Characterization of the high resolution ESR spectra of the methoxyl radical adducts of 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DEPMPO)

Spin-trapping investigators are largely limited by the instability of the radical adducts. Spin trap 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DEPMPO) forms very stable alkoxyl radical adducts. However, the presence of two chiral centers in the DEPMPO alkoxyl radical adduct results in two diastereomers with distinctive ESR spectra, which complicates the interpretation of the ESR spectra. We have analyzed the high resolution ESR spectra of the DEPMPO/_•OCH₃ radical adduct. DEPMPO/_•OCH₃ has been synthesized by the nucleophilic addition of alcohols to DEPMPO. The electron spin resonance (ESR) spectrum of DEPMPO/_•OCH₃ in oxygen-free methanol solution reveals superhyperfine structure with hyperfine coupling constants as small as 0.3 G. In order to simplify the analysis of the electron spin resonance (ESR) spectrum, we synthesized the DEPMPO/_•OCD₃ radical adduct. Computer simulation of the DEPMPO/_•OCD₃ ESR spectrum revealed two diastereomers. Hyperfine coupling constants of γ-protons and ₁₇O from the -OCH₃ group were also determined. ESR spectra of DEPMPO/_•OCH₃ in phosphate buffer have also been characterized. The presence of specific hyperfine couplings from the -OCH₃ group can be used for the unambiguous identification of the DEPMPO/_•OCH₃ radical adducts. We suggest that the analysis of high resolution ESR spectra can be used for the unambiguous characterization of DEPMPO radical adducts.     

Catalytic reduction of acetylene in the presence of molybdenum and iron clusters, including FeMo cofactor of nitrogenase

Acetylene was reduced by zinc amalgam in the presence of three synthetic polynuclear complexes: {[Mg₂Mo₈O₂₂(OMe)₆(MeOH)₄]⁻²·[Mg(MeOH)₆]²⁺}6MeOH (I), (Bu₄N)₂[Fe₄S₄(SPh)₄] (II), [Me₄N][VFe₃S₄Cl₃(DMF)₃]·2DMF (III) and the iron-molybdenum cofactor of nitrogenase Azotobacter vinelandii MoFe₇(S²⁻)₉·homocitrate, FeMo-co (IV). Thiophenol was found to greatly facilitate the reaction in the presence of complexes I, II, IV. The reaction is catalytic and for I and IV proceeds at the amalgam surface. Thiophenol seems to increase the adsorption of the complexes, serving as an electron bridge to transfer electrons to the catalyst. In the case of II a homogeneous reduction of the substrate occurs presumably after the cluster reduction at the surface and with III the catalytic reduction proceeds only under the action of sodium amalgam; no thiophenol cocatalytic action is observed. Relevance to N₂ enzymatic reduction is discussed.     

Hydroxyl radical generation and lipid peroxidation in C2C12 myotube treated with iodoacetate and cyanide

To mimic exercise-induced events such as energetic impairment, free radical generation, and lipid peroxidation in vitro, mouse-derived C₂C₁₂ myotubes were submitted to the inhibition of glycolytic and/or oxidative metabolism with 1 mM iodoacetate (IAA) and/or 2 mM sodium cyanide (CN), respectively, under 5% CO₂/95% air up to 180 min. Electron spin resonance (ESR) analysis with a spin-trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) revealed time-course increases in spin adducts from hydroxyl radical (DMPO-OH) and carbon-centered radical (DMPO-R) in the supernatant of C₂C₁₂ myotubes treated with the combination of IAA + CN. In this condition, malondialdehyde (MDA) and lactate dehydrogenase (LDH) were released into the supernatant. By the addition of iron-chelating 1 mM deferoxamine to the C₂C₁₂ preparation with IAA + CN, both ESR signals of DMPO-OH and DMPO-R were completely abolished, and the release of MDA and LDH were significantly reduced, while cyanide-resistant manganese superoxide dismutase had neglegible effects on these parameters. Hence, a part of the injury of C₂C₁₂ myotube under IAA + CN was considered to result from the lipid peroxidation, which was induced by hydroxyl radical generated from iron-catalyzed systems such as the Fenton-type reaction. This in vitro model would be a helpful tool for investigating the free radical-related muscle injury.     

Organometallic amphiphiles: novel mechanisms for redox chemical control of aggregation behavior

Many natural and synthetic organic amphiphiles have been discovered, prepared, and/or characterized. Aggregation behavior has been studied for many of these monomers. Very few of these many amphiphiles are organometallic compounds and almost nothing is known about this novel group of amphiphiles. Under appropriate circumstances, aggregation of certain organometallic amphiphile monomers can be controlled by use of redox switching. Compounds which are not amphiphilic can be made so and amphiphilic compounds can be deprived of this property by appropriate alterations in the metal ion's oxidation state. Redox-switched aggregation-deaggregation behavior is described for bis(hexadecycloxy)-1,10-phenanthrolinium perchlorate (2), its nickel complex (3), [CH₃(CH₂)₁₅NH₂]₂Ag⁺AcO⁻ (4) and bis(hexadecylamine)copper dichloride (5), chloride acetate (6) and diacetate (7), all of the general formula: [CH₃(CH₂)₁₅NH₂]₂Cu²⁺X₂². Two completely new switching mechanisms are disclosed for the first time which involve electron transfer from dilute aqueous sugar solutions or from solid zinc metal which are effective in collapsing [CH₃(CH₂)₁₅NH₂]₂Cu²⁺X₂²⁻ vesicles.     

Spectral and electrochemical properties of vanadyl hexadecafluorophthalocyanine

A vanadyl complex with perfluorinate phthalocyanine, VOPcF₁₆, was prepared. The monomer-dimer solvent dependence was confirmed based on the solvent effect for the Q-band position-that is, VOPcF₁₆ exists as a monomer in a nonpolar solvent such as benzene, but dimerizes in a polar solvent such as acetone. Electron spin resonance data also supported the solvent dependence found. In addition, the substituent effect of fluorine atoms on the redox properties was investigated by measuring the cyclic voltammograms in dichloromethane. On the reduction side, three redox couples were observed, the first two of which were assigned as being due to the reduction of the phthalocyanine ring (to LUMO), whose potentials are 0.4–0.5 V higher than those of the tetra-t-butyl and octabutoxy derivatives, VOPc(t-Bu)₄ and VOPc(O-n-Bu)₈.     

Monomeric and dimeric mixed-ligand copper(II) complexes of 2,2′-bipyridine/1,10-phenanthroline and 1-methylimidazole with imidazoles as catalysts for superoxide dismutation

Monomeric complexes [Cu(LL)(L′)(NO₃)₂] (where LL is 2,2′-bipyridine or 1,10-phenanthroline and L′ is 1-methylimidazole) and dimeric complexes [Cu₂(LL)₂(L″)]NO₃ (where L″ is an anion of imidazole or 2-methylimidazole) have been synthesized. These complexes show a d-d transition in the range of 600 to 710 nm. The infrared spectra of monomeric complexes show that the NO₃⁻ is coordinated to copper as a monodentate ligand through an oxygen atom. The ESR spectra of monomeric complexes indicate that the ligands are bonded in axial environment around copper (square pyramidal geometry) with three nitrogen donors occupying an equatorial plane. The ESR spectra of dimeric complexes show a broad signal at about G = 2 with an additional weak signal at about G = 4. This suggests that two copper atoms are in close proximity of < 7 Å. The ESR studies reveal that the formation of imidazolate-bridged binuclear copper(II) complexes from [Cu(LL)(L′)(NO₃)₂] and imidazole is pH dependent with apparent pK_a values of 8.25 to 8.30. The superoxide dismutase activity of ICu(phen)(L′)(NO₃)₂], [Cu(bipy)(L′)(NO₃)₂], and [Cu₂(bipy)₂(L′)₂(L″)]NO₃ has been measured and the latter two complexes show better activity than the former complex.     

Electrochemistry and spectroelectrochemistry of a linear triiron cluster

This work reports electrochemical and spectroelectrochemical studies of a unique linear triiron cluster carbonyl complex, Fe₃(CO)₇L₂, where L is a -diazothioketone. Oxidation and reduction reactions have been observed in non-aqueous media over the temperature range −40 to 20 °C by differential pulse voltammetry, cyclic voltammetry, thin-layer, UV-Vis spectroelectrochemistry and ESR spectrometry. The sequence of the individual electron-transfer steps comprising the overall redox process is described, and a comparison between the electrochemistry of different non-linear ironcarbonyl complexes is discussed. A single one electron reduction produces the radical anion, [Fe₃(CO)₇L₂]-, which decomposes at temperatures greater than −10 °C to species which are reduced at a more negative potential, an ECE mechanism. A single one-electron oxidation produces the radical cation, [Fe₃(CO)₇L₂]⁺, which is unstable, decomposing completely at room temperature, an EC mechanism. Spectroscopic evidence indicates that in non-bonding solvents, the Fe₃(CO)₇L₂ framework remains intact at low temperatures for both the anion and cation radical produced electrochemically with radical stability higher than might be expected for a linear structure. Observations indicate only strongly bonding solvents disrupt the structure. Low temperature stability occurs at relatively high temperatures, with the cation radical less than stable and vulnerable to strongly bonding solvents.     

Manganese(II) complexes of an acyclic phenol-based dinucleating ligand with four methoxyethyl chelating arms: synthesis, structure, magnetism and electrochemistry

Dinuclear manganese(II) complexes [Mn₂(bomp)(PhCO₂)₂]BPh₄ (1), [Mn₂(bomp)(MeCO₂)₂]BPh₄ (2), and [Mn₂(bomp)(PhCO₂)₂]PF₆ (3) were synthesized with a dinucleating ligand 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-methylphenol [H(bomp)]. Dinuclear zinc complex [Zn₂(bomp)(PhCO₂)₂]PF₆ (4) was also synthesized for the purpose of comparison. X-ray analysis revealed that the complex 1·CHCl₃ contains two manganese ions bridged by the phenolic oxygen and two benzoate groups, forming a μ-phenoxo-bis(μ-benzoato)dimanganese(II) core. Magnetic susceptibility measurements of 1–3 over the temperature range 1.8–300 K indicated antiferromagnetic interaction (J=−4 to −6 cm⁻¹). Cyclic voltammograms of 3 showed a quasi-reversible oxidation process at +0.9 V versus a saturated sodium chloride calomel reference electrode, assigned to Mn^IIMn^II/Mn^IIMn^III.     

Kinetics of ligand substitution in bis(N-alkylsalicylaldiminato)nickel(II) complexes: A search for kinetically-effective aromatic ring stacking

The square-planar bis chelate complexes Ni(R-sal)₂ (= bis(N-alkyl)salicylaldiminato)nickel(II)) with R = (CH₂)₂Ph (I; Ph = phenyl), (CH₂)₃Ph (II), (CH₂)₄Ph (III) and (CH₂)₂(4-hydroxyphenyl) (IV) were prepared and characterized. ComplexesII and III meet the steric requirements for intramolecular aromatic ring stacking. Stopped-flow spectrophotometry was used to study the kinetics of ligand substitution in complexesI–IV by H₂salen (=N,N′-disalicylidene-ethylenediamine) in acetone. For the substitution of the two bidentate ligands in Ni(R-sal)₂ only one step is kinetically observed which follows a second-order rate law, rate =k[H₂salen] [Ni(R-sal)₂], with k = 43.4 (I), 64.0 (II), 87.0 (III) and 49.5 (IV) M⁻¹ s⁻¹ at 298 K. It is found, therefore, that the size of k does not change significantly upon lengthening of the alkane chain in Ni(Ph(CH₂)_nsal)₂ from n = 2 to 4 and that there is no kinetic evidence for intramolecular stacking interactions. The equilibrium constants and thermodynamic parameters for the formation of the bis adductsIII·(py)₂ and III·(MeOH)₂ in acetone are reported.     

Spectroscopic and electrical properties of the [W(C3Se5)3] anion complex (C3Se5 = 1,3-diselenole-2-selone-4,5-diselenolate) and the oxidized species

[NBuⁿ₄]₂[W(C₃Se₅)₃] (C₃Se₅²⁻ = 1,3-diselenole-2-selone-4,5- diselenolate(2−)) was prepared by the reaction of Na₂[C₃Se₅] with WCl₆ in ethanol, followed by addition of [NBuⁿ₄]Br. The cyclic voltammogram in dichloromethane exhibits two oxidation peaks at −0.04 and +0.03 V (versus SCE). The complex reacted with [Fe(C₅Me₅)₂][BF₄], iodine or [TTF]₃[BF₄]₂ (TTF^·+ = the tetrathiafulvalenium radical cation) in acetonitrile to afford the oxidized complexes [Fe(C₅Me₅)₂]_0.5[W(C₃Se₅)₃], [NBuⁿ₄]_0.1[W(C₃Se₅)₃] and [TTF]_0.5[W(C₃Se₅)₃], respectively. Current-controlled electrochemical oxidation of the complex in acetonitrile gave [NBuⁿ₄]_0.6[W(C₃Se₅)₃]. The oxidized complexes exhibit electrical conductivities of 4.7×10 ⁻⁵−1.5×10⁻³ S cm⁻¹ at room temperature measured for compacted pellets. Electronic absorption, IR and ESR spectra of these complexes are discussed.     

Formation of dioxygen complexes of transition metal chelates in oxygen saturated aprotic solvents. Cyclic voltammetric evidence at a micro glassy carbon disk electrode

Cyclic voltammetry at a micro electrode of Co(II) salen, Fe(II) salen, electrode generated Fe(II)(acac)₂, Fe(II) (salicylaldehyde)₂, Fe(II) (salicylaldoxime)₂, Fe(II) (bipy)₃, Fe(II) (bipy)₂, Co(II) (bipy)₃, Co(II) (benzacac)₂, and electrode generated Co(acac)₂ in oxygen saturated aprotic solvents show positive shift of the O₂ sigmoidal wave, as well as enhancement of the limiting current in the case of the first five compounds. In the case of Co(II) (bipy)₃ the slope of the sigmoidal wave due to O₂ becomes more positive, while for the other two Co(II) complexes there is no change except a small decrease in the wave height. The data are used to correlate and predict the O₂ binding properties of the chelates in solution. The data for the diketone complexes of Co(II) indicate absence of any direct association, which is in line with the interpretation offered in the literature on the mechanism of their catalytic role in the O₂ oxidation of substrates. The mechanism of the autoxidation of dimethylformamide in the presence of Fe(III) (bipy)₃ and Cu(II) (bipy)₂ is elucidated by the observation that these higher valent compounds are reduced to their next lower oxidation state by DMF.     

Dinuclear palladium(II) complexes containing two monofunctional [Pd(en)(pyridine)Cl] units bridged by Se or S. Synthesis, characterization, cytotoxicity and kinetic studies of DNA-binding

Two novel dinuclear palladium(II) complexes, {[Pd(en)Cl]₂(bpse)}(NO₃)₂ (1) and {[Pd(en)Cl]₂ (bpsu)}(NO₃)₂ (2), (where en is ethylenediamine; bpse is bis(3-methyl-4-pyridyl) selenide; bpsu is bis(3-methyl-4-pyridyl) sulfide) have been synthesized. The complexes have been characterized by elemental analysis, IR, ¹H NMR, and ¹³C NMR. They have been assayed for antitumor activity in vitro against the mice leukemia L1210 and the human coloadenocarcinoma HCT8 cell lines. The results show that compound 1 has a lower I.D.₅₀ value against the two cancer cell lines as compared to compound 2; the compounds also shows a lower I.D.₅₀ value than cisplatin against the HCT8 cell line, but a higher I.D.₅₀ value than cisplatin against the L1210 cell line. Binding studies indicate that compound 1 possibly interacts with DNA by a nonintercalative mode. Kinetics of binding of the two compounds to DNA are firstly studied using ethidium bromide as a fluorescence probe with stopped-flow spectrophotometer under pseudo-first-order condition. The stronger binding of two steps in the process of the compounds interacting with DNA are observed, and the k_obs and E_a of binding of the two steps (where k_obs is the observed pseudo-first-order rate constant, E_a is the observed energy of activation) are obtained.     

Ligand connected metal clusters. The molecular structures and solid state packing of {Ru3(CO)11}2(bis(diphenylphosphino)ethane) and {Ru3(CO)11}2(1,4-bis(diphenylphosphino)benzene)

The preparation and structural characterization of {Ru₃(CO)₁₁}₂(1,4-bis(diphenylphosphino)benzene), a modified synthesis of 1,4-bis(diphenylphosphino)benzene, and the structural characterization of {Ru₃(CO)₁₁}₂(bis(diphenylphosphino)ethane) are reported. In both compounds two metal cluster units are connected through ditertiary-phosphine ligands. Both molecules consist of centrosymmetric units in which the diphosphine ligands are largely covered by the triangular ruthenium clusters. No direct interaction between the two cluster units occurs within individual molecules. Molecular packing in the solid state is dominated by interactions between sets of carbon monoxide ligands in motifs that were previously identified in the solid state structure of the parent cluster, Ru₃(CO)₁₂.     

Peroxidase-Mediated Oxidation, a Possible Pathway for Activation of the Fungal Nephrotoxin Orellanine and Related Compounds. ESR and Spin-Trapping Studies

Orellanine is the tetrahydroxylated and di-N-oxidized bipyridine toxin extracted from several Cortinarius mushrooms among them C. orellanus. The pathogenic mechanism involved in the C. orellanus-poisoning by orellanine leading to kidney impairment is not yet fully understood until now. Electron spin resonance (ESR) spectroscopy has been used to study the activation of orellanine by horseradish peroxidase/H₂O₂ system at physiological pH. Evidence for a one-electron oxidation of the toxin by this enzymatic system to an ortho-semiquinone radical intermediate is presented.

The orellanine ortho-semiquinone generated by the peroxidase/H₂O₂ system abstracts hydrogen from glutathione, generating the glutathionyl radical which is spin-trapped by 5,5'-dimethyl-1-pyrroline N-oxide (DMPO) and subsequently detected by ESR spectroscopy. Similarly, the ortho-semiquinone abstracts hydrogen from ascorbic acid to generate the ascorbyl radical which is detected by direct ESR. The peroxidatic oxidation of orellanine to semiquinone followed by its reduction by glutathione or ascorbic acid does not induce dioxygen uptake. The relationship between chemical structure and HRP oxidation of orellanine-related molecules, namely orelline and DHBPO₂ (the parent molecule lacking of hydroxyl groups in 3 and 3' position) has been investigated in absence or in presence of reducing agents. None of the orellanine-related compounds can be oxidized by the HRP/H₂O₂ system, showing that both catecholic moieties and aminoxide groups are necessary for observing the formation of the ortho-semiquinone form of orellanine. As shown for the (photo)chemical oxidation of orellanine, the mechanism of toxicity could be correlated with a depletion of glutathione and ascorbate levels which are implicated in the defence against oxidative damage.     

Chemistry of cyclodicarbaphosphatriazene: Synthesis and structural studies of pentaerythritoxy-bridged and lariat ether type spirocyclic derivatives

Reactions of dilithiated diols [HO(CH₂CH₂O)_n+1H, n = 1, 2 and 3] with 3,5-bis(N,N-dimethylamino)-1,1-dichlorodicarbaphosphazene (1) in THF have been carried out to afford the first examples of lariat ether type cyclocarbaphosphazene derivatives (C₄H₈O₃PN)(Me₂NCN)₂ (2), (C₆H₁₂O₄PN)(Me₂NCN)₂ (3) and (C₈H₁₆O₅PN)(Me₂NCN)₂ (4). Reaction of the tetrasodium salt of pentaerythritol with 1 and bis(morpholino)dichlorodicarbaphosphazene (1a) yielded the first examples of pentaerythritoxy-bridged cyclodicarbaphosphatriazenes [(Me₂NCN)₂PN(OCH₂)₂]₂C (5) and [(OC₄H₈NCN)₂PN(OCH₂)₂]₂C (6). The spectral and structural properties of these compounds are determined and compared with spirocyclic 1,3-propanedioxy derivative of 1 (7) and analogous compounds of cyclophosphazenes. The crystal structures of the compounds 4, 5 and 7 are reported. In addition, complexation studies of compounds 3 and 4 with Na^I, K^I, Ag^I and Cu^II ions were carried out by conductance measurements. The studies indicate mostly 1:1 complex formation between the metal ions and lariat ether type cyclocarbaphosphazene derivatives.     

Scavenging of reactive oxygen species by chlorophyllin: An ESR study

The antioxidant effects of chlorophyllin (CHL), a water-soluble analog of the green plant pigment chlorophyll, on different reactive oxygen species (ROS) were investigated by electron spin resonance (ESR) spectroscopy. As a standard, we have used the ability of CHL to scavenge the stable 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. CHL inhibits the formation of 5,5-dimethyl-1-pyrroline-N-oxide adduct with hydroxyl radical (DMPO-OH adduct) generated by γ-radiation in a dose-dependent manner. At a concentration of 1 mM, CHL caused more than 90% inhibition of ESR signal intensity of this adduct. However, the results obtained with the Fenton reaction were different. We also found evidence for the inhibition of ¹O₂-dependent formation of the 2,2,6,6-tetramethyl-piperidine oxide (TEMPO) radical during photosensitization of methylene blue with visible light. CHL was also able to inhibit hydrogen peroxide induced oxidation of phenol red. The rate constant of the reaction of CHL with H₂O₂ was found to be 2.7×10⁶ M^-1s^-1. In conclusion, CHL has potent antioxidant ability involving scavenging of various physiologically important ROS.     

The synthesis, structure and SOD-like behaviors of a μ-imidazolato-dicopper(II) complex with a binucleating hexaazamacrocycle

The synthesis, crystal structure and magnetic properties of the imidazolate-bridged dinuclear copper(II) complex [LCu₂(Im)(DMSO)₂](ClO₄)₃(DMSO), where ImH is imidazole, and L is 3, 6, 9, 17, 20, 23-hexaazatricyclo[23.3.1.1^11,13]triaconta-1(29), 11(30), 12, 14, 25(26), 27-hexaene, have been studied. Single crystal X-ray diffraction determination reveals the distorted tetragonal pyramid geometries of the imidazolate bridged dicopper(II) center are incorporated within the binucleating macrocycle. Both copper atoms are five-coordinated by four basal nitrogen atoms (three from the macrocycle and one from the imidazolate) and one oxygen atom from the DMSO molecule. Two coordinated DMSO molecules are situated at the same side of the macrocycle. The Cu–Cu separation in the complex is 5.93 Å. Magnetic measurements and ESR spectroscopy studies exibit an antiferromagnetic exchange interaction with a coupling constant of J= − 26.94 cm⁻¹. Investigations on the pH-dependent ESR of the title compound in frozen 50% aqueous DMSO solution confirm the existence of the bridged cation [LCu₂(Im)]³⁺ as a major species in solution mainly in the range 5.2pH11.5. The imidazolate bridge is broken in the pH range of 5.2–3.3, which is close to that for the native enzyme.     

Chemistry in environmentally benign media Part 1. Synthesis and characterization of 1,2-bis[bis(hydroxymethyl)phosphino]ethane (‘HMPE’). X-ray structure of [Pt{(HOH2C)2PCH2CH2P(CH2OH)2}2](Cl)2

The water-soluble bisphosphine, 1,2-bis(bis(hydroxymethyl)phosphino)ethane (1), was synthesized in near quantitative yield by the reaction of bisphosphine, H₂PCH₂CH₂PH₂, with an aqueous formaldehyde in the presence of K₂PtCl₄. The reaction of this water-soluble bisphosphine 1 with cis-Pt(COD)Cl₂ affords the mononuclear bischelate complex, [Pt{(HOH₂C)₂PCH₂CH₂P(CH₂OH)₂}₂](Cl)₂ (2), in near quantitative yield. The new ligand and complex have been characterized spectroscopically and the structure of the metal complex, 2, was determined by X-ray crystallography. The Pt(II) complex 2 crystallizes in the orthorhombic space group Pbca(a=14.623(1), B=16.216(2), C=9.319(4) Å) with Z=4. The final R value is 0.024.     

Synthesis, spectroscopic properties and X-ray crystal structures of two dinuclear alkoxo-bridged copper(II) compounds with the ligand bis(1-methyl-2-benzimidazolyl) propane. A unique alkoxo-bridged Cu(II) dinuclear compound with an additional bidentate bridging triflate anion

Based on the new ligand bis(1-methyl-2-benzimidazolyl) propane (abbreviated as mtbz) several new copper(II) coordination compounds have been prepared and characterized structurally and spectroscopically. Two representative compounds, i.e. [Cu₂(mtbz)₂(CH₃)₂- (CF₃SO₃)](CF₃SO₃) (1) and [Cu₂(mtbz)₂(CH₃O)₂](ClO₄)₂ (4) were characterized structurally by X-ray diffraction. Crystal data for 1: monoclinic, space group P2₁/c, a=13.6585(5), B=39.981(3), C=20.919(1) Å, β=125.98(1)°, Z=8. Crystal data for 4: monoclinic, space group P2₁/c, a=13.115(2), B=9.523(2), C=17.908(4) Å, β=111.71(1)°, Z=2. Structures 1 and 4 each consist of a dinuclear unit with bridging methoxo groups and one ligand linked to each copper via an N atom. Structure 1 (which consists of two dinuclear, crystallographically independent, but chemically identical units) has the two copper atoms bridged by a triflate anion, providing each copper atom a square-pyramidal coordination, while the copper atoms in structure 4 have an almost a square-planar geometry. The Cu---Cu distances (Å) within the dinuclear units are: 1, 2.9775(13), 2.9751(13); 4, 2.9872(16); the Cu---O---Cu bridging angles (°) are: 1, 101.7(3), 101.7(3), 100.9(3), 102.1(3); 4, 103.2(2). The mid-IR section focused on the vibrations of the triflate anion reveals interesting results concerning the assignments of that anion related to the v_as(S---O) band. Characteristic Cu---O vibrations in the far-IR section were found at 386 and 230 cm⁻¹ for the methoxo-bridged and 454 and 332 cm⁻¹ for the ethoxo-bridged compounds. These dinuclear species are EPR silent, and only a weak signal of monomeric impurities is observed. They also show a diamagnetic behavior below room temperature.     

Free Radical Formation from the Antineoplastic Agent VP 16-213

Free radical formation from VP 16-213 was studied by ESR spectroscopy. Incubation of VP 16-213 with the one-electron oxidators persulphate-ferrous, myeloperoxidase (MPO)/hydrogen peroxide and horseradish peroxidase (HRP)/hydrogen peroxide readily led to the formation of a free radical. The ESR spectra obtained in the last two cases, were in perfect accord with that of a product obtained by electrochemical oxidation of VP 16-213 at +550 mV. The half-life of the free radical in 1 mM Tris (pH 7.4), 0.1 MNaClat 20°C, was 257 ± 4 s. The signal recorded on incubation with HRP/H₂O₂ or MPO/H₂O₂ did not disappear on addition of 0.3 - 1.2 mg/ml microsomal protein. From incubations with rat liver microsomes in the presence of NADPH, no ESR signals were obtained.