Adsorption behavior of surface chemically pure N-cycloalkylaldonamides at the air/water interface

Pyrenyl-linker-glucono gelators. Correlations of gel properties with gelator structures and characterization of solvent effects

A series of glucono-appended 1-pyrenesulfonyl derivatives containing α,ω-diaminoalkane spacers (Pn, where n, the number of methylene units separating the amino groups, is 2, 3, 4, 6, 7, and 8) have been prepared. Careful analyses of correlations between the structures of these molecules and their gels have provided important insights into the factors responsible for one-dimensional aggregation of small molecules containing both lipophilic and hydrophilic parts. The gelation behavior has been examined in 30 liquids of diverse structure and polarity, and the properties of their gels and the gelation mechanisms have been investigated using a variety of techniques. Possible reasons are discussed regarding why the Pn are better gelators than the corresponding naphthyl analogues (Nn) which had been investigated previously. P2 and P3 are ambidextrous gelators (i.e., they gelate both water and some organic liquids), and P4-P8 gelate some organic liquids which are protic and aprotic, but not water. In at least one of the liquids examined, P3, P4, P6, P7, and P8 form gels at less than 1 w/v % concentrations, and some of the gels in 1-decanol are thixotropic. Analyses of the gelation abilities using Hansen solubility parameters yield both qualitative and quantitative insights into the role of liquid-gelator interactions. For example, the critical gelation concentrations increase generally with increasing polar and hydrogen bonding interactions between the gelators and their liquid components. As revealed by FT-IR, (1)H NMR, UV-vis, and fluorescence spectra, hydrogen-bonding between glucono units and π-π stacking between pyrenyl groups are important in the formation and maintenance of the gel networks. The results from this study, especially those relating the aggregation modes and liquid properties, offer insights for the design of new surfactant-containing low-molecular-mass gelators with predefined gelating abilities.

Glucose-based fluorescent low-molecular mass compounds: creation of simple and versatile supramolecular gelators

Five novel glucose-based naphthalene derivatives with linkers containing hydrazine, ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, and 1,6-hexanediamine, respectively (1, 2, 3, 4, and 5) were designed and prepared. The gelation test revealed the following points: (1) within the 30 solvents tested, 1 gels water only; (2) in contrast, 2 gels not only water, but also 11 of the organic solvents tested, a typical "ambidextrous gelator"; (3) 3, 4, and 5, however, gel organic solvents only, and the numbers of solvents gelled are 11, 11 and 13, respectively. Clearly, these compounds are effective low-molecular mass gelators, and show transitions from a low-molecular mass hydrogelator to an ambidextrous gelator and then to low-molecular mass organogelators with a slight increase in the length of the spacers. Interestingly, 5 is a super gelator to acetonitrile, of which the minimum gelation concentration is only 0.07%, w/v. The morphology, microstructure and molecular aggregation of the system strongly depend on the transition, as revealed by SEM, contact angle, energy dispersive X-ray spectroscopy, and XRD measurements. More interestingly, an aggregation-induced enhanced emission was observed along with gelation. Furthermore, the system appeared as a supramolecular chiroptical switch in the sol-gel process that is the chirality disappeared when the gel was heated to solution, whereas it reappeared when cooled to a gel.

Investigations on foamability of surface-chemically pure aqueous solutions of functionalized alkylaldonamides

The foamability of the aqueous solutions of functionalized, surface-chemically pure surfactants of the nonionic saccharide-type: N,N-di-n-alkylaldonamides, N-alkyl-N-(2-hydroxyethyl)aldonamides, and N-cycloalkylaldonamides, derivatives of D-glucono-1,5-lactone and/or D-glucoheptono-1,4-lactone, were investigated. The approach of Lunkenheimer and Małysa for the characterization of the foamability and foam stability of these surfactant solutions was applied for these investigations. Using standard parameters related to the different physical stages of the foaming process, foam stability can be described in a simple and easy manner. In general, the investigated alkylaldonamides form foams of medium stability. However, for some homologues a transition from unstable to stable foam systems is observed with increasing concentration. Modifications of the molecular structure of the alkylaldonamides are distinctly reflected in their foam properties. This fact concerns not only changes of the hydrophobic moiety and its functionalization but also slight variations of the saccharide residue. Each homologous series reveals an exceptional foam behavior. In the case of the N,N-di-n-alkylaldonamides the increase of the n-alkyl chain length is accompanied by an increase of the foam stability. The aqueous solutions of the N-alkyl-N-(2-hydroxyethyl)aldonamides reveal most favorable foaming properties for homologues with average alkyl chain lengths. Moreover, it was found that the occurrence of a phase transition in the adsorption layers of the N-cyclooctylgluconamides previously observed by surface tension and surface potential measurements is also remarkably reflected in their foam stability.