic enzymes, preferably trypsin, have been used for the chemical characterisation and identification of many known bioactive peptides. For example, ACE-inhibitory peptides as well as CPPs are most commonly produced by trypsin (Maruyama and Suzuki, 1982 Berrocal et al., 1989). On the other hand, other enzymes and different enzyme combinations of proteinases, including alcalase, chymotrypsin, pancreatin and pepsin, as well as enzymes from bacterial and fungal sources have also been utilised to generate bioactive peptides. Higher yields of CPPs and, particularly, higher amounts of asl-casein f(59-79) in the hydrolysate have been obtained with casein micelles successively digested with pepsin and trypsin... 

In our model study reported in this contribution, we have chosen two double-chained C-13 alkylbenzenesulphonate surfactants (SLABS) of closely-related structure, which form micelles in aqueous solution in the absence of salt. However, when small amounts of electrolyte are added (e.g., —20mM NaCl), vesicles are spontaneously formed over a time period of seconds/minutes. These vesicle structures are then reasonably stable over a period of hours/days. The onset of vesicle formation can be readily characterised by the determination of the critical salt concentration (esc), needed to induce the formation of vesicles, from smaller aggregates or monomers. This parameter is easily determined experimentally from the increase in light scattering associated with self-assembly. It has now been determined for a number of electrolyte systems. 

Pilon, L. N., et al. (2006), Synthesis and characterisation of new shell cross-linked micelles with amine-functional coronas, Eur. Polym. J., 42(7), 1487-1498. 

Ashok, B. Arleth, L. Hjelm, R.P. Rubenstein, I. Onytlksel, H. In vitro characterisation of PEGylated phospholipid micelles for improved drug solubilisation effect of PEG chain length and PC incorporation. Journal of Pharmaceutical Sciences 2004, 93, 2476-2487. 

Xi increases slowly with concentration. It can be shown that if the chemical potential of a monomer in an aggregate is sharply distributed about some N, then the distribution of aggregates peaks at a value of N just less than the N with minimum fifp and is also sharply distributed. Otherwise, pronoimced polydispersity may occur e.g. for long cylindrical micelles). Thus reduced to bare bones it can be seen that the use of the word "theory" is dubious. We have simply characterised the observation of micelles, and claim that it can be shown that the law of mass action is an appropriate vehicle for this characterisation. 

Vitrac H., Hauville C., Collin F., Couturier M., Therond P., Delaforge M., Remita S., Jore D., Gardes-Albert M., Hydroperoxide characterisation as a signature of the micelle/monomer balance in radiation-induced peroxidation of arachidonate. Free Radical Research, 2005,39,519-528. 

Upper triplet states of biphenyls in micelles ionize to produce hydrated electrons . Diffuse reflective laser flash photolysis has been used to characterise the triplet states of p-terphenyl generated in powder systems. Other triplet states which have been characterised include those of naphthalene and acenaphthene in the solid state", those involved in photoreactions of tetracene with anthracene and 9-bromoanthrene", phenanthrene and biphenylene, highly excited triplet states... 

Benzo-fused pyridinium systems also undergo the reaction and a new example, the photocyclisation of (153) to (154) in the presence of iodine, has been published. The quantum efficiency of photocyclisation of l,2-jbis-(a-naphthyl)ethylene to dihydropicene has been examined in micelles and the cyclisation of [5]-helicene (155) to dihydrobenzperylene (156) has been carried out at 4K (156) was characterised by its fluorescence and phosphorescence emission. The effect of different substituents on the photocyclisation of the symmetrically tetra-substituted stilbene (157) has been probed. 

The as-synthesized materials, /. e. micelle-bearing systems, were characterised by XRD and UV-Vis spectroscopy. XRD patterns were recorded using an XTert Philips diffractometer, with CuKa radiation. Reflectance UV-visible spectra were recorded using a Varian Cary 5 spectrophotometer. 

J. Taillefer, M.-C. Jones, N. Brasseur, J.E. van Lier, J.-C. Leroux (2000). Preparation and characterisation of pH-responsive polymeric micelles for the delivery of anticancer photosensitizing drugs. J. Pharm. Sci., 89, 52-62. 

Besides choline, the cationic character of phosphatides is created also by 2-aminoethanol, sphingosine and other aminoalcohols. Phosphatides with two hydrocarbon chains attached to the same head group are more lipophilic amphiphiles characterised by vesicular (liposomal) aggregation in water contrary to single-chain surfactants that typically form micelles. Synthetic monoalkylphosphorylcholines are essentially water-soluble zwitter-ionic surfactants [120] the distinction of which consist in the hindered compatibility with anionics in view of the end position of the cationic betaine group. 

A and B are constant factors, and cu and cm are the concentrations of monomers and micelles, respectively. However, it was noted later that the condition (5.1) corresponds only to the inflection point of the dependence d([)/dctoti = fictoii) but not to the point of maximum curvature of the function < ) = ())(ctoti) [9]. The latter point is characterised mathematically by the following condition... 

The kinetics of formation and disintegration of micelles has been studied for about thirty years [106-130] mainly by means of special experimental methods, which have been proposed for investigation of fast chemical reaction in liquids [131]. Most of the experimental methods for micellar solutions study the relaxation of small perturbations of the aggregation equilibrium in the system. Small perturbations of the micellar concentration can be generated by either fast mixing of two solutions when one of them does not contain micelles (method of stopped flow [112]), or by a sudden shift of the equilibrium by instantaneous changes of the temperature (temperature jump method [108, 124, 129, 130]) or pressure (pressure jump method [1, 107, 116, 122, 126]). The shift of the equilibrium can be induced also by periodic compressions or expansions of a liquid element caused by ultrasound (methods of ultrasound spectrometry [109-111, 121, 125, 127]). All experimental techniques can be described by the term relaxation spectrometry [132] and are characterised by small deviations from equilibrium. Therefore, linearised equations can be used to describe various processes in the system. 

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