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

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.nanochemistry ͉ scanning tunneling microscopy ͉ supramolecular engineering ͉ surface chemistry ͉ x-ray photoemission spectroscopy T he controlled self-assembly of functional molecular species on well defined surfaces is a promising approach toward the design of nanoscale architectures (1). By using this methodology, regular low-dimensional systems such as supramolecular clusters, chains, or nanoporous arrays can be fabricated (2-6). A wide variety of molecular species as well as substrate materials proved to be useful (7), exploiting noncovalent directional interactions including dipole-dipole coupling (2, 3), hydrogen bridges (4,5,(8)(9)(10)(11), and metal-ligand interactions (6,(12)(13)(14)(15). With the exception of multiple H-bonded networks or coordination networks incorporating metal centers, it remains challenging to realize robust systems, and there is a need to develop protocols exploiting stronger intermolecular bonds to realize purely organic low-dimensional architectures. Small biological molecules such as amino acids or DNA base molecules represent an important class of building blocks that are of interest for molecular architectonic on surfaces because they inherently qualify for molecular recognition and self-assembly (16)(17)(18)(19)(20). The interaction between biomolecules and solid surfaces is decisive for the development of bioanalytical devices or biocompatible materials (21-23) as well as for a fundamental understanding of protein-surface bonding (24). Moreover, in three dimensions the amino acids provide assets to engineer distinct network structures based on zwitterionic coupling schemes (25-27), which may be categorized as subclass of ionic self-assembly (28), and thus are promising units to create robust nanoarchitectures. However, to date, the advantages of zwitterionic supramolecular synthons have not been exploited in ...

Structure and Energetics of Diphenylalanine Self-Assembling on Cu(110)

“…We note that a similar zwitterionic bonding scheme has been recently reported for methionine assembling on Ag(111). 38 From the energy results above, a lower limit to the energy barrier for the dissociation of a molecule from a chain can be estimated to be 0.47 eV. However, as described above, dissociation events are observed when a new molecule approaches a pre-existing dimer or trimer and interacts with one of their end molecules.…”

Bicomponent Supramolecular Architectures at the Vacuum–Solid Interface

“…312,313,314,315,134,135 For instance, the four nucleobases cytosine (C), 316 guanine (G), 317 adenine (Ad), 103 and thymine (T) 318 form well-organized 1D and 2D structures on Cu, Ag and Au surfaces. The H-bonding in these homomolecular systems is sufficiently strong that the role of the surface can be idealized as a simple support with minimal influence over the self-assembly process.…”

“…This inter-row distance can be tuned (27.5 nm, 19.0 nm, 9.4 nm, 8.5 nm, or 4.4 nm) by adjusting the methionine concentration. 134 This area offers a track for guest molecules such as tetracene molecules, which are confined in one dimension. These guest molecules do not decorate the methionine rims but instead stay surprisingly near the centers of the trenches.…”

Self-assembly of strongly dipolar molecules on metal surfaces

“…40,41 Earlier studies have already demonstrated that metallic substrates can indeed mediate long-range interactions and influence atomic and molecular ordering. Examples include shells of atoms, 41 zwitterionic nano gratings, 42 the self-aligned atomic strings in bimolecular gratings, 43 and porous networks of anthraquinone molecules. 44 Reported energies for substratemediated interactions are of the order of one or more milli electron volts over a distance of a few nanometers (see overview in Ref.…”