Salvatore Fasone

A calorimetric study of the different thermal behaviour of DNA in the isotropic and liquid-crystalline states

Abstract A difference between the thermal behaviour of the isotropic and liquid-crystalline state of sonicated DNA in aqueous salt solution containing poly(ethyleneglycol)(PEG) has been demonstrated. On cooling, a different degree of renaturation of thermally denaturated DNA is observed between samples which form the isotropic state and more concentrated samples which on cooling form the cholesteric state.

The effects of scan rate and protein concentration on DSC thermograms of bovine superoxide dismutase

Abstract DSC thermograms of bovine CuZn superoxide dismutase (BSOD) have been recorded at different scan rates and protein concentrations in order to clarify the process of its unfolding. The lack of calorimetric reversibility made direct thermodynamic analysis of the thermograms impossible. The study of the effect of the scan rate on the shape of the heat capacity (Cp) profiles of BSOD has allowed the calculation of the apparent activation energy (Eapp) for the whole irreversible process. Extrapolation of the excess heat capacity curves (Cpexc) to infinite scan rate has provided the scan-rate-independent part of the thermograms. The protein concentration effect is explained by a change in molecularity that takes place before the kinetically-controlled step. The data collected suggest that, on thermal denaturation, BSOD dissociates during the thermally-induced transitions of the protein; this is followed by a kinetically controlled, exothermic step which is responsible for the global irreversibility of the entire process.

AN ALTERNATIVE APPROACH IN THE STRUCTURE-BASED PREDICTIONS OF THE THERMODYNAMICS OF PROTEIN UNFOLDING

A new approach for a first-order prediction of the thermodynamic properties of small globular proteins has been developed. The method put forward here has been shown to be successful in predicting, within acceptable margins of uncertainty, the denaturational heat capacity changes of a given protein if its amino acid composition is known. If compared with other models this method has the following advantages: (1) no details about the three-dimensional structure of the protein are required; (2) comparison with the thermodynamic properties of small model compounds is not necessary; (3) the temperature dependence of the denaturational heat capacity change is taken into account. Moreover, the equations developed have allowed us to point out the errors that can be made if the temperature-dependence of the denaturational heat capacity change is not taken into account in the calculation of the unfolding thermodynamic functions.

Transition entropies and mesomorphic behaviour of p-n-alkoxybenzyliden-p′-butoxyanilines

Abstract Calorimetric data on the mesogenic homologous series H 9 C 4 OC 6 H 4 NCHC 6 H 4 OC n H 2 n + 1 are presented. Trends in the nematic-isotropic liquid transition temperatures, enthalpies and entropies are briefly discussed. A remarkable polymorphism is evidenced in several compounds. The importance of the thermal history of the samples in relation to their thermal behavior is shown.

Transition entropies and mesomorphic behaviour of p-n-alkoxy-benzyliden-p′-ethoxyanilines

Abstract Calorimetric data on the nematogenic homologous series H 7 C 3 -O-C 6 H 4 -NCH- C 6 H 4 -O-C n H 2 n +1 are presented. Trends in the nematic-isotropic transition temperatures. enthalpies and entropies are briefly discussed. The importance of the thermal history of the system in relation to its thermal behaviour is evidenced.

A combined scanning dilatometric and differential scanning calorimetric study of the thermal unfolding of bovine serum albumin

Abstract Here we report the first results of combined scanning calorimetric and dilatometric investigations carried out on bovine serum albumin in aqueous solution at 30–97°C. Comparison of experimental data obtained by the two techniques suggests a “steps” model for the thermal denaturation of the protein. Moreover, the results in the high-temperature region, after aggregation of the unfolded chain, show a subsequent, previously unreported, spatial rearrangement of the polypeptidic chain network, during which the order of the system increases with an increase in temperature. The results indicate that scanning dilatometry is a very useful method of detecting phenomena which are not seen by calorimetry. The results also demonstrate the determinant role of water in the unfolding process.

Calorimetry of homologous p-n-alkoxybenzyliden-p'-n-pentyloxyanilines

Abstract Calorimetric data are presented for the homologous p-n -alkoxybenzyliden- p′-n -pentyloxyanilines. The solid-state polymorphism is discussed in terms of free energy-temperature diagrams. Trends in the nematic-isotropic liquid transition temperatures, enthalpies and entropies are discussed briefly.

On the experimental validity of recent developments of solvent-shift theory

Abstract The validity of the equations reported by Amos and Burrows on solvent shifts has been tested in several solvents for seven different symmetrical compounds. The results confirm that their approximation introduced to simplify the interpretation of experimental data generally is not valid.

Calorimetric evidence for different structural roles of Glu132 and Glu133 residues in human superoxide dismutase

DSC measurements have been performed on human superoxide dismutase (HSOD) and on its mutants on the Glu132 and Glu133 residues which have been alternatively modified to a Gln residue. In both cases, the substitution has dramatic effects on the thermal denaturation of HSOD as evidenced by the calorimetric experiments. In particular, replacement of the Glu residue in position 132 seems to have a greater effect on the stabilization of the protein, highlighting the key role played by this position. All the experimental data are qualitatively explained in terms of interactions between the groups which form the active site channel.

Mesomorphic behaviour of forty benzylidene-aniline-p,p′-dialkoxy derivatives

Abstract The transition temperatures of forty mesomorphic homologous benzylidene-aniline- p,p ′-dialkoxy derivatives are reported. The transition diagrams show different paths for heating and cooling for most of the compounds. Moreover, some compounds with higher length-breadth ratios, show very complicated thermal cycles with some monotropic phases. In any case, the clearing temperatures ( T c ) alternate within every series. The experimental data are discussed briefly and some general considerations on the structure and mesomorphic behaviour are suggested.