Incorporation of Pendant Bases into Rh(diphosphine)_2 Complexes: Synthesis, Thermodynamic Studies, And Catalytic CO_2 Hydrogenation Activity of [Rh(P_2N_2)_2]^+ Complexes

A series of five [Rh(P_2N_2)_2]^+ complexes (P_2N_2 = 1,5-diaza-3,7-diphosphacyclooctane) have been synthesized and characterized: [Rh(P^(Ph)_2N^(Ph)_2)_2]^+ (1), [Rh(P^(Ph)_2N^(Bn)_2)_2]^+ (2), [Rh(P^(Ph)_2N^(PhOMe)_2)_2]^+ (3), [Rh(P^(Cy)_2N^(Ph)_2)_2]^+ (4), and [Rh(P^(Cy)_2N^(PhOMe)_2)_2]^+ (5). Complexes 1–5 have been structurally characterized as square planar rhodium bis-diphosphine complexes with slight tetrahedral distortions. The corresponding hydride complexes 6–10 have also been synthesized and characterized, and X-ray diffraction studies of HRh(P^(Ph)_2N^(Bn)_2)_2 (7), HRh(P^(Ph)_2N^(PhOMe)_2)_2 (8) and HRh(P^(Cy)_2N^(Ph)_2)_2 (9) show that the hydrides have distorted trigonal bipyramidal geometries. Equilibration of complexes 2–5 with H_2 in the presence of 2,8,9-triisopropyl-2,5,8,9-tetraaza-1-phosphabicyclo[3,3,3]undecane (Verkade’s base) enabled the determination of the hydricities and estimated pK_a’s of the Rh(I) hydride complexes using the appropriate thermodynamic cycles. Complexes 1–5 were active for CO_2 hydrogenation under mild conditions, and their relative rates were compared to that of [Rh(depe)_2]^+, a nonpendant-amine-containing complex with a similar hydricity to the [Rh(P_2N_2)_2]^+ complexes. It was determined that the added steric bulk of the amine groups on the P_2N_2 ligands hinders catalysis and that [Rh(depe)_2]^+ was the most active catalyst for hydrogenation of CO_2 to formate

Comparison of Peptide Array Substrate Phosphorylation of c-Raf and Mitogen Activated Protein Kinase Kinase Kinase 8

Kinases are pivotal regulators of cellular physiology. The human genome contains more than 500 putative kinases, which exert their action via the phosphorylation of specific substrates. The determinants of this specificity are still only partly understood and as a consequence it is difficult to predict kinase substrate preferences from the primary structure, hampering the understanding of kinase function in physiology and prompting the development of technologies that allow easy assessment of kinase substrate consensus sequences. Hence, we decided to explore the usefulness of phosphorylation of peptide arrays comprising of 1176 different peptide substrates with recombinant kinases for determining kinase substrate preferences, based on the contribution of individual amino acids to total array phosphorylation. Employing this technology, we were able to determine the consensus peptide sequences for substrates of both c-Raf and Mitogen Activated Protein Kinase Kinase Kinase 8, two highly homologous kinases with distinct signalling roles in cellular physiology. The results show that although consensus sequences for these two kinases identified through our analysis share important chemical similarities, there is still some sequence specificity that could explain the different biological action of the two enzymes. Thus peptide arrays are a useful instrument for deducing substrate consensus sequences and highly homologous kinases can differ in their requirement for phosphorylation events

Whole-body tissue stabilization and selective extractions via tissue-hydrogel hybrids for high-resolution intact circuit mapping and phenotyping

To facilitate fine-scale phenotyping of whole specimens, we describe here a set of tissue fixation-embedding, detergent-clearing and staining protocols that can be used to transform excised organs and whole organisms into optically transparent samples within 1–2 weeks without compromising their cellular architecture or endogenous fluorescence. PACT (passive CLARITY technique) and PARS (perfusion-assisted agent release in situ) use tissue-hydrogel hybrids to stabilize tissue biomolecules during selective lipid extraction, resulting in enhanced clearing efficiency and sample integrity. Furthermore, the macromolecule permeability of PACT- and PARS-processed tissue hybrids supports the diffusion of immunolabels throughout intact tissue, whereas RIMS (refractive index matching solution) grants high-resolution imaging at depth by further reducing light scattering in cleared and uncleared samples alike. These methods are adaptable to difficult-to-image tissues, such as bone (PACT-deCAL), and to magnified single-cell visualization (ePACT). Together, these protocols and solutions enable phenotyping of subcellular components and tracing cellular connectivity in intact biological networks

Identification of genetic variants associated with Huntington's disease progression: a genome-wide association study

Background Huntington's disease is caused by a CAG repeat expansion in the huntingtin gene, HTT. Age at onset has been used as a quantitative phenotype in genetic analysis looking for Huntington's disease modifiers, but is hard to define and not always available. Therefore, we aimed to generate a novel measure of disease progression and to identify genetic markers associated with this progression measure. Methods We generated a progression score on the basis of principal component analysis of prospectively acquired longitudinal changes in motor, cognitive, and imaging measures in the 218 indivduals in the TRACK-HD cohort of Huntington's disease gene mutation carriers (data collected 2008–11). We generated a parallel progression score using data from 1773 previously genotyped participants from the European Huntington's Disease Network REGISTRY study of Huntington's disease mutation carriers (data collected 2003–13). We did a genome-wide association analyses in terms of progression for 216 TRACK-HD participants and 1773 REGISTRY participants, then a meta-analysis of these results was undertaken. Findings Longitudinal motor, cognitive, and imaging scores were correlated with each other in TRACK-HD participants, justifying use of a single, cross-domain measure of disease progression in both studies. The TRACK-HD and REGISTRY progression measures were correlated with each other (r=0·674), and with age at onset (TRACK-HD, r=0·315; REGISTRY, r=0·234). The meta-analysis of progression in TRACK-HD and REGISTRY gave a genome-wide significant signal (p=1·12 × 10−10) on chromosome 5 spanning three genes: MSH3, DHFR, and MTRNR2L2. The genes in this locus were associated with progression in TRACK-HD (MSH3 p=2·94 × 10−8 DHFR p=8·37 × 10−7 MTRNR2L2 p=2·15 × 10−9) and to a lesser extent in REGISTRY (MSH3 p=9·36 × 10−4 DHFR p=8·45 × 10−4 MTRNR2L2 p=1·20 × 10−3). The lead single nucleotide polymorphism (SNP) in TRACK-HD (rs557874766) was genome-wide significant in the meta-analysis (p=1·58 × 10−8), and encodes an aminoacid change (Pro67Ala) in MSH3. In TRACK-HD, each copy of the minor allele at this SNP was associated with a 0·4 units per year (95% CI 0·16–0·66) reduction in the rate of change of the Unified Huntington's Disease Rating Scale (UHDRS) Total Motor Score, and a reduction of 0·12 units per year (95% CI 0·06–0·18) in the rate of change of UHDRS Total Functional Capacity score. These associations remained significant after adjusting for age of onset. Interpretation The multidomain progression measure in TRACK-HD was associated with a functional variant that was genome-wide significant in our meta-analysis. The association in only 216 participants implies that the progression measure is a sensitive reflection of disease burden, that the effect size at this locus is large, or both. Knockout of Msh3 reduces somatic expansion in Huntington's disease mouse models, suggesting this mechanism as an area for future therapeutic investigation

Synthesis and Characterization of Heteroleptic Ni(II) Bipyridine Complexes Bearing Bis(N-heterocyclic carbene) Ligands

The synthesis and characterization of four new Ni­(II) bis­(NHC) bipy complexes (bipy = 4, 4′-bipyridine, NHC = N-heterocyclic carbene) are reported. These represent the first examples of the Ni^II(NHC₂) L₂ class of compounds, where L is a two-electron-donor ligand. The introduction of a double propyl bridged bis-NHC ligand (C^Prop2C) imparts reversibility to the electrochemistry of these complexes. The electrochemical response includes two reductions, the first believed to be bipy ligand based, bipy^0/–, and the second metal based. The unusual ligand arrangements in these complexes result in electronic structures in which both the HOMOs and LUMOs are ligand-based, as determined by DFT analysis of all four compounds

Synthesis and Structural Studies of Nickel(0) Tetracarbene Complexes with the Introduction of a New Four-Coordinate Geometric Index, τ_δ

The synthesis and characterization of two homoleptic chelating nickel(0) tetracarbene complexes are reported. These are the first group 10 M(0) (M = Ni, Pd, Pt) tetracarbene complexes. These species have geometries intermediate between <i>C</i>_2<i>v</i> sawhorse and tetrahedral and show high UV–vis absorption in the 350–600 nm range, with extinction coefficients (ϵ) between 5600 and 9400 M^–1 cm^–1. Density functional theory analysis indicates that this high absorptivity is due to metal-to-ligand charge transfer. In order to better describe the unusual geometries encountered in these complexes, an adjustment to the popular τ₄ index for four-coordinate geometries is introduced in order to better delineate between sawhorse and distorted tetrahedral geometries

Incorporation of Pendant Bases into Rh(diphosphine)₂ Complexes: Synthesis, Thermodynamic Studies, And Catalytic CO₂ Hydrogenation Activity of [Rh(P₂N₂)₂]⁺ Complexes

A series of five [Rh­(P₂N₂)₂]⁺ complexes (P₂N₂ = 1,5-diaza-3,7-diphosphacyclooctane) have been synthesized and characterized: [Rh­(P^Ph₂N^Ph₂)₂]⁺ (<b>1</b>), [Rh­(P^Ph₂N^Bn₂)₂]⁺ (<b>2</b>), [Rh­(P^Ph₂N^PhOMe₂)₂]⁺ (<b>3</b>), [Rh­(P^Cy₂N^Ph₂)₂]⁺ (<b>4</b>), and [Rh­(P^Cy₂N^PhOMe₂)₂]⁺ (<b>5</b>). Complexes <b>1</b>–<b>5</b> have been structurally characterized as square planar rhodium bis-diphosphine complexes with slight tetrahedral distortions. The corresponding hydride complexes <b>6</b>–<b>10</b> have also been synthesized and characterized, and X-ray diffraction studies of HRh­(P^Ph₂N^Bn₂)₂ (<b>7</b>), HRh­(P^Ph₂N^PhOMe₂)₂ (<b>8</b>) and HRh­(P^Cy₂N^Ph₂)₂ (<b>9</b>) show that the hydrides have distorted trigonal bipyramidal geometries. Equilibration of complexes <b>2</b>–<b>5</b> with H₂ in the presence of 2,8,9-triisopropyl-2,5,8,9-tetraaza-1-phosphabicyclo­[3,3,3]­undecane (Verkade’s base) enabled the determination of the hydricities and estimated p<i>K</i>_a’s of the Rh­(I) hydride complexes using the appropriate thermodynamic cycles. Complexes <b>1</b>–<b>5</b> were active for CO₂ hydrogenation under mild conditions, and their relative rates were compared to that of [Rh­(depe)₂]⁺, a nonpendant-amine-containing complex with a similar hydricity to the [Rh­(P₂N₂)₂]⁺ complexes. It was determined that the added steric bulk of the amine groups on the P₂N₂ ligands hinders catalysis and that [Rh­(depe)₂]⁺ was the most active catalyst for hydrogenation of CO₂ to formate