Symmetries of Itô and Stratonovich Dynamical Systems and Their Conserved Quantities

A new definition for the symmetries of Itô and Stratonovich dynamicalsystem is given. Determining systems of symmetries for Itô andStratonovich systems have been obtained, and their relation has beendiscussed. It has been shown that some of the Lie point symmetries ofthe Fokker–Planck equation can be constructed using the symmetries ofItô dynamical systems. Conserved quantities can be found from thesymmetries of stochastic dynamical systems which do not arise from aHamiltonian. The results have been applied to an example.     

Approximate symmetries and conservation laws for Itô and Stratonovich dynamical systems

A new definition for the approximate symmetries of Itô dynamical system is given. Determining systems of approximate symmetries for Itô and Stratonovich dynamical systems have been obtained. It has been shown that approximate conservation laws can be found from the approximate symmetries of stochastic dynamical systems which do not arise from a Hamiltonian. The results have been applied to an example.     

Selective LC Determination of Cabergoline in the Bulk Drug and in Tablets: In Vitro Dissolution Studies

Cabergoline (CAB) is an ergot alkaloid derivative with dopamine agonist activity. A novel, simple, and rapid stability-indicating high-performance liquid chromatographic (HPLC) method for assay of CAB in tablets has been developed and validated. Chromatography was performed on a 4.6 mm i.d. × 250 mm, 5 μm particle, cyano column with acetonitrile–10 mM phosphoric acid, 35:65 (v/v), containing 0.04% triethylamine, as mobile phase, at a flow rate of 1.0 mL min^?1, and UV detection at 280 nm. Response was a linear function of concentration in the range 0.1–4 μg mL^?1 (r ² = 0.9999). The recovery of the method was good (99.45%) and RSD values for intra-day and inter-day precision were 0.24–0.88% and 0.66–1.19%, respectively. The method can be used for quality-control assay of CAB in tablets, for stability studies, and for in vitro dissolution studies.     

Electrochemical studies and square-wave voltammetric determination of fenofibrate in pharmaceutical formulations

The electrochemical reduction of fenofibrate at a hanging mercury drop electrode (HMDE) was investigated by cyclic voltammetry, square-wave voltammetry, and chronoamperometry. Different buffer solutions were used over a wide pH range (3.0–10.0). The best definition of the analytical signals was found in borate buffer (pH 9.0)–tetrabutylammonium iodide mixture containing 12.5% (v/v) methanol at –1.2 V (versus Ag/AgCl). According to cyclic voltammetric studies, the reduction was irreversible and diffusion controlled. The diffusion coefficient was 2.38×10^–6 cm² s^–1 as determined by chronoamperometry. Under optimized conditions of square-wave voltammetry, a linear relationship was obtained between 0.146–4.96 g mL^–1 of fenofibrate with a limit of detection of 0.025 g mL^–1. Validation parameters such as sensitivity, accuracy, precision, and recovery were evaluated. The proposed method was applied to the determination of fenofibrate in pharmaceutical formulations. The results were compared with those obtained by a published high-performance liquid chromatography method. No difference was found statistically.     

Cyclotriphosphazene,a scaffold for 19F MRI contrast agents

A cyclotriphosphazene substituted with six 3,5-bis(trifluoromethyl) benzyloxy units was designed as a novel ¹⁹F MRI contrast agent. The resulting molecule has 36 magnetically equivalent fluorine atoms and exhibited suitable MRI properties with high imaging sensitivity, confirming the proof-of-concept as a convenient scaffold for the production of new ¹⁹F MRI contrasts agents.     

Sonochemical synthesis and electrochemical characterization of α-nickel hydroxide: precursor effects

Sonochemical degradation of urea was employed to synthesize alpha-nickel hydroxide from different nickel salts. Utilization of ultrasound yielded products with properties significantly different than the products obtained by thermal degradation of urea. The effect of intercalating chloride, nitrate, acetate, and sulfate anions on morphology and electrochemical performance was studied. The sulfate-intercalated sample had the smallest interlayer spacing when obtained by the sonochemical method, contradicting all the previous thermal synthesis results. The specific capacitance trend also differed from the literature values, and the value for the sulfate-intercalated sample was larger than that of acetate- and nitrate-intercalated samples. Ultrasonic synthesis increased the specific capacitance of the sulfate-intercalated sample significantly. This sample was also the most reversible and had the highest charge efficiency.     

Optimization of chemical and instrumental parameters in hydride generation laser-induced breakdown spectrometry for the determination of arsenic,antimony, lead and germanium in aqueous samples

A laser induced breakdown spectrometry hyphenated with on-line continuous flow hydride generation sample introduction system, HG-LIBS, has been used for the determination of arsenic, antimony, lead and germanium in aqueous environments. Optimum chemical and instrumental parameters governing chemical hydride generation, laser plasma formation and detection were investigated for each element under argon and nitrogen atmosphere. Arsenic, antimony and germanium have presented strong enhancement in signal strength under argon atmosphere while lead has shown no sensitivity to ambient gas type. Detection limits of 1.1 mg L⁻¹, 1.0 mg L⁻¹, 1.3 mg L⁻¹ and 0.2 mg L⁻¹ were obtained for As, Sb, Pb and Ge, respectively. Up to 77 times enhancement in detection limit of Pb were obtained, compared to the result obtained from the direct analysis of liquids by LIBS. Applicability of the technique to real water samples was tested through spiking experiments and recoveries higher than 80% were obtained. Results demonstrate that, HG-LIBS approach is suitable for quantitative analysis of toxic elements and sufficiently fast for real time continuous monitoring in aqueous environments.     

Cyanines comprising barbiturate group facilitate NIR-light assisted ATRP under anaerobic and aerobic conditions at two wavelengths using Fe(III) catalyst

Cyanines with heptamethine pattern namely 5-(6-(2-(3-ethyl-1,1-dimethyl-1H-benzo[e]indol-2(3H)-ylidene)ethylidene)-2-(2-(3-ethyl-1,1-dimethyl-1H-benzo[e]indol-3-ium-2yl) vinyl) cyclo-hex-1-en-1-yl)-1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydropyrimidin-4-olate comprising a barbiturate group facilitate controlled radical polymerization using FeBr₃ in the ppm range applying radiation at 790 nm. Tris(4-methoylphenyl)phosphine, Tris(2-pyridylmethyl)amine or tetrabutylammonium bromide served as ligand. The latter showed the best performance resulting in a system needing no amino nitrogen for photo-ATRP. Ethyl α-bromophenylacetate worked as initiator. The cyanine interacts with FeBr₃ resulting in a new absorption band at 877 nm that also resulted in formation of polymer exhibiting similar molecular weight but higher dispersity compared to that obtained by 790 nm radiation by exposure with a light-emitting diode (LED) emitting at 870 nm. This explains the reactivity of the system while other cyanines such as 2-[2-[3-[2-(1,3-Dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)-ethylidene]-2-(1-phenyl- 1H-tetrazol-5-ylsulfanyl)-1-cyclohexen-1-yl]-ethenyl]-1,3,3-trimethyl-3H-indolium chloride showed no activity by exposure at 790 nm in combination with FeBr₃/Br⁻. Controlled radical polymerization was confirmed by successful chain extension and block copolymerization experiments resulting in polymers, which exhibit a dispersity of about 1.3. Interestingly, the new system comprising the aforementioned barbiturate substituted cyanine, FeBr₃/Br⁻ and ethyl α-bromophenylacetate showed a certain oxygen tolerance. Polymers obtained exhibited similar dispersity as those made under inert conditions.