Supramolecular control over the structural organization of a second-order NLO-active organogelator

A study of the structural parameters which govern the supramolecular organization of an organogelator built from the Disperse Red moiety is proposed. In particular, the key balance between intermolecular H-bonding and/or π-π interactions is addressed by comparing the effect of a secondary amide vs. an ester linker within the molecular structure. Solution ¹H-NMR studies show the superiority of the former interaction in promoting the nanostructuring process, allowing it to reach a gel state in toluene. The nanostructures obtained from both the amide and the ester derivatives were also studied in the solid state. In particular, the use of second-harmonic generation microscopy demonstrates that an anisotropic organization of the material can even be observed in the case of the ester derivative, which demonstrates the efficiency of the tris(alkoxy)benzene unit in directing the self-assembly process, independently of additional H-bond interactions.

Development of solvent-free synthesis of hydrogen-bonded supramolecular polyurethanes

A solvent free ball-milling method for the synthesis of small molecule and oligomeric carbamates is described that is applicable to supramolecular polymer synthesis.

In this work we describe the solvent free synthesis of supramolecular polyurethanes held together by heterocomplementary triple hydrogen bonding. We perform a systematic evaluation on the base catalyzed synthesis of small molecule ureas and carbamates from a range of isocyanates, amines and alcohols in solution and in the solid state using ball milling. These optimized procedures are then shown to be applicable to the synthesis of supramolecular polyurethanes using solvent-free methods.

Linear free energy relationships reveal structural changes in hydrogen-bonded host-guest interactions

Hydrogen bond strength in host–guest systems is modulated by many factors including preorganization, steric effects, and electronic effects. To investigate how electronic effects impact barbiturate binding in bifurcated Hamilton receptors, a library of receptors with differing electronic substituents was synthesized and ¹H NMR titrations were performed with diethyl barbital. The Hammett plot revealed a clear break between the different electronic substituents suggesting a change in binding conformation. The titration data were complimented with computational studies confirming the change in structure.

NMR diffusion: an update

NMR diffusion methods continue to attract increasing attention from practising chemists. This short article summarizes some of the more recent developments and highlights the areas in which these methods are finding application, specifically: estimating molecular volumes; investigating the degree of aggregation (especially in salts); studying host–guest interactions; recognizing hydrogen bonds; and directly proving the presence and extent of ion pairing.