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