Modes of association

The conclusion of all these thermodynamic studies is the existence of thiazole-solvent and thiazole-thiazole associations. The most probable mode of association is of the n-rr type from the lone pair of the nitrogen of one molecule to the various other atoms of the other. These associations are confirmed by the results of viscosimetnc studies on thiazole and binary mixtures of thiazole and CCU or QHij. In the case of CCU, there is association of two thiazole molecules with one solvent molecule, whereas cyclohexane seems to destroy some thiazole self-associations (aggregates) existing in the pure liquid (312-314). The same conclusions are drawn from the study of the self-diffusion of thiazole (labeled with C) in thiazole-cyclohexane solutions (114). 

Examples of crystalline associates where dimethyl sulfoxide is involved as one of the heteromolecular constituents are known in an appreciable number1. Certainly the associate between dimethyl sulfoxide and trimesic acid 84 (cf. Chapter 5 in Vol. 140 of this series) is one of the important individual cases. Characteristic modes of association between the carboxylic hosts discussed here and dimethyl sulfoxide are illustrated in Fig. 24. Pertinent geometry data are listed in Tables 17 and 18. One may realize from Fig. 24 that the fundamental mode of association of the host acids 20, 26, 37, and 41 is the formation of discrete H-bonded islands of host and (usually) one guest molecule. 

By correlating the observed spectral changes with the concentrations of added cycloamylose, dissociation constants of the cycloamylose-substrate adducts may be calculated (Rossotti and Rossotti, 1961). Values of the dissociation constants determined in this manner for a variety of complexes are presented in Table II. In most cases, stoichiometries of the complexes have been shown to be 1 1 from the presence of distinct isosbestic points in the spectrophotometric titrations. In a few cases, additional spectral perturbations are observed as the cycloamylose concentration is increased, indicating more complex modes of association. Methyl orange, for example,... 

The solid-state structures of many of these radicals comprise n -n bonded diamagnetic dimers indicative of the fact that AE > PE. The symmetry of the SOMO often permits a number of symmetry-allowed n -n dimerisation processes. Among these five-membered heterocyclic radicals, the 1,2,3,5-di-thiadiazolyl radicals 2 are perhaps the most extensively studied and four different modes of association have been reported (Figure 3). 

Figure 3 Four modes of association of 1,2,3,5-dithiadiazolyl radicals (2)...

Figure 6.4 Graphical representation of mode of association of helicene 33 into helical columns. (Katz, T. J. Angew. Chem. Int. Ed. Engl. 2000, 39, 1921-1923, reproduced by permission of John Wiley Sons, Inc.)...

Suggested Modes of Association Between GPCR Monomers... 

There have been two basic approaches. First one involves isolation of the chromatin and nucleosome from the healthy and diseased cell line. The second approach is the reconstitution of the model target such as nucleosome followed by the association with the drug(s). The second approach has been extensively employed to identify the binding site in the protein-nucleic acid complex. A pre-knowledge about the components and their arrangements in the reconstituted system sometime makes it the preferred approach. Different biophysical, biochemical and genetic techniques have been employed to understand the mode of association and the effect of the drugs upon chromatin/nucleosome structure and function. 

The mode of association of peptides to liposome carriers might also be critical to induce a preferential immune response either humoral or cell mediated. For example, using a human mucin MUCl 20-mer peptide, it was found that only the physical association of the peptide to liposomes (either encapsulated or surface exposed after anchoring) was necessary to observe a cell-mediated response (34). In line with this observation, it was recently shown that a soluble peptide, representing a Melan-A/MART-1 tumor-associated antigen, when encapsulated into sterically stabilized liposomes, was able to stimulate a CTL response and this construct represented a suitable formulation for a specific tumor immunotherapy (69). In contrast, and in agreement with other studies (16), only the liposome surface exposed... 

Modes of Association Between Kraft Lignin Components... 

In concentrated solution 7-methylisatin-4-carboxvlic acid exhibits normal carboxylic acid dimerization, but in the solid state the lactol form 58 is present.228 Infrared studies indicate that hydrogen bonding as shown in 59 best represents the structure and mode of association of... 

Crystal properties of si, sll, and sH are given in Table 2.2a. Table 2.2b lists the atomic coordinates for these structures, which will enable the advanced reader to generate computer models of the hydrate crystals. The contrast of si and sll structures is obtained by linking the basic 512 cavity in two different ways to achieve fourfold hydrogen bonds. All modes of associating pentagonal... 

The crystals of radical 29, which are diamagnetic by electron spin resonance (ESR), consist of cofacial dimers with four dimers per unit cell linked by two long, albeit unequal (3.053 and 3.309 A), interannular S-S bond <2005IC1837>. This mode of association has not hitherto been observed for 1,2,3-dithiazolyls. Dimers of radical 29 do not form 7i-stacked arrays instead, they adopt the closed packed herringbone arrangement which allows for a clustering of the radical heads so as to maximize S- -S and S- -N contacts. 

In addition, clay particles can exhibit widely contrasting particle dimensions their ratio of particle diameter to thickness can range from 10 1, to 250 1, depending upon the nature of the day and its exchangeable ions [49]. Partides, which are frequently irregular in shape, are somewhat unique in the variety of associations that can take place in their dispersion. Figure 1.7 shows some of the modes of association among suspended day mineral partides [55],... 

Association reactions can be characterized by equilibrium constants. Experimental determination of equilibrium constants for each step in an association reaction provides vital information about the properties of the associating system. In particular, the mode of association (e.g., monomer-dimer, monomer-tetramer, indefinite), and the strength of the association (that is, the degree to which various oligomers can exist at various total concentrations) can be obtained. The evaluation of equilibrium constants over a range of solution conditions (such as salt concentration and temperature) can be used to obtain information on the enthalpy and entropy of the various steps in the association and the types of bonds involved in the assembly process. Note that this information can be obtained in the complete absence of structural information, although, of course, any available structural information can be used to aid in the interpretation of the thermodynamic data. 

Figure 18-C-9 (a) The mode of association of MOX4 molecules in the solid state, (b) The infinite chain structure of MoOC13, consisting of M0OCI5 octahedra sharing cis pairs of Cl atoms.

Figure 11. Modes of association of antigen/antibody complexes and other biomolecules with magnetic beads.

---