A Combined Solid-State NMR and Synchrotron X-ray Diffraction Powder Study on the Structure of the Antioxidant (+)-Catechin 4.5-hydrate.

Abstract

Analyses combining X-ray powder diffraction (XRD) and solid-state NMR (SSNMR) data can now provide crystal structures in challenging powders that are inaccessible by traditional methods. The flavonoid catechin is an ideal candidate for these methods, as it has eluded crystallographic characterization despite extensive study. Catechin was first described nearly two centuries ago, and its powders exhibit numerous levels of hydration. Here, synchrotron XRD data provide all heavy-atom positions in (+)-catechin 4.5-hydrate and establish the space group as C2. SSNMR data ((13)C tensor and (1)H/(13)C correlation) complete the conformation by providing catechin's five OH hydrogen orientations. Since 1903, this phase has been erroneously identified as a 4.0 hydrate, but XRD and density data establish that this discrepancy is due to the facile loss of the water molecule located at a Wyckoff special position in the unit cell. A final improvement to heavy-atom positions is provided by a geometry optimization of bond lengths and valence angles with XRD torsion angles held constant. The structural enhancement in this final structure is confirmed by the significantly improved fit of computed (13)C tensors to experimental data.

Cocrystallization of Nutraceuticals

“…108 The remaining phenolic substituent on ring B is hydrogen bonded to the oxygen atom of ring C. In comparison, the only stable hydrate seen for catechin (4.5) is the one in which three of the hydroxy substituents interact with water molecules, whereas the remaining two hydroxy substituents are involved in phenol O-H … O phenol hydrogen bonds (LUXWOR). 109 Cocrystal formation in epicatechincaffeine dihydrate (WUSFIA) 110 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 44 There are two known hydrated molecular complexes of catechin gallate with caffeine. 1 2 3 4 5 6 7 8 9 10 11 1...…”

Measurement and calculation of 13C chemical shift tensors in α-glucose and α-glucose monohydrate

“…Broadly referred to as "NMR crystallography", 5 innovative and creative ways of integrating solidstate NMR data with quantum chemical calculations and diffraction experiments have led to significant achievements in the structural characterization of inorganic [6][7][8][9][10][11][12] and organic solids. [13][14][15][16][17][18][19][20][21][22] However, before jumping right in to applying NMR crystallography approaches to the structures of cellulose, it is important to do some foundational work on model compounds to gain confidence that such an approach will be successful.…”

Chemical shift tensors: Theory and application to molecular structural problems

“…Grant and co-workers have presented a combined solid-state NMR and synchrotron X-ray diffraction powder study on the structure of the antioxidant (+)-catechin 4,5-hydrate [229]. As in the case of cellulose there is a marked improvement in the agreement between calculated and experimental chemical shifts upon refining the crystal structure using the NMR information.…”