Polymerization process, receptor binding

Recently, Takeuchi and coworkers [37] reported the use of molecular imprinting for constructing a highly specific porphyrin-based receptor site. 9-Ethyladenine [37] was chosen as the imprint molecule. Two different functional monomers were utilized to bind 58 during the polymerization process, methacrylic acid (MAA) and a polymerizable zinc-porphorin derivative, 59 (P-53), as shown in Fig. 20. Reference polymers imprinted with 56 were fabricated using either 59 or MAA (P-54 and P-55, respectively) and corresponding nonimprinted, blank polymers were prepared using MAA and 59, MAA, or 57 as functional monomers to form polymers P-56, P-57, and P-58, respectively (Fig. 21). 

Specific receptors are located on the cell membrane and binding of an extracellular messenger, e.g., a hormone, to these receptors activates the formation of an intraceUular messenger, a process that eventually results in the observed bioeffect. There is considerable evidence that adenosine is one of the extracellular messengers of neurosystems . In the central nervous system, for example, this compound inhibits activity and behaviorally has depressant effects The adenosine receptor seems to have a very specific steric requirement and, up to now, no polymeric purine derivative has been found effective in experiments in vivo however, the possibility of such applications has been demonstrated using isolated heart systems ... 

Selective binding between polymeric substrates and monolayered receptors has been accomplished more frequently. One of the most important recognition processes in nature is the pairing of nucleic acid bases, which can be mimicked with Langmuir films. Lipid monolayers with adenine head groups expand upon... 

Anticancer taxanes initially were isolated from the bark of the Pacific yew Taxus brevifolia) but are now produced semisynthetically from an inactive natural precursor found in the leaves of the European yew (Taxus baccata) a renewable resource. Taxanes bind to polymerized (elongated) (3-tubulin at a specific receptor site located within the tubular lumen. At standard therapeutic doses (which should lead to intracellular concentrations of 1-20 pM), taxane-tubulin binding renders the microtubules resistant to depolymerization and prone to polymerization (69). This promotes the elongation phase of microtubule dynamic instability at the expense of the shortening phase, and it inhibits the disassembly of the tubule into the mitotic spindle. In turn, this interrupts the normal process of cell division. At these concentrations, extensive polymerization causes the formation of large and ... 

The Noncooperative Model, (a = 7 = 1, c= 0). This model applies to assembhes that involve only intemiolecular interactions without any allosteric effect. The occupation of the various binding sites of the receptor is dictated only by statistics. This model is the reference for spotting the presence of allosteric effects in real systems. It also applies to the formation of a given ohgomer in isodesmic polymerizations. This process is exemplified by a monomer A—B that undergoes a reversible polymerization in which all of the stepwise association constants are identical and equal to K. The formation constant of each oligomer (A—B), is given by Eq. [51] in which a = y = 1, c = 0, = 1 and f) = 1 -... 

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