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Study of Solution Equilibria Between Gadolinium(III) Ion and Moxifloxacin
Abstract:
The complex formation equilibria between gadolinium(III) ion and moxifloxacin (MOXI) were studied in aqueous solutions. The investigations were performed by glass electrode potentiometric (ionic medium: 0.1mol dm-3 LiCl, 298 K) and UV spectrophotometric measurements. In the concentration range 0.5≤ [Gd3+] ≤ 1.0; 1.0 ≤ [MOXI] £ 2.0 mmol dm-3 ([MOXI]/[Gd] = 1: 1to 5: 1) and pH between 2.5and 9.0, gadolinium(III) and moxifloxacin form the complexes of the composition: Gd(HMOXI)3+, Gd(HMOXI)23+, Gd(HMOXI)33+, Gd(HMOXI)2MOXI2+, Gd(HMOXI)(MOXI)2+, Gd(MOXI)3. The stability constants of the complexes were calculated with the aid of Hyperquad2006 suite of programs, taking into account the hydrolysis of Gd3+ ion and protonation of moxifloxacin anion. The possible structure of the complexes, in solution, and their formation mechanism is suggested. The effect of moxifloxacin, and for comparison purpose, DTPA on gadolinium(III) plasma speciation was evaluated by computer simulation.
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Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.

