E. Utzig

THERMAL ANALYSIS OF CALIX(4)RESORCINARENE COMPLEXES WITH SECONDARY AND TERTIARY AMINES

Tetra-n-undecylcalix[4]resorcinarene forms solid adducts with secondary and tertiary amines. Thermal decomposition of these complexes was investigated by means of thermogravimetry (TG) and differential scanning calorimetry (DSC). It was found that deamination of complexes occurs as multi-step process. The stoichiometry of complexes was evaluated on the basis of TG studies and total heats of deamination were calculated from DSC measurements.

Thermochemical Investigation of Some Selected Solvates of Calix[4]resorcinarene

Lipophilic calix[4]resorcinarene derived from lauryl aldehyde forms stable crystalline solvates with a range of organic solvents: acetone, 1,4-dioxane, methylethylvketone, dimethylformamide, dimethylacetamide, N-methylpyrrolidinone, butyronitrile, methanol, 1,2-dimethoxybenzene and acetonitrile. The composition and thermal stability of these solvates was followed by thermogravimetric method, indicating a stoichiometry ranging from 1 to 3 (calixresorcinarene/solvent). The activation energy was evaluated for the selected solvates. Molecular modelling, using Hyperchem 5.0 software, was applied to the selected solvates.

Complexation of peptides with crown ethers: Part 1. Composition and thermal behaviour of compounds consisting of oligopeptides and some crown ethers

Abstract Crystals of the complexes 18-crown-6/diglycine, 18-crown-6/diglycine/water, 18-crown-6/triglycine, 18-crown-6/ l -α-alanyl- l -α-alanine and 1,10-diaza-18-crown-6/diglycine/water were obtained. The thermal behaviour of these compounds was investigated by DSC and TGA methods. It was found that the anhydrous complexes have at least two physicochemical transitions in the range 320–470 K: melting of the complexes at 360–380 K and decomposition above 410 K. Two types of water, i.e. weakly and strongly bound with the complex, were observed on heating the hydrated complexes. The enthalpic and entropic changes of the melting process are discussed in terms of the cationic and anionic binding of the peptide molecule to crown ether.

Thermogravimetric study of water state in wheat starch gels obtained under high pressures

Wheat starch gels containing 56.0% of water were obtained during thermal gelatinization under isobaric conditions at different pressures ranging from 0.5 to 100 MPa. Thermogravimetric analysis allowed determination of pressure influence on water behavior in gel matrix. The vaporization rate indicated that water is released in two main steps. The first step corresponds to the diffusion of the water fraction (so‐called nonbound water) from the porous structure of the amylose gel located between partially swollen starch granules. However, the second step that appears at higher temperature is related to the desorption of water molecules (bound water), included in the swollen granules. It was observed that the most important influence of pressure on water partitioning in the starch gel took place over a pressure range from 0.5 to 10 MPa. The results obtained indicate that pressure is a thermodynamical parameter, which stabilizes the native state of starch granules.

Thermophysical and structural investigations of crystalline solvates based on tetraphenylporphyrin and its copper complex

Abstract The influence of temperature changes on the thermal and structural behaviour of crystalline solvates of tetraphenylporphyrin (H 2 TPP) with 1,4-dioxane and of tetraphenylporphyrin copper complexes (CuTPP) with benzene were investigated using thermogravimetry, differential scanning calorimetry and X-ray powder diffraction. Simultaneous application of thermal and structural techniques made it possible to observe the complex evolution of the desolvation processes. These techniques enabled: (a) the separation of the two crystalline phases appearing during the process, (b) the detection of changes of the symmetry of the crystal lattice of CuTPP crystalline solvate from monoclinic and triclinic, (c) the determination of the heat and activation energy of desolvation process, and (d) the observation of reversible thermal effects for H 2 TPP.

Heat Conduction Microcalorimeter for Thermokinetics and Titration Experiments

A heat conduction microcalorimeter with a sensitivity of 103 µV mW-1 and a vessel of 3 cm3 has been designed. The device is equipped with an automatic dosimeter, an original system for injection in titration experiments, and a PC for control, data recording and data analysis. The software allows the determination of (i) overall heat effects, (ii) thermokinetics, and (iii) changes in enthalpy and equilibrium constants in titration experiments.

Complexation of peptides with crown ethers. Part 2. Thermokinetic behaviour of hydrated compounds consisting of α-amino acids, peptides and 18-crown-6

Abstract Crystals of 11 hydrated complexes consisting of α-amino acids, dipeptides, tripeptides and 18-crown-6 were isolated. The composition and thermal behaviour of these compounds were investigated and the temperatures, heat effects and activation energies of different stages of their decomposition were determined using DSC and TG. After preliminary dehydration at 300–350 K, the compounds undergo decomposition in one or two stages. It was found that the thermokinetic characteristics of the complexes are very sensitive to their structural features.

Calorimetric Investigations of the Lipase-catalysed Hydrolysis of Acylated Acyclonucleosides

Thermal power accompanying the hydrolysis of mono- and bi-acylated acyclonucleosides:(R,S)-1-N-(1-O-acetyl-3-hydroxypropoxymethyl)-thymine (ThL),1-N-(1,3-di-O-acetylpropoxymethyl)-thymine (ThAc), and1-N-(1,3-di-O-acetylpropoxymethyl)-5-fluorouracil (FAc), catalysed by lipase from Candida Cylindracea (Rugosa) was investigated by isothermal heat conduction microcalorimetry. Changes of the thermal power in time and the total heat effects were determined in long-lasting measurements. Hydrolysis of these compounds was examined also by TLC.For all three esters the thermal power curves reveal both a relatively intensive and slow heat evolutions. It is suggested that this complexity results from a superposition of: (i) a stereospecific hydrolysis of the ester bond connected to the heterocyclic moiety by a chain endowed with an appropriate chirality, and (ii) a non-specific hydrolysis of another ester bond. A partial chemical degradation of reactants in the buffer was also observed.

Crystal engineering of cytidine and deoxycytidine sulphates. I. Preparation, and unusual properties.

Abstract From three possible simple salts of Cyd (dCyd)1 with H2SO4, we succeeded in preparation of only one type of a crystalline salt in which two monoprotonated cations: 2CydH+ (2dCydH+) pair with one sulphate dianion (SO2−4) (Fig.3)4. Attempts to obtain crystalline sulphates with dimeric hemi-cations and/or hydrogen sulphate anions completely failed. The presence or absence of 2′OH group drastically changes the thermochemical properties of Cyd and dCyd sulphates (Fig.4). Cyd sulphate undergoes rapid one-step thermal decomposition within the range 205–260°C with subsequent smoth further mass loss up to 340°C, whereas dCyd sulphate (Form A and B) undergoes a three stage thermal decomposition: I. 25–170°C, II. 170–230°C, III. 230–340°C. Clear differences in the DSC and TGA curves of both types of salt may reflect dissimilar mechanisms of their crystal structure decomposition. An extremely easy transformation of dCyd sulphates into the hydrochloride salt in the crystal phase was discovered. The reaction proceeds both in finely ground stoichiometric mixtures of 2dCydH+·SO2−4 + 2NaCl or KCl, and also in a nujol suspension of pure dCyd sulphate placed between NaCl plates. Similar transformation occurs also with KBr and leads to the crystalline dCyd hydrobromide which is isostructural to dCyd hydrochloride. Form A of dCyd sulphate, which contains methanol trapped in its crystal lattice, is particularly susceptible to the above transformation. Cyd sulphate undergoes transformation to hydrochloride and hydrobromide salts by a few orders of magnitude slower. These unidirectional ion exchange reactions proceed quantitatively in crystalline phase only, showing the significance of crystal structures of nucleosides and their salts. Unusual properties of sulphate counter anions may be exploited for a controlled modulation of reactivity of nucleosides. The unidirectional ion exchange reactions take place in 100 % in crystalline phase only , revealing the significance of information coded in crystal structures of nucleosides.

Thermokinetic Studies of Porphyrin Complexation in Non-Aqueous Solutions by Heat Conduction Microcalorimetry

Porphyrins are known as unique ligands forming some of the most stable complexes with various metal ions. In this work the thermokinetic investigations of complex formation of tetraphenylporphyrins with copper(II) acetate were carried out in two anhydrous organic solvents: acetic acid and DMF at 25°C. Measurements were performed in a heat conduction microcalorimeter [7] adapted for non-aqueous solvents. Total heat effects and thermokinetics were determined. The results were discussed together with spectrophotometric data.Taking into account the high stability of metalloporphyrin complexes, the heat of their formation is rather small (in the case of acetic acid ΔQ=32.7±1.2 kJ mol−1, for DMF ΔQ=26.2±1.3 kJ mol−1). Such result can suggest that: 1) the stability of complexes is influenced strongly by an entropy factor, 2) the complexation involves breaking of the NH-bond in the porphyrin coordination centre, accompanied by high consumption of energy.