Which comes first in one- electron-reduction? The Electron or the Proton? Einar Uggerud University...

Which comes first in Which comes first in one-electron-one-electron-reduction?reduction?

The Electron or the The Electron or the Proton?Proton?Einar Uggerud

University of Oslo

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Park City, Utah, 2 July, 2007.Park City, Utah, 2 July, 2007.

Part 1. Cation-Electron RecombinationSmall molecule models of electron capture dissociation

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Solar wind (”day time”):

O2 O2+

+ e-

The green colour of Aurora Borealis

Night:

O2+

+ e- (O2)* O + O

O2+

+ e- (O2)* O + O

O2

h

One of the O atoms is exited:

1S

1D= 557,7 nm

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Electron capture dissociation (ECD) of proteins/peptides

MHMHnnnn++ + e + e–– MH MHnn

((nn-1)+ -1)+ fragments fragments

Zubarev, R. A.; Kelleher, N. L.; McLafferty, F. W.Electron Capture Dissociation of Multiply Charged Protein Cations - a Nonergodic ProcessJ. Am. Chem. Soc. 1998, 120, 3265-3266.

Characteristics of ECD of multiply protonated proteins/peptides

• Specific for dissociation of backbone N-C bond

• Cleaves disulfide bridges• Leaves most side-groups untouched• Fast (non-ergodic ?)• Loss of H

R NH3 + e R NH3

R NH2 + H

Electron capture of protonated side Electron capture of protonated side group (Lys): Release of ”hot” Hgroup (Lys): Release of ”hot” H

H + C

Rn

H O

NH C

Rn+1

H

C

Rn

H O

NH C

Rn+1

HH

C

Rn

H O

NH C

Rn+1

HH

+

Collisions between hot H and peptide ?

CRYRING in Stockholm

Reaction zoneIon energy: E(NH4

+)= 4.5 MeVVelocity =2 % of c

17 m

10-12 mbar

Andersson et al., in preparation

Small scale models of relevance to ECD:Small scale models of relevance to ECD:

NH4++ + e- NH3 + + H

CH3SSHCH3+ + e- → CH3SH + CH3S

CD3COHNHCH3+ + e- → CD3C(OH)NH + CH3

A. Al-Khalili, et al. J. Chem. Phys., 121(12) 5700-5708 (2004).P. Andersson et al., in preparation.

NH4+

NH4

HF/aug-cc-pVDZ 388 kJ/molMP2/aug-cc-pVDZ 429 kJ/molCCSD(T)/aug-cc-pVQZ 436 kJ/mol

HF/aug-cc-pVDZ 66 kJ/molMP2/aug-cc-pVDZ 52 kJ/molCCSD(T)/aug-cc-pVQZ 50 kJ/mol

HF/aug-cc-pVDZ 89 kJ/molMP2/aug-cc-pVDZ 53 kJ/mol CCSD(T)/aug-cc-pVQZ 40 kJ/mol

NH3 + H

HF/aug-cc-pVDZ 389 kJ/molMP2/aug-cc-pVDZ 431 kJ/molCCSD(T)/aug-cc-pVQZ 436 kJ/mol

V. Bakken, T. Helgaker, and E. UggerudEuropean Journal of Mass Spectrometry, 10 (2004), 625 – 638.

Product BTransition structure BProduct ATransition structure A

Reactant

Direct reaction dynamics

mi

d2qi

dt2=-

∂V(q)∂qi

mi

d2qi

dt2=-

∂V(q)∂qi

• Ab initio potential energy surfaceAb initio potential energy surfacegenereated in situ.genereated in situ.• Initial conditions sampled fromInitial conditions sampled fromBoltzmann distribution.Boltzmann distribution.• 20 – 100 trajectories20 – 100 trajectories

Helgaker, T.; Uggerud, E.; Jensen, H. J. A.Chem. Phys Lett. 1990, 173, 145-150.

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V. Bakken, T. Helgaker, and E. UggerudEuropean Journal of Mass Spectrometry, 10 (2004), 625 – 638.

Trajectory calculations, Trajectory calculations, NH4+ + e– NH4

HF/aug-cc-pVDZ

RC energy corresponds to ≈ 7000 K25 trajectories:

NH4 NH3 + H<T> = 221 kJmol-1 (50 %)

V. Bakken, T. Helgaker, and E. UggerudEuropean Journal of Mass Spectrometry, 10 (2004), 625 – 638.

ch3cohnch3 + h (298K,1500meV,traj0001) b3lyp/4-31g

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V. Bakken, T. Helgaker, and E. UggerudEuropean Journal of Mass Spectrometry, 10 (2004), 625 – 638.

N

O

H O

XH

X = O, NH etc.

e-

N

O

H O

XH

N

O

H O

X

H

N

O

H

O

X

H

fast, ps

+

N

O

H O

X

H

slow, RRKM

IVR

N

O

H O

X

H

thermal

Part 2. Electron-bound dimersFine-tuning H2 bond activation on a gliding scale from weak dihydrogen interaction to covalent H–H

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2H+ + 2e- = H2

Aqueous solution: Ered = 0.000 V

Gas phase: H° = -3060 kJmol-1

Two steps:Two steps:

2H+ + e- = H2+

H2+ + e- = H2

WikipediaWikipedia

Hydrogen Fuel CellHydrogen Fuel Cell

Laubereau, et al. TU Münchenwww.e11.ph.tum.de/forschung/ projekte/esolv.en.htm

Solvated electrons

Boag and Hart, Nature 1963, 197, 45.Keene, Nature 1963, 197, 47.

Electron solvated by two water molecules is not stableElectron solvated by two water molecules is not stable

(HOH)e-(HOH) H2O + H2O + e- H°= -152 kJmol-1

mp2/6-311+g(d,p)

SOMOSOMO

Surprise:Surprise:

Electron solvated by two HBr (or two HCl) molecules is stableElectron solvated by two HBr (or two HCl) molecules is stable

mp2/6-311+g(d,p)

Rauk, A.; Armstrong, D. A. J. Phys. Chem. A 2002, 106, 400-403.

(HBr)2-

Among the hydrides of the main group elements (EHn)only HBr and HCl and form stable electron boundDimers.

What about the isoelectronic (EHn)H+ ?

((EHn)H+)2- = [HnE–H–H–EHn]+.

[HnE–H–H–EHn]+.

HnEPoint group

r(HH),Å

MP2

(HH), cm-1

MP2

H3N D3d 2.17 2225

H3P D3d 0.94 1881

H3As C2 0.88 2349

H2O C2 1.17 1680

H2S C2 0.90 2176

H2Se C2h 0.84 2794

HF C2 1.08 2134

HCl C2 0.95 2094

HBr C2 0.89 2376

He Dh 1.05 2398

Ne Dh 1.05 2398

Ar Dh 1.00 2285

Kr Dh 0.94 2326

Xe Dh 0.87* -

[HnE–H–H–EHn]+.

*TZVPP*TZVPP

[HnE – H–H – EHn]+.

[H3N – H–H – NH3]+.

H–H+.

[H3P – H–H – PH3]+.

[H3As – H–H – AsH3]+.

H–H

Alternative point of view, electron donation to H2+

2HnE + H2+ HnE–H–H–EHn

+ Ecom

HnE E

H2losse

Ecrit

H2lossf

E

rearrg

Ecrit

rearrh

E

Hlossi

Ecrit

Hlossj

H3N 0 132 -58 22

H3P -63 38 12 35

H3As -80 21 33 56

H2O 56 74 -86 13

H2S -59 41 26 61

H2Se -80 27 52 91

HF 179 - -68 6

HCl -19 - -5 41

HBr -45 46 27 -

He 686  1 1 52 -

Ne 522 1 1 36 -

Ar 112 24 25 2 -

Kr 24 42 45 21 -

Xe -36 -36 45 91 n.c.a) Gain in energy for 2HnEH+ + e- HnE–H–H–EHn

+, b) Gain in energy for 2HnE + H2+ HnE–H–H–EHn

+.c) Proton affinity, data from ref Uggerud2006, d) Data from NIST web site.e) Energy of reaction for HnE–H–H–EHn

+ E2H2n+ + H2. f) Critical energy for HnE–H–H–EHn

+ E2H2n+ + H2.

g) Energy of reaction for HnE–H–H–EHn+ E2H2n–H–H+. h) Critical energy for HnE–H–H–EHn

+ E2H2n–H–H+. i) Energy of reaction for HnE–H–H–EHn

+ HnE–H–EHn+ + H, j) Critical energy for HnE–H–H–EHn

+ HnE–H–EHn+ + H.

Stability considerationsStability considerations

Two steps:Two steps:

2HnE–H+ + e- HnE–H–H–EHn

+

HnE–H–H–EHn+ 2HnE + H2

2H+ + 2e- = H2

Thank you for your attention!

Thanks are due to:

Patrik AnderssonVebjørn BakkenTrygve HelgakerAndreas KrappGernot Frenking