Functional groups physiologic significance

Functional Groups That Are Weak Acids Have Great Physiologic Significance... 

Drug molecules frequently contain functional groups such as amines and carboxylic acids that are ionized under normal physiological conditions. Typically, these are registered in databases in their neutral forms that are perfectly reasonable when the main objective is efficient retrieval of structures. Representation of tautomers [6, 7], which differ only in bond type and hydrogen atom connectivity, raises similar issues while measurement of the relevant equilibrium constants is significantly more difficult. 

Optical isomerism occurs in molecules with an asymmetric carbon atom - that is one that is attached to four different atoms or functional groups. The two different optical isomers are called optical isomers or enantiomers and rotate polarized light in opposite directions. The cZ-isomer rotates it clockwise and is called dextrorotatory the Z-isomer rotates it anticlockwise and is called Zaevorotatory. Despite their structural similarity, optical isomers exhibit significantly different physiological properties. In the case of essential oils their smells can be very dissimilar. When a compound is made up of equal amounts of the d- and Z-isomers it will be optically inactive and is called a racemic mixture, or racemate. 

The characteristics of the water associated with the polar lipid bilayer surfaces are of particular interest because they become very important in processes of physiological significance such as membrane fusion, and they may play a role in the mechanisms of association of proteins and small molecules with lipid bilayers and biological membranes. A very small fraction of the lipid bilayer-associated water molecules are actually immobilized, and a larger fraction (about 30% of the total bilayer-associated water in multilamellar PC bilayers in the L phase) has a probability distribution function that is more or less coincident with the probability distribution function for the polar head group of the lipids. Nevertheless, the pressure, P, which must be exerted to remove the bilayer-associated water, is large and varies (from 0.5-500 N cm ) with the thickness of the inter-bilayer water space as ... 

It is obvious that many various products are generated under these conditions that have different interactions. For instance, ROS generated under these conditions react with functional groups of enzymes that may significantly influence their enzymatic activities. Clearly, as the majority of ROS is generated by the enzymes, this fact also influences the yield of ROS. Thus, evaluation of the detailed role of ROS under physiological conditions is assuredly a rather difficult task. 

Esters are among the most important of the carboxylic acid (and alcohol) derivatives. Substances possessing this functional group are widely distributed in nature in the form of waxes, essential oils, fatty acid esters, and aromas. The ester functionality plays a significant role in biochemistry, both in primary metabolism and in a variety of substances exhibiting remarkable physiological activity in humans (hormones and neurotransmitters). Esters find extensive use in commercial products from fingernail polish remover and artificial sweeteners, to polymeric fibers, plasticizers, and surfactants. 

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