Isotropic surface area

The Isotropic Surface Area ISA) is the surface of the molecule accessible to nonspecific interactions with the solvent, that is, the surface of the molecule involved in specific hydrogenbonding with water is not considered [Gollantes and Dunn III, 1995 Koehler, Grigoras et al, 1988]. A hydration complex model needs to estimate the isotropic surface area. The Polar Surface Area (PSA) is defined as the part of the surface area of the molecule associated with... 

Amino acid descriptors can be z-scores, side-chain —> isotropic surface area (ISA), —> electronic charge index (ECI), and so on. 

ISA Isotropic Surface Area MDDM Main Distance-Dependent... 

Several hundreds of linear relationships between various kinds of (mostly nonspecific) biological data and n-octanol/water partition coefficients have been published e.g. [18, 182]). However, the choice of n-octanol/water as the standard system for drug partitioning must be reconsidered in the light of some recent results. Principal component analysis of partition coefficients from different solvent systems [188 —190] shows that lipophilicity depends on solute bulk, polar, and hydrogen-bonding effects [189] isotropic surface areas, i.e. areas where no water molecules bind and hydrated surface areas, were correlated with the first and the second principal components of such an analysis [190]. 

A careful analysis of molecular structures led Dunn et al. to associate the two principal components with the two molecular parameters described in Figure 7, namely, the isotropic surface area (ISA), related to the solute surface accessible to nonspecific solvent interactions, and the solvent-accessible, hydrated surface area (HSA) associated with hydration of polar functional groups. 

The geometry and structure of a bone consist of a mineralised tissue populated with cells. This bone tissue has two distinct structural forms dense cortical and lattice-like cancellous bone, see Figure 7.2(a). Cortical bone is a nearly transversely isotropic material, made up of osteons, longitudinal cylinders of bone centred around blood vessels. Cancellous bone is an orthotropic material, with a porous architecture formed by individual struts or trabeculae. This high surface area structure represents only 20 per cent of the skeletal mass but has 50 per cent of the metabolic activity. The density of cancellous bone varies significantly, and its mechanical behaviour is influenced by density and architecture. The elastic modulus and strength of both tissue structures are functions of the apparent density. 

The purpose of this chapter is to introduce the effect of surfaces and interfaces on the thermodynamics of materials. While interface is a general term used for solid-solid, solid-liquid, liquid-liquid, solid-gas and liquid-gas boundaries, surface is the term normally used for the two latter types of phase boundary. The thermodynamic theory of interfaces between isotropic phases were first formulated by Gibbs [1], The treatment of such systems is based on the definition of an isotropic surface tension, cr, which is an excess surface stress per unit surface area. The Gibbs surface model for fluid surfaces is presented in Section 6.1 along with the derivation of the equilibrium conditions for curved interfaces, the Laplace equation. 

If we apply another restriction, p=const., in addition to porosity, all other volume-related characteristics, such as (5, specific pore volume, Fpore, etc. become independent of scaling. Indeed, if the space is isotropic the unit volume is directly proportional to the unit mass. Scaling results in change of sizes and surface areas, but the volume related to the mass remains the same. 

The Nernst-Einstein relationship plotted in Fig. 36.1 motivated the development of DiagnoSwiss technology, namely reducing the analysis time and reaction volumes by replacing the commonly used microtitre plate wells with typical dimensions of 100 pL volume and 1 cm2 surface area by a microchannel with a volume of 60 nL and a surface area of 0.03 cm2. The microchannel is an isotropically etched microstructure (see Section 36.2) with a minimal cross-section dimension of 40 pm,... 

Microemulsions are defined as isotropic, transparent, and thermodynamically stable (in contrast to conventional emulsions) mixtures of a hydrophobic phase (lipid), a hydrophilic phase (often water), a surfactant, and in many cases a co-surfactant. From a lipid formulation perspective, microemulsions are generally regarded as the ultimate extension of the decreased particle size/increased surface area mantra, because emulsion particle sizes are usually less than 50 nm. Microemulsions also have additional pharmaceutical advantages in terms of their solubilizing capacity [54, 55], thermodynamic stability, and capacity for stable, infinite dilution. 

The measurement of the work needed to increase the surface area of a solid material (e.g., an electrode metal) is more difficult. The work required to form unit area of new surface by stretching under equilibrium conditions is the surface stress (g1 ) which is a tensor because it is generally anisotropic. For an isotropic solid the work, the generalized surface parameter , or specific surface energy (ys) is the sum of two contributions ... 

Because of the non-regularity of the polyhedral foam structure (lack of long-range order) the foam becomes macroscopically isotropic, the specific surface area (per unit volume) accepting the luminous flux, is uniformly distributed in direction normal to the films... 

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