Monthly Archives: January 2024

Facile Synthesis of β‐Brominated Manganese Porphyrins and their Catalytic Potentials for Haloperoxidases‐Like Activity

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Facile Synthesis of β-Brominated Manganese Porphyrins and their Catalytic Potentials for Haloperoxidases-Like Activity

Facile synthesis of β-brominated manganese porphyrins via self-catalytic reaction and their catalytic potentials for the oxidative-bromination via haloperoxidases-like activity have been explored.


Abstract

A novel and sustainable approach has been developed for the synthesis of β-brominated Mn porphyrins, [MnIII(Br)(TPPBr4)] (2), [MnIII(Br)(TPPBr6)] (3) and [MnIV(Br)2(TPPBr8)] (4) by self catalytic haloperoxidase mimicking activity of [MnIII(Br)(TPP)] [bromo(meso-tetraphenylporphyrinato)manganese(III)] (1) in aqueous medium under different mild and controlled reaction conditions. By precisely tweaking important parameters (e. g. H2O2, HClO4 and KBr), these polybrominated porphyrin complexes have been synthesized. This method is safer and applicable under milder reaction conditions than the conventional procedures for β-bromination of porphyrins. These complexes were characterized by various spectroscopic techniques, including UV–Vis spectroscopy, elemental analysis, MALDI-TOF mass spectrometry, cyclic voltammetry, DFT calculations and single crystal X-ray diffraction analysis. Bromination of various phenol derivatives via haloperoxidase-catalyzed reaction using these manganese complexes has been explored. Carrying out the catalytic reaction at room temperature in the presence of H2O2 as an oxidant and KBr as a brominating agent in a mild aqueous acidic condition results in good to excellent yield of the brominated product(s). Extra stability of 4 compared to other catalysts due to trans-[Br−MnIV−Br] structure possibly prevents the interaction of Mn with oxidant which makes it less potential catalyst compared to 1, 2 and 3. Suitable catalytic reaction mechanism has been proposed for the bromination of substrates after identifying the reaction intermediates using mass spectrometry.

Comparison of Different Advanced Oxidation Processes (AOPs) and Photocatalysts for the Degradation of Diclofenac

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Comparison of Different Advanced Oxidation Processes (AOPs) and Photocatalysts for the Degradation of Diclofenac

Different advanced oxidation processes (AOPs), such as Fenton, photo-Fenton and heterogeneous photocatalysis have been tested towards the degradation of Diclofenac sodium salt. Toxicity tests performed using Daphnia magna as model species unveiled the type of treatment which allows detoxification of the solution.


Abstract

Diclofenac sodium salt was photodegraded by means of advanced oxidation processes (AOPs), such as Fenton, photo-Fenton and heterogeneous photocatalysis. For the latter different photocatalysts were compared, namely commercial titania P25 and titania metallized with gold (0.1 % Au/P25), silver (1 % Ag/P25) and palladium (0.1 % Pd/P25). Homogeneous treatments demonstrated effective in the degradation of the selected pollutant (>80 % conversion @2 h) when the irradiation occurred within the solution. Also, photo-Fenton process assisted by visible light rather than UV was effective but slower and characterized by a toxicity of the residual solution due to unreacted H2O2. The photocatalyzed treatment performed at its best when P25 was used (70 % conversion @2 h), while modified photocatalysts reached the same conversion when H2O2 was added to the solution. Overall, in vitro toxicity tests using Daphnia Magna unveiled that the wastewater treated via M/TiO2 treatment and photo-Fenton under UV in combination with H2O2 showed an acute toxicity comparable with the control group (almost 100 % viability @48 h). Conversely, the other processes failed to degrade completely either the pollutant or the hydrogen peroxide, leading to the mortality of 30–80 % of the individuals. An important outcome of the work is the direct comparison of different treatments to optimise the outcome, i. e. rapidity of degradation and non toxicity of the treated solution for living bodies.

Computational Study of the Fries Rearrangement Catalyzed by Acyltransferase from Pseudomonas protegens

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Computational Study of the Fries Rearrangement Catalyzed by Acyltransferase from Pseudomonas protegens

Density functional theory (DFT) calculations are employed to uncover the detailed reaction mechanism for the Fries rearrangement of 3-hydroxyphenyl acetate to 2′,4′-dihydroxyacetophenone catalyzed by the acyltransferase from Pseudomonas protegens (PpATase). Relative binding energies of other acetyl acceptors are also calculated to evaluate the possibility of PpATase catalyzing an intermolecular Fries rearrangement.


Abstract

The acyltransferase from Pseudomonas protegens (PpATase) catalyzes in nature the reversible transformation of monoacetylphloroglucinol to diacetylphloroglucinol and phloroglucinol. Interestingly, this enzyme has been shown to catalyze the promiscuous transformation of 3-hydroxyphenyl acetate to 2′,4′-dihydroxyacetophenone, representing a biological version of the Fries rearrangement. In the present study, we report a mechanistic investigation of this activity of PpATase using quantum chemical calculations. A detailed mechanism is proposed, and the energy profile for the reaction is presented. The calculations show that the acylation of the enzyme is highly exothermic, while the acetyl transfer back to the substrate is only slightly exothermic. The deprotonation of the C6−H of the substrate is rate-limiting, and a remote aspartate residue (Asp137) is proposed to be the general base group in this step. Analysis of the binding energies of various acetyl acceptors shows that PpATase can promote both intramolecular and intermolecular Fries rearrangement towards diverse compounds.

Decoration of 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid (DOTA) with N‐oxides increases the T1 relaxivity of Gd‐complexes

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Decoration of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) with N-oxides increases the T1 relaxivity of Gd-complexes

Decoration with N -oxide groups is a valuable method to increase the T 1-relaxivity of the well-known cyclic Gd-chelator DOTA. The synthesis of Gd-DOTA-NOx has been achieved via copper catalyzed alkyne azide cycloaddition. The complex is water soluble, stable against transchelation, has a twisted square antiprismatic (TSAP) complex geometry and a high T 1-relaxivity of 7.7 mm −1 s−1 (1.41 T, 37 °C).


Abstract

High complex stability and longitudinal relaxivity of Gd-based contrast agents are important requirements for magnetic resonance imaging (MRI) because they ensure patient safety and contribute to measurement sensitivity. Charged and zwitterionic Gd3+-complexes of the well-known chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) provide an excellent basis for the development of safe and sensitive contrast agents. In this report, we describe the synthesis of DOTA-NOx, a DOTA derivative with four N-oxide functionalities via “click” functionalization of the tetraazide DOTAZA. The resulting complexes Gd-DOTA-NOx and Eu-DOTA-NOx are stable compounds in aqueous solution. NMR-spectroscopic characterization revealed a high excess of the twisted square antiprismatic (TSAP) coordination geometry over square antiprismatic (SAP). The longitudinal relaxivity of Gd-DOTA-NOx was found to be r 1=7.7 mm −1 s−1 (1.41 T, 37 °C), an unusually high value for DOTA complexes of comparable weight. We attribute this high relaxivity to the steric influence and an ordering effect on outer sphere water molecules surrounding the complex generated by the strongly hydrated N-oxide groups. Moreover, Gd-DOTA-NOx was found to be stable against transchelation with high excess of EDTA (200 eq) over a period of 36 h, and it has a similar in vitro cell toxicity as clinically used DOTA-based GBCAs.

Rare Earth 2‐Methyl‐3‐furoate Complexes: Effect of Steric Hindrance on Corrosion Inhibitor Properties

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Rare Earth 2-Methyl-3-furoate Complexes: Effect of Steric Hindrance on Corrosion Inhibitor Properties

The preparation and characterization of six rare earth 2-methyl-3-furoate (2m3fur) complexes are reported. All compounds belong to two structural groups: {[RE2(2m3fur)6(EtOH)] ⋅ H2O}n (RE=La, Ce, Pr) and [RE3(2m3fur)9]n (RE=Y, Er, Yb). In corrosion inhibition tests on mild steel in 0.01 M NaCl solution, the maximum efficiency was observed with [Y3(2m3fur)9]n. The results suggest that the steric effect of the methyl group adversely affects corrosion inhibition.


Abstract

The preparation and characterization of six rare earth 2-methyl-3-furoate (2m3fur) complexes are detailed in this study. Analysis through single-crystal X-ray diffraction, as well as powder XRD, reveals that all six compounds belong to one of two structural groups: {[RE2(2m3fur)6(EtOH)] ⋅ H2O}n (RE=La, Ce, Pr) and [RE3(2m3fur)9]n (RE=Y, Er, Yb). These structural groups feature carboxylate coordinated linear polymers. The former complexes have two distinct metal centers, one ten coordinate and one nine, with lattice water participating in a hydrogen bond with coordinated ethanol. The latter structures, involving erbium, ytterbium, and yttrium, have three unique metal centers: two eight coordinate, and one seven-coordinated. In corrosion inhibition tests on mild steel in 0.01 M NaCl solution, the maximum efficiency was observed with [Y3(2m3fur)9]n at 59 %, which is less effective than yttrium 3-furoate (90 % efficiency). The results suggest that the steric effect of the methyl group adversely affects corrosion inhibition.

A systematic look at structural diversity of metal phosphonates

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A systematic look at structural diversity of metal phosphonates

Three novel metal-phosphonate frameworks, namely, rod-shaped one-dimensional [{Cu(terpy)}(H6-MTPPA)(H2O)]⋅2H2O, three-dimensional [{Cu5(2,2’-bpy)2}(H2-MTPPA)(H4-MTPPA)] and one-dimensional [{Cu2(phen)2)}(H4-MTPPA)]⋅4H2O, constructed from tetrahedral shaped methane-p-tetraphenylphosphonic acid (MTPPA) and N-ancillary organoimine ligands were synthesized and characterized by X-ray crystallography. Magnetic analysis of [{Cu5(2,2’-bpy)2)}(H2-MTPPA)(H4-MTPPA)] exhibited paramagnetic behavior.


Photoluminescence lifetime stability studies of β‐diketonate europium complexes based phenanthroline derivatives in poly(methyl methacrylate) films

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Photoluminescence lifetime stability studies of β-diketonate europium complexes based phenanthroline derivatives in poly(methyl methacrylate) films

This study contributes to a deeper understanding of the design and development of stable β-diketonate europium complexes based on phenanthroline ligands in PMMA films. The synthesis, characterization, thermal, and photoluminescence properties are provided accompanied by long lifetime stability tests in different conditions which indicate the potential for these complexes as candidates for future optoelectronic devices, including luminescent solar concentrators.


Abstract

In this work, five phenanthroline derivatives substituted with different methyl groups have been selected to synthesize β-diketonate-based europium complexes to check the influence of the substitutions on the degradation effect of those complexes in poly(methyl methacrylate) (PMMA) films. The photophysical properties of Eu(III) complexes, including absorbance, excitation, and emission have been carefully investigated in solution, solid-state, and doped in PMMA film. In all these states, the complexes exhibit an impressive red emission at 614 nm with a high photoluminescence quantum yield of up to 85 %. The films have been exposed under outdoor, indoor, and dark storage stability lifetime conditions for 1200 hours. The photoluminescence measurements recorded every 400, 800, and 1200 hours demonstrated that the film containing europium complex with phenanthroline ligand substituted by a high number of methyl groups (Eu(TTA)3L5) showed good photoluminescent stability in indoor and dark conditions, and exhibited better resistance to degradation in outdoor conditions compared to other complexes. This study has proved that phenanthroline ligands could be tuned chemically leading to better stability of those types of complexes in films which can be end-used for future stable optoelectronic devices such as luminescent solar concentrators.