Experimental and quantum chemical study on the IR, UV and electrode potential of 6-(2,3-dihydro-1,3-dioxo-2-phenyl-1H-inden-2-yl)-2,3-dihydroxybenzaldehyde

Electrode potential of 6-(2,3-dihydro-1,3-dioxo-2-phenyl-1H-inden-2-yl)-2,3-dihydroxybenzaldehyde (DPDB) in methanol have been calculated theoretically. For the achievement of this task, the density functional theory (B3LYP/6-31G(d)) was employed with the inclusion of the entropic and thermochemical corrections to yield the free energies of the redox reactions. The electrode potential was also obtained experimentally by means of an electrochemical technique (cyclic voltammetry). The geometric parameters, the vibrational frequency values and the UV spectrum of DPDB and 2-(2,3-dihydro-1,3-dioxo-2-phenyl-1H-inden-2-yl)-5,6-dioxocyclohexa-1,3-dienecarbaldehyde (DPDD is the oxidized form of DPDB), were computed using the same methods. The calculated IR spectrum of DPDB, used for the assignment of the IR frequencies, was observed in the experimental FT-IR spectrum. The correlation between the theoretical and experimental DPDB vibrational frequencies was 0.996. This agreement mutually verified the accuracy of the experimental method and the validity of the applied mathematical model.     

Molecular parameterization and determination of the electrode potentials of anticoagulant derivatives: Electrochemical and quantum chemical study

This research presents calculations and computation of two anticoagulant derivatives electrode potentials in methanol. For this purpose, the ab initio molecular orbital calculations (HF) and density functional theory (DFT) together with the 6-31G(d) basis set were utilized. The calculated values were compared with the experimental values obtained by linear sweep voltammetry. The observed and the calculated changes in the reduction potential of the anticoagulant derivatives differed from those of the reference compound (catechol), being less than 20 mV. In this way, a method was provided, by which the reduction potentials of the related molecules could be predicted very accurately. Actually, the resulting data illustrated that the method was likely to be useful for the prediction of biomolecules electrode potentials in different aprotic solvents. The bond lengths, bond angles and dipole moment of the studied compounds were calculated in two different solvents and the solvent effects were discussed.     

Determination of the formation constant for the inclusion complex between Lanthanide ions and Dansyl chloride derivative by fluorescence spectroscopy: Theoretical and experimental investigation

In this paper, a sensitive, easy, efficient, and suitable method for the calculation of K_f values of complexation between one derivative of Dansyl chloride [5-(dimethylamino) naphthalene-1-sulfonyl 4-phenylsemicarbazide] (DMNP) and Lanthanide(III) (Ln) ions is proposed, using both spectrofluorometric and spectrophotometric methods. Determination of K_f showed that DMNP was mostly selective towards the erbium (III) ion. The validity of the method was also confirmed calculating the Stern–Volmer fluorescence quenching constants (K_sv) that resulted in the same consequence, obtained by calculating the K_f of complexation values. In addition, the UV–vis spectroscopy was applied for the determination of K_f only for the Ln ions that had interactions with DMNP. Finally, the DFT studies were done on Er³⁺ and the DMNP complex for distinguishing the active sites and estimating the pair wise interaction energy. It can be concluded that this derivative of Dansyl chloride with inherent high fluorescence intensity is a suitable reagent for the selective determination of the Er³⁺ ion which can be used in constructing selective Er³⁺ sensors.     

Design of a fast convergent backpropagation algorithm based on optimal control theory

The main contribution of this paper is using optimal control theory for improving the convergence rate of backpropagation algorithm. In the proposed approach, the learning algorithm of backpropagation is modeled as a minimum time control problem in which the step-size of its learning factor is considered as the input of this model. In contrast to the traditional backpropagation, learning algorithms which select the step-size by trial and error, it is selected adaptively based on optimal control criterion. The effectiveness of the proposed algorithm is evaluated in two simulations: XOR and 3-bit parity. In both simulation examples, the proposed algorithm outperforms well in speed and the ability to escape from local minima.     

Development of Flow Injection Spectrofluorimetric Detection System for the Determination of Homocysteine

In this work, a new simple and sensitive flow injection method is developed for the determination of homocysteine with spectrofluorimetric detection technique. This method is based on the oxidation of homocysteine with Tl (III) in acidic media, producing fluorescence reagent, TlCl₃^2- (λ_ex = 237 nm, λ_em = 419 nm). The effects of chemical parameters (including pH of the solutions, the buffer, Tl (III) and potassium chloride concentrations), instrumental parameters (such as flow rate of the solutions, reaction coil length, and sample loop volume) and temperature on the fluorescence intensity as an analytical signal are studied and optimized. In the optimum conditions of the above variables, homocysteine can be determined in the range 4.0 × 10^-7–40.0 × 10^-6 M with the LDR from 4.0 × 10^-7 to 25.0 × 10^-6 M. The detection limit (with S/N = 3) is 6.0 × 10^-8 M of homocysteine and precision for the injection of 5.0, 10.0 and 15.0 μM of homocysteine are 0.8%, 1.5% and 2.5% (n = 10) respectively. The rate of analysis is 90 samples per hour. The influence of potential interfering substances, including amino acids and carbohydrates is also studied. The proposed method has been successfully used for the determination of homocysteine in the real sample (blood serum and tap water) matrix.     

Flow Around a Crack in a Porous Matrix and Related Problems

The equations governing plane steady-state flow in heterogeneous porous body containing cracks are presented first. Then, a general transformation lemma is presented which allows extending a particular solution obtained for a given flow problem to another configuration with different geometry, behaviour and boundary conditions. An existing potential solution in terms of discharges along the cracks, established by Liolios and Exadaktylos (J Solids Struct 43:3960–3982, 2006) for non-intersecting cracks in isotropic matrix, is extended to intersecting cracks in anisotropic matrix. The basic problem of a single straight crack in an infinite body submitted to a pressure gradient at infinity is then investigated and a closed-form solution is presented for the case of void cracks (infinite conductivity), as well as a semi-analytical solution for the case of cracks with Poiseuille type conductivity. These solutions, derived first for an isotropic matrix, are then extended to anisotropic matrices using the general transformation lemma. Finally, using the solution obtained for a single crack, a closed-form estimation of the effective permeability of micro-cracked porous materials with weak crack density is derived from a self-consistent upscaling scheme.     

Stability study of the gastric floating dosage form of capecitabine

Since administration of capecitabine tablets leading to dose limiting makes the unfavorable toxicity, preparation of sustained-release tablets will overcome most of these side effects. The aim of this study was to prepare and study the stability of capecitabine sustained-release tablets. Sustained-release tablets of capecitabine were characterized by differential scanning calorimetry, X-ray diffraction, and infrared and ultraviolet spectroscopy techniques to determine the stability of the tablets. All tests carried out for tablets upon preparation as well as 6 and 12 months after preparation. The gradual decomposition of capecitabine sustained-release tablets stored at accelerated conditions (40 °C in 75 % of relative humidity) was indicated by decreasing values of peak purity and melting temperature, calculated from the Van’t Hoff equation. Except for the occurrence of one sharp peak for long-term stability and some sharp peaks in the accelerated condition, all peaks showed a crystallized nature. But the FTIR and UV results showed that there were no changes between the initial sustained-release tablets and stored tablets. Although the XRD results showed more peaks in the accelerated condition tablets, the crystalline form of capecitabine was maintained. These findings demonstrate that the capecitabine sustained-release tablet has excellent stability in normal and long-term storage conditions, with slight changes in the accelerated condition.     

Hopf bifurcation analysis on an Internet congestion control system of arbitrary dimension with communication delay

This paper carries out a Hopf bifurcation analysis on a model of Internet congestion control system for a network with arbitrary topology. The general form of the rate-based Kelly model for a multi-source multi-link network with a communication delay is considered. Assuming the communication delay as a bifurcation parameter, we find that when the delay parameter passes a critical value, a periodic solution bifurcates from the equilibrium point. The stability and direction of bifurcating periodic solutions are studied by using the center manifold theorem and the normal form theory. We simulate our model for a typical example to show the applicability of the approach.     

Amplification of optical delay by use of matched linearly chirped fiber Bragg gratings

We describe the use of a matched linearly chirped fiber Bragg grating (FBG) pair as a key element in an adjustable optical delay line. This delay line has the unique property that the achievable optical group delay is orders of magnitude greater (factor of 10(2) in our experiment) than the actual physical displacement. We demonstrate operation of such an optical delay line over a delay range of 3.5 mm using a pair of matched 1300-nm chirped FBGs with a bandwidth of 20 nm each.