A. Varnek et al., Molecular dynamics and free energy perturbation studies of Ca2+/Sr2+ complexation selectivities of the macrocyclic ionophores DOTA and TETA in water, J CHEM S DA, (23), 1999, pp. 4155-4164
Citations number
50
Categorie Soggetti
Inorganic & Nuclear Chemistry
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS
Molecular dynamics simulations have been performed on the uncomplexed tetra
anionic macrocyclic ionophores DOTA I and TETA II and on their complexes wi
th Ca2+ and Sr2+ cations in the gas phase and in water. We have found that
for both ligands, the most stable complex is the one where the cation is co
mpletely encapsulated in a pseudocavity formed by four nitrogens and four o
xygens (one per carboxylate group). All stereoisomers for this type of comp
lex have similar coordination and hydration patterns. Water molecules do no
t coordinate to the cation when it is encapsulated by the ligand but form h
ydrogen bonds with non-coordinating carboxylic oxygens, leading to repulsiv
e interactions with the cation. The higher binding affinity of I compared t
o II for Ca2+ is explained by better preorganization of I for complexation.
Free energy perturbation simulations performed on I . M2+ and II . M2+ com
plexes show that the preference of both ligands for Ca2+ over Sr2+ in water
results from their higher intrinsic binding affinities for Ca2+ rather tha
n the difference between hydration energies of the uncomplexed cations.