Biomedical subjects
Publications and source records attributed to Mamoru Fujitsuka.
Synthesis and properties of oligodeoxynucleotides (ODNs) containing terthiophene (Thp) were described. One-electron oxidation of Thp-modified ODN resulted in the formation of Thp radical cation (Thp(.+)), which remained stable in the experimental time window up to 200mus, showing that charge may be carried along DNA by Thp as Thp(.+).
The formation of the pyrene (Py) dimer radical cation (Py(2)(*+)) was used to measure the kinetics of the intrastrand end-to-end contact rates of single-stranded DNAs (ssDNAs) in the 10 nanoseconds to the tens of microseconds time range. ssDNAs labeled with Py at both ends with the lengths of 3, 6, and 9 mer were synthesized, and the two-photon ionization method was employed to generate a Py(*+), which enables the measurements of the end-to-end contact rates from 10 ns. The formation rate of Py(2)(*+) depended on the length and the sequence of the ssDNAs, and about 1 order of magnitude faster rates were observed for the T-rich ssDNAs compared to those for the corresponding length of A-rich ssDNAs, showing that ssDNA made from adenines is much more rigid than that composed of thymidines. As for the T-rich ssDNAs, the formation of Py(2)(*+) attributed to the misfolded structures was also observed, which is consistent with the configurational diffusion model suggested by Ansari and co-workers.
The influence of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) on the one-electron oxidation reaction of aromatic sulfides (S) with Br2*- and the decay process of the S radical cation (S*+) was investigated by pulse radiolysis. The dissociation kinetics of S*+ from the CD cavity was examined in terms of the apparent equilibrium constants (Kapp) for the formation and decay processes of S*+. Inhibition of the one-electron oxidation reaction of S by Br2*- was clearly observed in the presence of HP-beta-CD. On the basis of a comparison between the determined Kapp values, it was found that the binding ability of S*+ with HP-beta-CD is much lower than that of S, because of the hydrophobic nature of the cavity. The formation process of the dimer radical cation of 4-(methylthio)phenylmethanol ((MTPM)2*+), which is generated between MTPM(*+) and neutral MTPM in solution, was also inhibited by the addition of HP-beta-CD.
[reaction: see text] DNA-porphyrin conjugates having four DNA strands were designed and synthesized. Four double helices were assembled using two DNA-porphyrin conjugates and their complementary strands, and the formation of the four double-helix assembled structures with the two DNA-porphyrin units was examined by gel electrophoresis and spectroscopic analysis. The interaction between two porphyrin chromophores in the complex was investigated by measurement of fluorescence lifetimes, and the singlet energy transfer between the two different phorphyrin units (Zn-porphyrin and H2-porphyrin) was observed. These results indicate that multiple and different porphyrin chromophores can be integrated into the DNA structures by programming the sequences of the DNA strands.
Efficient monomer and excimer emission from various donor-acceptor substituted phenylethynes (PE), which are known as efficient electrogenerated chemiluminescent molecules, was observed with time-resolved fluorescence measurement during the pulse radiolysis in benzene. On the basis of the transient absorption and emission measurements, and steady-state measurements, the formation of PE in the singlet excited state (1PE*) and the excimer (1PE2*) can be interpreted by the charge recombination between the PE radical cation (PE.+) and the PE radical anion (PE.-) which are generated initially from the radiolytic reaction in benzene. It is suggested that the positive and negative charges are localized on the donor and acceptor moieties in the radical cation and anion, respectively. This mechanism is reasonably explained by the relationship between the annihilation enthalpy changes (-DeltaH' degrees ) and singlet excitation energies of donor-substituted phenyl(9-acridinyl)ethynes (1(a-e)). In addition to the monomer emission, the compounds bearing weak donors (1(a-d)) show the excimer emission due to a very small twist angle between the donor and acceptor moieties. For the phenyl(9-cyano-10-anthracenyl)ethynes (2(c) and 2(f)), although they also show the monomer and excimer emissions, it cannot be explained by the relationship between -DeltaH' degrees values and their singlet excitation energies, suggesting the formation of the ICT state and H-type excimer in which two 9-cyano-10-anthracenyl moieties are stacked face-to-face with donor bearing a benzene ring projecting perpendicularly away from each other through the charge recombination between 2.+) and 2.-) and/or triplet-triplet annihilation.
Dual intermolecular electron transfer (ELT) pathways from 4,4'-dimethoxybenzophenone (1) ketyl radical (1H*) in the excited state [1H*(D1)] to the ground-state 4,4'-dimethoxybenzophenone [1(S0)] were found in 2-methyltetrahydrofuran (MTHF) by observing bis(4-methoxyphenyl)methanol cation (1H+) and 4,4'-dimethoxybenzophenone radical anion (1*-) during nanosecond-picosecond two-color two-laser flash photolysis. ELT pathway I involved the two-photon ionization of 1H* following the injection of electron to the solvent. The solvated electron was quickly trapped by 1(S0) to produce 1*-. ELT pathway II was a self-quenching-like ELT from 1H*(D1) to 1(S0) to give 1H+ and 1*-. From the fluorescence quenching of 1H*(D1), the ELT rate constant was determined to be 1.0 x 10(10) M(-1) s(-1), which is close to the diffusion-controlled rate constant of MTHF. The self-quenching-like ELT mechanism was discussed on the basis of Marcus' ELT theory.
The dramatic changes of the lifetimes of the charge-separated (CS) states were confirmed in zinc porphyrin (ZnP)-oligothiophene (nT)-fullerene (C(60)) linked triads (ZnP-nT-C(60)) with the solvent polarity. After the selective excitation of the ZnP moiety of ZnP-nT-C(60), an energy transfer took place from the (1)ZnP moiety to the C(60) moiety, generating ZnP-nT-(1)C(60). In polar solvents, the CS process also took place directly via the (1)ZnP moiety, generating ZnP(*+)-nT-C(60)(*-), as well as the energy transfer to the C(60) moiety. After this energy transfer, an indirect CS process took place from the (1)C(60) moiety. In the less polar solvent anisole, the radical cation (hole) of ZnP(*+)-nT-C(60)(*-) shifted to the nT moiety; thus, the nT moiety behaves as a cation trapper, and the rates of the hole shift were evaluated to be in the order of 10(8) s(-1); then, the final CS states ZnP-nT(*+)-C(60)(*-) were lasting for 6-7 mus. In the medium polar solvent o-dichlorobenzene (o-DCB), ZnP-nT(*+)-C(60)(*-) and ZnP(*+)-nT-C(60)(*-) were present as an equilibrium, because both states have almost the same thermodynamic stability. This equilibrium resulted in quite long lifetimes of the CS states (450-910 mus) in o-DCB. In the more polar benzonitrile, the generation of ZnP-nT(*+)-C(60)(*-) was confirmed with apparent short lifetimes (0.6-0.8 mus), which can be explained by the fast hole shift to more stable ZnP(*+)-nT-C(60)(*-) followed by the faster charge recombination. It was revealed that the relation between the energy levels of two CS states, which strongly depend on the solvent polarity, causes dramatic changes of the lifetimes of the CS states in ZnP-nT-C(60); that is, the most appropriate solvents for the long-lived CS state are intermediately polar solvents such as o-DCB. Compared with our previous data for H(2)P-nT-C(60), in which H(2)P is free-base porphyrin, the lifetimes of the CS states of ZnP-nT-C(60) are approximately 30 times longer than those in o-DCB.
The C-O bond cleavage from benzophenone substituted with 4-CH2OR (p-BPCH2OR, 1-3), such as p-phenoxymethylbenzophenone (1, R= C6H5) and p-methoxymethylbenzophenone (2, R= CH3), occurred by a stepwise two-photon excitation during two-color, two-laser flash photolysis. On the other hand, no C-O bond cleavage occurred from p-hydroxymethylbenzophenone (3, R = H). The first 355-nm laser excitation of 1-3 generates p-BPCH2OR in the lowest triplet excited state (T1) which has an absorption at 532 nm. When p-BPCH2OR(T1) is excited with the second 532-nm laser to p-BPCH2OR in the higher triplet excited state (T(n)), the C-O bond cleavage occurred within the laser flash duration of 5 ns. The quantum yields of the C-O bond cleavage during the second 532-nm laser irradiation were found to be 0.015 +/- 0.007 and 0.007 +/- 0.003 for 1 and 2, respectively. Although these values are low, the diminishing 1(T1) or 2(T1) was found to convert, in almost 100% yield, to phenoxyl (C6H5O*) and p-benzoylbenzyl (BPCH2*) radicals or methoxyl (CH3O*) and BPCH2* radicals, respectively. The T(n) excitation energy, the energy barrier along the potential surface between the T(n) states and product radicals, and delocalization of the T(n) state molecular orbital including BP and CH2OR (R = C6H5, CH3, H) moieties are important factors for the occurrence of the C-O bond cleavage. It is found that the C-O bond cleavage and production of free radicals, such as BPCH2*, C6H5O*, and CH3O*, can be performed by a stepwise two-photon excitation. The present study is an example in which the chemical reactions can be selectively initiated from the T(n) state but not from the S1 and T1 states.
We have investigated the excited-state properties and singlet oxygen ((1)Delta(g)) generation mechanism in phthalocyanines (4M; M = H(2), Mg, or Zn) and in low-symmetry metal-free, magnesium, and zinc tetraazaporphyrins (TAPs), that is, monobenzo-substituted (1M), adjacently dibenzo-substituted (2AdM), oppositely dibenzo-substituted (2OpM), and tribenzo-substituted (3M) TAP derivatives, whose pi conjugated systems were altered by fusing benzo rings. The S(1)(x) and S(1)(y) states (these lowest excited singlet states are degenerate in D(4)(h) symmetry) split in the low-symmetry TAP derivatives. The excited-state energies were quantitatively determined from the electronic absorption spectra. The lowest excited triplet (T(1)(x)) energies were also determined from phosphorescence spectra, while the second lowest excited triplet (T(1)(y)) states were evaluated by using the energy splitting between the T(1)(x) and T(1)(y) states previously reported (Miwa, H.; Ishii, K.; Kobayashi, N. Chem. Eur. J. 2004, 10, 4422-4435). The singlet oxygen quantum yields (Phi(Delta)) are strongly dependent on the pi conjugated system. In particular, while the Phi(Delta) value of 2AdH(2) is smallest in our system, that of 2OpH(2), an isomer of 2AdH(2), is larger than that of 4Zn, in contrast to the heavy atom effect. The relationship between the molecular structure and Phi(Delta) values can be transformed into a relationship between the S(1)(x) --> T(1)(y) intersystem crossing rate constant (k(ISC)) and the energy difference between the S(1)(x) and T(1)(y) states (DeltaE(S)(x)(T)(y)). In each of the Zn, Mg, and metal-free compounds, the Phi(Delta)/tau(F) values (tau(F): fluorescence lifetime), which are related to the k(ISC) values, are proportional to exp(-DeltaE(S)(x)(T)(y)), indicating that singlet oxygen ((1)Delta(g)) is produced via the T(1)(y) state and that the S(1)(x) --> T(1)(y) ISC process follows the energy-gap law. From the viewpoint of photodynamic therapy, our methodology, where the Phi(Delta) value can be controlled by changing the symmetry of pi conjugated systems without heavy elements, appears useful for preparing novel photosensitizers.
A kinetic study of the single-step hole transfer in DNA was performed by measuring time-resolved transient absorption. DNA molecules with various sequences were designed and conjugated with naphthalimide (NI) and phenothiazine (PTZ) to investigate the sequence and distance dependence of the single-step hole transfer between guanines (Gs). Hole injection into DNA was accomplished by excitation of the NI site with a 355 nm laser pulse, and the kinetics of the hole-transfer process were investigated by monitoring the transient absorption of the PTZ radical cation (PTZ.+). Kinetic analysis of the time profile of PTZ.+ based on the kinetic model showed that the distance dependence of the hole-transfer process was significantly influenced by the DNA sequence. Results of temperature- and isotope-effect experiments demonstrated that the activation energy increased as the number of bridge bases separating the Gs increased. This is because of the distance-dependent reorganization energy and contribution of the proton-transfer process to the hole transfer in DNA.
Efficient emission from various donor-acceptor quinolines with an ethynyl linkage (PnQ), which are known as efficient electrogenerated chemiluminescent molecules, was observed with time-resolved fluorescence measurement during the pulse radiolysis in benzene. On the basis of the transient absorption and emission measurements, and steady-state measurements, the formation of PnQ in the singlet excited state can be interpreted by charge recombination between the PnQ radical cation and the PnQ radical anion which are generated initially from the radiolytic reaction in benzene. The strong electronic coupling between the donor and acceptor through conjugation is responsible for the efficient emission during the pulse radiolysis of PnQ in benzene. It is suggested that the positive and negative charges are localized on the donor and acceptor moieties in the radical cation and anion, respectively. This mechanism is reasonably explained by the relationship between the annihilation enthalpy changes and singlet excitation energies of PnQ. The formation of the intramolecular charge transfer state is assumed for PnQ in the singlet excited state with a strong electron donating substituent. The emission from PnQ is suggested to originate from PnQ in the singlet excited state formed from the charge recombination between the PnQ radical cation and the PnQ radical anion during the pulse radiolysis. This is strong evidence for the efficient electrogenerated chemiluminescence of PnQ.
Substituent effect on the lifetimes of a series of substituted naphthalenes (Np) in the higher triplet excited state (Tn) was studied with transient absorption measurements using the two-color two-laser flash photolysis technique. Lifetimes of Np(Tn) in cyclohexane solution were determined from the triplet energy transfer quenching by carbon tetrachloride to be 0.98-63 ps. The different lifetimes of Np(Tn) were explained by the energy gap law for the internal conversion from Np(Tn) to Np(T1), indicating that Np(Tn) quenched by carbon tetrachloride is assigned to Np(T2) with the longest lifetime among Np(Tn). The lifetime of Np(Tn) was correlative with the Hammett sigmap constant. Electronic characters of substituents showed a more significant influence on the energy of the T2 state than that of the T1 state.
Photophysical properties of oligo(2,3-thienyleneethynylene)s (nTE, n denotes the number of thiophene rings, n = 2, 3) in benzene were investigated using steady-state, time-resolved fluorescence, and transient absorption spectroscopies. For 2TE, generation of the radiative S2 and nonradiative S1 states was confirmed. Upon excitation, the S2 state was initially generated and deactivated to the S1 state within 10 ps. The S1 state exhibited the transient absorption band at 470 nm, of which the lifetime was estimated to be 5.3 ns. In the case of 3TE, on the other hand, it was revealed that the radiative S1 state with a transient absorption peak at 650 nm was generated upon excitation. The T1 states of nTE were generated from the S1 states. The quantum yields were estimated to be 0.52 and 0.54 for 2TE and 3TE, respectively. Extremely fast reactions in the higher triplet excited state were indicated for both 2TE and 3TE.
Formation and decay of radical cations of trans-stilbene and p-substituted trans-stilbenes (S.+) during the resonant two-photon ionization (TPI) of S in acetonitrile in the presence and absence of O(2) have been studied with laser flash photolysis using a XeCl excimer laser (308 nm, fwhm 25 ns). The transient absorption spectra of S.+ were observed with a peak around 470-490 nm. The formation quantum yield of S.+ (0.06-0.29) increased with decreasing oxidation potential (E(ox)) and increasing fluorescence lifetime (tau(f)) of S, except for trans-4-methoxystilbene which has the lowest E(ox) and longer tau(f) among S. The considerable low yield and fast decay in a few tens of nanoseconds time scale were observed for trans-4-methoxystilbene.+ in the presence of O(2), but not for other S.+ . It is suggested that formation of the ground-state complex between trans-4-methoxystilbene and O(2) and the distonic character of trans-4-methoxystilbene.+ with separation and localization of the positive charge on the oxygen of the p-methoxyl group and an unpaired electron on the beta-olefinic carbon are responsible for the fast reaction of trans-4-methoxystilbene.+ with O(2) or superoxide anion, leading to the considerable low yield and fast decay of trans-4-methoxystilbene.+ . The mechanism based on the transient absorption measurement of S.+ during the TPI is consistent with the relatively high oxidation efficiency of trans-4-methoxystilbene among S based on the product analysis during the photoinduced electron transfer in the presence of a photosensitizer such as 9,10-dicyanoanthracene and O(2) in acetonitrile.
Stepwise photocleavage of naphthylmethyl-oxygen (C-O) bonds of mono(substituted-methyl)naphthalenes [1- and 2-ROCH2Np, R = 4-benzoylphenyl (BP), phenyl (Ph), and methyl (CH3)] and bis(substituted-methyl)naphthalenes [1,8-(ROCH2)2Np and 1,4-(ROCH2)2Np, R = BP and Ph] was observed to give the naphthylmethyl radicals (NpCH2* or ROCH2NpCH2*) in almost 100% yield with two-step or three-step excitation by the two-color two-laser or three-color three-laser irradiation, respectively, at room temperature. The C-O bond cleavage quantum yields of 1-PhOCH2Np, 2-PhOCH2Np, 1,8-(PhOCH2)2Np, and 1,4-(PhOCH2)2Np were higher than those of 1-BPOCH2Np, 2-BPOCH2Np, 1,8-(BPOCH2)2Np, and 1,4-(BPOCH2)2Np. No C-O bond cleavage occurred from 1,8-(HOCH2)2Np and 2-CH3OCH2Np in the higher triplet excited state (T(n)). The experimental results show that the C-O bond cleavage was determined not only by the position of the substituents on Np but also by the type of the substituents. The C-O bond cleavage of 1-ROCH2Np was more efficient than that of 2-ROCH2Np. In the case of 1,8-(ROCH2)2Np and 1,4-(ROCH2)2Np (R = BP and Ph), the first C-O bond cleavage from the T(n) states occurred to give ROCH2-substituted naphthylmethyl radicals (1,8- and 1,4-ROCH2NpCH2*) when the T1 states, generated with the 308-nm first laser irradiation, were excited using the 430-nm second laser. The second C-O bond cleavage occurred when 1,8- and 1,4-ROCH2NpCH2* in the ground state [1,8- and 1,4-ROCH2NpCH2*(D0)] were excited to the excited states [1,8- and 1,4-ROCH2NpCH2*(D(n))] using the third 355-nm laser during the three-color three-laser flash photolysis at room temperature. It was revealed that acenaphthene was produced as the final product during the stepwise C-O bond cleavages of 1,8-(BPOCH2)2Np and 1,8-(PhOCH2)2Np. This is a successful example of stepwise cleavage of two equivalent C-O bonds in a molecule using the three-color three-laser photolysis method.
Formation of radical cation and charge-transfer complex of [3n]cyclophanes (n = 3, 5, 6) was investigated by transient absorption spectroscopy during pulse radiolysis. Radical cations of [3n]cyclophanes showed the charge resonance band around 700 nm which exhibited a blue-shift as the number of trimethylene bridges increased, indicating formation of highly stabilized intramolecular dimer radical cation of [3n]cyclophanes. The absorption peak of the charge-transfer complex with chlorine atom also showed the shift in accord with the oxidation potential of [3n]cyclophanes.
[structure: see text] Photoreaction of trans-4'-benzyl-5-styrylfuran (trans-BSF) has been studied by the 355-nm laser flash photolysis (LFP) in CH2Cl2 using a Nd3+:YAG laser (30 ps, 5 mJ pulse(-1) or 5 ns, 30 mJ pulse(-1)). Transient fluorescence and absorption spectra assigned to the singlet excited trans-BSF were observed during the 30-ps LFP, whereas a transient absorption spectrum with two peaks at 400 and 510 nm, assigned to the trans-fused dihydrophenanthrene (DHP)-type intermediate (DP1), was observed during the 5-ns LFP. It is clearly suggested that a two-photon absorption process is involved in the formation of DP1. The first photoreaction is the photoisomerization of trans-BSF, which occurs to give cis-BSF. The second photoreaction process is photocyclization of cis-BSF, which occurs to give DP1 decaying with the half lifetime (tau1/2) of 2.8-4.0 micros to produce another DHP-type intermediate (DP2) with an absorption peak at 400 nm in the absence of O2, through [1,9]-hydrogen shift. DP2 decayed with tau1/2 > 500 micros to give the product through aromatization. In O2-saturated CH2Cl2, DP1 decayed with tau1/2 = 250 ns to give a radical intermediate (X) with two peaks at 410 and 510 nm, through hydrogen abstraction of DP1 by O2. X decayed with tau1/2 = 150 micros to give the product through successive hydrogen abstraction.
The properties and reactivities of the xanthone (Xn) ketyl radical (XnH*) in the doublet excited state (XnH*(D1)) were examined by using two-color two-laser flash photolysis. The absorption and fluorescence of XnH*(D1) were observed for the first time. Several factors governing the deactivation processes of XnH*(D1) such as interaction and reaction with solvent molecules were discussed. The remarkable change of reactivity of XnH*(D1) compared with that in the ground state (XnH*(D0)) was indicated from the experimental results. The rapid halogen abstraction of XnH*(D1) from some halogen donors such as carbon tetrachloride (CCl4) was found to occur. The halogen abstraction occurred more efficiently in the polar solvents than in the nonpolar solvents. It is suggested that the polar solvents promote the spin distribution of XnH*(D1) of the phenyl ring favorable to the halogen abstraction.