Phototreatment of Water by Organic Photosensitizers and Comparison with Inorganic Semiconductors

Phototreatment of water is drawing the attention of many as a promising alternative to replace methods like chlorination, ozonization, and other oxidation processes, used in current disinfection methods limiting harmful side-products and by-products that can cause damage to the fauna and flora. Porphyrins, phthalocyanines, and other related organic dyes are well known for their use in photodynamic therapy (PDT). These photosensitizers cause cell death by generating reactive oxygen species (ROS) especially singlet oxygen in the presence of light. Such molecules are also being explored for photodynamically treating microbial infections, killing of unwanted pathogens in the environment, and oxidation of chemical pollutants. The process of photosensitisation (phototreatment) can be applied for obtaining clean, microbe-free water, thus exploiting the versatile properties of photosensitizers. This review collects the various attempts carried out for phototreatment of water using organic photosensitizers. For comparison, some reports of semiconductors (especially TiO2) used in photocatalytic treatment of water are also mentioned

22π‑Electrons [1.1.1.1.1] pentaphyrin as a new photosensitizing agent for water disinfection: experimental and theoretical characterization

In view of their promising photosensitizing features, expanded porphyrins are gaining wide attention for their potential use in both photodynamic therapy (PDT) of cancer or as likely photoactivated agent for water disinfection. Herein, we report a joint experimental and theoretical investigation on the 20-(4’-carboxyphenyl)-2,13-dimethyl-3,12-diethyl-[22]pentaphyrin complex 4. The synthesis, NMR, UV-Vis and mass characterization of the new compound together with a detailed theoretical investigation of the photophysical properties are presented. In particular, type I- and type II- photoreactions have been explored by means of DFT and its TDDFT formulation characterizing the electronic absorption spectra, providing singlet-triplet energy gap, vertical ionization potential and electron affinity. Results show that title compound is able to generate the cytotoxic singlet oxygen species supporting the application of the proposed molecule as a photoactivated agent for water disinfection

Abatement of the ecotoxicological risk of landfill leachate by heterogeneous Fenton-like oxidation

Landfill leachates are highly contaminated liquid waste, and their treatment and detoxification are a challenging task. The current system of ecotoxicological risk assessment is complex and time-consuming. It is of fundamental importance to develop simpler and faster tools for the evaluation of the treated liquid waste and for an easier preliminary screening of the most active catalytic formulation/reaction conditions of the Fenton-like process. Here, several analytical techniques have been used for the assessment of the reduction of toxicity of the landfill leachate after Fenton process over copper-zirconia catalyst (ZrCu). Ultraviolet-visible (UV-vis) spectroscopy and absorbable organic halogens (AOX) analysis have been coupled to achieve further insight into the degradation of contaminants. In addition, for the first time, the qualitative abatement of organic compounds is monitored through proton nuclear magnetic resonance (H-1 NMR) analysis, providing a new method for evaluating the effectiveness of the treatment. Spectroscopic techniques reveal that the Fenton process induces a significant abatement of the aromatic and halogen compounds (51%) in the landfill leachate with a reduction of the toxicity that has been confirmed by ecotoxicological test with algae. These results validate the investigated tool for a simple rapid preliminary evaluation of the detoxification efficacy

Selectivity and Efficiency of Conductive Molecularly Imprinted Polymer (c-MIP) Based on 5-Phenyl-Dipyrromethane and 5-Phenol-Dipyrromethane for Quorum Sensing Precursors Detection

Functional polymers that selectively recognize target compounds are developed by imprinting polymerization. In the present paper, two different dipyrromethanes, 5-phenol-dipyrromethane (5-pOH-DP) and 5-phenyl-dipyrromethane (5-ph-DP), are synthetized and investigated to develop conductive molecularly imprinted polymer (cMIP) sensors. As target molecules, two homoserine lactone derivatives were templated by an electrochemically driven polymerization process. Acyl-homoserine lactones (AHLs), also called homoserine lactones (HS), are a class of signaling molecules involved in bacterial quorum sensing (QS), which is a strategy of coordination among bacteria mediated by population density. The preparation of cMIP from 5-pOH-DP and 5-ph-DP in the presence of acetyl-homoserine lactone (Acetyl-HS) or carboxybenzyl-homoserine lactone (Cbz-HS) was performed by cyclic voltammetry (CV). The cMIP selectivity and sensitivity were assessed by microgravimetry (QCM). Both series of measurements were performed with the aid of an Electrochemical Quartz Crystal Microbalance (EQCM/QCM). The experimental evidences are discussed with respect to NMR measurements that were conducted to gain insight into the interactions established between monomers and templates. The NMR data interpretation offers preliminary information about the most probable positions involved in interaction development for both molecules and highlights the role of the hydration shell. The QCM-cMIP sensor was able to detect the analyte in the linear range from 10−8 mol·L−1 to 10−6 mol·L−1 and a limit of detection (LOD) of 22.3 ng (3σ of the blank signal) were evaluated. QCM rebinding tests demonstrated that cMIP selectivity was driven by the pendant group of dipyrromethane, which was also confirmed by the NMR data

Bactericidal activity characterization of an expanded porphyrin on Gram-positive bacteria.

Porphyrines and their derivatives application, commonly associated with Photodynamic Therapy (PDT), is currently being applied to the treatment of diseases caused by bacteria, yeasts, viruses and parasites, as well as to sterilisation of blood and other products. We tested the bactericidal activity of an anionic expanded porphyrin on Gram-positive bacteria, including Enterococcus hirae and Staphylococcus aureus, under visible light eccitation (2W/m2). This activity is mediated by reactive oxygen species (ROS) produced by the molecule in presence of oxygen and light. Study of the kinetics of bacterial killing showed that 99% or more of S.aureus had been killed after 15 minutes of treatment with a 5 \u3bcM molecule dose and 80% of E.hirae had been killed after 1 hour of treatment with a 20 \u3bcM molecule dose. An incubation step in the dark didn\u2019t improve the bactericidal activity. The interaction of the molecule with the bacterial cytoplasmic membrane and its ability to disrupt the membrane potential was analyzed. Cytoplasmic membrane depolarization was determined using the membrane potential-sensitive dye 3,3V-dipropylthiadicarbocyanine iodide (DiSC3(5)). Implication of ROS in cytoplasmic membrane depolarization was indirectly evaluated by the use of ROS scavengers (sodium benzoate, sodium thioglycollate). The data obtained from these experiments suggest that the primary mechanism of action of the molecule is bacterial cytoplasmic membrane lysis mediated by ROS