@article {2698,
	title = {Barrier Capacity of Hydrophilic Polymer Brushes To Prevent Hydrophobic Interactions: Effect of Graft Density and Hydrophilicity},
	journal = {Macromolecules},
	volume = {42},
	number = {13},
	year = {2009},
	note = {ISI Document Delivery No.: 472NJTimes Cited: 7Cited Reference Count: 57Zou, Yuquan Rossi, Nicholas A. A. Kizhakkedathu, Jayachandran N. Brooks, Donald E.},
	month = {Jul},
	pages = {4817-4828},
	type = {Article},
	abstract = {The performance of biomaterials in contact with biological systems can be greatly affected by hydrophobic interactions at the interface between the biomaterial surface and surrounding biomolecules. Polymer brushes can function as a protective layer, preventing such interfacial hydrophobic interactions. In this paper, a systematic study of the barrier properties of a hydrophilic polymer brush is made by investigating the influence of graft density and its chemical nature (hydrophilicity/hydrophobicity) on hydrophobic interactions with the surface. To achieve this, it series of novel thermoresponsive poly-N-[(2,2-dimethyl-1,3-dioxolane)methyl]acrylamide (PDMDOMA) polymer brushes were grown from silicon wafers via surface-initiated atom transfer radical polymerization. Without changing graft density or degree of polymerization, the hydrophilicity of the PDMDOMA brushes was manipulated by partial or complete hydrolysis or the pendent dioxolane moieties. A lower critical solution temperature (LCST) was observed at 22-24 degrees C, below which the PDMDOMA brush was Found to be in a hydrated state (amphiphilic), while at temperatures above the LCST, the PDMDOMA brush formed a collapsed. more hydrophobic structure. A physical method was developed to analyze the ability of these brushes to act as a barrier against hydrophobic interactions based on AFM force-distance measurements. The adhesive forces between the Si3N4 tip and the silicon wafer surface upon (a) modification with ATRP initiator, (b) grafting of PDMDOMA brushes, and (c) partial and complete hydrolysis of PDMDOMA were investigated. Hydrophobic interactions decreased after each modification, while graft density and the degree of hydrolysis increased the barrier function of the surface layer. In particular, when graft density was above 0.22 chains/nm(2), the barrier capacity completely counteracted the hydrophobic interactions, as evidenced from the disappearance of the adhesive force in AFM measurements. Further Studies revealed that the barrier property its assessed by AFM correlated well with the wettability of the surfaces.},
	keywords = {ATOMIC-FORCE MICROSCOPY, BLOOD-PLASMA, CELL-ADHESION, CHAIN-LENGTH, HUMAN, MOLECULAR-WEIGHT, protein adsorption, SERUM-ALBUMIN, SINGLE-MOLECULE, SURFACE, TRANSFER RADICAL POLYMERIZATION},
	isbn = {0024-9297},
	url = {<Go to ISI>://000268138500067},
	author = {Zou, Y. Q. and Rossi, N. A. A. and Kizhakkedathu, J. N. and Brooks, D. E.}
}
@article {2030,
	title = {Direct observation of Markovian behavior of the mechanical unfolding of individual proteins},
	journal = {Biophysical Journal},
	volume = {95},
	number = {2},
	year = {2008},
	note = {ISI Document Delivery No.: 318WGTimes Cited: 8Cited Reference Count: 20Cao, Yi Kuske, Rachel Li, Hongbin},
	month = {Jul},
	pages = {782-788},
	type = {Article},
	abstract = {Single-molecule force-clamp spectroscopy is a valuable tool to analyze unfolding kinetics of proteins. Previous force-clamp spectroscopy experiments have demonstrated that the mechanical unfolding of ubiquitin deviates from the generally assumed Markovian behavior and involves the features of glassy dynamics. Here we use single molecule force-clamp spectroscopy to study the unfolding kinetics of a computationally designed fast-folding mutant of the small protein GB1, which shares a similar beta-grasp fold as ubiquitin. By treating the mechanical unfolding of polyproteins as the superposition of multiple identical Poisson processes, we developed a simple stochastic analysis approach to analyze the dwell time distribution of individual unfolding events in polyprotein unfolding trajectories. Our results unambiguously demonstrate that the mechanical unfolding of NuG2 fulfills all criteria of a memoryless Markovian process. This result, in contrast with the complex mechanical unfolding behaviors observed for ubiquitin, serves as a direct experimental demonstration of the Markovian behavior for the mechanical unfolding of a protein and reveals the complexity of the unfolding dynamics among structurally similar proteins. Furthermore, we extended our method into a robust and efficient pseudo-dwell-time analysis method, which allows one to make full use of all the unfolding events obtained in force-clamp experiments without categorizing the unfolding events. This method enabled us to measure the key parameters characterizing the mechanical unfolding energy landscape of NuG2 with improved precision. We anticipate that the methods demonstrated here will find broad applications in single-molecule force-clamp spectroscopy studies for a wide range of proteins.},
	keywords = {ADHESION, BONDS, FORCE-CLAMP SPECTROSCOPY, MICROSCOPE, REVEALS, SINGLE-MOLECULE, UBIQUITIN},
	isbn = {0006-3495},
	url = {<Go to ISI>://000257122900033},
	author = {Cao, Y. and Kuske, R. and Li, H. B.}
}
