Exploring the effects of high pressure on hydrogen bonding in pharmaceutical cocrystals: A systematic study of pyridine dicarboxylic acid systems using synchrotron and neutron diffraction.

Pharmaceutical cocrystals use common robust hydrogen bonding synthons to create novel materials with different physicochemical properties. In this systematic study of a series of cocrystals, we explore the effect of high pressure on one of these commonly used motifs, the acid-pyridine motif, to assess the commonality of behaviour under extreme conditions. We have surveyed five pyridine dicarboxylic acid systems using both synchrotron and neutron diffraction methods to elucidate the changes in structure. We observe that the hydrogen bonding in these systems compress at a similar rate despite the changes to the molecular make-up of the solids and that on compression the changes in structure are indicative that the layers move along the major slip planes in the structure. We have observed two phase transitions to new forms of the pyrazine:malonic acid system, one for each stoichiometric ratio. This study demonstrates that the combination of two complementary diffraction approaches is key to understanding polymorphic behaviour at high pressure.

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Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.

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Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Iain D H Oswald reports financial support was provided by Engineering and Physical Sciences Research Council. Iain D H Oswald reports financial support was provided by Science and Technology Facilities Council. Iain D H Oswald reports a relationship with Science and Technology Facilities Council that includes: board membership, consulting or advisory, and travel reimbursement.