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Control of monolayer assembly structure by hydrogen bonding rather than by adsorbate-substrate templating

Journal of the American Chemical Society, ISSN: 0002-7863, Vol: 121, Issue: 22, Page: 5319-5327
1999
  • 124
    Citations
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  • 32
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Metrics Details

  • Citations
    124
    • Citation Indexes
      124
  • Captures
    32

Article Description

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.

Bibliographic Details

Robert S. Clegg; James E. Hutchison

American Chemical Society (ACS)

Chemical Engineering; Chemistry; Biochemistry, Genetics and Molecular Biology

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