Enantiomeric Adsorption of Lactic Acid Mixtures in Achiral Zeolites

We studied the adsorption of chiral mixtures of lactic acid in several zeolites. All zeolite systems showed either no selectivity or heteroselectivity in which the minority enantiomer is adsorbed by a higher fraction than its fraction in the reservoir. Analysis of the mechanism showed that none of the previously identified origins of enantioselective adsorption of scalemic mixtures apply to lactic acid. However, on the basis of the lack of any ordered distribution in the adsorbed phase, we postulate a new mechanism that is likely to be very generic for chiral adsorption processes that proceed via chaotic packing of the adsorbate molecules. The new mechanism can explain several characteristics of the adsorption data and hints at new prospective separation methods with a high potential for pharmaceutical applications

Double-Four-Ring [Si₈O₁₂][OH]₈ Cyclosilicate and Functionalized Spherosilicate Synthesis from [N(<i>n</i>‑C₄H₉)₄]H₇[Si₈O₂₀]·5.33H₂O Cyclosilicate Hydrate Crystals

A new synthesis method for preparing spherosilicates with a double-four-ring (D4R) silicate core (Si₈O₁₂) and functional siloxy substituents such as (OSi­(CH₃)₂Cl) on the vertices was discovered. Key to this achievement was the synthesis of [N­(<i>n</i>-C₄H₉)₄]­H₇[Si₈O₂₀]·5.33H₂O D4R cyclosilicate hydrate precursor crystals having only 5.33 water molecules per D4R unit, which is much smaller than the number in the state-of-the-art tetramethylammonium- and choline-containing cyclosilicate hydrate crystals that have up to 65 water molecules per D4R. The low water content allows the use of bifunctional silylating agents such as dichlorodimethylsilane that lose their chloride functionality upon reaction with water molecules. Dissolution of [N­(<i>n</i>-C₄H₉)₄]­H₇[Si₈O₂₀]·5.33H₂O crystals in acidified tetrahydrofuran liberates uncharged D4R [Si₈O₁₂]­[OH]₈ cyclosilicate molecules, as shown by small angle X-ray scattering and ²⁹Si nuclear magnetic resonance. A concentrated stable solution of [Si₈O₁₂]­[OSi­(CH₃)₂Cl]₈ spherosilicate compound was obtained by silylation with Cl₂(CH₃)₂Si. It is a unique way to prepare a stable solution of this attractive spherosilicate with dimethylsilyl chloride chemical functionality suited for derivatization or hybrid material synthesis. With the change in the silylating agent, the new synthesis pathway allows the quantitative synthesis of other spherosilicates such as [Si₈O₁₂]­[OSi­(CH₃)₂H]₈ with high yield and purity

Effets de l'ordonnance d'expropriation sur les baux ruraux

Important cellular events such as division require drastic changes in the shape of the membrane. These remodeling processes can be triggered by the binding of specific proteins or by changes in membrane composition and are linked to phospholipid metabolism for which dedicated enzymes, named phospholipases, are responsible. Here wide-field fluorescence microscopy is used to visualize shape changes induced by the action of phospholipase A1 on dye-labeled supported membranes of POPC (1-palmitoyl-2-oleoly-<i>sn</i>-glycero-3-phosphocholine). Time-lapse imaging demonstrates that layers either shrink and disappear or fold and collapse into vesicles. These vesicles can undergo further transformations such as budding, tubulation, and pearling within 5 min of formation. Using dye-labeled phospholipases, we can monitor the presence of the enzyme at specific positions on the membrane as the shape transformations occur. Furthermore, incorporating the products of hydrolysis into POPC membranes is shown to induce transformations similar to those observed for enzyme action. The results suggest that phospholipase-mediated hydrolysis plays an important role in membrane transformations by altering the membrane composition, and a model is proposed for membrane curvature based on the presence and shape of hydrolysis products

NO_<i>x</i> Adsorption Site Engineering in Ru/Ba,Na–Y Zeolite

Adsorption of gas molecules is a typical application for zeolites. Interaction of adsorbed molecules with cations in zeolite frameworks is responsible for selectivity and adsorption strength. Through detailed analysis of the cation distribution in zeolite Y containing Na⁺, Ba²⁺, and Ru³⁺ cations by NMR and X-ray diffraction combined with adsorption studies it was possible to develop a reversible, highly performant NO_<i>x</i> adsorbent. The results demonstrate intimate understanding of guest–host interactions can lead to rational tailoring of zeolite properties

Absolute Quantification of Water in Microporous Solids with ¹H Magic Angle Spinning NMR and Standard Addition

Zeolites are microporous materials driving industrial scale adsorption, ion exchange, and catalytic processes. Their water content dramatically impacts their properties, but its quantification with Karl Fisher titration or thermal gravimetric analysis is problematic. When standard addition of water is combined with ¹H magic angle spinning (MAS) NMR detection, absolute quantification of water in microporous materials becomes possible. The method was demonstrated on five different, commercially available zeolites

SEM images for BAG coatings in cross-sectional view.

<p>(A) before implantation, (B) after 2 weeks and (C) after 4 weeks of implantation. Images (D), (E) and (F) indicate the corresponding single point EDS analysis.</p

Bone-to-implant contact comparison in the bone adaptation area (BIC-BAA).

<p>The results are the mean values (bars) with standard errors of the mean. The horizontal lines indicate statistically significant difference. (P<0.05).</p

Bone growth into the pores of T2 coating after 4 weeks of healing.

<p>A similar phenomenon was observed for T1 surfaces after both the healing periods. The cells and the mineralized bone can be seen deep into the coating (up to the Ti substrate).</p

SEM images for experimental and control implants.

<p>(A) CTR, (B) T1, (C) T2, (D) BAG, (E) TiO₂ and (F) AMS. Images (G) and (H) represent the cross-sectional views of the thick porous Ti coatings T1 and T2 (as shown by figure (B) and (C)) respectively.</p

Representative histological section, retrieved after 4 weeks of healing.

<p>(A) Scanned image of the histological section. (B) The same image after being digitally processed for histomorphometrical analyses. Four well-defined areas of interest are delimitated: The bone regeneration area (BRA) divided into 100 and 400 µm zones for the measurement of bone area fraction parameters (BAF-100 and BAF-400 respectively) and two reference areas (RA's) positioned in non-affected cortical bone, at each side of the double-stepped cavity. Additionally, two bone adaptation areas (BAA's), on each side of the BRA were used to measure bone-to-implant contact (BIC-BAA).</p