Proton NMR spectroscopy and magnetic properties of a solution-stable dicopper(II) complex bearing a single mu-hydroxo bridge

The reaction of copper(II) perchlorate with the macrocyclic ligand [22]py4pz in the presence of base leads to formation of a dinuclear complex [Cu(2)([22]py4pz)(mu-OH)](ClO(4))(3)xH(2)O, in which two copper ions are bridged by a single mu-hydroxo bridge. Each copper ion is further surrounded by four nitrogen atoms of the ligand. The mu-hydroxo bridge mediates a strong antiferromagnetic coupling (2J = -691(35) cm(-1)) between the metal centers, leading to relatively sharp and well-resolved resonances in the (1)H NMR spectrum of the complex in solution. We herein report the crystal structure, the magnetic properties, and the full assignment of the hyperfine-shifted resonances in the NMR spectrum of the complex, as well as the determination of the exchange coupling constant in solution through temperature-dependent NMR studies.     

Development of acrylate-based monolithic stationary phases for electrochromatographic separations

Organic monolithic stationary phases were synthesized in fused-silica capillaries. They were prepared by in situ polymerization under UV irradiation of various alkyl acrylates, 1,3-butanediol diacrylate, and 2-acrylamido-2-methyl-1-propanesulfonic acid in a ternary porogenic solvent. The resulting stationary phases were tested in CEC. The influence of UV irradiation energy on the resulting separative performances of the monoliths was studied. It was thus demonstrated that the use of hexyl acrylate rather than butyl acrylate and lauryl methacrylate gives highly efficient monoliths (more than 300 000 plates per meter) with optimized EOF. It was also confirmed that the mobile phase ionic strength may affect significantly the separation efficiency. The influence of the nature of the mobile phase organic modifier (ACN or methanol) on EOF, retention, efficiency, and selectivity was studied and differences were observed. Finally, the performances of monolithic stationary phases developed and optimized for CEC separations were evaluated in nanoLC.     

Use of self assembled magnetic beads for on-chip protein digestion

The use of grafted trypsin magnetic beads in a microchip for performing protein digestion is described. The PDMS device uses strong magnets to create a magnetic field parallel to the flow with a strong gradient pointing through the center of the chip channel. This allows for the formation of a low-hydrodynamic resistance plug of magnetic trypsin beads that serves as a matrix for protein digestion. This device represents an inexpensive way of fabricating a multi open-tubular-like column with an appropriate pore size for proteins. Kinetics studies of the hydrolysis of a model peptide show a 100-fold increase in digestion speed obtained by the microsystem when compared to a batch wise system. This system also offers the great advantage of easy replacement, as the bead matrix is easily washed out and replaced. High performance and reproducibility for digesting recombinant human growth hormone are confirmed by analysing the digest products in both CE and MALDI-TOF MS. Similar sequence coverage (of about 44%) is obtained from MS analysis of products after 10 minutes on-chip and 4 h with soluble trypsin in bulk.     

Comb-like copolymers as self-coating,low-viscosity and high-resolution matrices for DNA sequencing

Comb-like copolymers with a polyacrylamide backbone and poly(N,N-dimethylacrylamide) grafts were prepared, as a way to combine the superior sieving properties of polyacrylamide with the self-coating properties of polydimethylacrylamide. These matrices function well in the absence of a capillary coating, and achieve separation performances for single-stranded DNA that are comparable to those of state-of-the-art long-chain linear polyacrylamide. Structural parameters such as the grafting density and the polymer molecular mass were varied, and good performance appears to be achieved with a relatively large range of parameters. Surprisingly, excellent separation is achieved even with matrices that have a viscosity as low as 200 mPa/s. A discussion of the physics underlying this behavior is provided.     

Sels d'aziridinium stables C-fonctionnalisés III: Synthèse et caractérisation d'aziridines protonées épimères à l'azote

Aziridinium ions were prepared from aziridines bearing a functionality on a ring carbon and as isolated crystalline fluorosulfate salts either by protonation in fluorosulfuric acid solution or by alkylation with methyl fluorosulfate. The structural assignement of these ions is based on nmr spectra and on quenching experiments with sodium carbonate. The configurations of the epimeric ions have been assigned by the nuclear Qverhauser effect and the stereoselectivity in protonation is disucussed.     

Groupe de Chow de codimension deux des variétés définies sur un corps de nombres: un théorème de finitude pour la torsion

Summary LetX be a smooth, projective variety defined over a number field and let CH² (X) denote the Chow group of codimension two cycles modulo rational equivalence. We show that if the cohomology groupH ²(X,O_x) vanishes then the torsion subgroup of CH² (X) is a finite group. This result covers all previous results in this direction. The hypothesisH ²(X,O_x)=0 is used to lift line bundles.

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Oblatum 17-IX-1990     

Some advantages of high temperature for the separation of pharmaceutical compounds with mass spectrometry detection

The beneficial effects of high temperature on separation and detection of basic compounds, the detection being performed by MS via ESI, are investigated. The influence of various parameters on both separation and detection performances is studied. These parameters include the mobile phase pH, the temperature, and the type of stationary phase. Experiments are performed under gradient elution conditions. The results obtained with four different supports, silica-, zirconia-, carbon-, and polymer-based columns, are compared by means of different criteria including the elution composition, the peak asymmetry, and the S/N. High temperature liquid chromatography at high pH with volatile buffers suitable for MS detection was shown to be an interesting choice for solutes with basic sites.     

Popularity of Sets Represented by the Partitions of n

Let us say that a partition of the positive integer n represents a, 0 a n, if there is a submultiset of the multiset of the parts whose sum is a. Erd os and Szalay have proved that almost all partitions of n represent all integers a, 0 a n. If is a finite set of positive integers, let us denote by p~(n, ) the number of partitions of n which represent all integers a, 0 a n, a , n – a but do not represent a for a . For instance, p~(n,) is the number of partitions of n which represent all integers between 0 and n; the result of Erd os and Szalay can be reformulated as p~(n,) p(n), where p(n) is the total number of partitions of n. The aim of this paper is the study of p~(n, ): we shall compare the values of p~(n, ) for small sets and we shall give a close formula for p~(n, ) when is the set of the first k integers.