Mutagenicity of a series of hexacoordinate cobalt(III) compounds

15 cobalt(III) compounds have been tested for DNA-damaging capabilities using an E. coli differential repair assay and for mutagenicity in strains of Salmonella typhimurium. 4 of these compounds were active in both systems. Although the general ligand requirements for genetic activity of cobalt(III) appear to closely parallel those of chromium(III) and rhodium(III), the genetic activity of cobalt compounds seems particularly dependent upon the structure of the ligands coordinated about the metal ion. By a simple methyl substitution on the organic ligands, a compound completely devoid of activity, e.g. trans-[Co(pyr)4Cl2]Cl, could be made slightly mutagenic in Salmonella typhimurium strains e.g. trans-[Co(3-pic)4Cl2]Cl. Substitution at the 4-position rather than the 3-position on the same pyridine ring, e.g. trans-[Co(4-pic)4Cl2]Cl, results in a 50-fold enhancement of activity in both repair and mutagenesis systems. The difference in genetic activity is attributed to the influence of the ligands on the relative lability of the metal complex.     

Diphosphinoazine rhodium(III) and iridium(III) octahedral complexes

Rhodium(III) and iridium(III) octahedral complexes of general formula [MCl₃{R₂PCH₂C(Bu^t)NNC(Bu^t)CH₂PR₂}] (M = Rh, Ir; R = Ph, c-C₆H₁₁, Prⁱ, Bu^t; not all the combinations) were prepared either from the corresponding diphosphinoazines and RhCl₃ · 3H₂O or by the oxidation of previously reported bridging complexes [{MCl(1,2-η:5,6-η-CHCHCH₂CH₂CHCHCH₂CH₂)}₂{μ-R₂PCH₂C(Bu^t)NNC(Bu^t)CH₂PR₂}] with chlorine-containing solvents. Depending on the steric properties of the ligands, complexes with facial or meridional configuration were obtained. Crystal and molecular structures of three facial and two meridional complexes were determined by X-ray diffraction. Hemilability of ligand in the complex fac-[RhCl₃{(C₆H₁₁)₂PCH₂C(Bu^t)NNC(Bu^t)CH₂P(C₆H₁₁)₂}] consisting in reversible decoordination of the phosphine donor group in the six-membered ring was observed as the first step of isomerization between fac and mer isomers.     

Five-coordinated rhodium(I) carbonyl compounds

The title compounds were synthesised by the replacement of chlorine in Rh(CO)(PPh₃)₂Cl with monobasic bidentate chelating ligands such as salicylaldehyde, acetylacetone, benzoylacetone, dibenzoylmethane, 8-hydroxyquinoline, benzoylphenyl hydroxylamine, 2-hydroxyacetophenone and 2-hydroxybenzophenone. IR spectral evidence points out that these compounds have a trigonal bipyramidal geometry around rhodium in the solid state. However, in benzene solutions, except for the 8-hydroxyquinoline and 2-hydroxybenzophenone derivatives they all take a square planar structure, as seen from their electronic spectra.     

Synthesis and characterisation of ferrocene-containing β-diketonato complexes of rhodium(I) and rhodium(III)

The synthesis of new β-diketonato rhodium(I) complexes of the type [Rh(FcCOCHCOR)(CO)₂] and [Rh(FcCOCHCOR)(CO)(PPh₃)] with Fc=ferrocenyl and R=Fc, C₆H₅, CH₃ and CF₃ are described. ¹H, ¹³C and ³¹P NMR data showed that for each of the non-symmetric β-diketonato mono-carbonyl rhodium(I) complexes, two isomers exist in solution. The equilibrium constant, K_c, which relates these two isomers in an equilibrium reaction, are concentration independent but temperature and solvent dependent. Δ_rG, Δ_rH and Δ_rS values for this equilibrium have been determined and a linear relationship between solvent polarity on the Dimroth scale and K_c exists. The relationship between RhP bond lengths, d(RhP), and ³¹P NMR peak positions as well as coupling constants ¹J(³¹P¹⁰³Rh) has been quantified to allow calculation of approximate d(RhP) values. Variations in d(RhP) for [Rh(RCOCHCOR′)(CO)(PPh₃)] complexes have also been related to the group electronegativities (Gordy scale) of the terminal β-diketonato R groups trans to PPh₃. A measure of the electron density on the rhodium centre of [Rh(RCOCHCOR′)(CO)(PPh₃)] may be expressed in terms of the IR carbonyl stretching wave number, ν(CO), the sum of the group electronegativities of the R and R′ groups, (χ_R+χ_R′), or the observed pK_a^′ values of the free β-diketones RCOCH₂COR^′. An empirical relationship between ν(CO) and either pK_a^′ or (χ_R+χ_R′) has also been quantified.     

Secondary ligand-metal interactions in rhodium(III) and iridium(III) phosphoramidite complexes

The synthesis, characterization, and application in asymmetric catalytic cyclopropanation of Rh(III) and Ir(III) complexes containing (S_a,R_C,R_C)-O,O′-[1,1′-binaphthyl-2,2′-diyl]-N,N′-bis[1-phenyl-ethyl]phosphoramidite (1) are reported. The X-ray structures of the half-sandwich complexes [MCl₂(C₅Me₅)(1,κP)] (M = Rh, 2a; M = Ir, 2b) show that the metal-phosphoramidite bond is significantly shorter in the Ir(III) analog. Chloride abstraction from 2a (with CF₃SO₃SiMe₃ or with CF₃SO₃Me) and from 2b (with AgSbF₆) gives the cationic species [MCl(C₅Me₅)(1,2-η-1,κP)]⁺ (M = Rh, 3a; M = Ir, 3b), which display a secondary interaction between the metal and a dangling phenethyl group (NCH(CH₃)Ph) of the phosphoramidite ligand, as indicated by NMR spectroscopic studies. Complexes 3a and 3b slowly decompose in solution. In the case of 3b, the binuclear species [Ir₂Cl₃(C₅Me₅)₂]⁺ is slowly formed, as indicated by an X-ray study. Preliminary catalytic tests showed that 3a cyclopropanates styrene with moderate yield (35%) and diastereoselectivity (70:30 trans:cis ratio) and with 32% ee (for the trans isomer).     

Synthesis of rhodium(III), iridium(III) and osmium(III) complexes with tris(2-aminoethanethiolato)cobalt(III)

Polynuclear sulfur bridged complexes where the neutral complex tris(2-aminoethanethiolato)cobalt(III) acts as a tridentate ligand to rhodium(III), iridium(III) and osmium(III) have been prepared. These complexes have been characterized by electronic spectroscopy, vibrational spectroscopy and nuclear magnetic resonance spectroscopy. Along with the previously prepared complexes of iron(III), ruthenium(III) and cobalt(III), these complexes form two series of complexes with the group 8 and group 9 elements from all three transition series.     

Synthesis, spectroscopy, and structures of new rhodium(I) and rhodium(III) corroles and catalysis thereby

The syntheses and molecular structures of six- and five-coordinated rhodium(III) corroles (by pyridines and a chiral amine, respectively) and the rhodium(I) complex of a chiral corrole are described, together with some interesting features in the NMR spectra of the complexes and their utilization as carbene-transfer catalysts.     

Cyclometalated rhodium(III) and iridium(III) complexes containing amino acids as N,O-chelates

The synthesis of bis-cyclometalated aminocarboxylato complexes [M(α-aminocarboxylato)(ptpy)₂] (M = Rh, 3, 4, 5; M = Ir, 6, 7, 8), ptpy = 2-(p-tolyl)pyridinato; aminocarboxylato = glycinato, l-alaninato, l-prolinato) from [{M(μ-Cl)(ptpy)₂}₂] (M = Rh, 1; M = Ir, 2) is described. The molecular structure of [Ir(l-alaninato)(ptpy)₂] (7) was confirmed by a single-crystal X-ray diffraction study. Compound 7 crystallized from methanol-iso-hexane in the space group P2₁. For 7 the two diastereoisomers Δ_Ir, S_C and Λ_Ir, S_C were found crystallizing twice per unit. Absorption and emission spectra were recorded. The rhodium compounds are weak yellow-green and the iridium species strong green emitters.     

Mutagenicity of polycyclic hydrocarbons III. Monitoring genetic hazards of benz(a)anthracene

Mutagenicity tests (micronucleus test and chromosome aberrations) have been performed with benz (a) anthracene in spermatogonia and bond marrow cells of Chinese hamsters and in NMRI mice oocytes. Mutagenic effects of the polycyclic hydrocarbon could be demonstrated.     

Reactions of 2-thiopyridone rhodium(III) complexes with tertiary phosphines

The rhodium(III) complexes containing 2-thiopyridone (pySH) and its conjugate anion 2-thiopyridonato (pyS) as the only ligands, [Rh(pyS)₂(pySH)₂]Cl, [Rh(pyS)₃(pySH)], and [Rh(pyS)₃], react with the tertiary phosphines PMe₂Ph, PPh₃, Ph₂PCH₂PPh₂ (dppm), and Ph₂PCH₂CH₂PPh₂ (dppe) to give mixed pyS/tertiary phosphine complexes of the type [Rh(pyS)₃L], [Rh(pyS)₃L₂], and [Rh(pyS)₂L₂]ClO₄ where L represents a single phosphorus donor atom. These compounds were characterized mainly by ¹H and ³¹P NMR spectroscopy.     

Mutagenicity of free-radical spin-trapping compounds

Spin-trapping compounds are used to detect the presence of free-radical intermediates in various chemical and biological processes. We have tested the mutagenicity of several newly synthesized and some commonly used spin-traps. Commonly used spin-traps were non-mutagenic at the levels tested; however, a few of the newly synthesized spin-traps are slightly mutagenic.     

Recovery of rhodium(III) from solutions and industrial wastewaters by a sulfate-reducing bacteria consortium

A quantitative analysis of the rate of removal of rhodium(III) by a resting sulfate-reducing bacteria (SRB) consortium under different initial rhodium and biomass concentrations, pH, temperature, and electron donor was studied. Rhodium speciation was found to be the main factor controlling the rate of its removal from solution. SRB cells were found to have a higher affinity for anionic rhodium species, as compared to both cationic and neutral species, which become abundant when speciation equilibrium was reached. Consequently, a pH-dependent rate of rhodium removal from solution was observed. The maximum SRB uptake capacity for rhodium was found to be 66 mg of rhodium per gram of resting SRB biomass. Electron microscopy studies revealed a time-dependent localization and distribution of rhodium precipitates, initially intracellularly and then extracellularly, suggesting the involvement of an enzymatic reductive precipitation process. When a purified hydrogenase enzyme was incubated with rhodium chloride solution under hydrogen, 88% of the rhodium was removed within 1 h, whereas with a soluble extract from SRB 77% was removed within 10 min. Due to the low pH of the industrial effluent (1.31), the enzymatic reduction of rhodium by the purified hydrogenase was greatly limited, and it was apparent that an industrial effluent pretreatment was necessary before the application of an enzymatic treatment. In the present study, however, it was established that SRB are good candidates for the enzymatic recovery of rhodium from both aqueous solution and industrial effluent.     

Synthesis and characterization of new cationic hydride complexes of rhodium(III)

New cationic hydride complexes of rhodium(III) with PR₃ and R-DAB ligands have been prepared and characterised. The tertiary phosphines employed were PPh₃, PMePh₂, PEt₃ and the R-DAB ligands, (RN:CR′CR′:NR), c-Hex-DAB, Ph-DAB, NH2-DAB-(CH₃,CH₃). Hexacoordinate-dihydride complexes, characterized by ¹H and ³¹P NMR, with stoichiometry [RhH₂(R-DAB)(PR₃)₂]X were obtained. Compounds with other stoichiometries (R-DAB/PR₃=1 or 2) are also possible. Preliminary studies of the catalytic activity in hydrogenation of olefins have been carried out.     

Synthesis,characterization and structure of cationic hydrides of rhodium(III). Part II. Crystal structure of dihydride(1,4-biscyclohexyl-diaza-1,3-butadiene)-bis(4-fluor-tristriphenylphosphine)rhodium(III) perchlorate

The reaction between [(R-DAB)Rh(PR₃)₂]⁺ and molecular hydrogen produces cationic cis-dihydride complexes of Rh(III), of general formula [RhH₂(R-DAB)(PR₃)₂]X. They are stable in air, 1:1 conductors and have been characterized by ¹H NMR, ³¹P NMR, IR and elemental analysis. The tertiary phosphines employed were: PPh₃, P(p-C₆H₄F)₃, PMePh₂, PEt₃, and the R-DAB ligands (RN:CR′CR′:NR)¹, Ph-DAB, c-Hex-DAB, NH₂-DAB(CH₃,CH₃), t-but-DAB.The structure of [RhH₂(c-Hex-DAB){P(p-C₆H₄F)₃}₂]ClO₄ has been determined by an X-ray diffraction study. Crystals are orthorhombic, space group Pbnm. Unit cell parameters are: a = 13.032(1), b = 18.166(2), c = 21.449(2) Å, Z = 4, R = 0.081, R_w = 0.082 for 2906 reflections, with I> 3σ(I) the rhodium atom is octahedrally coordinated with the two hydride-hydrogens and c-Hex-DAB in the equatorial plane; the two phosphine ligands are in an axial position bent towards the hydrogens making an angle of 164.9(4)°.     

Antileukemic activity and cellular effects of rhodium(III) crown thiaether complexes

The cytostatic properties of novel rhodium(III) thiacrown ether complexes [RhCl(LL)([9]aneS₃)]ⁿ⁺ with either aromatic κ² N ligands (n = 2) or anionic chelate ligands (n = 1) have been investigated for the human cancer cell lines HT-29 and MCF-7 and for immortalized HEK-293 cells. Taken together with literature IC₅₀ values for analogous complexes with polypyridyl ligands or 1,4-dithiane, the in vitro assays indicate that dicationic complexes with soft κ² N (imino) or κ² S (thiaether) ligands exhibit significantly higher antiproliferative effects than those with hard κ² N (amino) ligands. Dicationic complexes are more active than monocationic complexes with similar ligands. Pronounced apoptosis-inducing properties towards Jurkat cells were established for complexes with LL = bpm, dpq, and 1,4-dithiane. The order of activity (bpm > 1,4-dithiane > dpq > bpy) contrasts to that observed for adhesive cancer cells (bpm > bpy, 1,4-dithiane > dpq). Necrosis is insignificant in all cases. The percentage of Jurkat cells exhibiting apoptosis after 24 or 48 h incubation periods is directly correlated to the percentage of cells exhibiting high levels of reactive oxygen species. As established by online monitoring with a sensor chip system, treatment of MCF-7 cells with the bpm and 1,4-dithiane complexes leads to a significant and permanent concentration-dependent decrease in oxygen consumption and cellular adhesion.     

Mutagenicity of methyl bromide in a series of short-term tests

Methyl bromide is commonly used as a soil fumigant in greenhouses. In the framework of a toxicological evaluation, it was tested for possible genotoxic properties in two bacterial test systems (the fluctuation test using Klebsiella pneumoniae and the plate test using Salmonella typhimurium TA100 and TA98), two systems using mammalian cells in vitro (forward mutations at the TK and HPRT loci in L5178Y mouse lymphoma cells and unscheduled DNA synthesis in primary rat-liver cells) and in the sex-linked recessive lethal test using Drosophila melanogaster. Methyl bromide was active in all tests except the DNA-repair assay. The results indicate a relatively low mutagenic efficiency of the compound, as expected from its alkylating properties.