“…Additionally, the complex formation constant ( K f ) can be evaluated using the mathematical relationship given as: K f = (A/A m )/[1- (A/A m )] 2 C for 1:1 stoichiometry and K f = (A/A m )/4C 2 [1- (A/A m )] 3 for 1:2 stoichiometry, where; A is the observed maximum absorbance, A m is the absorbance obtained from the extrapolation of the two lines obtained from Job's continuous variation curve and C is the initial molar concentration of study metal ion [ 31 , 32 ]. Moreover, using the relationship; ΔG = - RTln K ; Gibbs free energy (ΔG, kJ mol −1 ) of the metal complexes formation can be estimated where, R is the gas constant (equal to 8.314 J mol −1 K −1 ), T is the temperature in Kelvin and K is the determined stability constant [ 33 ]. Figure 6 The determination of stoichiometry of HGAT – metal ions interaction in solution by Job's method: (a) Co(II)-HGAT interaction, (b) Ni(II)- HGAT interaction and (c) La(III)-HGAT interaction.…”
Herein, a simple and accurate spectrophotometric method was developed to detect gatifloxacin (HGAT) in a pure and ophthalmic formulation. The method depends on complexation of HGAT with Co (II), Ni (II) and La(III) ions in ethanol medium at room temperature. The experimental conditions have been investigated to reach optimum conditions for HGAT-metal ions interaction, including detection of a suitable wavelength, medium pH, reaction time and reactants concentration. Moreover, the composition of these complexes in addition to their stability constants were also investigated and the result indicated that the molar ratio of HGAT: Metal ion is 1:1 for Ni (II) and La(III) ions and 1:2 for Co (II) ion. Beer's law plots were obeyed in the concentration ranges 18.77–150.16, 18.77–131.39 and 18.77–112.62 (μg mL
−1
) for Co(II), Ni(II) and La(III) ions interaction, respectively. The apparent molar absorptivity, Sandell's sensitivity, standard deviation, detection and quantification limits were calculated. The proposed method was successfully applied for the determination of HGAT in the bulk and ophthalmic formulation. The obtained results were compared statistically with other published methods and the results were in good agreement with those obtained by reported methods.
“…Additionally, the complex formation constant ( K f ) can be evaluated using the mathematical relationship given as: K f = (A/A m )/[1- (A/A m )] 2 C for 1:1 stoichiometry and K f = (A/A m )/4C 2 [1- (A/A m )] 3 for 1:2 stoichiometry, where; A is the observed maximum absorbance, A m is the absorbance obtained from the extrapolation of the two lines obtained from Job's continuous variation curve and C is the initial molar concentration of study metal ion [ 31 , 32 ]. Moreover, using the relationship; ΔG = - RTln K ; Gibbs free energy (ΔG, kJ mol −1 ) of the metal complexes formation can be estimated where, R is the gas constant (equal to 8.314 J mol −1 K −1 ), T is the temperature in Kelvin and K is the determined stability constant [ 33 ]. Figure 6 The determination of stoichiometry of HGAT – metal ions interaction in solution by Job's method: (a) Co(II)-HGAT interaction, (b) Ni(II)- HGAT interaction and (c) La(III)-HGAT interaction.…”
Herein, a simple and accurate spectrophotometric method was developed to detect gatifloxacin (HGAT) in a pure and ophthalmic formulation. The method depends on complexation of HGAT with Co (II), Ni (II) and La(III) ions in ethanol medium at room temperature. The experimental conditions have been investigated to reach optimum conditions for HGAT-metal ions interaction, including detection of a suitable wavelength, medium pH, reaction time and reactants concentration. Moreover, the composition of these complexes in addition to their stability constants were also investigated and the result indicated that the molar ratio of HGAT: Metal ion is 1:1 for Ni (II) and La(III) ions and 1:2 for Co (II) ion. Beer's law plots were obeyed in the concentration ranges 18.77–150.16, 18.77–131.39 and 18.77–112.62 (μg mL
−1
) for Co(II), Ni(II) and La(III) ions interaction, respectively. The apparent molar absorptivity, Sandell's sensitivity, standard deviation, detection and quantification limits were calculated. The proposed method was successfully applied for the determination of HGAT in the bulk and ophthalmic formulation. The obtained results were compared statistically with other published methods and the results were in good agreement with those obtained by reported methods.
“…On the other hand, the release of the guest molecule from the complex becomes difficult when lgK is over 4 [17]. The stability constants of most CD-based complexes decreased as temperature elevated [18,19]. However, the two OL inclusion complexes did not exhibit such trend.…”
Compared to beta-cyclodextrins (beta-CD), hydroxypropyl-beta-cyclodextrins (HP-beta-CD) are a more popular material used to prepare inclusion complexes due to their superior solubility and intestinal absorption. In this study, oleuropein (OL) inclusion complexes with beta-CD (beta-CD:OL) and HP-beta-CD (HP-beta-CD:OL) were prepared and the formation of inclusion complexes was validated by IR, PXRD, and DSC. A phase solubility test showed that the lgK (25 °C) and binding energy of beta-CD:OL and HP-beta-CD:OL was 2.32 versus 1.98, and −6.1 versus −24.66 KJ/mol, respectively. Beta-CD:OL exhibited a more powerful effect than HP-beta-CD:OL in protecting OL from degradation upon exposure to light, high temperature and high humidity. Molecular docking, peak intensity of carbonyls in IR, and ferric reducing power revealed that beta-CD:OL formed more hydrogen bonds with the unstable groups of OL. Both inclusion complexes significantly enhanced the solubility, intestinal permeation and antioxidant activity of OL (p < 0.05). Though HP-beta-CD:OL had higher solubility and intestinal absorption over beta-CD:OL, the difference was not significant (p > 0.05). The study implies that lower binding energy is not always associated with the higher stability of a complex. Beta-CD can protect a multiple-hydroxyl compound more efficiently than HP-beta-CD with the intestinal permeation comparable to HP-beta-CD complex.
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