Enhanced mechanical and thermal strength in mixed enantiomers based supramolecular gel

• Published in: Langmuir
• Main Authors: Tómasson, Daníel Arnar, Ghosh, Dipankar, Krinik, Zala, Fasolin, Luiz H., Vicente, A. A., Martin, Adam D., Thordarson, Pall, Damodaran, Krishna Kumar
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Chemical Society 2018
• Subjects: Science & Technology; Iceland
• Online Access: http://hdl.handle.net/1822/56717; https://doi.org/10.1021/acs.langmuir.8b02729

Mixing supramolecular gels based on enantiomers leads to re-arrangement of gel fibers at the molecular level, which results in more favorable packing and tuneable properties. Bis(urea) compounds tagged with a phenylalanine methyl ester in racemic and enantiopure forms were syn-thesized. Both enantiopure and racemate compounds formed gels in a wide range of solvents and the racemate (1-rac) formed a stronger gel network compared to the enantiomers. The gel (1R+1S) obtained by mixing equimolar amount of enantiomers (1R and 1S) showed enhanced mechanical and thermal stability compared to enantiomers and racemate gels. The preservation of chirality in these compounds was analyzed by circular dichroism and optical rotation measurements. Analysis of the SEM and AFM images revealed that the network in the mixed gel is a combination of enantiomers and racemate fibers, which was further supported by solid state NMR. The analysis of the packing in xerogels by solid state NMR spectra and the existence of twisted-tape morphology in SEM and AFM images confirmed the presence of both self-sorted and co-assembled fibers in mixed gel. The enhanced thermal and mechanical strength may be attributed to the enhanced intermolecular forces between the racemate and enantiomer and the combination of both self-sorted and co-assembled enantiomers in the mixed gel. We thank University of Iceland Research Fund for financial support. D.G. thanks University of Iceland for the Doctoral Research grant and Z.K. thanks University of Ljubljana for the Erasmus exchange program. We thankfully acknowledge Dr. A. Rawal, The Mark Wainwright Analytical Centre, UNSW for solid state NMR studies and Dr. Sigrídur Jónsdóttir, University of Iceland for solution NMR and Mass spectroscopy. P.T. thanks the Australian Research Council for an ARC Centre of Excellence grant (CE140100036) and A.D.M. thanks the National Health and Medical Research Council for a Dementia Development Research Fellowship (APP1106751). L.F. and A.V. thank the FCT ...