Determination of the composition of mixed micelles of bile salts by kinetic dialysis

A kinetic dialysis method for determining the critical micelle concentration and the composition of mixed micelles has been adapted to study a binary system of bile acids. Using kinetic dialysis, the critical micelle concentrations of taurocholate, deoxycholate and taurodeoxycholate were determined. Monomer analysis was performed by colorimetric and radioactive tracer techniques on aliquots of the dialysates. Similarly, the composition of mixed micelles made from various molar fractions of deoxycholate and taurocholate containing tritium and¹⁴C tracers were determined by this method. The results suggest that, for these bile acids, mixed micelle composition is largely predicted by the molar composition of the binary system. Kinetic dialysis has proven to be a rapid procedure and to yield results that agree with critical micelle concentration values previously reported.     

Mixed micelles of cationic surfactants and bile acid salts in aqueous media

Critical micelle concentrations of cetyltrimethylammonium-p-toluene sulfonate (CTAT) and cetylpyridinium chloride (CPC) with sodium cholate (NaC) and sodium deoxycholate (NaDC) were determined in aqueous solutions by surface tension measurements. Interaction parameters and mole fraction of the components in mixed micelles were estimated using Rubingh's theory. Strong interaction was observed for each mixed system, a common feature shown by anionic-cationic mixtures. Dramatic effects on the viscosities of these cationic surfactant-bile salt mixtures were seen, and were markedly dependent upon the counterion of the cationic surfactant and the nature of bile salts. Micelles are small and spherical for cationic surfactants in the presence of NaC. Micelle growth was seen for CPC in the presence of NaDC by an increase in viscosity, but a CTAT solution showed an opposite effect on addition of NaDC. Conductance results supported this view. Different behavior of the two bile salts is explained on the basis of their orientation in cationic micelles.     

Dietary fat alters the distribution of cholesterol between vesicles and micelles in hamster bile

The type of dietary fat strongly affects the incidence of gallstones in the hamster model of cholesterol cholelithiasis. The present study was designed to determine whether dietary fats could affect gallstone formation by altering the microstructure (vesicular/micellar ratio) of cholesterol in bile. Golden Syrian hamsters from Sasco (Omaha, NE) or Charles River (Wilmington, MA) were fed nutritionally adequate semipurified diets to which were added: (i) 4.0% butterfat without added cholesterol; (ii) 1.2% palmitic acid plus 0.3% cholesterol; or (iii) 4.0% safflower oil plus 0.3% cholesterol. Gallstone incidence and the percentage of cholesterol in vesicles and micelles were determined after two- or six-week feeding periods. Three out of ten Sasco hamsters fed the 1.2% palmitic acid diet for two weeks had cholesterol stones, while none of the eight Charles River animals had stones. In the Sasco hamsters, a significant proportion of the biliary cholesterol was found in void volume vesicles (28.8%) and small vesicles (17.1%); Charles River hamsters had negligible proportions (1.1%) of cholesterol in void volume vesicles and 15.4% in small vesicles. Cholesterol gallstones were most abundant in Sasco hamsters fed 1.2% palmitic acid for six weeks (nine out of ten animals); the mean cholesterol saturation index of the bile was 1.27. A significant proportion of the biliary cholesterol was eluted in the void volume vesicles (21.4%) and in small vesicles (15.0%). Five of the eight identically treated Charles River hamsters had cholesterol stones; the cholesterol saturation index averaged 1.36, and the biliary cholesterol was present in void volume vesicles (31.3%) and small vesicles (14.3%). Vesicles were not detected in the bile of hamsters fed cholesterol-free diets, and none of these animals developed cholesterol gallstones. Safflower oil diets inhibited stone formation even though the cholesterol saturation index was above unity. After six weeks, biliary cholesterol transported in void volume vesicles was highest for Sasco hamsters (13.3%) as compared to Charles River animals (6.9%), but total cholesterol transported in void volume vesicles plus small vesicles was similar in both groups (33.5% vs. 26.2%), respectively. These results suggest that in both strains of hamsters dietary fat influences gallstone formation by modulating the vesicular/micellar distribution of biliary cholesterol. Apparently, the presence of cholesterol/phospholipid vesicles in bile is associated with cholesterol gallstone formation.     

Solubilization of cholesterol in two binary mixed micelles of bile salt and nonionic surfactant

The saturated amounts of solubilized cholesterol (C_ch) in mixed micelles of sodium cholate (NaC) and octaoxy-ethylene glycol monon-decyl ether (C₁₀E₈) and of sodium zyme assay at 25, 29, 33 and 37°C. The C_ch values in both systems increase with the total surfactant concentration. Because the mixed micelles for both systems tend to form C₁₀E₈-rich micelles near the critical micellar concentration (CMC) of the mixed system, the curves of cholesterol solubility approached the C_ch curve for C₁₀E₈ alone near the CMC. The tendency of C_ch to decrease in both systems with increasing mole fractions of bile salts resembled that of the mean aggregation number of micelles. Thermodynamic analyses of cholesterol solubilization showed that the free energy of solubilization, if considered as the transfer of cholesterol from solid state to micellar environment, increased with increasing mole fraction of bile salt. The enthalpy of cholesterol solubilization (ΔH_S→M) decreased with the mole fraction of bile salts and showed break points around the mole fraction of 0.75 for the NaC−C₁₀E₈ system and at 0.60 for the NaDC−C₁₀E₈ system, respectively. These phenomena resemble earlier hydrophobicity data for mixed micelles by fluorescence measurements. Furthermore, C_ch values for the NaDC−C₁₀E₈ system were larger than those for the NaC−C₁₀E₈ system because of the structural differences at the 7α hydroxyl group between NaC and NaDC. This fact was confirmed by thermodynamic calculations.     

Effects of sodium glycocholate and sodium taurocholate on the mixed micelles of bile salts and nonionic surfactant

Effects of sodium glycocholate (NaGC) and sodium taurocholate (NaTC) on the mixed micelles for two systems consisting of NaGC-octaoxyethylene glycol monon-decyl ether (C₁₀E₈) and NaTC-C₁₀E₈ have been studied as a function of the mixed micelles’ compositions, polarities of the micelles’ interior and mean aggregation numbers. The compositions of the mixed micelles are calculated from critical micelle concentration (CMC) data by using excess thermodynamic quantities. The polarities and mean aggregation numbers are determined from pyrene fluorescence in the mixed micelles. Both mixed systems were nonideal, and the mole fraction of NaGC or NaTC in a mixed micelle near the CMC was less than that in the aqueous mixed solution. However, the mixed micelle of the NaTC-C₁₀E₈ system contained more bile salt molecules than that of the NaGC-C₁₀E₈ system because of a good miscibility of NaTC and C₁₀E₈ molecules. The pyrene fluorescence results suggested that the mixed micelles changed from C₁₀E₈-rich micelles to NaGC- or NaTC-rich micelles, and mean aggregation numbers of the mixed micelles decreased abruptly with increasing mole fraction of bile salts. In the low mole fraction range of bile salts, however, both the polarities and the mean aggregation numbers for the NaTC-C₁₀E₈ system are lower than those for the NaGC-C₁₀E₈ system because of the high mole fraction of NaTC in a mixed micelle, and also because of the different effect of the conjugated group between NaTC and NaGC molecules in the mixed micelles.     

Polymeric micelles based on hyaluronic acid and phospholipids: Design,characterization, and cytotoxicity

Novel amphiphilic copolymers were synthesized and characterized by ¹H NMR using Hyaluronic acid (HA) as a hydrophilic part and phosphatidylethanolamine (PE) including 1,2‐dimiristoyl‐sn‐glycerol‐3‐phosphatidylethanolamine (DMPE) and 1,2‐distearoyl‐sn‐glycerol‐3‐phosphatidylethanolamine (DSPE) as a hydrophobic segment. The newly developed HA‐PE copolymers form a micelle in an aqueous media. The micellar properties, including critical micelle concentration (CMC) with pyrene as a fluorescence probe and micelle morphology, using transmission electron microscopy were assessed. It was found that the CMC values for HA‐DMPE and HA‐DSPE were 15.5 and 13.4 μg/mL, respectively. Also micelles were spherical in shape and within the size range of 162–214 nm. The solubility of cholesterol, a highly hydrophobic compound, was enhanced to 0.25 mg/mL which is much higher than it is in water (0.0001 mg/mL). In vitro cytotoxicity assay of HA‐PE copolymers showed no toxicity on human breast cancer cell line (MCF‐7). These results suggest that HA‐PE micelles could be considered as a promising carrier for delivery of hydrophobic compounds. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40944.     

Effect of dietary bile acids,cholesterol, and β-sitosterol upon formation of coprostanol and 7-dehydroxylation of bile acids by rat

During studies of sterol metabolism in the rat, the fecal neutral sterol fraction was analyzed by a combination of thin layer chromatography and gas liquid chromatography. On a stock diet of rat chow supplemented with 5% corn oil, the rats excreted 14.5 mg/day of total neutral sterols. Coprostanol comprised 35% (5 mg/day) of this fraction. When the diet was supplemented with 0.5% sodium taurochenodeoxycholate, the amount of coprostanol in the feces remained the same as in the controls (3.2 mg/day, 32%). The addition of 0.5% sodium taurocholate to the diet resulted in a fivefold reduction of coprostanol formation (0.6 mg/day, 8%). When 1.2% cholesterol was added to the stock diet, the amount of coprostanol present in the feces decreased to an average of 11% compared to controls, but the absolute amount formed was greater (35 mg/day). On a diet enriched with 0.8% β-sitosterol, the rats, on the average, converted 23% of the cholesterol to coprostanol. Feeding diets enriched with sodium taurochenodeoxycholate and sodium taurocholate reduced the 7-dehydroxylation of primary bile acids in the feces by 28% and 42%, respectively. The conversion of primary bile acids to secondary bile acids in the feces of control, cholesterol, and β-sitosterol fed rats was the same (64%).     

Effects of dietary cholesterol and triglycerides on lipid concentrations in liver, plasma, and bile

Dietary cholesterol (CHL) and triglycerides (TG) can influence plasma, hepatic, and biliary lipid composition, but effects on lipids in these three compartments during the early stages of CHL gallstone formation have not been studied in parallel. We fed prairie dogs diets containing one of four tes oils (safflower, coconut, olive, or menhaden) at either 5 or 40% of calories, in the presence of 0 or 0.34% CHL, for 3 wk. In the absence of dietary CHL, increases in dietary TG produced 50–200% increases in the concentrations of biliary CHL and hepatic cholesteryl ester (CE), while the concentrations of hepatic free CHL (FC) as well as plasma FC and CE remained relatively unchanged. Increasing dietary CHL to 0.34% resulted in increases in hepatic FC of approximately 50% for all four fats regardless of whether they were supplied at 5 or 40% of calories. CHL supplementation caused more pronounced increases in biliary CHL (200–400%), hepatic CE (50–200%), plasma FC (up to 100%), and plasma CE (up to 150%), and these increases were exacerbated by concurrent supplementation of dietary fat and CHL (biliary CHL: 300–700%; hepatic CE: 100–250%; plasma FC: up to 165%; plasma CE: 100–350%). These results indicate that enhanced secretion of biliary CHL and, to a lesser extent, increased synthesis of hepatic CE, may be primary mechanisms for maintaining the hepatic FC pool. Furthermore, dietary CHL and high levels of fat intake are independent risk factors for increasing biliary CHL concentrations, and adverse effects on lipid concentrations in plasma and bile tend to be exacerbated by ingestion of diets rich in both fat and CHL.     

Dietary oligofructose lowers triglycerides,phospholipids and cholesterol in serum and very low density lipoproteins of rats

The present study was aimed at answering the question why feeding rats an oligofructose (OFS) supplemented diet could cause a significant reduction in plasma lipid levels. Daily administration of a 10% (w/w) OFS-containing diet to normolipidemic male rats resulted in a decrease in plasma triglycerides, phospholipids and cholesterol. The triglyceride-lowering effect was observed after one week and lasted for at least 16 wk and was associated with a reduction in plasma very low density lipoproteins, indicating that the hypolipidemic effect of OFS may be due to changes in liver lipid metabolism. We therefore tested whether OFS feeding modified the capacity of the liver to synthesize triglycerides from free fatty acids. Hepatocytes isolated from livers of control and OFS-fed rats were incubated in the presence of [1-¹⁴C]palmitate, and both intracellular and extracellular [¹⁴C]triglyceride formation were quantified. We found that chronic feeding of an OFS-supplemented diet to rats significantly reduced the capacity of isolated hepatocytes to synthesize triglycerides from palmitate. The results suggest that, like other soluble dietary fibers, OFS significantly alters liver lipid metabolism, resulting over time in a significant reduction in plasma triglyceride, phospholipid and cholesterol levels.     

Contrasting effects of water-soluble and water-insoluble dietary fibers on bile acid conjugation and taurine metabolism in the rat

The effect of the type of dietary fiber on the bile acid and taurine metabolism was examined in rats. Diets containing 10% of various water-soluble fibers (citrus pectin, konjak mannan, guar gum) as compared to a fiber-free diet increased biliary excretion of total bile acids. In contrast, water-insoluble dietary fibers (cellulose, corn bran, chitin; 10% in the diets) as well as cholestyramine (5% in the diet) considerably, decreased bile acid excretion. Water-soluble dietary fibermediated increases in bile acid excretion were totally attributable to increases in glycine-conjugates. Thus, these fibers greatly increased by the bile acid glycine-to-taurine ratio (G/T). Excretio of glycine conjugates decreased more than that of taurine conjugates in rats fed various water-insoluble dietary fibers. As a results, G/T in rats fed water-insoluble fibers was significantly lowered as compared to G/T in animals fed a fiber-free diet. Cholestyramine did not affect the G/T ratio of bile acids. Fecal bile acid excretion and the activities of hepatic cholesterol 7α-hydroxylase (EC 1.14.13.17) in rats fed various water-soluble dietary fibers approximately doubled as compared to the respective values for rats fed a fiber-free diet. Whereas cholestyramine greatly increased these parameters, water-insoluble fibers did not significantly affect them. Various water-soluble fibers decreased hepatic concentration and urinary excretion of taurine as well as the activity of hepatic cysteine dioxygenase (EC 1.13.11.20). In contrast, water-insoluble fibers considerably increased hepatic taurine concentrations and enzyme activities. The parameters for taurine metabolism were unaffected by cholestyramine. It was suggested that the types of dietary fiber affected hepatic taurine synthesis and thus modified bile acid glycine/taurine ratios.     

Dietary lipid,fatty acid oxidation and incorporation of carbon into cholesterol

Female rats (200 g) were fed a nutritionally adequate diet containing 1% by weight of corn oil (low-fat, LF), 21% of corn oil (CO) or 20% of beef tallow plus 1% of corn oil (BT) for two weeks. Food was removed for 8–12 hr, then each rat was refed for 1 hr. Each rat was injected ip with Na-³H-acetate and U-¹⁴C-Na-palmitate, (P),-oleate (O) or-linoleate (L). Expired CO₂ was collected for 2 hr. Liver, heart and serum were obtained for analysis of total lipid¹⁴C and³H and cholesterol¹⁴C and³H. Oxidation of L was twice as great as O or P when the LF diet was fed. CO and BT diets doubled oxidation of O to equal L, and increased oxidation of P, 50%. In liver and serum P was retained to a greater extent than O or L on BT and CO diets. Incorporation of acetate into total lipid was highest on LF diet and reduced by feeding either CO or BT. Incorporation of acetate into cholesterol was greater when BT or CO was fed than for LF.¹⁴C was incorporated into cholesterol in such small amounts that it was barely detectable and could not be counted accurately. Conclusions are that (a) dietary fat affects rate of oxidation of uniformly labeled palmitate and oleate, but not linoleate, (b) acetate is a more ready precursor to cholesterol than is fatty acid carbon, and (c) the acetate incorporated into cholesterol when polyunsaturated fat is fed is not derived directly from fatty acid carbon. The failure of incorporation of fatty acid carbon into cholesterol within 2 hr of administration opens the question of compartmentation of acetate as to its metabolic source. Colorado Agricultural Experiment Station Scientific Series Paper No. 1510.     

Octadecylsulfuric acid. Properties of the acid,amine salts,and salts of amino acids

Summary Octadecanol, hexadecanol, tetradecanol, and dodecanol were sulfated with chlorosulfonic acid, and the corresponding alkylsulfuric acids were isolated in a pure state as white crystalline solids with definite melting points. Octadecylsulfuric acid resembles sodium octadecyl sulfate in detergent and surface-active properties and in stability to hydrolysis at equal concentrations of hydrogen ion. It is more soluble in water than sodium octadecyl sulfate and readily soluble in organic solvents. The critical micelle concentration (0.0387 millimoles/I.) is only about one-third that of the sodium salt. Isolation of octadecylsulfuric acid as a useful chemical intermediate made possible the preparation of a number of salts with amines and amino acids and their rapid screening for useful properties. Presented at the spring meeting, American Oil Chemists' Society, New Orleans, La., April 20–22, 1959. Eastern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture.     

Oxidation of cod phospholipids in liposomes: Effects of salts,pH and zeta potential

This work examines how different salts and pH influence both the zeta potential and the lipid oxidation rate of liposomes made from cod phospholipids. The rate of Fe²⁺‐induced lipid oxidation was measured by consumption of dissolved oxygen by liposomes in a closed vessel. Cations (Na⁺, K⁺, Ca⁺, Mg⁺) did not influence the rate of oxidation in the tested range [ionic strength (I) 0–0.14 M). Among the tested anions, sulphates and nitrates did not significantly change the oxygen uptake rate, but chlorides (KCl, NaCl, CaCl₂) reduced the oxidation rate down to approximately 45%, and dihydrogen phosphate down to 14%, when I = 0.14 M. The effect of Cl^? and H₂PO4₄^? was additive. Addition of salts increased the zeta potential of the liposomes, divalent cation salts even resulted in a positive zeta potential. When the liposomes contained different concentrations of chlorides, a linear relationship between oxygen uptake rate and zeta potential was observed. When phosphate was added, the oxygen uptake rate was not related to the changes in zeta potential. The decrease in pH was followed by an increase in zeta potential. The oxygen uptake rate did not change significantly at different positive zeta potentials (pH <3). When the zeta potential was negative, the oxygen uptake rate was influenced by the zeta potential and may also be influenced by iron solubility. Absolute values of the zeta potential alone cannot be used to predict oxidation rates.     

Cholesterol metabolism in the liver and intestine of the chick: Effect of dietary cholesterol,taurocholic acid and cholestyramine

The effect of feeding cholesterol, taurocholic acid, or cholestyramine to chicks on cholesterolgenesis from [1-¹⁴C] acetate in liver and intestine was determined in vitro using tissue slices, and in vivo by i.v. injection of [¹⁴C] acetate. The conversion of cholesterol to bile acids in liver in vivo was measured in the same treatments after i.v. injection of [³H] cholesterol. Hepatic cholesterogenesis in vitro and in vivo was depressed by dietary cholesterol and taurocholate and enhanced by cholestyramine. Intestinal cholesterogenesis in vivo was depressed only by taurocholate whereas ileal cholesterogenesis in vitro was reduced by dietary cholesterol. Conversion of cholesterol to bile acids was enhanced by dietary cholesterol and cholestyramine and depressed by taurocholate. Hepatic cholesterol metabolism in the chick appears to be regulated by mechanisms similar to those reported for other species.     

Ionic graft copolymerization. V. Graft copolymerization of β-propiolactone onto the trunk polymers containing carboxylic acid,sulfonic acid,and other salts

β-Propiolactone (βPL) was graft-copolymerized onto styrene–divinylbenzene copolymers containing various carboxylates or sulfonates, composed of anions and cations having different electronegativities. In parallel, the mechanism of polymerizations of βPL by relatively neutral catalysts was studied in comparison with the behaviors of graft copolymerizations. In the graft copolymerization onto the trunk polymer containing various carboxylates, a lower electronegativity of countercation favors a higher anionic polymerization activity and the order of rate of polymerization coincides with that of anionic activities of catalysts. On the other hand, in the case of trunk polymer containing sulfonates, a higher electronegativity of countercation favors a cationic polymerization activity, and the order of rate of polymerization coincides with that of cationic activity of catalyst. The order of grafting efficiency at fixed total conversion coincides almost with that of anionic activity. The comparatively higher grafting efficiency in the grafting onto trunk polymer containing carboxylic acid might support an anionic graft copolymerization mechanism by carboxyl anion. The two following mechanisms were proposed for the initiation of the polymerization by the trunk polymer containing sodium sulfonate, in which acrylic acid is transformed from βPL.     

Increased biliary calcium in cholesterol and pigment gallstone disease: The role of altered bile acid composition

The present study was undertaken to define the relationship between calcium metabolism and bile acid composition in animal models of diet induced cholesterol and pigment gallstones. Groups of prairie dogs were fed either a control non-lithogenic chow (N=12), a 1.2% cholesterol enriched chow (N=6, XOL) for two weeks, or a high carbohydrate diet deficient in iron (N=6, CHO-FeD), or a high carbohydrate diet with normal iron levels (N=6, CHO) for eight weeks. Hepatic (HB) and gallbladder (GB) bile samples were analyzed for total calcium, cholesterol, phospholipids, total bile acids (TBA), and individual bile acid composition. In each of the four groups, TBA concentrations were essentially similar and taurine conjugates accounted for approximately 90% of TBA in HB bile and about 98% in GB bile. In the control group, cholic acid (CA) was the predominant bile acid and comprised 76% of TBA and chenodeoxycholic (CDCA) accounted for about 13% of the total. Feeding a diet rich in cholesterol caused a significant change in the relative concentrations of individual bile acids of hepatic bile—such that CA decreased significantly (p<0.001) while CDCA increased by 300% (p<0.001). The changes in secondary bile acids were insignificant. An identical shift in individual bile acid composition was noted in animals maintained on high carbohydrate diet, irrespective of iron content. Similar changes were observed in the GB in the experimental groups. Calcium concentrations of GB bile with or without gallstone formation showed a positive linear relationship with TBA (y=4.35+0.14X, p<0.001) and taurochenodoxycholic acid (TCDCA) (y=15.04+0.46X, p<0.001), but an inverse relationship with taurocholic acid (TCA) (Y=55.16−0.41X, p<0.008). However, such relationships were absent in hepatic bile. These data indicate that diet-induced alterations in bile acid composition may modify calcium solubility or GB function, thereby contributing to the increased GB calcium observed during cholesterol and pigment gallstone formation.     

Fatty acid composition of milk phospholipids. III. Camel,ass, and pig milks

Phospholipids were isolated from camel, ass, and pig milks, and their fatty acid compositions were determined by gasliquid chromatography. The specific distributions of fatty acids in phosphatidyl choline (PC) and phosphatidyl ethanolamine (PE) were determined. The results are compared with previous results for bovine, sheep, Indian buffalo, and human milks. The milk phospholipids which were studied can be grouped, on the basis of their fatty acid compositions, into those from ruminant herbivores, nonruminant herbivores, and nonherbivores. The phospholipids of camel milk however have features typical of all groups as well as 15% plasmalogen in the PE fraction. For Parts I and II, see References 1 and 2.     

Effects of perturbations in hepatic free and esterified cholesterol pools on bile acid synthesis,cholesterol 7α-hydroxylase,HMG-CoA reductase,acyl-CoA:Cholesterol acyltransferase and cytosolic cholesteryl ester hydrolase

Effects of expansion of the hepatic free cholesterol pool on bile acid and cholesterol metabolism and homeostasis were examined in rats fed cholesterol in high-fat diets or treated with oleyl-p-(n-decyl)-benzenesulfonate (ODS) or progesterone. Cholesterol feeding for 10–16 days, which increased free (33%) and esterified (6-fold) cholesterol, had no effect on cholate synthesis, total bile acid synthesis, or cholate turnover, whereas these activities were increased 60–80% by ODS and progesterone, which produced only small increases (19%) in free cholesterol. Cholesterol feeding reduced β-hydroxy-β-methylglutaryl (HMG)-CoA reductase (72%) and cholesteryl ester hydrolase (48%) and increased acyl-CoA:cholesterol acyltransferase (184%), whereas ODS and progesterone reversed these compensatory responses in cholesterol-fed rats. Cholesterol 7α-hydroxylase was changed no more than 22% by any treatment. A bolus of ODS elevated biliary cholesterol output 41% and shifted biliary bile acid synthesis and composition toward 12-deoxy bile acids. These effects were not seen in ODS-fed or progesterone-treated rats, in which cholesteryl ester stores were depleted. It is concluded that effects of free cholesterol on bile acid synthesis and biliary cholesterol are probably mediated by specific precursor or regulatory pools which can be independently regulated and which represent a relatively small fraction of hepatic free cholesterol.     

杂多酸及其盐催化D-果糖选择性合成5-羟甲基糠醛

考察了杂多酸及其盐对果糖脱水制备HMF的催化性能。研究表明,磷钨酸铯盐催化效果较好,高温反应对5-羟甲基糠醛(HMF)生成有利,添加助剂聚乙烯吡咯烷酮(PVP)可提高产率。通过对反应温度、催化剂、加料方式的考察,得出优化的反应条件为:将果糖溶于DMSO中,添加质量分数20%的PVP,升温至155℃加入占果糖摩尔分数1%的CsH2PW12O40,反应5 min,产率77.9%。     

Measurement of bile acid synthesis in man by release of14CO2 from [26-14C]cholesterol: Comparison to isotope dilution and assessment of optimum reference cholesterol specific activity

Bile acid synthesis can be measured as release of¹⁴CO₂ from [26-¹⁴C]cholesterol divided by cholesterol specific activity, but this method has not been validated in human subjects. We made twelve comparisons of this CO₂ method to standard isotope dilution in six normal subjects and found a mean discrepancy of 6%. Linear regression analysis of one value with respect to the other revealed a correlation coefficient of 0.83 (P<0.001), a Y-intercept close to zero (−4.98) and a slope close to 1 (1.06), suggesting good correspondence between the two methods. To assess the potential for error arising from use of serum cholesterol to estimate specific activity of cholesterol used for bile acid synthesis, we compared synthesis measured using serum free cholesterol specific activity to that measured using bile cholesterol specific activity, which is known to be near isotopic equilibrium with the precursor pool used for bile acid synthesis. Synthesis calculated in these two ways differed by less than 10%. The data indicate that the CO₂ method using either serum or bile cholesterol specific activity provides a valid estimate of bile acid synthesis in man.