Molecular modelling calixarene

Among several families of compounds used as molecular models for such surface silanolic grafting sites (mono or poly-silanols [10-12], heteropolyanions [13, 14], calixarenes [15, 16], tripodal amido complexes [17], etc.) some silsesquioxanes [18-23] can be considered among the most convincing molecular analogues of silica surface silanols. 

Molecular modeling of calixarenes and their host-guest complexes, F. C. J. M. van Veggel, in Calixarenes in Action, L. Mandolini and R. Ungaro, Eds., Imperial College Press, London, 2000. 

Until recently, the acid-catalyzed synthesis of calixarenes was limited to the calixresorcarenes. A kinetic and molecular modeling study of the acid-catalyzed reaction of acetaldehyde and resorcinol comes to the conclusions that... 

Rather little attention has been given to the measurement and calculation of dipole moments of calixarenes. The most comprehensive experimental study includes data on nine calix[4]arenes with examples of each of the four up-down conformations, as shown in Table 3.2. As anticipated from simple inspection of molecular models, the sequence of decreasing dipole moment is cone > partial cone > 1,2-alternate > 1,3-alternate. A computational study affirms the sequence of decreasing dipole moment as cone > partial cone > 1,2-alternate > 1,3-alternate but yields a value of only 0.46 D for 4 and values of 1.46,... 

Van Veggel, F.C.J.M. Molecular Modeling of Calixarenes and Their Host-Guest Complexes. In Calixarenes in Action Mandolini, L.. Ungaro, R.. Eds. Imperial College Press Singapore. 2000 11-36. 

The inclusion of aromatic guests in the hydrophobic pocket of the water-soluble calixarenes 7-9 (Fig. 11) was recently studied by H-NMR titration experiments in aqueous buffered solutions and molecular modeling studies combined with ab initio NMR shift calculations. ... 

Several reports in the literature show that calixarene derivatives play a crucial role in controlling the size and stability of MNPs [106-108]. For example, Raston reported on the synthesis of p-phosphonic acid calix[8]arene-modified Ru, Pt and Pd nanoparticles in aqueous solution (Fig. 37.16) [109]. The macrocycle was demonstrated to exert a control over the shape and size of the produced nanoparticles by acting as stabilizing agent. Molecular modeling revealed that 12 molecules of the macrocycle surround 2-nm Ru particles, where a H-bonding network among calix[8]arenes contribute to the interfacial self-assembly. 

Analysis of CP kinetics and the parameters obtained are a source of important information about host-guest interactions. From the classic I-S model of cross polarization, it was found that the values of T pH relaxation times for guest and host molecules are considerably different. This suggests that DMF carbons cross-polarize from the DMF protons, not from the remote protons, of calixarene. Moreover, such a result proves that the DMF is located outside the calices and between the calixarene molecules. The simple I-S model is not sufficient to describe the cross-polarization of the complex of tetra (C-undecyl)calix[4]resorcinarene with DMA. The best fit of experimental data was seen when the more advanced I-F-S model of cross polarization was adopted [57]. Analysis of CP kinetic parameters provides important information on molecular mobility (Fig. 19, Table 5). 

Naturally, quantum chemical approaches to molecular recognition are usually employed for selected systems since the complexity of these systems requires a system-specific analysis which makes it difficult to extract results of general validity for examples, see Refs. [13-16] for studies of molecular tweezers. Further examples are mentioned in a review article by Schatz considering ab initio calculations on calixarenes and calixarene complexes [17]. Schatz concludes that although the systems are quite big, useful contributions have been made by ab intio calculations. However, a general model is needed in order to make host-guest processes and template-assisted reactions accessible to a comparison of quantitative measurements and calculations, which may finally provide the basis for rational host design and for the prediction of template effects (compare the recent attempt by Hunter [18]). 

Artificial Enzymes, p. 76 Biological Ligands, p. 88 Biological Models, Clzaracteristics. p. 101 Calixarenes and Their Analogues Molecular Complexa-tion, p. 145... 

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