Synthesis and structure of copper(II) 3-(3′,5′-Di-<Emphasis Type="Italic">tert</Emphasis>-butyl-4′-hydroxybenzyl)acetylacetonate

Copper(II) 3-(3,5-di-tert-butyl-4-hydroxybenzyl)acetylacetonate was prepared, and its molecular and crystal structure were determined by single crystal X-ray diffraction. There are two crystallographically independent molecules of the complex in the crystal. In the first molecule, the square planar coordination of Cu(II) is virtually ideal, and in the second molecule it is somewhat distorted. On the whole, the conformations of the independent molecules are similar. The ESR spectrum of the polycrystalline complex suggests magnetic coupling of the Cu atoms and magnetic ordering. In solution in coordination-inert toluene, heating increases the contribution of tetrahedral distortions. In ethanol, the solvent molecule additionally coordinates at the axial positions of the complex.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1775–1781.Original Russian Text Copyright © 2004 by Podyachev, Bukharov, Litvinov, Morozov, Gubaidullin, Nugumanova, Mukmeneva.This revised version was published online in April 2005 with a corrected cover date.     

Phthalocyanines and related compounds: XXXVIII. Synthesis of symmetric taurine- and choline-substituted phthalocyanines

Procedures have been developed for the synthesis of a series of metal complexes derived from water-soluble anionic and cationic octa-4,5-carboxyphthalocyanine-taurine and choline conjugates.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1907–1911.Original Russian Text Copyright © 2004 by Mikhalenko, Soloveva, Lukyanets.For communication XXXVII, see [1].This revised version was published online in April 2005 with a corrected cover date.     

Efficient eco-friendly syntheses of dithiocarbazates and thiosemicarbazones

ABSTRACT

Eight Schiff bases have been synthesized by conventional and three different eco-friendly methods, whereby two aromatic carbonyl compounds viz. 2-thiophenecarboxaldehyde and salicylaldehyde were reacted with S-methyl, S-benzyl, and S-n-octyl-dithiocarbazates and thiosemicarbazide. In order to evaluate the efficiency of the synthesis methods, the time to complete the reaction and the yield of the Schiff base synthezised by eco-friendly methods, such as solvent-free grinding, water as a solvent, and lemon juice as catalyst, were compared with those synthesized by the conventional method. The chemical structures of all the synthesized Schiff bases, where two of them are novel and reported for the first time, were fully characterized by a variety of physico-chemical, analytical, and spectroscopic techniques. The molecular and crystal structures of the Schiff bases especially those having 2-thiophene moiety were further elucidated by single crystal X-ray diffraction analyzes.     

Beyond Zudilin's conjectured q-analogue of Schmidt's problem

Using the methodology of (rigorous) experimental mathematics, we give a simple and motivated solution to Zudilin's question concerning a q-analogue of a problem posed by Asmus Schmidt about a certain binomial coefficients sum. Our method is based on two simple identities that can be automatically proved using the Zeilberger and q-Zeilberger algorithms. We further illustrate our method by proving two further binomial coefficient sums.     

Solid-Phase Peptide Modification via Deaminative Photochemical Csp3-Csp3 Bond Formation Using Katritzky Salts

Introduction of unnatural amino acids can significantly improve the binding affinity and stability of peptides. Commercial availability of such amino acids is limited, and their synthesis is a long and tedious process. We here describe a method that allows the functionalization of peptides directly on solid-support by converting lysine residues to Katritzky salts, and subjecting them to a photochemical Giese reaction under mild reaction conditions. The method avoids the need for amino acid synthesis and instead offers a late-stage modification route for rapid peptide diversification. While numerous modification approaches at the lysine amine have been described, this work provides the first example of deaminative functionalization of peptides at lysine. The two-step protocol is compatible with various substrates, lysine analogues, resins, and all proteinogenic amino acids. Finally, by leveraging solid-phase modification, this protocol facilitates the functionalization of longer peptides as was demonstrated using biologically relevant peptides of up to 15 amino acids.     

Synthesis of Tris‐ and Tetrakis(pentafluoroethyl)silanes

The synthesis and complete characterization of functional, highly Lewis acidic tris(pentafluoroethyl)silanes as well as tetrakis(perfluoroalkyl)silanes Si(C₂F₅)₄ and Si(C₂F₅)₃CF₃ by direct fluorination is described. The reaction of SiCl₄ with LiC₂F₅ invariably affords (pentafluoroethyl)fluorosilicates. To avoid silicate formation by fluoride transfer from LiC₂F₅ the Lewis acidity of the silane has to be decreased by electron‐donating substituents, such as dialkylamino groups. The easily accessible Si(C₂F₅)₃NEt₂ is a valuable precursor for a series of tris(pentafluoroethyl)silanes.     

An Optimal Algorithm to Find the Jump Number of Partially Ordered Sets

The jump number of a partially ordered set (poset) P isthe minimum number of incomparable adjacent pairs (jumps) in some linearextension of P. The problem of finding a linear extension of Pwith minimum number of jumps (jump number problem) is known to beNP-hard in general and, at the best of our knowledge, no exactalgorithm for general posets has been developed. In this paper, wegive examples of applications of this problem and propose for thegeneral case a new heuristic algorithm and an exactalgorithm. Performances of both algorithms are experimentallyevaluated on a set of randomly generated test problems.     

Partial Flocks of Quadratic Cones with a Point Vertex in Pg(n,q), n Odd

We generalise the definition and many properties of flocks ofquadratic cones in PG(3,q) to partial flocks of quadratic coneswith vertex a point in PG(p,q), for n 3 odd.