Inorganic-organic hybrid molecular architectures of cyanometalate host and organic guest systems: specific behavior of the guests.

Molecular architectures built of inorganic cyanometalate building blocks provide variegated host structures with several organic guest molecules. The strategies to derive novel structures are presented briefly. The formation of a charge-transfer (CT) complex as the guest inside the cavity and the photochemistry of the CT complexes are discussed. The chemical pressure that the guest experiences inside the cavity is also discussed based on the vibrational spectroscopic results.

Visualization of complexes of Hoechst 33258 and DNA duplexes in solution by atomic force microscopy.

Tertiary structure changes in DNA duplexes, induced by Hoechst 33258 binding, have been examined by the use of atomic force microscopy. Besides minor groove binding, which is an established mode of binding for this drug, Hoechst 33258 has now been found to show another binding mode, which causes an unwinding of the duplex. When the drug concentration is as high as 0.5 microg/ml, the Hoechst 33258 molecule seems to function as a clamp for two DNA chains and forms a condensate. The condensate was found to have a toroidal shape. By surveying more than 100 microscopic images of such condensates formed in I microg/ml drug solution, a mechanism of toroidal condensate formation has been proposed.