Published online by Cambridge University Press: 06 August 2010
Introduction
A requirement in measuring transport (e.g., transmembrane) or exchange (e.g., ligand binding) is to be able to identify a measurable NMR parameter that has a different value in each state. Modulation of this parameter by the transport or exchange process is examined to characterise the process. Traditionally, NMR chemical shifts or relaxation times have been used for this purpose. With the advent of PGSE methods, a difference in diffusion properties (i.e., a difference in diffusion coefficient between sites or a difference in motional restriction) becomes another measurable NMR parameter that can be used to probe transport or exchange.
In the simplest case the exchange will occur between two freely diffusing sites (e.g., a ligand binding to a macromolecule; Figure 4.1); however, in many real systems (e.g., a suspension of biological cells) one site, or both sites if at higher cellular volume fractions, may be restricted. In contrast to the previous chapter where only simple restricting systems with reflecting boundary conditions were considered and the diffusing species did not interact with other restricting geometries, in real systems (e.g., biological cells, porous systems) it may also be necessary to consider the effects of a combination of exchange, restriction, obstruction and polydispersity in addition to surface and bulk relaxation as well as different bulk diffusion coefficients in each medium (e.g., Figure 4.2). As a consequence, modelling such systems can be very complicated and various approximations are necessarily used.
To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.