Permanent charge, drugs with

Evidence for a direct correlation between the turnover number for vinblastine-stimulated ATP hydrolysis and vinblastine transport rate was provided by Ambudkar and Stein [43]. Since compounds that interact with P-gp often exhibit a high lipid-water partition coefficient and can cross the lipid bilayer by passive diffusion, the stoichiometry between ATP hydrolysis and drug transport is difficult to assess. Using a permanently charged spin-labeled analogue of verapamil that cannot cross the membrane by passive diffusion [44], a direct correlation between ATP hydrolysis and drug transport was demonstrated [45]. 

Capillary zone electrophoresis, CZE, is the simplest CE mode in which the separation is based on differences in the charge-to-mass ratio of the analytes. This approach can be effective in a number of applications in particular, quaternary alkaloids owing to the permanent charge are ideal solutes in CZE, regardless of the pH of the running buffer. Below, the most important parameters affecting the CZE separation will be considered with emphasis on the relevant aspects involved in analysis of alkaloids in herbal drugs and medicinal plants. 

Dipoles and Polarization Phenomena. Many molecules do not carry formal electrical charges, so that their mutual interactions do not involve the direct coulombic interactions discussed above. However, if one examines the structures of many useful chemical species, including polymers, proteins, and drugs, it is apparent that they often include bonds that can impart an overall polar nature to the molecule as permanent dipoles, or they can be polarized by the effect of neighboring electric fields producing induced dipoles. The presence of permanent or induced dipoles means that the molecules can become involved in specific interactions with charged species, other dipoles, or nonpolar molecules, and those interactions can significantly affect the physical characteristics of the system. 

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