Figure 4. HR-TEM images and FFTs after 50 cycles under 3.0-4.8 V conditions. a) Lattice image of the surface region where (b-e) correspond to the FFTs of Regions 1-4, respectively. (11-1) c is the diffraction spot of the rock salt phase of the metal monoxide.

The ability of surface coatings containing poly(ethylene glycol) (PEG) to prevent nonspecific protein adsorption and cell adhesion has been recognized for decades and has resulted in many biomedical applications of this class of materials.[1] Selfassembled monolayers of oligo(ethylene glycol)-terminated alkanethiols [(EG) n ±SH self-assembled monolayers (SAMs)] present a dense ªnon-foulingº brush that confers protein resistance to gold, and are arguably the best non-fouling systems that are currently available, but they have limited robustness. [2,3] We believe that methods to synthesize non-fouling coatings that combine the advantages of SAMs, namely their high surface density and ease of formation, with those of polymersÐthicker, more robust films and versatile architecture and chemistryÐare of significant interest for a variety of applications. We demonstrate in this paper that (EG) n -functionalized polymer brushes of tunable thickness in the 5±50 nm range, a thickness inaccessible to SAMs or polymer grafts, can be easily synthesized by surface-initiated polymerization (SIP), [4] that these polymer brushes exhibit no detectable adsorption of proteins, and are cell-resistant for up to a month under typical cell culture conditions. We also show that the synthesis method is compatible with a range of patterning techniques from the nano-to the microscale, which enables the patterning of cells in a biologically relevant milieu over extended periods of time. [20,21] These factors contribute to the loss of cell resistance after a week in culture.[2]Surface-initiated polymerization of an (EG) n -functionalized polymer brush was carried out from an alkanethiol SAM on gold, as follows ( Fig. 1A): x-mercaptoundecyl bromoisobutyrate (1) was synthesized as previously described [22] and a SAM of 1 was formed by immersion of a freshly prepared gold substrate in an ethanol solution of 1; [23] in some experiments mixed SAMs were also prepared, where 1 was diluted with 1-undecanethiol (2) to vary the polymer brush density. (2), and a repeat unit of a tethered ªbottleº brush of poly(OEGMA) grown from a mixed SAM of 1 and 2. B) Ellipsometric thickness of the poly(OEGMA) brush, grown from a pure SAM of 1, as a function of polymerization time. The standard deviation (sd) for each data point is < 3 (n = 3). C) Poly(OEGMA) brushes were grown from mixed SAMs of 1 and 2 for a polymerization time of 40 min, and a saturation point in thickness of the polymer brush was observed at a bulk mole fraction of 1 of 0.6 v 1 ; the sd for each data point is < 4 . The lower panel in the figure shows the thickness of the mixed SAM as a function of v 1 . The curves in B and C are simply a guide to the eye.

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We describe the molecular recognition-mediated, stepwise fabrication of patterned protein nanostructures with feature sizes on the order of 200 nm. First, a self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid (MHA) is patterned onto gold by dip-pen nanolithography (DPN), and the unpatterned regions are passivated with a protein-resistant oligoethylene glycol-terminated alkanethiol SAM. Next, an amine-terminated biotin derivative is covalently conjugated with the chemically activated MHA SAM nanopattern. The surface is then incubated with streptavidin to form streptavidin nanostructures, mediated by molecular recognition between biotin and streptavidin. Finally, protein nanopatterns are fabricated by molecular recognition-mediated immobilization of biotinylated protein from solution. Our fabrication methodology is generically applicable because of the ubiquity of biotin-tagged molecules.

Previously reported syngas conversion experiments on silica-supported Rh nanoparticles show that CO conversion and oxygenate selectivity vary as a function of nanoparticle size. Theoretical studies in the literature have examined the effect of steps on CO dissociation, but structure sensitivity for C1 and C2 oxygenates has not been systematically investigated. In this study, density functional theory-based reaction energetics and kinetics for C−H, C−C, C−O, and O−H bond formation on flat Rh(111) and stepped Rh(211) surfaces are reported and compared. Multiple paths for methanol and ethanol formation are considered to ascertain the lowest energy pathways. Nearly an identical methanol formation route via CO → CHO → CH2O → CH3O → CH3OH is found to be favored on both Rh terrace and (211) sites. CO insertion into CH2 is deduced to be the precursor for C2 oxygenate formation irrespective of site structure. Ethanol formation pathways, however, are determined to be markedly different on flat and stepped Rh surfaces in terms of barriers and intermediates. Our results show that reaction pathways are typically preferred on Rh step sites irrespective of the bond-breaking and -making (C−H, C−C, and C−O) reactions considered.