THE X-RAY CRYSTAL-STRUCTURE OF N-TRIDECA-5,7-DIYNE-D-GLUCONAMIDE AT 295-K, 100-K AND 20-K - A SUPERSTRUCTURE-FORMING SYNTHETIC GLYCOLIPID

The X-ray crystal structure of N-trideca-5,7-diyne-D-gluconamide was determined at 295, 100 and 20 K (space group P1, a = 4.811(1)/4.775(4)/4.774(3), b = 5.160(1)/5.098(3)/5.087(2), c = 21.820(5)/21.54(1)/21.458(9) Angstrom, alpha = 92.44(2)/92.91(4)/93.02(4), beta = 107.76(2)/109.20(6)/109.57(5), gamma = 96.74(2)/96.81(5)/96.82(4)degrees (295/100/20 K)). The molecules display an extended conformation both in the tail and the head group tolerating a 1,3-syndiaxiale interaction. The hydrogen bonding scheme involves a homodromic, quadrilateral cycle and endless chains of the kind -H...O=C-N-H...O=C-. The molecules pack in an unusual head-to-tail arrangement without interdigitation of the head group or the alkadiyne tail. Comparison with the crystal structure of N-tetradeca-6,8-diyne-D-gluconamide (Fuhrhop, Blumtritt, Lehmann and Luger, J. Am. Chem. Sec. 113(1991) 7437-7439) demonstrates that N-alkadiyne-gluconamides display the same odd-even effect already known for the saturated derivatives. The thermal motion of the head and tail group atoms is discussed and an extreme decrease of mobility in the tail region is detected when the temperature is lowered via 100 to 20 K.