Ground State Electronic Structures from Multi-Edge Analysis

Ground State Electronic Structures

from

Multi-Edge Analysis

Robert K. Szilagyi Montana State University, Bozeman, MT

computational.chemistry.montana.edu

Reminders: unique research opportunities

(no other spectroscopic technique for S and Cl)

facilities

(beamlines, instrumentation, sample prep. expertise)

semi-empirical theory

(effective nuclear charge, transition dipole, covalency

On a gloomy and snowy November afternoon …

Nitrosated

β-subunit of human hemoglobin

N.-L.CHAN,P.H.ROGERS,A.ARNONE 1.9 Å CRYSTAL STRUCTURE OF THE S-NITROSO FORM OF LIGANDED HUMAN HEMOGLOBINBIOCHEMISTRY, 1998, 37, 16459

βCys93

RSNO compounds (CCDB)

RSNO compounds: geometric structure

RSNO compounds: electronic structure

S-N double (π) bond

S-N single (σ) bond

S-C single (σ) bond

large sulfurcontribution

Biochemical and Biophysical Research Communications, 2005, 330(1), 60-64

S K-edge XAS of S-nitrosated glutathione (GSNO)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

2460 2465 2470 2475 2480 2485calibrated (thiosulfate) photon energy, eV

norm

aliz

ed X

AS

inte

nsity

(FF/

I0)


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

2467 2469 2471 2473 2475 2477 2479calibrated (thiosulfate) photon energy, eV

norm

aliz

ed X

AS

inte

nsity

(FF/

I0)

S K-edge XAS of S-nitrosated glutathione (GSNO)

ON-S σ*S-C σ*

ON-S π*

2471.5 eV

2473.4 eV

2475.0 eV

(0.0 eV)

(2.1 eV)

(4.0 eV)

S K-edge XAS of SNO compounds

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2467 2469 2471 2473 2475 2477 2479 2481

Photon Energy, eV

Nor

mal

ized

XA

S In

tens

ity

GSNO

SNAP

S-nitroso glutathione

N-acetyloxy-3-nitrosothiovaline

S-NOπ*

S-NOσ* S-C

σ*

S K-edge XAS of S compounds

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2467 2469 2471 2473 2475 2477 2479 2481

Photon Energy, eV

Nor

mal

ized

XA

S In

tens

ity

S-C σ*

H-S σ*

S-C σ* NaSEt

Cys

Na+

-S-CH2

-CH3

H-S-CH2

-CH3

S charge becomes less negativeZeff (S) increases


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2467 2469 2471 2473 2475 2477 2479 2481

Photon Energy, eV

Nor

mal

ized

XA

S In

tens

ity

ON-S π*

ON-S σ*

S-C σ*

H-S σ*

S-C σ*

Cys

GSNO

H-S-CH2

-R


ON-S-CH2

-R

ON+ -S-CH2

-R


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2467 2469 2471 2473 2475 2477 2479 2481

Photon Energy, eV

Nor

mal

ized

XA

S In

tens

ity

ON-S π*

ON-S σ*

S-C σ*S-C σ*

H-S σ*

S-C σ* NaSEt

Cys

GSNO


S K-edge XAS as detection method for SNO

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2467 2468 2469 2470 2471 2472 2473 2474 2475 2476 2477

Photon Energy, eV

Nor

mal

ized

XA

S In

tens

ity

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0D

erivatives of XA

S IntensitySNO-hemoglobin

ON-S p* fit

First derivative

Second derivative

S 1s→ ON-S π* fit


Multi-edge XAS

Conceptually NOT an original idea!

Conscious exploitation of complementary ground state electronicstructure information from multiple absorbers

Molecular Orbital Theory:

Experimentally probing the excitation of an absorber core electron (1s for K) to a unoccupied/virtual molecular orbital with some absorber contribution.

Donor orbital: S 1s (localized on S, in MO picture as s.a.l.c.)

Acceptor orbital: ϕ* = Σ

ci

φi

for a ‘simple’

M-S

bond: ϕ* = cM,d

φM

(nd) + cM,s

φM

(n+1 s) + cM,p

φM

(n+1 p)

cS,s

φS

(3s) + cS,p

φS

(3p) + cS,d

φS

(3d)

Multi-edge XASfor a ‘simple’

M-S bond:

ϕ* = cM,d

φM

(nd) + cM,s

φM

(n+1 s) + cM,p

φM

(n+1 p) cS,s

φS

(3s) + cS,p

φS

(3p) + cS,d

φS

(3d)

metal contribution/character ligand character/covalency

for intense spectral features in absorption spectroscopy –

Δl = 1

M 2p M 1s L 2pL 1s

metal L-edge XAS metal K-edge XAS ligand K-edge L-edge

SSRL BL10-1/8-2 BL7-3/9-3/4-1/4-3 BL6-2/4-3 BL10-1/8-2

SSRL BL10-1 SSRL BL7-3 SSRL BL4-3

Multi-edge XAS

2000eV 3000eV 4000eV 5000eV

2146eVP

2472eVS

2822eVCl

3206eVAr

3608eVK

4038eVCa

4492eVSc

4966eVTi

5465eVV

K edgesexcitationform n=1orbital

L edgesexcitationsform n=2orbitals

2007eVSr

2156eVY

2307eVZr

2465eVNb

2625eVMo

2793eVTc

2967eVRu

3146eVRh

3330eVPd

2000eV 3000eV

M edgesexcitationsform n=3orbitals

2365eVHf

2469eVTa

2575eVW

2682eVRe

2792eVOs

2909eVIr

3027eVPt

2300eV 3000eV

Multi-edge XAS at SSRL BL6-2/4-3

Pd

Cl

Cl

PP

LUMO

Multi-edge XAS: A non-biological, but simple example

Inorganica Chimica Acta, 2008, 361(4), 1047-1058

2

Multi-edge XAS: A non-biological, but simple example

Phosphorous 3p character of the palladium-phosphorous bonds is determined from phosphorous K-edge XAS

Multi-edge XAS: phosphorous K-edge

Chlorine 3p character of the palladium-chlorine bonds is determined from chlorine K-edge XAS

Multi-edge XAS: chlorine K-edge

Metal 4d character of the palladium-ligand bonds is determined from palladium L-edge XAS (only LIII

edge is shown)

Multi-edge XAS: palladium L-edge

Multi-edge XANES: chloropalladium(II/IV)

K2

PdIICl4 K2

PdIVCl6closed shell d8 closed shell d6

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

2815 2817 2819 2821 2823 2825 2827 2829 2831 2833 2835Photon Energy, eV

Nor

mal

ized

XA

S In

tens

ity

Cs2ZnCl4

Cs2CuCl4

NaCl

D4h

Td

Cl 1s

Cl 3psalc

Cu 3dx2-y2

ϕ*

= Cu 3dx2-y2

_ α

Cl 3psalc)1( 2α−

Chlorine K-edge XANES: Cu(II) is the hydrogen atomof inorganic chemistry

(Solomon)

Multi-edge XANES: Cl Pd(II) is the hydrogen atomof organometallic chemistry


Multi-edge XANES: Pd


2

d,lligands ligands orbitals

o,lo,ld,ld,lligands

Md,l2 ||cc||c)1(I

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛>φφ<α−>φφ<α−∝ ∑ ∑ ∑∑ rr

Experimental M-L covalency

LM2

a )1( φα−φα−=Ψacceptor orbital ∑ ∑ φ=φligands orbitals

o,lo,lL c

d,lligands

d,ld c φ=Ψ ∑donor orbital (donor is 1s for K-edge excitations)

electric dipole allowed transition/Fermi golden rule: 2da ||I >ΨΨ<∝ r

ligand core/metal overlap ≈

0 ligand core/ligand core overlap ≈

0

>ΨΨ<α−>ΨΨ< ∑ )(Rad||)(Rad31cc|| s1,lnp,l

ligandsnp,ls1,lda rrfor 1s → np excitation

< R

> dipole integral

><α=>ΨΨ<= − R22)s1(L)p3(LM 3

1||I r

JACS, 1992, 112(4), 1643-1645

Multi-edge XANES: chloropalladium(II/IV)

using I(Cl-t ) = 21.0 eV → ~50% Cl covalency in both [PdIICl4 ]2-

and [PdIVCl6 ]2-

from complementarity this corresponds to ~50% Pd covalency ineach molecular orbital probed by XAS

from area under pre-edge features at Pd L-edges we get I(PdII) = 20.8 (SSRL) 16.9 (ALS) eVI(PdIV) = 14.1 (SSRL) 11.9 (ALS) eV

to test the transferability we used I(PdII) to determine the covalency of Pd-Cl bonds in PdCl2 to be ~50% with a new transition dipole integral for I(Cl-b )16.4 (SSRL) 14.5 (ALS)

Pd-Cl bond in organometallic chemistry is the

Fe-S bond in coordination chemistry

Multi-edge XANES: non-innocent ligands

C

A) Crystal structure of [Ph2

BPtBu2

]CuII(NTol2

)B) Structural overlay of reduced and oxidized formsC) Ligand based redox chemistry

2+

-

-

JACS, 2009, 131(11), 3878-3881


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

8967 8974 8981 8988 8995 9002Photon Energy, eV

Nor

mal

ized

Inte

nsity 8984.5 eV

8982.5 eV8982.2 eV

first electric dipole allowed Cu 1s → 4p transition

8987.4 eVCu K-edge

CuICl

anhydrous CuIICl2

{[Ph2BPtBu2]CuI(NTol2)}

{[Ph2BPtBu2]CuII(NTol2)}


0.0

0.5

1.0

1.5

2.0

2.5

3.0

2140 2142 2144 2146 2148 2150Photon Energy, eV

Nor

mal

ized

Inte

nsity

2145.3 eV

P 1s → P-C σ* P 1s → P 4p

2146.5 eV2146.5 eV

2147.9 eV2147.9 eV

P 1s → P 3p/4p basedelectric dipole allowedtransitions

P K-edge

PPh3



2171.1 eV


0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

922 925 928 931 934 937 940Photon Energy, eV

Nor

mal

ized

inte

nsity

Cu 2p → 3d transition

*

931.9 eV

*

930.4 eV

Cu → L backdonation

transition envelopes

Cu LIII-edge

CuICl

anhydrous CuIICl2



0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

922 925 928 931 934 937 940Photon Energy, eV

Nor

mal

ized

inte

nsity

931.9 eV

930.4 eV Cu LIII-edge

anhydrous CuIICl2


Multi-edge XANES: quantitative treatment

What is the Cu contribution to the redox active orbital?

What is the % Cu characterthe blue vs. green areascorrespond to?


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2720 2770 2820 2870 2920 2970 3020Photon Energy, eV

Ren

orm

aliz

ed In

tens

ity

Cs2CuIICl4

anhydrous CuIICl2

Cl K-edge

4 Cl absorbers

2 Cl absorbers


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2815 2818 2821 2824 2827 2830Photon Energy, eV

Ren

orm

aliz

ed X

AS

Inte

nsity

D2d Cs2CuCl4pre-edgearea = 0.521 eV~ 30% Cl 3p

anhydrous CuCl2 pre-edge area = 0.616 eV~ 35% Cl 3p

Cs2CuIICl4anhydrous CuIICl2

Cl K-edge

4 Cl absorbers

2 Cl absorbers


0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

922 925 928 931 934 937 940Photon Energy, eV

Nor

mal

ized

inte

nsity

931.9 eV

930.4 eV Cu LIII-edge

anhydrous CuIICl2


35% Cl 3p characterwith limited 4s mixingCu 3d character is ~ 65%pre-edge area = 4.114 eV

pre-edge area 0.910 eVCu 3d character ~14%

Calculated spin densities for [Ph2

BPtBu2

]CuII(NTol2

)

(p-tol)2

: 20%

BPh2

: 2%

PtBuPh2

: 15%

N: 49%

Cu: 13%

JACS, 2009, 131(11), 3878-3881

galactose oxidase

1GOGfungus Dactylium dendroides

OOH

CH2

OH

OH

OH OH

OOH

CH

OH

OH OH

O

+ O2

+ H2

O2

State-of-the-Art S K-edge Data

galactose oxidase

His581

His496

Tyr495

Tyr272Cu

water

Cu2+/•O(Tyr-Cys)

Cu2+/O(Tyr-Cys)

Cu+/O(Tyr-Cys)

400 mV

150 mV

Cys228


galactose oxidase

His581

His496

Tyr495

Tyr272Cu

water

Cys228

State-of-the-Art S K-edge Data GO samples:93% Cu-loaded

150 μL0.633 mM

In phosphate buffer

w/2M urea, pH=750-fold excess of

K3 Fe(CN)637±3% oxidation

BL6-2 only!LHe cryojet only!

19 absorbers:13 Met 4 Cys-Cysthioether crosslink

JACS, 2010, submitted


0.0

0.5

1.0

1.5

2.0

2.5

3.0

2465 2467 2469 2471 2473 2475 2477 2479

Photon Energy, eV

Nor

mal

ized

XA

S In

tens

ity ferricyanide oxidized

as isolated/semi reduced

dithionite reduced* buffer

contaminationTyrCys1-

(Met13Cys5)

TyrCys1-

(Met13Cys5)

His581

His496

Tyr495

Tyr272Cu

water

Cys228


0.0

0.5

1.0

1.5

2.0

2.5

3.0

2465 2467 2469 2471 2473 2475 2477 2479

Photon Energy, eV

Nor

mal

ized

XA

S In

tens

ity ferricyanide oxidized

as isolated/semi reduced

dithionite reduced

presence of Tyr-Cys• in Met13Cys5 background

TyrCys1-

(Met13Cys5)

TyrCys1-

(Met13Cys5)

oxidized-reducedXANES spectrum

renormalized pre-edgehhlw = 0.40 eV

A = 0.78thus D0 = 0.31

* buffer contamination


Experimental area D0

= 0.016 eV for Nabs

= 19 and nholes

= 1.

S character (α2) is defined by the transition dipole expression

3p) 1s I(S 3p) (SN

n 31D 2

absorber

holes0 →= α

I(S 1s→3p) for sulfide

(formally Z=-2)

6.54 eV

for thiolate (formally Z=-1)

8.47 eV

for thioether

(formally Z=0)

10.4 eV

and with corrections for partial Cu loading and Tyr-Cys oxidation:

S character (α2) from XAS for oxidized holo GO is 24±11% (calc.: 22±2%)

from EPR for oxidized apo GO is 20±3% (calc: 15±1%)JACS, 2010, submitted

Ground State Electronic Structures from Multi-Edge Analysis

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