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
Caudill Laboratories, Department of Chemistry, CB #3290, University of North
Carolina, Chapel Hill, North Carolina 27599-3290
‡
Supramolecular Photochemistry in β-Cyclodextrin
Hosts: A TREPR, NMR, and CIDNP Investigation
The Host-Guest systems as “nanocontainers” for the
photochemical reaction
hν
Carrying out photochemical reaction
in organized media can lead to the product
structure changing
It can be used for the directional synthesis
Alteration of the re-encounter statistics and average distance
between partners in radical pair
Alteration the nature of the excited states
Reactivity between host and guest
The application the Chemical Induced Dynamic Nuclear
Polarization (CIDNP) and TR EPR methods allows to obtain information
about the mechanism of photochemical reaction inaccessible
by other methods.
TR EPR method
M
h
M
*S
T
M
R1(H)••R2 T
R1(H)•
R1(H)••R2
•R2
EPR signal
Laser pulse
absorption
nonequilibrium population of
spin level
Direct observation of the short-lived
paramagnetic intermediates (triplet
molecules, radicals) formed during
photolysis
Investigation of the radical’s mobility
emission
S
CIDNP method
h
M
T
*S
M
M
R1(H)••R2 T
R1(H)•
Escape products
•R2
R1(H)••R2
In-cage products
2
1
3
enchanced
absorption
8'
6
8
7
9
4
emission
5
9.6
3
2
1
, ppm
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
S
Goal:
Investigation of the influence of β-cyclodextrin
presence on the mechanism of the ketones photolysis:
dibenzyl ketone (DBK), deoxybenzoin (DOB) and
benzophenone (BP)
Research Methods:
For the Complex formation : NMR and UV spectroscopy
For the Mechanism of photochemical reaction: TR EPR and
CIDNP methods
Ketone’s photolysis
Photolysis of b-CD / benzophenone complex
Guest
Ketyl radical
a)
1.1 mT
b) TR EPR spectrum
Observed
2.8 mT
NMR spectrum
c)
CD radical
CIDNP spectrum
PhCOPh
5.7 mT
CD
326
328
330
332
334
Магнитное
Magneticполе,
field,мТ
mT
336
hydrogen abstraction from CD cavity interior
location of ketyl radical inside CD cavity
OH
 increasing of the Radical Pair lifetime
Strong exchange interaction in radical pair
Photolysis of b-CD / deoxybenzoin complex
Guest
Ketyl radical
NMR spectrum
Observed TR EPR spectrum
(PhCH2)2
O
PhCH2COPh
CD
H
b-CD radical
CH2
CIDNP spectrum
H
Magnetic field, mT
H H
O
H
 α-cleavage and hydrogen abstraction
location of ketyl radical inside CD cavity
OH
Increasing of radical pair lifetime
Strong exchange interaction in radical pair
formation of rearrangement product
Photolysis of b-CD / dibenzyl ketone complex
Guest
NMR spectrum
NO! TR EPR Signal
(PhCH2)2
(PhCH2)2CO
CIDNP spectrum
O
H
CH2
H
(PhCH2)2CO
H
 α-cleavage
 fast radicals recombination inside CD
(t < 100 ns)
Results
Photophysics and photochemistry of DOB, DBK, and BP in βCD inclusion complexes had been examined in detail. The DOB
triplet state undergoes both reactions whereas the DBK triplet
shows exclusively a-cleavage and the BP triplet shows
exclusively H-atom abstraction.
Observation of rearrangement product of the radicals from acleavage 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 a-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.
Langmuir, 2010, 26 (11), pp 8971–8980
Supramolecular Photochemistry in β-Cyclodextrin
Hosts: A TREPR, NMR, and CIDNP Investigation
Olesya A. Krumkacheva
International Tomography Center SB RAS
olesya@tomo.nsc.ru
Thank you for your kind attention !
Photochemistry in Octa Acid capsules
Guest
H
NMR
method
H
H
H
H
H
O
H
H
O
H
H
H
O
CH3
H
H
H
PhCH2C6H4CH3
CIDNP
method
Guest
Radical, rotating in the capsule
PhCH2C(O)C6H4CH3
10
9
8
CH3
7
6
5
4
ppm
3
2
1
0
-1
CH3
H
H
O
Varying the correlation between host
and guest sizes we can manage the
chemical reaction way
O
CH3
H
O
CH3
H
CIDNP
method
Ph-C(H)(CH3)-C(H)(CH3)-Ph
10
H3C
9
8
7
6
5
4
ppm
3
2
1
0
-1
H
CH3
H
Radical, fixed into the capsule
ХПЭ при фотолизе кетонов в водном растворе ЦД
a)
a)
ДБК
1.9 mT
ДОБ
Нет сигнала
ХПЭ
БФ
1.1 mT
b)
b)
2.8 mT
2.2 mT
Быстрая рекомбинация
радикалов в ЦД
c)
c)
5.7 mT
5.7 mT
330 332 334 336 338 340 342 344
Магнитное поле, мТ
326
328 330 332 334
Магнитное поле, мТ
Кетильный радикал (a) + радикал от ЦД (c)
S-T- механизм формирования поляризации
336
O
CH3