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Experimental and theoretical investigation of chain length and surface coverage on fouling of surface grafted polypeptoids.

ABSTRACT: Numerous strategies exist to prevent biological fouling of surfaces in physiological environments; our strategy focuses on the modification of surfaces with poly-N-substituted glycine oligomers (polypeptoids). We previously reported the synthesis and characterization of three novel polypeptoid polymers that can be used to modify titanium oxide surfaces, rendering the surfaces resistant to adsorption of proteins, to adhesion of mammalian and bacterial cells and to degradation by common protease enzymes. In this study, we investigated the effect of polypeptoid chain length on the antifouling properties of the modified surfaces. For these experiments we used poly(N-methoxyethyl) glycines with lengths between ten and fifty repeat units and determined the influence of chain length on coating thickness and density as well as resistance to protein adsorption and cellular adhesion. Short-term protein resistance remained low for all polymers, as measured by optical waveguide lightmode spectroscopy, while fibroblast adhesion after several weeks indicated reduced fouling resistance for the polypeptoid-modified surfaces with the shortest chain length polymer. Experimental observations were compared to predictions obtained from a molecular theory of polymer and protein adsorption. Good agreement was found between experiment and theory for the chain length dependence of peptoid grafting density, and for protein adsorption as a function of peptoid grafting density. The theoretical predictions provide specific guidelines for the surface coverage for each molecular weight for optimal antifouling. The predictions show the relationship between polymer layer structure and fouling.

SUBMITTER: Statz AR

PROVIDER: S-EPMC2838250 | biostudies-literature | 2009 Jun

REPOSITORIES: biostudies-literature

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Experimental and theoretical investigation of chain length and surface coverage on fouling of surface grafted polypeptoids.

Statz Andrea R AR Kuang Jinghao J Ren Chunlai C Barron Annelise E AE Szleifer Igal I Messersmith Phillip B PB

Biointerphases 20090601 2

Numerous strategies exist to prevent biological fouling of surfaces in physiological environments; our strategy focuses on the modification of surfaces with poly-N-substituted glycine oligomers (polypeptoids). We previously reported the synthesis and characterization of three novel polypeptoid polymers that can be used to modify titanium oxide surfaces, rendering the surfaces resistant to adsorption of proteins, to adhesion of mammalian and bacterial cells and to degradation by common protease e ...[more]

PMID: 20300542

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Project description:Density functional theory (DFT) and measurements of rate are used to provide evidence for the rate determining step (RDS) and requirements of the active site for CH4 combustion on Pd-Pt bimetallic catalysts in five different distinct kinetic regimes. These five regimes exhibit different rate equations for methane combustion due to the reaction rate constants and diverse dominant adsorbed species for these different kinetically relevant steps. Oxygen chemical potential at the Pd-Pt surface was replaced by oxygen pressure, reflecting the kinetic coupling between C-H and O[double bond, length as m-dash]O bond cleavage steps. C-H bond cleavage occurs on different active sites in five of these kinetic regimes, evolving from vacancy-vacancy (*-*) to oxygen-vacancy (O*-*), oxygen-oxygen (O*-O*) site pairs, monolayer Pd-O, and ultimately to oxide bulk with Pd-O site pairs as the oxygen chemical potential increases. It is easier to form a metallic surface at low oxygen pressure, implying minimal O* coverage. The sole kinetically relevant step on uncovered Pd-Pt surfaces for methane combustion is O[double bond, length as m-dash]O bond cleavage. The supply of oxygen is obviously more important than the supply of methane in regime (I). As vacancies become less available on metallic surfaces, C-H bond cleavage occurs via O*-* paired sites, the energy barrier of which is much higher than that on uncovered Pd-Pt surfaces. In this regime (II), O[double bond, length as m-dash]O bond cleavage is still an irreversible process because O* will be consumed by the rapidly formed products of methane dissociation. For the oxygen saturated surfaces in regime (III), C-H bond cleavage occurs on two adjacent adsorbed oxygens that form OH and weak CH3-O bond interactions, resulting in a low activity for methane combustion. On the oxidation surfaces (IV and V), exposed metal atoms and their adjacent exposed lattice oxygen were the active sites, leading to a large decrease in C-H bond cleavage energy barrier, deduced from both experiment and theory. The increase of the metallic oxide thickness (increase of oxygen potential) increases the methane combustion turnover rates on Pd-Pt catalysts.

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Experimental and theoretical investigation of chain length and surface coverage on fouling of surface grafted polypeptoids.

Publications

Experimental and theoretical investigation of chain length and surface coverage on fouling of surface grafted polypeptoids.

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