Han-Cheng Yu

Tricationic pyridium porphyrins appending different peripheral substituents: Experimental and DFT studies on their interactions with DNA

Four tricationic pyridium porphyrins appending hydroxyphenyl, methoxyphenyl, propionoxyphenyl or carboxyphenyl group at meso-20-position of porphyrin core have been synthesized and their abilities to bind and cleave DNA have been investigated. Using a combination of absorption, fluorescence, circular dichroism (CD) spectra, thermal DNA denaturation as well as viscosity measurements, their binding modes and intrinsic binding constants (K(b)) to calf DNA (CT DNA) were comparatively studied and also compared with those of 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP). The results suggest that the K(b) values of these porphyrins are greatly influenced by the number of positive charges and steric hindrance. Theoretical calculations applying the density functional theory (DFT) have been carried out and explain their DNA-binding properties reasonably. The efficiency of DNA photocleavage by these porphyrins shows high dependence on the values of K(b).

DNA-binding and photocleavage properties of cationic porphyrin-anthraquinone hybrids with different lengths of links.

Four cationic porphyrin-anthraquinone (Por-AQ) hybrids differing in lengths of flexible alkyl linkage, 5-[4-(1-N-anthraquinonon-yl)-L-oxophenyl]-10,15,20-tris(N-methylpyridinium-4-yl)porphyrin triiodide, (L = acetyl, pentanoyl, octanoyl, undecanoyl, designed as [AQATMPyP]I3, [AQPTMPyP]I3, [AQOTMPyP]I3 and [AQUTMPyP]I3, respectively, see Fig. 1), were synthesized and their interactions with DNA were investigated. The results of spectroscopic, denaturation and viscosity measurements suggest that [AQATMPyP]I3 binds to DNA through non-intercalative mode while the other three hybrids with longer links bind via bis-intercalative mode. Ethidium bromide (EB) competition experiment was carried out to determine the binding constants (Kb) of these compounds for CT DNA, and [AQPTMPyP]I3 shows the largest Kb among these hybrids. The photocleavage mechanism and wavelength-dependent cleaving abilities of these hybrids to pBR322 plasmid DNA were also comparably investigated.

DNA binding and photocleavage properties of a novel cationic porphyrin-anthraquinone hybrid.

A novel cationic porphyrin-anthraquinone (Por-AQ) hybrid has been synthesized and characterized. Using the combination of absorption titration, fluorescence spectra, circular dichroism (CD) as well as viscosity measurements, the binding properties of the hybrid to calf thymus (CT) DNA have been investigated compared with its parent porphyrin. The experimental results show that at low [Por]/[DNA] ratios, the parent porphyrin binds to DNA in an intercalative mode while the hybrid binds in a combined mode of outside binding (for porphyrin moiety) and partial intercalation (for anthraquinone). Ethidium bromide (EB) competition experiment determined the binding affinity constants (K(app)) of the compounds for CT DNA. Theoretical calculational results applying the density functional theory (DFT) can explain the different DNA binding behaviors reasonably. (1)O(2) was suggested to be the reactive species responsible for the DNA photocleavage of porphyrin moieties in both two compounds. The wavelength-depending cleavage activities of the compounds were also investigated.

Experimental and DFT studies on DNA binding and photocleavage of two cationic porphyrins. Effects of the introduction of a carboxyphenyl into pyridinium porphyrin.

The DNA-binding affinities and DNA photocleavage abilities of cationic porphyrin, 5-(4-carboxyphenyl)-10,15,20-tris(4-methylpyridiniumyl)porphyrin (CTMPyP), and its reference compound meso-tetrakis(N-methyl-4-pyridiniumyl)porphyrin (H2TMPyP) have been investigated. The DNA-binding behaviors of the two compounds in NaH2PO4 buffer were compared systematically by using absorption, fluorescence and circular dichroism (CD) spectra, thermal denaturation as well as viscosity measurements. The experimental results show that CTMPyP binds to DNA in an outside binding mode, while H2TMPyP in an intercalative mode. Photocleavage experiments reveal that both two compounds employ 1O2-mediated mechanism in cleaving DNA and H2TMPyP can cleave DNA more efficiently than CTMPyP. Theoretical calculations were carried out with the density functional theory (DFT), and the calculated results indicate that the character and energies of some frontier orbitals of CTMPyP are quite different from those of H2TMPyP. These theoretical results can be used to explain their different DNA-binding modes and affinities to a certain extent.

Synthesis, Characterization, and Photocatalytic Activity of TiO2 Microspheres Functionalized with Porphyrin

In order to utilize visible light more efficiently in the photocatalytic reaction, TiO2 microspheres sensitized by 5-(4-allyloxy)phenyl-10,15,20-tri(4-methylphenyl)porphyrin (APTMPP) were prepared and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen physisorption, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and UV-vis diffuse reflectance spectroscopy, and so forth, The characterization results indicated that APTMPP-MPS-TiO2 was composed of the anatase crystal phase. The morphology of the composite materials was spheriform with size of 0.3–0.7 μm and the porphyrin was chemisorbed on the surface of TiO2 through a Si–O–Ti bond. The photooxidation of α-terpinene was employed as the model reaction to evaluate the photocatalytic activity of APTMPP-MPS-TiO2 microspheres under visible light. The results indicated that the photodegradation of α-terpinene was significantly enhanced in the presence of the APTMPP-MPS-TiO2 compared with the nonmodified TiO2 under visible light.

The interface structure and magnetic and electronic properties of a Co2FeAl0.5Si0.5/MgO/Co2FeAl0.5Si0.5 magnetic tunneling junction

Magnetic tunnel junctions (MTJs) consisting of ferromagnet-insulator-ferromagnet sandwiches have attracted significant interest, and the structure of the interfaces in MTJs plays a crucial role in their performance. The interface structure, and magnetic and electronic properties of a Co2FeAl0.5Si0.5/MgO/Co2FeAl0.5Si0.5 MTJ are studied by first-principles calculations. It is found that three interface structures, the Co-, Fe-, and Al-terminated interfaces, are thermally stable. Local density of states calculations show that interface states form at the Fermi level for the Co- and Fe-terminated interfaces, and their half-metallic properties are destroyed. For the Al-terminated interface, half-metallic behavior remains at the interface, and there are no interface states at the Fermi level. This should heavily suppress the spin-flipping and tunneling caused by interface states located at the Fermi level of a Co2FeAl0.5Si0.5/MgO interface, allowing the transport properties of Co2FeAl0.5Si0.5/MgO/Co2FeAl0.5Si0.5 MTJs to be improved.

Luminescence quenching in low doped polymer light-emitting diodes

Transient luminescent dynamics in low doped porphyrin side-chain polymer film, poly(porphyrin acrylate-styrene) (P[(por)A-S]), were measured by using time-resolved photoluminescence spectroscopic technology. At relative higher intrachain porphyrin comonomer concentration (0.27%), the transient luminescence relaxation becomes more rapid with the increase in the interchain polymer concentration, resulting in low luminescence efficiency. The origin has been analyzed according to the Forster-type bimolecular annihilation theory. However, at the porphyrin comonomer concentration (0.1%), the luminescence relaxation of the P[(por)A-S] film becomes faster with the decrease in the interchain polymer concentration, inducing lower luminescence efficiency. The luminescence quenching has been analyzed according to the theory of MM+ force field and exciton rotational diffusion. The theoretical analyses are in good agreement with the experimental results.