Estimating the Ground and Excited State Dipole Moments of Levofloxacin and Norfloxacin Drugs Using Solvatochromic Effects and Computational Work

Abstract

Levofloxacin (LVF) and norfloxacin (NRF) are a group of fluoroquinolone antibiotics, broad spectrum used to treat various infections caused by many bacterial species. The drugs contain functional groups which control the type and degree of interaction with different solvents. In this research, the ground and excited state dipole moments of LVF and NRF drugs were estimated using solvatochromic effects and computational work. The dipole moments were estimated from absorption and emission spectra in polar and nonpolar solvents using Bakhshiev’s, Kawski–Chamma–Viallet, Lippert–Mataga, and Reichardt models. The results indicated the emission spectra are more strongly affected by solvent polarity than the absorption spectra. The calculated excited state dipole moment is larger than that of the ground state, indicating that the probe compounds are significantly more polarized in the excited state than in the ground state. From computational work, the HOMO-LUMO energy band gap, the dipole moments, electron charge density distribution, and oscillator strength were determined using the semiempirical MP6 method, DFT-B3LYP-6-31G, and DFT-B3LYP-3-21G employing Gaussian 09 software. In general, larger dipole moments were obtained by computation rather than from experiments due to the absence of solvent effects.

Effect of Solvent Polarity on the Absorption and Fluorescence Spectra of Nicotinamide: Determination of Ground and Excited State Dipole Moments

“…( 14) is larger than the value obtained by other methods. This is due to the fact that the Lippert-Mataga equation neglected the polarizable nature of the solute molecules [55]. It has also been reported previouslythat the change in dipole moment obtained using the Lippert-Mataga equation is larger than the values calculated by other methods [55,23,40,61].…”

“…This is due to the fact that the Lippert-Mataga equation neglected the polarizable nature of the solute molecules [55]. It has also been reported previouslythat the change in dipole moment obtained using the Lippert-Mataga equation is larger than the values calculated by other methods [55,23,40,61]. Furthermore, the ground and excited E-nicotinamide results from individual stark lobe measurements were obtained and reported [51], 0.315 g   and 0.316 e D   using microwave spectrum.…”

“…Furthermore, quantum chemistry approaches often produce an exaggerated electron distribution in molecules, making them more polar than they are in reality [23]. Another reason is that experimental methods take into account solvent and environmental influences (solvent-solvent interaction), whereas ab initio calculations only provide results for a free solute molecule in vacuum [53][54][55].…”

“…8(b&c), allows the nucleophilic and electrophilic areas of the molecules to be estimated. Identifying these nucleophilic and electrophilic areas is critical for the design of nonlinear optical materials [56] and helps prediction of the site of attack in various photochemical processes [23,55]. The electrostatic potential map of NIC is represented in red and blue colours.…”

“…The electrostatic potential map of NIC is represented in red and blue colours. The blue colour represents a positive phase that corresponds to a nucleophilic region and the red colour represents a negative phase that corresponds to an electrophilic region [55,57]. Oxygen creates an electron-rich region and the lowest electrostatic potential of the molecule, and nitrogen is relatively electron deficient for NIC molecules.…”