Mixed-ligand complexes of copper(II) ions with AMP and CMP in the systems with polyamines and non-covalent interaction between bioligands

Synthesis, Protonation and CuII Complexes of Two Novel Isomeric Pentaazacyclophane Ligands: Potentiometric, DFT, Kinetic and AMP Recognition Studies

“…In general, the values of the constants in Table 4 are of the same order as those found for the interaction of AMP with the protonated forms of some other polyaza macro- cycles [36,38] and significantly higher than those found for smaller amines and for biogenic amines such as spermidine or putrescine. [8,40] It is also interesting to note that the stability of the AMP-H x L species is also lower with polyaza macrocycles that are larger than the present cyclophanes. [41] This appears to show that the interaction is optimised for macrocycles of intermediate size in which the phosphate group better matches the positive charges of the macrocyclic cavity.…”

“…In addition, the interaction probably becomes stronger for the case of cyclophanes because of additional π stacking interactions and actually, the stability constants found in this work are larger than those found for macrocycles of a similar size but lacking aromatic spacers. [8,[36][37][38][39][40] Another interesting conclusion from the data in Table 4 is that the strength of the interaction between AMP 2-and the different H x L x+ forms does not appear to be affected significantly when the positive charge on the cyclophane is in-creased which strongly suggests that the strength of the interaction is not dominated only by charge-charge electrostatic factors. Other factors like hydrogen bonding should also significantly affect the interaction.…”

“…Other factors like hydrogen bonding should also significantly affect the interaction. In this sense, it must be pointed out that although the stability of H x L x+ -AMP adducts usually tends to increase with the protonation state of L because of the increased coulombic attractions and the larger number of possible hydrogen bonds between the host and the guest, [38,40,41] there are also literature reports showing similar stability constants for the interaction of AMP with the different protonated forms of some tripodal polyamines. [42] The determination of the stability constants for the Cu-L-AMP systems (L = L 1 , L 2 and L 3 ) through the analysis of the titration curves is much more complex because of the large number of species present in solution.…”

“…However, it must be pointed out that the nature of the interaction between AMP and the receptor is presumably different in both cases because Cu-L complexes are coordinatively unsaturated and so they are susceptible to AMP coordination. At this point, it is interesting to note that all the log K values in Table 5 indicate that all the Cu-L complexes interact with AMP more strongly than Cu 2+ (log K Cu-AMP = 3.0-3.2) [40,[43][44][45] although the values can be considered to [a] Charges omitted for clarity. [b] Values in parentheses are standard deviations in the last significant Figure. be similar to those found for other Cu-polyamine complexes.…”

“…[b] Values in parentheses are standard deviations in the last significant Figure. be similar to those found for other Cu-polyamine complexes. [40,41,46] The stability of the interactions with mononuclear Cu-L 3 complexes are among the most stable. These results, and especially the large stabilisation observed for the L 3 complexes, strongly suggest that selectivity in recognition is probably determined more by other interactions (hydrogen bonding, π stacking) than by direct coordination to the metal centre.…”