Crystalline aggregate formation

The presence of hemoglohin-S (Hb-S) ia red blood cells leads to the formation of Hquid crystalline aggregates iaside the ceU under conditions of low oxygen tension (43,44). The morbid aggregates ultimately arrange themselves iato a gel-like material composed of long fibers that extend the entire length of the ceU and distort its usual shape. 

Polypropylene molecules repeatedly fold upon themselves to form lamellae, the sizes of which ate a function of the crystallisa tion conditions. Higher degrees of order are obtained upon formation of crystalline aggregates, or spheruHtes. The presence of a central crystallisation nucleus from which the lamellae radiate is clearly evident in these stmctures. Observations using cross-polarized light illustrates the characteristic Maltese cross model (Fig. 2b). The optical and mechanical properties ate a function of the size and number of spheruHtes and can be modified by nucleating agents. Crystallinity can also be inferred from thermal analysis (28) and density measurements (29). 

The appreciably lower micellar solubilities of oleic acid, oleyl alcohol, and propylene glycol monooleate are consistent with the view that the formation of a liquid crystalline aggregate—lamellar, cylindrical, or... 

The overall rate of crystallisation of a super-cooled liquid is determined by the two factors mentioned the rate of formation of nuclei (above the critical size) and the rate of growth of such nuclei to the final crystalline aggregates. 

The incorporation of plasticizer into the RIM elastomer A inhibited the formation of crystalline aggregates. The physical crosslink densities were significantly decreasing with the increasing amount of plasticizer (Figure 9). 

Small amounts of plasticizer included in RIM formulations inhibit the formation of crystalline aggregates and the development of physical crosslinks. 

Blood dyscrasias associated with sulfonamide use are not related to dose or blood concentration of the drug. The predominant toxicity associated with sulfonamide use is the formation and deposition of crystalline aggregates in the kidney, ureter, and bladder. The safe and effective peak concentration of these drugs in serum (75 to 125[tg/mL) is well separated from the serum concentration at which crystallization in the urinary tract occurs. Serum concentrations in excess of 300pg/mL maintained for prolonged periods of time have been associated with such crystal formation. The method of choice for quantification of sulfonamides is HPLC. ... 

The collision-coalescence mechanism of particle growth discussed in this chapter is thought to control primary particle size in Hame reactors. The emphasis is on the synthesis of transition metal oxide particles, which are important in the manufacture of pigments, addili ve.s, and ceramic powders. Also discussed are the factors that determine the formation of necks between particles and particle crystallinity. As demands on product quality become more stringent, more research will be needed on particle size, unifonnity. crystallinity, and aggregate formation. 

As discussed, the major determinant of the distribution coefficient between the aqueous phase and the oil phase of relatively nonpolar lipids such as cholesterol is the concentration of lipolytic products in the aqueous phase, since the paraffin chains of the lipolytic products, forming the lipid core of the micelle, are responsible for its solvent capacity (23,73). Micelle formation and the associated appearance of new solvent properties result from a cooperative effect of bile acids and lipolytic products (Fig. 16). Bile acids alone aggregate to form micelles, but these micelles have extremely poor solvent properties. Lipolytic products alone form very large liquid crystalline aggregates which probably have excellent solvent properties for lipids. When mixed, micelles of intermediate size are formed. The size is sufficiently small to permit rapid diffusion, and the lipolytic products in the center of the micelle provide a core of liquid hydrocarbon with useful solvent properties. 

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