Chelation of hypocrellin B with zinc ions with electron paramagnetic resonance (EPR) evidence of the photodynamic activity of the resulting chelate

FeIII, CuII and ZnII Complexes of the Rigid 9-Oxido-phenalenone Ligand-Spectroscopy, Electrochemistry, and Cytotoxic Properties

The three complexes [Fe(opo)3], [Cu(opo)2], and [Zn(opo)2] containing the non-innocent anionic ligand opo- (opo- = 9-oxido-phenalenone, Hopo = 9-hydroxyphenalonone) were synthesised from the corresponding acetylacetonates. [Zn(opo)2] was characterised using 1H nuclear magnetic resonance (NMR) spectroscopy, the paramagnetic [Fe(opo)3] and [Cu(opo)2] by electron paramagnetic resonance (EPR) spectroscopy. While the EPR spectra of [Cu(opo)2] and [Cu(acac)2] in dimethylformamide (DMF) solution are very similar, a rather narrow spectrum was observed for [Fe(opo)3] in tetrahydrofuran (THF) solution in contrast to the very broad spectrum of [Fe(acac)3] in THF (Hacac = acetylacetone, 2,4-pentanedione; acac- = acetylacetonate). The narrow, completely isotropic signal of [Fe(opo)3] disagrees with a metal-centred S = 5/2 spin system that is observed in the solid state. We assume spin-delocalisation to the opo ligand in the sense of an opo- to FeIII electron transfer. All compounds show several electrochemical opo-centred reduction waves in the range of -1 to -3 V vs. the ferrocene/ferrocenium couple. However, for CuII and FeIII the very first one-electron reductions are metal-centred. Electronic absorption in the UV to vis range are due to π-π* transitions in the opo core, giving Hopo and [Zn(opo)2] a yellow to orange colour. The structured bands ranging from 400 to 500 for all compounds are assigned to the lowest energy π-π* transitions. They show markedly higher intensities and slight shifts for the CuII (brown) and FeIII (red) complexes and we assume admixing metal contributions (MLCT for CuII, LMCT for FeIII). For both complexes long-wavelength absorptions assignable to d-d transitions were detected. Detailed spectroelectrochemical experiments confirm both the electrochemical and the optical assignments. Hopo and the complexes [Cu(opo)2], [Zn(opo)2], and [Fe(opo)3] show antiproliferative activities against HT-29 (colon cancer) and MCF-7 (breast cancer) cell lines in the range of a few µM, comparable to cisplatin under the same conditions.

Internal heavy atom effect of Au(III) and Pt(IV) on hypocrellin A for enhanced in vitro photodynamic therapy of cancer

Hypocrellin A (HA), an a natural perylene quinine photosensitizers (PSs), can chelate with heavy metal ions, including Au(III) and Pt(IV), to form a 1:2 complex, which exhibits enhanced (1)O2 generation quantum yield through the increased intersystem crossing efficiency mediated by internal heavy atom effect. Besides, the chelate process greatly improved the water solubility of HA. Comparative studies with HA and complexes have demonstrated that the heavy-atom effect on HA molecules enhances the efficiency of in vitro photodynamic (PDT) efficacy.

A molecular logic gate for the highly selective recognition of pyrophosphate with a hypocrellin A-Zn(II) complex

Pyrophosphate (PPi) participates in many biological and chemical processes such as energy transduction so that investigations on its role and detection have become very significant. In this contribution, we have developed a molecular logic gate for the recognition of PPi with a fluorescent hypocrellin A-zinc(II) complex (HA-Zn(2+)), and the outputs of which correspond to the fluorescence emission ratio at 604 nm and wavelength shift relative to 629 nm. The emission at 604 nm is the intrinsic fluorescence of HA, which can be effectively quenched by Zn(2+) with a new emission at 629 nm owing to the formation of the HA-Zn(2+) complex. It was found, however, that the new emission at 629 nm is highly selectively quenched with the addition of PPi, recovering the emission at 604 nm, and the recovery ratio is linearly correlated with PPi in the range of 1.8 × 10(-5) mol L(-1) to 2.4 × 10(-4) mol L(-1). ATP, UTP, CTP, GTP, GDP and GMP cannot demonstrate the same spectral actions as PPi. Since the inputs of PPi and the phosphate anions obtain different logical outputs, the designed logic gates have good selectivity and can distinguish PPi from the other anions.