Structural and solvent effects on the 13C and 15N NMR chemical shifts of indoloquinoline alkaloids: experimental and DFT study
2008
Indoloquinoline alkaloids represent an important class of
antimalarial, antibacterial and antiviral compounds. They have
been shown to bind to DNA via intercalation preferentially at
GC-rich sequences containing nonalternating CC sites. The
stability of complexes formed with biological macromolecules
depends on noncovalent binding. In the present study, the
ability of indoloquinolines to form intermolecular interactions
with solvents was investigated by using NMR spectroscopy and
density functional theory (DFT) (B3LYP/6-31G**) calculations.
NMR data measured for indoloquinoline bases and the
corresponding hydrochlorides are discussed in relation to the
structure. DFT calculations of shielding constants in vacuo and
in solution allowed the investigation of the influence of the
environment on the NMR parameters. Calculations incorporating
solvent effects indicated significant changes in the anisotropy
of the electron distribution, reflected in the span of the
chemical shielding tensor (Omega = delta11 - delta33). Solvent
effects on the span of the 13C and 15N shielding tensor
depended on the type of atom and the data indicated a
significant influence of solute-solvent interactions.
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