Light Scattering Study of the Effect of n-Butanol on the Micellar Properties of Undecylammonium Chloride in Aqueous Electrolyte Solutions

Light scattering measurements have been performed on aqueous solutions of undecylammonium chloride in the presence of 0 to 0.2 mol dm(-3) NaCl and 0 to 0.5 mol dm(-3) n-butanol at 25 degrees C. The critical micelle concentration (CMC), aggregation number, and degree of dissociation of the micelles have been determined. The observed decrease of the CMC with the increase of the n-butanol concentration was explained by the effect of the n-butanol on water structure and by the selective solvation of the micelles with n-butanol, which counteract the decrease of the polar character of the solvent caused by n-butanol addition. An observed increase in the degree of dissociation of the micelles and a decrease in the aggregation number following alcohol addition have been explained by considering the effect of this additive on the electrostatic and other interactions involved in free energy of micellization. Our results support the concept of opposing effects between n-butanol and NaCl on the cooperativity in the micellization process of this surfactant, with the n-butanol disfavoring micellar growth. Copyright 2000 Academic Press.     

Mixed micelles of tetradecyltrimethylammonium bromide and chlorhexidine digluconate in aqueous solutions of isopropyl alcohol

The influence of isopropyl alcohol (IPA) on the size and composition of the mixed micelles in mixtures of tetradecyltrimethylammonium bromide (TTAB) and chlorhexidine digluconate (CG) has been determined as a function of the composition of the systems. The addition of 0.5 M and 1.0 M IPA had little significant effect on the composition of the mixed micelles as determined both by analysis of critical micelle concentration (CMC) data using a theoretical treatment based on excess thermodynamic quantities and by an empirical treatment of conductivity data. Static and quasielastic light scattering measurements showed a progressive decrease of the aggregation number and hydrodynamic radius of TTAB micelles on addition of IPA, but minimal changes in the properties of the small CG aggregates. The results show that the micellar weight in the TTAB/CG/IPA solutions is determined by the ratio of the surfactants in the system and for each TTAB/CG ratio decreases on addition of IPA.     

The effect of electrolyte on the micellar charge and hydration of a polyoxyethylene sulphate type of detergent in aqueous solution

Summary Measurements of the electrophoretic mobilities of the micelles of the anionic detergent C₁₆H₃₃(OCH₂ · CH₂)₇OSO₃Na have been made in aqueous sodium chloride solutions over the concentration range 0-0.01 M and used to calculate the magnitude of the electroviscous effect and the micellar charge in these solutions. The micellar hydration, as assessed from viscosity data, is shown to decrease as the salt concentration is increased and this is thought to be a consequence of the lower micellar charge in the more concentrated salt solutions which allows a greater contraction of the ethylene oxide chains resulting in a loss of water mechanically trapped by the micelles.     

FT-Raman spectroscopy of lichens on dolomitic rocks: an assessment of metal oxalate formation

The FT-Raman spectra of five epilithic lichen taxa growing on dolomite and magnesium-rich carbonate rocks have been analysed and interpreted for the key molecular marker bands associated with calcium oxalate monohydrate (whewellite), calcium oxalate dihydrate (weddelite) and magnesium oxalate dihydrate. From the results, it can be concluded that the biomineral product of lichen biodeterioration involves the calcareous part of the substratum only; no trace of magnesium oxalate has been found in the Raman spectra. Two of the species, Lecanora sulfurea and Aspicilia calcarea, produce calcium oxalate monohydrate exclusively, but Dirina massiliensis f. sorediata, D. massiliensis f. massiliensis and Tephromela atra produce significant quantities of the dihydrate. An explanation is advanced for the exclusive accumulation of calcium oxalate into the lichen thallus despite the significant presence of magnesium ions.     

A Calorimetric Study of the Influence of Temperature on the Self-Association of Amphiphilic Antidepressant Drugs in Aqueous Solution

Relative apparent molar enthalpies have been determined as a function of concentration (0.0001 to 0.2 mol kg(-1)) by heat conduction calorimetry for aqueous solutions of the structurally related antidepressant drugs imipramine and clomipramine in water over the temperature range 288 to 308 K. Critical concentrations determined from inflections in these plots for both drugs had minimum values at 298 K. The concentration dependence of the relative apparent molar enthalpy could be quantitatively described using a mass action model of association based on the Guggenheim equations for the activity coefficients of mixed electrolytes. Derived values of the monomer-counterion interaction coefficient for imipramine became increasingly negative with an increase in temperature over the temperature range 293 to 303 K, indicative of an increasing degree of premicellar association. In contrast, negative monomer-counterion interaction coefficients were obtained for clomipramine at only 303 and 308 K, suggesting an absence of premicellar association at lower temperatures. Values derived for the molar enthalpy of micellization of both drugs from the mass action model indicate an increasingly exothermic process with increase in temperature; positive values at 288 and 293 K arise from hydrophobic interactions while the negative values at higher temperatures suggest the importance of London dispersion interactions as the major driving force for aggregation. Copyright 2000 Academic Press.     

Nanoimaging with a compact extreme-ultraviolet laser

Images with a spatial resolution of 120-150 nm were obtained with 46.9 nm light from a compact capillary-discharge laser by use of the combination of a Sc-Si multilayer-coated Schwarzschild condenser and a free-standing imaging zone plate. The results are relevant to the development of compact extreme-ultraviolet laser-based imaging tools for nanoscience and nanotechnology.     

Transmission X-ray microscopy using X-ray magnetic circular dichroism

X-ray magnetic circular dichroism (X-MCD) was used as a large, element-specific and quantitative magnetic contrast mechanism in the soft X-ray microscopes at BESSY I (Berlin) and the ALS (Berkeley). The present state and potential of magnetic transmission X-ray microscopy (MTXM) is outlined. The possibility to record images in varying magnetic fields and the high spatial resolution down to 25 nm were used to image out-of-plane magnetized (4 ?Fe / 4 ?Gd)×75 systems. Magnetic domains could be studied in arrays of circular and square dots with lateral dimensions down to 180 nm. Hysteresis loops of individual dots were deduced using the direct proportionality of the X-MCD contrast to the sample magnetization. Images of a 3 nmCr / 50 nmFe / 6 nmCr film demonstrate for the first time that MTXM is also able to observe in-plane magnetized domains. In the future the possible applications of MTXM will be extended with regard to the strength of the external field, the available energy range and the sample conditions by building a dedicated transmission X-ray microscope for magnetic imaging at BESSY II. Received: 22 May 2001 / Accepted: 4 July 2001 / Published online: 5 October 2001     

Antitumor effect of pluronic F-127 gel containing mitomycin C on sarcoma-180 ascites tumor in mice.

Pluronic F-127 (PLF-127) gels were evaluated as a sustained-release vehicle for intraperitoneal administration of mitomycin C (MMC) in order to enhance the therapeutic effects of MMC against a Sarcoma-180 ascites tumor in mice. Tumor cell injections were made on day 0 and injections of MMC in 25% (w/w) PLF-127 on day 1, both intraperitoneally. A prolongation of the life span of tumor-bearing mice following injection of therapeutic PLF-127 was noted, and PLF-127 containing MMC was therapeutically more active than free drug. The high chemotherapeutic efficiency of MMC in PLF-127 was striking at high doses, which would be toxic in the case of the drug alone. PLF-127 gels exhibit reverse thermal behavior and are fluid at refrigerator temperature, but are soft gels at body temperature. The in vitro release experiments indicated that Pluronic gel might serve as a rate-controlling barrier and be useful as a vehicle for sustained-release preparations of MMC to be administered intraperitoneally. These results suggest that sustained-release occurs in the peritoneum and that effective drug concentrations can be maintained by the preparation.