Search results for "acids"
showing 10 items of 3520 documents
Effect of climate and vegetation on soil organic carbon, humus fractions, allophanes, imogolite, kaolinite, and oxyhydroxides in volcanic soils of Et…
2007
A soil sequence along an elevational gradient ranging from subtropical to subalpine climate zones in the Etna region (Sicily, southern Italy) was investigated with respect to organic C, kaolinite, and crystalline to noncrystalline Al and Fe phases. Special emphasis was given to the stabilization of soil organic carbon (SOC) and its interaction with the inorganic phases. The soils were variations of Vitric Andosols that developed on a trachy-basaltic lava flow with an age of 15,000 years. Two main vegetation systems dominated the sites: at the lower sites, it was mainly maquis vegetation and, at the higher elevated sites, predominantly coniferous forest. The concentration of SOC in the topso…
Quantitative separation of Trichoderma lipid classes on a bonded phase column.
1992
Bond Elut aminopropyl columns were used to purify the different lipid classes of Trichoderma harzianum and Trichoderma viride. This methodology permitted good separation of the fungal lipid classes in less time than traditional techniques. The incorporation of [1 (14)C]linoleic acid into neutral lipids, free fatty acids and phospholipids was quantified for both strains. The fatty acid profile of the different lipid classes of these fungal strains was determined as a function of culture time.
Stereoselective synthesis of unsaturated and functionalized L-NHBoc amino acids, using Wittig reaction under mild phase-transfer conditions.
2012
The stereoselective synthesis of a new amino acid phosphonium salt was described by quaternization of melting triphenylphosphine with the γ-iodo NHBoc-amino ester, derived from L-aspartic acid. The deprotection of the carboxylic acid function to afford the phosphonium salt with a free carboxylic acid group was achieved by a palladium-catalyzed desallylation reaction. This phosphonium salt was used in the Wittig reaction with aromatic or aliphatic aldehydes and trifluoroacetophenone, under solid-liquid phase-transfer conditions in chlorobenzene and in the presence of K(3)PO(4) as weak base, to afford the corresponding unsaturated amino acids without racemization. Thus, the reaction with subs…
Digestion and absorption of polyunsaturated fatty acids
1991
Polyunsaturated fatty acids play an important part in the structure and function of cellular membranes and are precursors of lipid mediators which play a key role in cardiovascular and inflammatory diseases. Dietary sources of essential fatty acids are vegetable oils for either linoleic or alpha-linolenic acids, and sea fish oils for eicosapentaenoic and docosahexaenoic acids. Because of the specificity of the pancreatic lipid hydrolases, triglyceride fatty acid distribution is an essential parameter in the digestibility of fats. The efficiency of the intestinal uptake depends on the hydrolysis and especially on their micellarization. n-3 polyunsaturated fatty acid ethyl ester digestion is …
Fluorous (Trimethylsilyl)ethanol: A New Reagent for Carboxylic Acid Tagging and Protection in Peptide Synthesis
2006
Starting with a fluorous analogue of 2-(trimethylsilyl)ethanol, we have designed an easy method for preparing a new fluorous tag ((F)TMSE) for the protection of carboxylic acids. Because mild conditions are employed in the tag cleavage (TBAF in the presence of 4 A molecular sieves, which prevent racemization), this tag can be advantageously used in the synthesis of peptides and modified peptides, as we have demonstrated with several examples, including the fluorous synthesis of short alpha- and beta-peptides as well as of modified fluorinated retropeptides.
Bis[(trimethylsilyl)methyl]manganese: Structural Variations of Its Solvent-Free and TMEDA-, Pyridine-, and Dioxane-Complexed Forms
2009
First synthesized in 1976 and recently taking on a new significance as a key precursor to heterobimetallic alkali-metal-manganese(II) complexes, bis[(trimethylsilyl)methyl] manganese has been structurally characterized by X-ray crystallography. It forms a polymeric chain structure of formula [{Mn(CH2SiMe3)(2)}(infinity)], 1, in which distorted tetrahedral, spiro Mn atoms are linked together via mu(2)-bonding alkyl ligands. The structure is notable for displaying two distinct categories of Mn-C bond lengths with a mean size differential of 0.225 angstrom and for being the first fully crystallographically characterized polymeric manganese(II) dialkyl compound. Magnetic measurements of 1 indic…
Phenylalanine hydroxylase from the sponge Geodia cydonium: implication for allorecognition and evolution of aromatic amino acid HYDROXYLASESfn1fn1The…
1998
Abstract The prophenoloxidase activating system is a defense system, frequently reported both in protostomes and in deuterostomes. The final product of the phenoloxidase activity is melanin which is ubiquitously present throughout the metazoan kingdom. The melanin synthesis pathway starts with the amino acid [aa] phenylalanine which is converted to tyrosine by the phenylalanine hydroxylase [PAH]. We show that after allo-transplantation in the marine sponge Geodiacydonium PAH is upregulated in the grafts. Enzyme determination studies revealed that PAH activity increases by three-fold two d after transplantation and reaches its maximum after 3 d (by 3.7-fold). This finding was supported by de…
Unsaturated fatty acid bioavailability in growing rats fed low or adequate protein diets with sunflower or soybean oils
1993
Abstract The relationship of serum very low density lipoproteins (VLDL) to hepatic lipid composition was studied after 28 days of protein depletion to determine the interactions between dietary protein levels and the essential fatty acid (EFA) availability. This was examined in rats using a dietary combination of 20% or 2% casein with 5% vegetable oils, variable in their n-6:n-3 fatty acid ratios. Rats were divided into four groups, SFC (20% casein + 5% sunflower oil ); SFd (2% casein + 5% sunflower oil ); SC (20% casein + 5% soybean oil ); Sd (2% casein + 5% soybean oil ). Dietary protein depletion decreased phospholipid and protein concentrations in liver and VLDL, whereas triacylglycerol…
Effects of gamma-irradiation on the alpha-tocopherol and fatty acids content of raw unpeeled almond kernels (Prunus dulcis)
2014
Abstract The present study evaluated fatty acid composition and α-tocopherol content of almond as a function of irradiation dose in order to determine dose levels causing minimal undesirable changes to almonds. Raw unpeeled almonds variety Tuono ( Prunus dulcis (Mill.) D. A. Webb) were irradiated using 60 Co source at dose of 0.5, 1.5, 3, 6, 8 and 10 kGy. Both control and irradiated samples were kept frozen and immediately analyzed. The data obtained showed no change in fatty acid compositions up to a dose of 10 kGy; on the contrary, a general trend observed is that increasing the dose of irradiation resulted in the decrease of α-tocopherol content. The study has shown that irradiation is a…
On the problematic nature of vitamin E requirements: net vitamin E
1991
The requirement for vitamin E is closely related to the dietary intake of polyunsaturated fatty acids (PUFA). By the protective mechanism to prevent PUFA from being peroxidized, vitamin E is metabolically consumed. In addition, PUFA impair the intestinal absorption of vitamin E. Therefore PUFA generate an additional vitamin E requirement on the order of 0.6, 0.9, 1.2, 1.5, and 1.8 mg vitamin E (RRR-alpha-tocopherol-equivalents), respectively, for 1 g of dienoic, trienoic, tetraenoic, pentaenoic, and hexaenoic acid. For this reason, the gross vitamin E content of food containing PUFA does not allow an evaluation of this food as a source of vitamin E. A suitable measure is the net vitamin E c…