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Transcript of soon to begin …
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soon to begin …
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Michael Probst
Sassari, September 27, 2007
Electron – Molecule Reactions:Quantum Chemistry of Electron Attachment to Biomolecules
Institute of Ion Physics and Applied Physics, Innsbruck University, Technikerstraße 25, 6020 Innsbruck, Austria
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Collaboration with:
Natcha Injan, Jumras Limtrakul
Stephan Denifl, Fabio Zappa, Ingo Mähr, Manuel Beikircher,Sylwia Ptasinska,Tilmann Märk and Paul Scheier
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Aim:Application and understanding of electron-driven processes
Electron – Molecule Reactions:
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electron-driven processes ...
... are dominant in many areas of basic and applied Science and Technology.
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for example (1) ... Atmospheric
physics and planetary atmospheres
Radiation damage of DNA and cellular material
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for example (2) - related to... Astrophysics -
reactions in space
Radiation treatment
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for example (3) ...
Semiconductorplasmas
Nanotechnologyand surface engineering
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Our topic is related to the 2nd...
Radiation damage of DNA and cellular material
somewhat
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e
e
... but what does really happen ?
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e
e
...but what does really happen ?
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oven
hemisphericalelectron monochromator
quadrupolemass filter
channeltron SEM
Experimental setup ...
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Experimental result:
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Typical mechanism
An electron is captured in a dipole – bound state.
It enters an antibonding * orbital to form a metastable anion that can weaken a N-H (or C-H) bond.
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N1N1C6C6
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Suggested mechanism
An electron is captured in a dipole – bound state.
It enters an antibonding * orbital to form a metastable anion that can weaken a N-H (or C-H) bond.
H can dissociate and [M-H]- remains.
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Example: Adenine
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What we worked on …
2. Neutral and anionic energy surface –where do they cross ?
3. Why do similar molecules show different spectra ?
1. Which H dissociates most easily ?
(calculations of BDE)
(calculation of stable and metastable potential energy curves)
(analysis of molecular orbitals)
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1. Which H dissociates most easily ?
BDE System
of H from neutral anion
C2 4.74 3.63
N6 4.69 1.72
C8 5.06 2.53
N9 4.38 0.94
QC calculations (G2(MP2) on adenine):
BDE System
of H from neutral anion
C2 4.74 3.63
N6 4.69 1.72
C8 5.06 2.53
N9 4.38 0.94
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Extrapolation methods for BDE:
Low qual. methodLarge basis set
Low qual. methodSmall basis set
High qual. methodLarge basis set
High qual. methodSmall basis set
Basis setenergy
correction
Correlation energy correction
(LL-LS)+ (HL-LS)
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Extrapolation methods - G2:
6-11G(d,p) 6-11+G(d,p) 6-11G(2df,p) 6-11+G(3df,2p)
MP2 I K L D
MP4 J B C
QCISD(T) A X
We want to arrive at X:E[+] = E[B] - E[J]; E[2df] = E[C] - E[J]
12= (E[D] - E[I]) - (E[K] - E[I]) - (E[L] - E[I]) ==E[D] + E[I] - E[K] - E[L]
E[X] = E[A] + E[+] + E[2df] + 12
average error in ∆Hf = ±1.59 kcal/mol = 0.06 eV
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DBS
(A-H)-+H
*(N(9)-H)
01
EA(A-H)-
r(N(9)-H) (Å)
Ep
ot (
eV
)
EA(P-H)-
Mechanism of dissociation:Potential energy curves:
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• Neutral curve:
YES
• Stable part of the anionic curve: (excited state but below neutral curve)
• Metastable part of the anionic curve (above neutral):
• Avoided crossing: (In principle easy, accuracy is difficult …)
Can we calculate these curves ?
YES
YES
NOWith extrapolation methods for the ‘metastable energy’
YES
X
Mechanism of dissociation:Potential energy curves:
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Mechanism of dissociation:Potential energy curves:
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In principle, the probability of
M + e- [M-H]- + H
can be calculated from these curves !
(via tunneling rates; the accuracy is a problem)
Mechanism of dissociation:Potential energy curves:
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[A-H]- … H potential energy:
Eanion = Eneutral + Eelectron
Eneutral are calculated from UB3LYP/aug-cc-pVTZ
Eelectron are calculated from UOVGF/aug-cc-pVTZ
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[A-H] … H:
0
2
4
6
0 1 2 3 4
r[N9-H]
En
erg
y in
eV
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-6
-4
-2
0
2
4
6
0 1 2 3 4
r[N9-H]
En
erg
y in
eV
ESOMO = f(rN9-H)
UOVGF/aug-cc-pVTZ
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-6
-4
-2
0
2
4
6
0 1 2 3 4
r[N9-H]
En
erg
y in
eV
ESOMO = f(rN9-H)
Metastable part
UOVGF/aug-cc-pVTZ
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-8
-6
-4
-2
0
2
4
0 1 2 3 4 5
En
erg
y in
eV
%q
r[N9-H] = 1.3 Å
• Stabilise the anion by slightly increasing the nuclear charge.• extrapolate.
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ESOMO = f(rN9-H)
-6
-4
-2
0
2
4
6
0 1 2 3 4
r[N9-H]
En
erg
y in
eV -8
-6
-4
-2
0
2
4
0 1 2 3 4 5
En
erg
y in
eV
%q
-6
-4
-2
0
2
4
6
0 1 2 3 4
r[N9-H]
En
erg
y in
eV
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-6
-4
-2
0
2
4
6
0 1 2 3 4
r[N9-H]
En
erg
y in
eV
-6
-4
-2
0
2
4
6
0 1 2 3 4
r[N9-H]
En
erg
y in
eV
ESOMO = f(rN9-H)
+
0
2
4
6
0 1 2 3 4
r[N9-H]
En
erg
y in
eV
0
2
4
6
0 1 2 3 4
r[N9-H]
En
erg
y in
eV
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0
2
4
6
0 1 2 3 4
r[N9-H]
En
erg
y in
eV
[A-H] … H neutral and anionic curves:
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Why do similar purine derivatives show different spectra ?
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LUMO & Electrostatic potential:
ESP: negative, positive
Purine Adenine Dimethyladenine
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Concluding …
Some (but not all) features of the DEA process can be predicted.
Ssummary of experimental and theoretical work published in Angew. Chemie IE 46, p.5238 (2007)
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Thank you …Thank you …