Transesterification is a widely used reaction in the chemical industry. Currently, industrial-scale transesterification is primarily performed via homogeneous catalysts. Because of downstream separation issues, there is a need for effective heterogeneous catalysts. However, heterogeneous catalysts introduce the drawback of mass-transfer limitations into the reaction system. The substrates associated with transesterification form a three-phase system that is inherently immiscible in each other with liquid/liquid/solid (L/L/S) interfaces. This study was conducted to ascertain the behavior of a solid catalyst that has amphiphilic properties in the transesterification system. It was hypothesized that the amphiphilic catalyst, depending upon its degree of polymerization, would orient itself at the interface of the two immiscible liquids, forming an emulsion. The catalytic active site, in the mean time, would catalyze the transesterification reaction. In this study, the catalytic aspects of the titanium-isopropoxide-based inorganic dendritic polymers were investigated. Titanium isopropoxide catalysts with varying degrees of polymerization were developed by sol−gel water condensation. The degree of polymerization was controlled by the amount of water addition. Five forms of catalysts with varying degrees of polymerization were subjected to transesterification at varying temperatures and time intervals. In this experiment, soybean oil was used as the triglyceride. Isopropanol and titanium isopropoxide were used as the catalyst precursors. The highest yield of 41.56% of propyl esters was obtained at 200 °C after 3 h with 1% (w/w) of the monomeric form of the catalyst. The behavior of the dimeric and higher forms was highly correlated with reaction temperatures and residence times.

Recent studies suggest an important role for L-homoarginine in cardiovascular, hepatic and neurological functions, as well as the regulation of glucose metabolism. However, little is known about whole-body L-homoarginine synthesis or its response to dietary L-arginine intake in animals. Four series of experiments were conducted to determine L-homoarginine synthesis and catabolism in pigs and rats. In Experiment 1, male and female pigs were fed a corn- and soybean meal-based diet supplemented with 0.0-2.42 % L-arginine-HCl. In Experiment 2, male and female rats were fed a casein-based diet, while receiving drinking water containing supplemental L-arginine-HCl to provide 0.0-3.6 g L-arginine/kg body-weight/day. In both experiments, urine collected from the animals for 24 h was analyzed for L-homoarginine and related metabolites. In Experiment 3, pigs and rats received a single oral dose of 1 or 10 mg L-homoarginine/kg body-weight, respectively, and their urine was collected for 24 h for analyses of L-homoarginine and related substances. In Experiment 4, slices of pig and rat tissues (including liver, brain, kidney, heart, and skeletal-muscle) were incubated for 1 h in Krebs-bicarbonate buffer containing 5 or 50 µM L-homoarginine. Our results indicated that: (a) animal tissues did not degrade L-homoarginine in the presence of physiological concentrations of other amino-acids; (b) 95-96 % of orally administered L-homoarginine was recovered in urine; (c) L-homoarginine was quantitatively a minor product of L-arginineg catabolism in the body; and (d) dietary L-arginine supplementation dose-dependently increased whole-body L-homoarginine synthesis. These novel findings provide a new framework for future studies of L-homoarginine metabolism and physiology in animals and humans.

In liquid/liquid/solid (L/L/S) systems pertinent to two immiscible reactant liquids mixed with a solid catalyst, the reaction efficacy depends on the mass transfer limitations at the L/L/S phase boundary. Formation of an emulsion in such a system will likely reduce the mass transfer barrier significantly. The stability of such an emulsion system depends on the hydrophilicity of the head group of the catalytic emulsifier toward the more polar liquid reactant and the hydrophobicity of the tail group toward the more nonpolar liquid reactant. This study looks at the effect of the alkyl groups with varying carbon numbers in titanium alkoxide as a catalyst that also has emulsification (amphiphilic) properties to transesterify triglycerides in alcohols. All forms of oligomeric titanium alkoxides tested were highly basic. Those with smaller alkoxide groups (lower carbon numbers) tended to be more basic than those with higher carbon numbers. The chirality did not affect the degree of basicity of the alkoxides. The maximum ester yield noticed was 64.25% (with 63.85% selectivity towards transesterification) with titanium methoxide after 3 hours of reaction. It was observed that higher the number of carbon atoms in the tail group the lower the catalytic ability of the amphiphile towards transesterification. It is expected that longer the carbon-chain in the tail group stronger the emulsification ability of the amphiphile in oil-in-alcohol systems. However, when looking at the efficacy of the amphiphile for the combined emulsification and catalytic ability, it is apparent that the length of the alkoxide group needs to be compromised.

L-Homoarginine (hArg) may play a role in regulating the metabolism of its structural homologue L-arginine via multiple pathways (including nitric oxide synthase) in animals. Accurate measurement of hArg is essential for studying its synthesis and utilization by cells and the whole body. Here, we describe a simple, sensitive and automated method for analysis of hArg in biological samples by high-performance liquid chromatography involving precolumn derivatization with o-phthalaldehyde (OPA) and N-acetyl-L-cysteine (NAC) as the thiol. The hArg-OPA-NAC derivative was separated at 25 °C on a reversed-phase C18 material and detected by fluorescence at excitation and emission wavelengths of 340 and 450 nm, respectively. The total running time for one sample (including the time for column regeneration) was 20 min, with the retention time for hArg being 10.03 min. The limit of detection was 188 fmol hArg, which was equivalent to 12 nM hArg in the 160-µl assay mixture. The assay was linear between 1.0 and 80 pmol hArg injected into the HPLC column (equivalent to 0.0625 and 5 µM hArg in the 160-µl assay mixture, respectively). The precision (relative deviation, %) and bias (relative error, %) of the HPLC method were 0.52-1.16 and 0.42-1.12, respectively, for aqueous solutions of hArg and for various biological samples (e.g., plasma, liver, brain and kidney). This is a highly sensitive, accurate, efficient and easily automated method for analysis of hArg in biological samples and provides a useful tool for studying the biochemistry, nutrition, physiology and pharmacology of hArg and arginine in animals and humans.

In vitro and in vivo experiments were conducted to determine the metabolism of rumen-protected or unprotected l-citrulline (Cit) plus l-glutamine (Gln) by ruminal microbes. In the in vitro experiment, whole ruminal fluid (3 mL, containing microorganisms) from steers was incubated at 37 ºC with 5 mM Cit plus 6 mM Gln (in a rumen-protected or unprotected form) for 0, 0.5, 2, or 4 h after which times 50 µL samples were collected for AA and ammonia analyses. In the in vivo experiment, at 0.5 h before and 0, 0.5, 1, 2, 4, and 6 h after cannulated adult steers consumed 0.56 kg dried-distillers’ grain mixed with 70 g Cit plus 70 g Gln (in a rumen-protected or unprotected form), samples of ruminal fluid and jugular venous blood were obtained for AA analyses. Results from both in vitro and in vivo experiments demonstrated extensive hydrolysis of rumen-unprotected Gln into glutamate, but little degradation of the rumen-protected Gln or rumen-protected and unprotected Cit by ruminal microbes. Concentrations of Cit and arginine in the plasma of steers consuming rumen-protected or unprotected AA increased at 1 and 2 h after the meal, respectively, when compared with values at 0 h. Collectively, these novel findings indicate that ruminal microbes of adult steers do not degrade extracellular Cit in a rumen-protected or unprotected form. Our results refute the view that all dietary AAs are extensively catabolized by ruminal microorganisms and also have important implications for dietary supplementation with Cit to ruminants to enhance the concentration of arginine in their plasma and their productivity.