Hydrophobic Forces, Electrostatic Steering, and Acid鈥揃ase Bridging between Atomically Smooth Self-Assembled Monolayers and End-Functionalized PEGolated Lipid Bilayers

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• 作者：Markus Valtiner ; Stephen H. Donaldson ; Jr. ; Matthew A. Gebbie ; Jacob N. Israelachvili
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：January 25, 2012
• 年：2012
• 卷：134
• 期：3
• 页码：1746-1753
• 全文大小：461K
• 年卷期：v.134,no.3(January 25, 2012)
• ISSN：1520-5126

文摘

A molecular level understanding of interaction forces and dynamics between asymmetric apposing surfaces (including end-functionalized polymers) in water plays a key role in the utilization of molecular structures for smart and functional surfaces in biological, medical, and materials applications. To quantify interaction forces and binding dynamics between asymmetric apposing surfaces in terms of their chemical structure and molecular design we developed a novel surface forces apparatus experiment, using self-assembled monolayers (SAMs) on atomically smooth gold substrates. Varying the SAM head group functionality allowed us to quantitatively identify, rationalize, and therefore control which interaction forces dominated between the SAM surfaces and a surface coated with short-chain, amine end-functionalized polyethylene glycol (PEG) polymers extending from a lipid bilayer. Three different SAM-terminations were chosen for this study: (a) carboxylic acid, (b) alcohol, and (c) methyl head group terminations. These three functionalities allowed for the quantification of (a) specific acid鈥揵ase bindings, (b) steric effects of PEG chains, and (c) adhesion of hydrophobic segments of the polymer backbone, all as a function of the solution pH. The pH-dependent acid鈥揵ase binding appears to be a specific and charge mediated hydrogen bonding interaction between oppositely charged carboxylic acid and amine functionalities, at pH values above the acid pK_A and below the amine pK_A. The long-range electrostatic 鈥渟teering鈥?of acid and base pairs leads to remarkably rapid binding formation and high binding probability of this specific binding even at distances close to full extension of the PEG tethers, a result which has potentially important implications for protein folding processes and enzymatic catalysis.