Danuta Pentak

Effect of urea on serum albumin complex with antithyroid drugs: fluorescence study

Abstract Comparative study of the ligand effect on the conformational stability of human (HSA) and bovine (BSA) serum albumin was performed using fluorescence spectroscopy. Tryptophan fluorescence emission spectra of serum albumin in the presence of mercaptopyrimidine (MPI) were recorded at the excitation wavelengths of 280 and 295 nm. The quenching of the fluorescence of protein in the presence of MPI resulted from the interactions with the drug in the subdomain IIA of α-helix where Trp 214 is located. The unfolding process of serum albumin on increasing the concentration of urea (1÷8 M) was studied. It was suggested that the destabilization of serum albumin structure in the presence of increasing urea concentration runs probably through intermediate state at 4÷6 M urea. The binding and quenching constants MPI–HSA and MPI–BSA has been calculated and compared with those obtained under urea-denatured conditions. An unfolding of serum albumin, induced by urea (within the concentration range 1÷5 M), involved diminishing of binding constant by ∼27% for HSA and by ∼49% for BSA. When concentration of urea exceeded 6 M, the binding constant raised by 21 and 27% for HSA and BSA, respectively. Anti-denaturant action of MPI was shown.

Effect of temperature on liposome structures studied using EPR spectroscopy

The effect of temperature on liposome structures has been investigated by means of electron paramagnetic resonance spectroscopy with the use of the spin labelling technique. The EPR spectra were recorded on a Bruker EMX spectrometer at the X band in the temperature range 300–340 K. Liposomes were prepared from L?a?phosphatidylcholine dipalmitoyl (1,2?dihexadecanoyl?sn?glycerol?3?phosphocholine) 99% (DPPC), DL?a?phosphatidylcholine dimyristoyl (1,2?ditetradecanoyl?rac?glycerol?3?phosphocholine) 99% (DMPC) and cholesterol (5?cholesten?3s?ol) 99

Physicochemical properties of liposomes as potential anticancer drugs carriers. Interaction of etoposide and cytarabine with the membrane: spectroscopic studies.

The interactions between etoposide, cytarabine and 1,2-dihexadecanoyl-sn-glycerol-3-phosphocholine bilayers were studied using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR). These techniques have proven to be a very powerful tool in studying the structure and dynamics of phospholipid bilayers. In particular, DSC can provide information on the phase transition temperature and cooperativity of the lipid molecules in the absence and presence of the drug. Vibrational spectroscopy is well suited to the study of drug-lipid interactions, since it allows for an investigation of the conformation of phospholipid molecules at different levels in lipid bilayers and follows structural changes that occur during the gel to liquid-crystalline phase transition. NMR supported the determination of the main phase transition temperatures (TC) of 1,2-dihexadecanoyl-sn-glycerol-3-phosphocholine (DPPC). The main phase transition temperature (TC) determined by (1)H NMR is comparable with values obtained by DSC for all studied liposomes. The location of cytarabine and etoposide in liposomes was also determined by NMR. Atomic force microscopy (AFM) images, acquired immediately after sample deposition on a mica surface, revealed the spherical shape of lipid vesicles.

Alterations of furosemide binding to serum albumin induced by increased level of fatty acid

Localization of high and low affinity binding sites of furosemide in human serum albumin (HSA) as well as the influence of myristic acid on the drug binding to the albumin using fluorescence quenching method was investigated. Two independent classes of binding site in subdomain IIA of HSA structure were found. Alteration of protein affinity towards the drug and the participation of tryptophanyl and tyrosil residues in drug-albumin interaction for the determined binding sites were studied. It was concluded that association of myristic acid in its low affinity binding sites which corresponds to elevated fatty acid level in vivo, significantly decreases albumin affinity towards furosemide.

Binding of 6-propyl-2-thiouracil to human serum albumin destabilized by chemical denaturants

We compared the binding affinity of 6-propyl-2-thiouracil (PTU) with native and destabilized human serum albumin (HSA) as a model to assess the binding ability of albumin in patients suffering from chronic liver or renal diseases. Urea (U) and guanidine hydrochloride (Gu.HCl) at a concentration of 3.0M were used as denaturation agents. Increasing the concentration of PTU from 0.8x10(-5) to 1.20x10(-4)M in the systems with HSA causes a decrease in fluorescence intensity of the protein excited with both 280 and 295nm wavelengths. The results indicate that urea and Gu.HCl bind to the carbonyl group and then to the NH-group. To determine binding constants we used the Scatchard plots. The presence of two classes of HSA-PTU binding sites was observed. The binding constants (K(b)) are equal to 1.99x10(4)M(-1) and 1.50x10(4)M(-1) at lambda(ex)=280nm, 5.20x10(4)M(-1) and 1.65x10(4)M(-1) at lambda(ex)=295nm. At lambda(ex)=280nm the number of drug molecules per protein molecule is a(I)=1.45 and a(II)=1.32 for I and II binding sites, respectively. At lambda(ex)=295nm they are a(I)=0.63 and a(II)=1.54 for the I and II binding sites. The estimation of the binding ability of changed albumin in the uremic and diabetic patients suffering from chronic liver or renal diseases is very important for safety and effective therapy.

Study of the sulfonation of expanded polystyrene waste and of properties of the products obtained

Waste-expanded polystyrene (EPS) and virgin polystyrene (VPS) were converted into ion exchangers by chemical modification. For this purpose, we used silica sulfuric acid as the sulfonating agent and conducted sulfonation under heterogeneous conditions. For VPS, the influence of the quantity of the sulfonating agent, the temperature, and the reaction time on the product properties were studied. As it appeared, silica sulfuric acid simplifies the reaction in comparison with the conventional sulfonation methods. Fourier transform-infrared (FT-IR) spectra and elemental analysis revealed that products were cross-linked and the content of sulfonate groups in a polymer chain varied. Some of the yielded polymers exhibited good water absorption and cation-exchange properties. The ion-exchange capacity (IEC) for chosen products was also determined, and it turned out to be similar to the commercial resin. The batch method was used to study the purification of solutions of Zn2+ and Cu2+ by the obtained resins. The performed study proved the usefulness of waste PS derivatives for the water treatment process.

Influence of some physical properties of 5-fluorouracil on encapsulation efficiency in liposomes

The aim of this study is to encapsulate two drugs: 5-fluorouracil (5-FU) with the hydrophobic properties and 1-β-D-arabinofuranosylcytosine (Ara-C) with the amphiphilic properties into liposomes prepared by the modified reverse-phase evaporation method (mREV) from L-α-phosphatidylcholine dipalmitoyl (DPPC). We studied the thermotropic phase behavior of liposome entrapped 5-FU and Ara-C. It is known that the stability of liposomes depends not only on the method of chemical gradient loading, the use of membrane stabilizer such as sterols, but also on the phase transition temperature (Tc) of phospholipids, which undergoes an alteration after encapsulation of drugs to liposomes. The competition of these two drugs entrapped in liposomes was analyzed 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. The percent of encapsulation in DPPC/Ara-C/5-FU liposome obtained by the use of UV spectroscopy amounted 93.84 and 96.05% for 5-FU and Ara-C, respectively. Phase transition temperature Tc of liposomes containing Ara-C did not significantly change while for the liposomes containing 5-FU it increased in comparison with Tc of the reference liposomes formed from DPPC.

Chemical Recycling of Polystyrene. Sulfonation with Different Sulfonation Agents

In this study waste polystyrene foam and virgin polystyrene as a reference materials were converted by chemical reactions under heterogeneous conditions into useful products. Polymeric flocculants were obtained from polystyrene during the sulfonation with sulfuric acid as the sulfonating agent and Ag2SO4 as the catalyst. The influence of temperature and time of reaction on the properties of the products were studied. The products were successfully used as flocculants in the treatment of the waste water. Solid silica sulfuric acid was also used to convert polystyrene. In comparison with the conventional sulfonation methods this sulfonating agent simplifies the reaction and makes easier separation of products from acid and solvent. The obtained products were cross-linked and exhibited cation-exchange properties. The batch method was used to study purification of solutions of Zn2+ and Cu2+ by the yielded resins. The performed study proved the usefulness of waste polystyrene derivatives for water treatment process.

Thermotropic Phase Behavior of Liposome Entrapped 5-FU and LCV

The aim of this work was to encapsulate two drugs: 5-Fluorouracil (5-FU) with the hydrophobic properties and 5-Formyl-5,6,7,8-tetrahydropteroyl-L-glutamic acid calcium salt (leucovorin) with the hydrophilic properties into liposomes prepared by the modified reverse-phase evaporation method (mREV) from L-α-phosphatidylcholine dipalmitoyl (DPPC). The drugs are used in the anticancer multidrug therapy FLv (5-fluorouracil, leucovorin) and ELF (etoposide, leucovorin, 5-fluorouracil). 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. Liposomes are highly versatile structures for research, therapeutic and analytical applications. We concluded that the liposomes obtained by the mREV method may transport more than one drug simultaneously.

Synthesis, crystal structure, spectroscopic, and magnetic properties of a manganese(II) methoxyacetate complex [Mn(C6O6H10)(H2O)] n

A metal-organic coordination polymer, [Mn(C6O6H10)(H2O)] n (1), has been synthesized and characterized by elemental analysis, FT-IR spectroscopy, and single-crystal X-ray diffraction. Thermogravimetric analysis and EPR spectrum of the compound have also been studied. Light pink crystals of the complex are monoclinic, space group P21 /c, with a = 7.9444(16) Å, b = 9.0802(18) Å, c = 13.142(3) Å, β = 93.53(3)°, V = 946.2(3) Å3, Z = 4, and R 1 = 0.0212. The compound is mononuclear and contains six-coordinate ions bound to bi- and tridentate methoxyacetate molecules and water. Each manganese ion is connected with the neighboring manganese via carboxylate bridges forming a polymeric chain of [Mn(C6O6H10)] n and water. The 1-D manganese polymer chains are further hydrogen-bonded via the carboxyl groups and water to produce a 3-D extended network. The FT-IR spectrum from 4000 to 400 cm−1 region confirms the bonding of water. Decomposition reaction takes place in the temperature range 25–900°C in nitrogen. The temperature dependence of magnetic susceptibility reveals weak antiferromagnetic coupling interaction (J = −0.74 cm−1) between the Mn(II) sites.