Bartłomiej Pałecz

Interactions between PAMAM dendrimers and bovine serum albumin.

Dendrimers are a new class of polymeric materials. They are globular, highly branched, monodisperse macromolecules. Due to their structure, dendrimers promise to be new, effective biomedical materials as oligonucleotide transfection agents and drug carriers. More information about biological properties of dendrimers is crucial for further investigation of dendrimers in therapeutic applications. In this study the mechanism of interactions between polyamidoamine (PAMAM) dendrimers and bovine serum albumin (BSA) was examined. PAMAM dendrimers are based on an ethylenediamine core and branched units are constructed from both methyl acrylate and ethylenediamine. We used three types of PAMAM dendrimers with different surface groups (-COOH, -NH(2), -OH). As BSA contains two tryptophan residues we were able to evaluate dendrimers influence on protein molecular conformation by measuring the changes in the fluorescence of BSA in the presence of dendrimers. Additionally experiments with a fluorescent probe 1-anilinonaphthalene-8-sulfonic acid (ANS) were carried out. The differential scanning calorimetry (DSC) was chosen to investigate impact on protein thermal stability upon the dendrimers. Our experiments showed that the extent of the interactions between BSA and dendrimers strongly depends on their surface groups and is the biggest for amino-terminated dendrimers.

Interaction between PAMAM-NH2 G4 dendrimer and 5-fluorouracil in aqueous solution

The formation equilibrium of poly(amidoamine) dendrimer (PAMAM-NH₂ G4) complex with an oncologic drug such as 5-fluorouracil (5-FU) in water at room temperature was examined. Using the results of the drug solubility in dendrimer solutions and the method of equilibrium dialysis, the maximal number of drug molecules in the dendrimer-drug complex and its equilibrium constant were evaluated. Solubility results show that PAMAM-NH₂ G4 dendrimer can transfer tens 5-fluorouracil molecules in aqueous solution. The number of active sites in a dendrimer macromolecule being capable of combining the drug, determined by the separation method, amounts to n=30 ± 4. The calculated equilibrium constant of the 5-FU-active site bonding is equal to K=(400 ± 120).

Thermochemical properties of l-α-amino acids in electrolyte–water mixtures

Abstract Dissolution enthalpies of l -α-alanine, dl -α-alanine, l -α-aminobutyric acid, l -α-valine, l -α-leucine, l -α-seryne and l -α-threonine in mixtures of water with NaCl, KCl and LiCl have been measured by calorimetry at 298.15 K. The enthalpic heterogeneuos interaction coefficients of the amino acid zwitterion with the electrolyte have been determined using the standard solution enthalpies of amino acid in water and in aqueous solution of electrolytes. The values of the resultant enthalpic pair interaction coefficients are interpreted assuming a criterion in the form of the effect of hydrophobic alkyl radicals of amino acids side chains on the interactions between the polar head of the amino acid and the dissociated electrolyte.

Studies on homogeneous interactions between zwitterions of severall-α-amino acids in water at a temperature of 298.15 K

Abstract Enthalpies of solution and dilution of L-α-aminobutyric acid, L-α-isoleucine, L-α-phenylalanine, L-proline and L-α-methionine in water at a temperature of 298.15 K have been measured. The values of dilution enthalpy were used to determine enthalpic homogeneous interaction coefficients which characterize the interactions between zwitterions of the examined L-α-amino acids in water. The effect of side substituents in a molecule of L-α-amino acids on the direct homogeneous interactions in water and the effect of these substituents on the surrounding water molecules have been discussed. Quantum chemical semiempirical calculations of the structure of L-a-aminobutyric acid and several of its hydrates were carried out.

Effect of inclusion of hydroxycinnamic and chlorogenic acids from green coffee bean in β-cyclodextrin on their interactions with whey, egg white and soy protein isolates

The aim of the study was to characterise the interactions of hydroxycinnamic and chlorogenic acids (CHAs) from green coffee, with isolates of proteins from egg white (EWP), whey (WPC) and soy (SPI), depending on pH and temperature. The binding degree was determined by liquid chromatography coupled to a diode array detector and an ultrahigh resolution hybrid quadruple-time-of-flight mass spectrometer with ESI source (LC-QTOF-MS/MS). As a result of binding, the concentration of CHAs in proteins ranged from 9.44-12.2, 11.8-13.1 and 12.1-14.4g/100g for SPI, WPC and EWP, respectively. Thermodynamic parameters of protein-ligand interactions were determined by isothermal titration calorimetry (ITC) and energetics of interactions at the atomic level by molecular modelling. The amount of CHAs released during proteolytic digestion was in the range 0.33-2.67g/100g. Inclusion of CHAs with β-cyclodextrin strongly limited these interactions to a level of 0.03-0.06g/100g.

Interactions of phosphorus-containing dendrimers with liposomes.

The influence of cationic phosphorus-containing dendrimers generation 3 and 4 on model DMPC or DPPC lipid membranes was studied. Measurements of fluorescence anisotropy and differential scanning calorimetry (DSC) were applied to assess changes in lipid bilayer parameters, including fluidity, anisotropy, and phase-transition temperature. Interaction with both hydrophobic and hydrophilic regions of the bilayer was followed by these methods. Dendrimers of both generations influence lipid bilayers by decreasing membrane fluidity. The results suggest that dendrimers can interact both with the hydrophobic part and the polar head-group region of the phospholipid bilayer. Higher generation dendrimers interact more strongly with model membranes, and the concentration, as well as the generation, is of similar importance.

Thermochemical and spectroscopic studies on the supramolecular complex of PAMAM-NH2 G4 dendrimer and 5-fluorouracil in aqueous solution

The equilibrium of the formation of polyamidoamine dendrimer (PAMAM-NH(2) G4) and an oncological drug, 5-fluorouracil (FU) in water at room temperature has been examined. Using calorimetric titration, the number of active sites in the dendrimer combining the drug molecules and the equilibrium constant of the dendrimer-drug complex were estimated. The addition of the drug to the dendrimer active sites is an exothermic process. This process is accompanied by a beneficial change in entropy. The number of drug molecules combined by the polymer was confirmed by means of (1)H NMR spectroscopy. (1)HNMR measurements show that the dendrimer macromolecule binds the drug molecules with superficial protonated or unprotonated amine groups.

Interaction of polyamidoamine (PAMAM) succinamic acid dendrimers generation 4 with human serum albumin

Dendrimers, a relatively new group of highly branched three dimensional polymers, are intensively investigated to use them in biomedical and physicochemical sciences. Their specific architecture gives them the ability to interact with many different types of molecules. In our studies the interaction between PAMAM succinamic acid dendrimers generation 4 (PAMAM-SAH G4) and human serum albumin (HSA) was examined. Experiments showed that a single molecule of a HSA can bind approximately 6 particles of dendrimers. The fluorescence studies demonstrated that dendrimers lead to a decrease in protein fluorescence but changes in fluorescence anisotropy were not observed. Alterations in the spectrum of circular dichroism indicated changes in the secondary protein structure. The results clearly show that this generation of dendrimers possesses a strong ability to interact with human serum albumin.

Dissolution enthalpy of glycine in aqueous solutions of bivalent metal electrolytes

Abstract Measurement of the dissolution enthalpies of glycine in aqueous solutions of MgCl 2 , CaCl 2 , SrCl 2 , BaCl 2 , Mg(NO 3 ) 2 and Ca(NO 3 ) 2 at 298.15 K have been undertaken. The enthalpic heterogeneous interaction coefficients of the glycine zwitterion with the dissociated electrolyte have been calculated using the standard enthalpies of solution of amino acid in water and in aqueous solution of electrolytes. The effect of the ion type and of the structure of glycine on the magnitude of the enthalpic interaction coefficients are discussed.

The enthalpies of interaction of glycine with some alkan-1-ols in aqueous solutions at 298.15 K

Enthalpies of dissolution of glycine (G) in aqueous solutions of methanol (MeOH), ethanol (EtOH), propan-1-ol (PrOH) and butan-1-ol (BuOH) at 298.15 K have been measured. The enthalpic pair interaction coefficients of glycine zwitterion and alkan-1-ol molecules were determined by using standard solution enthalpies of glycine in water and aqueous solutions of alkan-1-ols.