Interfacial water morphology in hydrated melanin.

Area of Science:

• Biomaterials Science
• Neutron Scattering
• Bioelectronics

Background:

• Electrically functional biomaterials are crucial for novel sensing applications.
• Material hydration significantly impacts conductivity, especially in ion/proton transport systems.
• The specific water morphology in hydrated biomaterials and its effect on conductivity remain under-explored.

Purpose of the Study:

• To investigate the 'water morphology' of hydrated eumelanin, a model bioelectronic material.
• To correlate water structure with ionic conductivity using inelastic neutron scattering (INS).
• To develop a methodology for hydration-dependent INS experiments.

Main Methods:

• Utilized inelastic neutron scattering (INS) to study eumelanin at varying hydration levels.
• Developed a new methodology for hydration-dependent INS experiments.
• Modeled dry eumelanin spectra and extracted water scattering signals from difference spectra at higher hydration.

Main Results:

• The water structure in hydrated eumelanin is primarily interfacial water, with 3-5 layers and no bulk water.
• Potential signatures of proton cations, likely the Zundel ion, were detected in the biopolymer/water system.
• These findings suggest a dominance of interfacial water in soft proton ionomer systems.

Conclusions:

• The water morphology in eumelanin is dominated by interfacial water, not bulk water.
• The detection of Zundel ion signatures offers new perspectives on proton transport in biomaterials.
• Understanding water morphology is key to advancing ionic charge transport mechanisms in hydrated bioelectronics.