Synthesis and characterization of poly-L-leucine initialized and immobilized by rehydrated hydrotalcite: understanding stability and the nature of interaction.

PLLs were synthesized by the ring-opening polycondensation (ROP) method using a-L-leucine N-carboxyanhydride (NCA) and initialized by triethylamine (Et3N), water or rehydrated hydrotalcite (HTrus). The role of temperature, different initiators and water in ROP was further investigated. In general, the initiators used in the polymerization reaction lead to PLL alpha-helical chains containing 5\u201340 monomers with NCA endgroups via a monomer-activated mechanism. However, the water has a twofold effect on ROP, as both a nucleophile and a base, which involves competition between two different types of initiating mechanisms (nucleophilic attack or deprotonation of the NCA monomer) in the polymerization reaction. This competition provides as a main product NCA endgroups with an alpha-helical structure and leads to the formation of the PLL cyclic-chains and beta-sheet structures which reduce the polymer Mw and the PD of the polypeptide. Furthermore, the water can hydrolyze the NCA endgroups resulting in PLL alpha-helical chains that contain living groups as the main product. On the other hand, the HTrus presents a double role: as both an initiator and a support. The polymers synthesized in the presence of HTrus presented a HT-carboxylate endgroup. The PLLs immobilized in HTrus through an anion-exchange method performed for just 30 minutes presented the PLL immobilized in the interlayer space of the HTrus. The PLL chains of the immobilized counterpart are stabilized by H-bonding with the M\u2013OH of the HT structure. All the polypeptides and biohybrid materials synthesized have been characterized using different techniques (EA, ICP, XRD, Raman, MALDI-TOF, ESI-TOF, FT-IR at increasing temperatures, TG/DT analyses and TEM)

Aldol condensation of campholenic aldehyde and MEK over activated hydrotalcites

International audienc

Structure and reactivity of alumina-supported iron catalysts for ammonia synth

Alumina-supported iron catalysts, obtained either by impregnation of iron from a K4[Fe(CN)6] aqueous solution upon several acid-modified γ-Al2O3 samples or by the incipient wetness method, were characterized and their activities for ammonia synthesis at atmospheric pressure and 593 K were studied. Characterization was carried out by temperature-programmed reduction (TPR), kinetics of hydrogen reduction, CO chemisorption, X-ray photoelectron spectroscopy (XPS), IR spectroscopy, and Mössbauer spectroscopy, resulting in the degree of reduction and the dispersion of the metallic phase dependent on the previous acid modification of the γ-Al2O3. The XPS surface composition expressed as (M = Fe, K) gave . IR experiments, with NO as probe molecule, exhibited bands for reduced catalysts at 1778 and 1712 cm−1 whose intensity and position depended on the protonation degree of γ-Al2O3 and promoter content, respectively. Mössbauer spectra of the reduced samples showed the presence of surface α-Fe, superparamagnetic Fe0, Fe2+, Fe3+, and α-Fe2O3 depending on the catalyst. Finally, the catalytic activity for ammonia synthesis was found to be dependent on the surface structure of the catalyst and hence on the method of preparation

Conversion of glycerol over 10%Ni/y-Al2O3 catalyst

10.1016/j.apcatb.2013.09.02