Self-assembly mechanism for a naphthalene-dipeptide leading to hydrogelation.
Suitably functionalized dipeptides have been shown to be effective hydrogelators. The design of the hydrogelators and the mechanism by which hydrogelation occurs are both currently not well understood. Here, we have utilized the hydrolysis of glucono-delta-lactone to gluconic acid as a means of adjusting the pH in a naphthalene-alanylvaline solution allowing the specific targeting of the final pH. In addition, this method allows the assembly process to be characterized. We show that assembly begins as charge is removed from the C-terminus of the dipeptide. The removal of charge allows lateral assembly of the molecules leading to pi-pi stacking (shown by CD) and beta-sheet formation (as shown by IR and X-ray fiber diffraction). This leads to the formation of fibrous structures. Electron microscopy reveals that thin fibers form initially, with low persistence length. Lateral association then occurs to give bundles of fibers with higher persistence length. This results in the initially weak hydrogel becoming stronger with time. The final mechanical properties of the hydrogels are very similar irrespective of the amount of GdL added; rather, the time taken to achieving the final gel is determined by the GdL concentration. However, differences are observed between the networks under strain, implying that the kinetics of assembly do impart different final materials' properties. Overall, this study provides detailed understanding of the assembly process that leads to hydrogelation.
Chen
Lin
L
Department of Chemistry, University of Liverpool, Crown Street, Liverpool, L69 7ZD, UK.
Morris
Kyle
K
Laybourn
Andrea
A
Elias
David
D
Hicks
Matthew R
MR
Rodger
Alison
A
Serpell
Louise
L
Adams
Dave J
DJ
D002942:Circular Dichroism; D004151:Dipeptides / Q000737:chemistry*; D005942:Gluconates / Q000737:chemistry; D020100:Hydrogels / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D046529:Microscopy, Electron, Transmission; D009281:Naphthalenes / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D014961:X-Ray Diffraction
D004151:Dipeptides; D005942:Gluconates; D020100:Hydrogels; D009281:Naphthalenes; C031721:naphthalene; C030691:gluconic acid