Grafting of Alkanethiol-Terminated Poly(ethylene glycol) on Gold

Abstract

The grafting of alkanethiol-terminated poly(ethylene glycol) [HS(CH2)11(OCH2CH2)n-OCH3; n ) 34-56, MW ≈ 2224 Da] onto polycrystalline gold from dilute solutions was investigated by ellipsometry, X-ray photoelectron spectroscopy, infrared reflection-absorption spectroscopy, and in situ second harmonic generation. After immersion of a gold-coated Si wafer into a 50 µM dimethylformamide solution, the thickness of the grafted layer increases in a first rapid step up to ∼20 Å. After about 10 min, the thickness rises notably again and reaches saturation after ∼2 h at ∼120 Å. The kinetics of film formation clearly deviate from Langmuir kinetics, which is normally observed for the self-assembly of nonfunctionalized alkanethiols. Our observation can be explained by a conformational transition of the grafted poly(ethylene glycol) chains from amorphous coils to a brush morphology, predominantly consisting of helices with an orientation perpendicular to the surface. The second harmonic generation experiments show that the coverage at saturation of adsorption corresponds to ∼90% that of self-assembled monolayers of alkanethiols, indicating a densely packed film.

Mixed poly (ethylene glycol) and oligo (ethylene glycol) layers on gold as nonfouling surfaces created by backfilling

“…There have been some reports on grafting 2 kDa PEG thiol chains. For example Unsworth et al 8 reported a maximum graft density of 0.58 chains/nm 2 using methoxy capped 2 kDa PEG thiol chains under cloud point conditions, and Tokumitsu et al 34 reported a maximum graft density of 3.6 chains/nm 2 using 2 kDa PEG conjugated to undecane thiols. Theoretical maximum graft density that can be obtained using PEG SAM is 4.8 chains/nm 2 , assuming the molecular cross-sectional area for PEG brush in helical conformation to be 22 Å 2 as reported by Harder et al 22 From XPS data we have calculated a graft density of PEG-COOH SAM to be 1.0 chain/nm 2 using Eqs.…”

Structural characterization of an elevated lipid bilayer obtained by stepwise functionalization of a self-assembled alkenyl silane film

“…Conversely, too many tethers may cause the resulting elevated membrane to be sparingly fluid and the compact structure of the elevated membrane may impede spanning of proteins through the bilayer. Therefore, a sparsely tethered bilayer resting over a protein resistant biocompatible support such as polyethylene glycol 28,29 ͑PEG͒ may provide a yet incremental advancement on previous work on elevated membranes. This type of architecture would also provide a truly biomimetic cell membrane model.…”

Structural and kinetic properties of laterally stabilized, oligo(ethylene glycol)-containing alkylthiolates on gold: A modular approach

“…50,51 The adsorption kinetics for these PEG-like thiol compounds deviated remarkably from a Langmuir model, and displayed an extended period ͑ϳ10 min͒ within which hardly no adsorption appears to take place. Contrary, the formation of the EG 6 C 16 SAM is reminiscent of Langmuir kinetics, which also was found to satisfactory describe the formation of "simple" alkylthiolate SAM studied under similar experimental conditions.…”