Coordinatively Unsaturated Polynuclear Mixed-Valent Sn<Superscript>II</Superscript>–Sn<Superscript>IV</Superscript> and Cu<Superscript>II</Superscript>–Sn<Superscript>IV</Superscript> Oxo-Centered Carboxylates

The tetranuclear mixed-valent oxo-cluster [Sn^IISn^IVO(O₂CCF₃)₄]₂ (1) has been prepared by reacting SnCl₂ with AgO₂CCF₃ in a sealed ampoule at 90 °C. Alternatively, 1 was obtained by acidolysis of Ph₃SnSnPh₃ with trifluoroacetic acid in solution. The X-ray diffraction study of 1 revealed the presence of a Sn^IIOSn₂^IVOSn^II core comprised of the penta-coordinated divalent and six-coordinated tetravalent tin atoms. The ¹¹⁹Sn NMR studies confirmed the stability of the cluster in solution and the presence of two different oxidation states of tin. An acidolysis of Ph₃SnSnPh₃ in the presence of [Cu₂^II(O₂CCF₃)₄] followed by sublimation of the resulting product at 90 °C afforded the first trinuclear mixed metal Sn–Cu cluster [(C₆H₅)₂Sn₂^IVCu^IIO(O₂CCF₃)₆] (2). The X-ray diffraction analysis of 2 revealed the presence of two phenyl groups attached to the six-coordinated tin(IV) atoms and the tetragonal pyramidal environment of the copper(II) atom. Both complexes have been obtained free of exogenous ligands.     

Phase-transfer Tsuji—Trost allylation of CH-acids with the assistance of palladium complexes with bidentate P<Superscript>III</Superscript>—N—P<Superscript>III</Superscript> ligands

The Tsuji—Trost allylation of CH acids, in particular, those of the YCH₂CO₂Et type (Y = CO₂Et, C(O)Me, CN), with allylic acetates in the K₂CO₃—DMF system in the presence of palladium catalysts with ligands RN(PPh₂)₂ (R = Ph, Prⁱ, c-C₆H₁₁) is accomplished.     

Synthesis of heteropolynuclear Cu<Superscript>I</Superscript> and Pd<Superscript>II</Superscript> complexes with polymeric 2,2′-biquinoline-containing ligands and investigation of their catalytic activity in the Sonogashira couplings

A method for electrosynthesis of heteropolynuclear biquinoline-containing Cu^I and Pd^II complexes using sacrificial Cu and Pd anodes was developed. The sequence of anode dissolution (first Pd and then Cu) was important for the synthesis of the complex. The opposite sequence of dissolution resulted in oxidation of the initially formed Cu^I ions to Cu^II. The obtained Cu^I and Pd^II complexes with polymer ligands had high catalytic activity in the reaction of aryl halides with phenylacetylene giving rise to a C(sp²)-C(sp) bond. The yield of arylphenylacetylene in the presence of 0.1 mol.% of Pd catalyst in relation to the starting halide was 50–90% depending on the nature of the aryl halide.     

Two oxamido-bridged binuclear Cu–M complexes (M = Co<Superscript>II</Superscript>, Cu<Superscript>II</Superscript>): synthesis,crystal structures and magnetic studies

Two novel oxamido-bridged macrocyclic complexes, [LCu(CH₃OH)Co(phen)₂](ClO₄)₂·CH₃OH (1) and [LCu(CH₃OH) Cu(phen)₂](ClO₄)₂·CH₃OH (2) (where H₂L = 2,3-dioxo-5,6:13,14-dibenzo-7,10,12-trimethyl-1,4,8,11-tetraazacyclo-tetradeca-7,12-diene, phen = 1,10-phenanthroline), have been prepared by stepwise synthesis and characterized. In both complexes, each Cu(II) atom from the precursor ligand CuL is connected to a Co(II) (or Cu(II)) atom via the exo–cis oxygen atoms, resulting in a binuclear subunit. Magnetic susceptibility measurements in the 2–300 K temperature range have been taken for the two complexes.     

Dependence of enthalpies of formation of the Cu<Superscript>2+</Superscript> complexes with glycinate ions on the composition of water—dimethylsulfoxide solvent

Enthalpies of the complexing reactions of copper (II) with glycinate ions in mixtures of water with dimethylsulfoxide (DMSO) containing up to 0.9 mole parts of organic component (298 K) were obtained using a titration calorimeter. It was established that upon an increase in the DMSO content, the exothermicity of complexing increases at the first and second steps of the coordination. The obtained results were analyzed from the viewpoint of the solvation approach, based on the thermodynamic characterization of all reagents. It was shown that the main origin of the increase in the exothermicity of the complexing reactions is a weakening of ligand solvation when the DMSO concentration increases.     

Quantum chemical studies on anion specificity of C<Superscript>α</Superscript>NN motif in functional proteins

Anion binding C^αNN motif is found in functionally important regions of protein structures. This motif based only on backbone atoms from three adjacent residues, recognizes free sulphate or phosphate ion as well as phosphate groups in nucleotides and in a variety of cofactors. The mode of anion recognition and microscopic picture of binding interaction remains unclear. Here we perform self-consistent quantum chemical calculations considering sulphate and phosphate bound C^αNN motif fragments from crystal structures of functional proteins in order to figure out microscopic basis of anion recognition. Our calculations indicate that stability and preference of the anion in the motif depends on the sequence of the motif. The stabilization energy is larger in case of polar residue containing motif fragment. Nitrogen atom of the polar residue of motif mainly participates in the coordination at the lowest energy levels. Anion replacement decreases stabilization energy along with coordination between motif atoms and oxygen atoms of anion shifted to higher energies, suggesting preference of the motif residues to specific anion. Our analysis may be helpful to understand microscopic basis of interaction between proteins and ionic species.     

Thermodynamics of the formation of Cu<Superscript>2+</Superscript>–glycyl-glycyl-glycine complex in water–ethanol solutions at 298 K

The stability constants of monoligand complexes of copper(II) ions with glycyl-glycyl-glycine zwitterions (triglycine, HL^±) and triglycinate ions (L^?) in a water–ethanol solvent with 0.0, 0.1, 0.3, and 0.5 mole fractions of ethanol at an ionic strength of 0.1 created by sodium perchlorate and temperature Т = 298.15 K are determined by means of potentiometric titration. It is found that an increase of ethanol content improves the stability of the investigated complexes, due mainly to the resolvation of ligands.     

Synthesis and structures of Cu<Superscript>I,II</Superscript> complexes with a 2,2´-bipyridine derivative bearing a (+)-3-carene moiety

The complex salt {[CuL₂][Cu₄I₆]?MeCN}_n (1) and the compound [Cu₄L₃I₄]?3 MeCN (2) (L is a chiral ligand bearing a natural monoterpene (+)-3-carene moiety) were synthesized. The crystal structures of compounds 1 and 2 were determined by X-ray diffraction. The structure of compound 1 consists of complex cations [CuL₂]²⁺ (N₃O₂ polyhedron is a trigonal bipyramid) and Cu^I coordination polymers (CuI₄ polyhedron is a tetrahedron) as anions. The experimental magnetic moment μ_eff at 300 K is 1.90 μ_B, which is consistent with the X-ray diffraction data and the assumption that compound 1 is mixed-valence. The structure of compound 2 comprises a tetranuclear Cu^I complex, in which three Cu atoms are coordinated by two N atoms of the ligand L and two I atoms, and the fourth Cu atom is coordinated by four I atoms (coordination polyhedra are distorted tetrahedra). Compounds L and 2 were found to influence the viability of human laryngeal carcinoma cells (Hep2). The IC₅₀ value for complex 2 (13.0±1.7 μM) is substantially smaller than IC₅₀ for compound L (30.5±0.5 μM).     

Iridium metal–polymer complexes based on bipyridyl ligands

Novel polymer macroligands—copolyamides containing different quantity of bipyridyl groups—were obtained from 4,4′-diamino-2,2′-bipyridine, 4,4′-diaminodiphenyl ether and terephthaloyl-bis(3-methoxy-4-hydroxybenzoic) acid dichloroanhydride by low-temperature polycondensation. Metal–polymer complexes with different content of Ir(ppy)2 were obtained by the interaction between polymer ligand and [Ir(ppy)2Cl]₂ (ppy–2-phenylpyridine). The properties of films and coatings based on these materials were studied.     

Cu<Superscript>I</Superscript> complexes with 2,2′-biquinolyl-containing polymeric ligands as electrocatalysts for the oxidative coupling of alkynes in the presence of dioxygen

Electrocatalytic oxidative coupling of terminal alkynes in the presence of atmospheric oxygen catalyzed by Cu^I complexes with polymeric biquinolyl ligands leads to the corresponding diynes in high yield. The reaction proceeds under mild conditions at a potential of Cu^II/Cu^I electroreduction (−0.55 V vs. Ag/AgCl/KCl) and is accompanied by O₂ reduction to H₂O.     

Quantum chemical study of cerium-subgroup LnF 6 3? complexes

Structural, energetic, and electronic properties of LnF ₆ ^3? (Ln = Ce-Gd) complexes have been calculated using density functional theory in the local-density approximation.     

Generation of peptide radical dications via low-energy collision-induced dissociation of [Cu<Superscript>II</Superscript>(terpy)(M + H)]<Superscript>·3+</Superscript>

The first example of the formation of hydrogen-deficient radical cations of the type [M + H](.2+) is demonstrated to occur through a one-electron-transfer mechanism upon low-energy collision-induced dissociation (CID) of gas-phase triply charged [Cu(II)(terpy)(M + H)](.3+) complex ions (where M is an angiotensin III or enkephalin derivative; terpy = 2,2':6',2'-terpyridine). The collision-induced dissociation of doubly charged [M + H](.2+) radical cations generates similar product ions to those prepared through hot electron capture dissociation (HECD). Isomeric isoleucine and leucine residues were distinguished by observing the mass differences between [z(n) + H](.+) and w(n)(+) ions (having the same residue number, n) of the Xle residues. The product ion spectrum of [z(n) + H](.+) reveals that the w(n)(+) ions are formed possibly from consecutive fragmentations of [z(n) + H](.+) ions. Although only the first few [M + H](.2+) species have been observed using this approach, these hydrogen-deficient radical cations produce fragment ions that have more structure-informative patterns and are very different from those formed during the low-energy tandem mass spectrometry of protonated peptides.     

X-ray emission study of the electronic structure of binuclear niobium complexes with (S<Subscript>2</Subscript>)<Superscript>2</Superscript>–disulfide bridging ligands

The electronic structure of binuclear niobium complexes [Nb₂S₄(acac)₄] and K₄[Nb₂S₄(ox)4] is studied by X-ray emission fluorescent spectroscopy and quantum chemistry techniques. Data on the partial atomic composition of highest occupied molecular orbitals of the complexes are obtained. The energy positions of bonding and antibonding frontier molecular orbitals observed in the X-ray emission spectra of binuclear [Nb₂((S₂)^2–)₂]⁴⁺ clusters are determined by the analysis of overlap populations.     

Study on the preparation and biological evaluation of <Superscript>99m</Superscript>Tc–gatifloxacin and <Superscript>99m</Superscript>Tc–cefepime complexes

The aim of this work is the development of new radiopharmaceuticals for imaging infection and inflammation in human. Gatifloxacin (fluoroquinolone derivative) and cefepime (cephalosporine derivative) are antibiotics used to treat bacterial infections were investigated to label with one of the most important radioactive isotopes (technetium-99m). The reaction parameters that affect the labeling yield such as substrate concentration, stannous chloride dihydrate concentration, pH of the reaction mixture, and reaction time were studied to optimize the labeling conditions. Maximum radiochemical yield of ^99mTc–gatifloxacin (90  ± 1.8%) complex was obtained by using 50 μg SnCl₂·2H₂O and 2.5 mg gatifloxacin at pH 10 while ^99mTc–cefepime was prepared at pH 8 with a maximum radiochemical yield of 98  ± 1.4% by adding ^99mTc to 5 mg cefepime in the presence of 50 μg SnCl₂·2H₂O. Biological distribution of ^99mTc–gatifloxacin and ^99mTc–cefepime was carried out in experimentally induced infection rats, in the left thigh, using Escherichia coli. Both thighs of the rats were dissected and counted and the ratio of bacterial infected thigh/contralateral thigh was then evaluated. T/NT for both ^99mTc–gatifloxacin and ^99mTc–cefepime was found to be 4.5  ± 0.3 and 8.4  ± 0.1, respectively, which was higher than that of the commercially available ^99mTc–ciprofloxacin. The abscess to normal muscle ratio indicated that ^99mTc–cefepime could be used for infection imaging. Besides, in vitro studies showed that ^99mTc–cefepime can differentiate between bacterial infection and sterile inflammation.     

Photo-induced reduction of Cr<Superscript>6+</Superscript> by the hybrid systems “Cu<Superscript>II</Superscript> complex with Schiff base and TiO<Subscript>2</Subscript>”: dependence on irradiation wavelength

The synthesis of novel Cu^II complexes with a Schiff base obtained by condensation of salicylaldehyde and an l-aspartic acid ester are described. The physicochemical properties of the complexes were compared with those of related Cu^II complexes obtained earlier. All the complexes studied were characterized by elemental analysis as well as by IR, UV-Vis, and EPR spectroscopies. The activity of the complexes and their hybrid systems (HS) with TiO₂ in visible-light-driven photocatalysis in organic solvents was investigated. After irradiation with visible light, the complexes and corresponding HS reduce Cr⁶⁺ to Cr³⁺ more efficiently than bare TiO₂. To determine the molecular orbital compositions and energies and to explain the electronic spectra and redox properties of the systems studied, density functional calculations of the optimized structures of representative model complexes were performed.     

Studies on a new dinuclear Co<Superscript>II</Superscript>–pterin complex exhibiting reactivity towards phenylalanine and bromobenzene

2-Pivaloylamino-6-acetonyl-isoxanthopterin (1, ) has been reacted with under suitable conditions for synthesizing the new compound ] (2). It has been characterized by elemental analysis, electrospray ionization mass spectrometry, magnetic susceptibility measurement, different spectroscopic techniques, and cyclic voltammetry. Molecular mechanics (MM2) method provided with its optimized geometry (having lowest steric energy), consistent with the above data; the optimized bond lengths and bond angles data tally with the literature X-ray structural data. Reactivity of (2) towards phenylalanine in the presence of in methanol has been followed both kinetically and stoichiometrically; a reasonable amount of tyrosine could be recovered from the reaction medium. The negative value (−274.0 J mol⁻¹ indicates an associative pathway for this process. (2) is also able to react with bromobenzene as indicated by time-dependent absorption spectra as well as product identification. Efficacy of the pterin ligand residue of (2) in rendering the latter reactive towards the above-mentioned organic compounds, has been discussed on the basis of experimental evidence.     

Quantum chemical study on the thermal rearrangements of HNCRCR''''CO

MINDO/3 molecular orbital theory has been used to study the thermal rearrangements of HNCRCR'CO.The results obtained show that the activation energy of this rearrangement depends on the migrating group R and the group R'.     

Thermodynamics of the complex formation between Cu<Superscript>2+</Superscript> and triglycine in water–ethanol solutions at 298 K

Thermodynamic functions Δ_r H, Δ_r G, and TΔ_r S of the complex formation between Cu²⁺ and triglycine in water–ethanol solutions are calculated on the basis of calorimetric data. It is found that raising the concentration of EtOH results in a monotonic increase in the exothermic effect of [CuHL]²⁺ complex formation due to the weakening of triglycine solvation with the mutual compensation of ion solvation contributions. The enthalpy of [CuL]⁺ complex formation has an exothermic maximum at 0.1?0.3 molar fractions of EtOH due to competition between the solvation contributions from ions and ligands.     

Optimization of the labeling yield by determination of the Cu<Superscript>+</Superscript>–acetonitrile complex constant in Cu<Superscript>+</Superscript>-catalyzed nucleophilic exchange reactions in mixed solvent conditions

To apply the Cu⁺-assisted nucleophilic exchange based radioiodination of aromatic compounds for more lipophilic compounds the reaction is carried out in mixed solvent conditions. Due to its physicochemical properties acetonitrile is an attractive solvent. Although acetonitrile forms complexes with Cu⁺ decreasing the labeling yield. This article describes a method for the determination of the complex constant at labeling temperature based on a Lineweaver–Burk approach, relating the reaction rate constant and the concentration of precursor in presence of different amounts of acetonitrile. The method also allows to calculate the adjusted amount of copper salt in order to obtain the same high labeling yield as obtained in absence of acetonitrile.     

Synthesis,X-ray analysis,and quantum-chemical DFT study of features in formation of a binuclear phenanthroline complex with a V<Superscript>IV</Superscript>–O–V<Superscript>V</Superscript> core

A new mixed-valence complex [(O)(phen)₂V^IV(μ-O)V^V(O)phen)(mal)]⁺ was synthesized and characterized by the X-ray structural analysis. Its geometric structure was simulated by the DFT M06/6-31G(d,p) method. Comparison of calculated and experimental data made it possible to draw a conclusion on the oxobridging nature of the bond between vanadium fragments and to confirm the value of the target compound charge. The energy characteristics of cation formation reactions in solution were estimated. It was found that the oxidation of V^IV to V^V assists subsequent substitution of ligands. Joining [(O)V^IV(phen)₂]²⁺ and [(O)V^V(O)(phen)(mal)]^– particles proceeds by the donor-acceptor mechanism.