The i‐E oxidation curves, obtained using a boron doped diamond electrode, for studies of oxidations of two piperazine derivatives ARIP (I) and PIRI (II), resulted in a sharp increase of current in the range of the oxidation potentials. After reaching a value, depending on concentration of I or II, the current remains practically constant up to +1.6 V. Such limiting currents i1 are a linear function of concentrations and depend on the v1/2. Hence it is diffusion controlled, shifts of the oxidation potentials indicate, that the monoprotonated forms are oxidized. At more negative potentials a limiting current i2 occurs, due to the oxidation of the diprotonated form. Current i2 increases with decreasing pH in a shape of a part of a dissociation curve. Diffusion control reflects the large size of molecules I and II. The two‐electron oxidations yield a C=N bond in the piperazine ring. It seems to be the first reported diffusion controlled oxidation curves obtained on a stationary solid electrode. 相似文献
Metal porphyrins assemble to form a supramolecular architecture with a characteristic structure and characteristic properties and functions upon complexation with appropriate ligands. However, there are few applications of these assembly processes to the construction of polymeric porphyrin arrays with useful functionalities. In this study, we found that meso–meso‐linked ZnII porphyrin arrays underwent zipperlike dimerization upon complexation with di(pyrid‐3‐yl)acetylene (DPA) in chloroform to form discrete double‐stranded porphyrin ladders. Similarly, the assembly of poly(zinc(II) porphyrinylene) with DPA gave a thermoresponsive gel, whose three‐dimensional network structure was so strong that a macroporous xerogel film was obtained. 相似文献
Ionics - Simple, rapid, sensitive, and reproducible methods were developed for the assay of paroxetine in tablets. The electrooxidative behavior and determination of paroxetine on boron-doped... 相似文献
Dimenhydrinate (DM) is used therapeutically for the prevention of motion sickness associated with nausea and vomiting. The aim of this investigation is the development of a new, rapid, sensitive, simple and fully validated RP-LC procedure for the suitable assay of DM in pharmaceutical formulation applied in blood samples. The method was validated before the amount determination studies in order to confirm linearity, precision, accuracy, selectivity, determination and quantification limit and consistency. High determination coefficient (r2 = 0.998) of the standard curve drawn in the linearity studies showed that the line equation can be used in the quantification of the DM. Literature was reviewed for the methods based on diphenhydramine (DIP), its metabolite dimenhydrinate, in the in vivo determination of dimenhydrinate amount. The most appropriate method to be used in LC was decided to be the method applied by benefitting from the fluorescence characteristic of DIP. Maximum excitation and emission wavelengths in the developed method were scanned using multiple wavelengths and, maximum excitation and emission wavelengths were found to be 215 and 300 nm, respectively. In the validation study used to prove validity of the method, determination coefficient of the developed standard curve was calculated as 0.998 (RSD %), and line equation was concluded to be appropriate for use in amount determination studies. BBS % (1.06, 1.84 %) values obtained as “<2 %” in the intra-day and inter-day precision studies proved the precision of the method. Selectivity study revealed that other materials used in the formulation did not exhibit absorbance in the same wavelengths. Detection and quantification limit were found as 1 and 5 ng mL−1, respectively. The determination of DM plasma concentrations using the proposed and fully validated LC assay has allowed us to characterize DMPK in the sheep, as well as determine DM relative bioavailability.
The mechanical anisotropy of polyvinyl chloride oriented in two perpendicular directions with different draw ratios has been studied. The results are compared with the anisotropy of uniaxial samples oriented at a common draw ratio. The propagation velocities of ultrasonic pulses have been measured by an immersion technique. Longitudinal wave velocities have been measured in three principal planes over a wide range of propagation directions. The limitations of measuring velocities in the planes containing the draw axes were mitigated by use of a special slicing technique. Measurements were performed at 2 MHz and 25°C. Velocities of the transverse waves were measured for incident wave angles greater than the critical angle. From these measurements, five elastic moduli were calculated for the uniaxially oriented samples, and nine elastic moduli were obtained for the biaxially oriented samples. In biaxially oriented samples, the moduli along the draw axes are directly proportional to the draw ratio in the same direction. 相似文献
In this study, the adsorption properties of unexpanded and expanded perlite samples in aqueous cetyltrimethylammonium bromide (CTAB) solutions were investigated as a function of ionic strength, pH, and temperature. It was found that the amount of cetyltrimethylammonium bromide adsorbed onto unexpanded perlite was greater than that onto expanded perlite. For both perlite samples, the sorption capacity increased with increasing ionic strength and pH and decreasing temperature. Experimental data were analyzed by Langmuir and Freundlich isotherms and it was found that the experimental data were correlated reasonably well by the Freundlich adsorption isotherm. Furthermore, the isotherm parameters (KF and n) were also calculated. The adsorption enthalpy was determined from experimental data at different temperatures. Results have shown that the interaction between the perlite surface and CTAB is a physical interaction, and the adsorption process is an exothermic one. 相似文献
The voltammetric behavior of cefixime was studied using cyclic, linear sweep, differential pulse and square wave voltammetric techniques. The oxidation of cefixime was irreversible and exhibited diffusion controlled process depending on pH. The oxidation mechanism was proposed and discussed. Different parameters were tested to optimize the conditions for the determination of cefixime. The dependence of current intensities and potentials on pH, concentration, scan rate, nature of the buffer was investigated. According to the linear relationship between the peak current and the concentration, differential pulse (DPV) and square wave (SWV) voltammetric methods for cefixime assay in pharmaceutical dosage forms and biological fluids were developed. For the determination of cefixime were proposed in acetate buffer at pH 4.5, which allows quantitation over the 6 × 10−6-2 × 10−4 M range in supporting electrolyte and spiked serum sample; 8 × 10−6-2 × 10−4 M range in urine sample; 6 × 10−6-1 × 10−4 M range in breast milk samples for both techniques. The repeatability, reproducibility, precision and accuracy of the methods in all media were investigated. No electroactive interferences from the excipients and endogenous substances were found in the pharmaceutical dosage forms and in the biological samples, respectively. 相似文献
The mechanism of oxidative polymerization of diphenylamine is considered. The kinetic study of diphenylamine polymerization and of the structure and molecular-mass characteristics of the reaction products has shown that the degree of oxidation of intermediates plays the key role in polyrecombination. The relationship between the polymerization procedure and the molecular mass of polydiphenylamine was revealed. 相似文献