A method for the generation of glycoprotein mimetics

A general method for preparing glycoprotein mimetics with defined glycan structure using the Z domain protein as an example is reported. An unnatural amino acid containing the keto group was site-specifically incorporated into a target protein, Z domain, in response to the amber nonsense codon with high translational fidelity and efficiency. An aminooxy saccharide derivative was then selectively coupled to this genetically encoded keto group. The resulting saccharide core was elaborated to a glycan complex with glycosyltransferases. Alternatively, aminooxy analogues of more complicated glycans were prepared and directly attached to the keto group. Homogeneous glycoprotein mimetics thus prepared should prove useful for the study of carbohydrate effects on glycoprotein structure and function. This method may also lead to the production of glycoprotein therapeutics from Escherichia coli.     

η-Alkynyl and vinylidene transition metal complexes: 10. Reaction of the metal-acetylide [(η-C5H5)(CO)(NO)W---CC---C(CH3)3]Li with 1,2-diiodoethane as electrophile and with various nucleophiles

Treatment of the η¹-acetylide complex [(η⁵-C₅H₅)(CO)(NO)W---CC---C(CH₃)₃]Li (4) with 1,2-diiodoethane in THF at −78 °C, followed by the addition of Li---CC---R [R=C(CH₃)₃, C₆H₅, Si(CH₃)₃, 6a–6c] or n-C₄H₉Li and protonation with H₂O, afforded the corresponding oxametallacyclopentadienyl complexes (η⁵-C₅H₅)W(I)(NO)[η²-O=C(CC---R)CH=CC(CH₃)₃] (7a–7c), 8c and (η⁵-C₅H₅)W(I)(NO)[η²-O=C(n-C₄H₉)CH=CC(CH₃)₃] (9). The formation of these metallafuran derivatives is rationalized by the electrophilic attack of 1,2-diiodoethane onto the metal center of 4 to form first the neutral complex [(η⁵-C₅H₅)(I)(CO)(NO)W---CC---C(CH₃)₃] (5). Subsequent nucleophilic addition of Li---CC---R 6a–6c or n-C₄H₉Li and a reductive elimination step followed by protonation leads to the products 7a–7c and 9. One reaction intermediate could be trapped with CF₃SO₃CH₃ and characterized by a crystal structure analysis. The identity of another intermediate was established by infrared spectroscopic data. The oxametallacyclopentadienyl complex 10 forms in the presence of excess 1,2-diiodoethane through an alternative pathway and crystallizes as a clathrate containing iodine.     

Nonparametric Gaussian inference for stable processes

Statistical Inference for Stochastic Processes - Jump processes driven by $$\alpha $$ -stable Lévy processes impose inferential difficulties as their increments are heavy-tailed and the...     

Discrete minimum and maximum principles for finite element approximations of non-monotone elliptic equations

Summary. Uniform lower and upper bounds for positive finite-element approximations to semilinear elliptic equations in several space dimensions subject to mixed Dirichlet-Neumann boundary conditions are derived. The main feature is that the non-linearity may be non-monotone and unbounded. The discrete minimum principle provides a positivity-preserving approximation if the discretization parameter is small enough and if some structure conditions on the non-linearity and the triangulation are assumed. The discrete maximum principle also holds for degenerate diffusion coefficients. The proofs are based on Stampacchias truncation technique and on a variational formulation. Both methods are settled on careful estimates on the truncation operator.Mathematics Subject Classification (2000): 65N30, 65N12     

In-Line Monitoring of Rheological Parameters with an Electromagnetic Flowmeter

Tomographic signal processing has been added to a conventional electromagnetic flowmeter. The result is a new method for measuring rheological parameters of viscous, non-Newtonian fluids. The practical realization requires only minor changes to existing instruments. Hence their main advantages are maintained, such as non-invasive, in-line measurement without pressure drop. The basic idea is to generate two different magnetic fields with the flowmeter by switching the current direction in one of the magnetic coils. The flowmeter measures two signals depending on the flow profile. Using simple parametric models for both the flow profile and the rheology, the flow profile can be calculated from the flowmeter signals, and from the flow profile the rheological behaviour is determined. The theory and experimental results with a slightly modified industrial flowmeter are presented.     

Geometric dilation of closed planar curves: New lower bounds

Given two points on a closed planar curve, C, we can divide the length of a shortest connecting path in C by their Euclidean distance. The supremum of these ratios, taken over all pairs of points on the curve, is called the geometric dilation of C. We provide lower bounds for the dilation of closed curves in terms of their geometric properties, and prove that the circle is the only closed curve achieving a dilation of π/2, which is the smallest dilation possible. Our main tool is a new geometric transformation technique based on the perimeter halving pairs of C.