Water and peptide structure at hydrophobic and hydrophilic surfaces
Date
2012-12-20
Authors
Roy, Sandra
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Abstract
In order to better understand the interfacial peptide–water interaction, molecular dynamics simulations were made for both water, and an amphipathic peptide, LKα14, adsorbed at hy- drophobic and hydrophilic surfaces. Structural and orientational analyses were performed on both systems. Vibrational mode frequency and oscillator coupling were analyzed for the interfacial water. When looking at the peptide, DFT (density functional theory) ab initio calculations were performed to obtain the non linear vibrational information of the different side chains conformers. Non linear vibrational spectra derived from these results were simulated for both interfacial water and adsorbed peptide. The sum frequency vibrational spectra obtained were correlated to the orientation analysis results. Comparison with literature results were made for both spectral and orientational analysis. The results obtained of water at hydrophilic surfaces lead us to conclude that the absence of signal in the 3700 cm−1 region is due to a cancellation of strongly opposite oriented water layers rather than the absence of O–H oscillators at this vibrational frequency region. The hydrophobic and water-air simulation resulted in surprisingly strong similarity but with difference in the depth of those features. When analyzing the structure of LKα14, results showed that it retained an α helix conformation preference in bulk and adsorbed
on surfaces. The hydrophobic surface results lead us to conclude a strong orientation of the leucine side chain towards the interface. Results from the adsorption of LKα14 at the hydrophilic surface proved that the adsorption process takes longer than for the hydrophobic surface. Due to results of water and peptide adsorption, we propose that the time scale of the adsorption process for peptide interaction with hydrophilic surface is partially due to the multiple, strongly orientated, water layers.
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Keywords
molecular dynamic, interface, water