Abstract The title complex crystallizes in the monoclinic space group of P21/c. The unit-cell dimensions are a=6.673(4), b=19.017(8), c=13.394(7) Å, and β=110.54(2)°. The crystal structure was solved by a direct method. By block-diagonal least-squares refinements, the R-value converged to 0.062. In this complex, a salt bridge is found between the anionic carboxyl group of phenylacetic acid (PAA) and the cationic amino group of tryptamine (TPA). All the hydrogen atoms attached to the nitrogen atoms participate in the hydrogen bonding. The two complex molecules are hydrogen-bonded around a center of symmetry to form one unit, which is held together by van der Waals contacts in the b- and c-directions. Each unit is also stabilized by forming a hydrogen bond with the unit of the neighboring cell translated in the a-direction.
Sessions 4inside surface is located at the D-pathway entrance.The zinc binding affinity for the second site suggests that the zinc site is tightly coupled with the proton-pumping site.Recently, we analyzed Zn/Cd-binding to monomeric CcO which gives crystal packing different from that in the dimeric CcO crystal.The x-ray structural analysis showed Znbinding to the Zn2, Zn3 and additional sites including the site near the K-pathway entrance.Several Zn-binding sites have been found on the outside surface.However none of them is located on the subunit I surface from which pumping protons exit.
