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Photosensitizing properties of
supramolecular systems based on
chlorine е6
I. V. Klimenko1, A.V. Lobanov2
1
Emanuel Institute of Biochemical Physics, Rus. Ac. Sci., Kosygin str. 4,
Moscow, Russia
2Semenov Institute of Chemical Physics, Rus. Ac. Sci., Kosygin str. 4
Moscow, Russia
*E-mail: [email protected]
INTRODUCTION



One of the most important tasks during the new medicines creation applied at
photodynamic therapy is the research of physico-chemical properties of the novel
porphyrine containing objects, such as the water-soluble derivative of chlorophyll chlorine e6 (Ce6), which belongs to the group of second generation photosensitizers
(PS).
Ce6 is absolutely non-toxical PS and at the same time anticancer immune response
modifier which is strongly activating system of cell-mediated immunity and,
especially, K cells, distinguishing and destroying tumor cells.
It has the following spectral and power characteristics: the maximum of Ce6 absorption
is in area of 660±5 nm that corresponds to area of the greatest optical transparency for
biological tissue, and a quantum yield of singlet oxygen reaches 0.7 [1].
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1. Parkhats M. V., Galievsky V. A., A. S. Stashevsky A. S., Trukhacheva T. V., Dzhagarov B. M. Dynamics and efficiency of the
photosensitized singlet oxygen formation by chlorin e6: the effects of the solution pH and polyvinylpyrrolidone. Optics and
Spectroscopy, 2009, v. 107, № 6, p. 974–980.

Nowadays a number of PS based on Ce6 is applied in clinical practice in Russia [2], but
searches of other, more effective medicines and ways of their receiving continue now.
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2. Akopov A.L., Kazakov N.V., Rusanov A.A., Karlson A., The mechanisms of photodynamic action for treating of cancer patients.
Photodynamic therapy and photodiagnostics, 2015, №2, p. 9-16
Purposes of research
 - To collect spectral data of optical absorption and fluorescence of different
supramolecular systems with the purpose of the optimum excipient selection
 - To study the influence of various excipients on spectral characteristic of this
supramolecular systems.
 - To define the influence of intermolecular interactions on aggregation
behavior of chlorine e6 in solutions.
 - To determine efficiency of data of supramolecular systems in generation of
singlet oxygen.
Objects of research:

We studied optical absorption and fluorescence of supramolecular systems based on
chlorine e6 (Ce6 ) (2•10-5 М) in different excipients such as poly- N vinylpyrrolidone
(PVP), polyethyleneglycol (PEG), bovine serum albumin (BSA), Triton X-100 (TX100)
NH
H
N
N
HN
PEG
PVP
H3 C
H
COOH
COOH
HOOC
Chlorine e6
ТХ-100
BSA
Research methods
- Absorption spectra (200-900 nm) were recorded with TU-1901 UV-Vis
spectrophotometer from Beijing Purkinje General Instruments Co Ltd. Poorly
resolved spectra were analyzed by decomposing the spectra into their Gaussian
constituents.
The fluorescence spectra in the range of 550-800 nm were recorded with Fluorat02-Panorama set-up (Lumex). The excitation wavelength was 410 nm. All
measurements were conducted at 20 0С in standard K10 quartz cuvettes with
optical path lengths of 1 cm.
– Registration of singlet oxygen was carried out by the method of "chemical traps".
1,3-diphenylisobenzofuran was used as a "trap".
Fig.1. Optical absorption spectra of Ce6 (2•10-5 М) in
aqueous solution
2,0
D
1,5
1,0
0,5
0,0
300
400
500
600
, nm
700
800
900
Fig.2. Optical absorption spectra of supramolecular systems based on Ce6 (210-5 М) in the
region of the Soret band: 1. Ce6 in aqueous solution, 2. Ce6 -BSА, 3. Ce6 -PEG, 4. Ce6 ТХ-100, 5. Ce6 -PVP
1
2,0
D
1,8
1,6
4
1,4
2
1,2
3
1,0
5
0,8
0,6
0,4
0,2
0,0
320
340
360
380
400
, nm
420
440
Fig. 3. Optical absorption spectra of supramolecular systems based on Ce6 (210-5 М): 1.
Ce6 in aqueous solution, 2. Ce6 -BSА, 3. Ce6 -PEG, 4. Ce6 -ТХ-100, 5. Ce6 -PVP
4
D
0,5
0,4
2
1
0,3
5
0,2
0,1
0,0
580
3
600
620
640
660
, nm
680
700
720
Ifl
Fig. 4. Fluorescence spectra of supramolecular systems based on Ce6 (210-5 М): 1. Ce6 in
aqueous solution, 2. Ce6 -BSА, 3. Ce6 -PEG, 4. Ce6 -ТХ-100, 5. Ce6 -PVP
0,35
5
0,30
4
0,25
2
0,20
3
0,15
1
0,10
0,05
0,00
600
650
, nm
700
750
RESULTS
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- When studying spectral properties of all presented supramolecular systems on the base of Ce6
the "blue" shift in the region of the peak Cope wasn't revealed. It testifies the identical
hydrophobic nature of all systems, similar to hydrophobic nature of Ce6.
- On the basis of optical density drop in the region of the peak Cope for all systems it is possible
to speak about the formation of singlet oxygen in all presented supramolecular systems. The
hypochromic effect is the result of the strengthening of intermolecular interactions and the
formation of molecular complexes.
- The spectral changes in the Q band region, connected with the bathochromic shift of a long wave
absorption band of a sensitizer, and essential reduction of half-width demonstrate the
disaggregation of the Ce6 molecules, their interaction with excipients in solutions and formation
of a molecular complex. The appearance of molecular complex band of the porphyrine with TX100, BSA and PVP at 615 nm is the confirmation of this.
-The specific characteristic of fluorescence spectra of all supramolecular systems is their overlap
with Q band of absorption spectra, that allows to consider the formed molecular associates and
complexes as donors of photoexcitation energy for Ce6 molecules. It is revealed that addition of
all studied excipients in Ce6 aqueous solution leads to the increase of fluorescence intensity of
Ce6. The greatest increase in intensity of fluorescence is observed at addition of PVP.
- As a part of the supramolecular complexes Ce6 is an effective photosensitizer of singlet oxygen
generation with a quantum yield 0.53 (Ce6-PVP), 0.50 (Ce6-PEG), 0.62 (Ce6-TH-100) and 0.56
(Ce6-BSA).
CONCLUSION
Thus, the study of spectral and fluorescent characteristics of various
supramolecular systems on the basis of chlorine e6 allow to conclude prospects
of further researches for search of new sensitizers in photodynamic therapy
The obtained results allow to develop promising method of controlled
aggregation of photosensitizers in the composition of supramolecular
complexes to create medicines of predictable photodynamic activity.