A study of the effects of column porosity on gradient separations of proteins

The type of the stationary phase for reversed-phase liquid chromatography significantly affects the sample elution. Hydrodynamic properties, efficiency and gradient elution of proteins were investigated on five commercial C18 columns with wide-pore totally porous particles, with superficially porous layer particles, non-porous particles and a silica-based monolithic bed. The efficiency in the terms of reduced plate height is higher for low-molecular ethylbenzene than for proteins, but depends on the character of the pores in the individual columns tested. The superficially porous Poroshell and the non-porous Micra columns provide the best efficiency for proteins at high mobile phase flow rates, probably because of similar pore architecture in the stationary phase. The Zorbax column with similar pore architecture as the Poroshell active layer, i.e. narrow pore distribution of wider pores shows better efficiency than the packed column with narrow pores and broad pore distribution. The monolithic column shows lower efficiency for proteins at high flow rates, but it performs better than the broad-pore distribution totally porous particulate columns. Different pore architecture affects also the retention and selectivity for proteins on the individual columns. The retention times on all columns can be predicted using the model for reversed-phase gradient elution developed originally for low-molecular compounds. Consideration of the limited pore volume accessible to the biopolymers has negligible effect on the prediction of retention on the columns packed with non-porous or superficially porous particles, but improves the accuracy of the predicted data for the totally porous columns with broad pore distribution.     

A multilevel characteristics method for periodic convection‐dominated diffusion problems

In this article we introduce a multilevel method in space and time for the approximation of a convection‐diffusion equation. The spatial discretization is of pseudo‐spectral Fourier type, while the time discretization relies on the characteristics method. The approximate solution is obtained as the sum of two components that are advanced in time using different time‐steps. In particular, this requires the introduction of two sets of discretized characteristics curves and of two interpolation operators. We investigate the stability of the scheme and derive some error estimates. They indicate that the high‐frequency term can be integrated with a larger time‐step. Numerical experiments illustrate the gain in computing time due to the multilevel strategy. © 2000 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 16: 107–132, 2000     

A Landscape of Lignocellulosic Biopolymer Transformations into Valuable Molecules by Heterogeneous Catalysis in C’Durable Team at IRCELYON

This review article highlights part of the research activity of the C’Durable team at IRCELYON in the field of sustainable chemistry. This review presents a landscape of the work performed on the valorization of lignocellulosic biopolymers. These studies intend to transform cellulose, hemicellulose and lignin into valuable molecules. The methodology usually consists in evaluating the behavior of the biopolymers in the absence of catalyst under various conditions (solvent, temperature), and then to assess the influence of a catalyst, most often a heterogeneous catalyst, on the reactivity. The most significant results obtained on the upgrading of cellulose and lignin, which have been mainly investigated in the team, will be presented with an opening on studies involving raw lignocellulose.     

Hydrostannylation of phosphaalkenes [1]

Hydrostannylation reactions of the phosphaalkenes 9,11, and 21 with the triorganotin hydrides 1 proceed by different routes. Whereas the trior-ganotin hydrides 1a,b undergo regioselective 1,2-addition to the P/C double bond of the P-aminophosphaalkene 9 to furnish the 2-stannylphosphanes 17a,b, the 1,2-addition products to the P-halophosphaalkenes 11 and 21 can only be postulated as the reactive intermediates 20 and 23, respectively. The reactions of 11 with 1a,b proceed with cleavage of the triorganotin halide via the diphosphene 15 to furnish the cyclophosphanes 18 and 19. On the other hand, the hydrostannylation reactions of the phosphaalkene 21 are not selective, and the 1,3-diphosphetane 22 is isolated as one of the reaction products. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:453–460, 1998     

Isolation and Characterization of Wax Esters in Fennel and Caraway Seed Oils by SPE-GC

A rapid method for the isolation and quantitative determination of wax esters in vegetable oils was developed. For the first time wax esters in oils were separated from the triglyceride matrix by means of solid-phase extraction, which allows rapid sample preparation in parallel and therefore a high sample throughput. The thus obtained wax ester fractions of fennel and caraway seed oils were analyzed by high temperature gas chromatography. GC-MS analyses were carried out using electron impact ionization in order to characterize the wax ester fraction. With respect to the results of the GC-MS analyses different isomers of saturated wax esters with the same carbon number were observed. Additional monounsaturated wax esters with an unsaturated fatty acid moiety were identified.     

Spectral and temporal features of multiple spontaneous NMR-maser emissions

When a system composed of dissolved laser-polarized xenon with negative spin temperature is put inside a high field NMR magnet, a series of spontaneous maser emissions can be observed. We report here their spectral and temporal features using a processing model derived from the solution of the Bloch equations in the presence of radiation damping. We show, in particular, that by combining Fourier transformation and squared modulus, a parameter allowing the characterization of the burst of transverse magnetization can be determined. This parameter is shown to be correlated with the radiated energy. Moreover, this processing clearly reveals features which can probably be assigned to effects resulting from distant dipolar fields. Finally, the analysis of the experimental data reveals an unexpected behavior of the ¹²⁹Xe transverse self-relaxation.     

Control of Duplex Formation and Columnar Self‐Assembly with Heterogeneous Amide/Urea Macrocycles

The perfect blend : A new class of self‐assembling cyclooligomers with mixed urea/amide backbone is described (see figure). A high level of hierarchical and directional control is achieved: depending on the level of backbone preorganization, columnar or tubular arrangements with either parallel or antiparallel growing modes can be selected.

     

Raman Spectroscopic Study of the Phase Transition of Amorphous to Crystalline β‐Carbonic Acid

What's the matter? The laboratory Raman spectra for carbonic acid (H₂CO₃), both for the β‐polymorph and its amorphous state, are required to detect carbonic acid on the surface of the pole caps of Mars in 2009, when the Mars Microbeam Raman Spectrometer lands on the planet. The picture shows a martian crater with ice of unknown composition, possibly containing carbonic acid (image adapted from DLR, with permission from ESA, DLR, and FU Berlin –‐G. Neukum).

     

Signal improvement in elemental analyzer/continuous flow isotope ratio mass spectrometry for samples with low sulfur contents using a pre-concentration technique for on-line concentration adjustment

Elemental analyzer/continuous flow isotope ratio mass spectrometry (EA/CF-IRMS) has become a standard procedure for the determination of delta(34)S values. Common procedures are, however, frequently less than satisfactory for organic as well as for mineral samples with very low concentrations of sulfur (<2000 ppm). Here we present a method which employs cold trapping of SO(2) to adjust the gas concentration for subsequent isotope signature determination. Analytical accuracy is comparable with common EA/CF-IRMS analysis without trapping, showing a precision of better than +/-0.4 per thousand in delta(34)S (1 SD). The virtual absence of memory effects was established by analyzing adjacent samples exhibiting a large difference in delta(34)S and by prolonged freezing of the carrier gas, yielding virtually no S concentration peak. The method was tested using less than 15% (6 microg) of the S required for a conventional isotope analysis at comparable signal intensity. Even smaller samples can be analyzed with high precision. This facilitates the on-line delta(34)S determination in small biological and mineral samples, minimizing matrix effects in various materials including sandstone, soil, and plant samples.