Quinolone Complexes with Lanthanide Ions: An Insight into their Analytical Applications and Biological Activity

Abstract

Quinolones comprise a series of synthetic bactericidal agents with a broad spectrum of activity and good bioavailability. An important feature of these molecules is their capacity to bind metal ions in complexes with relevant biological and analytical applications. Interestingly, lanthanide ions possess extremely attractive properties that result from the behavior of the internal 4f electrons, behavior which is not lost upon ionization, nor after coordination. Subsequently, a more detailed discussion about metal complexes of quinolones with lanthanide ions in terms of chemical and biological properties is made. These complexes present a series of characteristics, such as narrow and highly structured emission bands; large gaps between absorption and emission wavelengths (Stokes shifts); and long excited-state lifetimes, which render them suitable for highly sensitive and selective analytical methods of quantitation. Moreover, quinolones have been widely prescribed in both human and animal treatments, which has led to an increase in their impact on the environment, and therefore to a growing interest in the development of new methods for their quantitative determination. Therefore, analytical applications for the quantitative determination of quinolones, lanthanide and miscellaneous ions and nucleic acids, along with other applications, are reviewed here.

Keywords: biological activity; fluoroquinolones; lanthanides; metal complexes; quantitative determination.

Figure 1

(a) 7-chloroquinoline; (b) nalidixic acid; (c) general structure and main classes of quinolones.

Figure 2

Coordination of Mg²⁺ at the binding site of ciprofloxacin to topoisomerase IV in the quinolone–DNA–enzyme complex; the four water molecules are represented through four blue bullets (adapted from [19], with permission https://pubs.acs.org/doi/10.1021/bi5000564; further permissions related to the material excerpted should be directed to the ACS).

Figure 3

Donor atoms in the general structure of fluoroquinolones.

Figure 4

Equilibrium speciation distribution vs. pH for the Lu(NO₃)₃ system on the background of 0.1M KNO₃: (1) Lu³⁺, (2) Lu(OH)²⁺, (3) Lu(OH)₂⁺, (4) Lu(OH)₃—with permission from [36].

Figure 5

Main routes of contaminating the environment with quinolones for human or veterinary use (adapted after [59,63]).

Figure 6

Intramolecular energy transfer for Tb³⁺, with permission from [81].

Figure 7

(a) Hematoxylin and eosin coloring technique. (b) Coloring with quinolone–lanthanide complexes, with permission from [182].