Aggregation of amphiphilic compounds in dimethyl sulfoxide: example of non-ionic alkyl–fluoroalkyl lipopeptides

Abstract

The surface-active properties and association in dimethyl sulfoxide (DMSO) of two non-ionic alkyl-fluoroalkyl lipopeptides have been studied up to the limit of solubility (0.15-0.25) mol dm-3) by combined use of surface tension, ''F NMR, and small-angle neutron scattering (SANS) experiments. Various models of aggregation have been tested using least-squares procedures on both NMR and SANS data. The conclusion is a progressive and very limited aggregation of these surfactants in DMSO with a structure where the hydrophobic chains tend to gather together. Equilibrium constants for a multistep equilibrium are clearly weaker for the primary step of dimerization, thus showing the existence of weak cooperative solvophobic effects in higher aggregates.

Proton Transfers on Amphiphilic Molecules. A Nonionic Alkyllipopeptide in Dimethyl Sulfoxide

“…This is quite similar to analogous experiments performed with amides and peptides. ,,, The mechanism generally accepted to account for the above rate law, first proposed by Berger et al ., involves the protonation of the amide nitrogen according to the following scheme: followed by a fast diffusion-controlled deprotonation, k d ∼ 5 × 10 9 mol -1 dm 3 s -1 at 25 °C in DMSO (for a discussion, see ref and 19). In this view, the protonation rates k 1 are consequently twice as fast as the proton exchange rates k H ; hence, …”

“…In a second step, NMR spectroscopy was used to detect an eventual aggregation of monomeric DSG molecules in DMSO. As in the case of alkyl−fluoroalkyl lipopeptides, there is a continuous shift of 1 H lines as the analytical concentration C 0 of DSG is progressively increased from 0.013 to 0.6 mol dm -3 (Figure ). The NMR shifts may be observed for each isomer individually, using for this purpose the N -methylic protons.…”

“…The first example reported in this paper concerns a simple sarcosyl−glycine dipeptide doubly protected by long alkyl chains, namely a decyl ester on the carboxylate terminal and a dodecanoyl group on the amino end. In DMSO, aggregation phenomena are expected to be weak on the basis of prior structural investigations on related nonionic alkyl−fluoroalkyl lipopeptides . The very first step in these investigations is to compare acid-catalyzed proton transfers on these molecules and a structurally related non-tensioactive compound, the octyl N -acetylsarcosylglycyl ester (ASG) already described in a previous publication …”

Micellization of dodecyltrimethylammonium bromide in water–dimethylsulfoxide mixtures: A multi-length scale approach in a model system

“…By varying the composition of water-DMSO mixtures, the solutions range between a highly structured solvent with many H-bonds (water), to a solvent with no H-bonds (DMSO). Micellization has been studied in such mixtures and the composition x DMSO = 0.33 was also found to be a limit after which no micelles form, but these results are somewhat contradictory depending on the techniques and surfactants explored [13][14][15][16][17][18][19][20][21][22]. The main reason for this situation is that monotechnique approaches, which are the most common, cannot report of the various aspects of micellization and can only render a partial view of the phenomenon.…”

Tuning the solubility of hepta(p-benzamide)s via the monomer sequence

“…32 Micellation of alkyl group bearing amphiphiles in DMSO has been reported previously. 33,34,35 In 6 the edge opposite the hexyloxy side chains consists of carbonyl and N-H hydrogen bond acceptors and donors and can therefore interact strongly with the solvent DMSO. 7 forms aggregates via the same mechanism.…”