Biological processes solubility parameters

However, there are also biological factors such as metabolism in, for example, liver or the gastrointestinal tissues as well as active molecule transporters like P-gP or MRP in, e.g., the gastrointestinal tract which influence the bioavailability and can mislead the prediction of the dose. The influence of such active transports is particularly noted if the main driving forces of the absorption process, physicochemical parameters like solubility, dissolution rate, and permeability are low. 

The presence of charge serves as structural motifs underpinning various functionalities. Firstly, it increases the solubility of the molecules in aqueous solution. Even though not much is known about the environment that molecules experience inside a cell, many biological processes are assumed to occur in aqueous environment as thus, the many components should be water soluble and interact in a controllable fashion. Polyelectrolyte complexes adopt structures with extent of order depending on the type of molecules involved and their molecular parameters. The structures of PEC have conceptually been described to span Irom the formation... 

Oral availability is a complex parameter that involves several chemical and physiological processes such as solubility, chemical stability, permeability and first-pass metabolism, to mention a few. All of these subprocesses depend on two different types of factor (i) interaction of the drug compound with certain macromolecules, such as the metabolism mediated by the cytochromes P450 family and (ii) interaction of the drug molecule with a certain chemical or biological environment, that will determine the solubility or the passive permeability. 

The physico-chemical properties may provide indications about the absorption of the substance for various routes of exposure and may therefore be of importance in the evaluation whether an appropriate administration route has been applied in the available experimental toxicity studies. In order for a substance to be absorbed, it must cross biological membranes. Most substances cross biological membranes by passive diffusion. This process requires a substance to be soluble both in lipid and water. The most useful parameters providing information on the potential for a substance to diffuse across biological membranes are the logPoctanoi/water and the water solubility. 

In order for a substance to be absorbed, it must cross biological membranes. Most substances cross by passive diffusion. This process requires a substance to be soluble both in lipid and water. The most useful parameters providing information on the potential for a substance to diffuse across biological membranes are the octanol/water partition coefficient (Log P) value and the water solubility. The Log value provides information on the relative solubility of the substance in water and the hydrophobic solvent octanol (used as a surrogate for lipid) and is a measure of lipophilicity. Log P values above zero indicate that the substance is more soluble in octanol than water, i.e., is lipophilic, and values below zero (negative values) indicate that the substance is more soluble in water than octanol, i.e., is hydrophilic. In general, moderate Log P values (between 0 and 4) are favorable for absorption. However, a substance with a Log P value around 0 and low water solubility (around 1 mg/1) will also be poorly soluble in lipids and hence not readily absorbed. It is therefore important to consider both the water solubility of a substance and its Log P value when assessing the potential of that substance to be absorbed. 

The work described in the foregoing sections is of a preliminary nature. Nevertheless, it offers hope that experimental scales of free hydrogen ion concentration (pcn or pmn) in seawater may be feasible. One need not know pmn or pan to derive meaningful equilibrium data, such as acid-base ratios and solubilities, provided that suitable apparent equilibrium constants are chosen (7). In these cases, the unit selected for the acidity scale disappears by cancellation. Nevertheless, the acidity of seawater is a parameter of broader impact. It plays a role, for example, in the kinetics of organic oxidation-reduction reactions and in a variety of quasi-equilibrium processes of a biological nature. The concentration of free hydrogen ions is clearly understood, and its role in these complex interactions is more clearly defined than that of a quantity whose unit purports to involve the concept of a single-ion activity. 

The soil pH considerably affects soil characteristics. It is important for many soil-forming processes and it also affects the biological activity of soil organisms. The soil pH directly affects particularly the solubility of many substances, ion adsorption and desorption, coagulation and peptization of colloids and chemical reactions. By its action on the soil structure it also affects most of the physical properties of the soil. Thus, the soil pH is an important parameter of the soil fertility. 

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