Abstract
Understanding the role of water in governing the kinetics of the self-assembly processes of amphiphilic peptides remains elusive. Here, we use a multistage atomistic-coarse-grained approach, complemented by circular dichroism/infrared spectroscopy and dynamic light scattering experiments to highlight the dual nature of water in driving the self-assembly of peptide amphiphiles (PAs). We show computationally that water cage formation and breakage near the hydrophobic groups control the fusion dynamics and aggregation of PAs in the micellar stage. Simulations also suggest that enhanced structural ordering of vicinal water near the hydrophilic amino acids shifts the equilibrium towards the fibre phase and stimulates structure and order during the PA assembly into nanofibres. Experiments validate our simulation findings; the measured infrared O–H bond stretching frequency is reminiscent of an ice-like bond which suggests that the solvated water becomes increasingly ordered with time in the assembled peptide network, thus shedding light on the role of water in a self-assembly process.
Highlights
Understanding the role of water in governing the kinetics of the self-assembly processes of amphiphilic peptides remains elusive
By maintaining an atomistic resolution during the early stages of micelle and fibre formation to their subsequent aggregation into nanofibre bundles, we show that local interfacial ordering of water plays a key role in dictating the mechanism and dynamic equilibrium between the various phases during self-assembly of peptide amphiphiles (PAs)
The peak height for both 1st and 2nd peaks increases with an increase in simulation time. This suggests an increase in ordering of water molecules near the hydrophilic groups of PAs, enabling the stabilization of fibres during the process of bundle formation. This is corroborated by the order parameter calculations of water beads over the 16 ms of CG molecular dynamics (MD) simulations where we find that orientational order parameter (Q6) of the water beads increasing with increase in simulation time (Fig. 4b3)
Summary
Understanding the role of water in governing the kinetics of the self-assembly processes of amphiphilic peptides remains elusive. By maintaining an atomistic resolution during the early stages of micelle and fibre formation to their subsequent aggregation into nanofibre bundles, we show that local interfacial ordering of water plays a key role in dictating the mechanism and dynamic equilibrium between the various phases during self-assembly of PAs. Our results brings to the forefront the dual functionality of water; breaking of interfacial ordering near the hydrophobic groups which causes the aggregation of PAs, and the ordered water in the vicinity of hydrophilic amino acids provide structure and order for the PAs enabling the formation of fibres. Our findings illustrate how the chemical nature and molecular details of aqueous interfaces control the early stages of PA assembly and provide quantitative insights into the unique role of water by drawing on the interfacial nature of hydration and aggregation kinetics associated with peptide assemblies
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