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Abstract

The synthesis of a cylindrical, imine-based cage composed of two trimeric metallamacrocycles is described. The cage acts as a heterotopic receptor for alkali metal cations. The small cations Li⁺, Na⁺, and K⁺ bind to the outside of the cage with good selectivity for Li⁺, whereas the larger cations Rb⁺ and Cs⁺ are bound inside the cage to form unusual π complexes with a good selectivity for Cs⁺. Negative heterotopic cooperativity between the two binding sites is observed. The complexation of Cs⁺ is associated with a color change, which enables the cage to be used as a specific sensor for Cs⁺.

Selective M⁺ binding. A new imine-based cage has been synthesized that acts as a tritopic receptor by binding small alkali metal cations (Li⁺, Na⁺) on the outside and large alkali metal cations (Rb⁺, Cs⁺) on the inside of the cage (see figure). Association constants were determined for various alkali metal salts and a negative heterotopic cooperative effect between two different binding sites was observed.

Multiple (four) nonequivalent magnesium sites with very similar local Mg environments in a Mg-containing metal–organic framework, microporous α-Mg₃(HCOO)₆, have been resolved by ²⁵Mg natural-abundance triple-quantum magic-angle spinning (3QMAS) NMR spectroscopy at an ultrahigh magnetic field of 21.1 T. For more details, see the Communication by Y. Huang et al. on page 4432 ff.

Research infrastructure: Use foreign aid to help African science

Nature 495, 7440 (2013). doi:10.1038/495174e

Author: Khalid D. Awadelkarim

Scientific and technological research could solve many of Africa's local issues, but these problems persist despite generous international support.The situation is made worse by a severe shortage of well-trained, home-grown scientists, and aggravated by emigration and poor working environments (see, for example, M. H.