Saša Ž. Drmanić

Crystallization Behavior of Alkoxy-Derived Cordierite Gels

Alkoxy-derived cordierite gels were synthesized from tetraethylorthosilicate (TEOS), aluminum isopropoxide (Al(OPri)3), and magnesium ethoxide (Mg(OEt)2). TEOS was partially hydrolyzed at molar ratios H2O/TEOS = 1.2, in the presence of hydrochloric acid as a catalyst, HCl/TEOS = 0.1. Aluminum and magnesium alkoxides were added successively or as a double alkoxide. Phase transformations occurring in the gel were studied by differential thermal analysis, x-ray diffractometry, and Fourier-transform infrared spectroscopy. In all cases, μ-cordierite crystallized at similar temperatures (950–1000°C) with small amounts of spinel, which confirms dominant influence of the optimal conditions for partial hydrolysis of TEOS on the gels homogeneity. The transformation of μ- into α-cordierite began at about 1100°C. Broadening of diffraction peaks and appearance of new bands in the FT IR spectra confirmed the transformation of α- into modulated β-cordierite at temperatures above 1300°C. Differential thermal analysis under nonisothermal conditions also proved homogeneous nucleation with constant rate and three-dimensional crystallite growth during μ-cordierite crystallization. The overall activation energy of the crystallization of μ-cordierite is 580 ± 81 kJ/mol.

Synthesis of nanostructured mullite from xerogel and aerogel obtained by the non-hydrolytic sol-gel method

Abstract Synthesis and nanostructure evolution of mullite (3Al2O3.2SiO2) from xero- and aerogels, obtained by the non-hydrolytic sol-gel process are described. Mullite crystallization and gel nanostructure evolution after heat treatment were studied by differential-thermal, x-ray diffraction, infrared and thermomicroscopic analysis as well as by scanning electron microscopy. Crystallization of mullite from both gels starts at 900 °C and further increase in temperature increases the size of crystallites formed from 32 to 100 nm and 12 to 20 nm in the case of xero- and aerogels, respectively. Accelerated sintering of aerogels in the temperature range 900 to 1000° C is a consequence of the viscous flow of the amorphous SiO2 phase.

Effect of Substituteents on the 1H and 13C NMR Chemical Shift of trans-Pyridineacrylic and Substituted trans-Cinnamic Acids

The principles of linear free energy relationships were applied to the 1 H nmr and 13 C nmr chemical shifts induced by substituents in three isomeric trans-pyridineacrylic and substituted trans-cinnamic acids. The data for the carboxy proton chemical shift correlated well with the simple Hammett equation. Tafts dual substituent parameter equation was used for the interpretation of the balance of the inductive and resonance effects through the ethylenic bond for the C α and C β 13 C nmr shift. Using the nuclear Overhauser method, the conformation of the carboxylic group in 2-pyridineacrylic acid was determined, and its unexpected behaviour in both 1 H nmr chemical shifts;and in the previously studied reaction with diazodiphenylmethane was interpreted by the increased electron density in the π-electronic system favoured by the orbital symmetry of the part of the acid molecule

Preparation of α-TCP Cements from Calcium Deficient Hydroxyapatite Obtained by Hydrothermal Method

In this paper the synthesis of bioactive cement based on α-Ca3(PO4)2 (α-TCP) and calcium deficient hydroxyapatite (CDHAp), obtained by hydrothermal method from CaCl2, EDTA, NaH2PO4·12H2O and urea at 160oC, was described. According to the results of DTA, SEM, X-ray and FTIR analyses performed in this investigation, it is shown that CDHAp is transformed to β- TCP at 780oC, and to α-TCP at 1400oC. The hardening of the samples, prepared from the mixture of α-TCP and 2.5 % solution of Na2HPO4, in simulated body fluid at 37oC, was followed by the microstructure changes.

Transmission of electronic effects through the vinyl group. Reactivities of the (E)-α-4-substituted phenyl-β-pyridine acrylic acids

The reactivities of a series of 18 (E)-α-4-substituted phenyl-β-(3N and 4N)pyridineacrylic acids, with a wide range of substituent effects, were investigated in their reaction with diazodiphenylmethane, in dimethylformamide at 30°C, by the known spectrophotometric method. The Hammett equation in its original form has been applied to the results, using the sum of substituent constants from the both aromatic nuclei, but the overall correlation was only fair. Better insight into the transmission of substituent effects was obtained using Tafts Dual Substituent Parameter (DSP) method, where it was possible to distinguish the contributions from the inductive and resonance effects of the substituents

Detailed solvent, structural, quantum chemical study and antimicrobial activity of isatin Schiff base

The ratios of E/Z isomers of sixteen synthesized 1,3-dihydro-3-(substituted phenylimino)-2H-indol-2-one were studied using experimental and theoretical methodology. Linear solvation energy relationships (LSER) rationalized solvent influence of the solvent-solute interactions on the UV-Vis absorption maxima shifts (νmax) of both geometrical isomers using the Kamlet-Taft equation. Linear free energy relationships (LFER) in the form of single substituent parameter equation (SSP) was used to analyze substituent effect on pKa, NMR chemical shifts and νmax values. Electron charge density was obtained by the use of Quantum Theory of Atoms in Molecules, i.e. Baders analysis. The substituent and solvent effect on intramolecular charge transfer (ICT) were interpreted with the aid of time-dependent density functional (TD-DFT) method. Additionally, the results of TD-DFT calculations quantified the efficiency of ICT from the calculated charge-transfer distance (DCT) and amount of transferred charge (QCT). The antimicrobial activity was evaluated using broth microdilution method. 3D QSAR modeling was used to demonstrate the influence of substituents effect as well as molecule geometry on antimicrobial activity.

A study of the barrier properties of polyethylene coated with nanocellulose/magnetite composite film

The morphological, thermal and barrier properties of low-density polyethylene/polycaprolactone-modified nanocellulose hybrid materials were investigated in this study. Nanocellulose/magnetite (NC-Fe3O4) nanocompo- site and maleic acid functionalized NC/magnetite (NCMA-Fe3O4) nanocom- posite were prepared and used as fillers at various concentrations (5, 10 and 15 wt. %) in the polycaprolactone (PCL) layer. PE was coated with a PCL/NC/ /magnetite layer. The addition of the filler did not unfavorably affect the inherent properties of the polymer, especially its barrier properties. Oxygen permeation measurements showed that the oxygen barrier properties of mag- netite enriched PCL film were improved due to the chemical activity of the added material. The highest level of the barrier capacity was observed for PE samples coated with a PCL-based composite with NCMA-Fe3O4 micro/nano- filler, which implies a significant contribution of the surface modification of the nanocellulose with maleic anhydride residue to the improved barrier pro- perties.

Kinetics of the Reactions of Pyridine and Pyridine- N -oxide Carboxylic Acids and Substituted Benzoic Acids with Diazodiphenylmethane in Various Alcohols

Solvent effects on the reactivity of pyridine and pyridine-N-oxide carboxylic acids and p-substituted benzoic acids in their reaction with diazodiphenylmethane (DDM) in alcohols have been investigated and the rate constants interpreted by Hammett parameters using multiple regression analysis; the influence of solvents on the reactivity of these acids with DDM has not been reported previously.