Olesya A. Krumkacheva † , Vitaly R. Gorelik † , Elena G. Bagryanskaya † , Natalia V. Lebedeva ‡ and Malcolm D. E. Forbes ‡ Supramolecular Photochemistry in β- Cyclodextrin Hosts: A TREPR, NMR, and CIDNP Investigation † International Tomography Center, Institutskaya 3a, Novosibirsk 630090, Russia ‡ Caudill Laboratories, Department of Chemistry, CB #3290, University of North Carolina, Chapel Hill, North Carolina 27599-3290
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Supramolecular Photochemistry in β-Cyclodextrin Hosts: A TREPR, NMR, and CIDNP Investigation
Olesya A. Krumkacheva † , Vitaly R. Gorelik † , Elena G. Bagryanskaya † , Natalia V. Lebedeva ‡ and Malcolm D. E. Forbes ‡. † International Tomography Center, Institutskaya 3a, Novosibirsk 630090, Russia - PowerPoint PPT Presentation
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Olesya A. Krumkacheva†, Vitaly R. Gorelik†,
Elena G. Bagryanskaya†, Natalia V. Lebedeva‡ and
Malcolm D. E. Forbes‡
Supramolecular Photochemistry in β-Cyclodextrin Hosts: A TREPR, NMR, and CIDNP Investigation
† International Tomography Center, Institutskaya 3a, Novosibirsk 630090, Russia‡ Caudill Laboratories, Department of Chemistry, CB #3290, University of North
Carolina, Chapel Hill, North Carolina 27599-3290
The Host-Guest systems as “nanocontainers” for the photochemical reaction
It can be used for the directional synthesis
hν
The application the Chemical Induced Dynamic Nuclear Polarization (CIDNP) and TR EPR methods allows to obtain information about the mechanism of photochemical reaction inaccessibleby other methods.
Carrying out photochemical reaction in organized media can lead to the product structure changing
Alteration of the re-encounter statistics and average distance between partners in radical pairAlteration the nature of the excited statesReactivity between host and guest
TR EPR method
nonequilibrium population of spin level
EPR signal
Laser pulse
Direct observation of the short-lived paramagnetic intermediates (triplet molecules, radicals) formed during photolysis
M h R1(H)••R2 T R1(H)••R2
SM *S MT
R1(H)• •R2
absorption
emission
Investigation of the radical’s mobility
M h R1(H)••R2 T R1(H)••R2
S
In-cage products
M *S MT
R1(H)• •R2Escape products
CIDNP method
9.6 3 2 1
9
88'
7
6
5
4
3
2
1
, ppm
emission
enchanced absorption
Advantages:
1) Investigation of the mechanisms of photochemical radical
reactions
2) Possibility to detect product with low yield (10-6 M/l)
3) Detection of intermediate product
Investigation of the influence of β-cyclodextrin presence on the mechanism of the ketones photolysis:
dibenzyl ketone (DBK), deoxybenzoin (DOB) and benzophenone (BP)
For the Complex formation : NMR and UV spectroscopy
For the Mechanism of photochemical reaction: TR EPR and CIDNP methods
Goal:
Research Methods:
Ketone’s photolysis
326 328 330 332 334 336
2.8 mT
b)
a)
1.1 mT
c)
5.7 mT
Магнитное поле, мТ
Guest
NMR spectrum
OH
PhCOPh
CD
CIDNP spectrum
Observed TR EPR spectrum
Ketyl radical
CD radical
Magnetic field, mT
Photolysis of -CD / benzophenone complex
hydrogen abstraction from CD cavity interior
Strong exchange interaction in radical pair
location of ketyl radical inside CD cavity
increasing of the Radical Pair lifetime
H
H O
H H
OH
PhCH2COPh
(PhCH2)2
Magnetic field, mT
Ketyl radical
Observed TR EPR spectrum
NMR spectrum
CIDNP spectrum
Guest
α-cleavage and hydrogen abstraction
Photolysis of -CD / deoxybenzoin complex
Strong exchange interaction in radical pair
location of ketyl radical inside CD cavity
formation of rearrangement product
Increasing of radical pair lifetime
O
CH2
H
-CD radicalCD
NO! TR EPR Signal
fast radicals recombination inside CD ( < 100 ns)
H
H
(PhCH2)2CO (PhCH2)2
NMR spectrum
CIDNP spectrum
O
Guest
α-cleavage
O
CH2
H
Photolysis of -CD / dibenzyl ketone complex
(PhCH2)2CO
Photophysics and photochemistry of DOB, DBK, and BP in β-CD inclusion complexes had been examined in detail. The DOB triplet state undergoes both reactions whereas the DBK triplet shows exclusively -cleavage and the BP triplet shows exclusively H-atom abstraction.
Results
Observation of rearrangement product of the radicals from -cleavage implies that there is substantial mobility of the radicals into the CD interior
It was found that there is a fast radicals recombination inside CD in the case of the -cleavage reaction (t < 100 ns)
It was shown that there is a strong exchange interaction between the ketyl and CD radicals, due to location of ketyl radical inside CD.