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ADSORPTION of SMALL AMINO ACIDS on CHIRAL METAL SURFACES

ADSORPTION of SMALL AMINO ACIDS on CHIRAL METAL SURFACES. Tu ğç e Eralp University of Reading. Organic/Metal Interfaces Enantioselectivity?. Amino acids Carboxylic acids with extra NH 2 group Small Chiral, enatiomeric Additional functional groups

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ADSORPTION of SMALL AMINO ACIDS on CHIRAL METAL SURFACES

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  1. ADSORPTION of SMALL AMINO ACIDS on CHIRAL METAL SURFACES Tuğçe Eralp University of Reading

  2. Organic/Metal InterfacesEnantioselectivity? Amino acids Carboxylic acids with extra NH2 group • Small • Chiral, enatiomeric • Additional functional groups • Different side chains, intermolecular interactions Chiral Surfaces • Forming templates,chiral metal crystals • {h, k, l} with cubic crystal structure h≠k, k≠l and l≠h • Kink sites lack any inversion symmetry Cu{531}R&S

  3. Alanine on Cu{531} • Previously in our group.. • Alanine adsorbtion on Cu{531} Adsorbed in alaninate form through 2 O and N 2 adsorbtion sites; {311} and {110} microfacets Possible long range arrangement on (311) and (110) microfacets *M. J Gladys, A. V Stevens.; N. R Scott, G.; Jones, D. Batchelor, , G. HeldJ. Phys. Chem. C 2007; 111(23), 8331

  4. Our Experiments On Cu{531} surface GLYCINE SERINE

  5. GLYCINE on Cu{531} • Coverage Dependency (XPS, NEXAFS) • Temperature Effect (desorption properties) • Multilayers • NEXAFS

  6. Glycine Salt Forms Anionic Zwitterionic Neutral

  7. Saturation Coverage of Glycine 1 wide peak in O1s region, FWMH is 1.6514 eV 1 peak in N1s region, showing one state FWHM: 0.97 eV. 2 peaks in C1s region, carbonyl and methylene C ADSORBED AS ANIONIC SALT NH2CH2COO-

  8. Glycine Desorption, Annealing Steps 0.2 eV shift for C peaks 0.46 eV for the N peak Almost 0 for O peak Desorption, ALSO decomposition around 450K CO2 leaaving the surface

  9. Glycine Multilayers A broad N1s signal at 401.89 eV FWHM is 2.5 eV Possible two glycine species O1s spectrum, at 533.74 eV, shifted by 3.12 eV FWHM is 2.01 Two salts together zwitterionic and neutral

  10. NEXAFS • Angular dependency • p* resonance peak at 533 eV • s-resonances due to C-C and C-O • Two species, equal amounts, A1/A2=1 • a1 {311} microfacets Different azimuthal angles O K-Edge NEXAFS Spectrum Similar a values determined for alanine (-58o and 51o) Fit for the angle vs height of p-resonance peak Ip(f) = A1[cos(f - a1)]2 + A2[cos(f – a2)]2

  11. Half Saturation Coverage of Glycine Similar a values determined for alanine (-58o and 51o) • Two orientations • A1/A2 is 1.35 • one adsorption site is more • favourable O K-Edge NEXAFS Similar a values determined for alanine and sat glycine Fit for the angle vs height of p-resonance peak

  12. NEXAFS, Annealed to 400K • Two species • Equal amounts on the surface • The orientation not changing • with annealing O K-Edge NEXAFS Similar a values determined for alanine and sat glycine

  13. So Far, About Glycine on Cu{531} At room temperature, Glycine adsorbed in carboxylate form (anionic salt) through two O and N According to NEXAFS, 2 species, equal amount of each sitting on {311} and {110} microfacets like Alanine When annealed, no change in adsorption sites. Possibly decomposition around 450K, CO2 leaving the surface At 100 K, possibly two salts together, shift to higher BE For low and high coverages No difference in BE and in adsorbtion sites According to NEXAFS Difference in abundancy of one of the species Further LEED and TPD experiments will be performed

  14. SERINE on Cu{531} Serine enatiomers are chiral and have additional OH group L-Serine D-Serine

  15. THANK YOU!

  16. So Far, About L- and D- Serine Coverage Dependency • Low coverage, 4 bonds to surface, losing the H’s in carboxylic acid group and OH groups (-OCH2CHNH2COO-) • Higher coverage, O- gains H, hydrogen bonding, network (HOCH2CHNH2COO-) • With increasing coverage N peak shifts to lower BE • Symptoms for enantioselectivity • Differences in orientation (NEXAFS) • Differences in intensities (XPS) Further LEED and TPD experiments will be performed

  17. L-Serine Uptake Curves • In O1s Spectrum, • broad O peak with shoulder • In N1s Spectrum, shift of 0.3 eV • In C1s Spectrum, • carboxylate carbon highest BE Coverage effects the adsorbate bonds, Possibly OH---OH networks

  18. NEXAFS • Different polarization angles • Angular dependency • p* resonance peak at 289 eV • 2 species C-NEXAFS Sat coverage of L-Serine Angle vs height of p-resonance peak fit

  19. Any Enantioselectivity? High difference in a values between two enantiomers Also between two coverages

  20. Aim of the Project What? To answer... Any enantiospecifity/selectivity of the surface? • How? • With determining the followings.. • The orientations of the adsorbed of amino acids • Likely adsorption bonds of the adsorbate to the surface, • effect of coverage, temperature • Why? • Importance... In future, these chiral surfaces can be used for • Heterogenous catalysis reactions • Purifying/ seperating enantiomers

  21. Moreover... Peak intensities lower for D-serine R-alanine enantiomer also higher intensity on Cu{531}R surface In O1s region, 0.11 higher In the N1s spectrum, 0.10 In C1s spectrum 0.06 R-adsobate/R-surface&S-adsorbate/S-surface

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