Analysis of spin-labelled glycylglycine interactions with cupric ions

Summary Glycylglycine substituted with 4-amino-2,2,6,6-tetramethyl piperidineN-oxide on the carboxylic acid function was used as a ligand to complex cupric ions. In aqueous solutions, blue species, of low stability, were obtained. E.p.r. spectroscopy showed the formation of various complexes. At basic pH values, a paramagnetic signal is observed with A = 101 gauss and g = 2.16. The spectroscopic parameters are interpreted in terms of strong magnetic exchange between the spin-labelled ligand and cupric ions.     

Extraction of Cupric Ions with Ionic Liquids Containing Polypyridine‐type Small Molecules or Peripherally Pyridine‐modified Dendrimers

The hydrophobic ionic liquid N‐butyl‐N‐methylpyrrolidinium bis((trifluoromethyl)sulfonyl)amide (BMP‐TFSA IL), which contains a series of flexible ionophores of polypyridine‐type small molecules or two rigid ionophores of peripherally pyridine‐modified PAMAM dendrimers, was used to extract cupric ions from aqueous solutions. The polypyridine‐type ionophores show good selectivity toward cupric ions at pH 2. The selectivity is affected by the spacing between the two amino groups. However, the pyridine‐modified dendrimers showed poor selectivity, although their extraction efficiency still depended on the pH of the aqueous solution. The ionic liquids that contained small molecular ionophores and their dendrimer analogs were reused after acid washing or electrochemical reduction. During acid washing, the nitrogen atoms of the ionophores were protonated to release the cupric ions into the aqueous phase, and the copper atoms were deposited onto the electrode surface during the electrochemical reduction accompanied by the regeneration of the ionophores.     

Polymerization of aromatic nuclei. XXVII. ESR studies on polymers and oligomers from reaction of benzenoid and naphthalene monomers with lewis acid catalyst–oxidant systems

Chlorobenzene and toluene were polymerized with aluminum chloride–cupric chloride to produce materials that consist mainly of poly(o-phenylene) structures. These species exhibited radical cation concentrations comparable to that of poly(p-phenylene). Polymerization of naphthalene and 1-chloronaphthalene with aluminum chloride–cupric chloride or ferric chloride–water also resulted in products with high radical cation concentrations. Polynuclear structures may be responsible for the paramagnetic character; alternatively, p-quinoidal moieties may be present in naphthalenes. The depth of color in the samples is directly related to the concentration of radical cations.     

Mechanism of the reaction of cuprous dialkylthiophosphates with haloacetylenes

Conclusions The ethynylation of cuprous salts of dialkylthiophosphoric acids by substituted ethynyl bromides proceeds through the formation of paramagnetic cupric ion complexes. These complexes are unstable and, under ordinary conditions, decompose with the formation of substituted S-ethynylthiophosphates and cuprous ions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 686–690, March, 1987.     

1-D polymers with alternate Cu2 and Ln2 units (Ln = Gd, Er, Y) and carboxylate linkages

Three isostructural Cu 2Ln 2 1-D polymers [Cu 2Ln 2L 10(H 2O) 4.3H 2O] n where Ln = Gd ( 1), Er ( 2), and Y ( 3) and HL= trans-2-butenoic acid, were synthesized and characterized by X-ray crystallography, electron paramagnetic resonance, and magnetic measurements. Pairs of alternate Cu 2 and Ln 2 dinuclear units are combined into a linear array by a set of one covalent eta (2):eta (1):mu 2 carboxylate oxygen and two H bonds, at Cu...Ln distances of ca. 4.5 A. These units exhibit four eta (1):eta (1):mu 2 and two eta (2):eta (1):mu 2 carboxylate bridges, respectively. Magnetic measurements between 2 and 300 K, fields B 0 = mu 0 H between 0 and 9 T, and electron paramagnetic resonance (EPR) measurements at the X-band and room temperature are reported. The magnetic susceptibilities indicate bulk antiferromagnetic behavior of the three compounds at low temperatures. Magnetization and EPR data for 1 and 3 allowed evaluation of the exchange couplings between both Cu and Gd ions in their dinuclear units and between Cu and Gd neighbor ions in the spin chains. The data for the isolated Cu 2 units in 3 yield g || = 2.350 and g [symbol: see text] = 2.054, J Cu-Cu = -338 (3) cm (-1) for the exchange coupling [ H ex(1,2) = - J 1-2 S1 x S2], and D 0 = -0.342 (0.003) cm (-1) and E 0 = 0.003 (0.001) cm (-1) for the zero-field-splitting parameters of the triplet state arising from anisotropic spin-spin interactions. Considering tetranuclear blocks Gd-Cu-Cu-Gd in 1, with the parameters for the Cu 2 unit obtained for 3, we evaluated ferromagnetic interactions between Cu and Gd neighbors, J Cu-Gd = 13.0 (0.1) cm (-1), and between Gd ions in the Gd 2 units, J Gd-Gd = 0.25 (0.02) cm (-1), with g Gd = 1.991. The bulk antiferromagnetic behavior of 1 is a consequence of the antiferromagnetic coupling between Cu ions and of the magnitude, |J Cu-Gd|, of the Cu-Gd exchange coupling. Compound 2 displays a susceptibility peak at 15 K that may be interpreted as the combined result from antiferromagnetic couplings between Er (III) ions in Er 2 units and their coupling with the Cu 2 units.     

Temperature effects in x-ray photoelectron spectra of paramagnetic cupric and iron complexes with anomalous magnetic properties

The temperature dependence of the XPS spectra of paramagnetic cupric and iron complexes with anomalous magnetic properties is studied. It was found that the XPS spectra of polynuclear complexes with antiferromagnetic interaction, such as cupric acetate, do not change with temperature, although their magnetic moments diminish essentially. The Fe 2p spectra of mononuclear iron (III) complexes with the spin multiplicity transitions S = $\text{1}\text{2}$ ? S = $\text{5}\text{2}$ exhibit temperature-dependent reversible alterations of shake-up satellite intensity which correlate with the spin state of the paramagnetic Fe(III) ion. The results obtained prove the mechanism of appearance of intensive shake-up satellites in XPS spectra of paramagnetic 3d element complexes, which relates shake-up excitations with the interaction of the photoelectron with unpaired valence 3d electrons during photoionization.     

Synthesis,structure, and magnetic properties of a self-assembled salicylaldimine neodymium(III) nitrate coordination polymer

Complex formed by the reaction of neodymium nitrate with Schiff base has been synthesized and characterized by elemental analysis and IR spectroscopy. The crystal structure and magnetic properties of the self-assembled complex, [Nd₂(H₂salen)₃(NO₃)₆] _n (H₂salen =N,N′-ethylenebis(salicylideneimine)), are reported. The central Nd(III) ion is nine-coordinate with a typical tricapped trigonal prismatic coordination geometry with an infinite 2-D net structure, in which every Schiff-base ligand links two Nd(III) ions, and Nd(III) ions as nodes make up hexagons with 3 axes passing through the centers. The susceptibility data of the complex are well-fitted to the Curie–Weiss law and anti-ferromagnetic interactions take place between intermolecular adjacent paramagnetic ions.     

Single glass nanopore-based regenerable sensing platforms with a non-immobilized polyglutamic acid probe for selective detection of cupric ions

A single glass capillary nanopore-based sensing platform for rapid and selective detection of cupric ions is demonstrated by utilizing polyglutamic acid (PGA) as a non-immobilized probe. The detection is based on the significant decrease of ionic current through nanopore and the reversal of ion current rectification responses induced by the chelated cupric ions on the probes when in the presence of cupric ions. PGA shows high selectivity for detecting cupric ions rather than other metal ions. The sensitivity of the sensing platform can be improved about 1–2 orders of magnitude by employing asymmetric salt gradients during the measurements. And the PGA-based nanopore sensing platform shows excellent regenerability for Cu²⁺ sensing applications. In addition, the method is found effective and reliable for the detection of cupric ions in real samples with small volume down to 20 μL. This nanopore-based sensing platform will find promising practical applications for the detection of cupric ions.     

Noncovalent Tagging Proteins with Paramagnetic Lanthanide Complexes for Protein Study

The site‐specific labeling of proteins with paramagnetic lanthanides offers unique opportunities for NMR spectroscopic analysis in structural biology. Herein, we report an interesting way of obtaining paramagnetic structural restraints by employing noncovalent interaction between a lanthanide metal complex, [Ln(L)₃]^n? (L=derivative of dipicolinic acid, DPA), and a protein. These complexes formed by lanthanides and DPA derivatives, which have different substitution patterns on the DPA derivatives, produce diverse thermodynamic and paramagnetic properties when interacting with proteins. The binding affinity of [Ln(L)₃]^n? with proteins, as well as the determined paramagnetic tensor, are tunable by changing the substituents on the ligands. These noncovalent interactions between [Ln(L)₃]^n? and proteins offer great opportunities in the tagging of proteins with paramagnetic lanthanides. We expect that this method will be useful for obtaining multiple angles and distance restraints of proteins in structural biology.     

Linear Copper Complex Arrays as Versatile Molecular Strings: Syntheses,Structures, Luminescence,and Magnetism

The defined linear arrangement of metal atoms in discrete coordination complexes or polymers is still one of the most intriguing challenges in synthetic chemistry. These chain arrangements are of fundamental importance, because of their potential applications as molecular wires and single molecule magnets (SMM) in microelectronic devices on a molecular scale. Oligonuclear Group 11 metal complexes with suitable bridging ligands, specifically those that are based on copper as the first choice of a cheap precursor coinage metal, are of particular interest in this regard. This is due to the superior luminescence properties of these linear clusters that often show d¹⁰⋅⋅⋅d¹⁰ interactions in their molecular structures. The combination of Cu^I with heavier coinage metal ions results in tunable emissive arrays that are also stimuli-responsive. Thus, both linear multinuclear Cu^I and linear heteropolymetallic Cu^I/Ag^I as well as Cu^I/Au^I clusters are excellent candidates for applications in molecular/organic light-emitting devices (OLEDs). Alternatively, paramagnetic multinuclear cupric arrays are prominent as potential molecular wires with enhanced magnetic properties through multiple coupled d⁹ centers. This Review covers the whole range of linear multinuclear assemblies of cuprous and cupric ions in complexes and coordination polymers, their syntheses, photophysical behavior, and magnetic properties. Moreover, recent advances in the rapidly progressing field of hetero-Cu^I/Ag^I and Cu^I/Au^I molecular strings are also discussed.     

Magnetic and EPR Studies of α-, β-, and γ-Fe2WO6 Phases at Low Temperatures

The polymorphic modifications α-, β-, and γ-Fe₂WO₆ of the iron tungstate system were studied by means of magnetic susceptibility and EPR measurements at low temperatures. Both methods revealed a significant paramagnetic contribution, probably resulting from local distortions of the antiferromagnetic bulk structure induced by a disturbed cation ordering or the presence of Fe²⁺ ions. The magnetic susceptibility revealed a peak at 260 K for all samples which can be related with an AF phase transition. The EPR spectra comprised the contribution of various isolated paramagnetic iron centers, one arising from high-spin Fe³⁺ ions in rhombic crystal field symmetry with E/D ≈ 1/3 and D ≈ 0.22 cm^-1, an anisotropic EPR signal consistent with an S= 3/2 ground state with large zero-field splitting, and a dominant component in the g ≈ 2 region presumably arising from an S = 1/2; spin state. The latter spectra were tentatively attributed to the formation of multi-iron clusters, one of them invoking the presence of Fe²⁺ ions as well. For the βFe₂WO₆ phase an additional EPR spectrum was observed, which probably results from high-spin Fe³⁺ ions in a weak crystal field.     

A novel tetranuclear copper(II) complex with alternating mu 1,1-azido and phenoxo bridges: synthesis,structure, and magnetic properties of [Cu4(mu-salen)2(mu 1,1-N3)2(N3)2

A novel tetranuclear copper(II) complex containing alternating mu(1,1)-azido and monophenoxo bridges has been synthesized and characterized by spectroscopic methods, X-ray single-crystal analysis, and variable-temperature magnetic measurements. The magnetic behavior, investigated in the temperature range 2-300 K, indicates that the interactions between copper ions are antiferromagnetic in nature for both azido and phenoxo bridges. The temperature dependence of the magnetic susceptibility was fitted with J(1) = -12.8 cm(-1), J(2) = -10 cm(-1), g = 2.171, 2.1% paramagnetic component, and negligible temperature-independent paramagnetism (5 x 10(-8)). At variance with the earlier reports of these types of complexes containing a mu(1,1)-azido group, the end-on double-azido-bridged copper(II) center in this complex shows an antiferromagnetic interaction.     

Thermodynamic studies on the recognition of flexible peptides by transition-metal complexes

Strong and selective binding to a trihistidine peptide has been achieved employing Cu(2+)-histidine interactions in aqueous medium (25 mM HEPES buffer, pH 7.0). When the pattern of cupric ions on a complex matched with the pattern of histidines on the peptide, a strong and selective binding was observed. UV-vis spectroscopic studies show that the cupric ions coordinate to the histidines of the peptides. Thermodynamic studies reveal that the binding process is enthalpy driven over the entire range of working temperature (25-40 degrees C). An enthalpy-entropy compensation effect was also observed.     

Analytical determination of the [Ln-aminoxyl radical] exchange interaction taking into account both the ligand-field effect and the spin-orbit coupling of the lanthanide ion (Ln = DyIII and HoIII)

Numerous compounds in which a paramagnetic LnIII ion is in an exchange interaction with a second spin carrier, such as a transition metal ion or an organic radical, have been described. However, except for GdIII, very little has been reported about the magnitude of the interactions. Indeed, for these ions both the ligand-field effects and the exchange interactions between the magnetic centers become relevant in the same temperature range; this makes the analysis of the magnetic behavior of such compounds more difficult. In this study, quantitative analyses of the thermal variations of the static isothermal initial magnetic susceptibility measured on powdered samples of the [Ln(NO3)3-[organic radical]2] (Ln = DyIII and HoIII) compounds were performed. The ligand-field effects on the Ln ions were taken into account, and the exchange interactions within a molecule were treated exactly within an appropriate Racah formalism. Values of the intramolecular [Ln-aminoxyl radical] exchange parameter have thus been rigorously deduced for both the Dy Kramers and Ho non-Kramers ion-based compounds. Ferromagnetic [Ln-radical] interactions are found for both the Dy and Ho derivatives with J = 8 cm(-1) and J = 4.5 cm(-1), respectively.     

Interactions of Isoquinoline Alkaloids with Transition Metals Iron and Copper

Data on alkaloid interactions with the physiologically important transition metals, iron and copper, are mostly lacking in the literature. However, these interactions can have important consequences in the treatment of both Alzheimer’s disease and cancer. As isoquinoline alkaloids include galanthamine, an approved drug for Alzheimer’s disease, as well as some potentially useful compounds with cytostatic potential, 28 members from this category of alkaloids were selected for a complex screening of interactions with iron and copper at four pathophysiologically relevant pH and in non-buffered conditions (dimethyl sulfoxide) by spectrophotometric methods in vitro. With the exception of the salts, all the alkaloids were able to chelate ferrous and ferric ions in non-buffered conditions, but only five of them (galanthine, glaucine, corydine, corydaline and tetrahydropalmatine) evoked some significant chelation at pH 7.5 and only the first two were also active at pH 6.8. By contrast, none of the tested alkaloids chelated cuprous or cupric ions. All the alkaloids, with the exception of the protopines, significantly reduced the ferric and cupric ions, with stronger effects on the latter. These effects were mostly dependent on the number of free aromatic hydroxyls, but not other hydroxyl groups. The most potent reductant was boldine. As most of the alkaloids chelated and reduced the ferric ions, additional experimental studies are needed to elucidate the biological relevance of these results, as chelation is expected to block reactive oxygen species formation, while reduction could have the opposite effect.     

ESR study of MoY and PdMoY reduction

This paper deals with the reduction of MoY and PdMoY using ESR in order to study the effect of molybdenum on the reducibility of palladium ions. The evolution of signals of paramagnetic species of palladium (Pd3+ in 4d7 and Pd+ in 4d9) and molybdenum (Mo5+ in 4d1) was followed by EPR spectroscopy. Two paramagnetic species of Mo5+ were observed after reduction under hydrogen, the first with g// = 1.87 and the second with g// = 1.89. However, the Mo5+ ion on the zeolite exhibited various coordination symmetries upon reduction or other treatments, depending on the preparation method. The analysis of the g tensors allowed these signals to be attributed to molybdenyl ions in penta- (Mo5+(5C)) and hexacoordination (Mo5+(6C))symmetries.     

Computer Simulation of Water Clusterization on Chlorine Ions: 2. Microstructure

The molecular structure of Cl^–(H₂O) _n clusters, n = 1–60, in equilibrium with vapor, and the cluster with n = 500 was studied by the Monte Carlo method. The first hydrated layer of a cluster is formed in unsaturated water vapors. The second hydrated layer begins to be formed in saturated vapor. The position of hydrated layers is not changed with an increase in cluster size and coincides with the position of the hydrated layers of ions in aqueous solutions of weak electrolytes. Orientational order in a cluster also has the layered structure. The orientation of molecules between the layers is random. The stability of the first layer is ensured only due to direct interactions with ions, whereas the stability of subsequent layers is due to cooperative interactions between molecules and between molecules and ions. As temperature decreases, the effect of ion displacement to the cluster surface becomes stronger.     

Synthesis,characterization, antimicrobial activity, 3D-QSAR,DFT, and molecular docking of some ciprofloxacin derivatives and their copper(II) complexes

Six new derivatives of ciprofloxacin compounds and their copper(II) complexes were synthesized, characterized by spectroscopic methods (ultraviolet–visible [UV–vis], Fourier transform infrared [FTIR], nuclear magnetic resonance [NMR], mass spectrometry [MS], and electron paramagnetic resonance [EPR]), and tested for antibacterial activities against gram-negative and gram-positive bacteria. The data showed that ciprofloxacin derivatives act as bidentate ligands and the metal ions coordinate through the pyridone carbonyl and the carboxylate oxygen atoms. Tetragonally distorted octahedral ligand fields were assumed for all complexes based on their spectral studies. Copper(II) complexes of the synthesized ciprofloxacin derivatives revealed higher antibacterial activities against gram-positive and gram-negative bacterial species than the parent ciprofloxacin antibiotic. Furthermore, three-dimensional quantitative structure–activity relationship (3D-QSAR) models were evaluated by studying 30 antibiotic compounds of the quinolone class. Density function theory (DFT) calculations were applied to evaluate the optimized geometrical structures using the B3LYP method and 6-311G(d,p) basis set. The 3D-QSAR study revealed that there are eight optimum parameters that give the best predictive modulation with good reliability (R² = 0.996, F = 12.004, sigma = 0.426). In silico molecular docking was also performed on the derivatives, and the results revealed the presence of two types of interactions between the Escherichia coli and the derivatives, H-bonding and Van der Waals interactions, and an effective inhibition at the docked site.     

EPR, optical, infrared and Raman spectral studies of Actinolite mineral

Electron paramagnetic resonance (EPR), optical, infrared and Raman spectral studies have been performed on a natural Actinolite mineral. The room temperature EPR spectrum reveals the presence of Mn(2+) and Fe(3+) ions giving rise to two resonance signals at g = 2.0 and 4.3, respectively. The resonance signal at g = 2.0 exhibits a six line hyperfine structure characteristic of Mn(2+) ions. EPR spectra have been studied at different temperatures from 123 to 433 K. The number of spins (N) participating in the resonance at g = 2.0 has been calculated at different temperatures. A linear relationship is observed between log N and 1/T in accordance with Boltzmann law and the activation energy was calculated. The paramagnetic susceptibility (chi) has been calculated at different temperatures and is found to be increasing with decreasing temperature as expected from Curie's law. From the graph of 1/chi versus T, the Curie constant and Curie temperature have been evaluated. The optical absorption spectrum exhibits bands characteristic of Fe(2+) and Fe(3+) ions. The crystal field parameter Dq and the Racah parameters B and C have been evaluated from the optical absorption spectrum. The infrared spectral studies reveal the formation of Fe(3+)--OH complexes due to the presence of higher amount of iron in this mineral. The Raman spectrum exhibits bands characteristic of Si--O--Si stretching and Mg?OH translation modes.     

An EPR study of solid solutions ZnAl2O4ZnCr2O4

We studied the EPR spectra of ZnAl₂O₄-ZnCr₂O₄ solid solutions. The changes observed in the spectrum with increasing chromium concentration are attributed to the gradual development of magnetic interactions between paramagnetic ions in the solid solution. From the concentration dependence of the intensity of the isolated ions spectrum an approximate value of the range of the exchange interactions is deduced. The spectrum observed at high chromium concentrations is attributed to clusters of chromium ions coupled by exchange; the temperature dependence of its intensity indicates an antiferromagnetic character of the concentrated solid solutions.