Control of Monolayer Assembly Structure by Hydrogen Bonding Rather Than by Adsorbate−Substrate Templating

Abstract

Stratified amide-containing self-assembled monolayers (SAMs) provide opportunities for investigating the fundamental dependence of supramolecular structure upon molecular constitution. We report a series of amide-containing alkanethiol SAMs (C n -1AT/Au, n = 9, 11−16, 18) in which the hydrophobic overlayer thickness is systematically varied and the thickness of the polar region is held constant. The results from X-ray photoelectron spectroscopy, contact angle goniometry, reflective IR spectroscopy, and electrochemical measurements provide a consistent structural picture of the series. The amide underlayers in all the SAMs are well-ordered and extensively hydrogen bonded. However, the alkyl chains are disordered below n = 15. Comparison of the assembly structures shows that the chain length threshold for alkyl ordering is several methylenes higher than in n-alkanethiol SAMs. This indicates that alkyl chains adjacent to an amide underlayer are destabilized as compared to n-alkanethiols and that the amide underlayer destructively interferes with alkyl close packing as compared to the Au(111)−sulfur template. However, the amide regions of the SAMs are all well-ordered, showing that the amide sublayer acts as a “template” that is independent of alkyl chain length. The amide region dominates over gold−sulfur epitaxy in establishing the structure of these assemblies, and the amide−alkyl boundary provides an example of a “rigid−elastic” buried organic interface. Implications of these studies for molecular control of bulk properties, lipid-linked protein structure and function, buried organic interfaces in other systems, rationally designed ordered multilayers, and hybrid supramolecular systems are discussed.

Nanophase Segregation of Self-Assembled Monolayers on Gold Nanoparticles

“…22 In the TegA/MHA system intermolecular H-bonds between amide groups of neighboring TegA ligands ( Figure 5) 23,45 must drive phase separation in the ligand shell, as expected from simulations (Figure 3a).…”

Replacing −CH2CH2– with −CONH– Does Not Significantly Change Rates of Charge Transport through AgTS-SAM//Ga2O3/EGaIn Junctions

“…We are thus constrained to use relatively small R groups, where the molecular order of these groups in the SAM is not established, but is almost certainly less than in n-alkanethiolates. [51][52][53][54]77 Whatever the reason, the data in Figures 1 and 2 rates of tunneling. 56 The theory of tunneling through junctions containing SAMs is not sufficiently developed at present to give any guidance to these studies, and it is not clear whether this low sensitivity is expected or not.…”

“…The amide group (-CONH-) is one of the best understood in organic chemistry, 49,50 and while not isostructural with -CH 2 CH 2 -is similar in size, and is known, from prior work, to be compatible with the formation of SAMs. [51][52][53][54][55] ii) Perhaps more importantly, we wished to develop a system of SAMs to use in studies of charge transport that was more easily modified structurally than are derivatives of n-alkanethiolates. Preparing compounds of the structure HS(CH 2 ) n R, where n is 10 -20, and R is a group that we might wish to select, with as few restrictions as possible, from the full range of organic and organometallic groups, can be synthetically arduous.…”

Voltammetric study of adsorption layers of various 4-pyridyl terminated surfactants on a Au(111) electrode: Effects of electronic property of pyridyl group and intermolecular hydrogen bonding upon potential-driven phase changes

“…Clegg and coworkers prepared a series of SAMs of amide-containing alkanethiols on a Au substrate 5 [39,40]. Using the results of IR reflection-absorption spectral measurements, they revealed that the amide-containing alkanethiol molecules form extended hydrogen bonding networks and that the existence of amide group disrupts the ordering of the alkyl chains due to the steric effect.…”