Crystal and molecular structures of propanediamine complexed with L- and DL-glutamic acid: effect of chirality on propanediamine

Abstract

The structures of complexes of 1, 3-diaminopropane with L- and DL-glutamic acid have been determined. L-Glutamic acid complex: C₃H₁₂N₂²⁺.2C₅H₈NO^4-, M_r=368.4, orthorhombic. P2₁2₁2₁, a=5.199 (1), b=16.832 (1). c=20.076 (3) Å, V=1756.6 (4) ų, z=4, D_x=1.39 g cm^-3, λ(Mo Kα)=0.7107 Å, μ=1.1 cm^-1, F(000)=792. T=296 K, R=0.044 for 1276 observed reflections. DL-Glutamic acid complex: C₃H₁₂N₂²⁺.2C₅H₈NO^4-, M_r=368.4, orthorhombic, Pna2₁, a=15.219(2), b=5.169 (1), c=22.457 (4) Å, V=1766.6 (5) ų Z=4, D_x=1.38 g cm^-3, λ(Mo Kα)=0.7107 Å, μ=1.1 cm F(000)=792, T=296 K, R=0.056 for 993 observed reflections. The conformation of diaminopropane is all-trans in the DL complex but trans-gauche in the L complex. The main packing feature in the L complex is the arrangement of diaminopropane around dimers of antiparallel L-glutamic acid molecules. The diaminopropane in the DL complex is sandwiched between two antiparallel glutamic acid molecules of the same chirality and this forms the basic packing unit. This might be the dominant form of interaction between L-glutamic acid and diaminopropane in solution. The structures reveal the adaptability of the polyamine backbone to different environments and the probable reasons for their choice as biological cations.