adsorption of small amino acids on chiral metal surfaces tuğçe eralp university of reading
TRANSCRIPT
ADSORPTION of SMALL AMINO ACIDS on CHIRAL METAL SURFACES
Tuğçe Eralp
University of Reading
Organic/Metal InterfacesEnantioselectivity?
Amino acids
Carboxylic acids with extra NH2 group
– Small
– Chiral, enatiomeric
– Additional functional groups
– Different side chains, intermolecular interactions
Cu{531}R&S
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
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
*M. J Gladys, A. V Stevens.; N. R Scott, G.; Jones, D. Batchelor, , G. HeldJ. Phys. Chem. C 2007; 111(23), 8331
Possible long range arrangementon (311) and (110) microfacets
Our Experiments
GLYCINE
On Cu{531} surface
SERINE
GLYCINE on Cu{531}
• Coverage Dependency (XPS, NEXAFS)
• Temperature Effect (desorption properties)
• Multilayers • NEXAFS
Glycine Salt Forms
HO
O
NH2O
O
NH2
O
O
NH3
Neutral Anionic Zwitterionic
Saturation Coverage of Glycine
1.4
1.3
1.2
1.1
1.0
INT
EN
SIT
Y (
AR
B.U
NIT
S)
295 290 285 280BINDING ENERGY (eV)
40 MIN 60 MIN, SAT
C1s
3.0
2.5
2.0
1.5
1.0
534 532 530 528
40MIN 60MIN, SATO1s
1.6
1.4
1.2
1.0
402 400 398 396 394
SATURATION COVERAGE
N1s
1 wide peak in O1s region, FWMH is 1.6514 eV1 peak in N1s region, showing one state FWHM: 0.97 eV. 2 peaks in C1s region,
carbonyl and methylene C
ADSORBED AS ANIONIC SALTNH2CH2COO-
Glycine Desorption, Annealing Steps
1.8
1.6
1.4
1.2
1.0INT
EN
SIT
Y (
AR
B.
UN
ITS
)
402 400 398 396 394 392BINDING ENERGY (eV)
BEFORE ANNEALING 350K 450K 500K
N1s
3.0
2.5
2.0
1.5
1.0
532 531 530 529 528
BEFORE ANNEALING 350K 500K
O1s
292 290 288 286 284 282 280BINDING ENERGY (eV)
BEFORE ANNEALING 350K 450K 500K
C1s
0.2 eV shift for C peaks0.46 eV for the N peakAlmost 0 for O peak
Desorption, ALSO decomposition around 450KCO2 leaaving the surface
Glycine MultilayersIN
TE
NS
ITY
(A
RB
. U
NIT
S)
292 290 288 286 284 282 280BINDING ENERGY (eV)
C1s MONOLAYER MULTILAYER
INT
EN
SIT
Y (
AR
B.
UN
ITS
)
406 404 402 400 398 396 394 392 390BINDING ENERGY (eV)
N1s MONOLAYER MULTILAYER
INT
EN
SIT
Y (
AR
B.
UN
ITS
)
538 536 534 532 530 528 526BINDING ENERGY (eV)
O1sMONOLAYER MULTILAYER
A broad N1s signal at 401.89 eV FWHM is 2.5 eVPossible two glycine
speciesO1s spectrum, at 533.74 eV,
shifted by 3.12 eVFWHM is 2.01 Two salts together zwitterionic and neutral
NEXAFS
1.5
1.0
0.5
0.0
INT
EN
SIT
Y (
AR
B.
UN
ITS
)
560555550545540535530525PHOTON ENERGY (eV)
resonance
C-O sigma resonanceC-C sigma resonance -54deg -36deg -18deg 0deg 18deg 36deg 54deg 72deg
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
PE
AK
IN
TE
NS
ITY
(A
RB
. U
NIT
S)
806040200-20-40-60AZIMUTHAL ANGLE
peak height fit_height cos1_y cos2_y
Different azimuthal anglesO K-Edge NEXAFS Spectrum
• Angular dependency• * resonance peak at 533 eV• -resonances due to C-C and C-O• Two species, equal amounts, A1/A2=1• 1 {311} microfacets
Fit for the angle vs height of p-resonance peak
I() = A1[cos( - 1)]2 + A2[cos( – 2)]2
A1 1.17
1 -55.3o
A2 1.16
2 53.9o
Similar values determined for alanine (-58o and 51o)
Half Saturation Coverage of Glycine
2.5
2.0
1.5
1.0
0.5
0.0
INT
EN
SIT
Y
560555550545540535530PHOTON ENERGY (eV)
-90 deg 90 deg -72 deg 72 deg -54 deg 54 deg -36 deg 36 deg -18 deg 18 deg 0 deg
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Hei
ght
806040200-20-40-60Azimuthal Angle
Height fit_ColumnB cos2_y_2 cos1_y
A1 1.15
1 -55.5o
A2 0.85
2 48.7oFit for the angle vs height of -resonance peak
O K-Edge NEXAFS
• Two orientations • A1/A2 is 1.35
one adsorption site is more favourable
Similar values determined for alanine (-58o and 51o)
Similar values determined for alanine and sat glycine
NEXAFS, Annealed to 400K2.0
1.5
1.0
0.5
0.0INT
EN
SIT
Y (
AR
B.
UN
ITS
)
560555550545540535530525PHOTON ENERGY (eV)
-90 deg -72 deg -54 deg -36 deg -18 deg 0 deg 18 deg 36 deg 54 deg 72 deg 90 deg
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
806040200-20-40-60
peak height fit_height cos1_y cos2_y
O K-Edge NEXAFS
A1 0.94
1 -58.4
A2 0.95
2 52.4
• Two species• Equal amounts on the surface• The orientation not changing
with annealing
Similar values determined for alanine and sat glycine
So Far, About Glycine on Cu{531}
At room temperature, Glycine adsorbed in carboxylate form (anionic salt) through two O and NAccording to NEXAFS, 2 species, equal amount of each sitting on {311} and {110} microfacets like AlanineWhen annealed, no change in adsorption sites. Possibly decomposition around 450K, CO2 leaving the surfaceAt 100 K, possibly two salts together, shift to higher BE
For low and high coverages No difference in BE and in adsorbtion sitesAccording to NEXAFS
Difference in abundancy of one of the species Further LEED and TPD experiments will be performed
SERINE on Cu{531}
L-Serine D-Serine
Serine enatiomers are chiral and have additional OH group
THANK YOU!
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
Further LEED and TPD experiments will be performed
Symptoms for enantioselectivity – Differences in orientation (NEXAFS)– Differences in intensities (XPS)
L-Serine Uptake Curves
3.5
3.0
2.5
2.0
1.5
1.0
INT
EN
SIT
Y (
AR
B.
UN
ITS
)
535 534 533 532 531 530 529BINDING ENERGY (eV)
90 MIN 150 MIN 210 MIN 240 MIN
O1s
2.2
2.0
1.8
1.6
1.4
1.2
1.0
INT
EN
SIT
Y (
AR
B.
UN
ITS
)
404 402 400 398 396BINDING ENERGY (eV)
90 MIN 150 MIN 240 MIN
N1s2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
INT
EN
SIT
Y (
AR
B.
UN
ITS
)
290 288 286 284 282BINDING ENERGY (eV)
C1s 90 MIN 150 MIN 240 MIN
• 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
NEXAFS3
2
1
0
INT
EN
SIT
Y (
AR
B.
UN
ITS
)
320315310305300295290PHOTON ENERGY (eV)
Hz Vt 30º 45º 60º
C-NEXAFS
2.0
1.5
1.0
0.5
0.0
PE
AK
HE
IGH
T
806040200POLARIZATION ANGLE
Peak Height fit_height cos2_y cos1_y
Angle vs height of -resonance peak fit
SAT-L
A1 2.04
1 -59.4
A2 1.68
2 22.3
• Different polarization angles• Angular dependency• * resonance peak at 289 eV• 2 species
C-NEXAFS Sat coverage of L-Serine
Any Enantioselectivity?
SAT-L HALF-L SAT-D
A1 2.04 0.09 1.30
1 -59.4 -13.6 -20.1
A2 1.68 0.02 1.52
2 22.3 95.2 47.3
High difference in values between two enantiomersAlso between two coverages
Aim of the Project
What? To answer...
Any enantiospecifity/selectivity of the surface?
Why? Importance... In future, these chiral surfaces can
be used for Heterogenous catalysis reactions Purifying/ seperating enantiomers
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
Moreover...
3.5
3.0
2.5
2.0
1.5
1.0
INT
EN
SIT
Y (
AR
B.
UN
ITS
)
536 534 532 530 528BINDING ENERGY (eV)
L-SERINE, SAT D-SERINE, SAT
O1s
2.2
2.0
1.8
1.6
1.4
1.2
1.0
INT
EN
SIT
Y (
AR
B.
UN
ITS
)
402 400 398 396BINDING ENERGY (eV)
L-SERINE, SAT D-SERINE, SATN1s
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
INT
EN
SIT
Y (
AR
B.
UN
ITS
)
292 290 288 286 284 282 280BINDING ENERGY (eV)
L-SERINE,SAT D-SERINE, SAT
C1s
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