Nanozeolite NaX ion exchanged with different transition metals (Mn 2+ ,Cu 2+ , Co 2+ , Zn 2+ , Ni 2+ ) was used as a solid support for the immobilization of the lipases of Thermomyces lanuginosus (TLL) and Rhizomucor miehei (RML). The nanozeolite-enzyme complexes were used as heterogeneous catalysts for the transesterification reaction of palm oil to fatty acid ethyl esters (FAEEs). The most relevant results were obtained with the Thermomyces lanuginosus enzyme immobilized on nanozeolitic supports ion exchanged with Ni 2+ . Although these zeolitic supports were able to immobilize a relatively small amount of the enzyme (43.7%) in comparison with the other nanozeolitic supports, the FAEE yields obtained with Nano-X/Ni/0.5M-TLL complexes were above 94%. These results revealed an unusual synergistic effect between the Thermomyces lanuginosus enzyme and the nickel ion-exchanged nanozeolitic support; this effect was not observed for the complexes prepared with the Rhizomucor miehei enzyme. Bioinformatics calculations were performed for both enzymes by taking into consideration the crystallographic structures of the enzymes and the zeta potential of the surface of the nanozeolitic supports. By combining calculations of the protein electrostatic potential surface and normal mode analyses in a model, we were able to propose an explanation for the synergistic effect between the lipases and the nanozeolitic supports. The synergistic effect could be explained through an allosteric mechanism describing the interaction between aspartic acid residues 102 and 158 of the Thermomyces lanuginosus lipase and the positively charged zeolitic support surface. This interaction results in the stabilization of the opening of the enzyme lid and leaves its catalytic triad permanently exposed to the reaction medium.
Micro-and nanometric faujasite zeolites were tested as hemostatic coagulant agents. The as-made zeolites and their calcium ion exchanged derivatives were characterized by XRD, SEM, AFM, TGA, and DSC. Zeta potential measurements of the micro and nanometric zeolites, as a function of pH (1e12.5), revealed the hemostatic potential of the materials. The isoelectric point for FAU, FAU/Ca, Nano-FAU, and Nano-FAU/Ca were measured at pH 2.0, 1.9, 3.2, and 2.5, respectively. The hemostatic activity was confirmed by the TEG technique for both micro and nanometric zeolites, however a superior activity were observed for the nanometric materials. FAU and FAU/Ca exhibited a reduction of the R parameter (defined as period of time of latency from the start of test to initial fibrin formation for the formation of a clot of an amplitude of 2 mm) from 8.6 ± 0.7 min (control) to 3.2 ± 0.7 min and 2.3 ± 0.1 min, respectively. On the other hand, for the Nano-FAU, and Nano-FAU/Ca the observed decrease were to 2.4 ± 0.6 min, and 1.1 ± 0.2 min, respectively. The amounts of heat released were 105.60 J/g (FAU), 65.8 J/g (FAU/Ca), 85.48 J/ g (Nano-FAU), and 78.21 J/g (Nano-FAU/Ca). Statistical analysis using one-way analysis of variance showed a global value of p < 0.0001. Tukey-Kramer multiple comparisons revealed significant (p < 0.0001) differences for FAU, FAU/Ca, Nano-FAU, and Nano-FAU/Ca, relative to the control. Nano-FAU/ Ca showed the most important reductions of the R with significant differences compared to the control (p < 0.0001 and p < 0.0001, respectively) and FAU (p ¼ 0.0071 for the R parameter).
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