Atif Ali

Stable and improved visible-light photocatalytic hydrogen evolution using copper(II)–organic frameworks: engineering the crystal structures

Relatively high photocatalytic H2 production activities can be exhibited by metal–organic framework (MOF) materials using a compulsory cocatalyst or photosensitizer. However, no study has focused on the effect of the crystal structures of MOF materials on the photocatalytic H2 evolution activity when using the same organic ligand and metal ion. Therefore, by connecting the 4′-(2,4-disulfophenyl)-3,2′:6′,3′′-terpyridine (H2DSPTP) organic ligand with CuSO4·5H2O, different MOF photocatalyst crystalline structures, (1) and (2), were obtained. These products were then respectively characterized and employed for photocatalytic H2 evolution. In the absence of any photosensitizer and cocatalyst, compounds 1 and 2 exhibited efficient visible-light-driven photocatalytic H2 production at maximum rates of 5.77 μmol h−1 and 6.99 μmol h−1. Interestingly, compounds 1 and 2 also exhibited photocatalytic H2 generation when irradiated with near-infrared light. Compound 2 showed outstanding long-term stability, as evidenced by eight-cycle tests over 24 h. The charge separation and transfer process of the compounds were verified using PL, time-resolved PL spectroscopy, and photocurrent measurements.

The magnetic properties, DNA/HSA binding and nuclease activity of manganese N-confused porphyrin

The first oxidative cleavage of DNA by manganese N-confused porphyrin [chloro(2-aza-2-methyl-5,10,15,20-tetrakis(p-chlorophenyl)-21-carbaporphyrin)manganese(III), 1] using H2O2 as oxidant agent and its magnetic, calf thymus DNA(ct-DNA)- and human serum albumin (HSA) binding properties were investigated. The magnitude of the axial (D) zero-field splitting for the mononuclear Mn(III) center in 1 was determined to be approximately 2.71 cm−1 by paramagnetic susceptibility measurements. The DNA- and HSA binding experimental results showed that 1 bound to ct-DNA via an outside groove binding mode and the hydrophobic cavity located in subdomain IIA of HSA with the binding constant of 4.144 × 105 M−1 and ∼ 106 M−1, respectively. Thermodynamic parameters revealed that both DNA- and HSA binding were spontaneous process. The main driven forces were the hydrogen bond and van der Waals for the former, but hydrophobic interaction for the latter, which were further confirmed by molecular docking modeling. Manganese N-confused porphyrin 1 could cleave the supercoiled plasmid DNA efficiently in the presence of hydrogen peroxide. Hydroxyl radical (•OH) was found the active species for oxidative damage of DNA.

Copper porphyrin catalyzed esterification of C(sp3)–H via a cross-dehydrogenative coupling reaction

The crystal structure of 5,10,15,20-tetra(ethoxycarbonyl)porphyrin copper(II) showed that its central copper has a six-coordinate structure. An efficient copper porphyrin-catalyzed cross-dehydrogenative coupling (CDC) esterification reaction between C(sp3)–H and carboxylic acids using di-tert-butyl peroxide (DTBP) as an oxidant was established. The kinetic isotope effect (KIE) indicated that C(sp3)–H bond cleavage was the rate-determining step of this CDC reaction.

DNA-Binding, Photocleavage, and Photodynamic Anti-cancer Activities of Pyridyl Corroles

The DNA-binding, photocleavage, and antitumor activity of three free base pyridyl corroles 1, 2, and 3 have been investigated. The binding affinity toward CT-DNA decreases with increasing number of pentafluorophenyl, whereas the photocleavage activity toward pBR322 DNA becomes more efficient. Singlet oxygen was demonstrated as active species responsible for DNA cleavage. These corroles exhibited high cytotoxicity against three tested cancer cells (Hela, HapG2, and A549) and the cytotoxicity could be further enhanced under irradiation. Intracellular reactive oxygen species level was also monitored using HeLa Cells upon the combined treatment of corroles and light. These corroles could be absorbed by HeLa cells at low concentration. They can induce the decrease of mitochondrial membrane potential and apoptosis of tumor cells under irradiation.

In Situ Construction of Globe‐like Carbon Nitride as a Self‐Cocatalyst Modified Tree‐like Carbon Nitride for Drastic Improvement in Visible‐Light Photocatalytic Hydrogen Evolution

Photogenerated carriers possess high recombination efficiency in carbon–nitrogen materials, which results in lower photocatalytic H2 evolution activity. By reviewing the literature, it was concluded that relying only on a structure‐controlled technique was insufficient to reduce the combination of photogenerated carriers without introducing a foreign material or element. Hence, bulk‐like g‐C3N4 [CN (B)], globe/strip‐like g‐C3N4 [CN (G/S)], and globe/tree‐like g‐C3N4 [CN (G/T)] were in situ obtained through a facile calcination method. Similar to platinum (Pt) as a cocatalyst, globe‐like carbon nitride as a self‐cocatalyst was found to improve the separation efficiency of photogenerated carriers effectively. Interestingly, the hollow‐tree‐branch morphology of CN (G/T) effectively transmitted photogenerated holes, which thereby enhanced the photocatalytic H2 evolution activity. The H2 production rates of CN (G/S) and CN (G/T) were almost 10.7 and 18.3 times greater, respectively, than that of CN (B) without the addition of Pt as a cocatalyst. Notably, CN (G/S) and CN (G/T) displayed considerable rates of H2 production in water relative to that shown by CN (B) (no activity) without the use of any sacrificial agent and by using Pt as a cocatalyst. CN (G/T) showed outstanding long‐term stability, as evidenced by seven cycle tests performed over 28 h. The charge separation and transfer process of the compounds were verified by photoluminescence (PL), time‐resolved PL spectroscopy, and photocurrent measurements.

DNA-binding, photocleavage and anti-cancer activity of tin(IV) corrole

A new tin(IV) corrole, 5,10,15-tris(4-methoxycarbonylphenyl) corrole tin(IV) (1-Sn) was synthesized and characterized. The DNA binding, photocleavage and anti-cancer activity were studied and compared with its free-base. The interaction of 1-Sn and its free-base 1 with calf thymus DNA had been investigated by spectroscopic methods, viscosity measurements and molecular docking analysis. The results revealed that 1-Sn and 1 could interact with calf thymus DNA via an outside groove binding mode. Furthermore, although 1 displayed no photonuclease activity, 1-Sn exhibited good photonuclease activity as indicated by agarose gel electrophoresis, and superoxide anion might be the active intermediate for the DNA scission. Finally, 1 was nontoxic but 1-Sn displayed cytotoxicity towards A549 tumor cell lines.

Porphyrin–Coumarin Dyads: Investigation of Photophysical Properties and DNA Interactions

Two new nonconjugated porphyrin-coumarin dyads with different orientations with respect to donor-acceptor entities and their zinc complexes were synthesized. Single-crystal structures of the free-base porphyrin-coumarin dyads were successfully resolved. The absorption spectra of the dyads were linear combinations of the spectra of their corresponding monomers, indicating a negligible electronic communication between the coumarin and porphyrin moieties. However, the fluorescence emission of the coumarin entity in all of the dyads was quenched significantly compared to that of pristine coumarin, and this effect was attributed to intramolecular energy transfer from the coumarin to the porphyrin. The energy transfer kinetics from the coumarin to the porphyrin was shown to be fast ( kFörster = 1.13 × 1013 s-1 for the ortho-isomer and 5.13 × 1011 s-1 for the para-isomer in DMF) and efficient (transfer efficiency ca. 96-97%). Transient absorption studies showed that the excited state decay process (S2 → S1*, S1* → S1, S1 → S0, and S1 → T1) of the para-isomer was faster than that of the ortho-isomer in DMF. All of the synthesized dyads were tested for their interactions with ct-DNA and photocleavage activity toward PBR322-DNA. The results revealed that all of the dyads interacted with ct-DNA via only an external groove-binding mode; the binding constants were calculated to be 3.24 × 105 (3a), 3.05 × 105 (3b), 3.04 × 105 (4a), and 4.88 × 105 (4b), and the photocleavage activity was in the order 4b < 3b < 4a < 3a. Furthermore, only the zinc complexes of the porphyrin-coumarin dyads could be absorbed by tumor cells (A549). These complexes were mainly localized in the cytoplasm, exhibited red fluorescence, and showed low cytotoxicity toward all of the tumor cell lines tested. The results showed that these zinc complexes of the porphyrin-coumarin dyads have potential applications in fluorescence imaging.