[Thin-layer chromatographic-enzymatic determination of mono-, di-, and triglycerides in glyceride mixtures].
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After determination of charring conditions and the measurement by densitometry of lipids separated by thin-layer chromatography, a statistical analysis was performed to determine the significance of the results. Calibration curves were studied and response factors calculated for some saturated and unsaturated triglycerides.
Separation of triglyceride and diglyceride positional isomers by silver ion high-performance liquid chromatography coupled with an evaporative light-scattering detector is described. The triglyceride isomers had a fatty acid composition of CLC and CCL, where C and L were caprylic acid and linoleic acid, respectively. Diglyceride isomers, 1,2(2,3)-diglyceride and 1,3-diglyceride, which contained caprylic acid were separated too. A solvent system based on n-hexane, 2-propanol, ethyl acetate, and acetonitrile with a flow-rate of 0.8 ml/min was developed. Calibration curves of CLC and CCL were achieved with triolein as internal standard. Using this method, the incorporation of linoleic acid onto specific a position of glycerol backbone can be monitored.
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The aim of the present work was to evaluate the effect of sustained release of potassium chloride semi-solid matrices prepared with different kinds and added amounts of Gelucires by the in vitro dissolution test and in vivo oral absorption study, and compared with a commercial product (slow-K). The results indicating that the release rates of potassium from experimental formulations were dependent on the type of semi-solid matrices (Gelucires). The higher the melting point of the Gelucires was incorporated, the slower release rate of the active substance was observed. Moreover, the values of similarity factor of Formulae F05 and F09 versus the reference in three kinds of dissolution medium (f(2)) were higher than 50, indicating that these experimental formulations had similar sustained release effects to the reference (slow-K) in dissolution test. In vivo study, the cumulative amount (mEq) of potassium excreted curve and the excretion rate curve of F05 and F09 were found to be similar to that of slow-K, and there were no significant differences (P > 0.05) in the maximum excretion rate and the mean time to reach the maximum rate between formulations and slow-K, indicating that the potassium chloride sustained release dosage form could be prepared using the Gelucires as lipid excipients.
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Preferred conformations of the saccharide-ceramide linkage of glucosylceramides with different ceramide structures (normal and hydroxy fatty acids) were investigated by molecular mechanics (MM3) calculations and compared with conformational features obtained for glucosylglycerolipids (diacyl and dialkyl analogues). Relaxed energy map calculations with MM3 were performed for the three bonds (C1'-O1-C1-C2, torsion angles phi, psi, and theta 1) of the glucose-ceramide/diglyceride linkage at different values of the dielectric constant. For the phi torsion of the glycosidic C1'-O1 bond the calculations show a strict preference for the +sc range whereas the psi/theta 1 energy surface is dependent on the structure of the lipid moiety as well as on the dielectric constant (epsilon). Calculations performed on glucosylceramide with normal and hydroxy fatty acids at epsilon = 4 (bilayer subsurface conditions) show three dominating conformers (psi/theta 1 = ap/-sc, -sc/ap, and ap/ap). The ap/-sc conformer, which represents the global energy minimum, is stabilized by polar interactions involving the amide group. The +sc rotamer of theta 1 is unfavored in sphingolipids due to a Hassel-Ottar effect involving the sphingosine O3 and O1 oxygen atoms. Comparative calculations on glycosylglycerolipid analogues (ester and ether derivatives) show a distinct preference for the ap rotamer of theta 1. An evaluation of the steric hindrance imposed by the surrounding membrane surface shows that in a bilayer arrangement the range of possible conformations for the saccharide-lipid linkage is considerably reduced. The significance of preferred conformations of the saccharide-ceramide linkage for the presentation and recognition of the saccharide chains of glycosphingolipids at the membrane surface is discussed.
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The plasma-borne long-chain free fatty acids (FFA) enter skeletal muscle cells. Upon entering they are oxidized or esterified and a fraction remains free (non-esterified). The data on free fatty acids in skeletal muscles remain highly controversial. Furthermore, the composition of individual fatty acids in various lipid fractions including free fatty acids, monoglyceride and diglyceride in muscles has not been characterized. Also data on the composition of fatty acids esterified into muscle triglycerides and phospholipids are incomplete. The present study was undertaken to examine a composition of fatty acids in lipid fractions of different skeletal muscle types. For this purpose, samples of the rat soleus, red and white portions of gastrocnemius were excised, trimmed of visible fat and fascias and immediately frozen in liquid nitrogen. Samples were then pulverized and, lipids were extracted and fractionated by thin-layer chromatography. Individual long-chain fatty acids in different fractions were identified, characterized and quantitated by gas-liquid chromatography. FFA composition in the plasma was also determined. The total FFA content in the soleus, red and white gastrocnemius was 69.1 +/- 10.8, 49.0 +/- 13.6 and 22.7 +/- 8.6 nmol/g, respectively. Palmitic and oleic acids were the major fatty acids in the muscles FFA fraction. Monoglyceride fraction of each muscle contained palmitic, stearic and linoleic acid as the major fatty acids, Diglyceride fraction contained mostly palmitic and oleic acid whereas triglyceride fraction mostly palmitic and linoleic acid.. The fraction of phospholipids was composed mostly of palmitic and linoleic acid but contained also considerable percentage of archidonic acid. Total plasma FFA/muscle FFA ratio depended on a muscle type and was: 2.4 in the soleus, 3.5 in the red and 7.4 in the white gastrocnemius. This assured transport of FFA to the myocytes. However, there were great differences in the ratio between particular FFA within the same muscle as well between the muscles. It indicates that individual FFA are either selectively transported from the plasma to the muscles or selectively used within the myocytes or both.
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