Intermediate density composition

D. The lipoproteins include chylomicrons, HDLs, intermediate-density lipoproteins (IDLs), LDLs, and VLDLs, which differ by size, density, and composition of proteins and lipids. 

Partial summary of lipoprotein metabolism in humans. I to VII are sites of action of hypolipidemic drugs. I, stimulation of bile acid and/or cholesterol fecal excretion II, stimulation of lipoprotein lipase activity III, inhibition of VLDL production and secretion IV, inhibition of cholesterol biosynthesis V, stimulation of cholesterol secretion into bile fluid VI, stimulation of cholesterol conversion to bile acids VII, increased plasma clearance of LDL due either to increased LDL receptor activity or altered lipoprotein composition. CHOL, cholesterol IDL, intermediate-density lipoprotein. 

Between these two classes, in both size and composition, are the cholesteryl ester-rich low-density lipoproteins (LDLs), the intermediate-density lipoproteins (IDLs), and the triacylglycerol-rich very-low-density lipoproteins (VLDLs). 

Figure 26-19 Endogenous lipoprotein metabolism pathway. TG, Triglyceride CE, cholesterol ester FC, free cholesterol PL, phospholipids HDL, high-density lipoproteins LDL low-density lipoproteins IDL, intermediate-density lipoproteins VLDL very low-density lipoproteins FA, fatty acid LPL, lipoprotein lipase LCAL lecithin cholesterol acyltransferase B, apolipoproteln B-tOO A, apolipoprotein A-l C, apolipoprotein C-fl , apofipoprotein E. (From RIfai N. Lipoproteins and apolipoproteins Composition, metabolism, and association with coronary heart disease. Arch Pathol Lab Med 1986 110 694-701. Copyright 1986, American Medical Association.)...

Intermediate-density lipoproteins and LDLs are generated in the circulation by lipolysis of TGs within CM and VLDLs (Chapter 19). Apo B is an essential component of CM, VLDLs, and LDLs. Unlike the exchangeable plasma apolipoproteins (apo E, apo Al, apo A2, and apo C), apo B does not exchange among lipoproteins and is present in plasma only in association with lipid. In addition to apo B, VLDLs and CM contain apo E and apo C CM contain small amounts of apo Al and apo A2. In contrast, apo B is the only apolipoprotein of LDLs. HDLs are particles of diverse composition that are generated in the circulation by complex lipid transport processes (Chapter 19). 

Quantitative description of the induction period by a definite time interval, or induction time, ti, is aided by the precise time origin provided by a shock wave. The specification of the end of the induction period is conceptually more difficult, however, and no universally preferred criterion has been found. One approach, which is appealing when one wants to emphasize the induction time as a determinant of the time scale of the main reaction, is to reckon by the occurrence of an inflection or maximum in such quantities as the rate of exothermic expansion or in the formation of some product, byproduct (such as chemiluminescent photons), or intermediate. This approach suffers conceptually from the fact that such phenomena are generally not quite simultaneous with each other, even though the differences are minor in comparison with the major effects of varying gas density, composition and temperature. 

The polyphasic region contains a three-phase zone surrounded by three two-phases zones. Systems whose composition lies in the three-phase zone separate into an amphi-phUe-rich phase (m), which is in the middle of the diagram at the boundary of the single-phase region, and two excess phases, which are essentially pmre aqueous phase and pure oil. This amphiphile-rich phase, which is found to obey, in most cases, the definition proposed for a bicontinuous microemulsion or a liquid crystal, has been called a middle phase because its intermediate density makes it appear in between the oil and water phases in a test tube. Because the middle phase is at equilibrium with both excess phases, it cannot be diluted either by water or oil, and it is thus neither water nor oil-continuous. This is another hint of the bicontinuous nature of this phase, as conductivity and viscosity measurements and other experimental evidences have shown [20-22,37-40]. 

Figure 8.22 Contact response of glass drastically changed by changes in composition (a) low-density Si02 (b) large density (c, d) intermediate density. (Reprinted from Sehgal et al., 1995, with permission from Elsevier.)...

In Winsor s type 3 systems (r = 1), the surfactant s affinity for the oil and the water phases is balanced. The interface will be flat. A type 3 nSOW system can have one, two or three phases depending on its composition. In the multiphase region the system can be (a) two phase—a water phase and an oleic microemulsion (b) two phase—an oil phase and an aqueous microemulsion (c) three phase—a water phase containing surfactant monomers at CMC, an oil phase containing surfactant at CMC and a surfactant phase . The surfactant phase may have a bicontinuous structure, being composed of cosolubilised oil and water separated from each other by an interfacial layer of surfactant. The surfactant phase is sometimes called the middle phase because its intermediate density causes it to appear between the oil and the water phases in a phase-separated type 3 nSOW system. 

The type of catalyst influences the rate and reaction mechanism. Reactions catalyzed with both monovalent and divalent metal hydroxides, KOH, NaOH, LiOH and Ba(OH)2, Ca(OH)2, and Mg(OH)2, showed that both valence and ionic radius of hydrated cations affect the formation rate and final concentrations of various reaction intermediates and products.61 For the same valence, a linear relationship was observed between the formaldehyde disappearance rate and ionic radius of hydrated cations where larger cation radii gave rise to higher rate constants. In addition, irrespective of the ionic radii, divalent cations lead to faster formaldehyde disappearance rates titan monovalent cations. For the proposed mechanism where an intermediate chelate participates in the reaction (Fig. 7.30), an increase in positive charge density in smaller cations was suggested to improve the stability of the chelate complex and, therefore, decrease the rate of the reaction. The radii and valence also affect the formation and disappearance of various hydrox-ymethylated phenolic compounds which dictate the composition of final products. 

Electropolishing is performed in concentrated mixtures of acids (sulfuric, phosphoric, chromic, etc.). Often, organic acids and glycerol are added. It is somewhat inconvenient that almost all metals and alloys require their own solution composition. For electropolishing, intermediate and high current densities are used, between about 0.1 and 500 mA/cm. Depending on current density, the process requires between 30 s and 20 to 30 min. Usually, a metal layer 2 to 5 pm thick is removed under these conditions. 

The macrohomogeneous model was exploited in optimization studies of the catalyst layer composition. The theory of composifion-dependent performance reproduces experimental findings very well. - The value of the mass fraction of ionomer that gives the highest voltage efficiency for a CCL with uniform composition depends on the current density range. At intermediate current densities, 0.5 A cm < jo < 1.2 A cm , the best performance is obtained with 35 wt%. The effect of fhe Nation weight fraction on performance predicted by the model is consistent with the experimental trends observed by Passalacqua et al. ... 

On the alloy surface the reaction proceeded both via the anhydride and formate intermediates (117). As the copper concentration was increased, the formate species dominated the reaction, until at 63% copper the CO/COj ratio was less than 0.1. This change was due to the decrease in the amount of anhydride formed with increasing copper and the corresponding increase in formate. Since only the anhydride decomposition produced CO, the relative amount of anhydride formed could be determined as a function of surface composition. This relationship is shown in Fig. 21 the anhydride concentration fell as the fourth power of the nickel concentration, suggesting the requirement of four nickel atoms for its stabilization. This value agreed with the earlier determination for the saturation density of anhydride intermediates on Ni(llO) (99). 

Crade oil is a complex mixture that is between 50 and 95% hydrocarbon by weight. Table 1.5 shows the average elemental composition of crade oil. The oil industry classifies crade by its production location (e g., West Texas Intermediate, wn or Brent ), relative density (API gravity), viscosity ( light, intermediate, or heavy ), and sulfur content ( sweet for low sulfur, and soui for high sulfur). Additional classification is due to conventional and non-conventional oil as shown in Table 1.6. 

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