Preparation of association compound between rhodium(II) citrate and β-cyclodextrin

Inclusion compound of rhodium(II) citrate with β-cyclodextrin in a 1:1 molar ratio was prepared using freeze-drying method. X-ray diffactometry, thermal analysis (TG/DTG/DSC), infrared and ¹H-NMR with ¹H spin lattice relaxation (¹H T1) measurements and 13C techniques were used to characterize the system prepared. The results indicated the formation of inclusion or association compounds between rhodium(II) citrate and β-cyclodextrin.

Application of ftir in the determination of acrylate content in poly(sodium acrylate-co-acrylamide) superabsorbent hydrogels

Hydrogels have been prepared by free-radical solution copolymerization of acrylamide and sodium acrylate (NaAc), with molar ratio ranging from 25/75 to 80/20, respectively, using methylene bisacrylamide as the crosslinking agent. A FTIR spectroscopy procedure to determine the acrylate/acrylamide ratio in these hydrogels was proposed based on absorbance at 1410 cm-1 (nCOO-) and 2940 cm-1 (nCH and nCH2). A straight line with a good linear correlation coefficient (0.998) was obtained by plotting the acrylate content (Ac%) versus relative absorbance (Arel = A1410/A2940). Results were confirmed by the amount of sodium cation released in acid medium determined by atomic absorption spectrometry.

Alkaline earth layered benzoates as reusable heterogeneous catalysts for the methyl esterification of benzoic acid

This paper describes the synthesis and characterization of layered barium, calcium and strontium benzoates and evaluates the potential of these materials as catalysts in the synthesis of methyl benzoate. The methyl esterification of benzoic acid was investigated, where the effects of temperature, alcohol:acid molar ratio and amount of catalyst were evaluated. Ester conversions of 65 to 70% were achieved for all the catalysts under the best reaction conditions. The possibility of recycling these metallic benzoates was also demonstrated, evidenced by unaltered catalytic activity for three consecutive reaction cycles.

Epoxidação do óleo de soja com o sistema catalítico [MoO2(acac)2]/TBHP EM [bmim][PF6]

Epoxidation of soybean oil was investigated using 1-n-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6] ionic liquid as biphasic medium with molybdenum(VI) acetylacetonate complex and tert-butyl hydroperoxide TBHP as oxidizing agent. Reaction conditions were molar ratio TBHP:number of double bonds of oil:catalyst of 100:100:1, reaction temperature of 60 ºC and reaction time between 2 and 24 h. The proposed system showed catalytic activity for epoxidation reactions under tested conditions. Reuse of ionic liquid/catalyst system for epoxidation reactions was also investigated. Evaluation of epoxidation observed in this catalytic system was done by quantitative ¹H NMR data.

Otimização da esterificação de ácido hexanóico com n-butanol empregando lipase (Termomyces lanuginosus) imobilizada em gelatina

The application of Lipozyme (Termomyces lanuginosus) immobilized in gelatin gel in aliphatic ester synthesis was investigated taking the esterification of hexanoic acid with n-butanol as a model reaction. Conditions were optimized by factorial design and the highest conversion was obtained under the following conditions: molar ratio alcohol: acid of 2:1, reaction time of 48 h and biocatalyst weight of 7.0 g. Under these conditions the esterification yield was around 98 %. The operational stability of the immobilized lipase was assessed and results showed that after 12 batch runs, the enzyme showed no significant loss of activity.

Influência do método de preparação de eletrocatalisadores PtRu/C sobre a atividade catalítica frente à reação de oxidação de etanol em meio ácido

In this work the influence of variations in the borohydrate reduction method on the properties of PtRu/C electrocatalysts was investigated. The electrocatalysts were prepared using 1:1 ; 2:1; 5:1; 50:1 and 250:1 molar ratios of NaBH4 to metals. The reduction was also performed by dripping or by fast addition of the solution. The results showed that PtRu nanoparticles obtained by fast addition had the smallest crystallite sizes. It was also noted that the catalytic activity increased as the borohydrate:metal molar ratio increased. The PtRu/C electrocatalyst (50:1) obtained by fast addition presented the best catalytic activity for ethanol electro-oxidation.

Use of heterogeneous catalysts in methylic biodiesel production induced by microwave irradiation

The effect of different heterogeneous catalysts on the microwave-assisted transesterification of sunflower oil for the production of methylic biodiesel in a monomode microwave reactor is described. The experiments were carried out at 70 ºC with a 16:1 methanolsunflower oil molar ratio and different heterogeneous basic and acidic catalysts. The results showed that the microwave-heated reactions occur up to four times faster than those carried out with conventional heating. The reactions were performed with 24 catalysts; pure calcium oxide (CaO) and potassium carbonate, either pure or supported by alumina (K2CO3/Al2O3), were the most efficient catalysts.

ESTERIFICAÇÃO E TRANSESTERIFICAÇÃO SIMULTÂNEAS DE ÓLEOS ÁCIDOS UTILIZANDO CARBOXILATOS LAMELARES DE ZINCO COMO CATALISADORES BIFUNCIONAIS

Palm oil containing 40% fatty acids was converted to methyl esters using zinc carboxylates as the esterification/transesterification catalyst. The reaction was optimized using a factorial design in which the effects of the alcohol:fatty acids molar ratio (MRAG) and the catalyst concentration (CAT) were assessed. The best conversion was achieved with CAT at 4 wt% and MRAG at 4:1. However, the solid catalyst presented significant structural changes after use. For instance, laurate anions were replaced by carboxylates of higher molecular mass, leading to the formation of a new catalytically active layered structure. Also, the glycerin obtained as a co-product contained 86 wt% glycerol.

MICROWAVE ACTIVATION OF IMMOBILIZED LIPASE FOR TRANSESTERIFICATION OF VEGETABLE OILS

This work investigated the effect of microwave irradiation (MW) on the ethanolysis rate of soybean and sunflower oils catalyzed by supported Novozyme 435 (Candida antarctica). The effects of tert-butanol, water addition and oil:ethanol molar ratio on transesterification were evaluated under conventional heating (CH), and under optimum reaction conditions (with no added water in the system, 10% tert-butanol and 3:1 ethanol-to-oil molar ratio). The reactions were monitored up to 24 h to determine the conditions of initial reaction velocity. The investigated variables under MW (50 W) were: reaction time (5.0-180 min) and mode of reactor operation (fixed power, dynamic and cycles) in the absence and presence of tert-butanol (10% (w/w). The measured response was the reaction conversion in ethyl esters, which was linked to the enzyme catalytic activity. The results indicated that the use of microwave improved the activity at fixed power mode. A positive effect of the association of tert-butanol and MW irradiation on the catalytic activity was observed. The reaction rate improved in the order of approximately 1.5 fold compared to that under CH with soybean oil. Using soybean oil, the enzymatic transesterification under MW for conversion to FAEE (fatty acid ethyl esters) reached >99% in 3h, while with the use of CH the conversions were about 57% under similar conditions.

INFLUÊNCIA DO CATALISADOR EM SOLUÇÕES POLIMÉRICAS PARA O PREPARO DE GÉIS ORGÂNICOS DE RESORCINOL-FORMALDEÍDO

Resorcinol-formaldehyde (RF) organic gels have been extensively used to produce carbon aerogels. The organic gel synthesis parameters greatly affect the structure of the resulting aerogel. In this study, the influence of the catalyst quantity on the polymeric solution sol-gel process was investigated. Sodium carbonate was used as a basic catalyst. RF gels were synthesized with a resorcinol to formaldehyde molar ratio of 0.5, a resorcinol to catalyst (R/C) molar ratio equal to 50 or 300, and a resorcinol to solvent ratio of 0.1 g mL-1. The sol-gel process was evaluated in situ by Fourier transform infrared spectroscopy using a universal attenuated total reflectance sensor and measurements of the kinematic viscosity. The techniques showed the evolution of the sol-gel process, and the results showed that the lower catalyst quantity induced a higher gel point, with a lower viscosity at the gel point. Differential scanning calorimetry was used to investigate the thermal behavior of the RF dried gel, and results showed that the exothermic event related to the curing process was shifted to higher temperatures for solutions containing higher R/C ratios.

Titrimetric assay of lisinopril in aqueous and non-aqueous media

Four simple titrimetric procedures are described for the determination of lisinopril (LNP) in bulk and in pharmaceuticals based on the neutralization of basic-amino and acidic carboxylic acid groups present in LNP. Method A is based on the neutralization of basic amino groups using perchloric acid as titrant in anhydrous acetic acid medium. Method B, method C and method D are based on neutralization of carboxylic acid group using NaOH, sodium methoxide and methanolic KOH, as titrants, respectively. Method A is applicable over 2.0-20.0 mg range and the calculations are based in the molar ratio of 1:2 (LNP:HClO4). Method B, method C and method D are applicable over 2.0-20.0 mg, 1.0-10.0 mg and 5.0-15.0 mg range, respectively, and their respective molar ratios are 1:1 (LNP:NaOH), 1:2 (LNP:CH3ONa) and 1:1 (LNP:KOH). Intraday and inter day accuracy and precision of the methods were evaluated and the results showed intra- and inter-day precision less than 2.7% (RSD), and accuracy of < 2.5 % (RE). The developed methods were applied to determine LNP in tablets and the results were validated statistically by comparing the results with those of the reference method by applying the Student's t-test and F-test. The accuracy was further ascertained by recovery studies via standard addition technique. No interferences from common tablet exipients was observed.

Quenching of the intrinsic fluorescence of bovine serum albumin by chlorpromazine and hemin

The binding of chlorpromazine (CPZ) and hemin to bovine serum albumin was studied by the fluorescence quenching technique. CPZ is a widely used anti-psychotic drug that interacts with blood components, influences bioavailability, and affects function of several biomolecules. Hemin is an important ferric residue of hemoglobin that binds within the hydrophobic region of albumin with high specificity. Quenching of the intrinsic fluorescence of bovine serum albumin (BSA) was observed by selectively exciting tryptophan residues at 290 nm. Emission spectra were recorded in the range from 300 to 450 nm for each quencher addition. Stern-Volmer graphs were plotted, and the quenching constant estimated for BSA solution titrated with hemin at 25ºC was 1.44 (± 0.05) x 10(5) M-1. Results showed that bovine albumin tryptophans are not equally accessible to CPZ, in agreement with the idea that polar or charged quenchers have more affinity for amino acid residues on the outer wall of the protein. Hemin added to albumin solution at a molar ratio of 1:1 quenched about 25% of their fluorescence. The quenching effect of CPZ on albumin-hemin solution was stronger than on pure BSA. This increase can be the result of combined conformational changes in the structure of albumin caused firstly by hemin and then by CPZ. Our results suggest that the primary binding site for hemin on bovine albumin may be located asymmetrically between the two tryptophans along the sequence formed by subdomains IB and IIA, closer to tryptophan residue 212.

Fatty acid ethyl esters production using a non-commercial lipase in pressurized propane medium

The objective of this work is to investigate the production of fatty acid ethyl esters from soybean oil in compressed propane using a non-commercial lipase from Yarrowia lipolytica and two commercial ones as catalysts, Amano PS and Amano AY30. The experiments were performed in the temperature range of 35-65 °C. at 50 bar, enzyme concentration of 5 wt%, oil to ethanol molar ratio of 1:6 and 1:9, and solvent to substrates mass ratio of 2:1 and 4:1. The results indicated that low reaction conversions were generally obtained with the use of commercial and non-commercial lipases in pressurized propane medium. On the other hand, the aspects of low solvent to substrates mass ratio and mild temperature and pressure operating conditions used to produce ethyl esters justify further investigations to improve reaction yields.

The role of organic solvent amount in the lipase-catalyzed biodiesel production

This research note addresses the role of organic solvent amount in the production of fatty acid ethyl esters from soybean oil. N-hexane was chosen as solvent and two commercial immobilized lipases as catalysts, Novozym 435 and Lipozyme IM. The reactions were conducted in 6 hours, varying the solvent to oil ratio from zero to 50 (v/wt) and adopting adopting for Novozym 435: 65 ºC, enzyme concentration (E, wt%) = 5, oil to ethanol molar ratio (R) = 1:10, water addition (H, wt%) = 0, and for Lipozyme IM: 35 ºC, E = 5 wt%, R = 1:3, H = 10 wt%. For Lipozyme IM, an increase in solvent amount is shown to lead to an enhancement of reaction conversion, while a negligible effect was found for Novozym 435. When using 30 mL of solvent the reaction conversions were 88% for Lipozyme IM and 15% for Novozym 435.

Effect of soaking and cooking on phytate concentration, minerals, and texture of food-type soybeans

The increasing consumption of soybeans due to its bioactive compounds has attracted interest in describing the grain's constituents and variation during processing. Phytate has been the aim of much research since it chelates essential minerals but also has beneficial antioxidant effects. This study evaluated the variation of phytate, calcium, zinc, and iron during soaking and cooking of soybeans. The phytate: Zn and phytate: Fe molar ratios were determined in order to estimate the bioavailability of these minerals. Six food-type varieties were used: BR 36, BRS 213, BRS 216, BRS 232, BRS 155, and Embrapa 48. The samples were soaked in water 3:1 (w/w) for 12 hours at room temperature and cooked. Cooking time was determined by modeling the softening of each variety using fractional conversion. Water content, phytate, and minerals were determined in raw, soaked and cooked samples. The water content of raw grains for all varieties was 9.9 g.100 g-1 increasing to a range of 58.1-63.7 g.100 g-1 after soaking and 63.1-66.0 g.100 g-1 after cooking. Soaking caused a significant reduction in phytate (23-30%), but cooking caused no additional reduction. The phytate: Zn molar ratio was 20 indicating that zinc absorption could be impaired, while the phytate: Fe molar ratio was 8, below the level of compromising absorption