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DESCRIPTION
soon to begin …. Electron – Molecule Reactions: Quantum Chemistry of Electron Attachment to Biomolecules. Michael Probst. Institute of Ion Physics and Applied Physics, Innsbruck University, Technikerstraße 25, 6020 Innsbruck, Austria. Sassari, September 27, 2007. Collaboration with:. - PowerPoint PPT PresentationTRANSCRIPT
soon to begin …
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
Collaboration with:
Natcha Injan, Jumras Limtrakul
Stephan Denifl, Fabio Zappa, Ingo Mähr, Manuel Beikircher,Sylwia Ptasinska,Tilmann Märk and Paul Scheier
Aim:Application and understanding of electron-driven processes
Electron – Molecule Reactions:
electron-driven processes ...
... are dominant in many areas of basic and applied Science and Technology.
for example (1) ... Atmospheric
physics and planetary atmospheres
Radiation damage of DNA and cellular material
for example (2) - related to... Astrophysics -
reactions in space
Radiation treatment
for example (3) ...
Semiconductorplasmas
Nanotechnologyand surface engineering
Our topic is related to the 2nd...
Radiation damage of DNA and cellular material
somewhat
e
e
... but what does really happen ?
e
e
...but what does really happen ?
oven
hemisphericalelectron monochromator
quadrupolemass filter
channeltron SEM
Experimental setup ...
Experimental result:
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.
N1N1C6C6
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.
Example: Adenine
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)
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
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)
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
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:
• 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:
Mechanism of dissociation:Potential energy curves:
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:
[A-H]- … H potential energy:
Eanion = Eneutral + Eelectron
Eneutral are calculated from UB3LYP/aug-cc-pVTZ
Eelectron are calculated from UOVGF/aug-cc-pVTZ
[A-H] … H:
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)
UOVGF/aug-cc-pVTZ
-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
-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.
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
-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
0
2
4
6
0 1 2 3 4
r[N9-H]
En
erg
y in
eV
[A-H] … H neutral and anionic curves:
Why do similar purine derivatives show different spectra ?
LUMO & Electrostatic potential:
ESP: negative, positive
Purine Adenine Dimethyladenine
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)
Thank you …Thank you …