D-Mannose-molybdate complex

The D-mannose-molybdate complex shows an additional negative Cotton effect at 339 nm ([0]=36). 

Fig. 7. CD-spectrum of the D-mannose-molybdate complex. Sugar and molybdate concentrations 0.02 and 0.04 mol/I pH 5.4.

The n.m.r. spectra of aldoses complexed to molybdate show that D-ribose, D-talose, and D-allose behave as tridentate donors via hydroxy-groups at C-2, C-3, and C-4, whereas D-lyxose and D-mannose are donors via C-1, C-2, and C-3 hydroxy-groups. ... 

In aqueous solutions of ammonium molybdate, acyclic D-xylose, D-lyxose, D-glucose, and D-mannose formed binuclear bidentate molybdate complexes involving the hydrated carbonyl group as well as the hydroxy groups at C-2, C-3, and C-4. Epimerisation via these complexes was accompanied by skeletal rearrangement thus d-[2,3,4,5,6- C5] mannose isomerised to d-[1,3,4,5,6- C5] glucose. ... 

Two more sophisticated applications of the molybdate catalyst are worthy of mention. An anion-exchange resin immobiUzed heptamolybdate has provided an effective catalysis while the same resin activated with mononuclear sodium molybdate was completely ineffective [23]. In contrast, a patent apphcation claims a successful activation with the same sodium molybdate for an effective epimerization of D-glucose to o-mannose [28]. Therefore, attention has to be paid when performing such appUcations as the equilibria between the (poly)molybdate species in solution are very complex and extremely pH-sensitive [29]. 

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