Conformational changes of arginine dichloride dihydrate

Single crystal of Arginine dichloride dihydrate was studide by x-ray diffraction expriments in emphasis of main influence factors of arginine conformational variation,and was also compared with its other conformations in the existence of different anions.The single crystal is Monoclinic,P21/c,a=11.0490(18);b=8.4876(13);c=11.2261(17);β=91.386(2)°;Z=4;Dx=1.443 Mg·m-3.Arginine molecules interlaced with each other in cis-and trans-conformations to arrange along c axis,and the oxygen atoms on carboxyl group and the N-H on α-amino group connected with each other by hydrogen bonds to form a common head-tail connecting conformation.Crystal water molecules formed hydrogen bonds with arginine and acted as a salt bridge,and chloride ions were also involved in the formation of hydrogen bonds and static interactions with N-H on arginine and took part in the charge balance with arginine.All the above interactions make arginine form hydrogen bonding superamolecular network structure in three-dimension.