Use of the silylation reaction in synthesis of fragment 1–4 of the ACTH sequence

A new effective method of synthesizing fragment 1–4 of the ACTH sequence ensuring a high overall yield of the desired product is proposed. This result is achieved thanks to the wide use of the silylation reaction in the synthesis, which has permitted a considerable simplification of the process and the avoidance of the formation of by-products. The peptides synthesized have been characterized by their angles of optical rotation, chromatographic mobilities, and melting points. A table of chemical shifts in the¹³C NMR spectra of the final and intermediate compounds is given.All-Union Research Institute of Technology of Blood Substitutes and Hormone Preparations, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 248–253, March–April, 1988.     

Lower Bounds on the Distortion of Embedding Finite Metric Spaces in Graphs

The main question discussed in this paper is how well a finite metric space of size n can be embedded into a graph with certain topological restrictions. The existing constructions of graph spanners imply that any n -point metric space can be represented by a (weighted) graph with n vertices and n ^{1 +O(1/r)} edges, with distances distorted by at most r . We show that this tradeoff between the number of edges and the distortion cannot be improved, and that it holds in a much more general setting. The main technical lemma claims that the metric space induced by an unweighted graph H of girth g cannot be embedded in a graph G (even if it is weighted) of smaller Euler characteristic, with distortion less than g/4 - 3/2 . In the special case when |V(G)| =|V(H)| and G has strictly less edges than H , an improved bound of g/3 - 1 is shown. In addition, we discuss the case χ(G) < χ(H) - 1 , as well as some interesting higher-dimensional analogues. The proofs employ basic techniques of algebraic topology. Received September 26, 1995, and in revised form March 18, 1996.     

Analysis of the linear tension of two-dimensional droplets on heterogeneous adsorbents

A procedure for analyzing the formation processes of two-dimensional droplets of an adsorbate on a rigid adsorbent support is considered. The molecular theory is based on data on the potential functions between adsorbent atoms and adsorbate molecules. Interactions between nearest neighbors are considered in the quasi-chemical approximation. The internal motions of adsorbent atoms and adsorbate molecules are ignored. Problems of describing the formation of droplets on heterogeneous adsorbents are associated with calculations for binodals (illustrated with the simplest example of two different homogeneous crystal faces) due to the choice of methods for calculating linear tension and the structural model of the region of the liquid–vapor transition. The dependence of the characteristics of droplets in the layered structural model on the method for determining the reference lines of the tension is shown for their metastable and equilibrium states. It is found that for a number of structural parameters, the thermodynamic determination of the line of tensions of metastable droplets can result in nonmonotonic dependences of the linear tension on their radii. The characteristics of two-dimensional liquid–vapor interfaces are compared for two structural models: coordination sphere and layered. It is found that the coordination sphere model allows the exclusion of the structural parameter of the layered model, but both models need refinement at small radii.     

On dominatedl 1 metrics

We introduce and study a classl ₁ ^dom (ρ) ofl ₁-embeddable metrics corresponding to a given metric ρ. This class is defined as the set of all convex combinations of ρ-dominated line metrics. Such metrics were implicitly used before in several constuctions of low-distortion embeddings intol _p -spaces, such as Bourgain’s embedding of an arbitrary metric ρ onn points withO(logh) distortion. Our main result is that the gap between the distortions of embedding of a finite metric ρ of sizen intol ₂ versus intol ₁ ^dom (ρ) is at most , and that this bound is essentially tight. A significant part of the paper is devoted to proving lower bounds on distortion of such embeddings. We also discuss some general properties and concrete examples. Research by J. M. supported by Charles University grants No. 158/99 and 159/99. Part of the work by Y. R. was done during his visit at the Charles University in Prague partially supported by these grants, by the grant GAČR 201/99/0242, and by Haifa University grant for Promotion of Research.     

Direct Electrical Wiring of Oxidoreductase Enzymes to Silicate Based Electrodes

Three types of reagentless glucose biosensor based on composite graphite-ormosil materials are described: (1) a redox modified silicate-graphite electrode doped with glucose oxidase, (2) a methyl silicate-graphite material doped with redox modified glucose oxidase, and (3) a methyl silicate and redox modified graphite composite material doped with glucose oxidase.     

Analysis of van der Waals loops in the adsorption isotherms of porous systems

The properties of the van der Waals loops for isotherms of the adsorbate located in the slit-shaped and cylindrical pores of different width were analyzed. The adsorbate molecules are modeled by spherical Lennard-Jones type particles. The calculation was based on the latticegas model in the quasichemical approximation for intermolecular interactions. The accuracy of calculations of the adsorption hysteresis loops increases due to the use of distributed models, which reflect the spatial inhomogeneity of the distribution of molecules along the normal to the pore wall. The effect of the adsorbate-adsorbent interaction potential and pore width on the pattern of adsorption isotherms is considered. Taking into account the inhomogeneity of the spatial distribution of molecules changes the course of the spinodal sections of the adsorption isotherms.     

Synthesis and characterization of two new bulky tris(mercaptoimidazolyl)borate ligands and their zinc and cadmium complexes

The sodium salts of the tris(2-mercapto-1-benzylimidazolyl)borate [Tm^Bz]⁻ and tris(2-mercapto-1-p-tolylimidazolyl)borate [Tm^p-Tol]⁻ anions have been readily prepared in very good yield from NaBH₄ and 2-mercapto-1-benzylimidazole or 2-mercapto-1-p-tolylimidazole, respectively. These new monoanionic tripodal sulfur-donor ligands have been used to prepare the Group 12 derivatives (Tm^R)MBr (M=Zn, Cd; R=Bz, p-Tol), all of which have been characterized by a combination of analytical and spectroscopic techniques, including electrospray ionization mass spectrometry (ESI MS) and, in the case of both benzyl-substituted derivatives, single-crystal X-ray diffraction.     

Surface/interface phenomena in nano‐multilayer coating under severing tribological conditions

An extensive study of surface/interface phenomena during wear of an adaptive TiAlCrSiYN/TiAlCrN nano‐multilayer coating deposited using physical vapor deposition was undertaken under increasingly severe tribological conditions associated with dry end milling of H13 hardened tool steel. The results of FEM modeling on the temperature/stress distribution at different cutting speeds outline actual cutting conditions on the both rake and flank frictional surfaces of the coated tool. Studies of the surface/interface phenomena were made by means of SEM/high‐resolution transmission electron microscopy/XPS analyses. Results demonstrate that intensifying tribological conditions facilitates improved wear performance of the adaptive coating layer. In extreme tribological conditions of ultra‐performance machining (cutting speed of 500 m/min), the self‐organization process establishes entirely through the formation of a nano‐scale layer of dynamically re‐generating tribo‐ceramic films. The formation of these surface nano‐films results in exceptionally efficient protection of the underlying coating layers. In response to the extreme external environment, the coating layer remained almost undamaged during a long run, demonstrating the capacity to efficiently replenish necessary tribo‐ceramic films. In this way, interconnection of various surface and undersurface processes is established in the hierarchically structured tribo‐films/coating layer. This integral performance is responsible for exceptional wear resistance under intensifying and extreme tribological conditions. Copyright © 2016 John Wiley & Sons, Ltd.