The valence and core level photoelectron spectra of glycine, proline, and methionine in the gas phase have been investigated by VUV and soft X-ray radiation. The outer valence band photoemission spectra are similar to previously reported He I spectra, although relative peak intensities are different due to the different photon energy. We extended the spectral range to include the inner valence region. The carbon, nitrogen, and oxygen 1s as well as the sulfur 2p core level spectra of these amino acids have been measured and the states identified. Valence band spectra of proline have been recorded as a function of temperature, and they provide information about the relative populations of the lowest energy conformers.

Investigation of the amino acids glycine, proline, and methionine by photoemission spectroscopy.

Adsorption and self-assembly of bio-organic molecules at model surfaces: A route towards increased complexity

Establishing the nanoscale details of organized amino acid assemblies at surfaces is a major challenge in the field of organic-inorganic interfaces. Here, we show that the dense (4 x 2) overlayer of the amino acid, (S)-proline on a Cu(110) surface can be explored at the single-molecule level by scanning tunneling microscopy (STM), reflection absorption infrared spectroscopy (RAIRS), and periodic density functional theory (DFT) calculations. The combination of experiment and theory, allied with the unique structural rigidity of proline, enables the individual conformers and adsorption footprints adopted within the organized assembly to be determined. Periodic DFT calculations find two energetically favorable molecular conformations, projecting mirror-image chiral adsorption footprints at the surface. These two forms can be experimentally distinguished since the positioning of the amino group within the pyrrolidine ring leads each chiral footprint and associated conformer to adopt very different ring orientations, producing distinct contrasts in the STM images. DFT modeling shows that the two conformers can generate eight possible (4 x 2) overlayers with a variety of adsorption footprint arrangements. STM images simulated for each structural model enables a direct comparison to be made with the experiment and narrows the (4 x 2) overlayer to one specific structural model in which the juxtaposition of molecules leads to the formation of one-dimensional hydrogen bonded prolate chains directed along the [110] direction.

Probing conformers and adsorption footprints at the single-molecule level in a highly organized amino acid assembly of (S)-proline on Cu(110).

We have studied enantiospecific differences in the adsorption of (S)- and (R)-alanine on Cu{531}R using low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy, and near edge X-ray absorption fine structure (NEXAFS) spectroscopy At saturation coverage, alanine adsorbs as alaninate forming a p(1 × 4) superstructure LEED shows a significantly higher degree of long-range order for the S than for the R enantiomer Also carbon K-edge NEXAFS spectra show differences between (S)- and (R)-alanine in the variations of the π resonance when the linear polarization vector is rotated within the surface plane This indicates differences in the local adsorption geometries of the molecules, most likely caused by the interaction between the methyl group and the metal surface and/or intermolecular hydrogen bonds Comparison with model calculations and additional information from LEED and photoelectron spectroscopy suggest that both enantiomers of alaninate adsorb in two different orientations associated 

Enantiospecific Adsorption of Alanine on the Chiral Cu{531} Surface

The immobilisation and organisation of chiral biomolecules at surfaces is considered to be an important step towards the creation of single-handed biopolymers of life However, much of this behaviour remains little understood Recently, surface spectroscopic and imaging techniques have begun to map some of the primary adsorption and self-organisation events of such interfaces Here, a brief account of the current status of work conducted on amino acid and dipeptide adsorption on metal single crystal surfaces is presented, and shows that such monolayers show highly dynamic and polymorphic behaviour with various manifestations of chirality displayed at both the local and the organisational level Furthermore, it is seen that even simple amino acids at surfaces display important functional attributes such as chiral molecular recognition Finally, the effect of amino acids on the metal substrate is, in some cases, quite profound, leading to chiral imprinting via chiral faceting and reconstruction

L.B. Jones

Papers

The local adsorption geometry and electronic structure of alanine on Cu{110}