Dimeric Self-Assembly of Pyridyl Guanidinium Carboxylates in Polar Solvents

• Published in: Chemistry : a European journal 2010-11, Vol.16 (41), p.12387-12397
• Main Authors: Irfan Ashiq, Muhammad, Tesfatsion, Biniam F., Gaggini, Francesca, Dixon, Sally, Kilburn, Jeremy D.
• Format: Article
• Language: English
• Subjects: Amino acids; Bridges (structures); Calorimetry; Carboxylates; Carboxylic Acids - chemistry; Chemistry; Crystal structure; Crystallography, X-Ray; dimerization; Dimethyl Sulfoxide; Esters; Guanidine - chemistry; Magnetic Resonance Spectroscopy; Models, Molecular; Molecular Conformation; molecular recognition; Molecular Structure; Pyridines - chemistry; Self assembly; Solubility; Solvents; Solvents - chemistry; supramolecular chemistry; Thiourea - chemical synthesis; Thiourea - chemistry; Water - chemistry; X-rays
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201001861

A series of pyridyl guanidinium–carboxylates has been prepared and the dimeric self‐assembly of these studied in H2O/DMSO mixtures, principally using dilution isothermal calorimetry. Compounds 5 and 6, incorporating an aromatic ring in the “tethering” region between the guanidinium and carboxylate groups, demonstrate the strongest dimerisation in neat DMSO. X‐ray crystal structures of 5 and 6 reveal two different dimerisation architectures in the solid‐state, but both involve carboxylate–guanidinium salt bridges as anticipated, and π–π interactions. Compounds 10–16 incorporating peptidic fragments between the guanidinium and carboxylate groups, showed reduced dimerisation strength with increased amino acid content, but also sustained dimerisation under increasingly aqueous conditions, up to 50 % H2O/DMSO in the case of 14 and 15. The extent of our study in H2O/DMSO mixtures was determined by substrate solubility of 10–16, and not the limit of self‐assembly. Pairing up: A dimeric self‐assembly of pyridyl guanidinium carboxylates (see scheme) has been conceived as a simple model for characterisation of intermolecular interactions between a variable tethering region. We describe the synthesis and study of the self‐assembly in H2O/DMSO solvent systems using dilution microcalorimetry and 1H NMR spectroscopy.