Molecular modelling pyrrole structure

These qualitative assays show that one-armed cationic guanidiniocarbonyl pyrrole receptors can indeed effectively bind tetrapeptides even in water. Molecular modeling studies suggest a complex structure as shown for one specific example, the receptor Val-Val-Val-CBS, in Figure 2.3.11. Receptor and substrate form a hydrogen bonded //-sheet which is further stabilized by additional hydrophobic interactions between the apolar groups in the side-chains. Recognition of the tetrapep-tide thus seems to be controlled by a fine balanced interplay between electrostatic and hydrophobic interactions. 

Various PFs [61-63] and their pyrrole analogues [64] functionalized with chiral side chains exhibit NLO character and it is not clear how the chirality, helicity and NLO character are related. Because PF2/6 has become a model test system in the study of helical PFs, fully understanding its intramolecular structure can serve as a reference point for further comparisons. The molecular level heterogeneity intrinsic in the single chain structure of PF2/6 insures a high level of frustration and thus it represents a model polymer for paracrystals and paracrystallinity [24]. 

Coal is characterised by a non-uniform molecular structure within which aromatic structural units can be distinguished. They are composed of one to five condensed or directly joined aromatic rings substituted by heterocyles and aliphatic (mainly methyl) groups. Nitrogen is involved in pyridine and pyrrole rings and a part of sulphur in thiophene rings. C- and 0-alkylation may occur by the reductive alkylation reactions of coal. Lazarov et al. (1984) presented a structural model which fits the values of the structural parameters obtained by H and NMR spectroscpy of alkylated coal. 

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