Self-associative lateral interactions

From the asymmetrical concentration profile with front tailing (see Figure 2.4b), it can correctly be deduced that (1) the adsorbent layer is already overloaded by the analyte (i.e., the analysis is being run in the nonlinear range of the adsorption isotherm) and (2) the lateral interactions (i.e., those of the self-associative type) among the analyte molecules take place. The easiest way to approximate this type of concentration profile is by using the anti-Langmuir isotherm (which has no physicochemical explanation yet models the cases with lateral interactions in a fairly accurate manner). 

Analytes from class N neither self-associate nor participate in the mixed hydrogen bonds. Consequently, they cannot participate in lateral interactions of any kind, either. 

Analytes from classes A and B cannot self-associate through the hydrogen bonds and because of this, they cannot participate in the self-associative lateral interactions. However, they can participate in the mixed hydrogen bonds and take part in the mixed lateral interactions. For example, analyte A can laterally interact either with analyte B or analyte AB. In a similar way, analyte B can either interact with analyte A or analyte AB. 

Self-associative lateral interactions can only occur with the AB-type analytes, chromatographed in sufficiently mild chromatographic conditions. In planar chromatography, this type of lateral interaction was first demonstrated on monocarboxylic fatty acids and a,co-dicarboxylic acids, chromatographed on microcrystalhne cellulose with aid of decalin and 1,4-dioxane as monocomponent eluents, respectively [8,20,23]. 

Mixed lateral interactions can occur in the case of the following pairs of molecules A. .. B, AB. .. A, AB. .. B, and ABj. .. ABj. Their appearance is even more importunate than that of the self-associative lateral interactions. With the self-asso-ciative lateral interactions alone, tailing of chromatographic bands lowers separative performance of a given chromatographic system, whereas with the mixed lateral... 

In the case of the analytes able to participate in the self-associative lateral interactions (i.e., containing at least one AB functionality in their molecular structure), the negative impact of the interactions exerted on the separation performance depends on the number of the associated monomers per one H-bonded -meric unit, and the higher the number (n) of the self-associated analyte monomers in a given aggregate, the more crippled is the separation process. 

When collagen IV prepared from the EHS tumor is incubated at 37°C, it self-assembles, forming aggregates containing polygonal structures. These lateral associations are stabilized by the interaction between the domain NCI and sites that occur along the triple helix and are separated from one another by about 100 nm (Tsilibary and Charonis, 1986). The additional possibility of lateral aggregation of the molecules would lead to a much more complex three-dimensional structure. 

These complementarity rules owe their discovery to the chemical analysis of DNA by Chargaff and associates (3). The DNA from many different organisms shows the same patterns of base composition, namely A and T are always present in equal quantities, as are G and C. The immediate corollary of this observation, that a purine base (R) exists for every pyrimidine base (Y) and vice versa, led Watson and Crick to propose that two helical strands in DNA are held together by specific, intermolecular purine-pyrimidine (R Y) interactions (4). In turn, this unique chemical complementarity of the double-helical structure, proved to be a major breakthrough to understand the self-recognition and self-reproduction of DNA and forms the cornerstone of structmal biology as we know it today, more than half a century later. 

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