Study of copper sulfide crystallization in PEO-SDS solutions

The crystallization of copper sulfide in aqueous supersaturated solutions in the presence of the polymer poly(ethylene oxide), PEO, and the surfactant sodium dodecyl sulfate, SDS, was investigated. In these systems, copper sulfide precipitation competes with the reaction between copper cations and dodecyl sulfate anions. The competition of the two reactions may affect the reaction products significantly; therefore it is important to study the properties of the surfactant salt, copper dodecyl sulfate (Cu(DS)2), in detail. The thermodynamic solubility constant of Cu(DS)2 was measured at 8 degrees C and was equal to (2.4 +/- 0.4) x 10(-10) M3. The Krafft point of Cu(DS)2 and its solubility curve (precipitation temperature for a range of concentrations) were also measured. The latter was found to be very close to room temperature. Temperature is thus a very significant parameter in these systems and must be carefully controlled in all experiments. The crystallization of copper sulfide in PEO-SDS solutions was investigated in solutions with compositions above and below the solubility curve. Copper sulfide nanoparticles predominate and are stabilized at temperatures above the solubility curve. Surprisingly, at temperatures below the solubility curve CuxS coexists with Cu(DS)2, which appears in the form of lamellar crystals. The system is further complicated by the presence of at least two different types of copper sulfides corresponding to different oxidation states of copper. Our results suggest that the predominance of Cu(DS)2 at lower temperatures is due to its limited solubility and is modified by the CuI/CuII redox equilibrium in combination with the solution pH.     

Improvement of lysine production by analog-sensitive and auxotroph mutants of the acetylene-utilizing bacterium gordona bronchialis (Rhodococcus bronchialis)

An acetylene utilizingGordona (Rhodococcus) bronchialis strain, screened for the production of fine chemicals, was found to be capable of producing small amounts of lysine. Attempts to produce amino-acid analogresistant and/or sensitive mutants and auxotrophs of this strain with increased lysine production were made following UV-irradiation orN-methyl-N’-nitro-N-nitrosoguanidine (MNNG) treatment. The bacterium exhibited surprisingly high resistance levels to the aforementioned mutagens which is attributed to highly effective inborn-repair systems. Natural resistance to high levels ofS-(2-aminoethyl)-l-cysteine (AEC) (2%) was observed, in contrast withd, l-aspartic acid hydroxamate (AAH),l-lysine hydroxamate (LHX) and β-fluoropyruvate (FP). A variety of amino-acid analog-resistant (AAH^r, LHX^r) or analog-sensitive (FP^s) mutants were produced following UV-irradiation or MNNG treatment. Similarly, a large number of auxotrophs (68) of different types were also obtained. From these, one FP^s mono-auxotroph and two poly-auxotrophs (with at least one requirement for the aspartic acid family) showed an increased lysine production (~1.8 g/L) comparable (4 g/L) to that found in other bacteria capable of utilizing long-chain hydrocarbons(1).     

Determination of naturally occurring hydroxynaphthoquinone polymers by size-exclusion chromatography

Summary Polymerization of alkannin, shikonin, and their derivatives, potent pharmaceutical substances, crucially affects their use in pharmaceuticals, cosmetics, and as food colorants, because it leads to loss of their antimicrobial activity, reduction of the lustre of their red coloration, and a decrease in their solubility. In this study size-exclusion chromatography (SEC) has been used for the first time for qualitative and quantitative analysis of monomeric and polymeric hydroxynaphthoquinone alkannin and shikonin derivatives. The purity and degree of polymerization has been determined to evaluate severalAlkanna tinctoria root samples from different geographical sources, and commercial samples of alkannin and shikonin, as pharmaceutical raw materials. Conditions for extraction of hydroxynaphthoquinones fromAlkanna tinctoria roots with olive oil were optimized in terms of polimerization, aiming to improve the biological activity of the final pharmaceutical product, Helixderm.     

Formation mechanism of nanotubes comprising layers of PbS nanoparticles in polymer-surfactant solutions

The crystallization of PbS in aqueous solutions containing the surfactant sodium dodecyl sulfate (SDS) and hydrophilic polymers resulted in a novel type of metastable nanotubes, the walls of which consist of layers of ordered PbS nanoparticles, apparently separated by layers of surfactant molecules. Information on the mechanism of formation of these structures was obtained by focusing on the roles of the polymer, and of the insoluble lead dodecyl sulfate (Pb(DS)2) present in the system. TEM investigations of the early stages of crystallization revealed the coexistence of PbS and Pb(DS)2 precipitates, the latter being surprisingly important for nanotube formation, and allowed to follow the evolution of layered structures from combination of the two types of crystals. Six different hydrophilic polymers have been used, which interact with SDS with varying strengths. Surprisingly, and in contrast to previous hypotheses, layered nanostructures were observed in all polymer solutions, regardless of the strength of polymer-surfactant interactions. This indicates that, although the presence of a polymer is necessary, polymer-SDS interactions are not a driving force for the formation of the layered structures and nanotubes. On the contrary, the interactions between the polymer chains and the growing particles appear to be of the utmost importance. Results presented here can be interpreted in terms of two alternative mechanisms for layered nanostructure and nanotube formation.     

Heart ablation using a planar rectangular high intensity ultrasound transducer and MRI guidance

The aim of this study was to evaluate a flat rectangular (3 × 10 mm²) MRI compatible transducer operating at 5 MHz. The main task was to explore the feasibility of creating deep lesions in heart at a depth of at least 15 mm. The size of thermal necrosis in heart tissue was estimated as a function of power and time using a simulation model. The system was then tested in an excised lamb heart. In this study, we were able to create lesions of 15 mm deep with acoustic power of 6 W for an exposure of approximately 1 min. The contrast to noise ratio (CNR) between lesion and heart tissue was evaluated using fast spin echo (FSE). The CNR value was approximately 22 using T1 W FSE. Maximum CNR was achieved with repetition time (TR) between 300 and 800 ms. Using T2W FSE, the corresponding CNR was approximately 13 for the 14 in vivo experiments. The average lesion depth was 11.93 mm with a standard deviation of 0.62 mm. In vivo irradiation conditions were 6 W for 60 s. The size of the lesion in the other two dimensions was close to 3 × 10 mm² (size of the transducer element).     

Quantitative Determination of Hyponitrite and Hyponitrate by Ion Chromatography

A simple, sensitive and reliable method for the rapid determination of hyponitrite and hyponitrate (Angeli’s salt) in alkaline media, is presented where both species are relatively stable. The method is based on the separation of the two anions by an anion exchange column and thereafter UV spectrophotometric detection at 248 nm. The calibration curves were linear over the concentration range of 0.4–100 mg L^?1, whereas the detection limit was found to be 50 μg L^?1 for hyponitrite and 100 μg L^?1 for hyponitrate. Under these conditions, the determination of nitrate and nitrite is also possible.