A new class of efficient hydrogelators has been developed by a simple modification of the peripheral substituents of cyclohexane bis-urea organogelators with hydrophilic hydroxy or amino functionalities. These bis-urea hydrogelators were synthesised in two or three steps using an alternative procedure to the common isocyanate method. Gelation was obtained with organic solvents, water and strongly basic aqueous solutions like 25% ammonia. Hydrogelation was found to depend on a delicate balance between the hydrophobicity of the alkyl chains, hydrophilicity of the terminal substituents and the enantiomeric purity of the compound. The hydrogels consisted of a network of fibers, in which all urea groups are involved in intermolecular hydrogen bonding. Most likely, gelation is driven by hydrophobic interactions of the methylene units, whereas hydrogen bond formation between the urea groups provides the necessary anisotropy of the aggregation and the high thermal stability of the gels.
The formation of very thermostable gels with several solvents is reported for two cyclic depsipeptides o f comparatively low molecular mass.
Amphiphilic sugar derivatives, formed by condensation of functionalized aliphatic chains with aldoses, form liquid crystals, in most cases smectic. A puzzling observation was the failure of the S,S-acetals of 6-deoxy sugars, L-rhamnose and D-fucose, to form such phases. A satisfactory model to explain this behavior involves-in most cases-the formation of columns, which are destabilized with the deoxy sugars in which the apolar end methyl groups are pushed together.Despite the abundance of chiral centers in the mono-and disaccharides used the smectic phases themselves in general display no chirality. By appropriate molecular design in which the amphiphilic character was deliberately suppressed it was possible to prepare glucose derivatives that exhibit chiral nematic phases as well as impressive helical twisting powers. Simple condensation chemistry is used to produce such derivatives.The amphiphilic character can be deliberately enhanced, and this is readily achieved in double headed 'gemini' derivatives formed by condensation of glucose or lactose with a long chain diamine followed by reduction followed by acylation of the nitrogen atoms with long chain acyl anhydrides. The thermodynamics of micellization of precursors to these derivatives have been studied. The gemini derivatives themselves display remarkable properties including the formation of giant vesicles and an appreciable capacity for the solubilization of hydrocarbons.
ether gave pure la (30 mg, 15%): mp 188-189 "C; NMR7 (acetone-d6 + DzO) d 3.04 (s, 3, CH3), 4.38 (d of q, 1, H3), 4.78 (d, 1, H4), 6.08 (d of d, 1, Hz), 7.25-8.25 (m, 7, H1 and aromatic), 8.73 trans-3,4-Dihydroxy-anti-1,2-epoxy-1,2,3,4-tetrahydro-7methylbenz[a]anthracene (2). A solution of la (23 mg, 0.083 mmol) and rn-chloroperbenzoic acid (230 mg) in 25 mL of dry THF was stirred under Nz for 2 h at room temperature. The solution was diluted with ether, washed twice with 10% aqueous NaOH solution and water, and dried. Evaporation of the solvent (avoiding heating), followed by trituration with ether, gave 2 (13 mg, 57%) as a white solid: mp 183-185 "C; NMR ( a~e t 0 n e -d~ 4.88 (d, 1, H4), 5.40 (d, 1, H1), 7.38-8.41 (m, 6, aromatic), 8.85 (s, trans -1,2-Dihydroxy-an ti -3,4-epoxy-1,2,3,4-tetrahydro-7methylbenz[a]anthraoene (4a). Epoxidation of 3a (23 mg, 0.08 mmol) was carried out by the procedure employed for the analogous reactions of la. Evaporation of the solvent (avoiding heating) gave crude 4a (20 mg, 74%) which showed one major peak (80%) on LC on a Ihpont Si1 column (THF-heptane, 4555). The major peak was collected and identified as 3a: NMR (acetone-d6 + The reactions of 1,2,6-trimethyl-3,5-bis(methoxycarbonyl)-l,4-dihydropyridine (2a), l-methyl-3,5-bis(methoxycarbonyl 1-1,4-dihydropyridine (2b), and l-benzyl-3-acetamido-1,4-dihydropyridine (1) with various sulfonium salts have been investigated. On thermal (60 "C) activation 2a,b react with, for example, methylphenacylphenylsulfonium tetrafluoroborate (3b) to give the respective pyridinium salts, acetophenone, and phenyl methyl sulfide. There is some competing isomerization of the 1,4-dihydropyridines to their (nonreactive) 1,2-dihydro isomers, this being catalyzed by the pyridinium salt formed on reduction of the sulfonium salt. Phenacyl-, acetonyl-, and in some cases benzylsulfonium salts can be reduced. The group to which hydride transfer takes place should be electron deficient. These reductions can be initiated at rwm temperature with visible light (at rmm temperature pyridinium :salt induced isomerization of the 1,4-dihydropyridine to its 1,2 isomer occurs only over a period of several days:i. The effect of visible light can be enhanced greatly by adding small amounts of dyes to the reaction mixtures. Eosin sodium salt, tetraphenylporphine, and R~"(2,2'-bpy)~Cl~ are all capable of increasing the rate of reduction; the last dye is by far the most effective. The results of mechanistic investigations are consistent with the hypothesis that the light-induced reductions are one-electron transfer reactions. In some cases there appears to be a separate thermal mechanism not sensitive to either light or sensitizers. Some sulfonium salts react with dihydropyridines to give the pyridinium salt and sulfide in less than quantitative yield and no reduction products from the sulfonium salt. As determined for the case of the reaction of bromomalonitrile with 1, and presumably also for other reactions, alkylation of an enamine carbon in the dihydropyridine is ...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.