HPLC determination of estradiol, its degradation product, and preservatives in new topical formulation Estrogel HBF

This paper deals with the development of a novel method for simultaneous determination of estradiol, its degradation product estrone, and two preservatives, methylparaben and propylparaben, in the topical preparation Estradiol HBF. After optimization of the analytical conditions the method was validated and applied in studies of the stability of the topical preparation Estrogel HBF. Separation of all these compounds was performed on a Supelco Discovery C18 (250 mm×3.0 mm, 5 m) analytical column. A mixture of acetonitrile, methanol, and water (23:24:53 v/v) was chosen as mobile phase. UV absorbance at 225 nm was used for detection and quantitation of analytes. The total analysis time was less than 12 min at a flow rate of 0.9 mL min^–1. All the compounds were isolated from the topical gel by simple extraction with an acetonitrile solution of hydrocortisone, as internal standard, and using sonication and centrifugation thereafter. The supernatant was injected directly on to the analytical column. The recovery of the procedure was from 96.9 to 100.4%. Validation of method according international guidelines was successfully performed.     

Novel polycarbonate-based polyurethane elastomers: Composition–property relationship

Novel all-aliphatic polycarbonate-based polyurethane (PC-PU) elastomers, as well as PC-PU nanocomposites filled with organic-modified clays were synthesized, characterized and studied. It was found that they have very attractive mechanical properties (e.g., elongation at break between 600% and 800%). The prepared PC-PUs possess a distinctly segmented structure, which is the key prerequisite for their behavior as strong physical rubbery networks. All synthesized materials melt at elevated temperatures (between 110 and 200 °C) and hence can be processed like normal thermoplastics. The dispersion of the clay nanofiller was achieved by its one day swelling in the alcohol and a brief successive stirring. This procedure is very successful and leads to a partial exfoliation of the clay (documented by X-ray diffraction and TEM). The best nanocomposites with very good tensile properties, particularly with significantly increased moduli were obtained using the bentonite nanofiller. The study shows that the nanofiller interacts strongly with the hard domains and influences their melting temperature (DMTA and DSC), but it does not affect the glass transition temperature of soft domains. While Cloisite 15A was found to interact preferentially with the hard domains, the organic modified bentonite shows a strong interaction with both soft and hard segments, behaving as a blending agent. Hard domains in neat matrices, formed by hydrogen bonding of hard segments, were practically invisible by X-ray or TEM, but were successfully detected by AFM. Besides excellent mechanical properties, the prepared elastomers and their nanocomposites showed an interesting phase behavior (which was studied by combining DMTA and modulated DSC).     

Micellization and catalytic activity of the cetyltrimethylammonium bromide-Brij 97-water mixed micellar system

Surface tension measurements and the kinetic study of the basic hydrolysis of ethyl p-nitrophenyl chloromethyl phosphonate were used to examine the structural behavior and catalytic activity of the cethyltrimethylammonium bromide (CTAB)-polyoxyethylene (10) oleyl ether, C(18)H(35)(OCH(2)CH(2))(10)OH (Brij 97)-water mixed micellar system. Application of the regular solution model to the experimental data yields the value of the interaction parameter beta as -4.6, which indicates an attractive interaction of the surfactants in the mixed micelle and reflects synergistic solution behavior of the mixture. The mixed micellar composition is found to be enriched in the surfactant with the lower critical micelle concentration (cmc). In the kinetic study a nonmonotonic change in the pseudo-first-order rate constant of basic hydrolysis of the substrate is observed with increasing mole fraction of nonionic surfactant. The pseudophase micellar model reveals that the concentration factor mainly contributes to the catalytic effect, while the microenvironmental factor plays a negative role.     

Development of Novel Stability-Indicating Method for the Determination of Dimethindene Maleate and Its Impurities

A novel and selective stability-indicating liquid chromatographic method has been developed and validated for the analysis of dimethindene maleate, the related substance 2-ethylpyridine, and three degradation products. Dimethindene maleate was subjected to forced degradation study by acid and basic hydrolysis, oxidation, and thermal decomposition. Three degradation products that were formed during the forced degradation study were separated from dimethindene using a Zorbax SB CN column (150 × 4.6 mm; 5 μm); cyanopropyl-bonded stationary phase was applied for the first time for the separation of dimethindene and its impurities. The proposed method was validated and was found suitable for quality control and stability tests of pharmaceuticals containing dimethindene maleate.

     

Biophysical characterization of complexation of DNA with block copolymers of poly(2-dimethylaminoethyl) methacrylate, poly(ethylene oxide), and poly(propylene oxide)

The interactions of DNA (salmon testes) with two new cationic block copolymers made of poly(2-dimethylaminoethyl) methacrylate and poly(ethylene oxide), PEO-pDMAEMA, or poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), L92-pDMAEMA, were studied with the aim to understand their different in vitro transfection efficiencies when used as nonviral delivery vectors. PEO-pDMAEMA does not show surface activity while L92-pDMAEMA is as surface active as its parent Pluronic L92. Surface tension, titration microcalorimetry, ethidium bromide displacement, and zeta-potential measurements were carried out in phosphate buffers at pH 5 and 7. The association of L92-pDMAEMA with DNA was strongly exothermic at both pHs; the critical aggregation concentration (CAC) corresponded to a N/P ratio of 0.3, the maximum energy evolved was reached for N/P ratios of 0.82 and 1.27 at pH 5 and pH 7, respectively, and the saturation occurred for N/P ratios close to 2. The presence of L92 in the structure of this new block copolymer apparently did not modify the thermodynamic parameters of the interaction with DNA. In contrast, the interaction with PEO-pDMAEMA was significantly less exothermic, and CAC and saturation occurred for N/Ps equal to 0.43 and 1.37, respectively. The strong affinity of L92-pDMAEMA for DNA was reflected in its capacity to displace ethidium bromide and in the jump in the values of the zeta potential when N/P is near 1. Above the N/P ratio at which electroneutral polyplexes are formed, only at pH 5 an excess of L92-pDMAEMA is incorporated in the complexes, resulting in positively charged complexes. The profile of the zeta-potential values obtained for mixtures of L92-pDMAEMA with Pluronic P123 showed a shift to a lower N/P ratio, owing to an easier interaction of L92-pDMAEMA molecules with DNA in the presence of P123. Additionally, a visual inspection of the systems indicates that P123 contributes to stabilize/solubilize the DNA/cationic polymer aggregates, by avoiding the typical phase separation near the charge neutralization point. The information obtained can be particularly useful to optimize the conditions to form efficient polyplexes for gene delivery systems.     

The trans-1,4-cyclohexylene group as a structural fragment in liquid crystals

In this review the effect on physico-chemical and electro-optical properties of the introduction of the trans-1,4-cyclohexylene fragment into the molecular core of liquid crystals is discussed, rationalized in terms of existent theories, and compared with the effect of other well-known molecular fragments.     

On the absolute instability of semi-implicit schemes for hydrostatic models

The dependence of the linear stability of two-time-level finite-difference semi-implicit schemes on the choice of reference temperature profile is studied. Particular vertical profiles of the temperature are considered to derive analytical conditions of stability. Analysis is made for general form of different model parameters such as the number of vertical levels and their distribution, the time step size, and the values of the viscosity coefficients. The derived conditions of stability are more restrictive than those for three-time-level schemes, but obtained necessary and sufficient condition for constant vertical lapse rates of the temperature has the form frequently applied to three-time-level schemes: the basic temperature profile should be warmer than the actual one. Performed numerical experiments show that the last restriction is neither necessary nor sufficient condition of stability for general temperature profiles.     

Pyrazolyc 3-hydroxychromones: Regulation of ESIPT reaction by the “flavonol-like” intramolecular hydrogen bonding to carbonyl group oxygen,which dominates over the “alternative” H-bond to heterocyclic nitrogen

Two isomeric pyrazole derivatives of 3-hydroxychromone (3HC) with and without the possibility of the multiple intramolecular hydrogen bonds formation were compared theoretically and experimentally with the aim to find out whether the excited state intramolecular proton transfer (ESIPT) reaction follows the traditional to the most of 3HCs “flavonol-like” direction towards the CO group oxygen or an “alternative” direction towards the heterocyclic nitrogen atom.Quantum-chemical modeling and comparative study of the experimental spectral parameters of the title compounds indicated the preferential realization of “flavonol-like” ESIPT to oxygen channel.The 3HC systems with the “alternative” intramolecular hydrogen bond to nitrogen were characterized as low fluorescent and practically unable to ESIPT with participation of the nitrogen containing heterocyclic unit.     

Surprising secondary photochemical reactions observed on conventional photolysis of diazotetrahydrofuranones

The formation of C-H insertion products of the terminal N-atom of a diazo group into the α-СН-bond of tetrahydrofuran during direct photolysis of regioisomeric 2,2-dimethyl-5,5-diphenyl and 5,5-dimethyl-2,2-diphenyl-substituted 3-diazotetrahydrofuran-4-ones in THF is dictated by photochemical cycloelimination of the originally formed (1,1-dimethyl-2-oxa-3,3-diphenyl-propano)ketene and oxetanecarboxylic acid derivatives to yield benzophenone. The latter, under subsequent UV irradiation of the reaction mixture, initiates sensitized photolysis of the starting diazoketones resulting in the appearance of the insertion products with the solvent.