Membrane transport systems, biomimetic

Figure 2. Biomimetic controlled membrane transport systems.

A CRO may also allow for the in-house introduction of specialized lipophilic scales by transferring routine measurements. While the octanol-water scale is widely applied, it may be advantageous to utilize alternative scales for specific QSAR models. Solvent systems such as alkane or chloroform and biomimetic stationary phases on HPLC columns have both been advocated. Seydel [65] recently reviewed the suitabihty of various systems to describe partitioning into membranes. Through several examples, he concludes that drug-membrane interaction as it relates to transport, distribution and efficacy cannot be well characterized by partition coefficients in bulk solvents alone, including octanol. However, octanol-water partition coefficients will persist in valuable databases and decades of QSAR studies. 

Beyond the complete assembly of biomimetic membranes, interfacial supramolec-ular assemblies which incorporate biocomponents represent an important approach to replicating the biological functions outside of living systems. For example, the ability to link or wire otherwise electro-inactive enzymes to electrodes so that they can efficiently transport electrons allows sensitive and selective sensors to be developed for important bioactive molecules, e.g. glucose, lactate, urea, etc. 

Biomimetic artificiai membranes-factors Effects of pH and co-solvents on the BAMPA were investigated to determine the optimal conditions for the prediction of oral absorption. The permeability (Pam) of 33 structurally diverse drugs to the PC/PE/ PS/PI/CHO/1,7-octadiene membrane system [bio-mimetic lipid (BML) membrane] was measured at pH 5.5,6.5, and 7.4. The pH dependence of Pam was in accordance with the pH partition theory. The better prediction of oral absorption (fraction of a dose absorbed) was shown under the pH 5.5 condition for determining the permeability of poorly soluble compounds were examined. Dimethysulfoxide (DMSO), ethanol (EtOH) and polyoxyethyleneglycol 400 (PEG 400) were added up to 30% to the transport medium as solubilizers. DMSO, EtOH and PEG 400 decreased Pam of hydrocortisone and propranolol. For example, DMSO (30%) decreased Pam of hydrocortisone and propanol by 60 and 70%2, respectively. DMSO and PEG 400 also decreased Pam of ketoprofen. In contrast, EtOH produced an opposite effect on permeability, that is, an increased Pam of ketoprofen. Therefore, the high concentration of these co-solvents could lead to the under- or overestimation of drug permeability. 

Fig. 2 A biomimetic system for solar-energy conversion. A molecular triad embedded in the bilayer membrane allows photoexcited electrons to be transported across the membrane to acceptor species in the interior. This charge transport is accompanied by the transmembrane flow of hydrogen ions, leading to a decrease in pH inside the compartment. This proton-motive force is then used to drive ATP synthesis by the membrane protein ATP synthase, as it is in photosynthesis.

Efficient transport of saccharide-related, water-soluble artificial drugs into individual cells via the cell membrane are critical to the future development of drug design and delivery. Many biomimetic systems, which are capable of transporting neutral molecular species, are known, although examples of systems that can transport such species actively are rare. ... 

For electrode (conductor/semiconductor) surfaces, mass transport can be controlled with a variety of experimental protocols and the interfacial flux is measured directly via the current response (measured as a function of potential, time, etc.) [1], This is not true of other interfaces, such as minerals and many biomimetic surfaces in contact with the solution. In these instances, fluxes have often been deduced in a convoluted time- and space-averaged manner by determining the accumulation/loss of material in a bulk phase as a function of time. This leads to a considerable loss of dynamic resolution. Furthermore, in some systems, mass transport between the bulk and the interface is difficult to estimate, leading to incorrect mechanistic interpretation, with major implications for practical applications, whether this concerns drug transport across cell membranes or the growth of crystals. 

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