Synthesis of 3-hydroxy-4-pyridinone hexadentate chelators, and biophysical evaluation of their affinity towards lipid bilayers.

Iron is an essential micronutrient for almost every living organism, namely pathogenic bacteria. In an infection scenario, host-pathogen competitive relationships for the element are present and Fe withholding is a well known response of the host. Also, bacterial resistance is a major concern that can compromise public health and the WHO underlines an urgent need to search for new pharmaceutical ingredients or strategies to fight opportunistic bacteria.

NMR and EPR study of the interaction of tris(3-hydroxy-4-pyridinonato) Ga(III) complexes with liposomes that mimic plant membranes.

We performed an NMR and EPR study of the interaction of four [Ga(3,4-HPO)] chelates with liposomes derived from a soybean extract (SEL) and simpler formulations using POPC (100%) and POPE:POPC (50%). Parent [Fe(3,4-HPO)] chelates are eligible to prevent Iron Deficiency Chlorosis and we took advantage of the likenesses of the ions Fe (III) and Ga (III), and the fact their metal ion complexes are isostructural, to perform a combined NMR and EPR study to get information about the permeation properties of the complexes. The results demonstrate the presence of liposomes loaded with Ga-chelates and that the distribution of complexes alongside the bilayer is dependent on their structure.

Green Aromatic Epoxidation with an Iron Porphyrin Catalyst for One-Pot Functionalization of Renewable Xylene, Quinoline, and Acridine.

Sustainable functionalization of renewable aromatics is a key step to supply our present needs for specialty chemicals and pursuing the transition to a circular, fossil-free economy. In the present work, three typically stable aromatic compounds, representative of products abundantly obtainable from biomass or recycling processes, were functionalized in one-pot oxidation reactions at room temperature, using HO as a green oxidant and ethanol as a green solvent in the presence of a highly electron withdrawing iron porphyrin catalyst. The results show unusual initial epoxidation of the aromatic ring by the green catalytic system.

Multidimensional Ln-Aminophthalate Photoluminescent Coordination Polymers.

The development of straightforward reproducible methods for the preparation of new photoluminescent coordination polymers (CPs) is an important goal in luminescence and chemical sensing fields. Isophthalic acid derivatives have been reported for a wide range of applications, and in addition to their relatively low cost, have encouraged its use in the preparation of novel lanthanide-based coordination polymers (LnCPs). Considering that the photoluminescent properties of these CPs are highly dependent on the existence of water molecules in the crystal structure, our research efforts are now focused on the preparation of CP with the lowest water content possible, while considering a green chemistry approach.

Solvent-Free Desulfurization System to Produce Low-Sulfur Diesel Using Hybrid Monovacant Keggin-Type Catalyst.

Two quaternary ammonium catalysts based on the monovacant polyoxotungstate ([PWO], abbreviated as PW) were prepared and characterized. The desulfurization performances of the PW-based hybrids (of tetrabutylammonium and trimethyloctadecylammonium, abbreviated as TBA[PW] and ODA[PW], respectively), the corresponding potassium salt (KPWO, abbreviated as KPW) and the peroxo-compound (TBA-PO[WO(O)], abbreviated as TBA[PW]) were compared as catalysts for the oxidative desulfurization of a multicomponent model diesel (2000 ppm S). The oxidative desulfurization studies (ODS) were performed using solvent-free systems and aqueous HO as oxidant.

From Discrete Complexes to Metal-Organic Layered Materials: Remarkable Hydrogen Bonding Frameworks.

A series of metal-organic coordination complexes based on alkaline-earth metal centers [Mg(II), Ca(II), and Ba(II)] and the ligand 5-aminoisophthalate (aip) revealed notable structural diversity, both in the materials' dimensionality and in their hydrogen bonding networks: [Mg(HO)]∙[Mg(Haip)(HO)]∙(Haip)∙3(aip)∙10(HO) () and [Mg(aip)(phen)(HO)]∙(HO) () were isolated as discrete complexes (0D); [Ca(aip)(HO)]∙(HO) (), [Ca(aip)(phen)(HO)]∙(phen)∙(HO) (), and [Ba(aip)(phen)(HO)]∙2(phen)∙2(HO) () revealed metal-organic chain (1D) structures, while the [Ba(aip)(HO)] () showed a metal-organic layered (2D) arrangement. Furthermore, most of these metal-organic coordination materials revealed interesting thermal stability properties, being stable at temperatures up to 450 °C.

Mesoporous Silica vs. Organosilica Composites to Desulfurize Diesel.

The monolacunary Keggin-type [PWO] (PW) heteropolyanion was immobilized on porous framework of mesoporous silicas, namely SBA-15 and an ethylene-bridged periodic mesoporous organosilica (PMOE). The supports were functionalized with a cationic group (-trimethoxysilypropyl--trimethylammonium, TMA) for the successful anchoring of the anionic polyoxometalate. The PW@TMA-SBA-15 and PW@TMA-PMOE composites were evaluated as heterogeneous catalysts in the oxidative desulfurization of a model diesel.

Insights on the relationship between structure vs. toxicological activity of antibacterial rhodamine-labelled 3-hydroxy-4-pyridinone iron(III) chelators in HepG2 cells.

In the present study we investigated the hepatotoxicity of a set of rhodamine-labelled 3-hydroxy-4-pyridinones (3,4-HPO) that had previously demonstrated significant inhibitory effect in the intramacrophagic growth of . Our aim was to establish a correspondence between the molecular structure and the toxicological activity of these compounds. The impact of a set of bidentate (MRB2, MRB7, MRB8, and MRB9) and hexadentate (MRH7, MRH8, and MRH10) chelators on cellular metabolic competence and membrane integrity was investigated in HepG2 cells.

Influence of UiO-66(Zr) Preparation Strategies in Its Catalytic Efficiency for Desulfurization Process.

Porous metal-organic framework (MOF) materials UiO-66(Zr) obtained by solvothermal and microwave advanced synthesis (MWAS) procedures were characterized, and their catalytic efficiency was investigated for oxidative desulfurization (ODS) processes using a multicomponent model diesel containing benzothiophene and dibenzothiophene derivatives. The preparation parameters as the cooling time after oven use in the solvothermal procedure, and also the reaction time in the MWAS method seemed to play an important role in the catalytic performance of the UiO-66(Zr) material, as well as in its recycle capacity. The material prepared by the solvothermal procedure with a fast cooling time showed the best catalytic performance (desulfurization efficiency of 99.

Antibacterial activity of naphthyl derived bis-(3-hydroxy-4-pyridinonate) copper(II) complexes against multidrug-resistant bacteria.

In this work, we report the synthesis and characterization of three novel copper(II) complexes of naphthyl derived 3-hydroxy-4-pyridinone chelators. Their antibacterial activity against several Gram-positive and Gram-negative reference strains and multidrug-resistant clinical isolates was assessed through determination of the minimum inhibitory concentration (MIC). The complex Cu(naph1pp) shows the highest antibacterial activity, including against multidrug-resistant isolates, nonetheless, being more active against Gram-positive than Gram-negative bacteria.

Improving the Catalytic Performance of Keggin [PWO] for Oxidative Desulfurization: Ionic Liquids versus SBA-15 Composite.

Different methodologies were used to increase the oxidative desulfurization efficiency of the Keggin phosphotungstate [PWO] (PW). One possibility was to replace the acid proton by three different ionic liquid cations, forming the novel hybrid polyoxometalates: [BMIM]₃PW (BMIM as 1-butyl-3-methylimidazolium), [BPy]₃PW (BPy as 1-butylpyridinium) and [HDPy]₃PW (HDPy as hexadecylpyridinium. These hybrid Keggin compounds showed high oxidative desulfurization efficiency in the presence of [BMIM]PF₆ solvent, achieving complete desulfurization of multicomponent model diesel (2000 ppm of S) after only 1 h, using a low excess of oxidant (H₂O₂/S = 8) at 70 °C.

Design of a Water Soluble Fluorescent 3-Hydroxy-4-Pyridinone Ligand Active at Physiological pH Values.

In the present work we report the structure and the spectroscopic characterization of a new fluorescent 3-hydroxy-4-pyridinone ligand D-3,4-HPO. The synthesis of the compound was performed in two steps, which involve the reaction of the commercially available fluorophore dansyl chloride with a 3-hydroxy-4-pyridinone chelating unit and further deprotection. The new fluorescent chelator was characterized in the solid state by single-crystal X-ray diffraction and in solution by NMR, MS, absorption and fluorescence spectroscopies.

The Influence of the Amide Linkage in the Fe(III) -Binding Properties of Catechol-Modified Rosamine Derivatives.

The two new fluorescent ligands RosCat1 and RosCat2 contain catechol receptors connected to rosamine platforms through an amide linkage and were synthesized by using microwave-assisted coupling reactions of carboxyl- or amine-substituted rosamines with the corresponding catechol units and subsequent deprotection. RosCat1 possesses a reverse amide, whereas RosCat2 has the usual oriented amide bond (HNCO vs. CONH, respectively).

Production of ultra-deep sulfur-free diesels using a sustainable catalytic system based on UiO-66(Zr).

The porous metal-organic framework UiO-66(Zr) obtained via non modulated synthesis, has revealed to be a notable heterogeneous catalyst, enabling extremely fast and very efficient desulfurization of a multicomponent model diesel and also a real diesel fuel.

Isoxazolidine-fused meso-tetraarylchlorins as key tools for the synthesis of mono- and bis-annulated chlorins.

The microwave-assisted catalytic hydrogenation of the isoxazolidine-fused meso-tetrakis(pentafluorophenyl)chlorin afforded directly a mono-annulated chlorin with a singular 1-methyl-2,3-dihydro-1H-benzo[b]azepine ring that resulted from the cleavage of the isoxazolidine N-O bond followed by an intramolecular nucleophilic aromatic substitution of an o-F atom. The subsequent treatment of the mono-annulated chlorin with NaH induced a second intramolecular nucleophilic aromatic substitution, generating a bis-annulated chlorin having an additional 2H-pyran ring.

Fluoroquinolone-metal complexes: a route to counteract bacterial resistance?

Microbial resistance to antibiotics is one of the biggest public health threats of the modern world. Antibiotic resistance is an area of much clinical relevance and therefore research that has the potential to identify agents that may circumvent it or treat resistant infections is paramount. Solution behavior of various fluoroquinolone (FQ) complexes with copper(II) in the presence and absence of 1,10-phenanthroline (phen) was studied in aqueous solution, by potentiometry and/or spectrophotometry, and are herein described.

Synthesis, characterization and antibacterial studies of a copper(II) lomefloxacin ternary complex.

Solution behavior of lomefloxacin (lmx) complexes with copper(II) in the presence and absence of 1,10-phenanthroline (phen) was studied in aqueous solution, by potentiometry. The results obtained showed that under physiological conditions (micromolar concentration range and pH7.4) only copper(II):lmx:phen ternary complexes are stable.

Discrimination of fluorescence light-up effects induced by pH and metal ion chelation on a spirocyclic derivative of rhodamine B.

In the present work we describe the structure and the spectroscopic characterization of a spirocyclic derivative of a rhodamine B ligand whose properties allow discrimination of light-up effects induced by metal ion chelation and variation of pH. Distinction of the two effects is important for the use of this type of ligand to detect and monitor metal ions in aqueous solutions. The synthesis of the ligand was performed in two steps, which involve the reaction of rhodamine B with hydrazine hydrate to form rhodamine B hydrazide followed by condensation with 2-pyridinecarboxaldehyde and was successfully optimized using a solvent free approach under microwave irradiation.

Synthesis, characterization and antibacterial studies of a copper(II) levofloxacin ternary complex.

Solution behavior of levofloxacin (lvx) complexes with copper(II) in the presence and absence of phen was studied in aqueous solution, by potentiometry. The results obtained show that under physiological conditions (micromolar concentration range and pH 7.4) only copper(II):lvx:phen ternary complexes are stable.

One-pot synthesis of triangular gold nanoplates allowing broad and fine tuning of edge length.

A photocatalytic approach was used to synthesize triangular nanoplates in aqueous solution. The synthesis is based on the reduction of a gold salt using a tin(iv) porphyrin as photocatalyst, cetyltrimethylammonium bromide (CTAB) as a stabilizing agent, and triethanolamine (TEA) as the final electron donor. The average edge length of the triangular nanoplates can be easily changed in the range 45-250 nm by varying the concentration of photocatalyst, and fine-tuning of the average edge length is achieved by varying the concentration of CTAB.

Identification of a new hexadentate iron chelator capable of restricting the intramacrophagic growth of Mycobacterium avium.

Iron accumulation has been suggested to contribute to an increase of the susceptibility to mycobacterial infections. In this study we tested the effect of an array of iron chelating ligands of the 3-hydroxy-4-pyridinone family, in the intramacrophagic growth of Mycobacterium avium. We found that bidentate chelators, namely N-alkyl-3-hydroxy-4-pyridinones and N-aryl-3-hydroxy-4-pyridinones, did not affect the growth of M.

Novel 3-hydroxy-4-pyridinonato oxidovanadium(IV) complexes to investigate structure/activity relationships.

A previous evaluation of the insulin-like activity of three 3-hydroxy-4-pyridinonato oxidovanadium(IV) complexes raised questions about structure/activity relationships, namely the influence of the hydrophilic/lipophilic balance of the complex and the capacity of the ligand to stabilize the +4 oxidation state of vanadium ion, on achieving an positive effect. To address these questions, we synthesized six new oxidovanadium(IV) complexes with variable hydrophilic/lipophilic balance, obtained by introducing different substituents on the nitrogen atom, and used two 3-hydroxy-4-pyrones as starting reagents to provide methyl and ethyl groups in the ortho position of the ring. For the new and previously reported complexes, we studied the oxidation-reduction properties and insulin-like activity in terms of inhibitory effect on Free fatty acid (FFA) release in isolated rat adipocytes.

Benzodiazepine-mediated structural changes in the multidrug transporter P-glycoprotein: an intrinsic fluorescence quenching analysis.

P-glycoprotein expressed in Pichia pastoris was used to study the drug binding sites of different benzodiazepines. The effect of bromazepam, chlordiazepoxide, diazepam and flurazepam on P-glycoprotein structure was investigated by measuring the intrinsic fluorescence of the transporter tryptophan residues. Purified mouse mdr1a transporter in mixed micelles of 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonic acid and 1,2-dimiristoyl-sn-glycerol-3-phosphocholine emitted fluorescence at 340 nm indicative of the fluorophores in a relatively apolar environment.