Spectroelectrochemical Study Of Interfacial Water Structure And Function

The properties of water play an important role in many chemical,biological,and physical processes.As one of the main components of electric double layer,the structure and orientation of interfacial water have a great influence on many interfacerelated processes.At present,the research focus usually falls on the arrangement of solvated ions on the charged interface,but the structure,orientation,and hydrogen bonding network of solvent molecules are rarely reported.An in-depth understanding of the structure and function of interfacial water at the molecular level will provide theoretical guidance for many fields such as electrocatalysis,membrane science,and protein engineering,but there are still great challenges due to the limitations of available technologies.In this paper,a series of studies have been carried out using surface-enhanced infrared absorption spectroscopy(SEIRAS)combined with electrochemistry to reveal the structure and function of interfacial water.Using multiple perturbations,such as potential,ions,and light,the influence of the water molecule structure in the electric double layer on the interfacial potential and capacitance was successively revealed;and then,the structural changes of interfacial water were used to modulate the orientation of model voltage-gated ion channel peptides to reveal the voltage-gating mechanism;and based on the above work,a new strategy for confining water in a non-aqueous matrix was proposed to realize the precise analysis and regulation of the interfacial interaction forces.The content and innovation of this paper are mainly reflected in the following four aspects:1.Using a solid-supported phospholipid bilayer membrane as the model,the evolution of the local water structure at the biomimetic membrane interface with the transmembrane potential was revealed by SEIRAS combined with electrochemical techniques.In the attenuated total reflection mode,SEIRAS technology can directly access the solvent molecules at the charged interface without the interference of the bulk.Through the double perturbation of potential and ions,it was found that the water molecules bound to the negatively charged phosphate groups exhibits the characteristics of strong hydrogen bonding,and this portion of water has strong mechanical strength and can resist the interference of external electric field within a certain electrochemical window.In addition,removal of this portion of water using ions that specifically bind to phosphate groups greatly affects the electrostatic properties of phospholipid membranes.The combination of spectroscopy and electrochemistry provides a new research method for the evolution of the local water structure at the biomimetic membrane interface with the external electric field,deepening the fundamental understanding of the electric double layer structure at the membranes/solution interface.2.On the basis of the previous work,the contribution of loosely bound 4coordinated water at the interface to the model membrane capacitance was further revealed by SEIRAS combined with electrochemical techniques.Under the triple perturbation of potential,ions and light,it was found that the hydrogen bonding environment of the stern layer was of great role for the light-induced structural transformation of tetrahedral water and thus the conversion of optical signals to electrical signals,removing the strongly hydrogen bonding water bound to the phosphate groups can reconstruct the interfacial hydrogen-bonding environment and promote the cleavage of loosely bound 4-coordinated water under light irradiation.The feasibility of regulating the electrostatic properties of phospholipid membranes by light radiation is verified by constructing an optoelectronic model system,which solves the scientific problem that traditional electrical stimulation has low spatial and temporal resolution.Our work provides a new approach to explore the relationship between interfacial water structure and capacitance at the bioelectric interface.3.The above work have successively revealed the relationship between the water structure in the electric double layer and the interfacial potential and capacitance.Here,a new phospholipid bilayer membrane model with an ion reservoir was constructed to accommodate the voltage-gated ion channel peptides-Alamethicin by self-assembly of sulfhydryl molecules and vesicle fusion,and then the structural changes of interfacial water were further utilized to regulate the orientation of voltage-gated ion channel model.Using SEIRA spectroelectrochemistry combined with fluorescence spectroscopy,it was found that the orientation of the peptides inserted into the membranes was affected by membrane dipole potential regulated by chaotropic anions.The chaotropic anions caused a decrease in the membrane dipole potential by disrupting the hydrogen bonding network of the interfacial water,and a lower dipole potential could reduce the energy barrier of the insertion of peptides into the membranes,which facilitates the peptides to adopt a more upright orientation in the membranes.Our study provides a new method for exploring the gating mechanism of voltage-gated ion channel proteins,and has important guiding significance for the design of novel ion channel-related drug molecules.4.In the above work,despite adopting a series of experimental methods,it was found that the multiple interaction forces at the interface still overlap each other,including the interaction between electrode-water,electrode-ion,ion-ion,ion-water,and electrode-water.Based on this challenge,a nanoconfinement strategy was developed,using non-aqueous ionic liquids mixed with different concentrations of water and cations with different properties.A series of nanoreactors were constituted to confine water molecules in the nanodomains to decouple complex interactions at the interface.The structure and dissociation activity of water molecules dispersed in the ionic liquid matrix were investigated using SEIRAS,1H NMR spectroscopy and electrochemical techniques.It was showed that the formation of an asymmetric fourcoordinate water network at the electrode surface dominated the water dissociation activity,and the negative polarization potential induced the gradual transformation of isolated water into an asymmetric four-coordinated water network to ensure the efficient hydrogen evolution reaction.Moreover,the strength of the interaction between cations and water molecules can regulate the energy barrier of this water network formation.For hydrophobic quaternary ammonium salts,the unfavorable interaction between ions and water molecules led to enhanced water-electrode interactions and then promoted the formation of the interfacial hydrogen bond network,while the strong interaction between hydrophilic lithium salts and water molecules played an inhibitory role to a certain extent.The precise analysis of the complex interaction forces at the interface was achieved by manipulating the water concentration and the properties of the cations,which is of great significance for the understanding of the electrocatalytic reaction mechanism and provides theoretical guidance for the development of catalysts with higher performance and selectivity.