Application of silver/sulfide ion-selective electrode for the determination of aliphatic primary and secondary amines

Aliphatic primary and secondary amines were determined utilizing their reaction with carbon disulfide. A potentiometric titration of the formed dithiocarbamates (I) with silver nitrate using a silver/sulfide ion-selective electrode was carried out. The effects of solvent, base, temperature and reaction time were investigated. The optimum conditions for a quantitative formation of (I) requires a minimal amount of 1,4-dioxane, 2 drops of 0.2% sodium hydroxide solution, excess carbon disulfide to stand at room temperature for 15 min. The titration requires prior evaporation of the unreacted carbon disulfide at 46 ° C. An average recovery of 98.5% with a standard deviation of 0.69 was obtained for the analyzed amines.     

NOVAL REARRANGEMENT OF 5-ARYLAZO-2-THIOHYANTOIN DERIVATIVES WITH ALKALI AND AROMATIC AMINES

Abstract

Treatment of 5-arylazo-2-thiohydantoins with aqueous sodium hydroxide affected hetero-ring opening followed by recyclization via the loss of hydrogen sulphide with the formation of 1-aryl-Δ² -1, 2, 4-triazole-5-imino-3-carboxylic acids.     

Controlling semiconductor/metal junction barriers by incomplete, nonideal molecular monolayers

We study how partial monolayers of molecular dipoles at semiconductor/metal interfaces can affect electrical transport across these interfaces, using a series of molecules with systematically varying dipole moment, adsorbed on n-GaAs, prior to Au or Pd metal contact deposition, by indirect evaporation or as "ready-made" pads. From analyses of the molecularly modified surfaces, we find that molecular coverage is poorer on low- than on high-doped n-GaAs. Electrical charge transport across the resulting interfaces was studied by current-voltage-temperature, internal photoemission, and capacitance-voltage measurements. The data were analyzed and compared with numerical simulations of interfaces that present inhomogeneous barriers for electron transport across them. For high-doped GaAs, we confirm that only the former, molecular dipole-dependent barrier is found. Although no clear molecular effects appear to exist with low-doped n-GaAs, those data are well explained by two coexisting barriers for electron transport, one with clear systematic dependence on molecular dipole (molecule-controlled regions) and a constant one (molecule-free regions, pinholes). This explains why directly observable molecular control over the barrier height is found with high-doped GaAs: there, the monolayer pinholes are small enough for their electronic effect not to be felt (they are "pinched off"). We conclude that molecules can control and tailor electronic devices need not form high-quality monolayers, bind chemically to both electrodes, or form multilayers to achieve complete surface coverage. Furthermore, the problem of stability during electron transport is significantly alleviated with molecular control via partial molecule coverage, as most current flows now between, rather than via, the molecules.     

Performance analysis of a hybrid fiber Bragg grating-based spectral-amplitude-coding/successive interference cancellation for optical CDMA systems

Successive interference cancellation (SIC) scheme is proposed as a new technique that has the potential to reduce the interference and suppress the multiple-access interference (MAI) in spectral-amplitude-coding (SAC) optical-code-division-multiple access (OCDMA) systems. The proposed receiver-based on fiber Bragg gratings (FBGs) techniques. The performance of the proposed system is theoretically analyzed, taking into account various types of noise and interference, including both multiple-access interference (MAI) and receiver noise. Analytical results show that the proposed system offers significant improvement in terms of bit error rate and system capacity (number of users). We have tested our results with both modified prime codes (MPR) and modified quadratic congruence (MQC) codes. In addition, we have compared our proposed system with the corresponding one without cancellation. It has been shown that the proposed scheme gives a substantial increase in capacity.     

Spectroscopic study of oscillator strength and radiative decay time of colloidal CdSe quantum dots

Characterization of samples of cadmium selenide quantum dots (CdSe) QDs dissolved in toluene colloidal solutions at a concentration of 1.4 mg/ml was carried out through UV–Vis absorption and photoluminescence (PL) spectroscopy. The size-dependent absorption and red-shifted PL emission peak wavelengths could be tuned between 510–576 and 545–606 nm respectively. Optical absorption spectral measurements yielded CdSe QDs having diameters about ~ 2.44–3.69 nm with energy gaps 2.32–2.08 eV which are higher than the bulk CdSe (1.74 eV) reminiscent of quantum confinement. This is found to be in good agreement with the semi-empirical pseudopotential model. In addition, the first excitonic absorption transition 1S_(e)1S_3/2(h) oscillator strength and the corresponding fluorescence radiative decay time of CdSe QDs are assessed using relevant Einstein relations for absorption and emission in a two-level system. The elaborated calculations would anticipate that the transition oscillator scale with the CdSe QD radius as ~ R^2.54. Correspondingly, the calculated radiative decay times decrease from 56.4 to 23.2 ns which scale with CdSe QDs radius as ~ R^?2.155 in fairly good agreement with experimental values reported in the literature.     

Applying green analytical chemistry (GAC) for development of stability indicating HPLC method for determining clonazepam and its related substances in pharmaceutical formulations and calculating uncertainty

Clonazepam contains one benzodiazepine ring in its chemical structure which makes it vulnerable to degradation. In this study, green analytical chemistry approach was applied in attempts for the development of validated stability indicating RP-HPLC method for determining clonazepam and its related substances in pharmaceutical formulation. Validation has been performed according to ICH guidelines. Assay was capable of simultaneous monitoring of the intact drug in the presence of its related substances within the same run. HPLC assay involved an ODS column and a mobile phase composed of 2% sodium dodecyl sulfate, 0.05 M sodium acetate buffer pH 3.5 and isopropanol in ratio (25:55:20) at a flow rate of 1.5 mL/min and detection was carried out at 254 nm. HPLC method allowed good resolution between the peaks that corresponded to the active pharmaceutical ingredients and its degradation products with good linearity, precision, accuracy, specificity, LOD and LOQ. The expanded uncertainty (0.33%) of the method was also estimated from method validation data. This analytical technique is not only ecofriendly but also faster than the conventional liquid chromatographic system official in the USP-36.     

Laser thermal response of a finite slab as a function of the laser pulse parameters

This paper deals with the problem of heating a finite slab using laser radiation in relation to the parameters characterizing the laser pulse, namely: q_max(W/m²), the maximum laser power density, t₀ the time interval required to reach q_max and t_d, the pulse time duration. The pulse shape q(t) is suggested in the form: q(t)=βq_max(t/t_d)(1-(t/t_d))exp-B(t-t₀/t_d), where β and B are parameters. Fitting with published experimental pulse [Ready JF. Effects due to absorption of laser radiation. J Appl Phys 1965;36:462–68] is made. Fourier series expansion technique is considered to solve the problem. The critical time required to initiate melting t_m is estimated for four metallic elements and five semiconductors, namely: Al, Cu, Ag, Au (aluminum, copper, silver, and gold), cadmium sulfide, germanium, silicon, alpha beryllium oxide, and silicon carbide. Five pulses with different characteristic parameters are considered.Computations revealed that the thermal response of the targets is highly affected by q_max and t_o, while the pulse time duration is less effective in determining the value of t_m. Moreover, it is revealed that the relation between t_m and the melting temperature for the same laser pulse is nonlinear for the considered targets under the indicated conditions.     

Fast frequency modulation optical code division multiple access communication system

An optical fast frequency modulation code division multiple access communication system is proposed. In this system, an electrically controlled tunable optical filter (TOF) is used to encode the modulated broadband light source. The code depends on the function set to the controller. Two-dimensional code named functional code is also proposed based on a shifted sine function. The function defines the dynamic coding pattern of the central wavelength of the transmitted narrowband optical signal. Thus, the system will allow for an easy reconfiguration of the transmitter without the need for sophisticated encoder. At the receiver, a synchronized TOF with the same function is used as a decoder. The performance of this system is shown to be better compared with a fast frequency hopping and a spectral amplitude coding systems.     

Effect of N-substitution on the crystallinity of polylaurolactam

Poly(N-ethyl laurolactam) and poly(N-benzyl laurolactam) were prepared from the corresponding monomers by hydrolyic polymerization. Unlike the partially crystalline poly(N-methyl laurolactam), these two homopolymers were completely amorphous by x-ray diffraction. Diffraction patterns of copolymers of N-ethyl laurolactam or N-benzyl laurolactam with laurolactam were shown to be composition-dependent. For N-ethyl laurolactam copolymers, crystallinity developed with 20% laurolactam as a comonomer and increased steadily with a subsequent change in the x-ray pattern, up to 50% laurolactam. Higher laurolactam percentages resulted in copolymers having a nylon 12 x-ray pattern. N-Benzyl laurolactam copolymers with 30% laurolactam showed only 6% crystallinity. The x-ray patterns of N-benzylated nylon 12 made with more than 50% laurolactam showed patterns similar to that of nylon 12. Differential scanning calorimetry data of all these polymers substantiate the x-ray findings. The effect of type and concentration of the N-substituent on the glass transition, melting, and crystallization temperatures of the polymers is discussed.