Drugs adsorption behavior

The adsorption behavior of the psychotropic drug flunitrazepam (256) at the hanging mercury drop electrode was studied by staircase voltammetry and by adsorptive stripping differential pulse voltammetry. 256 can be determined down to nanomolar levels by using adsorptive preconcentration prior to the differential pulse voltammetry scan. The method was applied to determination of 256 in human urine530. 

In this study, the adsorption of polyelectrolytes, such as the class of PLL-g-PEG graft copolymers on metal oxide surfaces, was found to be consistent with the related observations from previous studies. In previous characterizations of the adsorption behavior of polyeleotrolytes on such metal oxide surfaces, polycations in particular, such as PLL, were found to form stable adsorbed layers on negatively charged oxides such as silicon dioxide and titanium dioxide. However, the class of PLL-g-PEG-based copolymers thus far had been evaluated only in the contexts of drug delivery and the reduction of cell adhesion without a thorough characterization of the related modified surfaces and their reduction of protein adsorption. 

As noted in Chapter 1, the most simple and theoretically sound model for drug-receptor interaction is the Langmuir adsorption isotherm. Other models, based on receptor behavior (see Chapter 3), are available. One feature of all of these models (with the exception of some instances of the... 

The choice of the ACE method most suited for a given drug-protein interaction will therefore depend on several factors. Among them are inherent properties of the complexation, such as the estimated dissociation constant, the on/off-rates or multiple binding sites, as well as properties related to the behavior under ACE conditions, such as solubility, detectability, adsorption to the inner capillary wall, and mobility of all species under investigation. 

It should be mentioned that certain anomalous behavior has sometimes been observed. For example, a lack, or even an inverse effect, of drug concentration on the iontophoretic flux [32,33,96] has been reported for the lipophilic, cationic drugs such as propranolol and quinine [32,33], and for peptides such as nafarelin, leuprolide, calcitonin, and octreotide [34,96,114]. This phenomenon has been associated with adsorption of the drug onto the skin and a progressive leads to a reversal of its permselective properties (see Figure 14.6) [32,33,96],... 

As noted in Chapter 1, the most simple and theoretically sound model for drug-receptor interaction is the Langmuir adsorption isotherm. Other models, based on receptor behavior (see Chapter 3), are available. One feature of all these models (with the exception of some instances of the operational model) is that they predict symmetrical curves. A symmetrical curve is one where the half-maximal abscis-sal point (EC50, concentration of x that yields 50% of the maximal value of y) and the inflection point of the curve (where the slope is zero) are the same see Figure 12.17A. However, many experimentally derived dose-response curves are not symmetrical because of biological factors in the system. Thus, there can be curves where the EC50 does... 

A new zeolite model, that features the a and c channels of clinoptilolite has been used to study the possible interactions of aspirin-water-zeolite, in order to know the behavior of the drug in a more complex system and the influence of water present in the zeolite channel. The calculations have been performed using the AMI semi-empirical method and acid and sodic clinoptilolite models. The results showed that the adsorption entalphy of aspirin in the acid structure is in the same order than that obtained for the sodic structure, although the nature of the interaction is different in each structure. The ester and aromatic groups were preferentially oriented to the model. In any case the chemical stability of aspirin is affected by the presence of water molecules in the system. 

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