Evidence for microplastics contamination of the remote tributary of the Yenisei River, Siberia - The pilot study results

This study is a pioneering attempt to count microplastics (MPs) in the Yenisei River system to clarify the role of Siberian Rivers in the transport of MPs to the Arctic Ocean. The average MPs content in the surface water of the Yenisei large tributary, the Nizhnyaya Tunguska River, varied from 1.20 ± 0.70 to 4.53 ± 2.04 items/m3, tending to increase along the watercourse (p < 0.05). Concentrations of MPs in bottom sediments of the two rivers were 235 ± 83.0 to 543 ± 94.1 with no tendency of downstream increasing. Linear association (r = 0.952) between average organic matter content and average counts of MPs in bottom sediments occurred. Presumably MPs originated from the daily activities of the in-situ population. Further spatial-temporal studies are needed to estimate the riverine MPs fluxes into the Eurasian Arctic seas

Steric control in the metal-ligand electron transfer of iminopyridine-ytterbocene complexes

International audienceA systematic study of reactions between Cp*Yb-2(THF) (Cp* = eta(5)-C5Me5, 1) and iminopyridine ligands (IPy = 2,6-(Pr2C6H3N)-Pr-i=CH(C5H3N-R), R = H (2a), 6-C4H3O (2b), 6-C4H3S (2c), 6-C6H5 (2d)) featuring similar electron accepting properties but variable denticity and steric demand, has provided a new example of steric control on the redox chemistry of ytterbocenes. The reaction of the unsubstituted IPy 2a with 1, either in THF or toluene, gives rise to the paramagnetic species Cp*Yb-2(III)(IPy)(center dot-) (3a) as a result of a formal one-electron oxidation of the Yb-II ion along with IPy reduction to a radical-anionic state. The reactions of 1 with substituted iminopyridines 2b-d, bearing aryl or hetero-aryl dangling arms on the 6 position of the pyridine ring occur in a non-coordinating solvent (toluene) only and afford coordination compounds of a formally divalent ytterbium ion, coordinated by neutral IPy ligands Cp*Yb-2(II)(IPy)(0) (3b-d). The X-ray diffraction studies revealed that 2a-c act as bidentate ligands; while the radical-anionic IPy in 3a chelates the Yb-III ion with both nitrogens, neutral IPy ligands in 3b and 3c participate in the metal coordination sphere through the pyridine nitrogen and O or S atoms from the furan or thiophene moieties, respectively. Finally, in complex 3d the neutral IPy ligand formally adopts a monodentate coordination mode. However, an agostic interaction between the Yb-II ion and an ortho C-H bond of the phenyl ring has been detected. Imino-nitrogens in 3b-d are not involved in the metal coordination. Variable temperature magnetic measurements on 3a are consistent with a multiconfigurational ground state of the Yb ion and suggest that the largest contribution arises from the 4f(13)-radical configuration. For complexes 3b and 3c the data of magnetic measurements are indicative of a Yb-II-closed shell ligand electronic distribution. Complex 3d is characterized by a complex magnetic behavior which does not allow for an unambiguous estimation of its electronic structure. The results are rationalized using DFT and CSSCF calculations. Unlike diazabutadiene analogues, 3a does not undergo a solvent mediated metalligand electron transfer and remains paramagnetic in THF solution. On the other hand, complexes 3b-d readily react with THF to afford 1 and free IPy 2b-d

A Massively Parallel Sequencing Approach Uncovers Ancient Origins and High Genetic Variability of Endangered Przewalski's Horses

The endangered Przewalski's horse is the closest relative of the domestic horse and is the only true wild horse species surviving today. The question of whether Przewalski's horse is the direct progenitor of domestic horse has been hotly debated. Studies of DNA diversity within Przewalski's horses have been sparse but are urgently needed to ensure their successful reintroduction to the wild. In an attempt to resolve the controversy surrounding the phylogenetic position and genetic diversity of Przewalski's horses, we used massively parallel sequencing technology to decipher the complete mitochondrial and partial nuclear genomes for all four surviving maternal lineages of Przewalski's horses. Unlike single-nucleotide polymorphism (SNP) typing usually affected by ascertainment bias, the present method is expected to be largely unbiased. Three mitochondrial haplotypes were discovered—two similar ones, haplotypes I/II, and one substantially divergent from the other two, haplotype III. Haplotypes I/II versus III did not cluster together on a phylogenetic tree, rejecting the monophyly of Przewalski's horse maternal lineages, and were estimated to split 0.117–0.186 Ma, significantly preceding horse domestication. In the phylogeny based on autosomal sequences, Przewalski's horses formed a monophyletic clade, separate from the Thoroughbred domestic horse lineage. Our results suggest that Przewalski's horses have ancient origins and are not the direct progenitors of domestic horses. The analysis of the vast amount of sequence data presented here suggests that Przewalski's and domestic horse lineages diverged at least 0.117 Ma but since then have retained ancestral genetic polymorphism and/or experienced gene flow

Selective Intermolecular C–H Bond Activation: A Straightforward Synthetic Approach to Heteroalkyl Yttrium Complexes Containing a Bis(pyrazolyl)methyl Ligand

The reactions of bis­(pyrazolyl)­methanes CH₂(C₃HN₂R₂-3,5)₂ (R = Me, <i>t</i>Bu) with Y­(CH₂SiMe₃)₃(THF)₂ and LY­(CH₂SiMe₃)₂­(THF)_<i>n</i> (L = amidopyridinate (Ap′), amidinate (Amd), tridentate amidinate bearing 2-methoxyphenyl pendant in a side arm (Amd^OMe) and pentamethylcyclopentadienyl (Cp*); <i>n</i> = 0, 1) were investigated. CH₂(C₃HN₂<i>t</i>Bu₂-3,5)₂ turned out to be inert in these reactions, while less bulky CH₂(C₃HN₂Me₂-3,5)₂ easily undergoes metalation by yttrium alkyls. The reaction of Y­(CH₂SiMe₃)₃(THF)₂ with CH₂(C₃HN₂Me₂-3,5)₂ regardless of the molar ratio of the reagents affords a homoleptic tris­(alkyl) species, Y­[CH­(C₃HN₂Me₂-3,5)₂]₃ (<b>1</b>). However, the reactions of equimolar amounts of LY­(CH₂SiMe₃)₂(THF)_<i>n</i> and CH₂(C₃HN₂Me₂-3,5)₂ occur selectively with replacement of a sole CH₂SiMe₃ fragment and afford the related heteroalkyl complexes LY­(CH₂SiMe₃)­[CH­(C₃HN₂Me₂-3,5)₂]­(THF)_<i>n</i> (L = Ap′, <i>n</i> = 1 (<b>6</b>); Amd, <i>n</i> = 0 (<b>7</b>); Amd^OMe, <i>n</i> = 1 (<b>8</b>); Cp*, <i>n</i> = 1 (<b>9</b>)) in good yields. The second equivalent of CH₂(C₃HN₂Me₂-3,5)₂ does not react with heteroalkyl yttrium complexes. The X-ray studies revealed that in complexes <b>1</b> and <b>6</b>–<b>9</b> the bis­(pyrazolyl)­methyl ligands are bound to the yttrium centers in a similar fashion via one covalent Y–C and two coordination Y–N bonds. Thermal decomposition of complexes <b>6</b>–<b>9</b> (C₆D₆, 80 °C) as evidenced by ¹H NMR spectroscopy resulted in SiMe₄ elimination, while no activation of the C–H bonds of bis­(pyrazolyl)­methyl ligands was detected. When <b>6</b> was treated with an equimolar amount of PhSiH₃, only the YCH₂SiMe₃ bond selectively underwent σ-bond metathesis and a dimeric yttrium alkyl-hydrido complex, {Ap′Y­[CH­(C₃HN₂Me₂-3,5)₂]­(μ²-H)}₂ (<b>10</b>), was formed. The reaction of <b>6</b> with 2,6-diisopropylaniline also resulted in the selective protonation of the YCH₂SiMe₃ bond and cleanly afforded alkyl-anilido complex Ap′Y­(NHC₆H₃<i>i</i>Pr₂-2,6)­[CH­(C₃HN₂Me₂-3,5)₂]­(THF) (<b>11</b>). The ternary catalytic systems <b>6</b>–<b>9</b>/borate/Al<i>i</i>Bu₃ (borate = [HNMe₂Ph]­[B­(C₆F₅)₄], [Ph₃C]­[B­(C₆F₅)₄]; [Ln]:[borate]:[Al<i>i</i>Bu₃] = 1:1:10) demonstrated moderate catalytic activity in isoprene polymerization; they allow quantitative conversion into polymer of up to 1000 equiv of monomer in 2–4 h. The best activity and 1,4-cis selectivity (83.5%) were demonstrated by amidinato complex <b>8</b>

Reversible Switching of Coordination Mode of ansa bis(Amidinate) Ligand in Ytterbium Complexes Driven by Oxidation State of the Metal Atom

Reaction of bisamidine C₆H₄-1,2-{NC­(<i>t</i>-Bu)­NH­(2,6-Me₂C₆H₃)}₂ (<b>1</b>) and [(Me₃Si)₂N]₂Yb­(THF)₂ (THF = tetrahydrofuran) (toluene; room temperature) in a 1:1 molar ratio afforded a bis­(amidinate) Yb^II complex [C₆H₄-1,2-{NC­(<i>t</i>-Bu)­N­(2,6-Me₂C₆H₃)}₂]­Yb­(THF) (<b>2</b>) in 65% yield. Complex <b>2</b> features unusual κ¹amide, η⁶-arene coordination of both amidinate fragments to the ytterbium ion, resulting in the formation of a bent bis­(arene) structure. Oxidation of <b>2</b> by Ph₃SnCl (1:1 molar ratio) or (PhCH₂S)₂ (1:0.5) leads to the Yb^III species [C₆H₄-1,2-{NC­(<i>t</i>-Bu)­N­(2,6-Me₂C₆H₃)}₂]­YbCl­(1,2-dimethoxyethane) (<b>3</b>) and {[C₆H₄-1,2-{NC­(<i>t</i>-Bu)­N­(2,6-Me₂C₆H₃)}₂]­Yb­(μ-SCH₂Ph)}₂ (<b>4</b>), performing “classic” κ²N,N′-chelating coordination mode of ansa bis­(amidinate) ligand. By the reduction of <b>3</b> with equimolar amount of sodium naphthalide [C₁₀H₈^•–]­[Na⁺] in THF, complex <b>2</b> can be recovered and restored to a bent bis­(arene) structure. Complex <b>3</b> was also synthesized by the salt metathesis reaction of equimolar amounts of YbCl₃ and the dilithium derivative of <b>1</b> in THF

Thermally Stable Ln(II) and Ca(II) Bis(benzhydryl) Complexes: Excellent Precatalysts for Intermolecular Hydrophosphination of C-C Multiple Bonds

International audienceA series of Ln(II) and Ca(II) bis(alkyl) complexes with bulky benzhydryl ligands, [(p-tBu-C6H4)(2)-CH](2)M(L-n) (M = Sm, L = DME, n = 2 (1); M = Sm, Yb, Ca, L = TMEDA, n = 1 (2, 3, 4), were synthesized by the salt-metathesis reaction of MI2(THF)(n) (n = 0-2) and [(p-tBu-C6H4)(2)CH]Na--(+). In complex 1, the benzhydryl ligands are bound to the metal center in eta(2)-coordination mode. Unlike complex 1, in isomorphous complexes 3 and 4, due to the coordination unsaturation of the metal center, the both benzhydryl ligands coordinate to the metal in eta(3)-fashion. In complex 2, one ligand is eta(3)-coordinated while the second one is eta(4)-coordinated to the Sm(II) ion. Complexes 2-4 demonstrated unprecedented thermal stability: no evidence of decomposition was observed after heating their solutions in C6D6 at 100 degrees C during 72 h. Complex 1 behaves differently: thermolysis in C6D6 solution at 75 degrees C results in total decomposition in 8 h. Addition of DME promotes decomposition of 2-4 and makes it feasible at 40 degrees C. Complexes 1-4 demonstrated high catalytic activity and excellent regio- and chemoselectivities in intermolecular hydrophosphination of double and triple C-C bonds with both primary and secondary phosphines. Complexes 2 and 3 enable addition of PhPH2 toward the internal C=C bond of Z- and E-stilbenes with 100% conversion under mild conditions. Double sequential hydrophosphination of phenylacetylene with Ph2PH and PhPH2 was realized due to the application of Yb(II) complex as a catalyst