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Abstract: EPR spectroscopy was applied to determine the binding site of chloro(triethylphosphine)gold(I), (ClAuPEt3), in bovine serum albumin (BSA). The EPR spectrum of the spin marker covalently bonded to the sulphydryl group of polypeptide chain shows the presence of two 3-maleimidoPROXYL populations which differ in their way of immobilization. The first population shows the spin marker with a strongly restricted rotation due to hydrogen bonds between the oxygen of the label agent nitroxyl group and hydrogen atoms of the polypeptide chain with possible participation of water. The second population contains the spin marker bound with Cys-34 sulphydryl group located outside the crevice between helices h2 and h3, weakly immobilized by water hydrogen bonds. The addition of ClAuPEt3 results in the changes of the shape of spin labeled albumin EPR spectra. The displacement of 3-maleimidoPROXYL is observed below ClAuPEt3:BSA molar ratio 0.5:1. It is possible that above this molar ratio another bonding of the displaced spin marker takes place, having a high freedom of movement. EPR spectra, recorded after dialysis, show displacement of 3-maleimidoPROXYL molecules and the competition between AuPEt3 and the spin marker to the mutual binding site with cysteine residue. [Copyright &y& Elsevier]

Abstract: The aim of this work was to encapsulate two drugs: 1-β-d-arabinofuranosylcytosine (Ara-C) with the amphiphilic properties and 5-fluorouracil (5-FU) with the hydrophobic properties into liposomes prepared by the modified reverse-phase evaporation method (mREV) from l-α-phosphatidylcholine dipalmitoyl (DPPC). Both drugs are used together in the anticancer multidrug therapy. We studied the competition for their encapsulation in liposomes by the use of two spectroscopies: 1H NMR and UV on the basis of the analysis of the signals of each drug in the liposome–drug system. We concluded that the mREV method allows us to obtain liposomes which may transport more than one drug simultaneously. The NMR and UV studies of the drug competitive encapsulation and transport in liposomes formed from DPPC by the mREV method should be the basis for the analysis of the changes which may occur in vivo. [Copyright &y& Elsevier]

Abstract: Pathologic structure of albumin is present in blood of uremic or diabetic patients. The defective binding of albumin can cause, among others, inhibition of the metabolism of amphipathic hormones and the enhancement of the toxicity of drugs. We aim to show the alteration of the binding site of 6-propyl-2-thiouracil (PTU) in bovine serum albumin (BSA) in the presence of urea and guanidine hydrochloride. This study shows that PTU has the tendency to interact within the hydrophobic domain IIA or IB of serum albumin and to quench the fluorescence of tryptophanyl side chains by the static and collisional quenching mechanism. For the binding to the native protein, two classes of binding sites are seen. In the first one, the binding constant is equal to KbI−9.6×104 M−1, and in the second class, the binding constant is KbII−7.1×103 M−1. For the binding to the denaturated serum albumin, only one class of the binding sites can be observed. The binding constants for BSA denatured with urea and Gu·HCl are lower and are equal to 2.2×104 M−1 and 3.5×104 M−1, respectively. Evaluation of the binding ability of serum albumin is also important in case of older people because weaker drug–protein interaction can result in the increase of drug concentration in the blood serum. [Copyright &y& Elsevier]

Abstract: The EPR and NMR spectroscopy was used to determine the structure and physicochemical properties of liposomes prepared from dl-α-phosphatidylcholine dimyristoyl (1,2-ditetradecanoyl-rac-glycerol-3-phosphocholine) (DMPC) by the modified reverse-phase evaporation (mREV). EPR study was carried out in the temperature range from 284 to 310K, i.e. below and above the phase transition temperature T c of DMPC. On the basis of EPR spectra of spin marker 2-(carboxypropyl)-4,4-dimethyl-2-tridecyl-3-oxazolidinyloxyl (5-DOXYL) incorporated into liposome, the parameters S (empirical order parameter), 2A max (line widths) and τ (rotational correlation time) were determined. Temperature and pH dependent structural changes of liposome were also described. 31P NMR study of the liposome in the temperature range from 340 to 350K allowed to suggest that the single-bilayered liposome were obtained. [Copyright &y& Elsevier]