Bloconjugate Chem. 1993, 4, 127-133
127
Photodegradation of the Cytosine Nucleosides Family by Water-Soluble Iron(II1) Porphyrins Yoshikatsu Ito Department of Synthetic Chemistry, Faculty of Engineering, Kyoto University, Kyoto 606, Japan. Received September 23, 1992
Aqueous solutions of cytosine nucleosidessuch as cytidine (C), 2'-deoxycytidine (dC),2',3'-dideoxycytidine (ddC), and 1-8-D-arabinofuranosylcytosine (ara-C) were irradiated with visible light in the presence of a water-soluble iron(II1) porphyrin photocatalyst (FeII'TMPyP or FeulTSPP) in air or under an argon atmosphere. HPLC analyses revealed release of cytosine as a dominant reaction. In the case of the irradiations of isomeric C and UFU-C, their interconversion was also observed as a minor reaction. Under an argon atmosphere, a stoichiometric reduction of the catalyst into FeIITMPyP or FeIITSPP was observable by UV-vis spectroscopy. Quantum yields for the cytosine release and the catalyst reduction (@m and @I+")were very much dependent both on the presence and the stereochemistry of the 2'-OH group. For the FeII'TMPyP case, for example, (a) aCytand decreased in the order C > UFU-C> dC > ddC and (b) oxygen lowered the of dC and ddC but not of C and UFU-C.These results strongly support the previously proposed mechanism, i.e., C and ara-C undergo the reaction via a C2' carbon radical (e.g., eq 4) and dC and ddC undergo the reaction via a C1' or C4' carbon radical (e.g., eq 3). The observed effects of 2-propanol and solution pH suggest that a main reactive species photogenerated from FeTSPP is a free hydroxyl radical ('OH), while that photogenerated from FeTMPyP is probably an iron-coordinated active oxygen species (crypto-OH or Fe=O).
INTRODUCTION In connection with the tumor phototherapy with hematoporphyrin derivatives, a number of works have been done about photochemical DNA cleavage by porphyrins (1-6'). We have been studying the photocatalytic activities of water-soluble metalloporphyrins having redox-active central metals, since they are relatively little studied from the viewpoint of organic photochemistry (7-11).Unlike non-redox-active metalloporphyrins such as zinc porphyrin, which can cause only simple photochemical electron or energy transfer reactions (121,novel photochemical oxidation-reduction reactivities are expected. Recently we have found that [meso-tetrakis(1-methyl4-pyridiniumy1)porphyrinatoliron(III), FenlTMPyP, p h e tocatalyzes the selective release of bases from nucleosides and their derivatives in aerated aqueous solution (e.g., eq 1)(11). Ribonucleosides afforded much higher yields of
Fe'I'TMPyP
atmosphere, virtually quantitative reduction of FelI1TMPyP into FeIITMPyP by C or 2'-deoxycytidine (dC) was observed in addition to the nearly stoichiometric release of cytosine and the reduction was much more effective by C than by dC. The increased reactivity (in both base release and iron reduction) for the ribonucleoside relative to that for the deoxyribonucleoside was ascribed to the difference in their binding strength to the porphyrin catalyst and to a facile base-releasing degradation of only the ribonucleoside from ita C2' carbon radical. In order to obtain more detailed information about the reaction mechanism, I noted the most reactive cytidine as a substrate for further study. Here, the release of cytosine from cytidine (C), 2'-deoxycytidine (dC), 2',3'-dideoxy-
Fe'hFyP HO OH
free base than the corresponding deoxyribonucleosides. The yields decreased in the following order among the ribonucleosides studied: cytidine (C) > uridine (U) = ribosylthymine (T)> adenosine (A) =guanosine (GI. This does not correlate with the order of oxidation potentials for the bases: uracil > cytosine > thymine > adenine > guanine. The free base release was a predominant reaction in all cases except for G and 2'-deoxyguanosine (dG),where decomposition of the guanine ring occurred in much preference to the release of guanine. The quantum yield for the disappearance of G or dG is found t o be comparable to that for cytosine released from C. Under an argon
HO
cytidine (ddC), and 1-8-D-arabinofuranosylcytosine (araC) photocatalyzed by iron(II1) complexes of meso-tetrakis(1-methyl-4-pyridiniuy1)porphyrin (FeInTMPyP) and
1Q43-78Q2I93l29Q4-Q 7 27$Q4.QQ/Q 0 1993 Amerlcan Chemlcal Society
120
Bioconjugate Chem., Vol. 4, No. 2, 1993
It0
Fe'I'TMPyP: X = "Me,
M = Fell'
Fe'I'TSPP: X = CSO,
M = Fe"'
meso-tetrakis(4-sulfonatopheny1)porphyrin(FeIIITSPP) will be reported (eq 2). Quantum yields for the release of
hv > 400 nm Fe'I'TMPyP or FeI'lTSPP R ' R
R , R = OH or H
air or argon in Hfl
(2) H
cytosine (both in air and under an argon atmosphere) and for the reduction of the Fe"' complexes into the Fe" ones (under an argon atmosphere) were estimated. Photochemical interconversion between isomeric C and ara-C with a low efficiency was also observed to occur. EXPERIMENTAL PROCEDURES Conditions for high-performance liquid chromatography (HPLC) analyses were described in a previous paper (11). Preparative HPLC was done with a Waters chromatographic system by using a Cosmosil5Cl~column (20 mm i.d. X 250 mm) and H2O/MeOH (97:3 v/v) as solvent. UVvis spectra were measured on a JASCO UVIDEC-610 spectrometer. NMR and mass spectra were recorded on Varian Gemini-200and JEOL JMS-DX 300 spectrometers, respectively. Cytosine nucleosides C, dC, ddC, and ara-C were purchased from Yamasa, Sigma, Aldrich, and Wako, respectively. Water (distilled, HPLC grade) was obtained from Wako. FeII'TMPyP was previously prepared (7). FelIITSPP was prepared according to the published procedure (13). Photolysis. Neutralized stock solutions of the iron(111) porphyrins (2.5 X lo4 M) were diluted to the onehalf concentration with an appropriate nucleoside aqueous solution. The solution pH was adjusted by using an aqueous NaOH or HC1 solution when necessary. Each sample solution was placed either (a) in a Pyrex tube for photolyses in the presence of air (5 mL) or (b) in a UV cell (path length, 1mm) with a two-way stopcock for photolyses under an argon atmosphere (0.5mL). Irradiations of these samples were performed with a 400-W high pressure mercury lamp through a 15%NaN02 filter solution (>400 nm) for a suitable time (vide infra). (a)Photolysis in the Presence of Air. In the experiments in Table I, irradiations were done for a long time (20 h) to obtain high product yields (cytosine yield 400 nm for 20 h in aerated solvent. subrun strate
experiments, the specificity in photoproduct formation should be the same as with FeTMPyP, except a t high pH (pH > 12), where the HPLC charts became somewhat complex in the case of FeTSPP. Table I demonstrates that the cytosine yield is highly dependent on the sugar structures of the nucleosides; i.e., it decreased in the order C > ara-C > dC > ddC, ranging from 1680 to 21% under the corresponding reaction conditions (runs 2 and 4-6); the yields are calculated on the basis of the catalyst employed. The solution pH, which also affected the cytosine yield, was lowered during the irradiation (see runs 1,2,7, and 8), but the use of neutral phosphate buffer retarded the reaction (run 3). Coordination of the phosphate ion to the iron atom may be decreasing the photocatalytic activity of FeTMPyP (11). FeTMPyP was appreciably more efficient than FeTSPP in photocatalyzing the degradation of C (compare runs 1 and 2 with runs 7 and 8). Quantum yields for the FeIIITMPyP- or FeII'TSPPphotocatalyzed decomposition of C, dC, ddC and ara-C under air were measured by a merry-go-round technique. Relative values for quantum yields for the liberation of cytosine (@.,fit)and for the interconversion of C and ara-C into each other (@isom) are summarized in Table 11. The absolute value for for the FeII'TMPyP-photocatalyzed cytosine release from C was estimated as 0.0010 on the basis of the FeII'TMPyP-photocatalyzed carbon-carbon bond cleavage of meso-hydrobenzoin (7). When the photolyses were carried out in a UV cell under an argon atmosphere, a quantitative reduction of the iron(111) catalysts into the iron(I1) species (FeIITMPyP and FeIITSPP) was spectrally observed. After enough irradiation times, the absorption bands for the Fe"' species were invisible, indicating complete conversion of Fe"' into FeII. The spectral changes obtained from reduction of FeInTMPyP by C and dC were already shown in a previous paper (111,and similar spectral changes were observed in other cases (e.g., Figure 1). From these spectral changes, the time-courses for the iron(I1) formation were calculated and they are displayed in Figure 2. From this figure, relative quantum yields for the reduction FeIII- Fen (@Fen) were estimated. After a complete photoreduction of Fe"' into Fe" under an argon atmosphere, oxygen was introduced into the UV cell by bubbling through the solution, which readily resulted in more than 97 % recovery of the Fe"' absorption
129
Table 11. Quantum Yields for the FeIIITMPyP- or FeIIITSPP-PhotocatalyzedDecomposition of Cytosine Nucleosides C, dC, ddC, and ara-C in the Presence of Air or under an Argon Atmosphered air argon substrate aisomrel aFenrel @&re1 @isomrel b @&Ie1
4
(A) FeII'TMPyP 0.13 3.7 0.92 0.17 0.33 0.026 0.14 0.013 0.18 0.10 0.13 0.0062 0.76 0.16 0.02 (B)FelIITSPP C 0.31 0.042 3.1 0.26 0.03 dC 0.043 0.31 0.17 ddC 0.025 0.23 0.11 ara-C 1.2 0.033 0.59 0.053 0.01 The relative value for @'cyt under argon was calculated by = @,pre1 X (the catalyst-based yield of cytosine after a complete conversion of FelI1 into Fe"). The relative value for @isom under argon was calculated by @.isomrel = @Fenre' x (the catalyst-based yield of ara-C or C after a complete conversion of FelI1 into Fe"). The absolute value for @'cyt (@'cytaba) is estimated as 0.0010 on the basis of the photocleavageof meso-hydrobenzoinby FemTMPyP(7). [FePl = 1.3 X lo-' M, [nucleoside] = 1.3 X M, in HzO (pH 7).
C dC ddC ara-C
l.W
400
300
500
600
7
600
700
WAVELENGTH, nm
(b)
s
p
s
3.0
1.5
0.0
300
400
500
WAVELENGTH, nm
Figure 1. Spectralchanges from visible light photolyses of FernTMPyP or FemTSPP with cytosine nucleosides under an argon atmosphere: [FeP] = 1.3 X 1VM, [nucleoside] = 1.3 X le2M, in HzO (pH 7); path length 1 mm. (a) FeIIITMPyPlara-C; the spectra were taken at t = 0, 0.1, 0.3, 1, 2.5 and 4 h. (b) FemTSPP/C; the spectra were taken at t = 0, 0.1, 0.2, 0.3 and 1 h.
in all cases. HPLC analyses were done before and after the oxygen bubbling, and it was found that the yields for the released cytosine (cytosine nucleoside cytosine) and for the isomers (C ara-C or ara-C C) were essentially
-
--
130
Bioconjugate Chem., Vol. 4, No. 2, 1993
It0
HoD:y
a
I /
HO X
0
CIFeTMPyP
+
ClFeTSPP
0
2o
v t
w
C-aralFeTMPyP
Ho HO
C-aralFeTSPP
' Fell
+
HO X
I
HO X
Fe"
H&
i
BaseH
+
0
3
2
1
4
irradiation time, h (3) HO X HO O G C H O
BaWH
hv
h
v
0
U
40
-
n dC1FeTMPyP dC/FeTSPP 0 ddC1FeTMPyP % ddC/FeTSPP
+ 20 -
0
1
0
2
.
1
4
.
I
6
.
I
8
*
I
10
.
/
Fe"
rPs
+
12
irradiation time, h Figure 2. Increase of the iron(I1) porphyrin yield with the irradiation time from visible light photolyses of FeInTMPyP or FenlTSPPwith cytosinenucleosidesC, dC, ddC, and ara-Cunder an argon atmosphere: reaction conditions,see the legend in Figure 1.
unaltered by the oxygen bubbling. On the basis of these yields and @ ~ obtained p above, quantum yields for cytosine (@,yt) and for the isomerization (@isom) under an argon atmosphere were estimated. Relative values for @F& @,yt, and @isom under an argon atmosphere are listed in Table 11, together with those for @'cyt and @isom under air. Previously (II), we have proposed two tentative mechanisms for the release of base from ribo- and deoxyribonucleosides (eqs 3 and 4). Eq 3 is a mechanism involving a C1' or C4' radical intermediate and may be disturbed by molecular oxygen in aerated aqueous solution, since the Cl'and C4' carbon radicals may be competitively trapped by a porphyrin and an oxygen molecule ([porphyrin] = [ 0 2 ] c lo4 M under the present reaction conditions). Eq 4 is applicable only for ribonucleosides. This mechanism involves a C2' radical intermediate, which may rapidly release base without being obstructed by oxygen (14). In aqueous solution, FeIIITMPyP and FeII'TSPP undergo acid-base and dimerization equilibria that depend on concentration, ionic strength, and pH (15). The identifications of the species relevant to these equilibria are still unsettled. However, since the aqua or hydroxo complexes appear to be main species in neutral aqueous solution a t concentrations of the present experiments (7,15),the porphyrin catalysts are written as a hydroxo species Fe"L
OH in eqs 3 and 4. It is assumed in eqs 3 and 4 that two molecules of Fe"LOH are consumed for the release of one molecule of base. In the presence of oxygen, however, Fe" will be oxidized to regenerate FelILOH (eq 5) (16)and the
reaction will become catalytic as was actually observed (Table I). A possible hydrogen-abstracting species in the first step of eqs 3 and 4 is a hydroxyl radical ('OH), which may be generated by photolysis of FelILOH (eq 6) (8,10,17,18), Fe"'-OH
hv
Fe" + -OH (orcrypteOH or Fe-0)
(6)
a hydroxyl radical coordinated to the iron atom (cryptoOH) (19,20),or a high-valent iron-oxo species Fe=O (21, 22). Crypto-OH and Fe=O may be considered equivalent species (20,21), since they are potentially in equilibration as shown in, for example, eq 7. The ferry1 oxide FerV=O
Bloconjugate Chem., Vol. 4, No. 2, 1993
Photodegradation of Nucleosides by Porphyrins Fd" + .OH
Fe'a
Fe'd
+
181
0
(coPt0.W is not a powerful hydrogen-abstracting agent, unlike the FeV=O species in cytochrome P-450 models (23),but can be under illumination conditions (24). The C2' radical intermediate in eq 4 may be generated via cytosine OH adduct radicals that are formed either by the addition of water to a radical cation of the cytosine moiety or by the addition of 'OH to the double bond of the cytosine moiety (25). However, I have previously (11) shown some experimental evidences that nucleobase radical cations do not participate in the present base-releasing reactions. In fact, C liberated undecomposed cytosine in a quantitative yield (vide supra). Variations in quantum yields in Table I1 can be well explained by taking eqs 3 and 4 into account, in the following ways. First, except for the unusually large relative aCyt(=1.2) for ara-CIFeTSPP under air, the acytand *Fen values for C are much larger than those for UFU-C, dC, and ddC under the corresponding reaction conditions. The only difference in structure between C and ara-C is a configuration of the 2'-OH group. dC and ddC do not carry a 2'-OH group. The observed much larger a'cytand @Fenvalues for c relative to those for dC and ddC indicate a crucial role of the 2'OH group in releasing cytosine from C. Furthermore, the striking difference in aCytand @ ~ values ~ n between C and am-C indicates that the 2'-OH stereochemistry also controls the efficiency of the cytosine release. These facts support that the cytosine release from C takes place according to eq 4, since it comprises the C2' carbon radical as a key intermediate. The fact that @Fe" for C is by far the largest as compared with that for ara-C, dC, and ddC implies a promoted photoreduction of Fe"' into Fe" as a result of cis-coordination of C through the 2'- and 3'-OH groups in the molecule (eq 8).
0-
E e . E
e
0.4
FeTMPyP/dC
-
0.2
I
I
I
I
I
0
1
2
3
4
0.0
[2-PrOH], M
Figure 3. Quenching by 2-propanol of the FeUITMPyP-and FemTSPP-photocatalyzed cytosine release from C or dC in the presence of air: [FeP] = 1.3 X lo-" M, [nucleoside] = 1.3 X 10-2 M, in 25 mM sodium phosphate buffer (pH 7.3). is scut in the absence of 2-propanol.
1
+
FeTMPyP/C FeTSPPiC
2.*' 1
2
Second, under an argon atmosphere, @ ~ ~2(aCyt) n for dC and ddC. This means that 1equiv of cytosine release from dC or ddC corresponds to 2 equiv of Fe" production, just as eq 3 predicts. By contrast, in the cases of C and ara-C, where @F$ = 4-l2(ac@)under an argon atmosphere, the cytosine release corresponds to production of 4-12 equiv of Fe". Hence, the Fe"' reduction into Fe" occurred more than predicted from eq 3 or 4. The carbon-carbon bonds of 1,kdiols are known to be photochemically cleaved by FeII'TMPyP (7).Therefore, the wastage of the Fe"' reduction observed for C and ara-C may be partly ascribed to the C2'-C3' bond cleavage in their ribose moiety. Third, in the case of dC and ddC, %yt under air is much smaller than aCytunder argon; i.e., the cytosine release was strongly disturbed by oxygen, as expected from eq 3. In the cases of C and ara-C, except for ara-CIFeTSPP, aCnunder air is approximately equal to %yt under argon, i.e., the inhibitory effect of oxygen is unobservable, as predicted from eq 4. In other words, for C and ara-C the cytosine release according to eq 3 is negligible. In the case of ara-CIFeTSPP, where aC@ under air is much larger than aC@ under argon, oxygen has an accelerating effect. This finding is interesting, but is unable to be understood a t this stage.
FeTMPyPiC FeTSPPiC
0.0
OH
+
-
4
.
-
I
6
.
I
8
'
I
10
'
I
12
'
t
14
PH Figure 4. Relative a'cyt vs pH for the FerUTMPyP-and FernTSPP-photocatalyzed cytosine release from C in the presence of air: [FePl = 1.3 X lo-" M,IC] = 1.3 X le2M, in HzO; pH was adjusted by NaOH/HCl.
Finally, the observed inefficient epimerization of C and UFU-C(@isom in Table 11) may have occurred through intermediacy of a planar or a rapidly inverting C2' carbon radical in eq 4. Figure 3 shows the effect of 2-propanol (0.16-3.3 M) on the photocatalytic release of cytosine from C or dC. The FeTSPP-photocatalyzed release was quenched by 2-propan01 much more efficiently than the FeTMPyP-photocatalyzed one was: the difference between their quenching efficiencies was especially remarkable a t lower concentrations of 2-propanol. Since 2-propanolis a good quencher for the hydroxyl radical (k, = 1.3 X lo9 M-ls-l) (26),this result indicates that a main active oxidant in the FeTSPPphotocatalyzed reactions is 'OH, while that for FeTMPyP may be other species such as high-valent iron-oxo complexes or crypto-OH. The photocatalytic release of cytosine from C strongly depended on the solution pH, and this dependence was dramatically different between FeTMPyP and FeTSPP (Figure 4). Although the reaction is very slow at acidic pH in both cases (i.e., acflis virtually zero a t pH 2), em for the FeTMPyP case reached a maximum value a t pH 7 and that for the FeTSPP case reached a plateau a t pH
132
Bioconjugate Chem., Vol. 4, No. 2, 1993 ---m
It0
- - - - - - - - - - - - - - - _ _ _ _- -_- - - - -n- -
carbon radical. Relatively large acyt and ~ F ~ values I I observed for C are also likely due to favorable coordination of C onto the central iron(II1) atom of the porphyrin through the 2'- and 3'-OH groups.
FeTMPyP/C 4-
LITERATURE CITED
FeTMPyPIdC FeTSPP/C
(1) Gutter, B., Speck, W. T., and Rosenkranz, H. S. (1977) The
Photodynamic Modification of DNA by Hematoporphyrin. Biochim. Biophys. Acta 475, 307-314. (2) Fiel, R. J., Datta-Gupta, N., Mark, E. H., and Howard, J. C.
0
10
20
30
[nucleoside], 10.' M
Figure 5. Relative @cut vs nucleoside concentration for the Fe*I1TMPyP- and FeIIITSPP-photocatalyzedcytosine release from C
or dC in the presence of air: [FeP] = 1.3 X lo4 M, [nucleoside] = 0.13-25.2 X M, in HzO (pH 7).
7, then abruptly increased around pH 11, and suddenly dropped above pH 12. This characteristic pH effect observed in the FeTSPP photocatalysis may also be explained in terms of formation of a reactive hydroxyl radical, since (a) FelIITSPP in aqueous solution is known to be able to photogenerate *OHwith an efficiency that is higher above pH 11 ( 1 7 ) and (b) most of the hydroxyl radical deprotonates above pH 12 ('OH G 0'- + H+,pK, = 11.9) (27). It has recently been reported that 'OH reacts faster than 0'- with the nucleosides by a factor of 6-7 (28).
Incidentally, it is very interesting to note that the radiolysis-generated hydroxyl radical exhibits little selectivity in reactions with various nucleosides (29). For example, U and 2'-deoxyuridine (dU) undergo a base release with similar efficiencies and, furthermore, the base release accounts for only less than 20 % of the total reaction (at pH 9) in either case. These results are quite different from the high selectivities observed here for the FeTMPyPphotocatalyzed reactions (also see ref 11). Effect of the nucleoside concentration (0.0013-0.25 M) on the efficiency of the photocatalytic release of cytosine from C or dC was examined (Figure 5). In the case of C/FeTMPyP and C/FeTSPP, aCytincreased up to ca. 0.05 M and then nearly leveled off at higher concentrations. In the case of dC/FeTMPyP, aCytalmost uniformly increased u p to 0.13 M. These facts may imply that C binds to the iron(II1) porphyrins more strongly than dC. Probably, the 2'-OH group of the sugar moiety in C (dC lacks 2'-OH) is acting as a coordinating ligand (cf. eq 8). The different binding strength of C and dC toward FeIIITMPyP was previously (11) inferred from both absorption spectral studies and the increased reactivity of C relative to dC (see Table 11; aCytand @J.F~II are larger for C than for dC). CONCLUSION A main reactive species involved in the Fe'I'TSPPphotocatalyzed cytosine releases from cytosine nucleosides C, dC, ddC, and ura-C is a free hydroxyl radical ('OH), while that involved in the FeII'TMPyP-photocatalyzed ones is presumably a n iron-coordinated active oxygen species (crypto-OH or Fe=O). It appears that C and am-C undergo the reaction via a C2' carbon radical (e.g., eq 4), dC and ddC undergo the reaction via a C1' or C4' carbon radical (e.g., eq 3), and that the 2'-OH group of the ribose moiety in C promotes the cytosine release via the C2'
(1981) Induction of DNA Damage by Porphyrin Photosensitizers. Cancer Res. 41, 3543-3545. (3) Kelly, J. M., Murphy, M. J., McConnell, D. J., and OhUigin, C. (1985) A Comparative Study of the Interaction of 5,10,15,20-Tetrakis(N-methylpyridinium-4-yl)porphyrin and ita Zinc Complex with DNA Using Fluorescence Spectroscopy and Topoisomerisation. Nucleic Acids Res. 13, 167-184. (4) Praseuth, D., Gaudemer, A., Verlhac, J., Kraljic, I., Sissoeff, I., and Guille,E. (1986) Photocleavageof DNA in the Presence of Synthetic Water-Soluble Porphyrins. Photochem. Photobiol. 44, 717-724. (5) Le Doan, T., Praseuth, D., Perrouault, L., Chassignol, M., Thuong, N. T., and HBlBne, C. (1990) Sequence-Targeted Photochemical Modifications of Nucleic Acids by Complementary Oligonucleotides Covalently Linked to Porphyrins. Bioconjugate Chem. 1, 108-113. (6) Komiyama, M., Kobayashi, M., Harada, M. (1991) Pheophorbide as Efficient Sensitizer for DNA Photocleavage. An Implication to its Role in Photodynamic Cancer Therapy. Chem. Lett. 2123-2126. (7) Ito, Y. (1991)PhotochemicalCleavage of l,2-Diphenylethane1,2-diolby Water-SolubleFe"I(tmpyp). J. Chem. Soc., Chem. Commun. 622-624. (8) Ito, Y., Kunimoto, K., Miyachi, S., and Kako, T. (1991) Photocatalytic Cleavageof 1,2-Diolsby a Cofacially Hindered Water-Soluble Iron(II1) Porphyrin. Tetrahedron Lett. 32, 4007-4010. (9) Ito, Y., Matsuoka,G. Solid-State Air-oxidationof Benzhydryl Ethers Catalyzedby Silica Gel-SupportedIron(II1)Porphyrins. Oxid. Commun., in press. (10)Ito, Y. Solid-state Photooxidation of Alkenes and Other Compounds by Silica Gel-SupportedPorphyrins. Oxid. Commun., in press. (11) Ito, Y., and Miyachi, S. (1992) Photochemical Release of Bases from Nucleosides and Their Derivatives by WaterSolubleIron(II1)Porphyrins. J. Photochem. Photobiol.B: Biol. 13, 29-37. (12) Wasielewski,M. R. (1992)Photoinduced Electron Transfer in Supramolecular Systems for Artificial Photosynthesis. Chem. Rev. 92,435-461. (13) Fleischer, E. B., Palmer, J. M., Srivastava, T. S., and Chatterjee, A. (1971)Thermodynamic and Kinetic Properties of an Iron-Porphyrin System. J . Am. Chem. SOC.93, 31623167. (14) Hildenbrand, K., and Schulte-Frohlinde, D. (1989) E.s.r. Studies on the Mechanism of Hydroxy Radical-InducedStrand Breakage of Polyuridylic Acid. Znt. J. Radiat. Biol. 55, 725738. (15) Ivanca, M. A., Lappin, A. G., and Scheidt, W. R. (1991) Water-SolubleFerric Porphyrinates: Solutionand Solid-state Species. Znorg. Chem. 30, 711-718, and references cited therein. (16) Balch, A. L., LaMar, G. N., Latos-Grazynski, L., Renner, M. W., and Thanabal, V. (1985) Nuclear Magnetic Resonance Studies of Axial Amine Coordination in Synthetic Ferryl, (Fe1V0)2+, Porphyrin complexes and in Ferryl Myoglobin. J . Am. Chem. SOC.107,3003-3007, and their previous papers of this series. (17) Faraggi,M., Carmichael,A., and Riesz,P. (1984) OH Radical Formation by Photolysis of Aqueous Porphyrin Solution. A Spin Trapping and e.s.r. Study. Int. J. Radiat. Biol. 46,703713. (18) Maldotti, A., Bartocci, C., Amadelli, R., Polo, E., Battioni, P., and Mansuy, D. (1991)Oxidation of Alkanes by Dioxygen
Photodegradation of Nucleosides by Porphyrins
Catalyzed by Photoactivated Iron Porphyrins. J.Chem. SOC., Chem. Commun., 1487-1489. (19) Johnson, G.R. A., and Nazhat, N. B. (1987)Kinetics and Mechanism of the Reaction of the Bis(1,lO-phenanthro1ine)copper(1) ion with Hydrogen Peroxide in Aqueous Solution. J. Am. Chem. SOC.109,1990-1994. (20) Sigman, D. S. (1986)Nuclease Activity of 1,lO-Phenanthroline-Copper Ion. Acc. Chem. Res. 19, 180-186. (21) Stubbe, J., and Kozarich, J. W. (1987)Mechanisms of Bleomycin-InducedDNA Degradation. Chem. Reu. 87,11071136. (22) Meunier, B. (1986)Metalloporphyrin-Catalyzed Oxygenation of Hydrocarbons. Bull. SOC.Chim. Fr. 578-594. (23) Suslick, K. S.,and Watson, R. A. (1991)Photochemical Reduction of Nitrate and Nitrite by Manganese and Iron Porphyrins. Znorg. Chem. 30, 912-919. (24) Mizutani, Y.,Hashimoto, S., Tatsuno, Y., and Kitagawa, T. (1990)Resonance Raman Pursuit of the Change from Fen-02
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