Organogel formation rationalized by Hansen solubility parameters: improved methodology

International audienceAn organogel is obtained when a low molar mass compound forms a network of anisotropic fibres in a liquid that is therefore transformed into a macroscopic solid. Various approaches have been proposed to correlate organogel formation and Hansen solubility parameters. These approaches are well adapted to specific experimental datasets but lack universality. A general method to determine the gelation domain from the solubility data of low molecular weight gelators is here reported

Ring distortions and nano-architecture formed by purpose designed phthalocyanines

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Hydrogen bonded supramolecular polymers in moderately polar solvents

International audienc

Direct probing of the free-energy penalty for helix reversals and chiral mismatches in chiral supramolecular polymers

The amplification of chirality, where a small imbalance in a chiral constituent is propagated into a strong optical purity, can occur in the spontaneous formation of helical 1-D stacks of molecules stabilized by hydrogen bonding, also known as supramolecular polymers. We have extended a statistical model by van Gestel et al. describing the highly nonlinear relationship between supramolecular helicity and enantiomeric excess for mixtures of enantiomers (the majority-rules effect) and quantitatively account for how this affects the thermodynamic stability of the assemblies. Our method allows for a direct comparison with experimental data, providing an unambiguous determination of the key parameters of the model (i.e., the mismatch and the helix reversal penalties). We demonstrate the successful application of this model to calorimetry data for bis-urea-based helical nanotubes, showing that reversals in the handedness of these nanotubes are not all that rare even though the helix reversal penalty is fairly large. By contrast, the mismatch penalty we obtain is small, implying that a large proportion of enantiomers are present in tube fractions not of their preferred handedness

Bisurea-based supramolecular polymers: From structure to properties11Dedicated to Professor Jean-Pierre Vairon on the occasion of his 78th birthday.

AbstractThis review focuses on the synthesis, self-assembled structure and properties of bisurea-based supramolecular polymers. The straightforward synthetic accessibility of the bisurea synthon has allowed the systematic description of the relationship between the molecular structure and supramolecular assembly. Remarkably, these systems self-assemble at equilibrium into two competing supramolecular structures. Therefore, the assembly of low molar mass bisureas can lead to stimuli responsive viscoelastic gels as well as to systems which are able to report on weak intermolecular interactions. When deposited on surfaces, these hydrogen-bonded chains of molecules form well-organized monolayers in spite of defects from the substrate. Moreover, polymers with improved rheological or adhesive properties can be designed by grafting bisurea stickers

Conformational Control of Hydrogen‐Bonded Aromatic Bis‐Ureas

International audiencehe phenylurea moiety is a ubiquitous synthon in supramolecular chemistry because it contains strong complementary hydrogen bonding groups and is synthetically very accessible. Here we investigate the possibility to strengthen self-association by conformational preorganization of the phenylurea moiety. In fact, we show that it is possible to strongly enhance intermolecular interactions between hydrogen bonded aromatic bis-ureas by substitution at the ortho positions of the phenylurea groups. Ortho substituents enforce a non-coplanar conformation of the urea and phenyl moieties better suited for hydrogen bonding. Substitution by methyl groups is more efficient than with larger groups, probably because of reduced steric hindrance. These effects have been demonstrated in the case of two different supramolecular architectures, which points to the probable generality of the phenomenon. In addition, this study has lead to the discovery of a new bis-urea able to form very stable self-assembled nanotubes in toluene up to high temperatures (boiling point) or low concentrations (10-7M) and in chloroform down to 3x10-4M

Orthohalogen substituents dramatically enhance hydrogen bonding of aromatic ureas in solution

International audienceThe phenylurea moiety is a ubiquitous synthon in supramolecular chemistry. Here we report that the introduction of chlorine or bromine atoms in the ortho positions to the urea unit is a simple and very efficient way to improve its intermolecular hydrogen bond (HB) donor character. This effect was demonstrated in solution both in the context of bis-ureas self-association and of mono-ureas hydrogen bonding to strong HB acceptors

Structural Control of Bisurea-Based Supramolecular Polymers: Influence of an Ester Moiety

International audienceA few examples of monomers are known that self-assemble into various high molar mass structures in solution. Controlling the morphology of the resulting supramolecular polymers is a highly desirable goal for many applications. Herein, we compare the self-assembling properties of newly prepared ester bisurea monomers with those of previously investigated alkyl bisurea monomers. The ester functionality decreases the hydrogen bonding strength of the bisurea monomers but does not prevent the formation of long assemblies in nonpolar solvents: gels are formed at millimolar concentration. Surprisingly, ester bisureas self-assemble at room temperature into rod-like urea-bonded supramolecular polymers that are different from the ones formed by alkyl bisureas. The rods formed by ester bisurea supramolecular polymers are compact (instead of tubular in the case of alkyl bisureas) and display two monomers in the cross-section (instead of three in the case of alkyl bisureas). The stability of the structures formed by ester bisureas can be easily tuned by changing the nature of the substituent in the α-position of the urea functions and/or the nature of the alkyl side chains

Two-component self-assemblies: investigation of a synergy between bis-urea stickers

International audienceIt is of interest to develop two-component systems for added flexibility in the design of supramolecular polymers, nanofibers or organogels. Bis-ureas are known to self-assemble by hydrogen bonding into long supramolecular objects. We show here that mixing aromatic bis-ureas with slightly different structures can yield surprisingly large synergistic effects. A strong increase in viscosity is observed when a bis-urea with the sterically demanding 2,4,6-trimethylbenzene spacer is combined with a bis-urea bearing no methyl group in position 2 of the aromatic spacer (i.e. 4-methylbenzene or 4,6-dimethylbenzene). This effect is the consequence of a change in supramolecular assembly triggered by the composition of the mixture. The mixture of complementary bis-ureas forms rod-like objects that are more stable by about 1 kJ/mol, and that are thicker than the rod-like objects formed by both parent systems