Isostere, defined

Table 4.3 Examples of isosteres. Each horizontal row represents a group of structures that are isosteric. Classical isosteres were originally defined by Erlenmeyer as atoms, ions and molecules with identical shells of electrons. Bioisosteres are groups with similar structures that usually exhibit similar biological activities...

High-throughput synthesis and combinatorial chemistry employing polymer supports, with computer-based rational design, are important tools for systematic optimization of the affinity, selectivity, and bio-availability of protease inhibitors. It is very likely that currently available isosteres will not suffice for addressing the natural selectivity of proteases. Thus, synthetic methodology must be devised not only to decorate a predefined isosteric core but to define novel active site binders. 

The maximum isosteric differential heat of adsorption interpolated from the heat-coverage plots. c The roughness factor is defined as the ratio of the experimental values of the weight of adsorbate required for monolayer coverage to that calculated for the same coverage of a geometrically planar surface. It can be interpreted as the ratio of the real area to the apparent area of the adsorbent. 

For the adsorbent used in these experiments, which is near-homotattic with a high value of y, the isosteric heats defined by Equations 28 and 30 should be the same. 

Similarly, we can derive the differential (or isosteric) enthalpy of adsorption (defined by Equation (2.51)) ... 

As a result of their systematic study of the adsorption of nitrogen and other gases on a number of different adsorbents, Emmett and Brunauer (1937) came to the conclusion that Point B marked the boundary between monolayer and multilayer adsorption. It will be recalled that Point B was defined as the beginning of the middle, nearly linear, region of an adsorption isotherm. On an empirical basis a number of other characteristic features (designated A, C, D, and E) were rejected in favour of Point B. The main reasons for the selection of Point B were (1) because it gave fairly consistent values of surface area, and (2) because at this point the isosteric heat of adsorption appeared to undergo an appreciable decrease. 

In connection with the temperature dependence of adsorption, an isosteric heat of adsorption can also be defined, for instance as... 

Just as with gas adsorption, an isosteric enthalpy of adsorption can also be defined for adsorption from solution. In sec. 2.3d we have refrained from deriving from isotherms, measured at different temperatures because a... 

Different types of heats of adsorption can be defined based on the variables which are kept constant during the experiment (F, F, p,/I, etc.). Here we shall discuss three such heats. The first heat is usually called the differential heat of adsorption although it is, in fact, defined as a change in internal energy the second is the isosteric enthalpy of adsorption formerly called isosteric heat of adsorption and the third is the isothermal heat of adsorption (ijth). We shall develop expressions that allow these heats to be determined from experimental calorimetric data and show how these quantities are interrelated. 

If the adsorption process is carried out instead at constant pressure p and temperature, for example, by having a frictionless piston in the calorimeter, the differential molar enthalpy of adsorption Aa/i or Agli , also called the isosteric enthalpy of adsorption, is defined as... 

Otlier heats of adsorption, defined differently, are also in use. However, tlie isosteric heat is the most common, and is tlie one needed for energy balances on adsorption columns. 

The differential and isosteric heats of adsorption are defined in terms of the integral heat as... 

---