Low-Energy Configurations of Methoxy Triethylene Glycol Terminated Alkanethiol Self-Assembled Monolayers and Their Relevance to Protein Adsorption

Abstract

Methoxy triethylene glycol terminated alkanethiol monolayers self-assembled on Au and Ag have recently been found to exhibit a striking difference in protein resistance, which has been interpreted in terms of the transition of the ethylene glycol tails from a helical to an all-trans conformation (Harder, P.; Grunze, M.; Dahint, R.; Whitesides, G. M.; Laibinis, P. E. J. Phys. Chem. 1998, 102, 426−436. Wang, R. L. C.; Kreuzer, H. J.; Grunze, M. J. Phys. Chem. 1997, 101, 9767−9773). To gain further arguments in favor of such a conformational transition, we undertake a search for the lowest energy monolayer configurations on Au and Ag by combining the methods of stochastic global search and static energy minimization. The conformational and intermolecular contributions to the monolayer lattice energy are calculated using a classical atomistic force field fitted to ab initio MP2 level calculation results for 1,2-dimethoxyethane. It is found that in the lowest energy monolayer configuration on Au the methoxy triethylene glycol tails really assume a helix-like conformation, with the three constituent O−C−C−O bond sequences being in the trans−gauche−trans form. The helical conformation is mainly stabilized by the intra- and intermolecular electrostatic interactions between the ethylene glycol units. In the Ag-supported monolayer, characterized by a perceptibly higher packing density, the helical conformer loses its stability due to conformational strains and becomes less favorable than a nearly planar all-trans conformer. The calculation results provide support to the view that the origin of the gauche effect observed in poly- and oligo(ethylene glycols) is in the influence of a polar environment and not in intrinsic properties of the ethylene glycol unit.

Formation and removal of alkylthiolate self-assembled monolayers on gold in aqueous solutions

“…Alkylthiolates containing ethylene glycol reduce the non-specific binding of proteins, bacteria, and cells to Au and Si surfaces. [37][38][39][40][41][42][43][44][45][46] We show that insulating TEG and BAT monolayers on Au surfaces were adsorbed from water at faster rates and with fewer monolayer pinholes than SAMs adsorbed from ethanol. Finally, electrochemical techniques efficiently remove contaminants from Au surfaces to enhance alkylthiolate monolayer formation in a manner that is addressable on a nanometer scale and does not damage the Au surfaces during repeated cleaning.…”

Metal ion recognition and molecular templating in self-assembled monolayers of cyclic and acyclic polyethers

“…Analysis of the spectra in the lower frequency region shows a strong absorption band in the region of 1,740-1,721 cm Ϫ1 for the OCOO stretching of the carbonyl group (52). Furthermore, absorption bands between 1,126-1,129 cm Ϫ1 are attributed to the parallel polarized OCOOOCO stretching mode of the OEG part of the monolayer (53). Shoulders are also observed in the lower frequency region of the OCOOOCO stretching band at 1,118 cm Ϫ1 for 3 and 1,121 cm Ϫ1 for 6, corresponding to the OCOOOCO stretching mode perpendicular to the OEG helical axis (54).…”

Improving the Performance of Organic Thin‐Film Transistors by Ion Doping of Ethylene‐Glycol‐Based Self‐Assembled Monolayer Hybrid Dielectrics

“…The relaxed structure was compared to the density functional theory (DFT) and molecular mechanics calculations of Grunze and co-workers who established that OEG moieties assume a helical or all-trans conformation in hexagonally structured SAMs depending on the packing density. [ 13,14 ] From the structural analyses of this work, ion incorporation appears favorable for the all-trans arrangement of the OEG chains, which applies to molecular spacing in the SAM of less than 4.38 Å, whereas the molecules curl into helices for less densely packed systems. The latter is the case even for the dense packing of PAs on sapphire (0001) with a spacing of 4.77 Å and indeed we observe helical structures for the pristine OEG SAM when modelled in the absence of solvent.…”