A straightforward synthesis of C2‐symmetric azole‐containing macrocyclic peptides is presented. This type of macrocycle possesses four amide groups directed into the interior of the scaffold that act as hydrogen‐bond donors and two nitrogen atoms from the azole unit that act as hydrogen‐bond acceptors. This arrangement makes them sensitive receptors for Y‐shaped anions like AcO– and H2PO4– with a selectivity for dihydrogen phosphate versus acetate, as was shown with 1H NMR titration techniques in [D6]DMSO/5 % CDCl3.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

A basic requirement for each molecular system that is supposed to perform work is a synchronized and unidirectional movement. Unidirectionality can be achieved by a change of configuration or conformation that is controllable by external stimulation. Molecular hinges based on a bipyridine unit work unidirectionally and are able to reach an amplitude of motion that amounts to about 180 degrees. To analyze if it is possible to adjust the height of the unidirectional amplitude of motion, three planar chiral molecular hinge systems with a 2,2'-bipyridine unit as functional element were designed and stimulated with various divalent metal ions in different solvents. The configurations of the hinges were determined by DFT calculations using B3LYP and the 6-31G* basis set and experimentally verified by 2D NMR NOESY spectra. Circular dichroism (CD) and UV spectroscopy were used to study the properties of the hinges by the addition of metal ions (primarily Zn(2+) and Hg(2+)) in dichloromethane and methanol. The choice of metal ions and solvents determines whether or not and how far the hinges are closed. Furthermore, a drastic change in the height of the amplitude of motion can be reached by modifying the position of the bipyridine unit in the hinge. Amplitude values from 45 up to 190 degrees were obtained from quantum mechanical calculations. This control of the amplitude of motion can in the future be used for more complex switching processes of molecular machines.

Configurationally stable triaryl phosphane oxides are important for reactions with transfer of chiral information. Apart from introducing bulky substituents to suppress fast inversion of helicity at room temperature, the use of a second chiral element which induces chirality in the triaryl phosphane oxide, so that it adopts only one configuration, is suitable. With regard to chirality transfer, C(2)-symmetric imidazole cyclopeptides were tested for obtaining a configurationally stable phosphane oxide. Density functional calculations showed almost equal energies of the three possible triaryl phosphane oxides (MMM)-1, (PPP)-1, and (MP)-1. Surprisingly, after synthesis only the MMM conformer is present in solution, and its configurational stability was proved by variable-temperature and 2D NMR experiments as well as CD measurements. In view of the results of the DFT calculations, formation of stable (MMM)-1 cannot be explained thermodynamically but by kinetic reaction control. This concept of freezing the conformation of a triaryl phosphane oxide can in future be used to easily prepare configurationally stable stereoisomeric propellerlike compounds.

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