Self-association hydrogen bonds

FIGURE 2.5 Schematic representation of hydrogen-bonded self-associative structures of higher fatty acids (a) cyclic associative dimer and (b) linear associative multimer. 

The crystal structure of isocytosine [ICYTIN] is interesting since it is a 1 1 complex of the 1,4- and 3,4-dihydro tautomers and has both triple and double hydrogen-bond self-association (Fig. 16.7). As outlined in Chapter 15, this tautomerism is not observed in the naturally occurring nucleic acid bases. 

A simple application of the self-assembly of complementary bifunctional small molecules to form extended-chain structures, or longitudinal PLCs, is given in references 6-8. Griffin and coworkers report that hydrogen bond-driven association between bispyridyl-terminated and bisbenzoic acid-terminated species can lead to liquid crystalline materials with polymeric characteristics. Typical compounds employed are shown in Figure 3.2. None of the starting components are liquid crystalline. 

The second use of hydrogen bonding to tune aromatic stacking interactions can be best explained by the relative lack of directionality associated with the r-stacking interaction. The last example in the previous section shows that, despite the introduction of four aromatic stacking interactions at the periphery of linear hydrogen-bonded self-assembled structures, no major perturbations affect... 

In another report, carboxylic acids were used to self-assemble azo dyes, which could be controlled by photoisomerization of the azobenzene dye [70]. The frans-azobenzene isomer 33 of this dye associates into hydrogen-bonded linear tapes, while the czs-azobenzene 34 yields hydrogen-bonded self-assembled tetramers that form rodlike aggregates by additional n-n stacking interactions (Fig. 23). 

It should be mentioned that in the last few years super-cooled water has attracted the interest of many scientists because of its exceeding properties and life at temperatures below 0 °C 1819). Speedy recently published a model which allows for the interpretation of the thermodynamic anomalies of supercooled water 20). According to this model there are hydrogen bonded pentagonal rings of water molecules which have the quality of self-replication and association with cavities. 

Obviously, this shift implies the self-association of DMSO. Further frequency shifts to even lower wave numbers (1050-1000 cm " ) are observed in both aprotic polar and protic solvents. In aprotic solvents such as acetonitrile and nitromethane, the association probably takes place between the S—O bond of DMSO and the —C=N or the —NOz group in the molecules by dipole-dipole interaction as shown in Scheme 331,32. Moreover, the stretching frequency for the S—O bond shifts to 1051 cm 1 in CHC13 and to 1010-1000 cm -1 in the presence of phenol in benzene or in aqueous solution33. These large frequency shifts are explained by the formation of hydrogen bonds between the oxygen atom in the S—O bond and the proton in the solvents. Thus, it has been... 

Dihydrodithiin sulphoxides, synthesis of 243 Dihydrothiophene dioxides, reactions of 653 /(,/( -Dihydroxyketones 619 Dimerization, photochemical 877, 884 Dimethyl sulphoxide anion of - see Dimsyl anion hydrogen bonding with alcohols and phenols 546-552 oxidation of 981, 988 photolysis of 873, 874, 988 radiolysis of 890-909, 1054, 1055 self-association of 544-546 Dimsyl anion... 

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. 

---