Combinatorial Chemistry for Ligand Development in Catalysis: Synthesis and Catalysis Screening of Peptidosulfonamide Tweezers on the Solid Phase

On the basis of a pyrrolidine tweezer 1, a library of peptidosulfonamide tweezers (15a-e, 16a-e) was synthesized on the solid phase. This library was screened in a simultaneous substrate screening procedure for the ability to enantioselectively catalyze the Ti(O-i-Pr)(4)-mediated addition of diethylzinc to aldehydes. One of the best solid-phase tweezer catalyst (i.e., 16d, giving an ee of 32% in solid-phase catalysis) was resynthesized in solution (compounds 20 and 21). The now homogeneous solution-phase catalysis showed even better enantioselectivity (i.e., up to 66%).     

Gamma-ray spectroscopy with relativistic exotic heavy-ions

Feasibility of gamma-ray spectroscopy at relativistic energies with exotic heavy-ions and new generation of germanium detectors (segmented Clover) is discussed. An experiment with such detector array and radioactive is discussed.     

Zur Theorie der Gammafunction

Ohne Zusammenfassung Vergl. meine Abhandlung:Om en ny klass af transcendenta functioner, hvilka ?ro n?ra besl?gtade med gammafunktionen, Acta soc. scient. Fennic?, Tom. XIV, XV; 1885, 1886.     

An efficient step size control for continuation methods

In solving a nonlinear equation by the use of a continuation method one of the crucial problems is the choice of the step sizes. We present a model for the total computational cost of a standard numerical continuation process and solve the problem of optimal step size control for this model. Using the theoretical results as a basis, we develop an adaptive step size algorithm for Newton's method. This procedure is computationally inexpensive and it gives quite satisfactory results compared to some other numerical experiments found in the literature.     

A tris(pyrazolyl) eta6-arene ligand that selects Cu(I) over Cu(II)

1,3,5-Tris{2'-[(pyrazol-1-yl)methyl]phenyl}benzene, 4, and its complexes with Cu(I) and Ag(I) have been prepared and characterized. Both CuI4 and AgI4 triflate crystallize in the rhombohedral space group R3, with the cations and anions each exhibiting crystallographically imposed 3-fold (C3) symmetry. In both complexes, 4 behaves as a tris(pyrazolyl) eta6-arene ligand whose arms act as three-pronged tweezers to form chiral, propeller-like cations with pyramidal MN(pyrazole)3 coordination geometries. Centers of symmetry in the space group ensure that the crystals are racemates, with equal numbers of P,P,P and M,M,M enantiomers. In broad outline, each cation is shaped like a three-legged stool, with the metal ion centered at the top and pointed downward from a triangular N(pyrazole) plane toward the center of gravity (Cg) of the central benzene ring (a metal-endo conformation), which constitutes the bottom shelf of the stool. The Cu(I)...Cg and Ag(I)...Cg distances, 3.195(2) and 3.165(2) A, respectively, support the existence of an eta6 bonding interaction with Ag(I) and, to a lesser extent, with Cu(I). NMR data for AgI4 suggest rapid interconversion of this cation in solution between P,P,P and M,M,M enantiomers. Our inability to prepare any Cu(II) complexes with 4 is consistent with cyclovoltammetric results, which suggest that the ligand is more easily oxidized than Cu(I).