Abstract
[Ni(R, R- or S, S- chxn)2]Br2.3 H20(abbreviated to [R, R] or [S, S]) reacts with certain aldoses in methanol to yield octahedral Ni(II) paramagnetic complexes [Ni(aldose-chxn)2]Br2containing two N-glycosides, where chxn is 1, 2-cyclohexanediamine. This reaction is sensitive to the absolute configuration on C2 of aldoses. In most cases, [R, R] reacts preferentially with aldoses having S configuration on their C2 atom, and [S, S] with corresponding C2-epimer having R configuration. Aldoses are easily recovered from the complexes by the treatment of slightly acidic aqueous solutions. Therefore, this reaction can be utilized for molecular recognition and separation of certain sugars. The 1:1 mixture of D-glucose and D-mannose which are mutual C2-epimers reacted with [R, R] in methanol to yield blue complex which contained only D-mannose. In other cases there occurred partial separation in a mixture of C2-epimers. This selectivity was discussed in terms of the stereochemical features of these complexes. As previously observed in N-glycoside complexes derived from en or tn (en=ethylenediamine, tn=trimethylenediamine), these N-glycosides which have been derived from chxn is also expected to coordinate with a Ni(II) ion stably as a tridentate ligand in meridional form. When the coordination was achieved in meridional form, these tridentate ligands containing two five-membered chelate rings linked with a glycoside nitrogen, will take its most stable form in such a way as one chelate ring is δ-gauche, and the other is λ. These stereochemical features seem to be very important to the molecular recognition of aldoses.
