Search

Mono- and binuclear Cu(+1/+2) complexes of bis-5-(2-pyridyimethylene)-2-selenohydantoins were obtained by the reactions of corresponding ligands with copper(+2) chloride or perchlorate in BuOH/DCM mixtures.

Freon matrices affected the nature of species stabilized upon the X-ray irradiation of frozen 1,7-dioxaspiro[5,5]undecane (DOSU)/CF3CCl3 or DOSU/CFCl3 solutions at 77 K. This manifested in the stabilization of a ring-closed DOSU radical cation (RC) with an absorption maximum at ∼440 nm in CF3CCl3 versus a paramagnetic intermediate with no absorption in this spectral region and a notably different EPR spectrum in CFCl3. Interestingly, the ultimate product in a sequence of photochemical and thermally induced transformations was the same in both matrices: a distonic DOSU RC with a terminal alkyl fragment afforded upon C–C bond cleavage at the spiro carbon atom.

The data on the structure and the features of the photochemical reactions for radical cations (RCs) derived from various oxiranes (epoxides) that can be stabilized in Freon matrices at 77 K are summarized. The nature of the RCs and the products of their photochemical transformations have been determined via quantum chemistry, electron paramagnetic resonance (EPR) and low-temperature UV/Vis spectroscopy. For the RCs, it is shown that, depending on the structure of the precursor molecule, transitions between their ring-open and ring-closed forms, deprotonation reactions affording C-centered radicals and more complex transformations can take place when exposed to light. Possible explanations of the observed effects are discussed.

Synthesis, characterization (HRMS, NMR, EPR, UV-Vis spectroscopy, and electrochemistry) and in vitro cytotoxic investigation of a series of new ferrocene-containing derivatives, based on ω-ferrocene carboxylic acids and 2-alkylthioimidazolin-4-ones as well as their copper coordination compounds, have been reported. A series of ferrocene–imidazolone conjugates with different lengths and donor properties of the linker fragments have been synthesized; all the obtained compounds were studied in complexation reactions with copper(I) and copper(II) perchlorates. It is shown that the synthesised conjugates rapidly and efficiently convert coordinating copper ions into the Cu(+1) oxidation state, but a change in the length of the linker in ferrocene–imidazolone ligands fundamentally changes the ratio of products formed as a result of iron oxidation/copper reduction and complexation by various mechanisms. After comparing the data on the qualitative and quantitative composition of the reaction mixtures and the kinetic characteristics of the processes occurring in the mixtures of ferrocene–imidazolones with copper(II) perchlorate, a scheme of the ongoing reactions was proposed which may fully explain all the observed processes and products. It has been shown that the obtained bimetallic Cu/Fe coordination compounds are more toxic than cisplatin and induce apoptosis in micromolar concentrations on Hek-293 and MCF-7 cell lines.

A series of 73 ligands and 73 of their Cu+2 and Cu+1 copper complexes with different geometries, oxidation states of the metal, and redox activities were synthesized and characterized. The aim of the study was to establish the structure-activity relationship within a series of analogues with different substituents at the N(3) position, which govern the redox potentials of the Cu+2/Cu+1 redox couples, ROS generation ability, and intracellular accumulation. Possible cytotoxicity mechanisms, such as DNA damage, DNA intercalation, telomerase inhibition, and apoptosis induction, have been investigated. ROS formation in MCF-7 cells and three-dimensional (3D) spheroids was proven using the Pt-nanoelectrode. Drug accumulation and ROS formation at 40-60 μm spheroid depths were found to be the key factors for the drug efficacy in the 3D tumor model, governed by the Cu+2/Cu+1 redox potential. A nontoxic in vivo single-dose evaluation for two binuclear mixed-valence Cu+1/Cu+2 redox-active coordination compounds, 72k and 61k, was conducted.

The structure and nature of the underlying photochemical transformations of radical cations formed upon irradiation of exo-2,3-norbornene oxide solutions in a CF3CCl3 matrix at 77 K have been established using electron paramagnetic resonance and UV-visible absorption spectroscopy as well as quantum chemical calculations. For photochemical reactions proceeding in this system, a mechanism has been proposed, which consists in the transformation of the initially formed ring-open radical cation into a ring-closed C-centered radical cation, followed by photoelimination of H2.

Photocatalytic activity of vanadium modified Hombikat UV 100 TiO2 was investigated in of the Rhodamine B photodegradation in a wide range of vanadium content. Structure and properties of VO2+ paramagnetic centers (PCs) formed on TiO2 surface were studied by X-band electron paramagnetic resonance (EPR). Two types of PCs, aggregated and isolated ones, were revealed and described quantitatively. EPR results in comparison with photocatalytic data allowed conclude that the most probable catalytically active centers are the isolated vanadium centers on the V-doped TiO2 surface.

A treatment of the ligands, 3‑(2‑methylbutyl)‑5‑pyridylmethylene-substituted 2‑thio‑3,5‑dihydro‑4Н‑imidazole‑4‑one (L) with CuCl2·2H2O in MeOH/CH2Cl2 or Cu(acac)2 in MeOH/CH2Cl2 affords to binuclear complexes with the [L-H]2Cu+1.5Cu+1.5Cl or [L-H]2CuICuI composition, respectively. X-ray crystallography demonstrated close Cu-Cu interaction for the first complex and the absence of Cu Cu bonding for the second one.

Synthesis, characterization (HRMS, NMR, EPR, XANES, UV-Vis spectroscopy, and electrochemistry), DNA and BSA binding and in vitro biological screening of two new ferrocene-incorporated thiohydantoin derivatives (5 and 6) and their copper coordination compounds are reported. The ferrocene-based thiohydantoin derivatives were prepared by copper-catalyzed azide alkyne cycloaddition reactions between alkynyl ferrocenes and 5-(Z)-3-(2-azidoethyl)-2-(methylthio)-5-(pyridin-2-ylmethylene)-1H-imidazol-4H-one. Alkynyl ferrocenes necessary for these syntheses were prepared by new procedures. Intermolecular redox reactions between the ferrocene fragment and copper(+2) coordinated ions were studied by different methods to determine the mechanism and kinetic constants of redox processes. Ferrocene-containing imidazolones (5 and 6) and their copper complexes were also tested for their in vitro cytotoxic activity against MCF-7 and A-549 carcinoma cells, and also against the noncancerous cell line Hek-293. The results showed modest cytotoxicity against the subjected cancer cell line compared with cisplatin. The ability of the obtained compounds to cause DNA degradation and cell apoptosis was investigated, and the distribution of cytosol/pellets was studied by AAS.

By employing EPR and UV/VIS spectroscopy and quantum chemical techniques, we demonstrated that the radical cations of cyclohexene oxide were stabilized upon radiolysis in freonic matrices at 77 K in their distorted form (with the C–C bond in the oxirane fragment elongated to 0.179 nm). Upon the action of light in the absorption band of these radical cations (λmax ∼ 480–490 nm), they undergo deprotonation, successively yielding 7-oxabicyclo[4.1.0]heptan-3-yl and 7-oxabicyclo-[4.1.0]heptan-2-yl radicals.

It has been established that the photoinduced process observed in EPR and in optical absorption spectra for 1,4-dithiane radical cations in the CF3CCl3 matrix at 77 K can be ascribed to a “boat”—“twist boat” conformational transition.

A reversible photochemical transition between an open pseudoallylic form and a cyclic form has been discovered for methylthiirane radical cations in the matrices of CFCl3 and CF3CCl3 at 77 K.

The radical cations of aziridine can be stabilized in the matrix of CF3CCl3 at 77 K in a cyclic form.

Metal/carbon nanocomposites have been studied by electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS). EPR study has revealed the existence of delocalized electrons on the carbon shells and the presence of reduced paramagnetic states of nickel in the nickel/carbon nanocomposite. XPS has detected the change in the atomic magnetic moment of the metal. For polycarbonate as an example, conditions for modification of the polymer composition with small amounts of metal/carbon nanoparticles (0.01–0.0001%) have been determined. On the basis of the data obtained, a mechanism of the effect of metal/carbon nanoparticles on the structure and properties of polymer materials has been suggested.

It has been established that transformations of azetidine radical cations observed in freonic matrices under the action of light with λ = 436 nm (T = 77 K) are associated with C-N bond cleavage which corresponds to the cyclic form yielding a mixture of open distonic C-centered radical cations of the following structure: ·CH2CH2CH=NH2+

Correction for ‘New ferrocene-based 2-thio-imidazol-4-ones and their copper complexes. Synthesis and cytotoxicity’ by D. A. Guk et al., Dalton Trans., 2018, DOI: 10.1039/c8dt03164a.

Values of the translational diffusion coefficient of a spin probe (2,2,6,6-tetramethyl-4-oxypiperidine-1-oxyl) are determined via cyclic voltammetry, chronoammetry, and EPR in ionic liquid (1-butyl-3methylimidazolium tetrafluoroborate) at 295 K. They are found to be (8 ± 3) × 10−12, (9 ± 3) × 10−12, and (11 ± 4) × 10−12 m2/s, respectively.

We have studied the rotational and translational diffusion of the spin probe 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPOL) in five imidazolium-based room-temperature ionic liquids (RTILs) and glycerol by means of X-band electron paramagnetic resonance (EPR) spectroscopy. Rotational correlation times and rate constants of intermolecular spin exchange have been determined by analysis of the EPR line shape at various temperatures and spin probe concentrations. The model of isotropic rotational diffusion cannot account for all spectral features of TEMPOL in all RTILs. In highly viscous RTILs, the rotational mobility of TEMPOL differs for different molecular axes. The translational diffusion coefficients have been calculated from spin exchange rate constants. To this end, line shape contributions stemming from Heisenberg exchange and from the electron-electron dipolar interaction have been separated based on their distinct temperature dependences. While the Debye-Stokes-Einstein law is found to apply for the rotational correlation times in all solvents studied, the dependence of the translational diffusion coefficients on the Stokes parameter T/η is nonlinear; i.e., deviations from the Stokes-Einstein law are observed. The effective activation energies of rotational diffusion are significantly larger than the corresponding values for translational motion. Effects of the identity of the RTIL cations and anions on the activation energies are discussed.

It has been established that reversible photoinduced transformations of 2,3-dimethyloxirane and methyloxirane radical cations (RCs), observed in freonic matrices at 77 K, are related to the conversion between the open and cyclic forms of the RCs. For the trimethyloxirane RC the action of light on the trans-isomer of the open form results in its photoinduced transformation into a C-centered radical with low quantum efficiency (≈4 × 10−3). Upon the X-ray irradiation of 2,2-dimethyloxirane in freonic matrices at 77 K, a cyclic form of the RC is stabilized (presumably, as part of a complex with matrix molecules) which transforms into a distonic C-centered RC under the action of light with the quantum yield of ≈10−3. Tetramethyloxirane RC, stabilized in its open form, is resistant to the action of light. Probable causes of the observed effects are discussed.

It has been established that, upon X-ray irradiation of various methyloxiranes in freonic matrices at 77 K, both open and cyclic (with the elongated C-C bond) forms of radical cations are stabilized. It has been shown that observed reversible photoinduced transformations of 2,3-dimethyloxirane and methyloxirane radical cations are related to the conversion between the open and cyclic forms of the radical cations with high quantum yields (0.02–0.39, depending on the oxirane and the matrix). For the trimethyloxirane radical cation the action of light on the trans-isomer of the open form results in its photoinduced transformation into a C-centered radical with low quantum efficiency (∼4 × 10−3). Tetramethyloxirane radical cations, stabilized in their open form, are resistant to the action of light. Probable causes of the observed effects are discussed. Upon the X-ray irradiation of 2,2-dimethyloxirane in freonic matrices at 77 K, a cyclic form of the radical cation is stabilized (presumably, as part of a complex with matrix molecules) which transforms into a distonic C-centered radical cation under the action of light with the quantum yield of ∼10−3.

The 13 C coupling constants in the β-and γ-positions of stable nitroxide radicals were obtained by the simulation of EPR spectra and quantum-chemical calculations.

Rotational and translational movements of 1-oxyl-2,2,6,6-tetramethyl-4-oxypiperidine (TEMPOL) spin probe in the room temperature ionic liquid (RTIL) 1-octyl-3-methylimidazolium tetrafluoroborate (omimBF4) and in two molecular solvents, 1-propanol and isopropyl benzene (cumene), have been studied by X-band electron paramagnetic resonance (EPR) spectroscopy. Rotational correlation times τ c of spin probes and the intermolecular spin exchange rate constants k e were measured from EPR spectra at different temperatures and TEMPOL concentrations, and compared with the published data. The τ c values were calculated both by known equations and from the EPR spectra simulation. Rotation movements of TEMPOL in omimBF4 cannot be described by the model of the isotropic Brownian diffusion, which is valid for conventional solvents. The correct modeling of EPR spectra in RTIL can be achieved with the assumption of different rotational mobility of the spin probe around different molecular axes. The rotational, D rot, and translational, D tr, diffusion coefficients were calculated from τ c and k e values. The Debye–Stokes–Einstein law is valid in all three solvents while the dependence of D tr on T/η is not linear in Stokes–Einstein coordinates. The effective activation energy E rot a of the rotational movements in omimBF4 is noticeably higher than the corresponding values for conventional solvents, while the effective activation energies E tr a of the translational movements are comparable in all solvents studied.

It was shown that trimethylene oxide (oxetane) radical cations were converted at 77 K into either distonic radical cations ·CH2CH2CH=OH+ or 2-oxetanyl radicals, depending on the freonic matrix used, by the action of light at λ = 546 nm and trimethylene sulfide radical cations transformed into distonic radical cations CH2CHSH+CH 2 · under 436-nm irradiation. The quantum yields of the photochemical reactions were determined. Quantum-chemical calculations on the structure and HFC constants of the radical cations and possible paramagnetic products of their transformation were performed. The reasons behind the observed difference in reactivity between the radical cations under the action of light are discussed.

The rotational mobility of Aerosil surface grafted ≡ SiNNO• radicals without adsorbate and in adsorbed carbon dioxide or sulfur hexafluoride layers was estimated at 77 K as (4–5) × 107 s−1.

Assignment of the bands in the optical absorption spectrum of ≡SiNNO• radicals grafted to activated Aerosil surface was performed. A photochemical transformation mechanism was proposed, and the quantum yields of the reaction of ≡SiNNO• radicals relevant to the long-wavelength absorption band at 77 K were determined in the absence and presence of adsorbed CO2 and SF6 on the surface. For the model radical F3SiNNO•, the parameters characterizing the equilibrium geometry of excited states and the geometry of transition states involved in the reaction were determined by quantum-chemical calculations.

Catalytic systems containing mainly mononuclear (CuCl 4 2− ) or dinuclear (Cu2Cl 6 2− ) tributylbenzylammonium chlorocuprates are prepared by adsorption on silica surfaces of different structures (Aerosil and Silokhrom). Using ESR, XANES, and electronic spectroscopy, the CuCl 4 2− ions are shown to be reduced rapidly under conditions of C-Cl bond metathesis, whereas the dinuclear chlorocuprates are relatively stable. A correlation between the number of copper ions in the chlorocuprate anion and its catalytic activity is established: the mononuclear complexes are several times more active than their dinuclear counterparts.

171 Stable organometallic compounds with a Cu(II)–C σ bond have not been described [1]. Pulse radiolysis and photolysis of divalent copper salts in aqueous solutions [2, 3] and in n -donor solvents [4] gave short-lived copper complexes with organic radicals in which the copper oxidation state was presumably two. Dissociation [2] CuR + Cu + + R • and bimolecular processes [3] 2CuR + 2Cu + + R 2 , CuR + + H 3 O + Cu 2+ + RH + H 2 O, were considered as the key routes for the destruction of these complexes. Copper(II) Organic Compounds as Intermediates of Photochemical Transformations of Quaternary Ammonium Tetrachlorocuprates E. N. Golubeva a, A. V. Lobanov a , V. I. Pergushov a , N. A. Chumakova a, and A. I. Kokorin b Presented by Academician A.L. Buchachenko February 5, 2008

The efficiency of photochemical reactions of radical cations of cyclic acetals (1,3-dioxolane, 1,3-dioxane) is measured in different Freon matrices at 77 K and the influence of the latter on the reaction path is discovered. The possible nature of the paramagnetic complexes that form in photochemical reactions of cyclic acetal radical cations in Freon-11 is suggested.

It was found that the principal photochemical reaction of 1,3,5-trioxane radical cations in freonic matrices at 77 K is their cycle-opening dissociation yielding the distonic radical cation in which the unpaired electron is preferentially localized on the oxygen atom. The dissociation of the trioxane radical cations at 77 K is characterized by high quantum yields, which vary from 0.24 to 0.36 in different matrices. The distonic radical cations produced during photolysis are unstable at 77 K and undergo further transformations, which occur at different rates in freonic matrices. The structure of the intermediates produced and a possible mechanism of the processes are discussed with the use of quantum-chemical calculation data.

Charge transfer to matrix molecules was found to be the principal photochemical reaction of the radical cations Me4Sn+· and Me6Sn 2 +· . It was shown that the difference in the localization of positive charge in the ground state of these radical cations (at the Sn-C bond in Me4Sn+· and at the Sn-Sn bond in Me6Sn 2 +· ) did not affect the pathways of their photochemical reactions.

The catalytic properties of silica-immobilized copper complexes with monoethanolamine in reactions of CCl4 addition to 1-octene and combined metathesis of C-Cl and C-H bonds in the CCl4-decane system were studied. The catalytic activity was found to be an extremal function of metal concentration. The increase of activity during the addition of CCl4 to octene as the metal content was decreased to ~0.3 wt % can be explained by an increase in the fraction of mononuclear copper complexes of differing composition. Further changes in activity were due to the formation of metal complexes with various ligand environments. A comparison between EPR data and catalytic properties suggested that the most active catalysts contained a considerable number of divalent copper complexes with a coordination environment of four nitrogen atoms, which are more effective than oxygen at increasing electron density on copper ion; this facilitated the reduction of Cu(II) to Cu(I). The above complexes are unstable because the ligands are rigidly fixed on the surface and strained structures are formed. Ligands in the coordination sphere of the metal can be readily replaced by substrate molecules, which exhibit weak solvating power.

As the formation of adsorption layers of carbon dioxide on the Aerosil surface proceeds, the character of rotational mobility of grafted radicals ≡SiOC·O changes from the anisotropic Brownian motion in vacuo to Brownian motion in a potential of 1.7–1.9 kcal mol−1. The ≡SiOC·O radicals were proposed for use as probes to study the dynamic characteristics of adsorbates on the Aerosil surface.

It has been shown that the quantum yield of the photochemical reaction of bromine replacement by the sulfo group in 1-bromo-2-hydroxynaphthalene decreases with an increase in the magnetic flux density. The participation of the triplet radical ion pair in the initiation of the chain photosubstitution reaction was directly confirmed. The lifetime of the radical ion pair was estimated.

It was found that the interaction of the modified paramagnetic defects ≡SiO(CH2)n\({\text{C}}^ \cdot\)H2 (n = 0.1) with nitromethane on a thermochemically activated silica surface at 300 K results in the formation of the following nitroxyl radicals: ≡SiO(CH2)nCH2ON(\({\text{O}}^ \cdot\))CH3 and ≡SiO(CH2)nCH2N(\({\text{O}}^ \cdot\))CH3. It was suggested that these radicals are the products of two different reactions of the modified paramagnetic defects: the first results from a reaction with free nitromethane; the second, from a reaction with nitromethane bound as complexes with diamagnetic surface defects.

The chloride complexes of copper(II) (catalysts or catalyst precursors for various reactions of halogenated hydrocarbons) were characterized using electron, EPR, and EXAFS spectroscopy. It was found that chlorocuprates occur as mononuclear ([CuCl4]2–), binuclear ([Cu2Cl6]2–), and, probably, polynuclear species in chlorobenzene solutions. The Cu–Cl bond length in [CuCl4]2– is 2.25 ± 0.2 A, which is close to the same values for crystalline tetrachlorocuprates. It was assumed that the chloride complexes of copper with counterions occur as globules in chlorobenzene.

The mechanism of photoinduced transformations of nitroxide radicals ≡SiON(O·)CH3 (I) and ≡SiOCH2N(O·)CH3 (II) obtained on the activated aerosil surface was studied. The nitroxides were photolyzed with 436-nm light at 77 K. It was shown that the action of light in the long-wavelength absorption band corresponding to the n–π* transition resulted in the dissociation of the O–N or C–N bond in radicals I or II, respectively. The quantum yields of these reactions were found to be ≈0.6 and ≈0.002, respectively.

The magnetic parameters of the ≡SiON(O·)CX3 nitroxides (X = H, D) grafted on an activated Aerosil surface were determined. The optimal geometry of the radicals was calculated and their rotational mobility was characterized. The activation energies to the rotation of radical fragments around various bonds were estimated.

The structure and activity of C–Cl bond metathesis catalysts containing CuCl2and triethylenetetramine (TETA) supported on silica were studied. The catalysts were found to contain ∼40% Cu(II) as paramagnetic complexes of the composition Cu(TETA)2Cl2and diamagnetic binuclear or polynuclear copper complexes, which are undetectable by EPR spectroscopy. The catalytic activity of the test systems in the radical reaction of C–Cl bond metathesis in the CCl4–C10H22system was maximum at a Cu(II) concentration of ∼0.5 wt % on the support. A kinetic scheme was proposed, which suggests that only mononuclear copper complexes participate at the stage of radical generation, whereas termination can also occur on binuclear or polynuclear complexes.

The chemical dynamics of≡SiOC.O radicals grafted on the silica surface was studied in the 77–290 K temperature interval. The rotation diffusion coefficients and characteristic times of rotational mobility of the radicals were estimated.

The conformation ofэSiOC·H2 radicals was determined by comparison of the ESR data and results of quantum-chemical calculations. Based on the experimental data, the characteristic times τc of rotational mobility ofэSiOC·H2 radicals grafted onto a silica surface were estimated over the temperature interval from 77 (τc = 15.8 · 10-8 s) to 295 K (τc 1.3 · 10-8 s).

Sol−gel-derived nanostructured TiO2 thin films and powders treated with Cu2+-containing solutions have been studied using electrochemical methods, ESR, XPS, and electroreflection spectroscopies. Analysis of the voltammograms in combination with ESR data has allowed us to reveal at least four types of copper species formed on the TiO2 surface after the adsorption of aqueous Cu2+ ions. These are monovalent copper ions, magnetically isolated Cu(II) ions, Cu(II) ions forming specific areas (“associates”) with a high local concentration and strong interaction between the ions, and formally diamagnetic copper hydroxide species. The last type dominates when adsorbing Cu(II) ions from solutions with pH > 5 and its fraction increase with increasing the Cu2+ ion concentration in solution. The presence of Cu(I) ions at the TiO2 surface was proved independently by XPS measurements. The appearance of them can be associated with the partial reduction of adsorbed Cu2+ ions by electrons of the TiO2 matrix. The Cu(II) ion...

Correlation times for≡SiOC·X2 radicals grafted onto activated silica surface were estimated to be 1.3·10−8s (X=H) and 2.5·10−8s (X=Me) at room temperature.

The formation of mixed CuI and CuII polynuclear complexes with dialkyl sulfide, which are active in the catalytic isomerization of chloroolefins, has been investigated by UV-Vis and ESR spectroscopy. The role of these complexes in catalysis is discussed.

New data referring to quantum efficiency of electronically excited macroradicals and radical anion reactions in various carbon- and heterochain polymers at temperatures below their glass transition or melting points are presented and discussed. The data on the mechanism of the photochemical reactions of peroxy radicals, the effect of various factors (photon energy, free volume, degree of crystallinity) on the direction and efficiency of reactions of electronically excited macroradicals are considered. The important role of photochemical chain reactions in photoageing is demonstrated. It is found that by varying photon energy, temperature, photolysis time and by taking advantage of the competition between thermal and photochemical reactions, it is possible to change the functional composition and molecular mass distribution of polymers in the desired direction.

The main mechanisms, the general features, the length of reaction chain and the effectivity of the photochemical stage of the reaction of photostimulated radical migration in the organic solids and the photostimulated migration of isopropyl benzene radicals in glass isopropyl benzene are considered.