Geometry Optimized Receptors

As frequently observed with naturally occiuring ionophores, geometry optimization of the cation-ligating donor array offered specific cation recognition in artificial receptor systems [16]. The munber of successful examples of acycUc systems is still limited, but a series of Ag+ cation-selective podands 12... 

Certain substituted urea compounds, such as phenylurea or thidiazuron. Fig. (1), are very effective in the replacement of adenine-based cytokinins in promoting callus growth and other bioassays [27,28]. Molecular modeling revealed that the energetically optimal conformation of active urea derivatives have similar geometry as the isoprenoid side chain, so they can bind to the active sites of cytokinin metabolic enzymes and/or activate cytokinin receptors [29]. Thus, these compounds are likely to enhance their cytokinin effect by simultaneous activation of the receptor and inhibition of some of the cytokinin deactivating enzymes [11,30]. 

Figures 2 and 3 show the optimized geometries obtained from both the PCILO and empirical energy methods for complexes of AMP and AMS with five of the eight compounds studied. The PCILO results give distinct n-ir complexes involving interaction of one oxygen lone pair of electrons with the ir-electron system of the substitutent. In all cases, the empirical energy method gives a totally optimized complex which involves mainly electrostatic and dispersion terms. As can be seen from Figures 2 and 3, the interaction of methylcyclopropane with the model anionic receptor site is the one with the greatest difference...

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