Detection of Pre-Sol Aggregation and Carbon Dioxide Scrambling in Alkylammonium Alkylcarbamate Gelators by Nuclear Magnetic Resonance

Abstract

The initial stages of aggregation of a series of organogelator salts, prepared from n-alkylamines by the rapid in situ and isothermal (at room temperature) uptake of the neutral triatomic molecule, CO2, have been probed by NMR spectroscopy in the nongelled liquid, chloroform-d. Evidence for specific interactions of the ionic headgroups in the aggregates is presented. The influences of concentration and temperature on the processes leading to pre-sol aggregates of decylammonium decylcarbamate (2b) have been investigated in detail. NMR spectra of selectively deuterated (at the R-methylene group) and selectively 13 C-enriched (at the carbonyl carbon) 2b demonstrate that CO2 is scrambled rapidly between the ammonium and carbamate parts of the molecule in chloroform solution. No scrambling of CS2 was detected in alkylammonium alkyldithiocarbamates under the same experimental conditions.

NMR study of the gelation of a designed gelator

“…This principal observation has already been made by Spevacek et al [18,19] when studying the aggregation of polymethylacrylates and was further used by different groups [20,21] in polymer NMR, but to the best of our knowledge not for the detection of the gelation point. Decreasing signal intensity of organogelator molecules in the gel state has also been described by Escuder et al [22] Very advanced NMR methods using double quantum methodology have recently been applied to this problem as well.…”

Bile acid alkylamide derivatives as low molecular weight organogelators: Systematic gelation studies and qualitative structural analysis of the systems

“…The concentration and temperature dependence of 1 H and 13 C NMR spectra of ammonium alkylcarbamates is delicate, leading to difficulties in proving their existence in minor amounts in a solution [72]. As an additional reference, we tried to make the ammonium carbamate salt derivative of 4, but were not successful for unknown reasons (see ESM).…”

CO2 in Supramolecular Chemistry: Preparation of Switchable Supramolecular Polymers

“…[8] Thermally reversible carbamate chemistry has been recently employed for the preparation of organogels from long-chain alkyl amines. [9,10] Our approach is sketched in Schemes 2 and 3 and introduces two generations of CO 2 -based self-assembling nanostructures. Monomeric units were designed, which a) strongly aggregate/dimerize in apolar solution, b) possess "CO 2 -philic" primary amino groups on the periphery, and c) form capsules upon self-assembly.…”

“…[4, [8][9][10] These features do not allow the high concentrations of free end groups in structure 11. On the other hand, carbamate-ammonium electrostatics is not directional and may offer significant flexibility to the resulting structures.…”