Ultrahigh Vacuum Deposition of l-Cysteine on Au(110) Studied by High-Resolution X-ray Photoemission:  From Early Stages of Adsorption to Molecular Organization

Abstract

We report on a high-resolution X-ray photoemission spectroscopy study on molecular-thick layers of L-cysteine deposited under ultrahigh vacuum conditions on Au(110). The analysis of core level shifts allowed us to distinguish unambiguously the states of the first-layer molecules from those of molecules belonging to the second layer. The first-layer molecules strongly interact with the metal through their sulfur headgroup. The multipeaked structure of the N 1s, O 1s, and C 1s core levels is interpreted in terms of different molecular moieties. The neutral acidic fraction (HSCH2CH(NH2)COOH) is abundant at low coverage likely associated with isolated molecules or dimers. The zwitterionic phase (HSCH2CH(NH3+)COO-) is largely dominant as the coverage approaches the monolayer limit and is related to the formation of ordered self-assembled molecular structures indicated by electron diffraction patterns. The occurrence of a small amount of cationic molecules (HSCH2CH(NH3+)COOH) is also discussed. The second-layer molecules mainly display zwitterionic character and are weakly adsorbed. Mild annealing up to 100 degrees C leads to the desorption of the second-layer molecules leaving electronic states of the first layer unaltered.

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

“…Moreover, the O 1s spectra of this same system show peaks at 531.2 eV, 532.3 eV, and 533.6 eV, with the first peak corresponding to the equivalent resonating oxygens of the carboxylate group COO Ϫ and the two others corresponding to the chemically inequivalent oxygens of the neutral carboxylic group COOH (36). Therefore, we deduce that the N 1s peak at 401.15 eV of our system represents a signature of the positively charged ammonium group NH 3 ϩ , whereas the singular maximum in the O 1s spectrum at 531.2 eV reflects the oxygen atoms of the carboxylate group COO Ϫ , i.e., the methionine molecules are in their zwitterionic state [the slight differences in binding energy are attributed to the different substrates; note that the superstructures occurring in the adsorption of cysteine on Au(110) imply both zwitterionic coupling schemes (36,37) and substrate reconstructions (38)]. This interpretation is in agreement with observations on the cysteine of the Pt(111) system in which similar trends are encountered (39).…”

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

“…[121]. (110)-(2×1) surface [121]. The general picture is that Cys adsorbs on the reconstructed Au(110) surface at room temperature and in the monolayer regime as a thiolate (E b (S 2p 3/2 )~162 eV), while molecules in the second layer show a dangling SH termination (E b (S 2p 3/2 )~164 eV).…”

Interface Electronic Structures of the L-Cysteine on Noble Metal Surfaces Studied by Ultraviolet Photoelectron Spectroscopy

“…Therefore, an understanding of the interaction of L-cysteine with metal surfaces is necessary. There have been experimental and theoretical research studies that examined the behavior of L-cysteine adsorbed on different faces of gold [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], silver [20][21][22][23], and copper [24][25][26] metallic single crystals as model systems for understanding the interaction of L-cysteine with metal surfaces and also L-cysteine adsorbed on some other surfaces considering technological interests [27][28][29][30][31][32][33][34][35]. In the experimental studies, the L-cysteine sample for investigation was formed using either the self-assembly or evaporation method.…”