Investigation and comparison of pristine/doped BN,AlN, and CN nanotubes as drug delivery systems for Tegafur drug: a theoretical study

Structural Chemistry - In this work, the potential of BN, AlN, and CN nanotubes as the drug delivery systems of Tegafur (TG) was investigated by the density functional theory (DFT). The doping...     

UV spectrophotometric study of the kinetics and mechanism of the reactions between triphenylphosphine, dialkyl acetylenedicarboxylates and NH-acid

To determine the kinetic parameters of the reactions between triphenylphosphine and dialkyl acetylenedicarboxylates in the presence of an NH-acid, such as 2,3-di-hydroxybenzaldehyde, the reactions were monitored by UV spectrophotometry. The second order fits were automatically drawn and the values of the second order rate constants (k₂) were calculated using standard equations as part of the program. The dependence of the second order rate constant (lnk₂) on the reciprocal temperature was in agreement with the Arrhenius equation, in the temperature range studied, providing the relevant plots to calculate the activation energy of all reactions. Furthermore, we evaluated the effects of solvent, structure of different alkyl groups within the dialkyl acetylenedicarboxylates, and their concentration on the rates of reactions. The proposed mechanism was confirmed by experimental results and steady-state approximation. The first step (k₂) of the reaction was recognized as the rate determining step on the basis of experimental data.     

Kinetic Investigation of the Reaction between Triphenylphosphine,Dialkyl Acetylenedicarboxylate,and Carbazole by the UV Spectrophotometry Technique

The major objectives of the work undertaken were to carry out kinetic studies of the reaction between triphenylphosphine and dialkyl acetylenedicarboxylate in the presence of strong NH-acids, such as carbazole. To determine the kinetic parameters of the reaction, it was monitored by the UV spectrophotometer technique. The values of the second order rate constant (k ₂ ) were automatically calculated using standard equations within the program when the second order fits of the mentioned reactions were automatically drawn by the software associated with a Cary UV spectrophotometer model Bio-300 at an appropriate wavelength. At the temperature range studied, the dependence of the second order rate constant (Ln k) on reciprocal temperature was in agreement with the Arrhenius equation. This provided the relevant plots to calculate the activation energy of all reactions. Furthermore, useful information was obtained from studies of the effect of solvent and different alkyl groups within the dialkyl acetylenedicarboxylates on the rate of reactions.     

Theoretical study of the mechanism of stable phosphorus ylides derived from 2-aminothiophenol in the presence of different dialkyl acetyelenedicarboxylates

A stepwise reaction mechanism between triphenylphosphine 1 and dialkyl acetylenedicarboxylates 2 in the presence of a SH-acid, such as 2-aminothiophenol 3, has been investigated theoretically with B3LYP method using 6-311++G(d,p) basis set. Potential energies of all structures participating along the reaction path have been evaluated. For all the reactions investigated, the first step was recognized to be the rate-determining step. Quantum mechanical calculations clarified the existence of reaction product as a mixture of two E- or Z-geometrical isomers, and indicate which one of them represents the major form. The effect of subsituated alkyl groups on the potential energy surfaces was investigated. Also, the natural bond orbital method was applied for better understanding the molecular interactions.     

Further Insight into the Mechanism of the Novel Multicomponent Reactions Involving Isoquinoline and Dimethyl Acetylenedicarboxylate in the Presence of 3‐Methylindole: Theoretical and Experimental Approach

The kinetics of the reactions among isoquinoline, dimethyl acetylenedicarboxylate, and 3‐methyl indole (as NH‐acid) was studied using UV spectrophotometry. The overall rate constant (k_ov) was evaluated from the slope of the plot of k_obs versus reactant concentration. A large deal of useful information was obtained from the study of the effects of solvent, temperature, and reactants and concentration on the reaction rates. Based on experimental data and theoretical concepts, the reaction's first step (k₁) was recognized as the rate‐determining step. Theoretical studies were performed to evaluate potential energy surfaces of all components participated in the reaction mechanism. Furthermore, the proposed mechanism was confirmed by the obtained results. The probable reaction path and product configuration were suggested based upon the theoretical results.     

NMR study,theoretical calculations for assignment of the Z‐ and E‐isomers,and kinetics investigation of stable phosphorus ylides involving a 2‐mercapto‐4,6‐dimethyl pyrimidine

In the present work, NMR, theoretical, kinetics, and mechanism investigations were undertaken for a one‐pot condensation reaction between 2‐mercapto‐4,6‐dimethyl pyrimidine and dialkyl acetylenedicarboxylates in the presence of triphenyphosphine containing novel stable phosphorus ylides 4a–c . Herein, theoretical calculations have been employed for assignment of the most stable isomers (Z or E) of phosphorus ylides 4a,c by natural population analysis, atoms in molecules methods, and CHelpG keyword, in which E‐ 4(a, c) are more stable forms as the majors. The ¹H, ¹³C, and ³¹P NMR data of these ylides are consistent with results obtained from theoretical calculations. In addition, kinetic investigation of new ylides was undertaken by ultraviolet spectrophotometry. Useful information was obtained from studies of the effect of solvent, structure of reactants (different alkyl groups within the dialkyl acetylenedicarboxylates), and also the concentration of reactants on the rate of reactions. The proposed mechanism was confirmed according to the obtained results and a steady‐state approximation, and the first step (k₂) of the reaction was recognized as a rate‐determining step on the basis of the experimental data. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:462–474, 2010; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20632     

Theoretical study on mechanism of reaction between tert-butyl isocyanide and dimethyl acetylenedicarboxylate in presence of ethanethiol or thiophenol

Research on Chemical Intermediates - The mechanism of the multicomponent reaction between tert-butyl isocyanide and dimethyl acetylenedicarboxylate in presence of ethanethiol and thiophenol (as...