Principle of specific interaction

We require the actinty coefficient of AgCl present as a trace in an excess of KNO,. The value of this certainly lies between the values of /k,(3 and /Ag,no,- - According to the principle of specific interaction (BrOnsted, J. Amer. Chem. Soc. 1923, 45, 2902 Guggenheim, Phfl. Mag. 1935, 19, 588) it will be equal to their geometric mean. We accordingly estimate... 

Hence according to the principle of specific interaction the activity coefficient of AgCl present as a trace in excess of KNOj will be given by... 

The principle of specific chemical recognition is common to ligand—macromolecule interactions, but this alone does not suffice to define a receptor in the pharmacologic sense. Rather, it is the combination of chemical specificity or recognition and the capacity to initiate biological response or transduction that define the pharmacologic receptor (1,10,11). 

In principle, the interaction of small molecules within a swollen polymer is one of the easiest situation to be proven, due to the large difference in size of species involved. Changes in the small molecule diffusivity will occur as a result of specific interactions between the diffusant and the polymeric matrix. 

The principles of specific protein-DNA interactions were first discovered during the study of bacterial repressors. Many bacterial repressors are dimeric proteins in which an a helix from each monomer Inserts into a major groove in the DNA helix (Figure 11-20). This a helix is referred to as the recognition helix or sequence-reading helix because most of the amino acid side chains that contact DNA extend from this helix. The recognition helix that protrudes from the surface of bacterial repressors to enter the DNA major groove and make multiple, specific interactions with atoms in the DNA is usually supported in the protein structure in part by hydrophobic interactions with a second a helix just N-termlnal to it. This structural element, which is present in many bacterial repressors, is called a helix-turn-helix motif. 

In accordance with the Bronsted principle of specific ion interac-tions the parameter p refers to a specific interaction coefficient. 

It has long been known that water is a structured liquid, and that this structure is a result of the tendency of water molecules to form hydrogen bonds. What is less recognized is that the specific correlation between local density and binding energy is a more fundamental principle of the interaction between water molecules. This feature, when implemented in a model system in any dimension can produce most of the outstanding properties of aqueous systems. 

The idea that unsymmetrical molecules will orient at an interface is now so well accepted that it hardly needs to be argued, but it is of interest to outline some of the history of the concept. Hardy [74] and Harkins [75] devoted a good deal of attention to the idea of force fields around molecules, more or less intense depending on the polarity and specific details of the structure. Orientation was treated in terms of a principle of least abrupt change in force fields, that is, that molecules should be oriented at an interface so as to provide the most gradual transition from one phase to the other. If we read interaction energy instead of force field, the principle could be reworded on the very reasonable basis that molecules will be oriented so that their mutual interaction energy will be a maximum. 

Two basic principles govern the arrangement of protein subunits within the shells of spherical viruses. The first is specificity subunits must recognize each other with precision to form an exact interface of noncovalent interactions because virus particles assemble spontaneously from their individual components. The second principle is genetic economy the shell is built up from many copies of a few kinds of subunits. These principles together imply symmetry specific, repeated bonding patterns of identical building blocks lead to a symmetric final structure. 

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