Unidirectional molecular motor on a gold surface

Molecules capable of mimicking the function of a wide range of mechanical devices have been fabricated, with motors that can induce mechanical movement attracting particular attention. Such molecular motors convert light or chemical energy into directional rotary or linear motion, and are usually prepared and operated in solution. But if they are to be used as nanomachines that can do useful work, it seems essential to construct systems that can function on a surface, like a recently reported linear artificial muscle. Surface-mounted rotors have been realized and limited directionality in their motion predicted. Here we demonstrate that a light-driven molecular motor capable of repetitive unidirectional rotation can be mounted on the surface of gold nanoparticles. The motor design uses a chiral helical alkene with an upper half that serves as a propeller and is connected through a carbon-carbon double bond (the rotation axis) to a lower half that serves as a stator. The stator carries two thiol-functionalized 'legs', which then bind the entire motor molecule to a gold surface. NMR spectroscopy reveals that two photo-induced cis-trans isomerizations of the central double bond, each followed by a thermal helix inversion to prevent reverse rotation, induce a full and unidirectional 360 degrees rotation of the propeller with respect to the surface-mounted lower half of the system.     

Avian oogenesis and yolk deposition

Zusammenfassung Es wird die Auffassung vertreten, dass bei Vögeln die grosse Masse des Eidotters extrazellulär ist. Dieser wird durch selektive Absorption von Blutplasma abgelagert, welches zwischen den Follikelzellen in die Follikelhöhlung eindringt. Wasser, Natrium and andere gelöste Stoffe werden wieder ins Blut abgegeben, und der kaliumreiche Eidotter bleibt zurück. Das Cytoplasma der Eizelle geht funktionell im Eidotter auf und spielt bei der Ablagerung des Dotters nur eine passive Rolle.     

Sr2+ can become incorporated into an agonist-sensitive,cytoplasmic Ca2+ store in a cell line derived from the equine sweat gland epithelium

We have explored the properties of a Ca²⁺-dependent cell-signalling pathway that becomes active when cultured equine sweat gland cells are stimulated with ATP. The ATP-regulated, Ca²⁺-influx pathway allowed Sr²⁺ to enter the cytoplasm but permitted only a minimal influx of Ba²⁺. Experiments in which cells were repeatedly stimulated with ATP suggested that Sr²⁺, but not Ba²⁺, could become incorporated into the agonist-sensitive, cytoplasmic Ca²⁺ store. Further evidence for this was provided by experiments using ionomycin, a Ca²⁺ ionophore which has no affinity for Sr²⁺.