Coordination compounds of chromium(III) with semicarbazones and thiosemicarbazones of heterocyclic aldehydes

Summary [CrCl₃(thf)₃] (thf=tetrahydrofuran) reacts with semicarbazones and thiosemicarbazones to yield adducts of the type, [CrCl₃L] and [CrCl₃L₂] (where L=semicarbazones or thiosemicarbazones of furfuraldehyde and indole-3-carboxaldehyde).I.r. data suggest that L bind via the azomethine nitrogen and oxygen/sulphur. Magnetic studies and lig-and field parameters suggest a tetragonal structure for these complexes.     

A comparative study of some oxygen and sulphur substituted alkyl radicals

Several sulphur containing alkyl radicals have been generated and their ESR spectra and hyperfine coupling constants compared with those of the oxygen analogues. Deviations from planarity are smaller when a tervalent carbon atom is bonded to sulphur than when bonded to oxygen. Moreover greater delocalization of the unpaired electron is apparent in the sulphur radicals and this leads to higher barriers to internal rotation in radicals of the form H₂SR compared with H₂OR.     

Mixed dimethyl sulfoxide-thiocarbamic ester complexes of platinum(II) halides

Summary The platinum(II) halidecis-[Pt(DMTC)(DMSO)X₂] andcis-[Pt(DETC)(DMSO)X₂](X=Cl or Br; DMSO=dimethyl sulfoxide; DMTC=EtOSCN-Me₂; DETC=EtOSCNEt₂) adducts and the platinum(II) and palladium(II) halide adducts,trans-[M(DETC)₂X₂] (M=Pt or Pd; X=Cl or Br), have been prepared. The complexes were characterized by i.r., and¹H and¹³Cn.m.r. spectroscopy. Both DMTC and DETC coordinate through the sulphur atoms. The 1:2 DETC complexes present the usualtrans configuration, whereas the presence of DMSO favourscis geometry in the mixed species.     

Gas‐phase radical–radical recombination reactions of nitroxides with substituted phenyl radicals

Fourier‐transform ion cyclotron resonance mass spectrometry has been used to examine gas‐phase reactions of four different nitroxide free radicals with eight positively charged pyridyl and phenyl radicals (some containing a Cl, F, or CF₃ substituent). All the radicals reacted rapidly (near collision rate) with nitroxides by radical–radical recombination. However, some of the radicals were also able to abstract a hydrogen atom from the nitroxide. The results establish that the efficiency (k_reaction/k_collision) of hydrogen atom abstraction varies with the electrophilicity of the radical, and hence is attributable to polar effects (a lowering of the transition‐state energy by an increase in its polar character). The efficiency of the recombination reaction is not sensitive to substituents, presumably due to a very low reaction barrier. Even so, after radical–radical recombination has occurred, the nitroxide adduct was found to fragment in different ways depending on the structure of the radical. For example, a cationic fragment was eliminated from the adducts of the more electrophilic radicals via oxygen anion abstraction by the radical (i.e., the nitroxide adduct cleaves heterolytically), whereas adducts of the less electrophilic radicals predominantly fragmented via homolytic cleavage (oxygen atom abstraction). Therefore, differences in the product branching ratios were found to be attributable to polar factors. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 216–229 2004     

Palladium(II) and platinum(II) halide complexes with 2,6-dimethyl-4H-pyran-4-thione

Summary 2,6-Dimethyl-4H-pyran-4-thione (DMTP) acts as a sulphur donor towards Pt^II and Pd^II halides yielding adducts of general formula [M(DMTP)₂X₂] (M=Pd or Pt; X=Cl, Br or I). When complex syntheses are performed in benzene, the solvated species [M(DMTP)₂X₂]·C₆H₆ (M=Pd or Pt; X=Cl or Br) are obtained. The compounds have been characterized by i.r. and n.m.r. (¹H and¹³C) spectroscopy and by thermogravimetric data. The adduct geometry and the influence of benzene are discussed.     

Composés d'addition des halogénures de niobium(V) et de tantale(V). V. Stabilité relative des composés des chlorures avec quelques oxydes et sulfures organiques

The adducts of niobium(V) and tantalum(V) chlorides with some aliphatic and cyclic oxides and sulfides, studied by NMR. spectroscopy in CHCl₃, are found to have 1:1 stoechiometry, at room temperature and lower. In the thioxane complex TaCl₅ · C₄H₈OS two species are present with the ligand coordinated by the sulfur atom or by the oxygen atom, respectively, in a proportion which has been determined. The thioxane adduct of niobium(V) chloride, however, is preferentially coordinated by the sulfur atom. There is also evidence for the species 2MCl₅ · C₄H₈OS. The relative basicity of each donor atom in dioxane, thioxane and dithiane is calculated and discussed. In contrast to the nitrile adducts, whose stability was found earlier to be controlled by inductive factors, the steric factors are more important for the ether and sulfide adducts: MCl₅ · Me₂X is more stable than the corresponding MCl₅ · Et₂X (M = Nb, Ta; X = O, S). Both niobium(V) and tantalum(V) chlorides have a soft behaviour, but NbCl₅ is a weaker Lewis acid than TaCl₅ and shows also a softer behaviour.     

Calculated hyperfine coupling constants for 5,5-dimethyl-1-pyrroline N-oxide radical products in water and benzene

The optimized structures of some radical adducts of 5,5-dimethyl-1-pyrroline N-oxide were computed by different methods on ESR spectra. As trapped radicals, H, N₃, NH₂, CH₃, CCl₃, OOH in water and F, OH, CF₃, CH₂OH, OC₂H₅ in benzene solutions were used. The calculated isotropic hyperfine coupling constants of all the trapped radicals were compared with the corresponding experimental data. The hyperfine coupling constant due to the β proton of the nitroxide radical was seen to be consist with the McConnel’s relation α_β = B ₀ + B ₁cos²θ and, to be effected with the opposite spin density of oxygen nucleus bonded to the nitrogen. It was concluded that in hyperfine calculations the DFT(B3PW91)/LanL2DZ level is superior computational quantum model relative to the used other level. Also, the study has been enriched by the computational of the optimized geometrical parameters, the hyper conjugative interaction energies, the atomic charges and spin densities for all the radical adducts.     

The reaction of RTiBr3 (R = methyl,phenyl and p-tolyl) with some monodentate and bidentate ligands

RTiBr₃ (R = CH₃, C₆H₅ and (4-CH₃)C₆H₄) forms 1/2 adducts, RTiBr₃2L, with a number of monodentate ligands containing nitrogen, oxygen ad sulphur donor atoms. Bidentate ligands normally give 1/1 adducts, as do the bulky monodentate ligands (C₆H₅)₃PO. Dioxan gives 1/1 adducts with CH₃TiBr₃ and C₆H₅TiBr₅ but a 1/2 adduct with (4-CH₃)C₆H₄TiBr₃.Structures are assigned on the basis of IR and NMR data.     

Effect of copper(II) ions on the stability of spin adducts formed by the reaction of 5,5-dimethylpyrroline-N-oxide with hydroxyl and hydroxylalkyl radicals

The reactions of copper(II) species with spin adducts formed by reaction of OH·, CH₃CHOH or (CH₃)₂COH with DMPO (5,5-dimethylpyrroline-N-oxide) have been investigated. The spin adducts prepared by -irradiation of appropriate solutions were detected using esr. Copper(II) in the form of aqua, phen, or 1-alanine complexes reacted rapidly with the OH· adduct to give products that gave no esr signal, but with the hydroxylalkyl adducts, reacted to give a new 9-line esr signal, identified as due to the H· adduct, (DMPO-H·). Measurement of the yield of Cu(phen) ₂ ⁺ formed by reaction of the copper(II) complex with the spin adduct showed that approximately 25% of the radiation-produced radicals formed esr detectable spin adducts. The implications of these findings for the use of spin trapping to detect radical intermediates in biological systems is discussed.     

Enhancement of polymer hydrophobicity by SF6 plasma treatment and argon plasma immersion ion implantation

In this study sulphur hexafluoride (SF₆) plasmas and argon plasma immersion ion implantation (ArPIII) techniques have been applied to improve the hydrophobicity of poly(tetrafluoroethylene) (PTFE), polyurethane and silicone surfaces. As evaluated by water contact angle measurements, all the treatments resulted in a significant enhancement in the hydrophobicity of the polymers. However, exposure of the treated samples to air induced a strong variation in their hydrophobicity as a consequence of post‐plasma reactions between atmospheric species and remnant surface free radicals. X‐ray photoelectron spectroscopy results strongly suggest that for polyurethane and silicone the surface fluorination by SF₆ plasmas and the creation of new carbon bonds and radicals are the main agents for hydrophobicity enhancement. The PTFE exposed to ArPIII revealed increases in the contact angles after exposure to air. A significant incorporation of oxygen and the formation of new carbon bonds were revealed by XPS measurements. Copyright © 2003 John Wiley & Sons, Ltd.     

Spin trapping studies of poly(methyl methacrylate) degradation in solution

Free radicals produced either by γ or ultrasonic irradiation of poly(methyl methacrylate) (PMMA) in benzene solution were stabilized by spin trapping; they were identified by analysis of ESR spectra of the trapped radicals (the spin adducts). The radical species identified after γ-irradiation were methyl, ester (COOCH₃), a pair of the chain scission radicals, ～CH₂C(CH₃)(COOCH₃) and CH₂C(CH₃)(COOCH₃)～, and phenyl radical originating from the solvent. The chain scission radicals were also detected by spin trapping after ultrasonic irradiation of the benzene solution. Taking account of the difference in the trapping rate for two spin trapping agents, 2,4,6-tri-t-butylnitrosobenzene (BNB) and penta-methyl-nitrosobenzene (PMNB) the radical species trapped by PMNB are assumed to be precursors of those trapped by BNB. Based on the radical species found by the spin trapping method, plausible degradation processes for PMMA in benzene solution are proposed.     

CuNPs as an activator of K2S2O8 for the decolorization of diazo dye in aqueous solution

Degradation of trypan blue (TB) by persulfate/CuNPs system was investigated as a function of TB concentration, persulfate concentration, CuNPs concentration, pH, and reaction temperature in aqueous solution. The rate of the decolorization and destruction of aromatic ring were studied spectrophotometrically. The dye mineralization was performed with potassium dichromate for the determination of chemical oxygen demand (COD) in solution. The blue color reaction mixture became red-chocolate, purple, light blue to dark blue as a function of time. The CuNPs acted as an activator of K₂S₂O₈ and generates various reactive oxygen and/or sulphur species. Decolorization of dye starts due to the cleavage of azo bond by the generated radical species. The role of sulfate radicals (SO₄^?-), and hydroxyl radicals (HO^?) were established by using different radical scavengers. Degradation and mineralization of dye follows first-order kinetics. These results can support the design of remediation processes and also assist in predict their fate in environment.     

NMR evidence for single-site and synchronous double-site inversion at pyramidal sulphur atoms in mono- and bi- nuclear complexes of trimethylplatinum(IV) halides with bidentate thioethers

Adducts of the type Me₃PtXL (X = C1, Br, I; L = MeSCH₂CH₂SMe) exhibit pyramidal inversion at individual sulphur atoms, whereas the adducts (Me₃PtX)₂L′ (L′ = MeSCH₂SMe, X = C1, Br, I) exhibit both ring inversion, and synchronous inversion about both sulphur atoms.     

Synthesis,characterisation and reactions of pentacoordinated iridium(I) complexes

Stable, pentacoordinated iridium(I) complexes have been synthesised by the replacement of the chlorine in IrCO(PPh₃)₂Cl by bidentate chelating ligands such as β-diketones, N-benzoyl-N-phenyl hydroxylamine, salicylaldehyde, 8-hydroxyquinoline, 2-hydroxybenzophenone and 2-hydroxy 4-methoxybenzophenone. Most of them gave stable oxygen adducts IrCO(PPh₃)₂(L)O₂ and all of them underwent oxidative addition with bromine in methylene chloride giving IrCO(PPh₃)₂(L)Br₂. These chelated iridium(I) compounds reacted with liquid sulphur dioxide to produce two types of SO₂ insertion products.     

Biological Activity of Flavonoids Copper Complexes

Three flavonoid copper(II) complexes Cu₂(quercetin)(CH₃COO)₃(CH₃OH) ( 1 ), Cu(anthrarufin)(CH₃COO)·1/2H₂O ( 2 ) and Cu(naringin)(OCH₃)(CH₃OH)₂ ( 3 ) have been synthesized and characterized by elemental analysis, IR, electronic absorption and EPR (X‐band) spectroscopy. The complexes have a strong protective action over the Δsod1 mutant of S. cerevisiae against reactive oxygen radicals generated by an external source of free radicals (H₂O₂ or the superoxide‐generating, menadione). On the other hand, the complexes cleave DNA efficiently even in the absence of reducing agents. The main reactive oxygen species responsible for the DNA strand cleavage have been determined using radical scavengers. A probably mechanism of the DNA damage is proposed.     

Formation of negative ions of monosubstituted group VIB pentacarbonyls during fast atom bombardment mass spectrometry

The first negative-ion fast atom bombardment mass spectra of a related series of monosubstituted Group VIB transition metal pentacarbonyls, M(CO)₅L (M = Cr), Mo or W and L = P(Ph)₃, As(Ph)₃ or Sb(PH)₃), have been obtained. Instead of molecular ion radicals, pseudomolecular adduct ions, [M + H]^? and [M + 15]^?, were detected, with the hydride species being much more abundant. High-resolution measurements and comparison of observed isotope clusters with computer-generated theoretical isotope patterns confirmed that ionization occurred by several mechanisms, including electron capture, charge dissociation and formation of adducts with charged species. Fragmentation consisted primarily of elimination of neutral ligands, i.e. ([MH - L]^?, [MH - CO]^?, [MH - 2CO]^?, etc. B/E and constant neutral loss linked scanning with collisional activation were used to confirm fragmentation pathways and characterize the site of hydride attachment on the transition metal complex. The information obtained demonstrates the utility of fast atom bombardment mass Spectrometry in the analysis of metal carbonyls.     

The origin of the radiobiological damage in cells stored in cryostatic conditions

The radiation induced free radical damage in Chinese hamster lung fibroblast V-79 cells stored in DMEM culture medium containing 10% DMSO has been investigated by matrix EPR spectroscopy in connection with the H₂O/DMSO binary phase diagram. A major part of the indirect effect is due to radicals from the DMSO·3H₂O phase in the freezing medium, which are released on warming in the temperature range between 130 K and 160 K, that is, far below the eutectic melting temperature (210 K). The radicals trapped in the DMSO·3H₂O phase react with oxygen above 160 K giving reactive oxygen species (ROS) of the type of peroxyl radicals. A lower limit yield of 10–15% was calculated for this conversion. Scavenging experiments with a stable nitroxyl radical (tempol) have demonstrated that part of the DMSO·3H₂O radicals escape by mutual recombination on melting and are therefore available for inducing indirect cell damage. The same experiments performed with pure frozen water have shown that OH radicals are not available for inducing cell damage. The EPR measurements performed on H₂O/DMSO frozen mixtures suggest that the radiation induced radical forming process does not change when passing to the low dose range below 1 Gy, in agreement with the linear model.     

Basicity of transition metal carbonyl complexes : IX. An infrared study of lewis acid reactions with cyclopentadienyl and arene derivatives of groups VI and VII transition metal carbonyls and nitrosyls

The different courses of the interactions of cyclopentadienyl and arene derivatives of Group VI and VII transition metal carbonyl and transition complexes with Lewis acids, in solutions, have been studied by IR spectroscopy.The information of adducts involving the metal atom was observed for CpRe(CO)₂L (L = CO, PR₃) with SnCl₄, SnBr₄, TiCl₄; AreneM(CO)₃ (M = Cr, Mo, W) with SnCl₄, TiCl₄; and Ph₃PC₅H₄M(CO)₃ (M = Cr, Mo, W) with TiCl₄ and AlCl₃. Complexes CpM(CO)₂NO and CpM(CO(NO)PPh₃, depending on thier donor and acceptor nature, form adducts involving the oxygen atoms of CO or NO groups or the metal atom. CpCr(NO)₂Cl reacts with Lewis acids via the chlorine atom. The relative basicity of the different sites in the complexes investigated is discussed.     

Free radicals derived from 1,4-diaza-1,3-butadiene: II. Adducts with metal carbonyls and reactions with derivatives of group VB elements

The paramagnetic adducts formed when photochemically generated Mn(CO)₅ or Re(CO)₅ radicals are trapped by N,Nt?-di-t-butyl-1,4-diaza-1,3-butadiene (t-Bu-DAB) have been characterized by ESR spectroscopy. Adducts containing phosphorus have also been observed but attempts to produce adducts containing As, Sb or Bi have been unsuccessful. In a number of systems an identical ESR spectrum was observed. This has been shown to arise from the N,N′-di-t-butylpyrazinium cation.