Zwitterionic self-assembly of l -methionine nanogratings on the Ag(111) surface

doi:10.1073/pnas.0607867104

Zwitterionic self-assembly of l-methionine nanogratings on the Ag(111) surface

*Departments of Chemistry and of Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada V6T 1Z4;
^†Department of Physics and Astronomy, Western Washington University, Bellingham, WA 98225;
^‡Department of Physics, University of Ljubljana, SI-1001 Ljubljana, Slovenia;
^§Laboratorio Istituto Nazionale per la Fisica della Material/Tecnologie Avanzate e Nanoscienza (INFM/TASC), 34012 Trieste, Italy; and
^¶Dipartimento di Fisica, Università di Trieste, 34127 Trieste, Italy;
^‖Physik Department E20, Technische Universität München, D-85478 Garching, Germany

Edited by Royce W. Murray, University of North Carolina, Chapel Hill, NC, and approved January 11, 2007 (received for review September 8, 2006)

Abstract

The engineering of complex architectures from functional molecules on surfaces provides new pathways to control matter at the nanoscale. In this article, we present a combined study addressing the self-assembly of the amino acid l-methionine on Ag(111). Scanning tunneling microscopy data reveal spontaneous ordering in extended molecular chains oriented along high-symmetry substrate directions. At intermediate coverages, regular biomolecular gratings evolve whose periodicity can be tuned at the nanometer scale by varying the methionine surface concentration. Their characteristics and stability were confirmed by helium atomic scattering. X-ray photoemission spectroscopy and high-resolution scanning tunneling microscopy data reveal that the l-methionine chaining is mediated by zwitterionic coupling, accounting for both lateral links and molecular dimerization. This methionine molecular recognition scheme is reminiscent of sheet structures in amino acid crystals and was corroborated by molecular mechanics calculations. Our findings suggest that zwitterionic assembly of amino acids represents a general construction motif to achieve biomolecular nanoarchitectures on surfaces.

Footnotes

**To whom correspondence should be addressed. E-mail: jvb{at}ph.tum.de
Author contributions: J.V.B. designed research; A.S., A.R., W.A., Y.P., A.W.-B., D.C., A.C., and A.M. performed research; A.S., A.R., W.A., Y.P., A.W.-B., D.C., A.C., and A.M. analyzed data; and A.S., A.R., A.M., and J.V.B wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS direct submission.
Abbreviations:

STM,

scanning tunneling microscopy;

HAS,

helium atomic scattering;

XPS,

x-ray photoemission spectroscopy;

ML,

monolayer.