Complexes cis- [PtR,(dmso),] and cis- [PtRCl(dmso),] (dmso = dimethyl sulphoxide) are readily obtained from K, [PtCI,] and SnMe,R (R = aryl or Me) in dmso at 70-90 "C. Hydrogen-1 n.m.r. spectra show that the dmso ligands are bound through sulphur in solution and that the dmso ligand trans to R in cis-[PtRCl(dmso),] undergoes dissociation and exchange a t ambient temperature. With anionic reagents X-(X = Br, I, or SCN) the complex cis- [PtPhCl(dmso),] forms bridged complexes [Pt,Ph,(p-X),(dmso),].In addition to the diaryl complex, SnMe,-(C,H,OMe-2) forms the cyclometallated complex [Pt(C6H,0dH,-2) (dmso),]. The dmso ligands of all the complexes are readily displaced by phosphorus donors, AsPh,, SbPh,, or 2,2'-bipyridyl ; 'H} n.m.r. parameters are reported for the phosphorus-containing complexes.L~KYLTHIMI-'l.HYLTIN compounds (Snhle,R) have been shown to react with a number of chloro-complexes of platinum( 11) and the reactions with [PtCl,(cod)] (cod = cyclo-octa-1 ,Tj-diene) provide a convenient route to the complexes [PtR,(cod)], [PtRCl(cod)], and complexes derived from them by displacement of cod by a variety of N, Y , and As donors.l This route can he of particular value when the corresponding aryl-lithium or Grignard reagent is not available [for example, R = Cr(q-C,H,)(CO),] or is not obtainable in a pure form [for example, R = 1,2-dihydrobenzocyclobutenyl] . , However, this and other methods of introducing alkyl and aryl ligands into platinum(I1) complexes have the disadvantage of requiring that the common starting material K,[PtCl,] must first be converted into a complex [PtCl,L2] (L = $cod, PR,, etc.) which is normally isolated before being treated with an organometallic reagent to give the organoplatinum( 11) complex.We have now found that platinum(I1) methyl and aryl complexes may be obtained by a very simple procedure from K2[PtC1,] and organotin compounds using dime thy1 sulphoxide (dmso) as solvent. This and the related method starting from [PtCl,(dmso),] are described here, and we also describe a number of comparisons between these routes and the previously described reaction between the organotin compounds and [PtCl,(cod)] ; a preliminary account of some of this work has a~p e a r e d .~ RESULTSA N D DISCUSSION In a typical procedure (method A), K,[PtCl,] (0.002 mol) was dissolved in dmso (8 cm3) at room temperature, an excess of SnMe,R (R = Me or aryl; 0.004-0.01 mol) added, and the mixture stirred for several hours at 70-90 "C. After removal of dmso under vacuum the complexes [PtR,(dmso),] were readily isolated. Use of equimolar proportions of K,[PtCl,] and SnMe,R gave the complexes [PtRCl(dmso),]. The reaction mixtures were initially red owing to the presence of [PtC1,I2-, and during the course of a few minutes became yellow because of formation of cis-[PtCl,(dmso),]. The course of the reaction and yield were similar irrespective of whether t No reprints available.the tin conq)ound was introduced before or after this colour change. W i t m the product was colourless, the mixture after complet...

Biodegradation of persistent micropollutants like pesticides often slows down at low concentrations (μg/L) in the environment. Mass transfer limitations or physiological adaptation are debated to be responsible. Although promising, evidence from compound-specific isotope fractionation analysis (CSIA) remains unexplored for bacteria adapted to this low concentration regime. We accomplished CSIA for degradation of a persistent pesticide, atrazine, during cultivation of Arthrobacter aurescens TC1 in chemostat under four different dilution rates leading to 82, 62, 45, and 32 μg/L residual atrazine concentrations. Isotope analysis of atrazine in chemostat experiments with whole cells revealed a drastic decrease in isotope fractionation with declining residual substrate concentration from ε(C) = −5.36 ± 0.20‰ at 82 μg/L to ε(C) = −2.32 ± 0.28‰ at 32 μg/L. At 82 μg/L ε(C) represented the full isotope effect of the enzyme reaction. At lower residual concentrations smaller ε(C) indicated that this isotope effect was masked indicating that mass transfer across the cell membrane became rate-limiting. This onset of mass transfer limitation appeared in a narrow concentration range corresponding to about 0.7 μM assimilable carbon. Concomitant changes in cell morphology highlight the opportunity to study the role of this onset of mass transfer limitation on the physiological level in cells adapted to low concentrations.

Exploring adaptive strategies by which microorganisms function and survive in low-energy natural environments remains a grand goal of microbiology, and may help address a prime challenge of the 21st century: degradation of man-made chemicals at low concentrations (“micropollutants”). Here we explore physiological adaptation and maintenance energy requirements of a herbicide (atrazine)-degrading microorganism (Arthrobacter aurescens TC1) while concomitantly observing mass transfer limitations directly by compound-specific isotope fractionation analysis. Chemostat-based growth triggered the onset of mass transfer limitation at residual concentrations of 30 μg L−1 of atrazine with a bacterial population doubling time (td) of 14 days, whereas exacerbated energy limitation was induced by retentostat-based near-zero growth (td = 265 days) at 12 ± 3 μg L−1 residual concentration. Retentostat cultivation resulted in (i) complete mass transfer limitation evidenced by the disappearance of isotope fractionation (ε13C = −0.45‰ ± 0.36‰) and (ii) a twofold decrease in maintenance energy requirement compared with chemostat cultivation. Proteomics revealed that retentostat and chemostat cultivation under mass transfer limitation share low protein turnover and expression of stress-related proteins. Mass transfer limitation effectuated slow-down of metabolism in retentostats and a transition from growth phase to maintenance phase indicating a limit of ≈10 μg L−1 for long-term atrazine degradation. Further studies on other ecosystem-relevant microorganisms will substantiate the general applicability of our finding that mass transfer limitation serves as a trigger for physiological adaptation, which subsequently defines a lower limit of biodegradation.