Understanding the Exchange Interaction between Paramagnetic Metal Ions and Radical Ligands: DFT and Ab Initio Study on Semiquinonato Cu(II) Complexes

The exchange coupling, represented by the J parameter, is of tremendous importance in understanding the reactivity and magnetic behavior of open-shell molecular systems. In the past, it was the subject of theoretical investigations, but these studies are mostly limited to the interaction between metallic centers. The exchange coupling between paramagnetic metal ions and radical ligands has hitherto received scant attention in theoretical studies, and thus the understanding of the factors governing this interaction is lacking. In this paper, we use DFT, CASSCF, CASSCF/NEVPT2, and DDCI3 methods to provide insight into exchange interaction in semiquinonato copper(II) complexes. Our primary objective is to identify structural features that affect this magnetic interaction. We demonstrate that the magnetic character of Cu(II)-semiquinone complexes are mainly determined by the relative position of the semiquinone ligand to the Cu(II) ion. The results can support the experimental interpretation of magnetic data for similar systems and can be used for the in-silico design of magnetic complexes with radical ligands

Toward an Understanding of the Ambiguous Electron Paramagnetic Resonance Spectra of the Iminoxy Radical from <i>o</i>‑Fluorobenzaldehyde Oxime: Density Functional Theory and <i>ab Initio</i> Studies

Iminoxy radicals (R₁R₂CNO^•) possess an inherent ability to exist as <i>E</i> and <i>Z</i> isomers. Although isotropic hyperfine couplings for the species with R₁ = H allow one to distinguish between <i>E</i> and <i>Z</i>, unequivocal assignment of the parameters observed in the EPR spectra of the radicals without the hydrogen atom at the azomethine carbon to the right isomer is not a simple task. The iminoxyl derived from <i>o</i>-fluoroacetophenone oxime (R₁ = CH₃ and R₂ = <i>o</i>-FC₆H₅) appears to be a case in point. Moreover, for its two isomers the rotation of the <i>o</i>-FC₆H₅ group brings into existence the <i>syn</i> and <i>anti</i> conformers, depending on the mutual orientation of the F atom and CNO^• group, making a description of hyperfine couplings to structure even more challenging. To accomplish this, a vast array of theoretical methods (DFT, OO-SCS-MP2, QCISD) was used to calculate the isotropic hyperfine couplings. The comparison between experimental and theoretical values revealed that the <i>E</i> isomer is the dominant radical form, for which a fast interconversion between <i>anti</i> and <i>syn</i> conformers is expected. In addition, the origin of the significant <i>A</i>_F increase with solvent polarity was analyzed

New copper(II) complexes of the anti-inflammatory drug mefenamic acid: A concerted study including synthesis, physicochemical characterization and their biological evaluation

Reaction of hydrated copper(ii) mefenamate in the presence of diverse N-donor ligands such as N,N,N′,N′-tetramethylethylenediamine (temed), ethylenediamine (en), β-picoline (β-pic) in a methanol:water mixture (4:1, v/v) yielded crystalline monomeric copper(ii) complexes [Cu(temed) (mefenamato)2], 1, [Cu(en)2(H2O)2](mefenamato)2, 2 and [Cu(β-pic)2(mefenamato)2]·H2O, 3. The newly synthesized complexes have been characterized by elemental analysis, spectroscopic methods (FT-IR, UV-Vis and EPR), thermogravimetric analyses and single-crystal X-ray structure determination in the case of complexes 2 and 3. The ground-state geometry optimization of complex 1 was performed by DFT calculations. In order to verify the complexes capability to get bound and possibly transported by the albumin towards their biological targets (cells and/or tissues), the interaction with bovine (BSA) and human serum albumin (HSA) was studied by fluorescence emission spectroscopy. The interaction of complexes 1-3 with calf-thymus DNA (CT DNA) was monitored by UV-Vis spectroscopy, cyclic voltammetry, viscosity measurements and via the ethidium bromide (EB) displacement from the EB-DNA conjugate performed by fluorescence emission spectroscopy, as a preliminary approach to evaluate their potential biological activity

Antiradical Properties of N-Oxide Surfactants—Two in One

Surfactants are molecules that lower surface or interfacial tension, and thus they are broadly used as detergents, wetting agents, emulsifiers, foaming agents, or dispersants. However, for modern applications, substances that can perform more than one function are desired. In this study we evaluated antioxidant properties of two homological series of N-oxide surfactants: monocephalic 3-(alkanoylamino)propyldimethylamine-N-oxides and dicephalic N,N-bis[3,3′-(dimethylamino)propyl]alkylamide di-N-oxides. Their antiradical properties were tested against stable radicals using electron paramagnetic resonance (EPR) and UV-vis spectroscopy. The experimental investigation was supported by theoretical density functional theory (DFT) and ab initio modeling of the X–H bonds dissociation enthalpies, ionization potentials, and Gibbs free energies for radical scavenging reactions. The evaluation was supplemented with a study of biological activity. We found that the mono- and di-N-oxides are capable of scavenging reactive radicals; however, the dicephalic surfactants are more efficient than their linear analogues

Synthesis, characterization, single crystal X-ray structure, EPR and theoretical studies of a new hybrid inorganic-organic compound [Cu(Hdien)2(H2O)2](pnb)4·4H2O and its structural comparison with related [Cu(en)2(H2O)2](pnb)2

A new hybrid inorganic-organic compound [Cu(Hdien)2(H2O)2](pnb)4·4H2O (1) (where pnb = p-nitrobenzoate), in which the tridentate ligand diethylenetriamine (dien) shows an unusual coordination behavior acting as a bidentate ligand when present in its monoprotonated form (Hdien+) has been synthesized by the reaction of copper(II) p-nitrobenzoate and slight excess of dien in methanol-water mixture (4:1v/v). Re-crystallization of the violet precipitated product from hot water gave single crystals suitable for X-ray diffraction studies. The newly synthesized compound 1 has been characterized by spectroscopic techniques (UV-Vis, FT-IR, EPR), and theoretical methods (DFT and MRCI/SORCI). Single crystal X-ray structure determination revealed the existence of the cationic species [Cu(Hdien)2(H2O)2]4+, four p-nitrobenzoate as counter anions and four water molecules are present as solvent of crystallization. Packing analyses of title compound as well as of the structurally similar [Cu(en)2(H2O)2](pnb)2, 2 has shown similarities in the crystalline architecture that both hybrid inorganic-organic compounds is stabilized by various non-covalent interactions such as N-H⋯O, C-H⋯O, O-H⋯O etc

Can Carbamates Undergo Radical Oxidation in the Soil Environment? A Case Study on Carbaryl and Carbofuran

Radical oxidation of carbamate insecticides, namely carbaryl and carbofuran, was investigated with spectroscopic (electron paramagnetic resonance [EPR] and UV–vis) and theoretical (density functional theory [DFT] and ab initio orbital-optimized spin-component scaled MP2 [OO-SCS-MP2]) methods. The two carbamates were subjected to reaction with ^•OH, persistent DPPH^• and galvinoxyl radical, as well as indigenous radicals of humic acids. The influence of fulvic acids on carbamate oxidation was also tested. The results obtained with EPR and UV–vis spectroscopy indicate that carbamates can undergo direct reactions with various radical species, oxidizing themselves into radicals in the process. Hence, they are prone to participate in the prolongation step of the radical chain reactions occurring in the soil environment. Theoretical calculations revealed that from the thermodynamic point of view hydrogen atom transfer is the preferred mechanism in the reactions of the two carbamates with the radicals. The activity of carbofuran was determined experimentally (using pseudo-first-order kinetics) and theoretically to be noticeably higher in comparison with carbaryl and comparable with gallic acid. The findings of this study suggest that the radicals present in soil can play an important role in natural remediation mechanisms of carbamates

Hybrid inorganic-organic complexes: Synthesis, spectroscopic characterization, single crystal X-ray structure determination and antimicrobial activities of three copper(II)-diethylenetriamine-p-nitrobenzoate complexes

Three new hybrid inorganic-organic complexes: [Cu(dien)(pnb)2]·H2O, 1; [Cu(dien)2](pnb)2, 2; and [Cu(dien)(pnb)(H2O)](pnb)(Hpnb), 3 (where pnb = p-nitrobenzoate, dien = diethylenetriamine, tridenate N-donor ligand), have been synthesized at room temperature and characterized by spectroscopic (FT-IR, UVâ\u80\u93Vis, EPR) methods. The structures of all newly synthesized complexes 1â\u80\u933 have been unambiguously established by single crystal X-ray structure determination. All the complexes 1â\u80\u933 showed variation in the coordination environment around copper(II) metal center obtained under slightly different reaction conditions by using same reactants but different synthetic routes at room temperature. Crystal lattices of coordination complexes 1â\u80\u933 are stabilized by various non-covalent interactions such as N-Hâ\u80¦O, C-Hâ\u80¦O, O-Hâ\u80¦O etc. All the three copper(II) complexes 1â\u80\u933 show significant antimicrobial activity against gram positive bacteria