How do horses (Equus caballus) learn from observing human action?

A previous study demonstrated that horses can learn socially from observing humans, but could not draw any conclusions about the social learning mechanisms. Here we develop this by showing horses four different human action sequences as demonstrations of how to press a button to open a feed box. We tested 68 horses aged between 3 and 12 years.

Reduction of ferricytochrome c catalyzed by optically active chromium(III) complexes.

The reduction rates of horse heart ferricytochrome c by amalgamated zinc or by electrolysis at fixed potential on a mercury pool as the cathode have been measured in a buffered solution at pH 7.5 by absorption spectrophotometry. In both cases, the reaction was strongly accelerated by the presence of the optically active complexes Lambda-[Cr(III)((S,S)-promp)H(2)O](+) (H(2)promp = N,N'-[(pyridine-2,6-diyl)bis(methylene)]-bis[(S)-proline]), Delta-[Cr(III)((R,R)-alamp)H(2)O](+) (H(2)alamp = N,N'-[(pyridine-2,6-diyl)bis(methylene)]-bis[(R)-alanine]) and Lambda-[Cr(III)((S,S)-alamp)(H(2)O)(2)](+).

The proton complex of a diaza-macropentacycle: structure, slow formation, and chirality induction by ion pairing with the optically active 1,1'-binaphthyl-2,2'-diyl phosphate anion.

The protonation of a sterically crowded [N2S6] macropentacycle (1) with 1 equiv of CF3SO3H in CDCl3 is slow and gives the singly (oo(+) [1 x H](+)) and doubly (o(+)o(+) [1 x 2H](2+)) protonated forms as kinetic products, the i(+)o form of [1 x H](+) being the thermodynamic product. i(+)o [1 x H](+) is C3 helically chiral in the solid state and in solution. The barrier to racemization (DeltaG(double dagger)) of the [1 x H](+) propeller is >71 kJ mol(-1).

Electron-transfer-mediated binding of optically active cobalt(III) complexes to horse heart cytochrome c.

Optically active cobalt(II) complexes are used as reducing agents in the electron-transfer reaction involving horse heart cytochrome c. Analysis of the circular dichroism (CD) spectra of reaction products indicates that the corresponding cobalt(III) species of both enantiomers of [CoII(alamp)] (H2alamp=N,N'-[(pyridine-2,6-diyl)bis(methylene)]-bis[alanine]) are partly attached to the protein during electron transfer by coordination to an imidazole unit of one of the histidine residues. His-26 and His-33 are both solvent exposed, and the results suggest that one of these histidine residues acts as a bridge in the electron transfer to and from the haem iron of cytochrome c.

(Strept)avidin as host for biotinylated coordination complexes: stability, chiral discrimination, and cooperativity.

Incorporation of a biotinylated ruthenium tris(bipyridine) [Ru(bpy)(2)(Biot-bpy)](2+) (1) in either avidin or streptavidin-(strept)avidin-can be conveniently followed by circular dichroism spectroscopy. To determine the stepwise association constants, cooperativity, and chiral discrimination properties, diastereopure (Lambda and Delta)-1 species were synthesized and incorporated in tetrameric (strept)avidin to afford (Delta-[Ru(bpy)(2)(Biot-bpy)](2+))(x)() subsetavidin, (Lambda-[Ru(bpy)(2)(Biot-bpy)](2+))(x)() subsetavidin, (Delta-[Ru(bpy)(2)(Biot-bpy)](2+))(x)() subsetstreptavidin, and (Lambda-[Ru(bpy)(2)(Biot-bpy)](2+))(x)() subsetstreptavidin (x = 1-4) For these four systems, the overall stability constants are log beta(4) = 28.6, 30.