Thermal stabilities of copolymers of styrene and methacrylic acid and their salts

The thermal stabilities of copolymers of styrene and methacrylic acid and their sodium salts have been studied. The values of the thermal stability IDT,T _s and the kinetic parametersn, E, S andZ have been determined and the results are discussed. It has been found that the thermal stabilities of the investigated copolymers of styrene and methacrylic acid and their sodium salts are practically independent of the amount of methacrylic acid or sodium methacrylate introduced.     

O-Trimethylsilylenol ethers as versatile building blocks in a modular preparation of polyenic backbone

Versatility and synthetic potential of 1-(trimethylsilyloxy)-1,3-butadiene, 1-(trimethylsilyloxy)penta-1,3-diene, and their methyl substituted derivatives have been demonstrated in a modular synthetic methodology of stereodefined π-conjugated unsymmetrical, symmetrical two-dimensional, and octupolar polyenal structure.     

Surface and micellar properties of new nonionic gemini aldonamide-type surfactants

A new group of gemini aldonamide-type surfactants-N,N'-bisalkyl-N,N'-bis[(3-gluconylamide)propyl]ethylenediamines, N,N'-bisdodecyl-N,N'-bis[(3-glucoheptonylamide)propyl]ethylenediamine, and N,N'-bisalkyl-N,N'-bis[(3-lactobionylamide)propyl]ethylenediamines, (alkyl: n-C(8)H(17), n-C(12)H(25)), were synthesized and characterized. The surface properties, such as surface excess concentration, Gamma(cmc), surface area demand per molecule, A(min), efficiency in surface tension reduction, pC(20), the effectiveness of surface tension reduction, gamma(cmc), critical micelle concentration, cmc, and a measure of the tendency of the surfactant to adsorb at the aqueous/air interface relative to its tendency to form micelles in the bulk surfactant solution, cmc/C(20), and standard free energy of micellization, DeltaG(mic)(0), have been obtained by means of surface tension measurements. The standard fluorescence shift technique using PRODAN as a probe provide confirmation of the cmc values by an alternative method. Additionally, the micellar properties for the concentration near above the cmc have been characterized by the aggregation number, N(agg). The presence of the dimeric segments with the aldonamide hydrophilic units in the surfactant molecule is found to be the source of their unusual physicochemical behavior. They are very efficient at adsorbing at the free surface and at forming micelles in water. Their critical micelle concentration values are remarkably low. They reveal remarkably low A(min) values in relation to conventional nonionic surfactants, which is unexpected from the molecular dimensions for the molecule but which is possible if one assumes some type of multilayer structure or a coherent interfacial film.     

Comparative study on camphor enantiomers behavior under the conditions of gas-liquid chromatography and reversed-phase high-performance liquid chromatography systems modified with alpha- and beta-cyclodextrins

The dependence of retention and selectivity parameters of camphor enantiomers on the concentration of alpha- and beta-cyclodextrins were studied under conditions of GLC (matrix solvent: Glycerol, 95 degrees C) and RP-HPLC (matrix solvent: Aqueous methanolic, 20 degrees C). It has been found that beta-cyclodextrin forms complex of 1:1 stoichiometry and does not recognize enantiomers of camphor. In contrast alpha-CD forming complexes of 1:2 stoichiometry appeared to be very efficient chiral selector of (+) and (-)-camphor. Relatively considerable differences have been observed between stability constants determined by GLC and RP-HPLC, what may be explained by the various natures of the matrix solvents and the various temperatures of the measurements. On the contrary, the enantioseparation factor alpha observed at higher concentrations of alpha-cyclodextrin stabilizes on the very similar value alpha+/-(GLC) approximately = alpha-/+(HPLC) approximately = 1.6. Simple theoretical considerations focusing on the differences in the mechanisms of the studied processes have been performed. According to them the enantiomer forming the more stable complex with the cyclodextrin should be eluted from the RP-HPLC column first and GLC column last. This fact has been confirmed experimentally.     

Influence of N-hexadecyl-N,N,N-trimethylammonium nitrate on the dehydrobromination reaction of 2-phenylethyl derivatives

The basis dehydrobromination of p-substituted 2-phenylethyl bromides promoted by hydroxide ion has been studied in micelles of N-hexadecyl-N,N,N-trimethylammonium nitrate (CTANO₃). The pseudophase ion exchange model can be adapted to explain the kinetic results at low hydroxide ion concentration, i.e., less than 0.075 M of NaOH. At high hydroxide ion concentration in solution the applied model does not describe the kinetic results unless the empirical variations are applied for the mol ratio of reactive ion to micellar head group (β) and the binding constant of the organic reagent to the micelle (K_s).     

Potentiometrische Titrationen in der L?sung vom Triacetatsolvat des Trimethylaminacetats

Zusammenfassung Es wird über die physikalischen Eigenschaften und den chemischen Charakter des Triacetatsolvats des Trimethylaminacetats berichtet sowie über die Möglichkeit, diese Verbindung als wasserfreies Lösungsmittel anzuwenden. Viele anorganische und organische Verbindungen sind in TAT löslich. Die untersuchten potentiometrischen Fällungs- und Redoxtitrationen in TAT ergeben potentiometrische Kurven von normalem Verlauf und guter Reproduzierbarkeit.     

Microparticles vs. Macroparticles as Curcumin Delivery Vehicles: Structural Studies and Cytotoxic Effect in Human Adenocarcinoma Cell Line (LoVo)

This study aimed to characterize the hydrogel micro- and macro-particles designed to deliver curcumin to human colon cancer cells (LoVo). Six series of vehicles based on sodium alginate (micro- and macro-particles, uncoated, coated with chitosan or gelatin) were synthesized. The uncoated microparticles were fabricated using an emulsion-based technique and the uncoated macroparticles with an extrusion technique, with both coupled with ionotropic gelation. The surface morphology of the particles was examined with scanning electron microscopy and the average size was measured. The encapsulation efficiency, moisture content, and swelling index were calculated. The release of curcumin from the particles was studied in an experiment simulating the conditions of the stomach, intestine, and colon. To evaluate the anticancer properties of such targeted drug delivery systems, the cytotoxicity of both curcumin-loaded and unloaded carriers to human colon cancer cells was assessed. The microparticles encapsulated much less of the payload than the macroparticles and released their content in a more prolonged manner. The unloaded carriers were not cytotoxic to LoVo cells, while the curcumin-loaded vehicles impaired their viability—more significantly after incubation with microparticles compared to macroparticles. Gelatin-coated or uncoated microparticles were the most promising carriers but their potential anticancer activity requires further thorough investigation.     

Characterization of the Microenvironments of Alkylamidoamine-N-oxide Surfactant Aggregates by the EPR Spin Labeling Method

Spin labeling EPR methods were applied to characterize the local microviscosity and micropolarity of micellar aggregates formed by 3-(alkanoylamino)ethyldimethylamine-N-oxides (alkyl = nonyl, undecyl and tridecyl) in an aqueous environment in the temperature range 297?C337?K. Four doxylstearic derivatives: 5-doxylstearate methyl ester (5-DSE), 16-doxylstearate methyl ester (16-DSE), 5-doxylstearic acid (5-DSA) and 16-doxylstearic acid (16-DSA) were used as spin probes to monitor mainly the rotational correlation time ?? _R and the isotropic hyperfine splitting constant A _N. In the case of anisotropic spectra, the order parameter S was also determined. The selected probes were found to be sensitive to the microenvironments whereby it was possible to characterize in detail local changes in composition and micelle formation.     

The kinetics of propylene oxide reaction with certain alkylamino alcohols in the presence of basic catalysts

Rate constants for direct reactions of propylene oxide with certain aminoisopropanols in the presence of basic catalysts were studied at a temperature of 363–383 K. This reaction was found to be of the first order in propylene oxide, amino alcohol and catalyst. The observed kinetics are consistent with a termolecular mechanism.     

Fluorescence resonance energy transfer in a non-conjugated system of CdSe quantum dots/zinc-phthalocyanine

Energy transfer between CdSe quantum dots (QDs) as donors and Zn phthalocyanine (Zn-Pc) molecules as acceptors was studied using steady-state photoluminescence and time-correlated single photon counting techniques. With the latter technique it is evaluated that the lifetime of Zn-Pc emission increases from 4 ns to ca. 30 ns on 460 nm excitation in the presence of the QDs. The concomitant decrease in the lifetime of the QDs emission (from 23.5 to 18.4 ns) indicates that the excitation of Zn-Pc occurs not only through reabsorption but also through fluorescence resonance energy transfer.