Lijin Jiang

Two-photon excitation studies of hypocrellins for photodynamic therapy

The photophysical and photochemical properties of hypocrellins (HA and HB) are examined with two-photon excitations at 800 nm using femtosecond pulses from a Ti:sapphire laser. The two-photon excited fluorescence spectra of HA and HB are very similar to those obtained by one-photon excitation, which may indicate that the two-photon induced photodynamic processes of hypocrellins are similar to one-photon induced photodynamic processes. The two-photon excitation cross sections of HA and HB are measured at 800 nm as about 34.8 x 10(-50) cm(4) s/photon and 21.3 x 10(-50) cm(4) s/photon, respectively. The large two-photon cross sections of both HA and HB, suggest that the hypocrellins can be potential two-photon phototherapeutic agents. As an example for two-photon photodynamic therapy of hypocrellins, we also further examine the cell-damaging effects of HA upon two-photon illumination. Our preliminary results of cell viability test indicate hypocrellins can effectively damage the Hela cells under two-photon illumination.

Temperature-induced decoupling of phycobilisomes from reaction centers.

Temperature-induced decoupling of phycobilisomes (PBSs) from the reaction centers in the PBS-thylakoid membrane complexes was observed at 0 degrees C. The fluorescence yields of photosystem (PS) I and PSII decreased and that of PBSs increased with selective excitation of PBSs at 0 degrees C, while the yield of PBSs decreased and those of the two photosystems increased with selective excitation of chlorophyll a at room temperature (RT). It indicated that the decoupling of PBSs from the two photosystems led to changes of energy transfer efficiencies, which can be explained by partial detachment of PBSs from thylakoid membrane. The temperature-dependent processes were reversible, i.e. with temperature going up to RT, the complexes could restore to the functionally coupled state with a time constant about 30 s. Based on these results, it could be deduced that PBSs should be in parallel connection with the two photosystems.

Photophysics, photochemistry and photobiology of hypocrellin photosensitizers

Hypocrellins are novel photosensitizers from China, which are demonstrated to have significant antitumor and anti-virus activity and to be potential photodynamic therapy (PDT) agents. As compared with hematoporphyrin, the only approved photosensitizer, hypocrellins have several advantages, such as easy preparation and easy purification, high triplet quantum yield, high singlet-oxygen quantum yield, high phototoxicity but low dark toxicity, and rapid clearance from normal issues. This article reviews briefly the photophysics, photochemistry and photobiology of hypocrellins on the basis of the domestic and international research results.

Effect of Structural Modification on Photodynamic Activity of Hypocrellins

Aluminum ion complexed 5,8‐di‐Br‐hypocrellin B is a new water‐soluble perylenequinonoid derivative with enhanced absorption over hypocrellin B (HB) in the phototherapeutic window (600–900 nm). Electron paramagnetic resonance and 9,10‐diphenyl‐anthracene bleaching methods were used to investigate the photosensitizing activity of [Al2(5,8‐di‐Br‐HB)Cl4]n in the presence of oxygen. Singlet oxygen, superoxide anion radical and hydroxyl radical can be generated by [Al2(5,8‐di‐Br‐HB)Cl4]n photosensitization. Singlet oxygen (1O2) is formed via energy transfer from triplet‐state [Al2(5,8‐di‐Br‐HB)Cl4]n to ground‐state molecular oxygen. 1O2 participates in the generation of a portion of superoxide anion radical (O2·−). Besides superoxide anion radical (O2·−) may originate from the electron transfer between the triplet‐state [Al2(5,8‐di‐Br‐HB)Cl4]n and the ground‐state molecular oxygen. ·OH is formed through the Fenton–Haber–Weiss reaction and the decomposition of DMPO–1O2 adduct. Compared with HB [Al2(5,8‐di‐Br‐HB)Cl4]n primarily remains and enhances the generation efficiency of superoxide anion radical and hydroxyl radical but that of singlet oxygen decreases.

Photosensitization mechanism of active species by the complex of hypocrellin B with aluminum ion

To improve the water solubility and red absorption of the parent hypocrellin B (HB), the complex of HB with aluminum ion has been first synthesized in high yield. The photodynamic action of Al3+-HB, especially the generation mechanism of active species, ([Al3+-HB]·-, O·-2 and 1O2) was studied using electron paramagnetic resonance (EPR) and spectrophotometric methods. In the deoxygenated DMSO solution of Al3+-HB, the semiquinone anion radical of Al3+-HB is photogenerated via the self-electron transfer between the excited and ground state species. The presence of electron donor significantly promotes the reduction of Al3+-HB. When oxygen is present, superoxide anion radical (O·-2) is formed via the electron transfer from [Al3+-HB]·- to the ground state molecular oxygen. Singlet oxygen (1O2) can be produced via the energy transfer from triplet Al3+-HB to ground state oxygen molecules. Furthermore, it is very significant that the accumulation of [Al3+-HB]·- would replace that of O·-2 or 1O2 with the consumption of oxygen in the sealed system.

Studies on kinetics of reactions between phycobiliproteins and hydroxyl radicals by a pulse radiolytic technique

Scavenging of hydroxyl radical (· OH) by phycobiliproteins (C-phycocyanin, Allophycocyanin and R-phycoerythrin) was studied by competitive kinetics methods. Hydroxyl radicals were generated from pulse radiolysis of aqueous systems saturated with nitrous oxide (N2O). The experimental results indicated that the three types of phycobiliproteins are all strong scavengers of · OH, the rate constants are around (2.8-5.6)×109 L · mol-1 · s-1.

PHYCOBILISOME FROM ANABAENA VARIABILIS KUTZ. AND ITS MODEL CONJUGATES

The model conjugates phycocyanin-allophycocyanin (C-PC-APC) and phycoerythrocyanin-phycocyanin-allophycocyanin (PEC-C-PC-APC) were synthesized by using a heterobifunctional coupling reagent N-succinimidyl-3-(2-pyridyldithio)propionate. The rod-core complex (αβ)6PCLRC27(αβ)3APCLC8.9 and phycobilisomes were separated from Anabaena variabilis. Energy transfer features for the conjugates and the complexes were compared. The absorption and fluorescence emission spectra indicated that the linker-peptides mediate interaction of phycobiliproteins and prompt energy transfer. The energy transfer in the conjugates was detected by fluorescence emission spectra and confirmed by the addition of dithiothreitol. The conjugates may be used as models for studying the energy transfer mechanism in phycobilisomes.

Synthesis of a novel hypocrellin B derivative and its photogeneration of semiquinone anion radical.

In order to improve the photosensitizing activity of HB further, the complex of 5,8-di-Br-HB with Al(3+) was first designed and synthesized in high yield. 5,8-di-Br-HB forms a 2:1 type (metal-ligand ratio) complex with Al(3+) measured by molar ratio and continuous variation methods. The new photosensitizer was characterized by UV-Vis, IR, 1H NMR and elemental analysis measurements. Based on the above experimental results, we first proposed a polymer-like structural model of the complex. The water-solubility and red absorption of the [Al(2)(5,8-di-Br-HB)Cl(4)](n) complex are both enhanced over hypocrellin B. In addition, the EPR and spectrophotometric measurements demonstrate that semiquinone anion radical of [Al(2)(5,8-di-Br-HB)Cl(4)](n) can be produced by [Al(2)(5,8-di-Br-HB)Cl(4)](n) photosensitization. The generation efficiency of ([Al(2)(5,8-di-Br-HB)Cl(4)](n))(.-) is almost equal to that of HB(.-). These results obtained indicated that [Al(2)(5,8-di-Br-HB)Cl(4)](n)was at least a favorable Type I phototherapeutic agent.

ENERGY TRANSFER IN ALLOPHYCOCYANIN HEXAMER FROM ANABAENA VARIABILIS BY TIME-RESOLVED SPECTROSCOPY

Abstract The process and mechanism for energy transfer in an allophycocyanin hexamer from Anabaena variabilis have been studied by time-resolved fluorescence spectroscopy. Deconvolution of isotropic time-resolved fluorescence spectra shows that the energy transfer time between two allophycocyanin trimers is about 14 ps, while the energy transfer time from the linker polypeptide (L cm 42 ) to the final emission is about 65 ps. The anisotropic results of time-resolved fluorescence spectra show that the energy transfer process among three ring-like ( α - 84 / α - 84 ) chromophore pairs still plays an important role with a time constant of about 45 ps. The facts support the idea that the mechanism for energy transfer in the allophycyanin hexamer should be described by Foster dipole—dipole interaction rather than by an exciton interaction.

Photochemistry of hypocrellin derivatives under aerobic conditions

Hypocrellins are a novel type of photosensitizers. A series of new hypocrellin B (HB) derivatives have been synthesized to overcome their limitations, i.e. to improve their red absorption and amphiphilicity. The generation of reactive oxygen species (including Superoxide anion radical, hydroxyl radical and singlet oxygen) is investigated in the presence of oxygen. The chemical structures of HB derivatives affect not only the generation efficiencies of Superoxide and hydroxyl radicals, but also quantum yields of singlet oxygen.