The effects of gamma rays upon monohydrated and anhydrous asparagine: a DSC study in sealed pans
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The effects of gamma rays upon monohydrated and anhydrous asparagine: a DSC study in sealed pans M. Contineanu • Ana Neacsu • Iulia Contineanu • Stefan Perisanu
Received: 23 March 2012 / Published online: 18 August 2012 Akade´miai Kiado´, Budapest, Hungary 2012
Abstract Non-irradiated and gamma irradiated monohydrated (L AsnH2O) and anhydrous (L Asn) asparagines, in solid state, were studied by means of DSC. The samples were irradiated at room temperature with gamma radiations using a 137Cs source. The exposure doses ranged between 1 and 10 kGy. All samples were scanned in sealed pans, from room temperature to a temperature beyond the melting point. The DSC scans of L AsnH2O samples in sealed crucibles revealed the presence of two dehydration processes and one of decomposition and only decomposition in the case of L Asn. The influence of gamma irradiation consisted in decreasing the enthalpy of dehydration and of decomposition. A decomposition mechanism is proposed. Keywords Gamma rays DSC Asparagine monohydrate Anhydrous asparagine Sealed crucible Decomposition
M. Contineanu Faculty of Chemistry, University of Bucharest, 4-12 Regina Elisabeta Blvd, 030018 Bucharest, Romania e-mail: [email protected] A. Neacsu (&) I. Contineanu Institute of Physical Chemistry, ‘‘I. Murgulescu’’, 202 Spl. Independentei, 060021 Bucharest, Romania e-mail: [email protected] I. Contineanu e-mail: [email protected] S. Perisanu Faculty of Applied Chemistry and Material Science, University Politehnica Bucharest, 1 Polizu Str, 011061 Bucharest, Romania e-mail: [email protected]
Introduction The present paper is a continuation of previous study on the effect of c rays upon monohydrated asparagine by DSC [1]. Working conditions were changed in that we performed DSC measurements with sealed crucible which significantly modified the behavior of monohydrated asparagine on heating. We have performed the same type of measurements with anhydrous asparagine too. Asparagine is one of the 20 most common natural amino acids in living organisms. It is stable in both hydrated (with one water molecule) and anhydrous forms, and contains carboxamide as the side chain functional group. Asparagine is considered as a non-essential amino acid because animal organisms can synthesize it. It is very important because is part of different foods and drugs. The thermal behavior of drug constituents, especially possible dehydration is extremely important for their preparation, processing and storage. In L AsnH2O there is a total of seven hydrogen bonds per hydrated molecule three of which involve the water molecule [2]. The water of hydration is usually divided into two broad categories: the strongly bound primary hydration and the more loosely bound secondary hydration [3]. In the case of hydrated asparagines the water of hydration is involved in a complex network of hydrogen bonds, which helps to hold the lattice together [2, 4]. Compared with monohydrated asparagine the anhydrous form has been less studied from the structural point o
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