EPR Parameters Research Articles

Nitroxide Spin Labels for Exploring Relationships Between Molecular Structure, Microenvironment and EPR Parameters: A Mini-review Dedicated to Carlo Corvaja

AbstractThis mini-review is dedicated to Carlo Corvaja (University of Padova) in recognition of his important contributions to the study of biomimetic donor–acceptor model dyads and triads and to the understanding of spin exchange in excited fullerene–nitroxide derivatives. We report on attractive examples of multi-frequency and multi-resonance EPR spectroscopy, highlighting recent work in Padova and Berlin/Mülheim. The examples selected include TR-EPR, ENDOR, and EDNMR experiments on photoexcited spin-labeled macromolecules, such as fullerene–nitroxide complexes or photosynthetic bacterial reaction centers, which were optionally NO spin-labeled. From the spin interaction parameters measured, detailed information about structure and dynamics of macromolecules embedded in liquid-solution or solid-state microenvironments could be extracted.

Structure and Kinetics of Organic Acid Radicals Formed in Reaction with •OH Radicals.

The study investigated •OH-derived radicals from certain organic acids employed in nuclear fuel processing and separation using EPR spectroscopy and quantum chemistry methods. Hydroxyl radicals were generated through a Fenton-like reaction within the EPR resonator under both acidic and basic conditions, allowing for the detection of neutral and radical anions, respectively. The spectral assignment and analysis were conducted using a combination of literature data and quantum chemical calculations employing DFT theory with B3LYP or LPBE functionals and the L2a_3 basis set. The reaction of the •OH radical with lactic and glycolic acids yielded primary C-centered radicals through hydrogen abstraction from these acids. In contrast, the •OH radical exclusively generated secondary radicals from oxalic acid, whereas for citric acid, it resulted in both primary and secondary species induced by decarboxylation. The EPR spectrum of acetohydroxamic acid, upon reaction with the •OH radical, displayed a complex pattern featuring primary •N-type and N-O•-type radicals. The decay pathways of the generated radicals were primarily attributed to radical-radical reactions, with the extracted reaction rate constants generally falling within the typical range observed for such reactions. The EPR parameters calculated for potential radicals using B3LYP and LPBE functionals with L2a_3 basis set demonstrated good accuracy for neutral radicals, albeit requiring minor adjustments for radical anions.

Relationship among EPR oxidative stability and spectrophotometric parameters connected to antioxidant activity in beer samples

A relationship between EPR and spectrophotometric parameters related to beer staling and antioxidant activity, was identified. AUC (area under the curve), intensity at 150 min (T150), radical scavenging activity (RSA), total phenolic compounds (TPC), hydroxyl radical scavenging capacity (HRSC) and one parameter linked to staling degree of beers (thiobarbituric index, TBI) were related. Temperature was modified to find the proper working conditions for EPR spin-trapping experiments and it was found that it affected the kinetic of PBN adduct evolution. For the samples reaching a maximum intensity signal, the higher the heating temperature, the shorter the time interval needed to reach it. No linear relationship was detected among parameters obtained with EPR spin trapping experiments and RSA, TPC, TPI, and HRSC when correlating one parameter with another. On the contrary, a good linear relationship was found among AUC or T150 and a combination of RSA, TPC, TPI, and HRSC (R2 = 0.9562 and 0.9694, respectively). The goodness of fit increased to R2 = 1 when a combination of AUC and T150 was related to a combination of RSA, TPC, and TPI, and HRSC.

Synthesis, structural and computational study, DNA binding and cytotoxic activity of Cu(II) complexes of 6- and 7-chloro-2-oxo-1,2-dihydroquinoline-3-carbaldehyde-2-furoyl-hydrazones

Three new coordination complexes of Cu(II) ions made from two hydrazone ligands, 7-chloro-2-oxo-1,2-dihydroquinoline-3-carbaldehyde-2-furoyl-hydrazone (HL1) and 6-chloro-2-oxo-1,2-dihydroquinoline-3-carbaldehyde-2-furoyl-hydrazone (HL2) have been synthesized and fully characterized by spectroscopic techniques. Their crystal and molecular structures revealed distorted square pyramidal mononuclear complexes: [(L1)Cu(H2O)2](NO3)·3H2O, 1(NO3), [(L2)Cu(H2O)2](NO3)·2H2O·CH3OH, 2(NO3), and [(L2)Cu(NO3)(CH3OH)]·2CH3OH, 3, comprising the ligand (L1 and L2) in tridentate fashion (ONO) with two water molecules in 1+ and 2+, and a single methanol molecule and a nitrate ion in 3 in their respective copper coordination spheres. EPR spectra in frozen methanol revealed the occurrence of several species arising from different coordination environments. A detailed DFT investigation on the energetics of solvents exchange (H2O, MeOH, and DMSO) and simulation of the EPR parameters showed that the exchange processes occur easily in solution. The value gz indicated the occurrence of a dimeric aggregate for 2+. The new copper complexes exhibited a noticeable antiproliferative activity with IC50 values in the micromolar range against HCT-15, H157, BxPC3, PNS-1, and A431 cell lines and they were found to be 3-fold more effective than cisplatin against pancreatic PSN-1 cell lines. Cross-resistance tests on A2780 and LoVo cancer cell lines and the corresponding multidrug or oxaliplatin resistant sublines showed that complexes 1(NO3) and 2(NO3) were equally cytotoxic to sensitive and resistant cells, thus overcoming multidrug and oxaliplatin resistance.

Monocopper model of CuB site of pMMO in N4‐environment oxidizes C−H bonds

AbstractDiscrepancies regarding the coordination environment, donor atoms, nuclearity, and oxidation state of the active site of particulate methane monooxygenase (pMMO), a copper‐dependent enzyme capable of activating the strong C−H bond of methane, persist despite numerous structural and spectroscopic studies. To address the proposed mono‐ (CuII) or bimetallic (2CuI) nature of the so‐called CuB site, we report the bis(benzimidazole)‐based NMe−N,N’‐(1‐Me‐2‐CH2C7H4N2)2C6H4 ligand (N4) and its copper complexes. In the solid state [Cu(N4)(ClO4)]ClO4 features tetragonal geometry defined by the chelating ligand and an axial perchlorate; geometric and EPR parameters are very close to those reported for the CuB site. Attempts to obtain a dicopper(I) analog resulted in [Cu(N4)][CuCl2], based on spectroscopic, electrochemical, and ESI‐MS data. Although these results support the assignment of CuB as a monometallic site, air exposure of [Cu(N4)][CuCl2] leads to ligand oxidation in the structurally characterized [Cu(N4=O)Cl], raising the possibility of distorted tetragonal Cu(I) centers activating O2 and oxidizing substrates, in C−H activation chemistry that may take place at CuB.

Hydrogen-bonded supramolecular structures in copper(II) nitrobenzoates with N-methylnicotinamide: synthesis, supramolecular structure, Hirshfeld surface analysis, spectral and DFT study

The synthesis of six new copper(II) nitrobenzoate complexes with N-methylnicotinamide, used as an auxiliary ligand for a supramolecular interaction study, is reported. Crystal structures of six novel compounds [Cu(2-NO2bz)2(mna)2(H2O)2] (1), [Cu(2-NO2bz)2(mna)2(H2O)2]∙2H2O (2), [Cu(3-NO2bz)2(mna)2(H2O)2] (3), [Cu(3,5-(NO2)2bz)2(mna)2(H2O)2]∙2H2O (4), [Cu(4-NO2bz)2(mna)2(H2O)2]∙2(4-NO2bzH) (5) and [Cu(3,5-(NO2)2bz)2(mna)(H2O)3] (6) (mna = N-methylnicotinamide, 2-NO2bz = 2-nitrobenzoate, 3-NO2bz = 3-nitrobenzoate, 4-NO2bz = 4-nitrobenzoate, 3,5-(NO2)2bz = 3,5-dinitrobenzoate) were determined by X-ray analysis. Compounds 1–6 are mononuclear with a tetragonal-bipyramidal geometry around the Cu2+ ion. The molecules of the studied complexes are mostly linked by a combination of N–H…O and O–H…O hydrogen bonds between N-methylnicotinamide and water molecules into supramolecular hydrogen-bonded coordination chains and networks. Intermolecular interactions in the supramolecular structures were also studied using Hirshfeld surface analysis. In addition, the complexes 1–6 have been characterised by elemental analysis, IR, UV–Vis and EPR spectroscopy. Density functional theory calculations were performed in order to reproduce the EPR magnetic parameters. DFT calculations of the EPR parameters show a good agreement with the experimental results.

Deep Levels and Electron Paramagnetic Resonance Parameters of Substitutional Nitrogen in Silicon from First Principles.

Nitrogen is commonly implanted in silicon to suppress the diffusion of self-interstitials and the formation of voids through the creation of nitrogen-vacancy complexes and nitrogen-nitrogen pairs. Yet, identifying a specific N-related defect via spectroscopic means has proven to be non-trivial. Activation energies obtained from deep-level transient spectroscopy are often assigned to a subset of possible defects that include non-equivalent atomic structures, such as the substitutional nitrogen and the nitrogen-vacancy complex. Paramagnetic N-related defects were the object of several electron paramagnetic spectroscopy investigations which assigned the so-called SL5 signal to the presence of substitutional nitrogen (NSi). Nevertheless, its behaviour at finite temperatures has been imprecisely linked to the metastability of the NSi center. In this work, we build upon the robust identification of the SL5 signature and we establish a theoretical picture of the substitutional nitrogen. Through an understanding of its symmetry-breaking mechanism, we provide a model of its fundamental physical properties (e.g., its energy landscape) based on ab initio calculations. Moreover by including more refined density functional theory-based approaches, we calculate EPR parameters (↔g and ↔A tensors), elucidating the debate on the metastability of NSi. Finally, by computing thermodynamic charge transition levels within the GW method, we present reference values for the donor and acceptor levels of NSi.

Single-Oxidation of Ni(II) Complexes of Bidentate Fused N-Heterocyclic Carbene–Phenol Conjugates

The pro-ligands (H2LtBu)+ and (H2LOMe)+ were synthesized as chloride salts. They associate an imidazo [1,5-a] pyridinium ring and an electron-rich 2,4-(di-tert-butyl)phenol or 2-(tert-butyl)-4-methoxyphenol, respectively. The homoleptic Ni(II) complexes of H2LtBu (1) and H2LOMe (2) were prepared and structurally characterized, showing a four-coordinate nickel center with two ligands bound by one phenolate oxygen and one carbene each. Complexes 1 and 2 show two reversible oxidation waves in their cyclic voltammetry curve, at E1/21 = 0.19 V and E1/22 = 0.59 V, and E1/21 = 0.03 V and E1/22 = 0.32 V, respectively. The one-electron oxidized forms were generated and characterized by spectroscopy, while 2+ could be isolated as single crystals. They both demonstrate two remarkable NIR bands indicating radical species in CH2Cl2. The EPR parameters are 2.097, 2.023, and 1.997 (gaverage = 2.039) for 1+ and 2.030, 2.016, and 1.994 (gaverage = 2.013) for 2+. Both gaverage values are slightly higher than those reported for genuine phenoxyl radicals but far below those of Ni(III) complexes, supporting a metalloradical character of 1+ and 2+, whereby one metal d-orbital contributes to the singly occupied molecular orbital (SOMO). A very good agreement is found between DFT calculated and experimental vis–NIR and EPR data. Both metalloradical cations could be converted into Ni(III) species by addition of pyridine. The redox isomerism could be monitored by EPR spectroscopy: the [1•Py]+ species exhibits for instance the g-values 2.157, 2.136, and 2.014 (gaverage = 2.103). The Ni(III) adducts are thermally unstable and undergo reduction back to the neutral precursor at room temperature.

A Complete Triad of Zero-Valent 17-Electron Monoradicals of Group 7 Elements Stabilized by m-Terphenyl Isocyanides.

The first consistent series of mononuclear 17-electron complexes of three Group 7 elements has been isolated in crystalline form and studied by X-ray diffraction and spectroscopic methods. The paramagnetic compounds have a composition of [M0 (CO)(CNp-F-ArDArF2 )4 ] (M=Mn, Tc, Re; ArDArF2 =2,6-(3,5-(CF3 )2 C6 H3 )2 C6 H2 F) and are stabilized by four sterically encumbering isocyanides, which prevent the metalloradicals from dimerization. They have a square pyramidal structure with the carbonyl ligands as apexes. The frozen-solution EPR spectra of the rhenium and technetium compounds are clearly anisotropic with large 99 Tc and 185,187 Re hyperfine interactions for one component. High-field EPR (Q band and W band) has been applied for the elucidation of the EPR parameters of the manganese(0) complex.

Ein m‐Terphenylisocyanid stabilisiert 17‐Elektronen‐Monoradikale von drei Elementen der Gruppe 7

AbstractEine erste konsistente Serie einkerniger 17‐Elektronenkomplexe von drei Elementen der Gruppe 7 wurde in kristalliner Form hergestellt und durch Röntgenkristallstrukturanalyse sowie spektroskopische Methoden untersucht. Die paramagnetischen Verbindungen der Zusammensetzung [M0(CO)(CNp‐F‐ArDArF2)4] (M=Mn, Tc, Re; ArDArF2=2,6‐(3,5‐(CF3)2C6H3)2C6H2F)) werden durch jeweils vier sterisch anspruchsvolle Isocyanid‐Liganden stabilisiert, wodurch auch eine Dimerisierung der Metalloradikale verhindert wird. Die Verbindungen besitzen eine quadratisch‐pyramidale Struktur mit jeweils einem Carbonyl‐Liganden als Apex. EPR‐Spektren der Technetium‐ und Rheniumverbindungen zeigen eine deutliche Anisotropie mit großen 99Tc und 185,187Re‐Hyperfeinstrukturkopplungen für jeweils eine der Komponenten. Für die Bestimmung der EPR‐Parameter des entsprechenden Mn0‐Komplexes wurde Hochfeld‐EPR (Q‐Band und W‐Band) verwendet.

Correlation of magnetic resonance (EPR, ssNMR) parameters and crystal-microstrain in marbles as a tool to probe their provenance.

Marbles constitute a significant family of materials, for antiquities, as well as modern constructions. Herein, we have studied Greek marbles, using electron paramagnetic resonance (EPR) and solid-state nuclear magnetic resonance (ssNMR) spectroscopies, focusing on their structural microenvironment. Spin-Hamiltonian parameters derived from EPR spectra of naturally occurring 55Mn2+ (S = 5/2, I = 5/2) atoms in marbles, were studied as structural-probes. EPR data at 300 K provide a library of 55Mn2+ zero-field-splitting parameters (E, D). The effect of temperature (300 up to 700 K) on 55Mn2+-ZFS (E, D) and the strain of the D-tensor (Dstrain) was studied by high-temperature EPR spectroscopy. The EPR data, combined with 13C-ssNMR, provide detailed physicochemical information of the calcite and dolomite crystal phases in the marbles. In parallel, we have analyzed the lattice-microstrain (ε0) of the marbles' crystallites using high-resolution XRD data. Analysis of the correlation between the D-values of Mn2+ centers and (ε0)-XRD, reveals trends that reflect the provenance of the marbles. In this context, we discuss the correlation between the D-values of Mn2+ centers and (ε0)-microstrain as a novel tool to elucidate the provenance of marbles.

Theoretical Studies of the Local Structure and EPR Parameters of Tetragonally Distorted Tetrahedral Cu2+ Sites in Phosphate Glasses

Theoretical Studies of the Local Structure and EPR Parameters of Tetragonally Distorted Tetrahedral Cu2+ Sites in Phosphate Glasses

Exploring EPR Parameters of 187Re Complexes for Designing New MRI Probes: From the Gas Phase to Solution and a Model Protein Environment

Breast cancer is one of the major types of cancer around the world, and early diagnosis is essential for successful treatment. New contrast agents (CAs), with reduced toxicology, are needed to improve diagnosis. One of the most promising Magnetic Resonance Imaging (MRI) CA is based on rhenium conjugated with a benzothiazole derivate (ReABT). In this sense, DFT has been used to evaluate the best methodology for calculating the hyperfine coupling constant (Aiso) of ReABT. Then, a thermodynamic analysis was performed to confirm the stability of the complex. Furthermore, a docking study of ReABT at the enzyme PI3K active site and Aiso calculations of ReABT in the enzyme environment were carried out. The best methodology for the Aiso calculation of ReABT was using the M06L functional, SARC-ZORA-TZVP (for Re) and TZVP (for all other atoms) basis set, relativistic Hamiltonian, and the CPCM solvation model with water as the solvent which confirm that the relativistic effects are important for calculating the Aiso values. In addition, thermodynamic analysis indicates that ReABT presents a higher stability and a lower toxicity than Gd-based CAs. The docking studies point out that ReABT interacts with amino acids residues of alanine, aspartate, and lysine from the PI3K active site. Considering the enzyme environment, Aiso values decrease significantly. These findings indicate that the CA candidate ReABT could be a good candidate for a new contrast agent.

A Combined Experimental and Theoretical Investigation of Oxidation Catalysis by cis-[VIV(O)(Cl/F)(N4)]+ Species Mimicking the Active Center of Metal-Enzymes.

Reaction of VIVOCl2 with the nonplanar tetradentate N4 bis-quinoline ligands yielded four oxidovanadium(IV) compounds of the general formula cis-[VIV(O)(Cl)(N4)]Cl. Sequential treatment of the two nonmethylated N4 oxidovanadium(IV) compounds with KF and NaClO4 resulted in the isolation of the species with the general formula cis-[VIV(O)(F)(N4)]ClO4. In marked contrast, the methylated N4 oxidovanadium(IV) derivatives are inert toward KF reaction due to steric hindrance, as evidenced by EPR and theoretical calculations. The oxidovanadium(IV) compounds were characterized by single-crystal X-ray structure analysis, cw EPR spectroscopy, and magnetic susceptibility. The crystallographic characterization showed that the vanadium compounds have a highly distorted octahedral coordination environment and the d(VIV-F) = 1.834(1) Å is the shortest to be reported for (oxido)(fluorido)vanadium(IV) compounds. The experimental EPR parameters of the VIVO2+ species deviate from the ones calculated by the empirical additivity relationship and can be attributed to the axial donor atom trans to the oxido group and the distorted VIV coordination environment. The vanadium compounds act as catalysts toward alkane oxidation by aqueous H2O2 with moderate ΤΟΝ up to 293 and product yields of up to 29% (based on alkane); the vanadium(IV) is oxidized to vanadium(V), and the ligands remain bound to the vanadium atom during the catalysis, as determined by 51V and 1H NMR spectroscopies. The cw X-band EPR studies proved that the mechanism of the catalytic reaction is through hydroxyl radicals. The chloride substitution reaction in the cis-[VIV(O)(Cl)(N4)]+ species by fluoride and the mechanism of the alkane oxidation were studied by DFT calculations.

Synthesis of Genuine Germenyl Lithiums and the First Persistent Germenyl Radicals.

The first isolated genuine germenyl lithiums (R3Si)(1‐Ad)C=Ge(SiMetBu2)(Li⋅2 L) (R3Si=tBu2MeSi, L=THF (1 a), or L=12‐crown‐4 (1 b) and R3Si=tBuMe2Si, L=THF (2 a), or L=12‐crown‐4 (2 b)), were synthesized by reaction of the corresponding acyl germanes 3 and 4, respectively, with tBu2MeSiLi in THF at 70 °C. The novel 1 a and 2 b were characterized by NMR and UV/Vis spectroscopy, and also by X‐ray crystallography (r(C=Ge)=1.865 Å for 1 a and 1.877 Å for 2 b). Nucleophilic addition reaction of 1 a with MeI and a C−H insertion reactions to the C=Ge bond of 1 a, 2 a and 2 b, are reported. Oxidation of 1 a and 2 b (toluene, 230 K) produces the first persistent germenyl radicals (R3Si)(1‐Ad)C=Ge⋅‐(SiMetBu2) (R3Si=tBu2MeSi (13 a), R3Si=tBuMe2Si (13 b)), which were characterized by EPR spectroscopy (t 1/2≈30 min at 230 K, g=2.029, a av(73Ge) is 55.0G for 13 a and 60.2G for 13 b). The experimental EPR parameters and DFT calculations indicate that 13 a and 13 b have a strongly bent structure at Ge (calc. ∡(C=Ge−Si)=136.7° (13 a), 135.9° (13 b)), and that the unpaired electron has a substantial s‐character.

Synthesis of Genuine Germenyl Lithiums and the First Persistent Germenyl Radicals

AbstractThe first isolated genuine germenyl lithiums (R3Si)(1‐Ad)C=Ge(SiMetBu2)(Li⋅2 L) (R3Si=tBu2MeSi, L=THF (1 a), or L=12‐crown‐4 (1 b) and R3Si=tBuMe2Si, L=THF (2 a), or L=12‐crown‐4 (2 b)), were synthesized by reaction of the corresponding acyl germanes 3 and 4, respectively, with tBu2MeSiLi in THF at 70 °C. The novel 1 a and 2 b were characterized by NMR and UV/Vis spectroscopy, and also by X‐ray crystallography (r(C=Ge)=1.865 Å for 1 a and 1.877 Å for 2 b). Nucleophilic addition reaction of 1 a with MeI and a C−H insertion reactions to the C=Ge bond of 1 a, 2 a and 2 b, are reported. Oxidation of 1 a and 2 b (toluene, 230 K) produces the first persistent germenyl radicals (R3Si)(1‐Ad)C=Ge⋅‐(SiMetBu2) (R3Si=tBu2MeSi (13 a), R3Si=tBuMe2Si (13 b)), which were characterized by EPR spectroscopy (t1/2≈30 min at 230 K, g=2.029, aav(73Ge) is 55.0G for 13 a and 60.2G for 13 b). The experimental EPR parameters and DFT calculations indicate that 13 a and 13 b have a strongly bent structure at Ge (calc. ∡(C=Ge−Si)=136.7° (13 a), 135.9° (13 b)), and that the unpaired electron has a substantial s‐character.

Investigation of the C-N Bond-Forming Step in a Photoinduced, Copper-Catalyzed Enantioconvergent N-Alkylation: Characterization and Application of a Stabilized Organic Radical as a Mechanistic Probe.

Whereas photoinduced, copper-catalyzed couplings of nitrogen nucleophiles with alkyl electrophiles have recently been shown to provide an attractive approach to achieving a variety of enantioselective C-N bond constructions, mechanistic studies of these transformations have lagged the advances in reaction development. Herein we provide mechanistic insight into a previously reported photoinduced, copper-catalyzed enantioconvergent C-N coupling of a carbazole nucleophile with a racemic tertiary α-haloamide electrophile. Building on the isolation of a copper(II) model complex whose EPR parameters serve as a guide, we independently synthesize two key intermediates in the proposed catalytic cycle, a copper(II) metalloradical (L*CuII(carb')2) (L* = a monodentate chiral phosphine ligand; carb' = a carbazolide ligand), as well as a tertiary α-amide organic radical (R·); the generation and characterization of R· was guided by DFT calculations, which suggested that it would be stable to homocoupling. Continuous-wave (CW) and pulse EPR studies, along with corresponding DFT calculations, are among the techniques used to characterize these reactive radicals. We establish that these two radicals do indeed combine to furnish the C-N coupling product in good yield and with significant enantiomeric excess (77% yield, 55% ee), thereby supporting the chemical competence of these proposed intermediates. DFT calculations are consistent with R· initially binding to copper(II) via a dative interaction from the closed-shell carbonyl oxygen atom of the radical, which positions the α-carbon for direct reaction with the copper(II)-bound carbazole N atom, to generate the C-N bond with enantioselectivity, without the formation of an alkylcopper(III) intermediate.

Structural and theoretical studies on copper(II) and zinc(II) complexes with a 9-anthraldehyde-derived thiosemicarbazone

Complexes [Cu(ATPh)2]·H2O (1) and [Zn(ATPh)2] (2) were obtained with 9-anthraldehyde-N(3)-phenyl thiosemicarbazone (HATPh). The g|| ≈ 2.15 and A|| ≈ 180 G EPR parameters of complex (1) are compatible with two nitrogen and two sulfur donor atoms in a nearly square planar geometry. The first excited state of complex (1) is not emissive due to fluorescence quenching by the paramagnetic copper(II) ion. The crystal structure of [Zn(ATPh)2]·2DMF (2a) shows that in 2a the anionic thiosemicarbazone ligands are attached to the metal through the NS chelating system in a distorted tetrahedral arrangement. Computational studies revealed that the S1 → S0 emission of complex (2) is attributed to anthracene, the emission band involving two electronic transitions centered at the anthracene rings. The HOMO-1 → LUMO transition is characterized as a ligand-to-ligand charge transfer (LLCT) between anthracene groups, which contributes with 12% and an intra-ligand charge transfer transition (ILCT) centered in the anthracene group of one of the ligands, which contributes with 77% to the emission band. The emission intensity of complex (2) is lower than that of the free thiosemicarbazone, but the presence of two ligand molecules in the complex increases the fluorescence efficiency and the computed fluorescence rate constant for 2 is ∼ 600-fold higher than that of the free ligand.

Copper hydrazone complexes with different nuclearties and geometries: Synthesis, characterization, single crystal structures, Hirshfeld analysis and superoxide dismutase mimetic activities

Three new copper(II) hydrazone complexes [Cu(L)(neocuproine)]NO31, [Cu(L)(6-benzylaminopurine)ClO4] 2 and [Cu(L)μ(1,1-N3)Na(H2O)2] 3 with different nuclearties and geometries using acetic acid(2‑hydroxy-3‑methoxy-benzylidene)-hydrazide (HL) as proligand and neucuproine, 6-benzylaminopurine and sodium azide as co-ligands have been synthesized and characterized using several physico-chemical and spectral methods. Molecular structures of complexes were obtained by single crystal diffraction technique. The coordination sphere in complexes 1 and 2 can be illustrated as distorted square pyramidal geometry whereas 3 has distorted square planar geometry. Supramolecular structures were formed via different intermolecular interactions like hydrogen bondings and CH⋯π in 1, hydrogen bondings, CH⋯π and lp⋯π in 2 and hydrogen bondings, CH⋯π, lp⋯π and π⋯π(chelate-chelate) interactions in 3. The Hirshfeld surface analysis exhibited O⋯H, N⋯H and C⋯H interactions in all complexes. The optimized geometry of newly synthesized complexes were obtained by B3LYP/LANL2DZ model. From the differences in energies of frontier molecular orbitals (ΔEg), reactivity parameters like, ionization potential (IP), electron affinity (EA), electronegativity (χ), softness (S), hardness (η) and electrophilicity index (ω) were determined. In these complexes the Epr parameters (g-) showed the trend g∥>g⊥>2.0023, which is consistent with a dx2−y2 ground state in a square based geometry. Electrochemical properties also determined using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Additionally, superoxide dismutase catalytic activity measurements were performed by nitro blue tetrazolium chloride (NBT) assay in phosphate buffer. All complexes catalyzed the dismutation of superoxide at biological pH. Enhancement in the SOD activity of 2 can be credited to the coordinated poorly bound ClO4− ion which is easily replaced by O2·− ion.

EPR Study of CeO2 Nano Particles

In this paper, we have studied the EPR spectra, X-ray diffraction and Raman Analysis, Microstructures-morphology of the Ceria NPs calcined at different temperatures of 700 °C, 850 °C ,these materials have been synthesized by Co precipitation (CPT) method by using Cerium tri-nitrate hexahydrate and potassium carbonate solutions. Then synthesized precipitate was heated at 70 °C for 20 hour. Slow grinding of the precipitate and calcined for 3 hours at different temperatures viz. 700 °C and 850 °C to form fine Cerium oxide powder-Ceria NPs. The EPR measurements were made using continuous wave spectrometer (X-band, Bruker Biospin EMX Plus). The g values were obtained by using diphynelpirichylhydrageyl (DPPH-C18H12N5O6) sample and got g value is around 1.97. This g tensor is decreased when the calcined temperature are increased, EPR parameters are also changed as the calcined temperature increases. When the calcined temperature is increased from 700 °C to 850 °C, a doublet separated, intensity increased. The X-Ray diffraction pattern shows the nature of the Ceria NPs crystal, with a cubic structure and got the lattice parameters 5.392 Å for samples calcined at temperature of 700 °C and 5.357 Å at 850 °C which shows decreasing trend in lattice parameter with calcination temperature. The intensity of Raman peaks is also shifted upwards with a rise in temperature. This intensity difference could be because of the rise in vibrational amplitudes of the closest neighboring bonds because of the increase in particle size 11.3± 1.0 to 15.6± 1.0 nm at calcination temperatures of 700 °C and 850 °C and the Raman peak of peak I, 461 cm-1 and peak II, 463 cm-1 respectively. Other peaks were not observed in this Raman pattern. The EDS analysis confirms the presence of the Ce and O atoms in the synthesized samples. Spherical shapes and homogeneously distributed Ceria NPs and a rather tendency for agglomeration were confirmed.