Geminal Bis-ureas as Gelators for Organic Solvents: Gelation Properties and Structural Studies in Solution and in the Gel State

Abstract

Several geminal bis-urea compounds were synthesised by means of an acid-catalysed condensation of various benzaldehydes with different monoalkylureas. Many of these compounds form thermoreversible gels with a number of organic solvents at very low concentrations (< 3 mm) and which are stable to temperatures higher than 100 8C. Electron microscopy revealed a three-dimensional (3D) network of intertwined fibres, which are several tens of micrometers long and have a width ranging from approximately 30 to 300 nm. The possible aggregate forms and aggregate symmetries were evaluated by means of molecular mechanics calculations. 1 H NMR, 2D NMR, 13 C NMR and 13 C-CP/MAS NMR techniques were used to obtain information about the aggregation and possible aggregate symmetry of geminal bis-ureas in solution, in the gel state, and in the solid state.

Halogen Bonding in Supramolecular Chemistry

“…297e In contrast, the bis(pyridylurea) component ( Figure 71) did not gel polar organic or organic−aqueous solvent owing to the presence of gel-inhibiting HB between pyridyl and urea groups, which prevented the formation of the infinite urea α-tape motif. 299 In the presence of 1,4-diiodoperfluorobenzene, gelation of polar organic−water mixtures has also been reported. Gelation was attributed to XB formation between polarized iodine atoms and XB acceptor pyridyl subunits, as shown by the 1:1 single-crystal X-ray structure (Figure 71a).…”

Organic gels prepared from side‐chain liquid crystalline polymers without the spacer

“…As shown in Figure 5, m = 10, 12, 14 was chosen as an example to test its liquid crystal properties by POM, and birefringence was observed in all polymers. The gelation process may be based on a subtle balance between solubility and insolubility, 15,16 which requires to possessing both moderate affinity with solvent molecules and the moderate self-aggregation ability. In the case of aromatic solvents, the good compatibility between biphenyl mesogens group and aromatic solvents may destroy the π-π interaction of biphenyl mesogens, resulting in the aggregation among biphenyl mesogens that did not occur on cooling.…”

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A series of side-chain liquid crystal polymers (SCLCPs) without the spacer, named poly[ω-(4′-nalkyl oxybiphenyl-4-oxy)methacrylate (PMBiCm, m = 1,2,4,6,8,10,12,14,16,and 18), have been synthesized. The novel polymer organogels were prepared by introducing PMBiCm into common organic solvents.

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Dutch Resolution of Racemates and the Roles of Solid Solution Formation and Nucleation Inhibition

“…5. Long fibers form and these, if entangled, lead to gels rather than crystals [38][39][40]. The coils formed lead to gelation of organic solvents.…”