Cyclodextrins are used as encapsulation agent for food additives, flavoring and vitamins. Cyclodextrins are receiving attention as suitable drug delivery systems because of their ability to subtly modify the physical, chemical, and biological properties of guest molecules through labile interactions by formation of inclusion and/or association complexes. Cavity size is the major determinant as to which cyclodextrin is used in complexation. The cavity diameter of �-cyclodextrins has been found to be the most appropriate size for compounds frequently used in tissue and cell culture applications. (RW)4-NH2 is a cationic antimicrobial peptide, rich in arginine and tryptophan residues. (RW)4-NH2 has been shown to inhibit the growth of biofilms of Escherichia Coli. Other gram positive and negative bacteria are being tested in different labs. In this study, we investigate the association between �-cyclodextrin and the antimicrobial peptide (RW)4-NH2 using Fourier transform infrared (FTIR) spectroscopy, UV visible, fluorescence, and atomic force microscopy (AFM). FTIR spectra of samples containing (RW)4-NH2-�-cyclodextrin showed a change in RW4 secondary structure, attributed to the presence of (RW)4-NH2-�-cyclodextrin complex. Absorption spectra indicated a strong interaction between (RW)4-NH2 and �-cyclodextrin, in agreement with IR data. Thermodynamic parameters involved in the complex formation (?G, ?H, ?S) were calculated from the UV visible data. The enhancement of the fluorescence intensity of (RW)4-NH2 in the presence of �-cyclodextrin suggests that a certain fraction of (RW)4-NH2 molecules in solution are in a more hydrophobic environment, which is inside the �-cycodextrin cavity. The formation constants of the complexes were also calculated from the fluorescence data using the modified Benesi-Hildebrand equation. AFM images of (RW)4-NH2 alone showed fibril-like structures at high concentration. AFM images of (RW)4-NH2-�-cyclodextrin system showed aggregates of micelle-like globules. Our data provide new insights into the activity mechanism of (RW)4-NH2 and may be useful for the design of (RW)4-NH2 delivery system.

Biophysical studies of the supramolecular complex between �-cyclodextrin and an antimicrobial peptide

247th National Meeting (2014)

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