Qianxiong Zhou

A new squaraine and Hg2+-based chemosensor with tunable measuring range for thiol-containing amino acids

A new squaraine, that undergoes absorption and fluorescence bleaching upon binding Hg2+, can serve as a turn-on colorimetric or fluorescent chemosensor for thiol-containing amino acids, presenting tunable measuring range by changing the concentration of Hg2+.

Greatly enhanced binding of a cationic porphyrin towards bovine serum albumin by cucurbit[8]uril

Binding affinity towards serum albumin and intracellular proteins is of importance for a photodynamic therapy (PDT) sensitizer to selectively localize in tumours and efficiently induce cell death. In this paper, it was found that cucurbit[8]uril (CB8) can greatly improve the binding affinity of 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetra(p-toluenesulfonate) (TMPyP), a promising PDT photosensitizer, towards bovine serum albumin (BSA). Absorption, fluorescence emission, (1)H NMR, dynamic light scattering, atomic force microscope, as well as protein photocleavage measurements suggest that the binding enhancement originates from the formation of a ternary complex of CB8·TMPyP·tryptophan residues. This finding opens up a new approach for the development of more efficient PDT agents.

DNA photocleavage by a cationic BODIPY dye through both singlet oxygen and hydroxyl radical: new insight into the photodynamic mechanism of BODIPYs.

Two new NIR-absorbing BODIPY dyes, each bearing two pyridinium groups, are synthesized and their DNA-binding affinities and DNA photocleavage abilities examined in depth. While one BODIPY dye photocleaves DNA mainly through singlet oxygen, the other photocleaves DNA through both singlet oxygen and hydroxyl radical. To the best of our knowledge, this is the first example of a hydroxyl radical being involved in the photodynamic behavior of BODIPY-type dyes. EPR experiments confirm the ability of these and several related BODIPYs to generate superoxide anion radical and hydroxyl radical. This finding may shed light on the mechanism of BODIPY-based photodynamic therapy (PDT) and open a new avenue for development of more efficient BODIPY-type PDT agents.

Fine tuning of the photophysical and electroluminescent properties of DCM-type dyes by changing the structure of the electron-donating group

Using 2H-indene-1,3-dione as an electron-withdrawing group and aromatic amines of different structures as electron-donating groups, four new DCM-type dyes, IN-1, IN-2, IN-3, and IN-4, were designed and synthesized for application in organic light-emitting diodes (OLEDs) as red light-emitting materials. IN-2 exhibits a red shift in fluorescence but a blue shift in absorption with respect to IN-1. Similarly, IN-4 exhibits a red shift in fluorescence but a blue shift in absorption with respect to IN-3. These unique photophysical properties were utilized to optimize the electroluminescence color purity and efficiency of these red emitters in OLEDs. In EL devices with the configuration of ITO/NPB (60 nm)/Alq3 (or Gaq3) : red dopant (2.0 wt%) (7 nm)/BCP (12 nm)/Alq3 (45 nm)/LiF (0.3 nm)/Al (300 nm), IN-3 in Alq3 and IN-1 in Gaq3 show CIE coordinates of (0.64, 0.36) and (0.65, 0.34), and current efficiencies of 3.24 cd A−1 and 3.02 cd A−1, respectively, much better than the other guest/host combinations. This can be ascribed to the good spectrum overlap either between IN-3 and Alq3 or between IN-1 and Gaq3, indicating that the absorption spectrum has the same importance as the fluorescence spectrum in the improvement of color purity of red emitters.

Selective Photodynamic Inactivation of Bacterial Cells over Mammalian Cells by New Triarylmethanes

Three new triarylmethane dyes (TAMs), MPCV, DPCV, and AEV, were synthesized and their photodynamic inactivation abilities against E. coli and human pulmonary carcinoma A549 cells were compared to two commercial TAMs, CV and EV. The enhanced hydrophilicity of MPCV and AEV decreases their cellular uptake to A549 cells dramatically. However, their binding affinity toward E. coli cells are comparable to that of CV and EV by virtue of the improved electrostatic attraction with highly negatively charged E. coli outer membranes. MPCV and AEV were also found to generate hydroxyl radicals more efficiently upon irradiation than CV and EV. Consequently, MPCV and AEV exhibited markedly improved photodynamic inactivation of E. coli cells but remarkably diminished photodynamic inactivation of A549 cells than CV and EV. The photodynamic inactivation ability of DPCV was much lower than that of CV due to its high propensity for bleaching in neutral aqueous solution. Our work demonstrates that the introduction of protonatable groups in a proper manner into the structures of TAMs may lead to selective binding and photodynamic inactivation toward bacterial cells over mammalian cells. This strategy may be extended to other types of photodynamic antimicrobial chemotherapy (PACT) agents to improve their clinical potential.

DNA photocleavage in anaerobic conditions by a Ru(II) polypyridyl complex with long wavelength MLCT absorption

Ru(II) polypyridyl complexes possessing long wavelength absorption and an efficient DNA photocleavage activity exhibit a potential application in photodynamic therapy (PDT). In this article, we reported a Ru(II) polypyridyl complex, [Ru(bpy)2(dpb)]2+ (bpy = 2,2′-bipyridine, dpb = 2,3-bis(2-pyridyl)benzoquinoxaline), that exhibits a very long wavelength 1MLCT absorption, with a maximum at 550 nm, and DNA photocleavage activity in anaerobic conditions in the presence of suitable oxidative quenchers, showing a promising potential application in the PDT of hypoxic tumors.

A new Co(III)–hypocrellin B complex with enhanced photonuclease activity

Hypocrellin B (HB), a naturally occurring photosensitizer, has been extensively and intensively studied as a promising photodynamic therapy (PDT) agent. In this work, a new Co(III) complex [Co(2)(HB)(tmp)(4)](4+) (tmp=3,4,7,8-tetramethyl-1,10-phenanthroline) was designed and synthesized with HB as bridging ligand and tmp as terminal ligand. [Co(2)HB(tmp)(4)](4+) exhibits improved water solubility, enhanced absorptivity in the phototherapeutic window, increased binding affinity and DNA photocleavage capability toward dsDNA with respect to HB. The photodynamic activity of [Co(2)(HB)(tmp)(4)](4+) stems from its (1)O(2) photosensitization ability, in sharp contrast to [Cu(2)(HB)(tmp)(2)](2+) which relies on superoxide anion radical (O(2)(-)) and hydroxyl radical (·OH) to photocleave DNA, though the both complexes possess similar electrochemical properties. The remarkable difference between the photodynamic mechanisms of [Co(2)(HB)(tmp)(4)](4+) and [Cu(2)(HB)(tmp)(2)](2+) was discussed in detail.

The synthesis and 1O2 photosensitization of halogenated asymmetric aniline-based squaraines

The halogenated (brominated or iodinated) squaraines have promising potential in the application of photodynamic therapy (PDT). Though aniline-based squaraines are the most classical squaraine dyes, no halogenated derivatives with the halogen atoms directly incorporated in the conjugation skeleton of the squaraine chromophore have been reported so far. In this work, a stepwise synthetic approach, i.e. by way of the halogenated semi-squaraines, was applied successfully to prepare halogenated asymmetric aniline-based squaraines. Such a structure makes iodine atoms be able to exert significant heavy atom effect on the intersystem crossing (ISC) efficiency of the squaraine dye. As a result, the iodinated asymmetric squaraine (SQ–OH–I) exhibits a singlet oxygen (1O2) quantum yield as high as 0.54. In contrast, the 1O2 quantum yield of the non-halogenated squaraine analogue (SQ–OH) is only 0.02.

Host–Guest Interaction of Hoechst 34580 and Cucurbit[7]uril

To track nuclear dynamic processes by fluorescence imaging, nuclear stains should be highly fluorescent, resistant to photobleaching, and inert to nuclear processes. The nuclear stains of the Hoechst family, such as Hoechst 34580, show bright fluorescence only on groove binding to DNA, and therefore may interfere with visualization of nuclear dynamic processes induced by other stimuli. We study host-guest interactions between Hoechst 34580 and Cucurbit[7]uril (CB7) in aqueous solutions. The formation of CB7-Hoechst 34580 inclusion complexes with stoichiometry of 2:1 in water and 1:1 in phosphate-buffered saline (PBS) solution (pH 7.0) is confirmed by (1)H NMR, absorption spectra, fluorescence spectra, MALDI-TOF MS, and molecular modeling. Compared to Hoechst 34580, the inclusion complex exhibits redshifted absorption, intensified fluorescence, improved photostability, weakened DNA binding affinity, comparable ability to penetrate cell nuclei, and better nuclear-staining capability, and thus a new avenue for the application of cucurbituril in fluorescence imaging is opened.

Photodynamic properties of a bispyrrolecarboxamide-modified hypocrellin B: the role of affinity and ascorbic acid.

The photodynamic properties of a new hypocrellin B (HB) derivative bearing a bispyrrolecarboxamide pendant (HB-Net) were investigated in detail. EPR experiments revealed that the generation ability of reactive oxygen species (ROS) of HB-Net is inferior to that of HB. DNA melting temperature measurements and ethidium bromide (EB) displacement assay illustrated the affinity of HB-Net toward dsDNA as the result of the bispyrrolecarboxamide unit, which is structurally related to the well-known minor groove binder netropsin. The radical generation abilities of HB and HB-Net can be enhanced by ascorbic acid via the photoinduced electron transfer from ascorbic acid to the photosensitizer, however, only the DNA photodamage capability of HB-Net can be improved significantly by ascorbic acid due to the stronger affinity of HB-Net to DNA. Consequently, the combination of HB-Net and ascorbic acid may lead to efficient DNA photodamage even in anaerobic conditions.