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Tetracycline (TC) derivatives comprise a group of bacteriostatic antibiotics extensively used in human and veterinary medicine and in acquaculture, and as animal growth promoters due to their safe toxicological profile.1) More recently, they have been proposed as anti-amyloidogenic drugs since they can interfere with protein conformational changes and self-assemblies associated with protein misfolding and deposition diseases. 2-4)Despite their popular use, TC derivatives are highly unstable and some degradation products formed during the storage or normal use of the drugs are pharmacologically toxic or inactive compounds.5) Anhydrotetracycline (AHTC) is one of the major degradation products of TC that has been linked to several side effects of the drug, e.g., cutaneous phototoxicity 6) and Fanconi-type syndrome. 7) AHTC has also proven to be more toxic than TC against environmentally relevant bacteria. 8)AHTC can be produced by dehydration in acid media, 5,8) by photolysis in mild reducing conditions 6,9,10) or during high-temperature treatments.11) Removal of a water molecule from the C5a-C6 positions of TC by treatment with warm mineral acid gives the anhydroderivative (Fig. 1).12) Dehydration leads to significant changes in aromatization and planarity of the tetracyclic moiety, 13,14) showing variations in potency, 15) mechanism of action 1) and lipophilicity 16,17) as compared to the parent compound. Changes in chemical configuration can also modulate the interaction of drugs with serum proteins. 18)Serum albumins are the main carriers of physiological metabolites and pharmacological drugs in blood. Protein binding has a significant impact on the pharmacokinetics and biological activity of drugs and modulates the toxicity of bound substances, attenuates adverse reactions and prolongs the in vivo half-life of therapeutic agents. 18-21)The facts outlined above prompted us to investigate the interaction of AHTC with bovine serum albumin (BSA) using three biophysical techniques. Binding affinity and number of interacting ligands were assessed by fluorimetric titration. . Drug binding was enthalpically and entropically driven and seemed to involve hydrophobic interactions. AHTC fluorescence enhancement and hypsochromic shifts observed upon binding suggested a low-polarity location excluded from water for the bound drug. Our data are useful for evaluating the biodisponibility of the pharmacophore and the dynamic distribution of the toxic derivative.

The main aspects related to the charge transfer reactions occurring at the interface between two immiscible electrolyte solutions (ITIES) are described. The particular topics to be discussed involve simple ion transfer. Focus is given on theoretical approaches, numerical simulations, and experimental methodologies. Concerning the theoretical procedures, different computational simulations related to simple ion transfer are reviewed. The main conclusions drawn from the most accepted models are described and analyzed in regard to their relevance for explaining different aspects of ion transfer. We describe numerical simulations implementing different approaches for solving the differential equations associated with the mass transport and charge transfer. These numerical simulations are correlated with selected experimental results; their usefulness in designing new experiments is summarized. Finally, many practical applications can be envisaged regarding the determination of physicochemical properties, electroanalysis, drug lipophilicity, and phase-transfer catalysis.