Calorimetric investigation of Al–Zn alloys using Oelsen method

The results of calorimetric study of binary Al–Zn system done according to the Oelsen thermodynamic method are presented in this paper. Main thermodynamic properties, including activities, activity coefficients, partial/integral molar Gibbs excess, and mixing energies were determined at 1,000 K. Positive deviation from Raoult law was noticed, with minimal values of ΔG ^M about ?3 kJ mol^?1 and maximal values of ΔG ^E about +2 kJ mol^?1. The energetics of mixing in liquid Al–Zn alloys has been analyzed through the study of concentration fluctuation in the long-wavelength limit, and weak affinity between Al and Zn atoms in the system was observed. Differential thermal analysis and light optic microscopy were applied in the frame of characterization of investigated binary alloys and phase diagram examination, and the results obtained were in accordance with available literature data.     

Synthesis of 1-(2-Oxoalkyl)-2-acyltetrahydro-isoquinolines by α-Amidoalkylation of Methylene Active Carbonyl Compounds with N-Acyliminium Intermediates

Intermolecular α-amidoalkylation reaction of methylene active carbonyl compounds with N-acyliminium salts of 3,4-dihydroisoquinolines and acyl chlorides has been used for synthesis of 1-(2-oxoalkyl)-2-acyltetrahydroisoquinolines.     

Infinite dimensional time varying systems with nonlinear output feedback

This paper deals with time-varying systems on Banach-spaces with unbounded input and output operators and considers nonlinear dynamical perturbations of the output feedback type. We develop an analysis which would establish existence conditions for the perturbed equations and investigate the robustness of stability for this wide class of perturbations.     

Polarographic investigation of the Cu(II) complex with ampicillin

The complex of Cu(II) ion and ampicillin is investigated polarographically in aqueous medium, at pH = 6, an ionic strength = 0.2, and room temperature. The stoichiometric ratio of Cu(II) and ampicillin in the complex, and the stability constant, logK = 5.1, were determined by Lingane's method.     

Study of the reactions of cisplatin with ranitidine and nizatidine by means of 1H NMR spectroscopy in D2O

The reactions of cisplatin with nizatidine and ranitidine were studied in D₂O at pD 7.4 and 298 K by means of ¹H NMR spectroscopy. The second order rate constants, k ₂, for the reaction of cisplatin with nizatidine is (2.71 ± 0.11) × 10⁻⁴ M ⁻¹ s⁻¹, and for the reaction with ranitidine (6.72 ± 0.17) × 10⁻⁴ M ⁻¹ s⁻¹. The reactions of nizatidine and ranitidine were also studied with other Pd(II) and Pt(II) complexes. The set of the complexes was selected because of their difference in reactivity, steric hindrance, and binding properties. Correspondence: Prof. Dr. Živadin D. Bugarčić, Faculty of Science, University of Kragujevac, Radoja Domanovića 12, 34000 Kragujevac, Serbia.     

Integrity of liposomes in presence of various formulation excipients, when dispersed in aqueous media and in hydrogels

The integrity of liposomes when dispersed in presence of various common formulation excipients is studied. Additionally, the effect of the excipients on the release of calcein from the same liposomes when dispersed in hydrogels is investigated and the results of the two sets of experiments are compared. Propyleneglycol (PG), transcutol CG (TR), cremophor EL (CR) and labrafac hydro WL 1219 (LB) are used at 10 or 25% (v/v) and the retention of liposome encapsulated calcein is followed for 24 or 48 h periods. Calcein entrapping multilamellar liposomes composed of phosphatidylcholine (PC) or 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) with or without addition of different amounts of cholesterol (Chol) were prepared by the thin film hydration method.

Experimental results reveal that liposomes are affected more by the excipients in the order: LB > CR > PG  TR. Particularly LB and in some cases also CR result in rapid release of most or the entire vesicle encapsulated dye. Addition of Chol in both PC and DSPC liposomes results in substantial increase of vesicle integrity in all cases. Concerning the release of calcein form the liposomal gels, from DSPC/Chol (1:1) liposomal gels calcein release was not affected by addition of 25% of TR or PG in all gels studied, but LB caused a significant increase in calcein release. However, from PC-liposomal gels even TR and PG (at 25%), increases calcein release.

Conclusively, the results of this study suggest that liposomes are protected from excipients when dispersed in gels compared to aqueous media. This should be taken into account when liposomal drug formulations are designed.     

Spectroscopic investigations and crystal structure from synchrotron powder data of the inclusion complex of beta-cyclodextrin with atenolol

Inclusion complexes of atenolol with beta-cyclodextrin (beta-CD) in aqueous solution have been investigated with (1)H NMR and UV-vis spectroscopy. The stoichiometry of this inclusion complex was established to be equimolar (1:1) and its stability constant was determined by UV-vis spectroscopy. The crystal structure of the beta-CD-atenolol (1:1) inclusion compound has been solved from synchrotron powder diffraction data using direct-space search techniques. The crystal structure model and (1)H NMR data are in good agreement and, with support of Hyperchem MM+ molecular dynamics results, suggest which protons are likely to be involved in the inclusion process that leads to the supramolecular architecture of this guest-host complex.     

Combined X-ray diffraction and QM/MM study of the Burkholderia cepacia lipase-catalyzed secondary alcohol esterification

To understand the origin of high enantioselectivity of Burkholderia cepacia lipase (BCL) toward secondary alcohol, (R,S)-1-phenoxy-2-hydroxybutane (1), and its ester (E1), we determined the crystal structure of BCL complexed with phosphonate analogue of S-E1 and accomplished a series of MM, MC, and QM/MM studies. We have found that the inhibitor in the S configuration binds into the BCL active site in the same manner as the R isomer, with an important difference: while in case of the R-inhibitor the H-bond between its alcohol oxygen and catalytic His286 can be formed, in the case of the S-inhibitor this is not possible. Molecular modeling for both E1 enantiomers revealed orientations in which all hydrogen bonds characteristic of productive binding are formed. To check the possibility of chemical transformation, four different orientations of the substrate (two for each enantiomer) were chosen, and a series of ab initio QM/MM calculations were accomplished. Starting from the covalent complex, we modeled the ester (E1) hydrolysis and the alcohol (1) esterification. The calculations revealed that ester release is possible starting with all four covalent complexes. Alcohol release from the BCL-E1 complex in which the S-substrate is bound in the same manner as the S-inhibitor in the crystal structure however is not possible. These results show that the crystallographically determined binding modes should be taken with caution when modeling chemical reactions.     

Monte Carlo-based QSAR modeling of dimeric pyridinium compounds and drug design of new potent acetylcholine esterase inhibitors for potential therapy of <Emphasis Type="Italic">myasthenia gravis</Emphasis>

The Monte Carlo method was used for QSAR modeling of dimeric pyridinium compounds as acetylcholine esterase inhibitors. QSAR model was developed for a series of 39 dimeric pyridinium compounds. QSAR models were calculated with the representation of the molecular structure by the simplified molecular-input line-entry system. One split into the training and test set have been examined. The statistical quality of the developed model is very good. The calculated model for dimeric pyridinium derivatives had following statistical parameters: r ² = 0.9477 for the training set and r ² = 0.9332 the test set. Structural indicators considered as molecular fragments responsible for the increase and decrease in the inhibition activity have been defined. The computer-aided design of new dimeric pyridinium compounds potential acetylcholine esterase inhibitors with the application of defined structural alerts has been presented.