Gelation of graphene oxides induced by different types of amino acids |
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| Affiliation: | 1. School of Chemistry, Monash University, Clayton, Victoria 3800, Australia;2. School of Applied Sciences, RMIT University, GPO Box 2476V, VIC 3001, Melbourne, Australia;3. Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC 3052, Australia;4. School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, GPO Box 2434, QLD 4001, Brisbane, Australia;1. Department of Chemistry, Yonsei University, Seoul 03722, Republic of Korea;2. Center for Nanomedicine, Institute for Basic Science (IBS), Seoul 03722, Republic of Korea;1. Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia;2. Faculty of Mechanical Engineering, University of Maribor, Smetanova ulica 17, 2000 Maribor, Slovenia;3. Jo?ef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia;4. Alma Mater Studiorum – Università di Bologna, Dipartimento “Giacomo Ciamician”, Via San Giacomo 11, I-40126 Bologna, Italy |
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| Abstract: | We have investigated gelation of graphene oxide (GO) sheets induced by amino acids. For gelation of single layer GO sheets, six different types of amino acids were added to GO suspension as gelators. To understand gelation mechanism, we varied the concentration and type of amino acids as well as the pH of suspension, and monitored the morphology and rheological properties of reaction mixtures. Gelation was observed in acidic pH only with three types of amino acids (arginine, tryptophan, and cysteine) whereas no gel was formed at other pH values (neutral and basic). As the type of amino acid was varied, both the binding strength between amino acid and GO and the moduli (G′ and G′′) of reaction mixtures followed the same order, arginine > cysteine > tryptophan > asparagine > aspartic acid > glycine. To rationalize these results, we considered interactions between amino acid side chains and GO sheets (i.e., electrostatic interaction, π–π stacking, and hydrogen bonding), and found that the hydrogel formed by electrostatic attraction with arginine exhibited shorter gel time and larger moduli than the other samples. Finally, synthesis of GO hydrogel at physiological pH was demonstrated by increasing the concentration of GO sheets. |
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