Antimicrobial Photosensitizing Material Based on Conjugated Zn(II) Porphyrins

The widespread use of antibiotics has led to a considerable increase in the resistance of microorganisms to these agents. Consequently, it is imminent to establish new strategies to combat pathogens. An alternative involves the development of photoactive polymers that represent an interesting strategy to kill microbes and maintain aseptic surfaces. In this sense, a conjugated polymer (PZnTEP) based on Zn(II) 5,10,15,20-tetrakis-[4-(ethynyl)phenyl]porphyrin (ZnTEP) was obtained by the homocoupling reaction of terminal alkyne groups. PZnTEP exhibits a microporous structure with high surface areas allowing better interaction with bacteria. The UV-visible absorption spectra show the Soret and Q bands of PZnTEP red-shifted by about 18 nm compared to those of the monomer. Also, the conjugate presents the two red emission bands, characteristic of porphyrins. This polymer was able to produce singlet molecular oxygen and superoxide radical anion in the presence of NADH. Photocytotoxic activity sensitized by PZnTEP was investigated in bacterial suspensions. No viable Staphylococcus aureus cells were detected using 0.5 µM PZnTEP and 15 min irradiation. Under these conditions, complete photoinactivation of Escherichia coli was observed in the presence of 100 mM KI. Likewise, no survival was detected for E. coli incubated with 1.0 µM PZnTEP after 30 min irradiation. Furthermore, polylactic acid surfaces coated with PZnTEP were able to kill efficiently these bacteria. This surface can be reused for at least three photoinactivation cycles. Therefore, this conjugated photodynamic polymer is an interesting antimicrobial photoactive material for designing and developing self-sterilizing surfaces.

MORPHOLOGICAL CHANGES AND OXIDATIVE HOMEOSTASIS IN THE LIVER TISSUES DURING LONG CENTRAL DEPRIVATION OF LUTEINIZING HORMONE SYNTHESIS BY TRIPTORELIN

In recent years, researchers have focused on the problem of the dependence of the functioning of various organs and systems on the level of androgens. The effect of long inhibition of testosterone synthesis by triptorelin on liver tissue is poorly understood. The aim of this research was to establish the microscopic organization of rat livers, production of nitric oxide and the intensity of oxidative stress in the rat livers during experimental central deprivation of luteinizing hormone synthesis by diphereline injection on the 270-360th day of the experiment. The experiments were carried out on 30 sexually mature male white rats of the Wistar line. Rats were divided into 2 groups: the control group (10) and the experimental group (20). Animals from the experimental group were subcutaneously injected triptorelin at a dose of 0.3 mg of the active substance/ per kg of body weight for 360 days, while the control group received an injection of saline. It was found that oxidative stress develops in hepatocytes, which is morphologically confirmed by karyopyknosis of the nuclei, oxyphilia of the cytoplasm with the appearance of a significant number of vacuoles in it. The vessels of the microcirculatory bed react with stasis. An increase in the production of superoxide radical anion in rat liver may be due to the absence of an inhibitory effect of testosterone on macrophages and liver mitochondria, which is accompanied by depletion of antioxidant enzymes and the development of oxidative stress. The intensity of biochemical markers of oxidative stress on the 360th day is lower than on the 270th day, which is due to an increase in the activity of antioxidant enzymes and a decrease in the production of reactive oxygen species.

Electrochemical and Mechanistic Study of Reactivities of α-, β-, γ-, and δ-Tocopherol toward Electrogenerated Superoxide in N,N-Dimethylformamide through Proton-Coupled Electron Transfer

Scavenging of superoxide radical anion (O2•−) by tocopherols (TOH) and related compounds was investigated on the basis of cyclic voltammetry and in situ electrolytic electron spin resonance spectrum in N,N-dimethylformamide (DMF) with the aid of density functional theory (DFT) calculations. Quasi-reversible dioxygen/O2•− redox was modified by the presence of TOH, suggesting that the electrogenerated O2•− was scavenged by α-, β-, γ-TOH through proton-coupled electron transfer (PCET), but not by δ-TOH. The reactivities of α-, β-, γ-, and δ-TOH toward O2•− characterized by the methyl group on the 6-chromanol ring was experimentally confirmed, where the methyl group promotes the PCET mechanism. Furthermore, comparative analyses using some related compounds suggested that the para-oxygen-atom in the 6-chromanol ring is required for a successful electron transfer (ET) to O2•− through the PCET. The electrochemical and DFT results in dehydrated DMF suggested that the PCET mechanism involves the preceding proton transfer (PT) forming a hydroperoxyl radical, followed by a PCET (intermolecular ET–PT). The O2•− scavenging by TOH proceeds efficiently along the PCET mechanism involving one ET and two PTs.

Electrochemical and Mechanistic Study of Structure–Activity Relationship of α-, β-, γ-, and δ-Tocopherol on Superoxide Elimination in N,N-Dimethylformamide through Proton-Coupled Electron Transfer

Elimination of superoxide radical anion (O2•−) by tocopherols (TOH), and related compounds was investigated on the basis of cyclic voltammetry and in situ electrolytic electron spin resonance spectral measurements in N,N-dimethylformamide (DMF) with the aid of density functional theory (DFT) calculations. Quasi-reversible O2/O2•− redox was modified by the presence of TOHs, suggesting that the electrogenerated O2•− was eliminated by α-, β-, γ-TOH through proton-coupled electron transfer (PCET), but not by δ-TOH. The structure–activity correlation of α-, β-, γ-, and δ-TOH characterized by methyl group on the 6-chromanol ring was experimentally confirmed, where the methyl group promotes the PCET mechanism. Furthermore, comparative analyses using some related chemical analogues suggested that methoxyl group of the 6-chromanol ring is required for a successful electron transfer (ET) to O2•− through the PCET. The electrochemical and DFT results in dehydrated DMF suggested that the PCET mechanism involves preceding proton transfer (PT) forming hydroperoxyl radical followed by a concerted PCET (ET–PT). The O2•− elimination by TOH proceeds efficiently along the net PCET mechanism involving one ET and two PTs.

Electrospinning preparation of g-C3N4/Nb2O5 nanofibers heterojunction for enhanced photocatalytic degradation of organic pollutants in water

In this study, graphitic carbon nitride (g-C3N4) and niobium pentoxide nanofibers (Nb2O5 NFs) heterojunction was prepared by means of a direct electrospinning approach combined with calcination process. The characterizations confirmed a well-defined morphology of the g-C3N4/Nb2O5 heterojunction in which Nb2O5 NFs were tightly attached onto g-C3N4 nanosheets. Compared to pure g-C3N4 and Nb2O5 NFs, the as-prepared g-C3N4/Nb2O5 heterojunction exhibited remarkably enhanced photocatalytic activity for degradation of rhodamine B and phenol under visible light irradiation. The enhanced catalytic activity was attributed predominantly to the synergistic effect between g-C3N4 sheets and Nb2O5 NFs, which promoted the transferring of carriers and prohibited their recombination, confirmed by the measurement of transient photocurrent responses and photoluminescence spectra. In addition, the active species trapping experiments indicated that superoxide radical anion (·O2–) and hole (h+) were the major active species contributing to the photocatalytic process. With its high efficacy and ease of preparation, g-C3N4/Nb2O5 heterojunction has great potentials for applications in treatment of organic pollutants and conversion of solar energy.

The Reactive Oxygen Species Singlet Oxygen, Hydroxy Radicals, and the Superoxide Radical Anion—Examples of Their Roles in Biology and Medicine

Reactive oxygen species comprise oxygen-based free radicals and non-radical species such as peroxynitrite and electronically excited (singlet) oxygen. These reactive species often have short lifetimes, and much of our understanding of their formation and reactivity in biological and especially medical environments has come from complimentary fast reaction methods involving pulsed lasers and high-energy radiation techniques. These and related methods, such as EPR, are discussed with particular reference to singlet oxygen, hydroxy radicals, the superoxide radical anion, and their roles in medical aspects, such as cancer, vision and skin disorders, and especially pro- and anti-oxidative processes.

EPR Study of KO2 as a Source of Superoxide and •BMPO-OH/OOH Radical That Cleaves Plasmid DNA and Detects Radical Interaction with H2S and Se-Derivatives

Superoxide radical anion (O2•−) and its derivatives regulate numerous physiological and pathological processes, which are extensively studied. The aim of our work was to utilize KO2 as a source of O2•− and the electron paramagnetic resonance (EPR) spin trapping 5-tert-butoxycarbonyl-5-methyl-1-pyrroline N-oxide (BMPO) technique for the preparation of •BMPO-OOH and/or •BMPO-OH radicals in water solution without DMSO. The method distinguishes the interactions of various compounds with •BMPO-OOH and/or •BMPO-OH radicals over time. Here, we show that the addition of a buffered BMPO-HCl mixture to powdered KO2 formed relatively stable •BMPO-OOH and •BMPO-OH radicals and H2O2, where the •BMPO-OOH/OH ratio depended on the pH. At a final pH of ~6.5–8.0, the concentration of •BMPO-OOH radicals was ≥20 times higher than that of •BMPO-OH, whereas at pH 9.0–10.0, the •BMPO-OH radicals prevailed. The •BMPO-OOH/OH radicals effectively cleaved the plasmid DNA. H2S decreased the concentration of •BMPO-OOH/OH radicals, whereas the selenium derivatives 1-methyl-4-(3-(phenylselanyl) propyl) piperazine and 1-methyl-4-(4-(phenylselanyl) butyl) piperazine increased the proportion of •BMPO-OH over the •BMPO-OOH radicals. In conclusion, the presented approach of using KO2 as a source of O2•−/H2O2 and EPR spin trap BMPO for the preparation of •BMPO-OOH/OH radicals in a physiological solution could be useful to study the biological effects of radicals and their interactions with compounds.

Complexes of Copper and Iron with Pyridoxamine, Ascorbic Acid, and a Model Amadori Compound: Exploring Pyridoxamine’s Secondary Antioxidant Activity

The thermodynamic stability of 11 complexes of Cu(II) and 26 complexes of Fe(III) is studied, comprising the ligands pyridoxamine (PM), ascorbic acid (ASC), and a model Amadori compound (AMD). In addition, the secondary antioxidant activity of PM is analyzed when chelating both Cu(II) and Fe(III), relative to the rate constant of the first step of the Haber-Weiss cycle, in the presence of the superoxide radical anion (O2•−) or ascorbate (ASC−). Calculations are performed at the M05(SMD)/6-311+G(d,p) level of theory. The aqueous environment is modeled by making use of the SMD solvation method in all calculations. This level of theory accurately reproduces the experimental data available. When put in perspective with the stability of various complexes of aminoguanidine (AG) (which we have previously studied), the following stability trends can be found for the Cu(II) and Fe(III) complexes, respectively: ASC < AG < AMD < PM and AG < ASC < AMD < PM. The most stable complex of Cu(II) with PM (with two bidentate ligands) presents a ΔGf0 value of −35.8 kcal/mol, whereas the Fe(III) complex with the highest stability (with three bidentate ligands) possesses a ΔGf0 of −58.9 kcal/mol. These complexes can significantly reduce the rate constant of the first step of the Haber-Weiss cycle with both O2•− and ASC−. In the case of the copper-containing reaction, the rates are reduced up to 9.70 × 103 and 4.09 × 1013 times, respectively. With iron, the rates become 1.78 × 103 and 4.45 × 1015 times smaller, respectively. Thus, PM presents significant secondary antioxidant activity since it is able to inhibit the production of ·OH radicals. This work concludes a series of studies on secondary antioxidant activity and allows potentially new glycation inhibitors to be investigated and compared relative to both PM and AG.

COVID-19 and the ethnicity link – is there a photochemical link?

A hypothesis is proposed to explain the increased detrimental effect of COVID-19 for Black, Asian and Minority Ethnic (BAME) men and women compared to Caucasian individuals. This is based on the differing photochemistry of phaeomelanin in fair skin and eumelanin in dark/black skin. It is suggested that a range of reactive oxygen species, including, singlet oxygen and the superoxide radical anion, derived via direct photolysis of phaeomelanin, may escape the melanocyte and cause subsequent damage to the SARS-CoV-2 virus. It is further suggested that (large) carbon and sulphur peroxy radicals, from oxygen addition to radicals formed by carbon–sulphur bond cleavage, may assist via damage to the cell membranes. It is also speculated that light absorption by phaeomelanin and the subsequent C-S bond cleavage, leads to release of pre-absorbed reactive oxygen species, such as singlet oxygen and free radicals, which may also contribute to an enhanced protective effect for fair-skinned people.