Adsorption of Histidine and a Histidine Tripeptide on Au (111) and Au

Article pubs.acs.org/JPCC

Adsorption of Histidine and a Histidine Tripeptide on Au(111) and Au(110) from Acidic Solution Vitaliy Feyer,*,†,‡ Oksana Plekan,‡,§ Sylwia Ptasińska,∥ Marianna Iakhnenko,⊥ Nataliya Tsud,# and Kevin C. Prince‡,∇ †

Peter Grünberg Institute (PGI-6) and JARA-FIT, Research Center Jülich, D-52425 Jülich, Germany Sincrotrone Trieste S.C.p.A., in Area Science Park, Strada Statale 14, km 163.5, I-34149 Basovizza, Trieste, Italy § Aarhus University, Department of Physics and Astronomy, Ny Munkegade 120, DK-8000 Aarhus C, Denmark ∥ Radiation Laboratory and Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, United States ⊥ Taras Shevchenko National University of Kyiv, Faculty of Physics, Academician Glushkov avenue 4, 01601 Kyiv, Ukraine # Charles University, Faculty of Mathematics and Physics, Department of Surface and Plasma Science, V Holešovičkách 2, 18000 Prague 8, Czech Republic ∇ CNR-IOM Laboratorio TASC, Basovizza (Trieste), I-34149, Italy ‡

ABSTRACT: The adsorption of histidine (His), and its peptide glycyl-glycyl-histidine (Gly-GlyHis), on Au(111) and Au(110) has been studied by soft X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) at the nitrogen and oxygen K-edges. The molecules were adsorbed on surfaces from acidic (pH ∼3) solution. The results are compared with our previous studies of the adsorption of histidine and its peptides on Au(111) deposited on Au(111) from neutral solutions. When deposited from acidic solution, His adsorbs as carboxylic and carboxylate forms on both Au(111) and Au(110) surfaces, whereas its peptide is present mainly in the carboxylic form. In contrast, both molecules deposited from neutral solution adsorbed mainly as carboxylates. The imino nitrogen atom of the imidazole ring plays a crucial role in the interaction with gold surfaces. The Au 4f core level shift indicates that a chemisorption rather than a physisorption process occurs.

1. INTRODUCTION

and the distribution of lengths between the N in the IM ring and the carboxylic group.4 Liquid phase deposition is a soft method, because it is free of thermal decomposition, which could happen with UHV evaporation, and an important advantage is that it is a step closer to possible real world applications.5 Depending on the pH, amino acids and their peptides may interact with the surface as anions, cations, or neutrals (zwitterionic).6−8 Because our previous studies were done using solutions at moderate pH (pH 6−8)3 the next logical step is to vary this parameter. The imidazole ring and amino group of His can readily switch between protonated and not protonated states, and as well the carboxylic (COOH) moiety can lose the hydrogen atom and form a carboxylate (COO−). The different charged forms of His and its peptides which can exist as a function of the pH are: IM+/NH2/COOH, IM/NH3+/COOH (cationic forms), IM−/NH2/COOH, IM−/NH2/COO−, IM/NH2/ COO− (anionic forms), IM−/NH3+/COOH, IM/NH3+/ COO−, IM+/NH2/COO− (zwitterionic forms).9,10 Synchrotron-based photoelectron spectra are very sensitive to the

Metal−organic interfaces with biologically active molecules are important topics in biocatalysis, biocompatibility, and biosensors. Histidine and its peptides are interesting for possible applications, and one example is the electrochemical detection of metal ions. Yang et al.1 constructed a metal ion sensor with subppt detection limits by attachment of the tripeptide GlyGly-His to a gold electrode. Because of the presence of the imidazole side chain the molecules may also have important applications as corrosion inhibitors.2 Recently, we have reported an experimental photoemission study of the adsorption of histidine and three His-derived peptides on the Au(111) surface.3 The molecules were adsorbed on the gold surface at monolayer coverage from saturated aqueous solutions. His and its peptides interacted with the surface in anionic form via the imino nitrogen atom of the imidazole ring (IM) and the oxygen atoms of the carboxylate group, with the peptide group located at a steep angle to the surface. This system was recently investigated in detail by Xu et al.4 using molecular dynamic simulations and found to be in good agreement with our published work.3 The authors analyzed statistical properties such as free energy of adsorption, the self-diffusion coefficient, atomic density profile © 2012 American Chemical Society

Received: July 27, 2012 Revised: October 2, 2012 Published: October 5, 2012 22960

dx.doi.org/10.1021/jp307463z | J. Phys. Chem. C 2012, 116, 22960−22966

The Journal of Physical Chemistry C

Article

Figure 1. Schematic structure of Histidine (a) and Glycyl-Glycyl-Histidine (b). Colors represent: red, oxygen; dark blue, nitrogen; light blue, carbon; magenta, hydrogen.

charge distribution as chemical shifts in inner-shell ionization energy are observed. Therefore, in this study we aim to investigate the adsorption of self-assembled His-containing peptides from aqueous acidic solution and establish methodologies of surface modification. His and its tripeptide Gly-GlyHis are shown in Figure 1. Additionally, in the present work we have studied the effect of the crystal orientation on the adsorbed monolayer by comparing the Au(111) and Au(110) surfaces.

2. EXPERIMENTAL METHODS The experiments were performed at the Materials Science Beamline at the Elettra synchrotron light source in Trieste.11 The experimental details and sample preparation were described in.3 Briefly, the photoelectron spectra were recorded in normal emission geometry (incidence/emission angles of 60°/0°). The Au 4f core level spectra were collected at 120 eV photon energy and the total resolution (analyzer+beamline) was 0.15 eV, the C 1s and N 1s spectra were measured at photon energy and total resolution of 500 and 0.45 eV respectively. The O 1s core level spectra were measured with the same Phoibos analyzer using Mg Kα radiation as the excitation source and the total energy resolution was 0.85 eV. The binding energy (BE) was calibrated by measuring the Fermi edge. The NEXAFS spectra were taken at the N and O K edges using the nitrogen and oxygen KVV Auger yield, at normal (NI, 90°) and grazing (GI, 10°) incidence of the photon beam with respect to the surface. The energy resolution for the N and O K edge spectra was estimated to be 0.35 and 0.8 eV, respectively. The polarization of light from the beamline has not been measured, but is believed to be between 80 and 90% linear, as the source is a bending magnet. The raw NEXAFS data were normalized to the intensity of the photon beam, measured by means of a high transmission gold mesh and divided by corresponding spectra of the clean sample, recorded under identical conditions. The crystal was cleaned in situ using standard procedures: cycles of Ar+ sputtering followed by annealing to 723−773 K. The surface order and cleanliness were monitored by LEED and XPS, which showed that contaminants (such as C, N and O) were below the detection limits. The compounds, His and Gly-Gly-His, with the highest commercially available purities, were obtained from Sigma Aldrich and used without further purification. The samples were prepared from saturated aqueous solutions, made from distilled water and the compound, and the pH ∼3 was adjusted by adding concentrated hydrochloric acid.

Figure 2. Au 4f7/2 core-level spectra of clean surface and after deposition of molecules. Photon energy 120 eV.

manifest a doublet structure assigned to the surface A and bulk B states. The surface states for the Au(111) and Au(110) are at 83.64 and 83.61 eV respectively, whereas the bulk states for both surfaces are at 83.95 eV of binding energy. After adsorption, the features A due to the surface state decreased in intensity, and an energy shift of ∼50 meV to higher binding energy was observed. This demonstrates that the adsorbed molecules are more likely chemisorbed rather than physisorbed on the gold surfaces. It is also possible that the surface state intensity and energy vary due to a change of the reconstruction of the surfaces.12,13 Since alteration of the reconstruction requires a chemical interaction, this interpretation is in any case indirect evidence of chemical effects. To obtain a semiquantitative estimate of coverage, we use the parametrized inelastic mean free path of Seah and Dench14 for organic materials: λm = 49/E k2 + 0.11 ×

E k mg/m−2

where Ek is the kinetic energy of the photoelectron. The obtained values were converted to distance by dividing by the known densities of each compound,15 which are 1.42 g/cm3 for His and 1.68 g/cm3 for Gly-Gly-His. Because these densities are rather similar, we expect to observe only small variations in mean free paths. The effective film thicknesses for His were calculated from the attenuation of the Au 4f peak and found to be 4.2 and 4.3 Å respectively on the Au(111) and Au(110) surfaces. The same calculation for Gly-Gly-His gives values of 4.4 and 5.5 Å for the film thicknesses on Au(111) and Au(110) surfaces, respectively. The effective thickness is an index of how thick a layer is within a continuum model of the overlayer, so the number is essentially qualitative as we do not have enough

3. RESULTS AND DISCUSSION 3.1. XPS and NEXAFS Results. The Au 4f core level spectra of Au(111) and Au(110) surfaces, both clean and after adsorption of His and Gly-Gly-His, recorded at photon energy 120 eV, are shown in Figure 2. The spectra of the clean surfaces 22961



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Figure 3. Oxygen 1s (a), nitrogen 1s (b), and carbon 1s (c) photoionization spectra of saturated coverages of His and Gly-Gly-His adsorbed on Au(111) and Au(110).

hydrogen bond network formation. The effective film thickness for the Gly-Gly-His derived from the attenuation of the Au 4f peak shows smaller numbers compared with the calculated length of the molecule, and it supports formation of a single layer of adsorbed molecules. Detailed information about the chemical forms of the adsorbed molecules can be gained from an analysis of the O 1s, N 1s, and C 1s XPS spectra presented in Figure 3. The O 1s spectra can be decomposed into the two contributions A and B at binding energy ∼531.9 and 533.5 eV, respectively. In the O 1s spectra of His adsorbed on both gold surfaces, the feature A corresponds to the double bonded oxygen atom of carboxylic (COOH) and also the oxygen atoms of carboxylate (COO−) if deprotonation has taken place.3,6−8 The B component in the spectra is related to the oxygen of OH of adsorbed molecules with a neutral COOH group. In the O 1s spectra of the peptide, the extra oxygen of the amide (O C−NH) moiety contributes to the A peak. The O 1s spectra were fitted with two Gaussian functions with equal widths and free variable intensity and binding energies. This analysis of the area of peaks allows direct extraction of the relative ratio of molecules adsorbed with neutral and deprotonated moieties, COOH versus COO− groups (Table 1). The XPS data suggest

structural information at the atomic level to quantify it more precisely. The previous experiment and theoretical calculation reported that His and its peptide bond to the Au(111) surface preferably via the imino nitrogen of the IM ring and via the carboxylate group (COO−).2 Therefore, the distance between these two groups is a key factor in the adsorption geometry as pointed out by Xu et al.4 The calculated average length between the imino N and carboxylate group of His in aqueous solution as well as after adsorption onto Au(111) is approximately equal to 2.55 Å. Therefore, only small changes in this length appeared during the adsorption. For the tripeptide Gly-Gly-His this value changed from 8.5 Å in aqueous solution to 7.75 Å after adsorption.4 On the basis of the calculated numbers of the average length between the IM and COO− groups for His, and the estimated effective film thicknesses, we may draw the conclusion that His molecules formed a double layer structure on both Au(111) and Au(110) surface. Previously, using similar experimental conditions for the molecular deposition we have achieved formation of single layers of histidine on the Au(111) surface from neutral solution. In the neutral solution, histidine molecules are mainly present in the carboxylate form, whereas in the acidic solution the molecules mostly have a neutral carboxylic (COOH) moiety. This can cause a difference in 22962



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Table 1. XPS Analysis Results of His and Gly-Gly-His Adsorbed on Au(111) and Au(110) Surfaces molecules/surface

core level

His/Au(111)

O 1s N 1s

assignments

binding energy, eV

CO and COO− OH imino NIM bonded imino NIM unbonded amino NIM and NNH2 N+NH3

C 1s

His/Au(110)

O 1s N 1s

protonated amino C−C and C−H C−N N−CN and COO− COOH CO and COO− OH imino NIM bonded imino NIM unbonded amino NIM and NNH2 protonated amino

C 1s

Gly-Gly-His/Au(111)

O 1s N 1s

C 1s

Gly-Gly-His/Au(110)

O 1s N 1s

C 1s

0.5/0.5, NIM bonded/NIM unbonded 0.8/0.2,NNH2/N+NH3

401.95 (E) 285.1 (A) 286.1 (B shoulder) 288.2 (C) 289.45 (D shoulder) 531.72 (A) 533.35 (B) 398.65 (A) 399.35 (B) 400.57 (D)

N+NH3

ratio 0.52/0.48, COO−/COOH

531.8 (A) 533.45 (B) 398.77 (A) 399.47 (B) 400.67 (D)

0.53/0.47, COO−/COOH 0.19/0.81, NIM bonded/NIM unbonded 0.78/0.22, NNH2/N+NH3

401.85 (E)

C−C and C−H C−N N−CN and COO− COOH CO and COO− OH imino NIM bonded imino NIM unbonded amino N peptide amino NIM and NNH2

285.2 (A) 286.05 (B shoulder) 288.05 (C) 289.45 (D shoulder) 531.9 (A) 533.55 (B) 398.77 (A) 399.47 (B) 399.85 (C) 400.67 (D)

protonated amino N+NH3

401.95 (E)

C−C and C−H C−N N−CO, N−CN and COO− COOH CO and COO− OH imino NIM bonded imino NIM unbonded amino N peptide amino NIM and NNH2

285.1 (A) 286.05 (B shoulder) 287.9 (C) 289.25 (D) 532.1 (A) 533.7 (B) 398.82 (A) 399.52 (B) 400.05 (C) 400.72 (D)

protonated amino N+NH3

402.0 (E)

C−C and C−H C−N N−CO, N−CN and COO− COOH

285.55 (A) 286.5 (B shoulder) 288.15 (C) 289.45 (D shoulder)

0/1.0, COO−/COOH 0.44/0.56, NIM bonded/NIM unbonded

0.97/0.03, NNH2/N+NH3

0.28/0.72, COO−/COOH 0.42/0.58, NIM bonded/NIM unbonded

0.96/0.04, NNH2/N+NH3

results3,6−8,16−21 of adsorbed histidine and other amino acids, we assign the higher BE feature E to the protonated amino nitrogen atom (NH+3 ). The amino nitrogen atoms of the alpha amino and the IM ring contribute to the broad feature D in the N 1s spectra. The peak C that is present in the peptide and absent in the histidine spectra is due to the photoionization of the nitrogen atoms in peptide groups. We assign the feature B to the imino nitrogen atoms of IM, whereas peak A is assigned to the nitrogen atoms strongly interacting with the gold surface. Our quantitative analysis listed below suggests that the imino rather than amino nitrogen atom of IM is more likely involved in this interaction with a chemical shift of 0.7 eV. Our previous detailed studies of adsorption of histidine on Cu(110) and Au(111) surfaces support this assignment.3,17 Chemical shifts in N 1s spectra due to the strong interaction of nitrogen in GlyPro or Gly-Pro-Glu with gold or copper surface were also

that His deposited on both Au(111) and Au(110) surfaces adsorbed in almost equal populations of molecules with COOH and deprotonated COO− groups. The deprotonated COO− moiety may be due to the adsorption of molecules in zwitterionic and/or anionic forms, whereas COOH can be attributed to the neutral and/or cationic molecular forms. In contrast, the peptide Gly-Gly-His on gold surfaces contains mainly the carboxylic group, indeed on Au(111) the ratio A/B = 3:1 suggests from molecular stoichiometry that the absorption takes place only with COOH moieties. However, on Au(110) a minority of adsorbates with COO− were observed (about 28%, Table 1). The N 1s spectra of His and Gly-Gly-His are shown in part b of Figure 3. The spectrum of His and Gly-Gly-His can be decomposed into four and five components, respectively. On the basis of the previous theoretical and experimental 22963



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Figure 4. N K-edge and O K-edge NEXAFS spectra of His and Gly-Gly-His adsorbed on Au(111) and Au(110).

observed by other authors.19,21 To get quantitative information about the adsorbed species, the N 1s spectra were fitted with the following assumptions. The ratios of the areas of the spectral features were normalized to the number of atoms contributing to the peak, with the ratio (A + B)/C/(D + E) equal to 1:2:2. The widths of the peaks related to the single (A, B, and E) nitrogen atoms or to the nitrogen atoms of the two peptide groups were equal in all spectra. The width of the peak D associated with the two amino nitrogen atoms was allowed to vary, as unresolved chemical shifts cause broadening of the peak; however, it was found to be constant by the fit. The binding energies were variable parameters in the fit. The analysis of the branching ratio of A and B in the N 1s spectra show that half of the His molecules bind strongly to the Au(111) surface via the IM group, whereas on the Au(110) substrate only ∼20% of the molecules are chemisorbed via this group. In the case of the peptide Gly-Gly-His, we observed about equal populations of species bonded and not bonded via the IM ring (Table 1). The spectral analysis shows that the imino nitrogen atom of the IM moiety plays an important role in the molecular surface bonding, whereas amino nitrogen atoms of peptide and amino groups are not involved in the interaction with the gold surface. The C 1s core level spectra of His and Gly-Gly-His adsorbed on Au(111) and Au(110) are shown in part c of Figure 3 and two prominent peaks labeled A and C as well as the shoulders B and D are present. The shoulder D at high energy is assigned to

the core level of the COOH carbon. The energy separation of ∼4 eV from the center of the peak A and shoulder D in the C 1s is similar to corresponding spectra of amino acids in the gas phase,22,23 and it supports the proposed assignment. The carbon atom of the carboxylate (COO−) group and the carbon of the peptide moiety (OC−N) contribute to the peak C in the C 1s spectra. The feature D is the fingerprint of the COOH group and it is stronger in the spectrum of Gly-Gly-His adsorbed on Au(111) than on Au(110), which indicates the higher population of COOH moieties in adsorbed molecular layers on the Au(111) surface. It is consistent with the O 1s data discussed above. The carbon atoms of C−N bonds appear as the shoulder B on the higher energy side of the strongest peak. The signal from the ionization of atoms of carbon− carbon and carbon−hydrogen bonds is localized in the low energy region, peak A. This assignment of the features in the C 1s spectra of His and Gly-Gly-His adsorbed on gold is also in agreement with published theoretical and experimental data for other amino acids and their peptides adsorbed on surfaces.7,18,19,24 The geometry of the adsorbed species has been analyzed using NEXAFS spectroscopy. The N and O K-edge NEXAFS spectra of His and its tripeptide deposited on the Au(111) and Au(110) surfaces were measured as a function of the incidence angle of the photons, and the spectra are shown in Figure 4. The N K-edge spectra show a sharp peak at photon energy 401.5 eV and two broad features at higher photon energy. A 22964



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overlaps the resonance due to the carboxylate and/or carboxylic moieties.24 This makes it difficult to draw meaningful conclusions. The NEXAFS results indicate that the IM ring of molecules deposited from an acidic solution is oriented and lying down on both gold surfaces. Similar behavior of this moiety was observed upon adsorption from neutral solution.3 The main difference in the adsorption models for neutral and acidic liquid phase deposition is observed with the other building blocks of these molecules, such as the carboxylate/carboxylic and peptide groups. When deposited from neutral solution on Au(111), His and its peptides strongly interact with the gold surface via the carboxylate (COO−) group at shallow angles to the surface, and no carboxylic group in absorbed molecules was observed. Under the same experimental conditions, the peptide group was oriented roughly perpendicular to the surface.3 In contrast, the present results of molecular deposition from acidic solution suggest a mostly random orientation of these two moieties on the gold surface. The reason can be that the presence of the carboxylic (COOH) group in molecules adsorbed from acidic solution causes a difference in hydrogen bond network formation and creates a disordered phase.

clear shoulder at 400.1 eV is manifested on the lower energy side of the main feature. The published N K-edge NEXAFS spectra of polycrystalline powder films showed two prominent peaks in the π* region centered at ∼400.0 and ∼401.5 eV, which correspond to the N(imino) 1s→π* and N(amino) 1s→ π* transitions of zwitterionic histidine.25,26 Imidazole in the solid state also showed a double structure due to the same transitions at 400.4 and 401.8 eV, with similar relative intensities for the two resonances.27 Following these assignments, the two features in the N K-edge NEXAFS spectra of His and Gly-Gly-His are attributed to transitions of the two IM nitrogen atoms, N(imino) 1s→π* and N(amino) 1s→π*. The two broad features are attributed to transitions of 1s electrons of all nitrogen atoms to σ* (N−C) resonances. The N K-edge NEXAFS spectra show strong angular dependence: the π* resonances are stronger than the σ* resonances at GI, whereas at NI the π*/σ* intensity ratios reverse, indicating that the IM rings of His and the His-peptide are oriented close to the surface rather than at steep angles. On the Au(110) surface the N K-edge NEXAFS spectra also show some angular dependence. The spectra were taken with the E-vector perpendicular ([001] direction) or parallel ([110̅ ] direction) to the close-packed rows at normal incidence; and nearly normal to the surface ([110] direction) at grazing incidence. The spectra of His and the peptide show strong π* resonances for E∥[110]. In contrast, the shape resonance (σ* symmetry) features at higher photon energies are stronger for E∥[11̅0] and E∥[001] geometries. These results show that the IM ring of the molecules is lying down on the surface. At the two NI geometries, the π* resonance shows similar behavior, and it indicates no preferable orientation along or perpendicular to close-packed rows. In the Gly-Gly-His spectra the π* resonance related to the peptide moiety CONH is assigned to the sharp peak at low photon energy, overlapping the π* resonance associated with the amino nitrogen atom of the IM ring. However, no particular differences have been observed in Gly-Gly-His spectra compared to the spectra of His measured under similar experimental conditions. This may suggest that the peptide group is randomly oriented or/and the oscillator strengths of the two resonances are very different, and indeed the π character of the N−C bond in the peptide group is due to conjugation with the adjacent CO bond. The O K-edge spectra of His and Gly-Gly-His are shown in Figure 4. Two prominent features are observed: the sharp peak at ∼532 eV and a broader one at 543 eV. On the basis of the NEXAFS and electron energy loss studies of amino acids in the solid state, the low energy feature in the His spectrum is assigned to the O 1s → π*COO‑, whereas the high energy band is attributed to the σ* resonances.25,27 A weak peak in the O Kedge spectra is visible at about 535 eV and it is characteristic of a hydroxyl group.22,23 This evidence is consistent with the core level spectra, where some of the adsorbed molecules contain a carboxylic group. The O K edge NEXAFS spectra of His adsorbed on Au(111) show some angular dependence: the π* resonances are stronger than the σ* resonances at GI, whereas at NI the intensity ratios reverse. The O−C−O triangle of carboxylate and/or carboxylic moieties is oriented more toward the surface than away from it. The spectra of His adsorbed on the Au(110) surface do not show an angular dependence suggesting a random orientation of the O−C−O moieties. In the π* region of the O K-edge spectra of Gly-Gly-His, the transition O 1s → π*CONH associated with the peptide group

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CONCLUSIONS The XPS data show that chemisorption of His via the imino nitrogen atom of the IM moiety takes place on the gold surfaces. The analysis of the N 1s spectra allowed us to determine the ratio of molecules bonded and not bounded via the IM ring, as well as of the different charged forms of the adsorbed species. The COOH and deprotonated COO− groups of histidine adsorbed from acidic (pH ∼3) solution were found to be in almost equal proportions on the gold surfaces. In contrast, Gly-Gly-His on Au(111) contains mainly protonated carboxylic groups, while on Au(110) a small amount of adsorbed species with carboxylate was also observed. The N K-edge NEXAFS spectra show that the IM ring of His and the His-peptides is oriented close to the Au(111) and Au(110) surfaces rather than at a steep angle. The O−C−O triangle of the carboxylic or carboxylate motif is lying on the Au(111) surface at a small angle, whereas on Au(110) no angular dependence was observed in the O K-edge NEXAFS spectra suggesting a random orientation of this moiety.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +390403758302, e-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge the assistance of our colleagues at Elettra for providing good quality synchrotron light. The Materials Science Beamline is supported by the Ministry of Education of Czech Republic under Grant No. LC06058 and LA08022. S.P. acknowledges the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy through award DE-FC02-04ER15533 (NDRL no: 4939).

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(2) Xue, G.; Dong, J.; Sun, Y. Langmuir 1994, 10, 1477−1481. (3) Feyer, V.; Plekan, O.; Tsud, N.; Cháb, V.; Matolín, V.; Prince, K. C. Langmuir 2010, 26, 8606−8613. (4) Xu, Z.; Yuan, S.-L.; Yan, H.; Liu, C.-B. Colloids Surfaces A 2011, 380, 135−142. (5) Kasemo, B. Surf. Sci. 2002, 500, 656−677. (6) Zubavichus, Y.; Zharnikov, M.; Yang, Y.; Fuchs, O.; Heske, C.; Umbach, E.; Tzvetkov, G.; Netzer, F. P.; Grunze, M. J. Phys. Chem. B 2005, 109, 884−891. (7) Vallée, A.; Humblot, V.; Méthivier, C.; Pradier, C. M. Surf. Interface Anal. 2008, 40, 395−399. (8) Vallée, A.; Humblot, V.; Méthivier, C.; Dumas, P.; Pradier, C. M. J. Phys.: Condens. Matter 2011, 23, 484002/1−8. (9) Henry, B.; Tekely, P.; Delpuech, J.-J. J. Am. Chem. Soc. 2002, 124, 2025−2034. (10) Munowitz, M.; Bachovchin, W. W.; Herzfeld, J.; Dobson, C. M.; Griffin, R. G. J. Am. Chem. Soc. 1982, 104, 1192−1196. (11) Vašina, R.; Kolařík, V.; Doležel, P.; Mynár,̌ M.; Vondrácě k, M.; Cháb, V.; Slezák, J.; Comicioli, C.; Prince, K. C. Nucl. Instrum. Methods Phys. Res. A 2001, 467−468, 561−564. (12) Reinert, F.; Nicolay. Appl. Phys. A: Mater. Sci. Process. 2001, 78, 817−821. (13) Nuber, A.; Higashiguchi, M.; Forster, F.; Blaha, P.; Shimada, K.; Reinert, F. Phys. Rev. B 2008, 78, 195412/1−7. (14) Seah, M. P.; Dench, W. A. Surf. Interface Anal. 1979, 1, 2−11. (15) http://www.chemspider.com (16) Barlow, S. M.; Raval, R. Surf. Sci. Reports 2003, 50, 201−341. (17) Feyer, V.; Plekan, O.; Skála, T.; Cháb, V.; Matolín, V.; Prince, K. C. J. Phys. Chem. B 2008, 112, 1365513660. (18) Chatterjee, A.; Zhao, L.; Zhang, L.; Pradhan, D.; Zhou, X.; Leung, K. T. J. Chem. Phys. 2008, 129, 105104/1−6. (19) Vallée, A.; Humblot, V.; Méthivier, C.; Pradier, C. M. J. Phys. Chem. C 2009, 113, 9336−9344. (20) Lee, H.; Youn, Y.-S.; Yang, S.; Jung, S. J.; Kim, S. Bull. Korean. Chem. Soc. 2010, 31, 3217−3220. (21) Mathivier, C.; Lebec, V.; Landoulsi, J.; Pradier, C. M. J. Phys. Chem. C 2011, 115, 4041−4046. (22) Plekan, O.; Feyer, V.; Richter, R.; Coreno, M.; de Simone, M.; Prince, K. C.; Carravetta, V. J. Phys. Chem. A 2007, 111, 10998−11005. (23) Zhang, W.; Carravetta, V.; Plekan, O.; Feyer, V.; Richter, R.; Coreno, M.; Prince, K. C. J. Chem. Phys. 2009, 131, 035103/1−11. (24) Feyer, V.; Plekan, O.; Tsud, N.; Lyamayev, V.; Cháb, V.; Matolín, V.; Prince, K. C.; Carravetta, V. J. Phys. Chem. C 2010, 114, 10922−10931. (25) Zubavichus, Y.; Shaporenko, A.; Grunze, M.; Zharnikov, M. J. Phys. Chem. A 2005, 109, 6998−7000. (26) Leinweber, P.; Kruse, J.; Walley, F. L.; Gillespie, A.; Eckhardt, K.-U.; Blyth, R. I. R.; Regier., T. J. Synchrotron Rad. 2007, 14, 500− 511. (27) Apen, E.; Hitchcock, A. P.; Gland, J. L. J. Phys. Chem. 1993, 97, 6859−6866.

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Adsorption of Histidine and a Histidine Tripeptide on Au (111) and Au

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