Exploring the salt-cocrystal continuum with solid-state NMR using natural-abundance samples: implications for crystal engineering

Rajput, Lalit and Banik, Manas and Yarava, Jayasubba Reddy and Joseph, Sumy and Pandey, Manoj Kumar and Nishiyama, Yusuke and Desiraju, Gautam R (2017) Exploring the salt-cocrystal continuum with solid-state NMR using natural-abundance samples: implications for crystal engineering. In: IUCRJ, 4 (4). pp. 466-475.

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Abstract

There has been significant recent interest in differentiating multicomponent solid forms, such as salts and cocrystals, and, where appropriate, in determining the position of the proton in the X-H center dot center dot center dot A-Y X-center dot center dot center dot H-A(+)-Y continuum in these systems, owing to the direct relationship of this property to the clinical, regulatory and legal requirements for an active pharmaceutical ingredient (API). In the present study, solid forms of simple cocrystals/salts were investigated by high-field (700 MHz) solid-state NMR (ssNMR) using samples with naturally abundant N-15 nuclei. Four model compounds in a series of prototypical salt/cocrystal/continuum systems exhibiting {PyN center dot center dot center dot H-O-}/{PyN+-H center dot center dot center dot O-} hydrogen bonds (Py is pyridine) were selected and prepared. The crystal structures were determined at both low and room temperature using X-ray diffraction. The H-atom positions were determined by measuring the N-15-H-1 distances through N-15-H-1 dipolar interactions using two-dimensional inversely proton-detected cross polarization with variable contact-time (invCP-VC) H-1 -> N-15 -> H-1 experiments at ultrafast (nu(R) >= 60-70 kHz) magic angle spinning (MAS) frequency. It is observed that this method is sensitive enough to determine the proton position even in a continuum where an ambiguity of terminology for the solid form often arises. This work, while carried out on simple systems, has implications in the pharmaceutical industry where the salt/cocrystal/continuum condition of APIs is considered seriously.

Item Type:	Journal Article
Publication:	IUCRJ
Additional Information:	Copy right for this article belongs to the INT UNION CRYSTALLOGRAPHY, 2 ABBEY SQ, CHESTER, CH1 2HU, ENGLAND
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	05 Aug 2017 09:01
Last Modified:	05 Aug 2017 09:01
URI:	http://eprints.iisc.ac.in/id/eprint/57581

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