Abstract The reversible photo-responsive isomerization of the azobenzene and its derivatives can control protein structure in an aqueous environment with the alternation of visible and UV lights for very promising applications in drug delivery and biomaterials. However, protein adsorption/desorption behavior on the azobenzene self-assembled monolayer surface (Azo-SAMs) is still elusive. In this study, atomistic molecular dynamics simulations and free energy computations were performed to study lysozyme adsorption and desorption on a silica surface grafted with Azo-SAMs, as well as the morphologies of the SAMs. Protein structural arrangements on the azobenzene SAMs and water diffusivity at the surface-water interface, are systematically investigated.

Lysozyme Adsorption and Desorption on the Azobenzene Derivatives Self-Assembling Surfaces Studied with Molecular Dynamics SimulationSymon Jahan Sajib1, Tao Wei1, Katherine Shing2

1. Dan .F. Smith Department of Chemical Engineering, Lamar University, Beaumont, TX777102. Mork Family Department of Chemical Engineering and Material Science, University of Southern California, Los Angeles, CA90089

Methodology

Trans50% Trans25%Cis50%

1.18 chain/nm22.35 chain/nm2

AzobenzeneForce field and charges parameters: Grubmller etc. Angew. Chem. 2007, 119, 1-7; Corni etc. Theor Chem Acc (2012) 131,1274-(CH2)20-OPLS-AA forcefieldalpha-cristobalite (101)Force field and charges parameters: Mulheran etc. J. Phys. Chem. B 2013, 117, 14666Gromacs 4.6.5 Parallel Computing

Z

Trans (50%) , 2.35 chain/nm2

Density Profile

Cis (50%) , 2.35 chain/nm2

Trans (25%) , 1.18 chain/nm2

Result & Discussion (Surface)

23cos 12

S

Protein Desorption: Free Energy Computation Non-equilibrium Approach

Jarzenski (JE)

Fluctuation-Disipitation (FD)

Umber Sampling (US) &Weighted Histogram Analysis (WHAM)

Equilibrium Approach

Azo has moderate antifouling functionalities and also enable to immobilize the protein by photo-irradiation with blue-wavelength light.

Belfort, etc. ACS Appl. Mater. Interfaces, 2015, 7, 2385

Watanabe etc., Langmuir 2006, 22, 2747

Introduction

Result & Discussion (Protein Adsorption: Secondary Structural Evolution)

1. Azo-SAM surface local structure is highly correlated with the surface density due to the strong π-π interactions.

2. Flexible hydrophobic Azo-SAMs surface is attractive to protein and immobilizes the protein with stable structures.

Conclusion Acknowledgement

REG fund from Lamar U.Azo-SAM surface structure is highly correlated with the surface density.Local ordered packing of benzene rings are observed at the high-density

packing due to the strong π-π interactions.

The structure of the adsorbed protein is relatively stable.

Flexible hydrophobic surface is attractive to protein and results in protein’s extremely low diffusivity.

Z

Z

On Surface In the Bulk*2.42 X 10-9 5.84 X 10-6

Protein Diffusivity(cm2/s)

Protein diffusivity significantly decreases under surface effects.

*Cadman,etc. Biophys. J. 1981, 37, 569

Free Energy Profile

Umbrella Histograms

𝑓ሺ𝑡ሻ= 𝑘[൫𝑍𝑐𝑜𝑚,0 + 𝑣𝑡൯− 𝑍𝑐𝑜𝑚 ሺ𝑡ሻ] 𝑊ሺ𝑧ሻ= 𝑓(𝑧) 𝑑𝑧𝑧0

∆𝐴= − 1𝛽𝑙𝑛ۃ�������𝑒𝑥𝑝 (−𝛽𝑊)ۄ����������

∆𝐴= ۃ�������𝑊ۄ����������− 𝛽2(ۃ�������𝑊2ۃ������� −ۄ����������𝑊2ۄ����������)