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. Here we report on CD and anisotropy spectra of amino acids recorded in the gas phase, where any asymmetry is solely determined by the genuine electromagnetic transition moments. Using a pressure- and temperature-controlled gas cell coupled to a synchrotron radiation CD spectropolarimeter, we found CD active transitions and anisotropies in the 130-280 nm range, which are rationalized by ab initio calculation. As gas phase glycine was found in a cometary coma, our data may provide insights into gas phase asymmetric photochemical reactions in the life cycle of interstellar gas and dust, at the origin of the enantiomeric selection of life's L-amino acids.

Crystal structures of titanium-aluminium and -gallium complexes bearing two µ2 -CH3 units.

The isotypic crystal structures of two titanocene complexes containing an EMe3 unit (E = Al, Ga; Me = meth-yl) with two µ2-coordinating methyl groups, namely [µ-1(η5)-(adamantan-1-yl-2κC1)cycylo-penta-dien-yl]di-µ2-methyl-methyl-2κC-[1(η5)-penta-methyl-cyclo-penta-dien-yl]aluminiumtitanium(III), [AlTi(CH3)3(C10H15)(C15H18)], and [µ-1(η5)-(adamantan-1-yl-2κC1)cycylo-penta-dien-yl]di-µ2-methyl-methyl-2κC-[1(η5)-penta-methyl-cyclo-penta-dien-yl]galliumtitanium(III), [GaTi(CH3)3(C10H15)(C15H18)], are reported. Reacting a dinuclear nitro-gen-bridged low-valent titanium(III) complex with the Lewis acids AlMe3 or GaMe3 results in the loss of mol-ecular di-nitro-gen and the formation of two monomeric titanocene(III) fragments bearing two µ2-bridging methyl groups. Single crystal X-ray diffraction reveals the formation of a new E-C bond involving the penta-fulvene ligand while the bridging and terminal methyl groups remain intact.