Glyceryl Tributyrate Research Articles

Metal-Loaded MgAl Oxides for Transesterification of Glyceryl Tributyrate and Palm Oil

MgAl hydrotalcites (Mg/Al molar ratios 3 and 4) were synthesized using alkali and alkali-free methods at different pH's. They were calcined to form MgAl oxides, and then loaded with Na, K metals at different content. The characterization was performed with XRD, BET, and FTIR techniques, and the basicity was determined using the Hammett titration method. The oxides prepared using the alkali method gave higher soluble basicity than ones using the alkali-free method. Glyceryl tributyrate was used as a model compound for vegetable oil to study transesterification with methanol catalyzed by the metal-loaded MgAl oxides. The results showed that the catalysts synthesized with a Mg/Al molar ratio of 4 and at pH 11 are more basic than those with a ratio of 3 and at pH 8, due to higher incorporation of Mg in the oxides, resulting in higher catalytic activity. For the metal-loaded catalysts, under the same reaction conditions, it was found that the MgAl oxide loaded with 1.5% K gave the highest activity. It was ther...

Biodiesel synthesis using calcined layered double hydroxide catalysts

The catalytic properties of calcined Li–Al, Mg–Al and Mg–Fe layered double hydroxides (LDHs) were examined in two transesterification reactions, namely, the reaction of glyceryl tributyrate with methanol and the reaction of soybean oil with methanol. While the Li–Al catalysts showed high activity in these reactions at the reflux temperature of methanol, the Mg–Fe and Mg–Al catalysts exhibited much lower methyl ester yields. CO2 TPD measurements revealed the presence of sites of weak, medium and strong basicity on both Mg–Al and Li–Al catalysts, the latter showing higher concentrations of medium and strong base sites; by implication, these are the main sites active in transesterification catalyzed by calcined Li–Al LDHs. Maximum activity was observed for the Li–Al catalysts when a calcination temperature of 450–500°C was applied, corresponding to decomposition of the layered double hydroxide to the mixed oxide without formation of crystalline lithium aluminate phases.

Detection of triglyceride using an iridium nano-particle catalyst based amperometric biosensor

The detection and quantification of triglyceride (TG) using an iridium nano-particle modified carbon based biosensor was successfully carried out in this study. The detection procedures were based on the electrochemical detection of enzymatically produced NADH. TG was hydrolyzed by lipase and the glycerol produced was catalytically oxidized by NAD-dependent glycerol dehydrogenase producing NADH in a solution containing NAD(+). Glyceryl tributyrate, a short chain triglyceride, was chosen as the substrate for the evaluation of this TG biosensor in bovine serum and human serum. A linear response to glyceryl tributyrate in the concentration range of 0 to 10 mM and a sensitivity of 7.5 nA mM(-1) in bovine serum and 7.0 nA mM(-1) in human serum were observed experimentally. The potential interference of species such as uric acid (UA) and ascorbic acid (AA) was assessed. The incorporation of a selected surfactant and an increase in the incubation temperature appeared to enhance the performance of this biosensor. The conditions for the determination of TG levels in bovine serum using this biosensor were optimized, with sunflower seed oil being used as an analyte to simulate the detection of TG in blood. The experimental results demonstrated that this iridium nano-particle modified working electrode based biosensor provided a relatively simple means for the accurate determination of TG in serum.

Structure-reactivity correlations in MgAl hydrotalcite catalysts for biodiesel synthesis

A series of [Mg (1− x) Al x (OH) 2] x+ (CO 3) x/ n 2− hydrotalcite materials with compositions over the range x = 0.25–0.55 have been synthesised using an alkali-free coprecipitation route. All materials exhibit XRD patterns characteristic of the hydrotalcite phase with a steady lattice expansion observed with increasing Mg content. XPS measurements reveal a decrease in both the Al and Mg photoelectron binding energies with Mg incorporation which correlates with the increased intra-layer electron density. All materials are effective catalysts for the liquid phase transesterification of glyceryl tributyrate with methanol for biodiesel production. The rate increases steadily with Mg content, with the Mg rich Mg 2.93Al catalyst an order of magnitude more active than MgO, with pure Al 2O 3 being completely inert. The rate of reaction also correlates with intralayer electron density which can be associated with increased basicity.

Li–CaO catalysed tri-glyceride transesterification for biodiesel applications

A series of Li-promoted CaO catalysts with Li loadings in the range 0.26–4.0 wt% have been prepared which are effective in the transesterification of glyceryl tributyrate and methanol to methyl butanoate. A Li content of 1.23 wt% provides the optimum activity towards methyl butanoate formation. Li doping increases the base strength of CaO, and XPS and DRIFTS measurements reveal that the optimum loading correlates with the formation of an electron deficient surface Li+ species and associated –OH species at defect sites on the support. High Li loadings result in bulk LiNO3 formation and a drop in surface area and corresponding catalytic activity.

Reagentless pH-based biosensing using a fluorescently-labelled dextran co-entrapped with a hydrolytic enzyme in sol–gel derived nanocomposite films

We report on the development of reagentless fluorescence-based sensing films utilizing hydrolytic enzymes co-entrapped with polymers that are labelled with pH sensitive fluorophores. Aqueous solutions of a hydrophilic enzyme (urease) or a lipophilic enzyme (lipase) containing fluorescein or carboxy-seminaphtharhodafluor-1 (SNARF-1), either free or conjugated to a dextran polymer backbone, were mixed with hydrolyzed alkoxysilane solutions and cast onto planar surfaces to form thin, biologically active sol–gel derived films (ca. 500 nm thick). The films also contained various additives, such as methyltrimethoxysilane, dimethyldimethoxysilane, polyethylene glycol or polyvinyl alcohol, to optimize the activity of the entrapped enzymes. The photostability, leaching, p K a and pH response of the entrapped probes were characterized, as was the performance of the entrapped enzymes, and an optimal set of processing conditions was obtained for each different sensing film. In general, the results indicated that SNARF-labelled dextran was the most useful pH sensitive dye owing to insensitivity to leaching and photobleaching. Furthermore, it was observed that the p K a and pH response of this probe was insensitive to preparation conditions. The performance of the co-entrapped enzymes was highly dependent on the type and level of additive, but in all cases, it was possible to obtain active enzymes with good performance characteristics. Reagentless sensing films for urea and glyceryl tributyrate (GTB) are demonstrated based on the detection of enzyme-mediated pH changes from films coated onto planar substrates.

Tributyrin-induced differentiation promotes apoptosis of LS 174T colon cancer cells in vitro

Tributyrin (glyceryl tributyrate, TB) is known to induce malignant cells to differentiate followed by arrest of cell growth and death via apoptosis. We investigated the effects of TB on the distribution of cell cycle phases, differentiation as measured by alkaline phosphatase activity (ALP), and apoptosis of LS 174T colon cancer cells expressed by morphological changes, externalization of phosphatidylserine and stimulation of various caspases. TB (0.6 mM) reduced the proliferation by a 5-fold decrease of tumor cells in the S-phase and 1.3-fold increase in the G2/M-phase of cell cycle after 24 h of incubation. The ALP activity was enhanced in a dose-dependent manner up to 180-fold by 1 mM TB. Apoptosis was seen only above 0.6 mM TB (5-fold increase). Studies with caspase inhibitors revealed that TB mediated cell death was linked to up-regulation of caspases 3 and 8. Our results indicate that TB-induced differentiation promotes apoptosis in LS 174T cells and may explain the mode of action of TB finally resulting in an arrest of tumor cell growth.

Overproduction in Escherichia coli, purification and characterization of a family I.3 lipase from Pseudomonas sp. MIS38

Determination of the nucleotide sequence of the gene encoding a lipase from Pseudomonas sp. MIS38 (PML) revealed that PML is a member of the lipase family I.3 and is composed of 617 amino acid residues with a calculated molecular weight of 64 510. Recombinant PML (rPML) was overproduced in Escherichia coli in an insoluble form, solubilized in the presence of 8 M urea, purified in a urea-denatured form and refolded by removing urea in the presence of the Ca 2+ ion. Gel filtration chromatography suggests that this refolded protein is monomeric. rPML showed relatively broad substrate specificities and hydrolyzed glyceryl tributyrate and olive oil with comparable efficiencies. rPML was active only in the form of a holo-enzyme, in which at least 12 Ca 2+ ions bound. These Ca 2+ ions bound too tightly to be removed from the protein upon dialysis, but were removed from it upon EDTA treatment. The resultant apo-enzyme was fully active in the presence of 10 mM CaCl 2, but was inactive in the absence of the Ca 2+ ion. PML has a GXSXG motif, which is conserved in lipases/esterases and generally contains the active-site serine. The mutation of Ser 207 within this motif to Ala completely inactivated PML, suggesting that Ser 207 is the active-site serine of PML.

Influence of chain structure and molecular weight of poly(vinylidene fluoride) on the morphology of its thermoreversible gels in acetophenone, ethyl benzoate, and glyceryl tributyrate

The morphology of thermoreversible gels of three commercial poly(vinylidene fluoride) (PVF 2 ) samples in the three solvents acetophenone (ACTP), ethyl benzoate (EB), and glyceryl tributyrate (GTB) are studied by means of scanning electron microscopy (SEM). The PVF 2 /ACTP gels have a spheroidal morphology, the PVF 2 /GTB gels have a fibrillar morphology, and the PVF 2 /EB gels have a mixed morphology containing both the fibrillar and the spheroidal texture. The fibrillar and spheroidal radii increase with increasing gelation temperature and polymer concentration. At identical gelation condition the radii decrease with increasing head to head (H-H) defect structure in the polymer chain and also with increasing molecular weight. These results are explained with the nucleation and growth mechanism of polymer crystals in solution. It is concluded from this study that though a polymer/solvent compound formation is responsible for the fibrillar morphology it does not affect the nucleation and growth process controlling the radii of spheroids and fibrils.

Influence of chain structure and molecular weight of poly(vinylidene fluoride) on the morphology of its thermoreversible gels in acetophenone, ethyl benzoate, and glyceryl tributyrate

Influence of chain structure and molecular weight of poly(vinylidene fluoride) on the morphology of its thermoreversible gels in acetophenone, ethyl benzoate, and glyceryl tributyrate

Gelation mechanism of thermoreversible poly(vinylidene fluoride) gels in glyceryl tributyrate

Poly(vinylidene fluoride) (PVF 2) gels in glyceryl tributyrate (GTB) with fibrillar morphology in the dried state. The gels are transparent and WAXS results indicate the presence of α-phase PVF 2 crystals in the gels. The gelation rate ( t −1 gel) has been measured by the test tube tilting method and has been analysed with the equation t −1 gel ∝ f(c)f(T) , where f( c)=concentration function and f( T)=temperature function. At a fixed temperature, the variation of t −1 gel with concentration suggests that the nature of the connectedness in this system obeys the three dimensional percolation mechanism. On the other hand, at a fixed concentration, the variation of the gelation rate with temperature suggests that the gelation is a two step concerted process of conformational ordering and crystallization, the former acting as the rate determining step. The formation of fibrillar gels in this system has been attributed to the solvation of the TGT G ̄ conformer of PVF 2 through compound formation in a 3:1 molar ratio of the monomeric units of PVF 2 and GTB.

A Thermodynamic Study on the Thermoreversible Poly(vinylidene fluoride) Gels in Acetophenone, Ethyl Benzoate, and Glyceryl Tributyrate

The gel melting temperatures of poly(vinylidene fluoride) (PVF2) gels in acetophenone (ACTP), ethyl benzoate (EB), and glyceryl tributyrate (GTB) are measured by differential scanning calorimetry (DSC) at high PVF2 concentration (WPVF2 ≥ 0.1) and visually for very low PVF2 concentration (WPVF2 ≤ 0.1). The gelation temperatures are also measured in DSC by dynamic cooling method. The enthalpy of gelation and enthalpy of gel fusion vs weight fraction of PVF2 (WPVF2) plots exhibit different nature in the three solvents. It is linear for the PVF2/ACTP gels but the PVF2 gels in the other two solvents exhibit positive deviation from linearity. A thermodynamic analysis of the enthalpy values in PVF2/EB and PVF2/GTB systems indicates the polymer−solvent complex formation in both the systems. The stoichiometry of the PVF2−EB compound is 1:1 molar ratio and that of PVF2−GTB compound is 3:1 molar ratio with respect to PVF2 monomeric unit and the solvent molecule, respectively. The phase diagram of the PVF2/ACTP system is linear, that of PVF2/EB system exhibits compound formation with incongruent melting point, and that of PVF2/GTB system exhibits compound formation with singular point. The spheroidal morphology of the PVF2/ACTP gels has been attributed to the chain folding process, whereas the fibrillar morphology of PVF2/GTB gels is due to polymer−solvent complex formation. The reason for the mixed morphology of PVF2/EB gels is not clear and is probably due to the comparable rates of the polymer−solvent compound formation and the chain-folding processes.

On the gelation rate of thermoreversible poly(vinylidene fluoride) gels in glyceryl tributyrate

AbstractThe gelation rate of poly(vinylidene fluoride) (PVF2)/glyceryl tributyrate (GTB) system has been measured. It has been analysed with the help of an equation which contains φn and f(T) term where φ is a reduced overlapping concentration and n is analogous to the percolation exponent β in a three‐dimensional lattice. f(T) is related to the temperature function of the coil‐to‐helix transition. Analysis of the gelation rates supports that the three‐dimensional percolation is a suitable mechanism in this gelation process and it also indicates that the gelation is caused by coil‐to‐helix transition followed by their association.

Gas-Liquid Chromatographic Determination of Isosorbide Dinitrate in Tablets

A gas-liquid chromatographic (GLC) method is described for determining isosorbide dinitrate (ISDN) in tablets. ISDN is extracted from tablet excipients by a 2-phase system composed of water-ethyl ether, and detected and quantitated with a flame ionization detector after separation from the internal standard (glyceryl tributyrate) on a 3% OV-210 column. Ten replicate assays on 2 different batches of tablets, each containing 5 mg ISDN, gave coefficients of variation of 1.16 and 1.48%, respectively. Comparison of results obtained for tablets containing 5, 10, and 40 mg ISDN, and for diluted isosorbide dinitrate raw material containing 25% ISDN, showed good correlation among the GLC, USP colorimetric, and USP polarographic procedures. Assay of synthetic mixtures containing ISDN, isosorbide-2-mononitrate, and isosorbide-5-mononitrate demonstrated that the GLC procedure is specific for ISDN, whereas the USP polarographic procedure is subject to interference from the mononitrates.

Esterolytic activities of rat intestinal mucosa. 2. Purification and properties of a glycerol-ester hydrolase.

A glycerol-ester hydrolase from rat intestinal cells has been purified using chromatography on carboxyhexanoyl-Sepharose-glyceryldioctanoate and preparative gel electrophoresis. The enzyme gives a single band by analytical gel electrophoresis; it is a monomer of molecular weight 68000. The optimum pH for its action on glyceryl tributyrate is between 8.0 and 8.5; the activation energy was calculated to be 8.7 kcal x mol-1 (36.4 kJ/mol). Its substrate specificity is mainly directed against esters of glycerol and of primary monoalcohols. Similarly to pancreatic lipase but contrary to liver esterase, it is inhibited by bile salts; relief of this inhibition by colipase is only observed for pancreatic lipase. The possible role of the glycerol-ester hydrolase in the absorption of short and of medium chain triglycerides is discussed.

The influence of chemical modification on the hydrolysis of fats by pancreatic lipase and pregastric esterase with reference to fat digestion in the pre-ruminant calf.

AbstractThe hydrolysis of various dietary fats and pure triglycerides by pregastric esterase and pancreatic lipase was studied in vitro in conjunction with a series of digestibility trials to examine the effect of various chemical modifications to beef tallow on its digestibility in milk replacers for pre‐ruminant calves. Using pure triglycerides, it was shown that pregastric esterase preferentially hydrolyses triglycerides containing short chain fatty acids; the rate was highest with glyceryl tributyrate and decreased markedly with increase in chain length. Using butterfat, tallow and various modified forms of tallow, it was shown that the inclusion of butyric acid in tallow by interesterification, which markedly improved its digestibility, substantially increased its rate of hydrolysis by pregastric esterase. The initial rate of hydrolysis of tallow by pancreatic lipase was substantially less than that of butterfat. Little improvement in the rate of hydrolysis and solubilisation was obtained when the tallow sample was interesterified or when it was supplemented with the long chain fatty acids, myristic and oleic, or with the short chain fatty acid, butyric. A considerable increase in the initial rate of hydrolysis and solubilisation did occur with tallow samples with a reduced content of stearic acid.The results suggest that hydrolysis by pregastric esterase is a major site of discrimination between different fats in the pre‐ruminant calf and an important factor in determining overall digestibility.