Bis(Amino Acid) Oxalyl Amides as Ambidextrous Gelators of Water and Organic Solvents: Supramolecular Gels with Temperature Dependent Assembly/Dissolution Equilibrium

Bis(LeuOH) (1 a), bis(ValOH) (2 a) and bis(PhgOH) (5 a) (Phg denotes (R)‐phenylglycine) oxalyl amides are efficient low molecular weight organic gelators of various organic solvents and their mixtures as well as water, water/DMSO, and water/DMF mixtures. The organisational motifs in aqueous gels are dominated primarily by lipophilic interactions while those in organic solvents are formed by intermolecular hydrogen bonding. Most of the gels are thermoreversible and stable for many months. However, 2 a forms unstable gels with organic solvents which upon ageing transform into variety of crystalline shapes. For some 1 a/alcohol gels, a linear correlation between alcohol dielectric constants (ε) and gel melting temperatures (Tg) was found. The 1H NMR and FTIR spectroscopic investigations of selected gels reveal the existence of temperature dependent network assembly/dissolution equilibrium. In the 1H NMR spectra of gels only the molecules dissolved in entrapped solvent could be observed. By using an internal standard, the concentration of dissolved gelator molecules could be determined. In FTIR spectra, the bands corresponding to network assembled and dissolved gelator molecules are simultaneously present. This enabled determination of the Kgel values by using both methods. From the plots of ln Kgel versus 1/T, the ΔHgel values of selected gels have been determined (−ΔHgel in 10–36 kJ mol−1 range) and found to be strongly solvent dependent. The ΔHgel values determined by 1H NMR and FTIR spectroscopy are in excellent agreement. Crystal structures of 2 a and rac‐5 a show the presence of organisational motifs and intermolecular interactions in agreement with those in gel fibres elucidated by spectroscopic methods. Bis(LeuOH) (1 a), bis(ValOH) (2 a) i bis(PhgOH) (5 a) (Phg označava (R)‐fenilglicin) oksal amidi su efikasni gelatori male molekulske mase koji geliraju različita organska otapala, njihove smjese kao i vodu te smjese voda/DMSO i voda/DMF. Njihovo uređenje u hidro‐ gelskim mrežama prvenstveno određuju međumolekulske lipofilne interakcije dok je uređenje u organskim gelovima određeno tvorbom međumolekulskih vodikovih veza. Gelovi su većinom termoreverzibilni i stabilni kroz više mjeseci. Međutim, 2 a tvori nestabilne gelove s organskim otapalima koji starenjem prelaze u različite kristalne oblike. Za gelove nekih nižih alkohola s 1 a utvrđeno je da postoji linearna međuovisnost dielektrične konstante (ε) alkohola i temperaturne točke taljenja gela (Tg). P