Calix[n]arenes (CX) are macrocyclic aromatic molecules, which originate from the coupling of phenols and aldehydes. The index [n] refers to the number of phenol aromatic cycles in the molecule. In a calixarene molecule, phenol subunits are bridged via methyl groups. This provides the characteristic vase-like shape of the CX molecule. Moreover, modification of the side groups of CX allows one to prepare tailor-made receptors with high affinity for specific target molecules1. Recently CX (n=6) sensitive to cytochrome c (cyt c) has been demonstrated2. Cyt c is small hemoprotein (M.w. 12.4 kDa) found in the intermembrane space of mitochondria. Under physiological conditions it is positively charged owing to lysine and arginine amino acid residues. Cyt c plays a dual role in living system. It participates in electron transport and is responsible for the activation of the apoptotic pathway through releasing from mitochondria into the cytosol. CX can be incorporated into the lipid films and this system may be useful for detection cyt c. The biosensor based on CX incorporated into the supported lipid membranes has been reported3. However, mechanism of cyt c interaction with CX is not yet known. G4 PAMAM (M.w. 14.1 kDa) has similar size like cyt c and is also positively charged. Therefore G4 can serve as a model of non-specific interactions. At the same time G4 is useful for drug delivery. Therefore analysis of G4 interaction with model membranes containing receptors is of high importance. We studied the interaction of cyt c and G4 PAMAM with CX incorporated into the large unilamellar vesicles (LUV, diameter 100 nm) composed of dimyristoylphosphatidylcholine (DMPC). We showed that with increasing concentration of CX the average size of LUV increased and zeta potential become more negative as it is suggested from dynamic light scattering experiments. Cyt c did not affect significantly the LUV size, bur reduced the negative zeta potential of CX containing vesicles. Similarly to cyt c G4 also reduced negative charge of CX containing LUV. G4 did not affect the size of unmodified LUV, however at c> 1 mM the average diameter of vesicles modified by CX substantially increased from 100 to approx. 500 nm which suggest vesicle aggregation. It is likely that main driving force of interaction cyt c and G4 with CX containing vesicles is negative charge of CX carboxyl groups.

Acknowlegements: This work was supported by Slovak Research and Development Agency (Contracts No. APVV-0410-10, LPP-0250-09 and SK-PL-0034-09) and Grant Agency VEGA (Project No.1/0794/10).

1.  Gutsche, C. D., Muthukrishnan, R. J. Org. Chem. 43 (1978), 4905-4906

2.  Oshima, T., Ishii, T., Baba, Y., Higuchi, H., Ohto, K., Inoue, K. Solv. Extr. Res. Dev. Japan 15 (2008), 89-98

3.  Mohsin, M.A., Banica, F-G., Oshima, T., Hianik, T. Electroanalysis 23 (2011) 1229 – 1235

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