Alsophis antiguae

Number of Pages: 3Integrative BiologyGeological Science

Switching and Extension of a [c2]Daisy-Chain Dimer Polymer

We report the synthesis of a [c2]daisy-chain dimer via ruthenium-catalyzed ring-closing olefin metathesis. Confirmation of the interlocked nature of the structure was achieved through single-crystal X-ray diffraction analysis. The dimer could be readily switched from the bound to the unbound conformation by treatment with 3.0 equiv of KOH and subsequently reprotonated by treatment with 3.0 equiv of HPF_6. Azide functionalization of the dimer enabled incorporation in linear step-growth polymer chains using the alkyne-azide “click” reaction. Gel permeation chromatography coupled with multiangle laser light scattering analysis showed the polymers contained 22 dimers and had a radius of gyration of 14.8 nm. Acylation of the amines of the dimers sterically forced elongation of the interlocked units, and MALLS analysis of the polymer showed a 48% increase in the R_g (21.4 nm)

Terminal ruthenium carbido complexes as σ-donor ligands

The terminal carbido ligand of (Pcy_3)_2(Cl)_2RuC coordinates to other metal centers in a σ-donor fashion, as in (Pcy_3)_2(Cl)_2Ru≡C–Pd(Cl)_2(Sme_2) and (Pcy_3)_2(Cl)_2Ru≡C–Mo(CO)_5

Transdifferentiation from cornea to lens in Xenopus laevis depends on BMP signalling and involves upregulation of Wnt signalling

<p>Abstract</p> <p>Background</p> <p>Surgical removal of the lens from larval <it>Xenopus laevis </it>results in a rapid transdifferention of central corneal cells to form a new lens. The trigger for this process is understood to be an induction event arising from the unprecedented exposure of the cornea to the vitreous humour that occurs following lens removal. The molecular identity of this trigger is unknown.</p> <p>Results</p> <p>Here, we have used a functional transgenic approach to show that BMP signalling is required for lens regeneration and a microarray approach to identify genes that are upregulated specifically during this process. Analysis of the array data strongly implicates Wnt signalling and the Pitx family of transcription factors in the process of cornea to lens transdifferentiation. Our analysis also captured several genes associated with congenital cataract in humans. Pluripotency genes, in contrast, were not upregulated, supporting the idea that corneal cells transdifferentiate without returning to a stem cell state. Several genes from the array were expressed in the forming lens during embryogenesis. One of these, <it>Nipsnap1</it>, is a known direct target of BMP signalling.</p> <p>Conclusions</p> <p>Our results strongly implicate the developmental Wnt and BMP signalling pathways in the process of cornea to lens transdifferentiation (CLT) in <it>Xenopus</it>, and suggest direct transdifferentiation between these two anterior eye tissues.</p

(Dicyclohexylphosphino)borane, BH_3PH(C_6H_(11))_2, a Precursor to Water-Soluble Phosphine Ligands

(Dicyclohexylphosphino) borane is a precursor in the synthesis of water-soluble phosphines. The boranato group can be removed quantitatively under mild conditions

Latent Olefin Metathesis Catalysts Featuring Chelating Alkylidenes

The synthesis of a series of ruthenium-based metathesis catalysts featuring imine donors chelated through the alkylidene group is described. The relative placement of the imine carbon−nitrogen double bond (exocyclic vs endocyclic) has a major impact on the initiation behavior. When used in metathesis applications, catalysts with an endocyclic imine bond show latent behavior and a high degree of tunability. The incorporation of additional donor atoms is an additional strategy for controlling initiation behavior. These latent catalysts could be useful in high-temperature applications

Mongolism. G. E. W. Wolstenholme and R. Porter (eds.). Little, Brown, Boston. 95 pp. 1967

No Abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38117/1/1420010413_ftp.pd

A Diphenylcyclopropene Complex of Tungsten, [WCl_2O(PMePh_2)_2(η^2-3,3-diphenylcyclopropene)], Precursor to a Tungsten–Oxo–Olefin Metathesis Catalyst

The title compound, dichlorobis(methyldiphenylphosphine-P) [(1,2-[η])-3,3-diphenylcyclopropene]oxotungsten, [WCl_2O(C_(15)H_(12))(C_(13)H_(13)P)_2], is a mononuclear complex of tungsten with an approximately octahedral environment around the metal atom. The ligand, 3,3-diphenylcyclopropene, is bonded to the W atom in a [η]^2-geometry with effectively identical metal-to-carbon bond distances [W-C1 = 2.133 (7) Å and W-C2 2.131 (7) Å]

Novel η^3- Vinylcarbene Complexes Derived from Ruthenium-Based Olefin Metathesis Catalysts

Electron-rich, disubstituted alkynes react with (H_2IMes)(PCy_3)(Cl)_2Ru═CHPh (1; H_2IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) to form phosphine-free η^3-vinylcarbene complexes. An X-ray diffraction study on (H_2IMes)(Cl)_2Ru[η^3-(CHPh)(CPh)(CPh)] (2) confirms the unusual structure. These complexes are relevant to the mechanisms of olefin metathesis and alkyne polymerization

Decomposition of a Key Intermediate in Ruthenium-Catalyzed Olefin Metathesis Reactions

Dinuclear ruthenium complex, with a bridging carbide and a hydride ligand, and methyltricyclohexylphosphonium chloride result from thermal decomposition of olefin metathesis catalyst, (ImesH_2)(PCy)_3)(Cl)_2Ru CH_2. Involvement of dissociated phosphine in the decomposition is proposed. The dinuclear complex has catalytic olefin isomerization activity, which can be responsible for competing isomerization processes in certain olefin metathesis reactions