Stefano Vecchio

Kinetic analysis of thermal decomposition for penicillin sodium salts: Model-fitting and model-free methods

A kinetic study on decomposition processes of some penicillin salts was carried out. Both isothermal and dynamic thermogravimetric curves were used. As expected by their complex structures, several steps with different energies were involved in decomposition processes. Model-fitting and -free kinetic approaches were applied to nonisothermal and isothermal data. The kinetic triplet (f(alpha),A and E(a)) related to model-fitting method that defines a single step reaction resulted to be at variance with the multi-step nature of salts-decomposition. The model-free approach represented by the isothermal and nonisothermal isoconversional methods, gave different dependencies of the activation energy on the extent of conversion. The complex nature of the multi-step process of the studied compounds was more easily revealed using a broader temperature range in nonisothermal isoconversional method. The failure in the model-fitting method did not allow calculating shelf life and half-life times.

Thermal stability of disodium and calcium phosphomycin and the effects of the excipients evaluated by thermal analysis.

In the present study, Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC) are simultaneously applied to determine the thermal properties of two antibiotic salts, disodium and calcium phosphomycin, used either pure or in association with several excipients. This study was carried out kinetically as well by mathematical elaboration of the TG curves performed according to an isothermal procedure applied at different fixed temperatures. Kinetic parameters showing agreement with those produced by the isothermal method were also obtained by means of a non-isothermal method using a dynamic TG curve alone. The main aims of the work were to provide reliable kinetic parameters (kinetic constant k, activation energy E(a) and pre-exponential factor A) to evaluate the thermal stability of phosphomycin salts in the presence and absence of the excipients generally contained in the phosphomycin-based pharmaceutical forms available on the market, and to obtain information concerning compatibility towards the active components. These kinetic parameters were then used to extrapolate shelf-life and half-life values at room temperature for pure active components in the solid state and for their pharmaceutical derivatives.

The use of thermoanalytical techniques in the characterization of ancient mortars

Abstract Using different techniques (TG/DTA, XRD and chemical analysis), a comparative investigation on calcitic and dolomitic mortars, from two different Italian buildings of the 11th and 14th centuries, has been performed. By correlating the thermal effects and the steps in the TG curves, it has been possible to reach a semi-quantitative evaluation of the binders in both types of mortars, the results being in good agreement with the chemical data, and to explain the influence of the other components on the thermal behaviour of such complex systems.

Thermal analysis and health safety

Hardwood dust is a human carcinogen; upon inhalation, it can cause sinonasal adenocarcinoma. Softwood, on the other hand, is only suspected of carcinogenic properties. However, the toxicology-based recommended exposure limits for hardwood and softwood dust in working environments have been derived identically. While it is very simple to distinguish the wood by morphological evaluations, the wood dust produced in working activities does not allow differentiation. Thermal analysis, especially thermogravimetry, was applied to evaluate the different characteristic thermal profile of standard hardwood and softwood dusts. The different TG and DTG traces allow to propose thermogravimetry as a new tool to distinguish and quantify the different dust origin.

Isopropenyl acetate, a remarkable, cheap and acylating agent of amines under solvent- and catalyst-free conditions: a systematic investigation

Isopropenyl acetate was proved to be an efficient reagent for acetylation of amine in the absence of solvent and catalyst. The corresponding acetamides were obtained in very high yields without any purification.

Compatibility between active components of a commercial drug.

A thermal and a kinetic analysis on the decomposition processes of a commercial drug named diamplicil (AD), obtained by an antibiotic combination of ampicillin (A) and dicloxacillin (D), have been carried out to find their thermal stability. The DSC/TG curves of this commercial drug were compared with those of its active components and an excipient, the magnesium stearate (M). Kinetic study was carried out using both isothermal and dynamic TG curves. Decomposition mechanisms for both active components and commercial drug tested were not found. The kinetic data obtained by the non-isothermal isoconversional method showed that D component causes a decrease of the kinetic stability of the active A component. Additive magnesium stearate does not decrease the stability of the two components. Moreover, storage time values at room temperature were calculated.

Multi-step decomposition processes for some antibiotics. A kinetic study

Abstract In the present study, a kinetic analysis on decomposition processes of some oxacillin salts (oxacillin, cloxacillin and dicloxacillin) was carried out to identify their kinetic parameters. As expected by their complex structures, several steps with different activation energies occurred in the decomposition processes. The application of the model-fitting kinetic method to multi-step decomposition process results to be unsuitable for the non-isothermal data. As far as isothermal data are concerned this method gives rises to more reliable results which, however, are likely to conceal the kinetic complexity. The model-free approach represented by isothermal and non-isothermal isoconversional methods, gives different dependencies of the activation energies as a function of the extent of conversion and allows detecting multi-step processes over a wide temperature range.

New investigation of the isothermal oxidation of extra virgin olive oil: determination of free radicals, total polyphenols, total antioxidant capacity, and kinetic data.

As a follow-up of the research programs carried out by our group concerning the artificial isothermal rancidification process in extra virgin olive oil (EVOO), in the present work the trends of both the total antioxidant capacity and the total polyphenols concentration as well as the main kinetic parameters of the process during the thermal oxidation of EVOO were studied and compared. In addition, the possibility of evaluating the increase in radicals concentration during the thermal oxidation process using a superoxide dismutase biosensor was also studied. The present investigation concerning this important food product is highly topical as it refers to the state of alteration of the EVOO used for cooking or frying, as a function of the temperature reached.

Kinetic Analysis of Single or Multi-Step Decomposition Processes; Limits introduced by statistical analysis

A kinetic study on decomposition processes of some penicillin and some commercial drugs was carried out. As expected by the complex structures of penicillins, several steps with different activation energies occurred in their decomposition processes.Model-fitting and model-free kinetic approach were applied to non-isothermal and isothermal data.In the model-fitting methods the kinetic triplets (f(α), A and Ea) that defines a single reaction step resulted in being at variance with the multi-step nature of penicillins decomposition.The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation energies on the extent of conversion. The complex nature of the multi-step process of the studied compounds was more easily revealed using a broader temperature range in non-isothermal isoconversional method. The failure in the model fitting method did not allow calculating storage times. Model-fitting and model-free methods, both isothermal and non-isothermal, showed that F1 mechanism is able to describe decomposition processes for drugs (having Phosphomycin salts as active component) for which a single decomposition process occurs. Statistical analysis allowed us to select reliable kinetic parameters related to the decomposition processes for these last compounds. This procedure showed that the values obtained by extrapolation, outside the temperature range where the processes occurred must be used with caution. Indeed half-life and shelf-life values, commonly extrapoled at room temperature, seemed to be unrealistic.

Application of TA and Kinetic Study to Compatibility and Stability Problems in Some Commercial Drugs. Remarks on statistical data

A thermal analysis and kinetic study on decomposition processes of some commercial drugs have been carried out to find their thermal stability.DSC/TG curves of some commercial drugs were compared with those of their active components, the excipients, the active component/excipient and the excipient/excipient mixtures.A kinetic study was carried out using both isothermal and dynamic TG curves. Both active components and commercial drugs tested show a first order decomposition mechanism. The kinetic data showed that excipients cause a decrease of the kinetic stability of the active components.Statistical analysis allowed us to select reliable kinetic parameters related to decomposition processes. This procedure showed that the values obtained by extrapolation,outside the temperature range where the processes occurred must be used with caution. Indeed half-time and shelf-time values, commonly used at room temperature, seemed to be unrealistic.