Asymmetric hydroformylation with Pt-phosphine-SnCl2 and Pt-bisphosphine-CuCl2 (or CuCl) catalytic systems

A study has been made of asymmetric hydroformylation of styrene with PtCl₂(PPh₃)₂ + bisphosphine + SnCl₂ (bisphosphine: BDPP = (−)-(2S,4S)-2,4-bis(diphenylphosphino)pentane or DIOP = (−)-(4R,5R)-2,2-dimethyl-4,5-bis(diphenylphosphinomethyl)-1,3-dioxolane) and PtCl₂(bisphosphine) + PPh₃ + SnCl₂ catalysts prepared “in situ”. The presence of an excess of the phosphine ligand slightly lowered the reaction rate, but the enantioselectivity of these systems is significantly higher than those involving PtCl(SnCl₃)(bisphosphine) catalysts. Under mild reaction conditions 88.8% enantiomeric excess was achieved. Replacing SnCl₂ in these catalysts by CuCl₂ or CuCl gave a new homogeneous catalytic system which is active at higher reaction temperature (> 100°C), but has a rather moderate enantioselectivity.     

Extensions of an inequality of Bonnesen toD-dimensional space and curvature conditions for convex bodies

For convex bodies inE ^d (d 3) with diameter 2 we consider inequalitiesW _i – W _d–1 +( - 1) W _d 0 (i = 0, , d – 2) whereW _j are the quermassintegrals. In addition, for a ball, equality is attained for a body of revolution for which the elementary symmetric functions _d–1–i of main curvature radii is constant. The inequality is actually proved fori = d – 2 by means of Weierstrass's fundamental theorem of the calculus of variations.Dedicated to Professor Otto Haupt with best wishes on his 100th birthday     

31P NMR Studies of Rhodium Complexes Containing Chelating Diphosphine

Abstract

Among the chiral phosphines prepared up to now BDPP appears to be unique in the sense that its rhodium(I) complexes serve as effective homogeneous asymmetric hydrogenation catalysts not only for the reduction of (Z)-α-acylaminoacrylic acids [1] but also for the reduction of α-ethylstyrene, acetophenone, and acetophenonebenzylimine [2].     

One-armed artificial receptors for the binding of polar tetrapeptides in water: probing the substrate selectivity of a combinatorial receptor library

We have recently developed a new class of one-armed artificial receptors 1 for the binding of the polar tetrapeptide N-Ac-D-Glu-L-Lys-D-Ala-D-Ala-OH (EKAA) 2 in water using a combined combinatorial and statistical approach. We have now further probed the substrate selectivity of this receptor library 1 by screening a second tetrapeptide substrate (3) with the inverse sequence N-Ac-D-Ala-D-Ala-L-Lys-D-Glu-OH (AAKE). This "inverse" substrate is also efficiently bound by our receptors, with K(ass) approximately 6000 M(-1) for the best receptors, as determined both by a quantitative on-bead binding assay and by UV and fluorescence titration studies in free solution. Hence, the inverse tetrapeptide 3 is in general bound two to three times less efficiently than the "normal" peptide 2 (K(ass) approximately 17,000 M(-1)), even though the complexation mainly involves long-range electrostatic interactions and both the receptor and substrate are rather flexible. Molecular modeling and ab initio calculations have been used to rationalize the observed substrate selectivity and to analyze the various binding interactions within the complex.     

Density, Overcompleteness, and Localization of Frames. I. Theory

Frames have applications in numerous fields of mathematics and engineering. The fundamental property of frames which makes them so useful is their overcompleteness. In most applications, it is this overcompleteness that is exploited to yield a decomposition that is more stable, more robust, or more compact than is possible using nonredundant systems. This work presents a quantitative framework for describing the overcompleteness of frames. It introduces notions of localization and approximation between two frames and ( a discrete abelian group), relating the decay of the expansion of the elements of in terms of the elements of via a map . A fundamental set of equalities are shown between three seemingly unrelated quantities: The relative measure of , the relative measure of — both of which are determined by certain averages of inner products of frame elements with their corresponding dual frame elements — and the density of the set in . Fundamental new results are obtained on the excess and overcompleteness of frames, on the relationship between frame bounds and density, and on the structure of the dual frame of a localized frame. In a subsequent article, these results are applied to the case of Gabor frames, producing an array of new results as well as clarifying the meaning of existing results. The notion of localization and related approximation properties introduced in this article are a spectrum of ideas that quantify the degree to which elements of one frame can be approximated by elements of another frame. A comprehensive examination of the interrelations among these localization and approximation concepts is presented.     

Invariances of frame sequences under perturbations

This paper determines the exact relationships that hold among the major Paley-Wiener perturbation theorems for frame sequences. It is shown that major properties of a frame sequence such as excess, deficit, and rank remain invariant under Paley-Wiener perturbations, but need not be preserved by compact perturbations. For localized frames, which are frames with additional structure, it is shown that the frame measure function is also preserved by Paley-Wiener perturbations.     

Using combinatorial methods to arrive at a quantitative structure-stability relationship for a new class of one-armed cationic peptide receptors targeting the C-terminus of the amyloid beta-peptide

A new class of one-armed tripeptide based cationic guanidiniocarbonyl pyrrole receptors is shown to strongly bind the tetrapeptide L-Val-L-Val-L-Ile-L-Ala, representing the C-terminus of the amyloid beta-peptide even under polar conditions. A medium sized combinatorial library of 125 receptors was synthesized on a solid support and their binding properties determined on bead using a quantitative fluorescence assay. The binding constants are in the order of 10(3)-10(4) M-1 (in the presence of a formate counter ion in methanol) for the most efficient ones but differ by more than a factor of 100 among the 125 library members. Based on the binding data of 12 receptors a structure-stability relationship was established for peptide binding by this new receptor class. Complex formation is controlled by a fine balanced interplay of hydrophobic and electrostatic interactions with none of these two interactions alone being strong enough to ensure complexation under these polar conditions.     

Changes in cell cycle distribution of V79 Chinese hamster fibroblasts after irradiation at different wavelengths

Changes in cell cycle distribution of V79 Chinese hamster fibroblasts were investigated at different wavelengths between 254 and 313 nm. The fluences applied led to surviving fractions of 0.61. In all cases, the S fraction was temporarily increased within 8-12 h after irradiation, whereas the G1 fraction was decreased. The maximum deviations from the initial values did not significantly depend on the wavelength.