Amino acid gas phase circular dichroism and implications for the origin of biomolecular asymmetry.

Life on Earth employs chiral amino acids in stereochemical L-form, but the cause of molecular symmetry breaking remains unknown. Chiroptical properties of amino acids - expressed in circular dichroism (CD) - have been previously investigated in solid and solution phase. However, both environments distort the intrinsic charge distribution associated with CD transitions.

Crystal structures of titanium-aluminium and -gallium complexes bearing two -CH units.

The isotypic crystal structures of two titanocene complexes containing an Me unit ( Al, Ga; Me = meth-yl) with two -coordinating methyl groups, namely [μ-1(η)-(adamantan-1-yl-2κ)cycylo-penta-dien-yl]di-μ-methyl-methyl-2κ-[1(η)-penta-methyl-cyclo-penta-dien-yl]aluminiumtitanium(III), [AlTi(CH)(CH)(CH)], and [μ-1(η)-(adamantan-1-yl-2κ)cycylo-penta-dien-yl]di-μ-methyl-methyl-2κ-[1(η)-penta-methyl-cyclo-penta-dien-yl]galliumtitanium(III), [GaTi(CH)(CH)(CH)], are reported. Reacting a dinuclear nitro-gen-bridged low-valent titanium(III) complex with the Lewis acids AlMe or GaMe results in the loss of mol-ecular di-nitro-gen and the formation of two monomeric titanocene(III) fragments bearing two -bridging methyl groups. Single crystal X-ray diffraction reveals the formation of a new -C bond involving the penta-fulvene ligand while the bridging and terminal methyl groups remain intact.