Guanine-specific DNA oxidation photosensitized by the tetraphenylporphyrin phosphorus(V) complex via singlet oxygen generation and electron transfer

The photosensitized DNA damage caused by dihydroxoP(V)tetraphenylporphyrin (P(V)TPP), a cationic water-soluble porphyrin, was examined. The study of near-infrared emission measurements demonstrated the photosensitized singlet oxygen ((1)O(2)) generation by P(V)TPP (quantum yield: 0.28 in ethanol). The fluorescence quenching of P(V)TPP by DNA showed the electron transfer (ET) from nucleobases to photoexcited P(V)TPP. These results have shown that P(V)TPP has ability to damage DNA through dual mechanisms, (1)O(2) generation and ET. Under aerobic conditions, P(V)TPP photosensitized damage was more severe for single-stranded DNA compared to its double-stranded counterpart. Photoexcited P(V)TPP damaged every guanine residue in single-stranded DNA. HPLC measurements confirmed the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), an oxidized product of 2'-deoxyguanosine, and showed that the yield of 8-oxodGuo in single-stranded DNA is larger than that in double-stranded DNA. The guanine-specific DNA damage and the enhancement in single-stranded DNA suggest that the (1)O(2) generation mainly contributes to the mechanism of DNA photodamage by P(V)TPP. Absorption spectrum measurements suggested the interaction between P(V)TPP and DNA. This interaction is expected to enhance the (1)O(2)-mediated DNA damage since the lifetime of (1)O(2) is very short. On the other hand, for double-stranded DNA, photosensitized damage at consecutive guanines was much less pronounced. Because the consecutive guanines act as a hole trap, this DNA-damaging pattern suggests the partial involvement of photoinduced ET. However, DNA damage by ET was not a main mechanism, possibly due to the reverse ET. In conclusion, P(V)TPP induces guanine specific photooxidation mainly via (1)O(2) generation. The interaction with DNA and the energy level of the photoexcited porphyrin may be advantageous for (1)O(2)-mediated DNA damage rather than ET mechanism.     

The microenvironment of DNA switches the activity of singlet oxygen generation photosensitized by berberine and palmatine

The effect of the interaction between DNA and the photosensitizer on photosensitized singlet oxygen (1O2) generation was investigated using DNA-binding alkaloids, berberine and palmatine. These photosensitizers were bound to DNA by electrostatic force. Near-infrared luminescence measurement demonstrated that the photoexcited alkaloids can generate 1O2 only when the photosensitizers are bound to DNA. A fluorescence decay study showed significant enhancement of the lifetime of their photoexcited state with the DNA binding. A calculation study suggested that the electrostatic interaction with DNA inhibits the quenching of the photoexcited state of these alkaloids via intramolecular electron transfer, leading to the prolongation of the lifetime of their excited state. This effect should enhance their intersystem crossing and the yield of energy transfer to molecular oxygen. The results show that the electrostatic interaction with DNA significantly affects the 1O2 generation activity of a photosensitizer. In addition, this interaction may be applied to the control and the design of photosensitizers for medical applications such as photodynamic therapy.     

Efficient charge injection from the S2 photoexcited state of special-pair mimic porphyrin assemblies anchored on a titanium-modified ITO anode

A novel surface fabrication methodology has been accomplished, aimed at efficient anodic photocurrent generation by a photoexcited porphyrin on an ITO (indium-tin oxide) electrode. The ITO electrode was submitted to a surface sol-gel process with titanium n-butoxide in order to deposit a titanium monolayer. Subsequently, porphyrins were assembled as monolayers on the titanium-treated ITO surface via phosphonate, isophthalate, and thiolate groups. Slipped-cofacial porphyrin dimers, the so-called artificial special pair at the photoreaction center, were organized through imidazolyl-to-zinc complementary coordination of imidazolylporphyrinatozinc(II) units, which were covalently immobilized by ring-closing olefin metathesis of allyl side chains. The modified surfaces were analyzed by means of X-ray photoelectron spectroscopy. Photoirradiation of the porphyrin dimer generated a large anodic photocurrent in aqueous electrolyte solution containing hydroquinone as an electron sacrificer, due to the small reorganization energy of the dimer. The use of different linker groups led to significant differences in the efficiencies of anodic photocurrent generation. The apparent flat-band potentials evaluated from the photocurrent properties at various pH values and under biased conditions imply that the band structure of the ITO electrode is modified by the anchoring species. The quantum yield for the anodic photocurrent generation by photoexcitation at the Soret band is increased to 15 %, a surprisingly high value without a redox cascade structure on the ITO electrode surface, while excitation at the Q band is not so significant. Extensive exploration of the photocurrent properties has revealed that hot injection of the photoexcited electron from the S2 level into the conduction band of the ITO electrode takes place before internal conversion to the S1* state, through the strong electronic communication of the phosphonyl anchor with the sol-gel-modified ITO surface.     

Time-Resolved Spectroscopic Study on Photoinduced Electron-Transfer Processes in Zn(II)porphyrin–Zn(II)chlorin–Fullerene Triad

Femtosecond time-resolved transient absorption studies have been performed to investigate the photoinduced energy and electron-transfer processes in Zn(II )porphyrin–Zn(II )chlorin–fullerene triad in which energy and oxidation potential gradients are directed along the donor–acceptor-linked arrays. Fast energy transfer (≈450 fs) from photoexcited Zn(II )porphyrin to Zn(II )chlorin was observed upon selective photoexcitation of Zn(II )porphyrin unit in the triad. In a nonpolar solvent such as toluene, the energy transfer from the excited singlet state of Zn(II )chlorin to fullerene occurs and is followed by the formation of an intermediate state with a time constant of nanoseconds, which was attributed to the intramolecular exciplex between Zn(II )chlorin and fullerene. In benzonitrile, on the other hand, the photoexcitation of the triad results in the fast electron transfer (<1 ps) from photoexcited Zn(II )chlorin to fullerene. The generated charge-separated species recombine with a time constant of ≈12 ps. The relatively fast charge separation and charge recombination rates imply that the strong electronic coupling between Zn(II )chlorin and fullerene moieties is probably induced by the folded conformation between Zn(II )chlorin and fullerene moieties which enhances direct through-space interaction between the proximately contacted π systems.     

Controlled generation of singlet oxygen by a water-soluble meso-pyrenylporphyrin photosensitizer through interaction with DNA

An electron donor-connecting water-soluble porphyrin, meso-(1-pyrenyl)-tris(N-methyl-p-pyridinio)porphyrin, did not demonstrate singlet oxygen generating activity under photo-irradiation. The interaction with DNA successfully recovered the photosensitized singlet oxygen generation by this porphyrin.     

Active oxygen species generated from photoexcited fullerene (C60) as potential medicines: O2-* versus 1O2

To characterize fullerenes (C(60) and C(70)) as photosensitizers in biological systems, the generation of active oxygen species, through energy transfer (singlet oxygen (1)O(2)) and electron transfer (reduced active oxygen radicals such as superoxide anion radical O(2)(-)* and hydroxyl radical *OH), was studied by a combination of methods, including biochemical (DNA-cleavage assay in the presence of various scavengers of active oxygen species), physicochemical (EPR radical trapping and near-infrared spectrometry), and chemical methods (nitro blue tetrazolium (NBT) method). Whereas (1)O(2) was generated effectively by photoexcited C(60) in nonpolar solvents such as benzene and benzonitrile, we found that O(2)(-)* and *OH were produced instead of (1)O(2) in polar solvents such as water, especially in the presence of a physiological concentration of reductants including NADH. The above results, together with those of a DNA cleavage assay in the presence of various scavengers of specific active oxygen species, indicate that the active oxygen species primarily responsible for photoinduced DNA cleavage by C(60) under physiological conditions are reduced species such as O(2)(-)* and *OH.     

Photohydrolysis of methotrexate produces pteridine,which induces poly-G-specific DNA damage through photoinduced electron transfer

Methotrexate (MTX), an antineoplastic agent, demonstrates phototoxicity. The mechanism of damage to biomacromolecules induced by photoirradiated MTX was examined using 32P-labeled DNA fragments obtained from a human gene. Photoirradiated MTX caused DNA cleavage specifically at the underlined G in 5'-GG and 5'-GGG sequences in double-stranded DNA only when the DNA fragments were treated with piperidine, which suggests that DNA cleavage was caused by base modification with little or no strand breakage. With denatured single-stranded DNA the damage occurred at most guanine residues. The amount of formation of 8-hydroxy-2'-deoxyguanosine (8-oxodGuo), an oxidative product of 2'-deoxyguanosine, in double-stranded DNA exceeded that in single-stranded DNA. These results suggest that photoirradiated MTX participates in 8-oxodGuo formation at the underlined G in 5'-GG and 5'-GGG sequences in double-stranded DNA through electron transfer, and then 8-oxodGuo undergoes further oxidation into piperidine-labile products. Fluorescence measurement, high-pressure liquid chromatography and mass spectrometry have demonstrated that photoexcited MTX is hydrolyzed into 2,4-diamino-6-(hydroxymethyl)pteridine (DHP). DNA damage induced by DHP was observed in a similar manner as was the damage induced by MTX. The extent of DNA damage and the formation of 8-oxodGuo by DHP were much larger than those induced by MTX. The kinetic analysis, based on the time course of DNA oxidation by photoirradiated MTX, suggests that DNA damage is caused by photoexcited DHP rather than by photoexcited MTX. In conclusion, photoexcited MTX undergoes hydrolysis through intramolecular electron transfer, resulting in the formation of DHP, which exhibits a phototoxic effect caused by oxidation of biomacromolecules through photoinduced electron transfer.     

Photoinduced electron transfer and solvation dynamics in aqueous clusters: comparison of the photoexcited iodide-water pentamer and the water pentamer anion

Upon photoexcitation of iodide-water clusters, I(-)(H(2)O)(n), an electron is transferred from iodide to a diffuse cluster-supported, dipole-bound orbital. Recent femtosecond photoelectron spectroscopy experiments have shown that, for photoexcited I(-)(H(2)O)(n) (n≥ 5), complex excited-state dynamics ultimately result in the stabilization of the transferred electron. In this work, ab initio molecular dynamics simulations of excited-state I(-)(H(2)O)(5) and (H(2)O)(5)(-) are performed, and the simulated time evolution of their structural and electronic properties are compared to determine unambiguously the respective roles of the water molecules and the iodine atom in the electron stabilization dynamics. Results indicate that, driven by the iodine-hydrogen repulsive interactions, excited I(-)(H(2)O)(5) rearranges significantly from the initial ground-state minimum energy configuration to bind the excited electron more tightly. By contrast, (H(2)O)(5)(-) rearranges less dramatically from the corresponding configuration due to the lack of the same iodine-hydrogen interactions. Despite the critical role of iodine for driving reorganization in excited I(-)(H(2)O)(5), excited-electron vertical detachment energies appear to be determined mostly by the water cluster configuration, suggesting that femtosecond photoelectron spectroscopy primarily probes solvent reorganization in photoexcited I(-)(H(2)O)(5).     

Photosensitized DNA damage and its protection via a novel mechanism

UVA, which accounts for approximately 95% of solar UV radiation, can cause mutations and skin cancer. Based mainly on the results of our study, this paper summarizes the mechanisms of UVA-induced DNA damage in the presence of various photosensitizers, and also proposes a new mechanism for its chemoprevention. UVA radiation induces DNA damage at the 5'-G of 5'-GG-3' sequence in double-stranded DNA through Type I mechanism, which involves electron transfer from guanine to activated photosensitizers. Endogenous sensitizers such as riboflavin and pterin derivatives and an exogenous sensitizer nalidixic acid mediate DNA photodamage via this mechanism. The major Type II mechanism involves the generation of singlet oxygen from photoactivated sensitizers, including hematoporphyrin and a fluoroquinolone antibacterial lomefloxacin, resulting in damage to guanines without preference for consecutive guanines. UVA also produces superoxide anion radical by an electron transfer from photoexcited sensitizers to oxygen (minor Type II mechanism), and DNA damage is induced by reactive species generated through the interaction of hydrogen peroxide with metal ions. The involvement of these mechanisms in UVA carcinogenesis is discussed. In addition, we found that xanthone derivatives inhibited DNA damage caused by photoexcited riboflavin via the quenching of its excited triplet state. It is thus considered that naturally occurring quenchers including xanthone derivatives may act as novel chemopreventive agents against photocarcinogenesis.     

Physicochemical and photophysical studies on porphyrin-based donor-acceptor systems: effect of redox potentials on ultrafast electron-transfer dynamics

We report new polychromophoric complexes, where different porphyrin (P) derivatives are covalently coupled to a redox active Mo center, MoL*(NO)Cl(X) (L* is the face-capping tridentate ligand tris(3,5-dimethylpyrazolyl) hydroborate and X is a phenoxide/pyridyl/amido derivative of porphyrin). The luminescence quantum yields of the bichromophoric systems (1, 2, and 5) were found to be an order of magnitude less than those of their respective porphyrin precursors. Transient absorption measurements revealed the formation of the porphyrin radical cation species (P(.)(+)) and photoinduced electron transfer from the porphyrin moiety to the respective Mo center in 1, 2, and 5. Electrochemical studies showed that the reduction potentials of the acceptor Mo centers in a newly synthesized pyridyl derivative (2; E(1/2)[Mo(I/0)] = approximately -1.4 V vs Ag/AgCl) and previously reported phenoxy- (1; E(1/2)[Mo(II/I)] = approximately -0.3 V vs Ag/AgCl) and amido- (3; E(1/2)[Mo(II/I)] = approximately -0.82 V vs Ag/AgCl) derivatives were varied over a wide range. Thus, studies with these complexes permitted us to correlate the probable effect of this potential gradient on the electron-transfer dynamics. Time-resolved absorption studies, following excitation at the Soret band of the porphyrin fragment in complexes 1, 2, and 5, established that forward electron transfer took place biexponentially from both S2 and S1 states of the porphyrin center to the Mo moiety with time constants 150-250 fs and 8-20 ps, respectively. In the case of MoL*(NO)ClX (where X is pyridine derivative 2), the high reduction potential for the MoI/0 couple allowed electron transfer solely from the S2 state of the porphyrin center. Time constants for the charge recombination process for all complexes were found to be 150-300 ps. Further, electrochemical and EPR studies with the trichromophoric complexes (3 and 4) revealed that the orthogonal orientation of the peripheral phenoxy/pyridyl rings negated the possibility of any electronic interaction between two paramagnetic Mo centers in the ground state and thereby the spin exchange, which otherwise was observed for related Mo complexes when two Mo centers are separated by a polyene system with comparable or larger separation distances.     

Electronic coupling effects on photoinduced electron transfer in carotene-porphyrin-fullerene triads detected by time-resolved EPR

Photoinduced charge separation and recombination in a carotenoid-porphyrin-fullerene triad C-P-C60 (Bahr et al., 2000) have been followed by time-resolved electron paramagnetic resonance. The electron-transfer process has been characterized in a glass of 2-methyltetrahydrofuran and in the nematic phase of two uniaxial liquid crystals (E-7 and ZLI-1167). In all the different media, the molecular triad undergoes two-step photoinduced electron transfer, with the generation of a long-lived charge-separated state (C*+-P-C60*-), and charge recombination to the triplet state, localized in the carotene moiety, mimicking different aspects of the photosynthetic electron-transfer process. The magnetic interaction parameters have been evaluated by simulation of the spin-polarized radical pair spectrum. The weak exchange interaction parameter (J = +1.7 +/- 0.1 G) provides a direct measure of the dominant electronic coupling matrix element V between the C*+-P-C60*- radical pair state and the recombination triplet state 3C-P-C60. Comparison of the estimated values of V for this triad and a structurally related triad differing only in the porphyrin bridge (octaalkylporphyrin vs tetraarylporphyrin) explains in terms of an electronic coupling effect the approximately 6-fold variation of the recombination rate induced by the modification of the porphyrin bridge as derived by kinetic experiments (Bahr et al., 2000).     

Synthesis, characterization, and DNA-binding and -photocleavage properties of water-soluble lanthanide porphyrinate complexes

A series of cationic lanthanide porphyrinate complexes of the general formula [(Por)Ln(H(2)O)(3)](+) (Ln(3+)=Yb(3+) and Er(3+)) were synthesized in moderate yields through the interaction of meso-pyridyl-substituted porphyrin free bases (H(2)Por) with [Ln{N(SiMe(3))(2)}(3)]·x[LiCl(thf)(3)], and the corresponding neutral derivatives [(Por)Ln(L(OMe))] (L(OMe)(-)=[(η(5)-C(5)H(5))Co{P(=O)(OMe)(2)}(3)](-)) were also prepared from [(Por)Ln(H(2)O)(3)](+) by the addition of the tripodal anion, L(OMe)(-), an effective encapsulating agent for lanthanide ions. Furthermore, the water-soluble lanthanide(III) porphyrinate complexes--including [(cis-DMPyDPP)Yb(H(2)O)(3)]Cl(3) (cis-DMPyDPP=5,10-bis(N-methylpyridinium-4'-y1)-15,20-di(phenyl)porphyrin), [(trans-DMPyDPP)Yb(H(2)O)(3)]Cl(3) (trans-DMPyDPP=5,15-bis(N-methylpyridinium-4'-y1)-10,20-di(phenyl)porphyrin), [(TMPyP)Yb(L(OMe))]I(4), and [(TMPyP)Er(L(OMe))]I(4) (TMPyP=tetrakis(N-methylpyridinium-4-y1)porphyrin)--were obtained by methylation of the corresponding complexes with methyl iodide and unambiguously characterized. The binding interactions and photocleavage activities of the water-soluble lanthanide(III) porphyrinate complexes towards DNA were investigated by UV-visible, fluorescence, and near-infrared luminescence spectroscopy, as well as circular dichroism and gel electrophoresis.     

Interaction of meso-tetrakis (4-sulfonatophenyl) porphyrin with cationic CTAC micelles investigated by small angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR)

Small angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR) have been used to investigate the interaction of the water-soluble meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS(4)) with cationic cethyltrimethylammonium chloride (CTAC) micelles. To evaluate if the porphyrin protonation state affects its interaction with the micelle, both SAXS and EPR measurements were performed at pH 4.0 and 9.0. The best-fit SAXS curves were obtained assuming for CTAC micelle a prolate ellipsoidal shape in the absence and upon incorporation of 2-10 mM TPPS(4). SAXS results show that the presence of porphyrin impacts on micellar hydrophobic core, leading to a micellar reassembling into smaller micelles. Lineshapes of EPR spectra of 5- and 16-doxyl stearic acids (5- and 16-DSA, respectively) bound to 100 mM CTAC micelles exhibited slight changes as a function of porphyrin concentration. Spectral simulations revealed an increase of mobility restriction for both spin probes, especially at higher porphyrin concentration, where a small reduction of environment polarity was also observed for 16-DSA. The spin labels monitored only slight differences between pH 4.0 and 9.0, in agreement with the SAXS results.     

Femtosecond Dynamics of Dioxygen - Picket-Fence Cobalt Porphyrins: Ultrafast Release of O(2) and the Nature of Dative Bonding

The ultrafast release of O(2) from the O(2) adduct of picket-fence cobalt porphyrin (see picture) has been probed in real time, and has a total reaction time of 2 ps, without subsequent recombination over several nanoseconds. The dynamics of this ultrafast release of O(2) shows that relaxation within the porphyrin system (200 fs) precedes porphyrin-to-metal electron transfer, but the latter occurs at an enhanced rate (500 fs as opposed to the more usual 1 - 2 ps) because of the dative bonding of cobalt and O(2), which gives the adduct ground state significant Co(III)-O(2)(-) character.     

Photoinduced magnetization of the cyano-bridged 3d-4f heterobimetallic assembly Nd(DMF)(4)(H(2)O)(3)(micro-CN)Fe(CN)(5).H(2)O (DMF = N,N-dimethylformamide)

Photoinduced magnetization of the cyano-bridged 3d-4f heterobimetallic assembly Nd(DMF)4(H2O)3(mu-CN)Fe(CN)5.H2O (1) (DMF = N,N-dimethylformamide) is described in this paper. The chiMT values are enhanced by about 45% after UV light illumination in the temperature range of 5-50 K. We propose that UV light illumination induces a structural distortion in 1. This small structural change is propagated by molecular interactions in the inorganic network. Furthermore, the cooperativity resulting from the molecular interaction functions to increase the activation energy of the relaxation processes, which makes observation of the photoexcited state possible. The flexible network structure through the hydrogen bonds in 1 plays an essential role for the photoinduced phenomenon. This finding may open up a new domain for developing the molecule-based magnetic materials.     

多苯并咪唑锰( Ⅱ )配合物的合成及对DNA凝聚的促进作用

以多苯并咪唑配体1,1,4,7,7-五(2-苯并咪唑甲基)-二乙基三胺(DTPB)为主配体, 合成了锰(Ⅱ)配合物[Mn(DTPB)Ac]Ac·8H₂O(1)和[Mn₂(DTPB)(NO₃)₂(H₂O)₂][Mn₂(DTPB)(NO₃)₂(H₂O)(CH₃OH)]·(NO₃)₄·5CH₃OH·H₂O(2), 并对其进行了表征. 利用紫外-可见吸收光谱和黏度实验研究了配合物1和2与DNA的相互作用, 发现这2个配合物均能与DNA结合, 并对配合物与DNA作用的机理进行了探讨. 利用琼脂糖凝胶电泳和直角光散射(RALS)技术研究了配合物1和2促进DNA凝聚的性质. 结果表明, 在近中性条件下2个配合物都能促使DNA凝聚. 利用透射电子显微镜(TEM)观察了不同凝聚体的形态.     

Synthesis of covalently linked unsymmetrical porphyrin pentads containing three different porphyrin subunits

The tetrafunctionalized AB3-type porphyrin building blocks containing two different types of functional groups with N4, N3O, N3S, and N2S2 porphyrin cores were synthesized by following various synthetic routes. The AB3-type tetrafunctionalized N4 porphyrin building block was synthesized by a mixed condensation approach, the N3S and N3O porphyrin building blocks by a mono-ol method, and N2S2 porphyrin building block by an unsymmetrical diol method. The tetrafunctionalized porphyrin building blocks were used to synthesize monofunctionalized porphyrin tetrads containing two different types of porphyrin subunits by coupling of 1 equiv of tetrafunctionalized N4, N3O, N3S, and N2S2 porphyrin building block with 3 equiv of monofunctionalized ZnN4 porphyrin building block under mild copper-free Pd(0) coupling conditions. The monofunctionalized porphyrin tetrads were used further to synthesize unsymmetrical porphyrin pentads containing three different types of porphyrin subunits by coupling 1 equiv of monofunctionalized porphyrin tetrad with 1 equiv of monofunctionalized N2S2 porphyrin building blocks under the same mild Pd(0) coupling conditions. The NMR, absorption, and electrochemical studies on porphyrin tetrads and porphyrin pentads indicated that the monomeric porphyrin subunits in tetrads and pentads retain their individual characteristic features and exhibit weak interaction among the porphyrin subunits. The steady state and time-resolved fluorescence studies support an efficient energy transfer from donor porphyrin subunit to acceptor porphyrin subunit in unsymmetrical porphyrin tetrads and porphyrin pentads.     

Light‐Induced Porphyrin‐Based Spectroscopic Ruler for Nanometer Distance Measurements

We present a novel pulsed electron paramagnetic resonance (EPR) spectroscopic ruler to test the performance of a recently developed spin‐labeling method based on the photoexcited triplet state (S=1). Four‐pulse electron double resonance (PELDOR) experiments are carried out on a series of helical peptides, labeled at the N‐terminal end with the porphyrin moiety, which can be excited to the triplet state, and with the nitroxide at various sequence positions, spanning distances in the range 1.8–8 nm. The PELDOR traces provide accurate distance measurements for all the ruler series, showing deep envelope modulations at frequencies varying in a progressive way according to the increasing distance between the spin labels. The upper limit is evaluated and found to be around 8 nm. The PELDOR‐derived distances are in excellent agreement with theoretical predictions. We demonstrate that high sensitivity is acquired using the triplet state as a spin label by comparison with Cu(II)–porphyrin analogues. The new labeling approach has a high potential for measuring nanometer distances in more complex biological systems due to the properties of the porphyrin triplet state.     

Rational design of iridium–porphyrin conjugates for novel synergistic photodynamic and photothermal therapy anticancer agents

Near-infrared (NIR) emitters are important probes for biomedical applications. Nanoparticles (NPs) incorporating mono- and tetranuclear iridium(iii) complexes attached to a porphyrin core have been synthesized. They possess deep-red absorbance, long-wavelength excitation (635 nm) and NIR emission (720 nm). TD-DFT calculations demonstrate that the iridium–porphyrin conjugates herein combine the respective advantages of small organic molecules and transition metal complexes as photosensitizers (PSs): (i) the conjugates retain the long-wavelength excitation and NIR emission of porphyrin itself; (ii) the conjugates possess highly effective intersystem crossing (ISC) to obtain a considerably more long-lived triplet photoexcited state. These photoexcited states do not have the usual radiative behavior of phosphorescent Ir(iii) complexes, and they play a very important role in promoting the singlet oxygen (¹O₂) and heat generation required for photodynamic therapy (PDT) and photothermal therapy (PTT). The tetranuclear 4-Ir NPs exhibit high ¹O₂ generation ability, outstanding photothermal conversion efficiency (49.5%), good biocompatibility, low half-maximal inhibitory concentration (IC₅₀) (0.057 μM), excellent photothermal imaging and synergistic PDT and PTT under 635 nm laser irradiation. To our knowledge this is the first example of iridium–porphyrin conjugates as PSs for photothermal imaging-guided synergistic PDT and PTT treatment in vivo.

Iridium–porphyrin conjugates assembled in nanoparticles are photosensitizers that exhibit excellent photothermal imaging and synergistic PDT and PTT in vivo.     

Synthesis, singlet oxygen photogeneration and DNA photocleavage of porphyrins with nitrogen heterocycle tails

Eight novel compounds were prepared by reaction of 5-(bromo- propoxyphenyl)-10,15,20-triphenylporphyrin with oxazole thiols, 1,3,4-oxadiazole thiols and 1,3,4-thiadiazole thiols, and their structures confirmed by UV-vis, IR, 1H-NMR, MS and elemental analysis. The assessment of indirectly measured 1O(2) production rates against 5,10,15,20-tetraphenyl porphyrin (H(2)TPP) were described and the relative singlet oxygen production yields were：porphyrin 5 > porphyrins 1, 3, 4, 6-8, H(2)TPP > porphyrin 2. Porphyrin 4 and porphyrin 7 showed substantial photocleavage activities toward DNA, with over 75% cleavage observed at 40 μM. It suggested that these those porphyrins with nitrogen heterocycle tails are potential photosensitive agents.