  Biocompatible and functionalizable hydrogels have a wide range of (potential)
medicinal applications. In contrast to conventional hydrogels formed by
interconnected or interlocked polymer chains, self-assembled hydrogels form
from small building blocks like short peptide chains. This has the advantage
that the building blocks can be functionalized separately and then mixed to
obtain the desired properties. However, the hydrogelation process for these
systems, especially those with very low polymer weight percentage (< 1 wt%), is
not well understood, and therefore it is hard to predict whether a given
molecular building block will self-assemble into a hydrogel. This severely
hinders the rational design of self-assembled hydrogels. In this study, we
demonstrate the impact of an N-terminal chromophore label amino-benzoic acid on
the self-assembly and rheology of hydrogel hFF03 (hydrogelating, fibril
forming) using molecular dynamics simulations, which self-assembles into
{\alpha}-helical coiled-coils. We find that the chromophore and even its
specific regioisomers have a significant influence on the microscopic structure
and dynamics of the self-assembled fibril, and on the macroscopic mechanical
properties. This is because the chromophore influences the possible
salt-bridges which form and stabilize the fibril formation. Furthermore we find
that the solvation shell fibrils by itself cannot explain the viscoelasticity
of hFF03 hydrogels. Our atomistic model of the hFF03 fibril formation enables a
more rational design of these hydrogels. In particular, altering the N-terminal
chromophore emergesas a design strategy to tune the mechanic properties of
these self-assembled peptide hydrogels.
