Method validation in analytical sciences: discussions on current practice and future challenges

Accreditation and Quality Assurance - Eurachem held a workshop on method validation in analytical sciences in Gent, Belgium, on 9–10 May 2016. A summary of the working group discussions is...     

Uniform approximation of eigenvalues in Laguerre and Hermite -ensembles by roots of orthogonal polynomials

We derive strong uniform approximations for the eigenvalues in general Laguerre and Hermite -ensembles by showing that the maximal discrepancy between the suitably scaled eigenvalues and roots of orthogonal polynomials converges almost surely to zero when the dimension converges to infinity. We also provide estimates of the rate of convergence. In the special case of a normalized real Wishart matrix , where denotes the dimension and the degrees of freedom, the rate is , if with , and the rate is , if with . In the latter case we also show the a.s. convergence of the largest eigenvalue of to the corresponding quantile of the Marcenko-Pastur law.

     

Morphology of magnetically aligning DMPC/DHPC aggregates-perforated sheets, not disks

The morphology of DMPC/DHPC mixtures at total lipid concentration cL = 5% (w/w) and DMPC/DHPC ratio q approximately 3, doped with small amounts of DMPG or CTAB, was investigated. 31P NMR was used to identify the magnetically aligning phase, and cryo-transmission electron microscopy (cryo-TEM) was employed for structural characterization. Magnetic alignment was found to occur between approximately 30 and approximately 45 degrees C, and cryo-TEM showed that the magnetically aligning phase consisted of extended sheets with a lacelike structure. The aggregates are best described as intermediates between two-dimensional networks of flattened, highly branched, cylindrical micelles and lamellar sheets perforated by large irregular holes. DHPC most likely covers the edges of the holes, while DMPC makes up the bilayer bulk of the aggregates. However, 20-43% of the DHPC takes part in the bilayer, corresponding to 6-12% of the bilayer being made up of DHPC. This fraction increases with increasing temperature. At temperatures above 45 degrees C, the aligning phase collapses.     

Reactions of ethyl(acetylacetonato)- (triphenylphosphine)nickel(II)- a new hydride nickel complex, (Ph3P)3Ni(H)Br

The reactions of EtNi(PPh₃)(acac) with various reagents have been discussed; the reaction with NaFe(CO)₂Cp or Fe(CO)₅ occurs via nickel(II) reductive carbonylation while EtNi(PPh₃)(acac) and Et₂AlCl afford the unstable EtNi(PPh₃)₂-Cl. The cleavage of the NiC bond with evolution of ethylene and ethane is observed when EtNi(PPh₃)(acac) reacts with CS₂, HgCl₂ and Et₂AlBr. A new nickel hydride complex, (Ph₃P)₃Ni(H)Br, has been obtained from EtNi(PPh₃)-(acac) and Et₂AlBr and its properties have been studied. Another method of synthesis of this hydride complex directly from Ni(acac)₂ and Et₂AlBr has been proposed.     

Intracellular protein scaffold-mediated display of random peptide libraries for phenotypic screens in mammalian cells

BACKGROUND: Mammalian cell screens of peptide libraries for changes in cellular phenotype may identify novel functional peptides and their cognate binding partners, and allow identification of signal transduction network members or proteins important in disease processes. RESULTS: Green fluorescent protein (GFP) peptide libraries with different structural biases were tested by retroviral expression in A549 carcinoma cells, HUVEC and other cell types. Three different loop replacement libraries, containing 12 or 18 random residues, were compatible with enhanced GFP (EGFP) folding, as was a C-terminally fused random 20-mer library. Library concentrations in A549 cells ranged from ca. 1 to 54 microM. Replacement of loop 3 with known nuclear localization sequence (NLS) peptides, but not with inactive mutants, directed EGFP to the nucleus. Microscopy-based screens of three different libraries for non-uniform localization revealed novel NLS peptides, novel variants of a peroxisomal localization motif, a variety of partial NLS peptides, peptides localized to the nucleolus, and nuclear-excluded peptides. CONCLUSIONS: Peptides can be presented by EGFP in conformations that can functionally interact with cellular constituents in mammalian cells. A phenotypic screen resulting in the discovery of novel localization peptides that were not cell type-specific suggests that this methodology may be applied to other screens in cells derived from diseased organisms, and illustrates the use of intracellular combinatorial peptide chemistry in mammalian cells.     

Proficiency testing in analytical chemistry,microbiology and laboratory medicine: discussions on current practice and future directions

Accreditation and Quality Assurance - A summary of the working group discussions on proficiency testing (PT) and external quality assessment (EQA) held at the Eurachem Workshop, Portorož,...