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Amphiphilic cyclodextrin (ACyD) provides water-soluble and adaptable nanovectors by modulating the balance between the hydrophobic and hydrophilic chains at both CyD sides. This work aimed to design nanoassemblies based on nonionic and hydrophilic ACyD (SC6OH) for the delivery of a poor-water-soluble organotin(IV)-porphyrin derivative [(Bu3Sn)4TPPS] to melanoma cancer cells. To characterize the porphyrin derivatives under simulated physiological conditions, a speciation was performed using complementary techniques. In aqueous solution (≤ 20 μM), (Bu3Sn)4TPPS primarily exists as a monomer (2 in Figure 1), as suggested by the low static anisotropy (ρ ≈ 0.02) with a negligible formation of porphyrin supramolecular aggregates. MALDI-TOF spectra indicate the presence of moieties (i.e., [(Bu3Sn)3TPPS](-)) that are derivatives of the monomeric species. Spectrofluorimetry coupled with potentiometric measurements primarily assesses the presence of the hydrolytic [(Bu3Sn)4TPPS (OH)4](4-) species under physiological conditions. Nanoassemblies of (Bu3Sn)4TPPS/SC6OH were prepared by dispersion of organic films in PBS at pH 7.4 and were investigated using a combination of spectroscopic and morphological techniques. The UV-vis and emission fluorescence spectra of the (Bu3Sn)4TPPS/SC6OH reveal shifts in the peculiar bands of the organotin(IV)-porphyrin derivative due to its interaction with the ACyD supramolecular assemblies in aqueous solution. The mean size was within the range of 100-120 nm. The ξ-potential was negative (-16 mV) for the (Bu3Sn)4TPPS/SC6OH nanoassemblies, with an entrapment efficiency of approximately 67%. The intracellular delivery, cytotoxicity, nuclear morphology and cell growth kinetics were evaluated via fluorescence microscopy on A375 human melanoma cells. The delivery of (Bu3Sn)4TPPS by ACyD with respect to free (Bu3Sn)4TPPS increases the internalization efficiency and cytotoxicity to induce apoptotic cell death and, at lower concentrations, changes the cellular morphology and prevents cell proliferation.

The total solubility of three penicillin derivatives was determined, in pure water and NaCl aqueous solutions at different salt concentrations (from ∼0.15 to 1.0 mol L(-1) for ampicillin and amoxicillin, and from ∼0.05 to 2.0 mol L(-1) for (+)6-aminopenicillanic acid), using the shake-flask method for generating the saturated solutions, followed by potentiometric analysis. The knowledge of the pH of solubilization and of the protonation constants determined in the same experimental conditions, allowed us to calculate, by means of the mass balance equations, the solubility of the neutral species at different ionic strength values, to model its dependence on the salt concentration and to determine the corresponding values at infinite dilution. The salting parameter and the activity coefficients of the neutral species were calculated by the Setschenow equation. The protonation constants of ampicillin and amoxicillin, determined at different temperatures (from T=288.15 to 318.15K), from potentiometric and spectrophotometric measurements, were used to calculate, by means of the Van't Hoff equation, the temperature coefficients at different ionic strength values and the corresponding protonation entropies. The protonation enthalpies of the (+)6-aminopenicillanic acid were determined by isoperibol calorimetric titrations at T=298.15K and up to I=2.0 mol L(-1). The dependence of the protonation constants on ionic strength was modeled by means of the Debye-Hückel and SIT (Specific ion Interaction Theory) approaches, and the specific interaction parameters of the ionic species were determined. The hydrolysis of the β-lactam ring was studied by spectrophotometric and H NMR investigations as a function of pH, ionic strength and time. Potentiometric measurements carried out on the hydrolyzed (+)6-aminopenicillanic acid allowed us to highlight that the opened and the closed β-lactam forms of the (+)6-aminopenicillanic acid have quite different acid-base properties. An analysis of literature solubility, protonation constants, enthalpies and activity coefficients is reported too., (Copyright © 2012 Elsevier B.V. All rights reserved.)