Silver(I) cation complexation with 3 alpha,3 'alpha-bis(pyridine-n-carboxy) lithocholic acid 1,2-ethanediol diesters (n=2-4): H-1, C-13 and N-15 NMR spectral studies and molecular orbital calculations

Three isomeric molecular clefts: 3 alpha,3'alpha-bis(pyridine-n-carboxy) li thocholic acid 1,2-ethanediol diesters (n = 2-4) 1-3 have been synthesized and their structures ascertained by H-1, C-13 NMR and MALDI TOF MS. Their c omplex formation with Ag+-cation (added as AgO3 SCF3) have been investigate d by means of NMR and molecular orbital calculations. The coordination beha viour of the silver(I) cation is dependent on the isomerism of the pyridine -n-carboxy moiety. In 1 (pyridine-2-carboxylato = picolinato) both NMR and theoretical calculations strongly suggest that the coordination occurs with the lone electron pairs of the pyridine nitrogen and carbonyl oxygen in bo th of the arms of the molecular cleft separately. In 2 and 3 (pyridine-3-ca rboxylato = nicotinato and pyridine-4-carboxylato = isonicotinato) where th e distance between the pyridine nitrogen and carbonyl oxygen is too large t o allow the same type of coordination as in 1, eta(1)-complexation with the pyridine ring and carbonyl oxygen of the different arms of the molecular c left simultaneously is suggested by molecular orbital calculations and supp orted also by NMR. No Ag+-cation coordination was observed with the 1,2-eth anediol oxygens in 1-3.