Abstract
The polymorphism is a characteristic of several active principles, and
can affect the bioavailability of a drug. Among the drugs used in the
treatment of heart diseases, captopril is one of the most widely used in
the world. Despite the knowledge of vibrational properties of captopril
under high temperature and under high pressure, a lack of information
impedes the understanding of the substance in the crystal form at low
temperatures. In this research, we investigated the vibrational
properties of captopril crystals under cryogenic conditions in the 300-8
K interval using Raman spectroscopy. By observing the behavior of the
inter- and intra-molecular vibrations it was possible to infer that the
captopril molecules suffered a rearranging into the unit cell due slight
orientational changes mainly involving C-H center dot center dot center
dot O hydrogen bonds. The phenomenon occurs in a large temperature
range. However, the observed changes do not suggest the occurrence of a
structural phase transition and the Raman spectra indicate that the
trans conformation is recorded down to the lowest temperature available
in the experiments. (C) 2020 Elsevier B.V. All rights reserved.
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