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Abstract

Determination of the Formation Constant of the Inclusion Complex from a Naphthoquinone

Dpto de Farmacia, Facultad de Ciencias Químicas, U.N.C. Ciudad Universitaria, 5000-Córdoba, Argentina
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Author to whom correspondence should be addressed.
Molecules 2000, 5(3), 510-511; https://doi.org/10.3390/50300510
Published: 22 March 2000

Abstract

:
Inclusion complexation of 1 with HP-β-CD or HP-β-CD:PVP K30 in aqueous solution was spectroscopically studied and the formation constant for a 1:1 complex was determined from these measurements.

Introduction

Molecules 05 00510 i001
Previously we have demonstrated by means of phase solubility diagrams that hydroxypropyl-β- cyclodextrin (HP-β-CD) increases the aqueous solubility of 2-hydroxy-N-(3-methyl-5-ethyl-4- isoxazolyl)-1,4-naphthoquinone-4-imine (1) [1], a compound that has antibacterial and tripanosidal activity [2]. Also, we have demonstrated that the improvement in solubility of 1 can be further increased by adding 0.5% (w/v) of polyvinylpyrrolidone K30 (PVP K30) to the HP-β-CD solution.
In this work our aim is to determine the formation constants of the inclusion complex (Kc) between the HP-β-CD and the naphthoquinone.

Experimental

The Kc values were determined by the UV spectrophotometric method (Shimadzu UV 160 UV/visible spectrophotometer).

Results and Discussion

The UV-visible spectrum of 1 is affected in the presence of HP-β-CD or HP-β-CD:PVP K30. The absorption band around 280 nm shifted towards longer wavelengths (306 nm ) with increasing concentration of HP-β-CD together with an increase in the intensity of the absorption band located between 400 and 550 nm. These spectral changes allowed us to obtain the Kc value using the Scott’s equation: (a b)/d = 1/(Kc εc) + b/εc, which assumes a complex stoichiometry of 1:1, where a is the total molar concentration of 1, b is the total molar concentration of the complexing agent, εc is the difference of the molar absorptivities for free and complex 1 and d is the change in absorbance of 1 caused by addition of the complexing agent [3].
The Kc between 1 and HP-β-CD was also studied in buffer solutions (ionic strength of 0.5 M) and was observed that Kc increased with the increment of the pH (the pKa value of 1 is 8.19). Kc between 1 and PVP K30 was significantly lower than Kc between 1 and HP-β-CD, but its value increased mark- edly in presence of 5% (w/v) HP-β-CD.
On the other hand, no bigger changes than those observed for the absorption spectra of zero order could be noticed in the derivative spectra.

References and Notes

  1. Granero, G.; Longhi, M.; María, M.; de Bertorello. Influencia de la HP-β-CD y la PVP sobre la solubilidad acuosa de una naftoquinona; 8vo Congreso Argentino de Farmacia y Bioquímica In- dustrial; Bs As., Junio, 1999. [Google Scholar]
  2. Granero, G.; de Bertorello, M.M.; Briñón, M. J. Chem. Res. 1999, 110–111.
  3. Letellier, S.; Maupas, B.; Gramond, J. P.; Guyon, F.; Gareil, P. Analytica Chimica Acta 1995, 315, 357–363.

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MDPI and ACS Style

Granero, G.; Longhi, M.; De Bertorello, M.M. Determination of the Formation Constant of the Inclusion Complex from a Naphthoquinone. Molecules 2000, 5, 510-511. https://doi.org/10.3390/50300510

AMA Style

Granero G, Longhi M, De Bertorello MM. Determination of the Formation Constant of the Inclusion Complex from a Naphthoquinone. Molecules. 2000; 5(3):510-511. https://doi.org/10.3390/50300510

Chicago/Turabian Style

Granero, Gladys, Marcela Longhi, and María M. De Bertorello. 2000. "Determination of the Formation Constant of the Inclusion Complex from a Naphthoquinone" Molecules 5, no. 3: 510-511. https://doi.org/10.3390/50300510

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