Investigating the adsorption of the amino acid L‐cysteine onto Ag(110)

Abstract

The adsorption of the amino acid L-cysteine (L-Cys) onto the Ag(110) surface at room temperature is investigated using reflection anisotropy spectroscopy (RAS). The adsorption of L-Cys at metal surfaces offers a route to the immobilisation of proteins with potential applications in the nanoscale fabrication of biomaterial surfaces. L-Cys binds strongly to Ag(110) by the formation of a thiolate linkage. Heating the L-Cys saturated surface to 580 K results in the decomposition of the adsorbate, leaving a chemisorbed S adlayer with a c(8 × 2) structure.1 Introduction The self-assembly of organic molecules into thin films at material surfaces is a process that offers a flexible route to the nanoscale engineering of chemically functionalised surfaces with applications in molecular electronics, corrosion inhibition, sensors and biomaterials. The surface-sensitive linear optical technique of reflection anisotropy spectroscopy (RAS) [1][2][3], in combination with electron-based probes, has been used to monitor the growth of ultra-high vacuum (UHV) deposited molecular films and RAS has shown sensitivity to molecular orientation and assembly [4][5][6][7]. These previous RAS studies have focused on the Cu(110) substrate to induce ordered anisotropy in the growing film and have exploited molecular adsorbates that interact via the Cu-carboxylate interaction.Another molecule-substrate interaction of technological importance is the metal-thiolate bond. This interaction is exploited in the routine preparation of self assembled monolayers of alkane-thiol molecules at Au surfaces [8,9]. While the Au-thiol interaction has been well studied, relatively little is currently known about the self-assembly and bonding of thiols on other metal surfaces.In the work presented here, we investigate the adsorption of the amino acid L-cysteine (L-Cys) [HS-CH 2 -CH(NH 2 )-COOH] on Ag(110). L-Cys contains a thiol (-SH) group and is known to adsorb onto Au surfaces via a thiolate (Au-S) linkage [10]. The adsorption of L-Cys at metal surfaces offers a route to the immobilisation of proteins with potential applications in the nanoscale fabrication of biomaterial surfaces. We find evidence for L-Cys binding to the Ag(110) surface through an Ag-thiolate linkage. Heating the L-Cys saturated surface results in the decomposition of the adsorbed L-Cys and leaves behind an ordered S adlayer.

The adsorption and stability of sulfur containing amino acids on Cu{531}

“…4B show the sulfur completely degenerating into its atomic form by 400 K. The evolution of the integrated atomic and molecular sulfur peak areas are shown in Fig. 4C and reveal that the transition process begins as low as 360 K, a much lower temperature than the 580 K 'break down' temperature discussed above for cysteine adsorbed onto a noble substrate [26,29,31,33]. A comparison of the C1s spectra for alanine on Cu{5 3 1} and Cu{1 1 0} [12,18] with the C1s spectra at 400 K in Fig.…”

“…For the single bonded species commonly cited, the molecule has been observed in two conformations, a neutral and zwitterionic form within a self assembled monolayer array [13][14][15]26,[29][30][31][32][33][34]. The general consensus is that electrons are donated from the sulfur atom to the gold substrate to form a very strong bond that is stable up to approximately 580 K, where after the molecule breaks up leaving sulfur on the surface [26,29,31,32]. Previous investigations of cysteine adsorption on Cu{1 1 0} surfaces show a variety of intact bonding arrangements, with bonding primarily observed through carboxylate, amino and thiolate groups, or combinations of these [28,35,36].…”

“…Cysteine binds to these surfaces typically through a thiolate species (sulfur atom) ''singular" footprint, however the possibility of bonding through the amine group has also been discussed [13][14][15][26][27][28][29][30][31][32][33][34]. For the single bonded species commonly cited, the molecule has been observed in two conformations, a neutral and zwitterionic form within a self assembled monolayer array [13][14][15]26,[29][30][31][32][33][34]. The general consensus is that electrons are donated from the sulfur atom to the gold substrate to form a very strong bond that is stable up to approximately 580 K, where after the molecule breaks up leaving sulfur on the surface [26,29,31,32].…”

Mobile Diagnostic Clinics

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