A heterometric study of the phenanthroline compounds with platinum,palladium and gold halides and their analytical application

The reactions between platinum, palladium and gold halides and phenanthroline were studied heterometrically By changing the composition of the solutions, six different final compounds were obtained Each of the compounds could be used for the determinations of the metals The errors were one per cent or less The most probable structural formulae for the final compounds are presented     

Minimizing symmetric submodular functions

We describe a purely combinatorial algorithm which, given a submodular set functionf on a finite setV, finds a nontrivial subsetA ofV minimizingf[A] + f[V A]. This algorithm, an extension of the Nagamochi—Ibaraki minimum cut algorithm as simplified by Stoer and Wagner [M. Stoer, F. Wagner, A simple min cut algorithm, Proceedings of the European Symposium on Algorithms ESA '94, LNCS 855, Springer, Berlin, 1994, pp. 141–147] and by Frank [A. Frank, On the edge-connectivity algorithm of Nagamochi and Ibaraki, Laboratoire Artémis, IMAG, Université J. Fourier, Grenbole, 1994], minimizes any symmetric submodular function using O(|V|³) calls to a function value oracle. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.A preliminary version of this paper was presented at the Sixth Annual ACM-SIAM Symposium on Discrete Algorithms (SODA) in January 1995. This research was supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada.     

Cutinase-peptide fusions in thermoseparating aqueous two-phase systems. Prediction of partitioning and enhanced tag efficiency by detergent addition

It is of increasing importance to develop efficient purification methods for recombinant proteins where the number of steps can be minimised. The aim has been to establish a method for predicting the partitioning of the wild-type target protein in an aqueous two-phase system, and with this as basis, develop fusion tags and optimise the phase system for enhanced partitioning of the target protein. The surface of the lipolytic enzyme cutinase from Fusarium solani pisi was investigated with a computer program, Graphical Representation and Analysis of Surface Properties (GRASP). The accessible surface areas for the different amino acid residues were used together with peptide partitioning data to calculate the partition coefficient for the protein. The separation system was composed of a thermoseparating random copolymer of ethylene oxide and propylene oxide. Breox PAG 50A 1000, as top phase forming polymer and a hydroxypropyl starch polymer, Reppal PES 200, as bottom phase polymer. The calculated partition coefficient for the wild-type protein (K= 1.0) agreed reasonably well with the experimentally determined value (K=0.85). Genetic engineering was used to construct fusion proteins expressed in Saccharomyces cerevisiae based on cutinase and peptide tags containing tryptophan, to enhance the partitioning in aqueous two-phase systems. The partitioning of the cutinase constructs could qualitatively be predicted from peptide partitioning data, i.e. the trends in partitioning could be predicted. A spacer peptide introduced between protein and tag increased the partitioning of the protein towards the ethylene oxide-propylene oxide (EOPO) copolymer top phase. The aqueous two-phase system was modified by addition of detergent to increase the partitioning of the cutinase variants towards the EOPO copolymer phase. Triton and a series of C12En detergents selectively increased the partitioning of cutinase constructs with (WP)4-based tags up to 14 times compared to wild-type cutinase. The protein partition could almost quantitatively be predicted from the peptide partition data.     

Direct synthesis of 3-arylpropionic acids by tetraphosphine/palladium catalysed Heck reactions of aryl halides with acrolein ethylene acetal

Through the use of [PdCl(C₃H₅)]₂/Cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)cyclopentane as a catalyst, a range of aryl bromides undergoes Heck reaction with acrolein ethylene acetal. With this acetal, the selective formation of 3-arylpropionic acids/esters was observed. The functional group tolerance on the aryl halide is remarkable; substituents such as fluoro, methyl, methoxy, acetyl, formyl, benzoyl, nitro or nitrile are tolerated. Furthermore, this catalyst can be used at low loading, even for reactions of sterically hindered aryl bromides.     

An alternative parametrization for the theory of complex spectra

The aim of this paper is to investigate a new parametrization for the matrix, set up on the states of an open (nuclear or atomic) shell, of any two-body interaction expandable in multipoles. Such a parametrization is particularly convenient for expressing the term energies in a simple form and for producing high degeneracies among the terms. Further, the parametrization considered allows the two-body interaction to be decomposed into a Dirac interaction and a remaining part.     

The site of ionization in the acetylation of aliphatic esters by [(CH3CO)3]+

A series of esters RCOOR′ (where R, R′ = CH₃, CH₃CH₂, (CH₃)₂CH, (CH₃)₃C) were reacted with the [(CH₃CO)₃]⁺ ion from biacetyl in an ion cyclotron resonance spectrometer. A steric effect influences the rate of formation of stable products [RCOOR′·CH₃CO]⁺ and is used to determine that either oxygen of the ester may be initially acylated by [(CH₃CO)₃]⁺.     

X=y-zh systems as potential 1,3-dipoles—5 : Intramolecular cycloadditions of imines of α-amino acid esters

Azomethine ylides are readily generated from imines of α-amino acid esters by a formal 1,2-H shift. A suitably positioned unactivated double or triple bond in either of the two precursors of the imines (aldehyde or α-amino ester) leads to an intramolecular cycloaddition generating fused ring systems in good yield. Cis stereochemistry is assigned to the newly created ring junction of the cycloadducts based on NOE difference spectroscopy and, in the case of 8a, by a single crystal X-ray structure. Equilibration of the kinetically formed dipole leads to mixtures of epimeric cycloadducts for imines of phenylglycine methyl ester but equilibration is not observed for other imines. Reasons for this are discussed. The intramolecular cycloaddition is sensitive to ring size with 6/5 and 5/5 cis-fused systems being most easily formed depending in which moiety (aldehyde or amino acid) the dipolarophile is located. Intramolecular trapping of the azomethine ylide by an alkyne is accompanied by variable amounts of aromatized pyrrolic products.     

Spin-independent three-body effective valence-shell operators: Application to molecular oxygen

A mathematical construction is presented that uniquely defines a set of spin-independent effective valence-shell Hamiltonian (H^v) three-body matrix elements. These spin-independent H^v matrix elements separate direct and exchange portions of the three-body H^v matrix elements and therefore provide the most natural form for comparisons with parameterization schemes of semiempirical electronic structure methods in which the three-body matrix elements are incorporated into semiempirical one- and two-body Hamiltonian matrix elements in an averaged manner. Ab initio H^v three-body matrix elements of O₂ are computed through third order of quasidegenerate perturbation theory and are analyzed as a function of internuclear distance and atomic orbital overlap to aid in understanding how these three-body matrix elements may be averaged into semiempirical one- and two-body matrix elements. © 1992 John Wiley & Sons, Inc.     

Horeau's Coupling of Enantiomers Revisited. The Reversible Coupling of Enantiomers to Form Diastereoisomers in Kinetically Labile Metal Complexes

Pairs of enantiomeric molecules (??,??) of a substrate of unknown, but incomplete enantiomeric purity may be coupled to each other through labile coordination to a metal center M. This results in the formation of an equilibrium mixture of diastereoisomeric complexes, viz. meso-L_nM????(=m) and a pair of enantiomers L_nM???? and L_nM????(= e), where L is an achiral auxiliary ligand. General expressions are presented for determining the ratio of enantiomers [??]₀/[??]₀ from experimental parameters, which may be obtained from NMR measurements. Effects of diastereoselectivity are specifically considered. Limiting cases (nearly pure or nearly racemic substrates, very high or no diastereoselectivity, very large or no excess of free substrate) are discussed. The cases of additional diastereoisomerism owing to different coordination geometries and of the formation of complexes with more than two substrate molecules per metal center are also investigated. The results presented can not only be used for determining the enantiomeric excess but also for designing optimal strategies for the successive resolution of partly enriched samples.