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Fundamental theoretical and practical investigations of the polymorph formation of small amphiphilic molecules, their co-crystals and salts

Title data

Martin, Thomas ; Niemietz, Paul ; Greim, Dominik ; Ectors, Philipp ; Senker, Jürgen ; Zahn, Dirk ; Breu, Josef:
Fundamental theoretical and practical investigations of the polymorph formation of small amphiphilic molecules, their co-crystals and salts.
In: Zeitschrift für Kristallographie : Crystalline Materials. Vol. 232 (2017) Issue 1-3 . - pp. 55-67.
ISSN 2196-7105
DOI: https://doi.org/10.1515/zkri-2016-1977

Project information

Project financing: Deutsche Forschungsgemeinschaft

Abstract in another language

The amphiphilic nature of benzoic acid, benzoates and benzamide causes an unexpected rich polymorphism. Featuring rather rigid and small molecular structures these compounds are ideal model systems for gaining a more fundamental understanding of molecular polymorphism by systematic and concerted investigations. The hydrophilic head allows for hydrogen bonding while the phenyl moiety gives rise to various π-stacking modes. Variations of hydrogen bonding versus π-stacking modes give rise to four polymorphs of benzamide. The central synthon in all phases is a dimer where hydrophilic units form double hydrogen bonds. As suggested by MD simulations of the nucleation process, variations of the crystallization conditions trigger whether the first self-assembly occurs via the hydrophilic head or the hydrophophic tail groups. Based on NMR crystallographic investigations for the co-crystallization of benzamide with benzoic acid, we observed yet another variation of the balance of the two dominating intermolecular interactions leading to the formation of a 1:1 co-crystal. The average crystal structure resembles the packing motive of pure benzoic acid with alternating ribbons of homogenous benzamide and benzoic acid dimers. For alkali-benzoate salts a coordination dilemma arises that is of general importance for many active pharmaceutical ingredients (APIs). A 1:1 stoichiometry requires condensation of coordination polyhedra of small inorganic cations which in turn causes steric stress that varies with the relative volumes of cation and anion. Interestingly, one way of resolving the dilemma is microphase separation which is directly related to the amphiphilic character of benzoate.

Further data

Item Type: Article in a journal
Refereed: Yes
Keywords: amphiphilic molecules; benzamide; benzoate; benzoic acid; co-crystal; crystal structure; polymorphism
Institutions of the University: Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Chemistry > Chair Anorganic Chemistry I > Chair Anorganic Chemistry I - Univ.-Prof. Dr. Josef Breu
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Chemistry > Chair Anorganic Chemistry III > Chair Anorganic Chemistry III - Univ.-Prof. Dr. Jürgen Senker
Faculties
Faculties > Faculty of Biology, Chemistry and Earth Sciences
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Chemistry
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Chemistry > Chair Anorganic Chemistry I
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Chemistry > Chair Anorganic Chemistry III
Result of work at the UBT: Yes
DDC Subjects: 500 Science > 540 Chemistry
Date Deposited: 28 Mar 2018 05:51
Last Modified: 28 Mar 2018 05:51
URI: https://eref.uni-bayreuth.de/id/eprint/43138