Entangled Porphyrins in Cyclodextrin Vesicles

The entanglement process between porphyrins and some amphiphiliccyclodextrins and the occurrence of different species have been proved by the combination of UV-Visabsorption, fluorescence anisotropy, resonance light scattering and ¹H NMR spectroscopy.     

Unorthodox intrasubunit interactions in the cellulosome ofClostridium thermocellum

Clostridium thermocellum, an anaerobic thermophilic cellulolytic bacterium, produces an extremely cohesive, very high-molecular-mass multicellulase-containing complex termed thecellulosome. One of its components, the S1 subunit, is a nonenzymatic, 210 kDa glycopolypeptide. Upon preconditioning of the intact cellulosome with lowionic-strength or low-pH solutions, the S1 subunit separates in hot sodium dodecyl sulfate (SDS) solutions into a series of defined lowermolecular-mass subcomponents. Under the same conditions, the purified S1 subunit demonstrated the same behavior. Higher levels of glycosylation associated with the larger S1 subcomponents. The data support alterations in the conformational state of the S1 structure that lead to its disintegration induced by combined treatments with SDS and heating. Evidence is provided that this phenomenon may reflect a physiological response of the cellulosome, since similar alterations in S1 appear to accompany its binding to cellulose.     

Ein kolloider Wärme-Indikator

Zusammenfassung Zur Aufdeckung der ?rtlichen W?rmeverteilungen in den nach J. Uri-Lloyd geb?nderten Flüssigkeiten lassen sich die Trübungen benutzen, welche gewisse Alkaloide infolge der Alkalit?tszunahme einer Sulfitl?sung beim Erw?rmen annehmen.     

Trimethylaluminum: Bonding by Charge and Current Topology

The charge density distribution of the trimethylaluminum dimer was determined by high‐angle X‐ray diffraction of a single crystal and quantum‐chemical methods and analyzed using the quantum theory of atoms in molecules. The data can be interpreted as Al₂Me₆ being predominantly ionically bonded, with clear indications of topological asymmetry for the bridging Al? C bonds owing to delocalized multicenter bonding. This interpretation is supported by the calculated magnetic response currents. The data shed new light on the bonding situation in this basic organometallic molecule, which was previously described by contradicting interpretations of bonding.     

Identification of Structure–Activity Relationships from Screening a Structurally Compact DNA‐Encoded Chemical Library

Methods for the rapid and inexpensive discovery of hit compounds are essential for pharmaceutical research and DNA‐encoded chemical libraries represent promising tools for this purpose. We here report on the design and synthesis of DAL‐100K, a DNA‐encoded chemical library containing 103 200 structurally compact compounds. Affinity screening experiments and DNA‐sequencing analysis provided ligands with nanomolar affinities to several proteins, including prostate‐specific membrane antigen and tankyrase 1. Correlations of sequence counts with binding affinities and potencies of enzyme inhibition were observed and enabled the identification of structural features critical for activity. These results indicate that libraries of this type represent a useful source of small‐molecule binders for target proteins of pharmaceutical interest and information on structural features important for binding.     

DNS of premixed turbulent V-flame: coupling spectral and finite difference methods

To allow for a reliable examination of the interaction between velocity fluctuations, acoustics and combustion, a novel numerical procedure is discussed in which a spectral solution of the Navier–Stokes equations is directly associated to a high-order finite difference fully compressible DNS solver (sixth order PADE). Using this combination of high-order solvers with accurate boundary conditions, simulations have been performed where a turbulent premixed V-shape flame develops in grid turbulence. In the light of the DNS results, a sub-model for premixed turbulent combustion is analyzed. To cite this article: R. Hauguel et al., C. R. Mecanique 333 (2005).     

Wrapping of nanoparticles by membranes

How nanoparticles interact with biomembranes is central for understanding their bioactivity. Biomembranes wrap around nanoparticles if the adhesive interaction between the nanoparticles and membranes is sufficiently strong to compensate for the cost of membrane bending. In this article, we review recent results from theory and simulations that provide new insights on the interplay of bending and adhesion energies during the wrapping of nanoparticles by membranes. These results indicate that the interplay of bending and adhesion during wrapping is strongly affected by the interaction range of the particle–membrane adhesion potential, by the shape of the nanoparticles, and by shape changes of membrane vesicles during wrapping. The interaction range of the particle–membrane adhesion potential is crucial both for the wrapping process of single nanoparticles and the cooperative wrapping of nanoparticles by membrane tubules.     

Adsorption studies of Cd(II) onto Al2O3/Nb2O5 mixed oxide dispersed on silica matrix and its on-line preconcentration and determination by flame atomic absorption spectrometry

The present study describes the adsorption characteristic of Cd(II) onto Nb₂O₅/Al₂O₃ mixed oxide dispersed on silica matrix. The characterization of the adsorbent has been carried out by infrared spectroscopy (IR), scanning electronic microscopy (SEM), energy dispersive spectroscopy (EDS), energy dispersive X-ray fluorescence analysis (EDXRF) and specific surface area (S_BET). From batch experiments, adsorption kinetic of Cd(II) was described by a pseudo-second-order kinetic model. The Langmuir linear isotherm fitted to the experimental adsorption isotherm very well, and the maximum adsorption capacity was found to be 17.88 mg g⁻¹. Using the effective material, a method for Cd(II) preconcentration at trace level was developed. The method was based on on-line adsorption of Cd(II) onto SiO₂/Al₂O₃/Nb₂O₅ at pH 8.64, in which the quantitative desorption occurs with 1.0 mol L⁻¹ hydrochloric acid towards FAAS detector. The experimental parameters related to the system were studied by means of multivariate analysis, using 2⁴ full factorial design and Doehlert matrix. The effect of SO₄²⁻, Cu²⁺, Zn²⁺ and Ni²⁺ foreign ions showed no interference at 1:100 analyte:interferent proportion. Under the most favorable experimental conditions, the preconcentration system provided a preconcentration factor of 18.4 times, consumption index of 1.08 mL, sample throughput of 14 h⁻¹, concentration efficiency of 4.35 min⁻¹, linear range from 5.0 up to 35.0 μg L⁻¹ and limits of detection and quantification of 0.19 and 0.65 μg L⁻¹ respectively. The feasibility of the proposed method for Cd(II) determination was assessed by analysis of water samples, cigarette sample and certified reference materials TORT-2 (Lobster hepatopancreas) and DOLT-4 (Dogfish liver).     

Fixed bed phosphate adsorption by immobilized nano-magnetite matrix: experimental and a new modeling approach

Nano-sized magnetite impregnated charcoal granular activated carbon (nFe-GAC) was utilized for the removal of phosphate from aqueous solutions using a fixed bed column. The dynamic of the phosphate adsorption was analyzed using a new approach to the Thomas model based on a two-step differential sorption rate process. The initial adsorption was found to be external mass transfer controlled, while intra-particle diffusion was the predominant mechanism in the latter stage. Consequently, two kinetic coefficients were calculated for each breakthrough curve resulting in an excellent model prediction. By implementing this approach a transition point, at which diffusion becomes the predominant adsorption mechanism, can be accurately determined. The effect of varying parameters, such as feed flow rates, feed pH, initial phosphate concentrations and adsorbent bed height were examined and described using the modified Thomas model. Reaction rates increased with augmentation of the flow rates from 1 to 40 mL/min while the adsorption capacity and transition point decreased. Similar transition points were obtained for initial phosphate concentrations between 10 and 100 mg/L. The unique characteristics of the nFe-GAC were evident as it exhibited very high phosphate adsorption capacity, at a wide range of pH values (4–9) with negligible effect of competing ions and short critical bed depth.