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