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Photophysical propeties of furocoumarins
N.E. Kovalskaya, I.V. Sokolova
Siberian Physical Technical Institute, 1, sq. Novo-Sobornaya,
Tomsk, 634050, Russia (e-mail: sokolova@ phys.tsu.ru)
Furocoumarins are active photosensitizing drugs widely used in photomedicine, in research on the structure of various biological macromolecules and on DNA repair. Furocoumarins are used in photomedicine from centuries: in fact, ancient Egyptian and Indian physicians used extract of leaves, seeds or roots from plants containing furocoumarins for the cure of vitiligo since thousands years BC. These preparations were applied on the skin or ingested and the patient was then exposed to sunlight. In seventy years, photochemotherapy PUVA (psoralen + UVA ) has been introduced: 8-methoxypsoralen (8-MOP), the active principle presented in Amni Majus, was administered orally; two hours later the skin area to be cured was exposed to UVA light (320-400). PUVA is effective against various skin diseases, such as vitiligo, psoriasis, alopecia aerata, atopic dermatitis, mycosis fungoides, etc. According to this therapy 8-MOP is administered orally; after two hours about 0.5 litres of blood were taken out by the patient, the lymphocytes were isolated and exposed to UVA light. Then, lymphocytes were returned back to the patient. This treatment is practically an auto vaccination against the same lymphocytes; because they are specific for the disease, a selective immuno modulation is induced, without danges of opportunistic infections [1].
In this work we present the photophysical propeties of linear and angular furocoumarins with conjugated external carbonyl substituents. The structures of these molecules are shown in Fig.1.
Siberian Physical Technical Institute, 1, sq. Novo-Sobornaya,
Tomsk, 634050, Russia (e-mail: sokolova@ phys.tsu.ru)
Furocoumarins are active photosensitizing drugs widely used in photomedicine, in research on the structure of various biological macromolecules and on DNA repair. Furocoumarins are used in photomedicine from centuries: in fact, ancient Egyptian and Indian physicians used extract of leaves, seeds or roots from plants containing furocoumarins for the cure of vitiligo since thousands years BC. These preparations were applied on the skin or ingested and the patient was then exposed to sunlight. In seventy years, photochemotherapy PUVA (psoralen + UVA ) has been introduced: 8-methoxypsoralen (8-MOP), the active principle presented in Amni Majus, was administered orally; two hours later the skin area to be cured was exposed to UVA light (320-400). PUVA is effective against various skin diseases, such as vitiligo, psoriasis, alopecia aerata, atopic dermatitis, mycosis fungoides, etc. According to this therapy 8-MOP is administered orally; after two hours about 0.5 litres of blood were taken out by the patient, the lymphocytes were isolated and exposed to UVA light. Then, lymphocytes were returned back to the patient. This treatment is practically an auto vaccination against the same lymphocytes; because they are specific for the disease, a selective immuno modulation is induced, without danges of opportunistic infections [1].
In this work we present the photophysical propeties of linear and angular furocoumarins with conjugated external carbonyl substituents.
The theoretical consideration of electronic structure and spectral properties of furocoumarins where carried out by INDO method using the special spectroscopic parameterization. The result of the quantum-chemical calculations of the excited states of furocoumarins given in Table 1.
Table 1 .
Spectrum S0-Si absorption of furocoumarins
|
Compounds |
i |
State |
l , нм |
Е, эВ |
F |
Polarization |
|
Psoralen |
1 2 3 |
p p * np * p p * |
314.4 306.9 284.5 |
3.94 4.04 4.36 |
0.103 0.007 0.448 |
xy z хy |
|
Isopsoralen |
1 2 3 |
p p * np * p p * |
324.6 302.1 287.6 |
3.82 4.10 4.31 |
0.085 0.0007 0.226 |
xy z xy |
|
Pseudoiso- psoralen |
1 2 3 |
p p * np * p p * |
323.4 303.6 300.0 |
3.83 4.08 4.13 |
0.298 0.0007 0.321 |
xy z xy |
|
5-МОР |
1 2 3 |
p p * np * p p * |
336.9 304.0 301.6 |
3.68 4.08 4.11 |
0.013 0.0004 0.326 |
xy z xy |
|
8- МОР |
1 2 3 |
p p * np * p p * |
345.2 315.7 297.0 |
3.59 3.93 4.17 |
0.022 0.0003 0.243 |
xy z xy |
The lowest excited singlet and triplet positions of molecules was compared with experimental data [2].The result given in Table 2.
Table 2
|
Compounds |
Experiment |
Calculation |
||
|
S1 |
T1 |
S1 |
T1 |
|
|
Psoralen |
330 nm |
456 nm |
314 nm |
479 nm |
|
8- МОР |
345 nm |
456 nm |
345 nm |
497 nm |
|
Isopsoralen |
330 nm |
452 nm |
325 nm |
488 nm |
The photophysical properties of the lowest excited states (singlet and triplet) of furocoumarins are very important. There studies indicate that the lowest excited singlet state of furocoumarins are p , p * state. The position of the energy level of an n,p * triplet state relative to that of the lowest energy p , p * singlet state to provide a very efficiency of 1(p , p * )-3(n,p * ) intersystem crossing (Kst ~ 1010- 1011 s-1). The phosphorescence is considerably more intense that the fluorescence.
This fact have great importance for used of furocoumarins as photosensing drugs for photochemotherapy.
References