Towards the Prediction of Global Solution State Properties for Hydrogen Bonded, Self-Associating Amphiphiles.

Lisa J White,Kendrick K L Ng,Helena J Shepherd,Ewan R Clark,Ben Wilson,Jennifer R Hiscock,Stilyana N Tyuleva,Simon J Holder

doi:10.1002/chem.201801280

Abstract

Through this extensive structure–property study we show that critical micelle concentration correlates with self‐associative hydrogen bond complex formation constant, when combined with outputs from low level, widely accessible, computational models. Herein, we bring together a series of 39 structurally related molecules related by stepwise variation of a hydrogen bond donor–acceptor amphiphilic salt. The self‐associative and corresponding global properties for this family of compounds have been studied in the gas, solid and solution states. Within the solution state, we have shown the type of self‐associated structure present to be solvent dependent. In DMSO, this class of compound show a preference for hydrogen bonded dimer formation, however moving into aqueous solutions the same compounds are found to form larger self‐associated aggregates. This observation has allowed us the unique opportunity to investigate and begin to predict self‐association events at both the molecular and extended aggregate level.

Highlights

Supramolecular self-assembly relies on the formation of non-covalent bonds
Within the extensive area of non-covalent self-associated material design, there is a growing interest in the focused use of intermolecular hydrogen bonds. Specific examples include those form Ikkala and co-workers who have used this class of non-covalent complex formation to drive the self-assembly of cobalt nanostructures for capsid production;[7] Yagai and co-workers who have used hydrogen bond formation within the construction of novel molecular semi-conductors;[8] Steed and co-workers who have shown that hydrogen bonds can act as a substitute for covalent bonds in the production of novel supramolecular gels;[9] and Zhou and co-workers who have used hydrogen bonded amphiphile self-association processes to drive the construction of novel drug/gene delivery systems.[10]
We have provided preliminary evidence to support the hypothesis that increasing strength of hydrogen bonded, selfassociative complex formation correlates to a decrease in critical micelle concentration (CMC).[17]

Summary

Introduction

Supramolecular self-assembly relies on the formation of non-covalent bonds. The formation of these bonds, combined with hydrophilic/hydrophobic solvent interactions, stabilise and direct the formation of any resultant aggregate, which in turn will dictate the global solution or solid state properties.[1]. A series of 1H NMR dilution studies conducted in DMSO-d6/H2O 0.5% solutions with 1-31 were performed to enable the observation and charicterisation of hydrogen bonded self-associative complexation events, through monitoring the downfield change in chemical shift of those signals corresponding to the HBD N-H resonances with increasing compound concentration.

Results

Conclusion