(S)-Cysteine Chemisorption on Cu(110), from the Gas or Liquid Phase:  An FT-RAIRS and XPS Study

Abstract

(S)-Cysteine has been deposited on a Cu110 surface from sublimation of a crystalline phase. The surface was characterized by Fourier transform reflection absorption infrared spectroscopy (FT-RAIRS) during exposure and compared to the same copper surface after immersion into cysteine solutions at various pH values. X-ray photoelectron spectroscopy (XPS) measurements provided a chemical characterization of the surface at certain stages. The combination of these two techniques highlighted the importance of the cysteine "source" for the adsorbed form of the molecules and the mode of interaction. The zwitterionic amino acid was found to be predominant after adsorption at pH values close to the isoelectric point (IEP) of the molecule but also when the layer was formed in the vapor phase. This state was very sensitive to the atmosphere, contained an excess of hydroxyls, and/or underwent reduction into the anionic form when in contact with water or air. Weakly bound cysteine or cystine molecules, formed in the adsorbed phase, were considered to explain the average thickness of the adsorbed layer that was close to 20 A. As expected, immersion in very acidic or very basic solutions led to cationic and anionic forms, respectively.

Statistic evaluation of cysteine and allyl alcohol as additives for Cu-Zn coatings from citrate baths

“…However, these thiol groups may suffer oxidation, causing the dimerization of the cysteine molecule. Cysteine can also adsorb onto the surfaces of different metals, which has been reported in the literature using several surface science and electrochemical techniques 6 .…”

“…As cysteine can adsorb on the copper surface 6 , it would be expected that a decrease in S should facilitate this adsorption, increasing the polarization and making the deposition of copper more difficult. In Bath 2, the bulk electrolytic solution is at pH = 6.77, which is higher than the first pK a of cysteine (pK a1CYS = 1.71) and smaller than its second pK a (pK a2CYS = 8.33), suggesting that the possible ionic forms of cysteine in solution at this pH range were NH 3 + /SH/COO -(zwitterionic form) and NH 2 /SH/COO -(basic form) 6 . It is known, however, that the pH in the substrate/solution interface may increase due to the HER reduction 13,14 , which can favor the presence of the basic form of cysteine.…”

“…It is known, however, that the pH in the substrate/solution interface may increase due to the HER reduction 13,14 , which can favor the presence of the basic form of cysteine. Using infrared analysis to study the adsorption of cysteine on copper surface, Marti et al 6 have shown that, at intermediate values of pH, there was a higher fraction of NH 2 groups adsorbed, which was reflected by the intense signal at 1080 cm -1 . Additionally, Sukava et al 24 have shown that the adsorption of cysteine onto copper electrodes during copper electrodeposition was sufficiently dynamic and the adsorbate phase was sufficiently mobile to enable the copper lattice to grow without covering the additive molecules.…”

“…The interaction of these compounds with metal surfaces may occur via either the amino or carboxylate groups, depending on the conditions of interaction and the substrate 6 . In an electrodeposition process, amino acids can act as ligands for metallic ions; they can also enhance or decrease the intensity of parallel reactions (for example, the hydrogen evolution reaction, HER) 7,8 .…”

Planetary Atmosphere and Surfaces Chamber (PASC): A Platform to Address Various Challenges in Astrobiology

“…Amino acids are the building blocks of proteins, and they are the essential units from which highly ordered molecular networks and more complex molecules are built up through polymerization reactions [26,27]. Therefore, in this new context, we can include the interactions of simple molecules as amino acids on catalytic surfaces, which may play a crucial role in the origin of life and the field of prebiotic chemistry.…”