Caco absorptive surface area

In addition, the results of absorption studies for a series of (i-adrenoceptor blockers in vitro using Caco-2 monolayers and rat intestinal segments have been used to test new descriptors [55]. For this purpose, the authors calculated dynamic molecular surface properties considering all low-energy conformations. Molecular mechanics were used to consider the flexibility of the molecules, and the van der Waals volume (vdW) and water-accessible surface areas were also calculated (Table 4.18 and 4.19). When the dynamic polar vdW surface areas were used in regression analysis to describe cell permeability data obtained in Caco-2 cells and in rat ileum, excellent correlations were obtained (r2 = 0.99 and 0.92 respectively). 

Several papers have also been published in which a correlation has been sought between permeation across Caco-2 cells and physicochemical properties of the compounds. The review article by Ekins et al. (2000) discusses several studies to predict Caco-2 cell permeation. Correlations have been found with polar surface area, hydrogen bond descriptors, VolSurf, and other parameters. Van de Waterbeemd et al. (2001a) also discuss models for predicting oral absorption of compounds, including the use of Caco-2 cell lines. This paper also provides much useful information on the optimization of pharmacokinetic parameters in drug development. 

Permeability-molecular surface area-in vitro-in silico model The permeability values obtained from the Caco-2 cell monolayers have been traditionally used to devise in silico models for the prediction of drug absorption. In this paper, the use of molecular surface areas as descriptors of permeability and solubility will be reviewed. Moreover, a virtual filter for the prediction of oral drug developability based on the successful combination of in vitro and in silico models of drug permeability and aqueous drug solubility will be discussed. 

Specific gravity (density) of calcium carbonate is typically 21-29 %/cva , Mohs hardness 3-4. The linear coefficient of thermal expansion of CaCOs is from 2 to 6 X 10 1/F, which is about 10-20 times lower than that of HOPE. Hence, HOPE filled with CaC03 typically has proportionately lower value of the coefficient of expansion. Particles of calcium carbonate have irregular shapes. Particle sizes of commercial CaC03 vary for different brands from 0.2 to 30 pm. Precipitated CaC03 can have smaller particles, such as down to 0.02 pm. Oil absorption is between 13 and 21 g/100 g. Specific surface area is between 5 and 24 mVg ([1], p.48). 

A serious limitation of the use of anodic inhibitors is that they must be used in sufficiently high concentration to eliminate all the anodic sites, otherwise the anodic area that remains will carry the whole corrosion current, which is usually cathodically controlled. Intense local corrosion may then result, possibly leading to failure of the specimen. Cathodic inhibitors, on the contrary, are helpful in any concentrations for example, the blanketing of only half the cathodic surface will still roughly halve the corrosion rate. The presence of temporary hardness or magnesium ions can help reduce corrosion through deposition of CaCOs or Mg(OH)2, specifically on the cathodic surfaces where OH is produced in the oxygen absorption reaction ... 

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