Glycosyl‐Substituted Dicarboxylates as Detergents for the Extraction,Overstabilization, and Crystallization of Membrane Proteins

To tackle the problems associated with membrane protein (MP) instability in detergent solutions, we designed a series of glycosyl‐substituted dicarboxylate detergents (DCODs) in which we optimized the polar head to clamp the membrane domain by including, on one side, two carboxyl groups that form salt bridges with basic residues abundant at the membrane–cytoplasm interface of MPs and, on the other side, a sugar to form hydrogen bonds. Upon extraction, the DCODs 8 b , 8 c , and 9 b preserved the ATPase function of BmrA, an ATP‐binding cassette pump, much more efficiently than reference or recently designed detergents. The DCODs 8 a , 8 b , 8 f , 9 a , and 9 b induced thermal shifts of 20 to 29 °C for BmrA and of 13 to 21 °C for the native version of the G‐protein‐coupled adenosine receptor A_2AR. Compounds 8 f and 8 g improved the diffraction resolution of BmrA crystals from 6 to 4 Å. DCODs are therefore considered to be promising and powerful tools for the structural biology of MPs.     

Efficient indirect electrochemical in-situ regeneration of nadh:electrochemically driven enzymatic reduction of pyruvate catalyzed by d-ldh

Using [Cp(Me)₅Rh(bipy)C1]C1 (1) as redox catalyst for the continous NADH regeneration it was possible to perform an electrochemically driven enzymatic reduction of pyruvate to D-lactate catalyzed by D-LDH at a rate of 5 turnovers per hour. This is by a factor of 20 faster than the best results obtained until now. Current yields of 50 to 70 % may be obtained.     

Simultaneous separation and analysis of water- and fat-soluble vitamins on multi-modal reversed-phase weak anion exchange material by HPLC-UV

Several methods for the separation of vitamins on HPLC columns were already validated in the last 20 years. However, most of the techniques focus on separating either fat- or water-soluble vitamins and only few methods are intended to separate lipophilic and hydrophilic vitamins simultaneously. A mixed-mode reversed-phase weak anion exchange (RP-WAX) stationary phase was developed in our laboratory in order to address such mixture of analytes with different chemical characteristics, which are difficult to separate on standard columns. The high versatility in usage of the RP-WAX chromatographic material allowed a baseline separation of ten vitamins within a single run, seven water-soluble and three fat-soluble, using three different chromatographic modes: some positively charged vitamins are eluted in ion exclusion and ion repulsion modes whereas the negatively charged molecules are eluted in the ion exchange mechanism. The non-charged molecules are eluted in a classical reversed-phase mode, regarding their polarities. The method was validated for the vitamin analysis in tablets, evaluating selectivity, robustness, linearity, accuracy, and precision. The validated method was finally employed for the analysis of the vitamin content of some commercially available supplement tablets.     

The Riemann Solution for the Injection of Steam and Nitrogen in a Porous Medium

We solve the model for the flow of nitrogen, vapor, and water in a porous medium, neglecting compressibility, heat conductivity, and capillary effects. Our choice of injection conditions is determined by the application to clean up polluted sites. We study all mathematical structures, such as rarefaction, shock waves, and their bifurcations; we also develop a systematic method to find fundamental solutions for thermal compositional flows in porous media. In addition, we unexpectedly find a rarefaction evaporation wave which has not been previously reported in any other study.     

Tailoring the morphology and properties of waterborne polyurethanes by the procedure of cellulose nanocrystal incorporation

Polyurethane waterborne synthesis was performed using a two-step method, commonly referred to as a prepolymer method. Nanocomposites based on waterborne polyurethane and cellulose nanocrystals were prepared by the prepolymer method by altering the mode and step in which the nanofillers were incorporated during the polyurethane formation. The morphology, structural, thermal, and mechanical properties of the resulting nanocomposite films were evaluated by Fourier transform infrared spectroscopy (FTIR), small angle X-ray scattering (SAXS), scanning electron microscopy (SEM), and tensile tests. FTIR results indicated that the degree of interaction between the nanofillers and the WPU through hydrogen bonds could be controlled by the method of cellulose nanocrystal incorporation. Data obtained from SAXS experiments showed that the cellulose nanocrystals as well as the step of the reaction in which they are added influenced the morphology of the polyurethane. The reinforcing effect of CNCs on the nanocomposites depends on their morphology.     

A novel family of ordered,mesoporous inorganic/organic hybrid polymers containing covalently and multiply bound microporous organic hosts

We have prepared a new family of periodic hybrid polymers containing microporous cavities provided by covalently bound organic hosts. Cyclodextrin (CD) or calixarene (CX) hosts are attached to four or more trialkoxysilyl groups, which are polymerized to form a polysilsesquioxane matrix. Structural integrity is provided by copolymerization with tetraethoxysilane, which produces a polysilicate co-matrix. Periodic order is created by carrying out the polymerization in the presence of a surfactant, cetyltrimethylammonium bromide. The resulting as-synthesized polymers from these three starting materials were characterized by solid-state nuclear magnetic resonance spectroscopy. The (13)C and (29)Si spectra provided evidence for intact polysilsesquioxane, polysilicate, organic host, and surfactant. Removal of the surfactant by washing produced a polymer containing cavities of mesoporous dimensions, in addition to the microporous host cavities. The purpose of introducing mesoporosity is to allow enhanced access of guests to the microporous hosts. Transmission electron microscopy demonstrated that both as-synthesized and solvent-extracted polymers have a periodic structure. All polymers are completely insoluble in water. The as-synthesized CD-containing polymers extracted up to >99% of 4-nitrophenol from aqueous solution, and the solvent-extracted CX-containing polymers extracted up to 67% of Fe(3+) and lesser amounts of other metal cations from aqueous solution, with interesting selectivity patterns. Simple filtration then removes the polymer containing the extracted organic molecule or metal cation. These extraction abilities are superior to previous materials.     

A general approach toward the synthesis of 8-acylamidopyrazolo[1,5-a]-1,3,5-triazines

An expedient synthesis of 8-acylamidopyrazolo[1,5-a]-1,3,5-triazines was developed by treating 8-amino-4-[N-(4-aminophenyl)-N-(methyl)amino]pyrazolo[1,5-a]-1,3,5-triazine with various acyl chlorides following by the displacement of the so-formed N-(methyl)-N-[4-(acylamido)phenyl]amino leaving group with various amines. Applications to high-throughput synthesis are suggested.     

Heptakis-6-(5-methylene-thioureido-5′-methyl-2,2′-bipyridyl)-β-cyclodextrin: synthesis and metal complexation study

A new heptapode heptakis-6-(5-methylene-thioureido-5′-methyl-2,2′-bipyridyl)-β-cyclodextrin was prepared and its complexation properties towards metal cations were investigated. Substituting the urea functions by the corresponding thioureas promoted the inversion of the metal coordination selectivity. Preliminary results showed the heptapode unable to complex lanthanides but authorise selective complexation of ‘soft’ and ‘borderline’ metal cations.     

Origin of high second- and third-order nonlinear optical response in ammonio/borato diphenylpolyene zwitterions: the remarkable role of polarized aromatic groups

We present a quantum-chemical analysis of the molecular structure and second- and third-order polarizabilities in a series of promising nonlinear optical (NLO) chromophores, the zwitterionic ammonio/borato diphenylpolyenes, R3N+Ph(C=C)nPhB-R3, whose synthesis has been reported recently. The molecular geometries are obtained via MP2/6-31G optimization, while the NLO properties are calculated with the INDO Hamiltonian using the sum-over-states and finite-field real-space methods. The real-space approach allows the direct evaluation of the NLO-active segments of the molecules, while the sum-over-states results illustrate the virtual excitations and charge-transfer pathways that are essential in the NLO response. Both methods highlight the remarkable and unexpected result that it is the strongly polarized phenylene groups that play the key role in generating a high NLO response.     

Analysis of the structure of very large bacterial aggregates by small-angle multiple light scattering and confocal image analysis

This work aims at developing a more accurate measurement of the physical parameters of fractal dimension and the size distribution of large fractal aggregates by small-angle light scattering. The theory of multiple scattering has been of particular interest in the case of fractal aggregates for which Rayleigh theory is no longer valid. The introduction of multiple scattering theory into the interpretation of scattering by large bacterial aggregates has been used to calculate the fractal dimension and size distribution. The fractal dimension is calculated from the form factor F(q) at large scattering angles. At large angles the fractal dimension can also be computed by considering only the influence of the very local environment on the optical contrast around a subunit. The fractal dimensions of E. coli strains flocculated with two different cationic polymers have been computed by two techniques: static light scattering and confocal image analysis. The fractal dimensions calculated with both techniques at different flocculation times are very similar: between 1.90 and 2.19. The comparison between two completely independent techniques confirms the theoretical approach of multiple scattering of large flocs using the Mie theory. Size distributions have been calculated from light-scattering data taking into account the linear independence of the structure factor S(q) relative to each size class and using the fractal dimension measured from F(q) in the large-angle range or from confocal image analysis. The results are very different from calculations made using hard-sphere particle models. The size distribution is displaced toward the larger sizes when multiple scattering is considered. Using this new approach to the analysis of very large fractal aggregates by static light multiple scattering, the fractal dimension and size distribution can be calculated using two independent parts of the scattering curve.