Physical Properties of Steroids

With few exceptions, the steroids arc white crystalline. solids. They may be in the form of needles, leafleis, platelets, or amorphous particles, depending on the particular compound, the solvent used in crystallization, and the skill and luck of the chemist. As the steroids have 17 or more carbon atoms, it is not surprising that they lend lo be water in.soluble. Addition of hydroxyl or other polar groups (or decreasing carbons) increases water solubility slightly, as expected. Salts arc the most water soluble. Examples are shown in Table 23-1. 

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S. Bernstein, J. P. Dusza, and J. P. Joseph, Physical Properties of Steroid Conjugates, Springer Verlag, New York, 1968. 

Selected physical properties of different forms of steroid receptors... 

Concomitant formation of [2 +1] adducts and C-H insertion (or their further transformations) products was observed in the phase-transfer catalyzed reaction of dichlorocarbene with various steroids" and adamantane derivatives. Due to the similar physical properties of these products, their separation is troublesome. 

In earlier sections of this chapter we focused on the distribution and physical properties of CE and on several intra- and extracellular enzymes and proteins that mediate CE formation, hydrolysis, and transfer. We turn now to a discussion of the major pathways of CE metabolism in plasma, and in cells such as fibroblasts, steroid hormone-forming cells, macrophages, and hepatocytes. These pathways seem to be integrated in such a way as to effect not only the transport and storage of cholesterol, but possibly also the transport of essential fatty acids. It can be argued in addition that the pathways of CE metabolism in plasma and in tissues provide a critical mechanism for buffering the content of UC in cell membranes and maintaining cholesterol homeostasis in the body (see Chapter 2). 

There seem to be distinct differences in the physical properties of the specific species of cytochrome P-450 involved in 7a-hydroxylation of cholesterol and most other species of cytochrome P-450. 7a-Hydroxylation is more sensitive to increasing concentrations of phosphate buffer and potassium thiocyanate than any other hydroxylation studied [77]. The 7a-hydroxylation is more dependent on reduced sulphydryl groups than the other C27-steroid hydroxylations [89]. 

Since its discovery in 1912 by von l.aue. X-ray diffraction has provided a wealth of important information to science and industry. For example, much of what is known about the arrangement and the spacing of atoms in crystalline materials has been determined directly from diffritciion studies. In addition, such studies have led to a much clearer tinderstftnding of the physical properties of metals, polymeric materials, and other solids. X-ray diffraction is one of the ntost important methods for determining the structures of such complex natural products as steroids, vittimins, and an tibtoiics. The details of these applications are beyxmd the scope of this book. 

Lipids are naturally occurring organic molecules that have limited solubility in water and can be isolated from organisms by extraction with nonpolar organic solvents. Fats, oils, waxes, many vitamins and hormones, and most nonprotein cell-meznbrane components are examples. Note that this definition differs from the sort used for carbohydrates and proteins in that lipids are defined by a physical property (solubility) rather than by structure. Of the many kinds of lipids, we ll be concerned in this chapter only with a few triacvlglycerols, eicosanoids, terpenoids, and steroids. 

The physical and chemical properties of individual oils and fats are determined by the nature and proportions of fatty acids that enter into the triglycerides composition. Animal and dairy fat like plant oils are dominated by triacylglycerols, with steroids present as minor components, cholesterol and its esters being the most significant. The triacylglycerols of animal fats differ from plant oils since they contain more of the saturated fatty acids and consequently are solid at room temperature. 

GlycoUpids, Synthesis of Imaging Techniqnes Lipids Labeling Techniqnes Lipids Lipidomics Lipids, Semi-synthetic Steroid and Triterpene Biosynthesis PHYSICAL PROPERTIES PHASE BEHAVIOR AND PHASE TRANSITIONS... 

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