New hydrate cocrystal of L-proline with 4-acetylphenylboronic acid obtained via mechanochemistry and solvent evaporation: An experimental and theoretical study

Ofelia Hernández-Negrete, Rogerio R. Sotelo-Mundo, Hilda E. Esparza-Ponce, Martín A. Encinas-Romero, Javier Hernández-Paredes*

*Corresponding author for this work

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Abstract

In this work, we present the formation of a new multi-component molecular complex by targeting the boronic acid moiety (-B(OH)2) of 4-acetylphenylboronic acid with the carboxylate group (-COO-) of L-proline using two different techniques: mechanochemistry and solvent evaporation. The experiments produced efficiently a new cocrystal named L-PRO4APBA. It was characterised to study its structural properties by X-ray powder diffraction (XRPD), infrared spectroscopy (FTIR), single-crystal X-ray diffraction (SCXRD), and quantum chemical methods based on QTAIM. Also, its thermal behaviour was analysed using a simultaneous DSC/TGA experiment. The results showed that L-PRO4APBA comprises discrete molecular units held together mainly by O–H⋯O and N–H⋯O hydrogen bonds. However, C–H⋯O, C–H⋯π, and other non-conventional interactions gave further stabilisation. Moreover, SCXRD showed that the asymmetric unit contains five independent molecules: two of L-proline (PRO1 and PRO2), two of 4-acetylphenylboronic acid (4APBA1 and 4APBA2) and one of water. PRO1 and PRO2 adopted different conformations with their carboxylate groups in equatorial and axial positions, respectively. This feature produced two independent helical chains running along the 21 screw axis in which 4APBA1 and 4APBA2 bound through the expected -B(OH)2···OOC- heterosynthon. Surprisingly, the presence of water molecules in the lattice did not disrupt the formation of this motif. However, water molecules played an essential role for the stabilisation of the 3D structure. These findings would set up the structural basis to continue exploring the formation of new cocrystals by combining L-proline with boronic acids.

Original languageEnglish
Article number123282
JournalJournal of Solid State Chemistry
Volume313
DOIs
StatePublished - Sep 2022

Bibliographical note

Funding Information:
Surprisingly, the presence of water in the lattice did not disrupt the -COO-···(OH)2B- heterodimeric motif as previously seen in hydrated cocrystals of boronic acids with proline [5]. Hence, the syn-syn configuration of the -B(OH)2 group supported the formation of charge-assisted solid O–H···−O interactions with carboxylates [4,5]. 4APBA1 is bound to PRO1 via O3–H3O⋯O1 (2.724(3) Å) and O4–H4O⋯O2 (2.684(3) Å) interactions. Meanwhile, 4APBA2 is connected to PRO2 through O9–H9O⋯O7 (2.740(3) Å) and O8–H8O⋯O6 (2.610(2) Å) interactions.The authors thank Consejo Nacional de Ciencia y Tecnología (CONACyT) México for funding through Grants INFR-2014-01-225455 to acquire the single crystal X-ray diffractometer Bruker D8 QUEST and CF-2019-610264 for equipment maintenance and database support. Javier Hernández-Paredes thanks PRODEP México (grant No. 511e6/18e8537) and División de Ciencias Exactas y Naturales (UNISON) for supporting this project. Theoretical calculations were possible thanks to ACARUS-UNISON. We also thank the Department of Physics of Universidad de Sonora and CIMAV (México) for allowing access to laboratories and facilities.

Funding Information:
The authors thank Consejo Nacional de Ciencia y Tecnología (CONACyT) México for funding through Grants INFR-2014-01-225455 to acquire the single crystal X-ray diffractometer Bruker D8 QUEST and CF-2019-610264 for equipment maintenance and database support. Javier Hernández-Paredes thanks PRODEP México (grant No. 511e6/18e8537) and División de Ciencias Exactas y Naturales (UNISON) for supporting this project. Theoretical calculations were possible thanks to ACARUS-UNISON. We also thank the Department of Physics of Universidad de Sonora and CIMAV (México) for allowing access to laboratories and facilities.

Publisher Copyright:
© 2022 Elsevier Inc.

Keywords

  • Boron compound
  • Cocrystal
  • Hydrogen bond
  • Mechanochemistry
  • Proline
  • QTAIM

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