Narrow Results

The water-soluble porphyrins meso-tetrakis[4-(carboxymethyleneoxy)phenyl]porphyrin (H₂T4CPP), meso-tetrakis[3-(carboxymethyleneoxy)phenyl]porphyrin (H₂T3CPP) and meso-tetrakis[3,4-bis(carboxymethyleneoxy)phenyl]porphyrin (H₂T3,4BCPP) cleave plasmid pBR322 DNA to single-strand breaks (SSBs) in the presence of molecular oxygen and visible light. These porphyrins induced SSBs in DNA as a function of irradiation time as well as porphyrin concentration. Under similar conditions (10 μM or more), H₂T3CPP showed more SSBs in DNA than the porphyrins H₂T4CPP and H₂T3,4BCPP. The DNA cleavage was more in D₂O-based buffer than in H₂O buffer. In addition, this DNA cleavage was inhibited by the presence of sodium azide and lipoic acid, which are potent quenchers of singlet oxygen (¹O₂). These observations suggest the involvement of ¹O₂ in photocleavage of DNA. Further, the DNA cleavage, to a limited extent, was also inhibited by tert-butanol and mannitol, both quenchers of hydroxyl radical (^·OH), suggesting the involvement of ^·OH in photocleavage of DNA. Thus both ¹O₂ and ^·OH are involved in photocleavage of plasmid DNA by these porphyrins.

The in vitro photodynamic effect of bis(tri-n-hexylsiloxy)silicon phthalocyanine has been evaluated against the melanotic M6 cell line. The results showed that at 10^-5 M dose, LD₅₀ is obtained for a 150 J cm^-2 light dose and LD₉₀ for 540 J cm^-2. Electron spin resonance spectroscopy was used with spin traps to study the type I and type II photochemical pathways involved and to detect active oxygen intermediates such as singlet oxygen, oxygen superoxide and hydroxyl radical. The two mechanisms occurred simultaneously and no change was observed when the phthalocyanine was entrapped in liposomes.

In this work, the interaction of hydroxyl and hydroperoxyl radicals with ethene in the presence of water molecules and the stability of C₂H₄ + HO_x + (H₂O)_y; x = 1–2, y = 0–5 clusters were investigated using computational methods. Also, hydrogen bond of these clusters was investigated using Density Functional Theory (DFT) and Atoms in Molecules (AIM) theory. Thermodynamical parameters for the interaction of hydroxyl and hydroperoxyl radicals with ethene in the presence of water molecules were also calculated. We report new results for the interaction of hydroxyl and hydroperoxyl radicals with ethene in the presence of water molecules.

Water and air pollution are among the major environmental challenges of this era. Waste management, economic sustainable development and renewable energy are unavoidable concomitant considerations. Over the past five years, nanosized metal-organic frameworks (nano-MOFs) have been developed for the elimination of pollutants in wet media and air-born toxins using the highly efficient reactive oxygen species (ROS) of type I (H₂O₂, •OH, O${}_2^{•-})$ and of type II (¹O${}_2)$. The ROS are catalytically and efficiently generated through photosensitization, and porphyrins and metalloporphyrins are pigments of choice for this purpose. This short review summarizes the fundamentals of ROS generation by porphyrin-based nano-MOFs (mainly through the formation of ROS type II) and their composites (leading to ROS type I), which includes energy and electron transfer processes, and their applications in these environmental issues.

A specific strategy is presented for the preparation of a NiFe₂O₄-rice husk char (RHC) nanocatalyst with different RHC contents. The recombination of nano-NiFe₂O₄ with RHC leads an opposite transformation of the unreactive NiFe₂O₄ to an upper active photocatalyst, which can be used for the photodegradation of methylene blue in the presence of H₂O₂ under visible light. In comparison with neat NiFe₂O₄ as a catalyst, the NiFe₂O₄-RHC plays a dual function as the photocatalyst for both the electrochemical photodegradation of methylene blue and the producer of the important oxidant hydroxyl radical from the electrochemical dissociation of H₂O₂ under visible-light irradiation. The photocatalyst displays such excellent stability in the reaction that it can be magnetically separated and recycled for more than five consecutive cycles without any significant loss of activity and degradation.

The radicals of ·OH and ·H are generated as cavities collapse. The hydroxyl radical, having strong oxidizing property and depending on the cavitation intensity, can react with refractory organic compound molecule. Using the choking cavitator as a cavitation generator, the influences of hydroxyl radical production on the initial concentration of methylene blue (MB), equivalent diameter of back-pressure holes and reaction time were analyzed with a visible spectrophotometer. The experimental results showed that the highest hydroxyl radical was acquired when the equivalent diameter of back-pressure holes was 5.4mm and the initial concentration of MB was 12mg/L.