Solid state to solution: crystal structure and molecular dynamics simulations of a polyammonium nitrate host

The crystal structure of a hexaprotonated octaaza macrocycle, 1,4,7,10,13,1 6,19,21-octaazacyclotetracosane, has been obtained as the nitrate complex, H(8)1 . NO3. The complex crystallizes in the monoclinic space group P2(1)/c with unit cell parameters a = 14.43(2), b = 8.36(1), c = 15.9(1) Angstrom, beta = 110.8(2)degrees and U = 1793(12) Angstrom(3). The macrocycle crysta llizes in a relatively flat elliptical conformation with dimensions of 11.9 and 7.2 Angstrom and a depth of 1.8 Angstrom, The crystallographic coordin ates formed the basis for molecular dynamics simulations over a 400 ps time frame using the all-atom CHARMM version 25 package. The major change in the conformational structure of the macrocycle during the simulations was the shifting of all NCCN dihedral angles to a trans conformation. Also, each co nformational transition in CNCC and CCNC angles flanking a central CC bond was found to be correlated. The macrocycle remained relatively flat through out the simulation, resulting in essentially complete hydration within the first 100 ps of the simulation. Extensive water relay networks could be ide ntified throughout the simulation, which are attributed to maintaining and stabilizing anion/cation interactions in solution.