Publication Date

2-15-2018

Department

Ames Laboratory; Chemistry

Campus Units

Chemistry, Ames Laboratory

Report Number

IS-J 9577

DOI

10.1021/acs.cgd.8b00203

Journal Title

Crystal Growth and Design

Abstract

Multicomponent solids such as cocrystals have emerged as a way to control and engineer the stability, solubility, and manufacturability of solid active pharmaceutical ingredients (APIs). Cocrystals are typically formed by solution- or solid-phase reactions of APIs with suitable cocrystal coformers, which are often weak acids. One key structural question about a given multicomponent solid is whether it should be classified as a salt, where the basic API is protonated by the acid, or as a cocrystal, where the API and coformer remain neutral and engage in hydrogen bonding interactions. It has previously been demonstrated that solid-state NMR spectroscopy is a powerful probe of structure in cocrystals and salts of APIs; however, the poor sensitivity of solid-state NMR spectroscopy usually restricts the types of experiments that can be performed. Here, relayed dynamic nuclear polarization (DNP) was applied to reduce solid-state NMR experiment times by 1–2 orders of magnitude for salts and cocrystals of a complex API. The large sensitivity gains from DNP facilitates rapid acquisition of natural isotopic abundance 13C and 15N solid-state NMR spectra. Critically, DNP enables double resonance 1H–15N solid-state NMR experiments such as 2D 1H–15N HETCOR, 1H–15N CP-build up, 15N{1H} J-resolved/attached proton tests, 1H–15N DIPSHIFT, and 1H–15N PRESTO. The latter two experiments allow 1H–15N dipolar coupling constants and H–N bond lengths to be accurately measured, providing an unambiguous assignment of nitrogen protonation state and definitive classification of the multicomponent solids as cocrystals or salts. These types of measurements should also be extremely useful in the context of polymorph discrimination, NMR crystallography structure determination, and for probing hydrogen bonding in a variety of organic materials.

DOE Contract Number(s)

AC02-07CH11358

Language

en

Department of Energy Subject Categories

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 73 NUCLEAR PHYSICS AND RADIATION PHYSICS

Publisher

Iowa State University Digital Repository, Ames IA (United States)

Available for download on Friday, February 15, 2019

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