Esterification of Levulinic Acid with Different Alcohols Using Mesoporous Stannosilicates As the Catalyst.

The mesoporous stannosilicates SnMCM-41-25 and SnMCM-41-80, synthesized, respectively, at 25 and 80 °C and exhibiting a well-ordered hexagonal structure, were applied for the first time as heterogeneous catalysts in the esterification of levulinic acid (LA) with different alcohols. The nonhydrothermal method was effective to obtain materials with a high degree of ordering, high acidity, and promising catalytic activity in this esterification. The SnMCM-41-80 led to conversions of 71.0 and 83.6% in 120 and 180 min, respectively, while the respective values for the material without Sn were 33.2 and 40.1% under the same conditions (MeOH:LA molar ratio of 5:1, 1 wt % catalyst, 3 h, 120 °C). In addition, concerning the use of different alcohols, the reaction rate constants (k ap) were related to the effects of substituents by Taft equation. In general, the polar and steric effects follow the Taft relation, and the length of the chain exerted less influence on the decrease in conversion in comparison to the presence of branches. These results indicate that it is possible to incorporate Sn into the structure of MCM41, thus, making the modified materials more active in the esterification investigated.

Dilute acid pretreatment for enhancing the enzymatic saccharification of agroresidues using a Botrytis ricini endoglucanase.

The enormous amount of agroindustrial residues generated in Brazil can be used as biomass to produce fermentable sugars. This study compared the pretreatments with different proportions of dilute acid. The method involved pretreatment with 0.5%, 1%, and 1.5% (v/v) sulfuric acid, followed by hydrolysis using the halotolerant and thermostable endoglucanase from Botrytis ricini URM 5627. The physicochemical characterization of plant biomass was performed using XRD, FTIR, and SEM. The pretreatment significantly increased the production of fermentable sugars following enzymatic saccharification from wheat bran, sugarcane bagasse, and rice husk: 153.67%, 91.98%, and 253.21% increment in sugar production; 36.39 mg⋅g-1 ± 1.23, 39.55 mg⋅g-1 ± 1.70, and 42.53 mg⋅g-1 ± 7.61 mg⋅L-1 of glucose; and 3.26 ± 0.35 mg⋅g-1 , 3.61mg⋅g-1 ± 0.74 and 3.59 mg⋅g-1 ± 0.80 of fructose were produced, respectively. In conclusion, biomass should preferably be pretreated before the enzymatic saccharification using B. ricini URM 5627 endoglucanase.

Characterization of antimicrobial effect of organotin-based catalysts on diesel-biodiesel deteriogenic microorganisms.

Organotin compounds are applied in several industrial reactions and can present antifungal and antibacterial activities. Incorrect handling and storage practices of biodiesel and diesel-biodiesel blends can lead to microbial development, impacting its final quality. Concerning this problem, this work investigated the antimicrobial action of two organotin catalysts used in biodiesel production with four isolated microroorganisms (Bacillus pumilus, Pseudomonas aeruginosa, Pseudallescheria boydii, and Aureobasidium pullulans) and a pool of microorganisms (ASTM E1259 standard practice). Samples of soybean biodiesel with different concentrations of dibutyl tin dilaurate (catalyst 1) and di-n-butyl-oxo-stannane (catalyst 2) were prepared and added of mineral medium. The pool of microorganisms was inoculated and incubated at 30 °C and final biomass was weighted after 14 days. Thereafter, soybean biodiesel with catalyst 2 was used. Fungal biomass was weighted, and plate count was used to assess bacterial growth. Results show that catalysts 1 and 2 presented no inhibitory activity on the pool of microorganisms evaluated. A slight inhibitory activity was observed for B. pumilus and A. pullulans growth, but not for P. boydii, P. aeruginosa, or the pool of microorganisms. All experiment exhibited acidification higher than sterile control. Infrared analysis show less microbiological degradation products in the tin-protected fuel with ASTM inoculum. These results suggest that these tin-based catalysts show no toxic effect on native microbial population and a slight effect on some isolated microbial population in laboratory scale and for the first time shows that these organotin compounds can be employed safely as biodiesel catalyst. Graphical abstract.

Synthesis and evaluation of the antibiotic and adjuvant antibiotic potential of organotin(IV) derivatives.

A series of organotin(IV) derivatives was investigated in vitro for their antibiotic and adjuvant antibiotic properties (efflux pump inhibitors) against Staphylococcus aureus strains that overexpress efflux pump proteins for norfloxacin (SA-1199B), erythromycin (RN-4220) and tetracycline (IS-58). Most organotin(IV) compounds showed significant antibacterial activity with small Minimum Inhibitory Concentration (MIC) values, some of which were close to 1.0µg/mL (3.1µM), but this feature was also associated with substantial cytotoxicity. Nevertheless, the cytotoxicity of these organotin(IV) compounds can be overcome when they are used as antibiotic adjuvants. Their remarkable adjuvant antibiotic properties allow potentiation of the action of tetracycline (against IS-58 strain) by up to 128-fold. This likely indicates that they can act as putative inhibitors of bacterial efflux pumps. These results reinforce organotin(IV) complexes as promising antibacterial agents, and many of these complexes, if associated with antibiotics, can act as potential adjuvant antibiotic candidates.