Department of the Physical Chemistry – Highlights from the Past and Prospects for Future Development [In Bulgarian]
Abstract. Some details of the research in thermodynamics of capillary systems, conducted at the Department of Physical Chemistry at Sofia University „St. Kliment Ohridski „in the years 1970 â€“ 1990, are presented in this article. The second part of the article analyzes some changes in research caused by major political changes in Europe and worldwide since 1990.
Keywords: Department of Physical Chemistry, University of Sofia, surface thermodynamics, capillarity, post-normal science
B.V. ToshevLog in to read the full text
Hard Spheres Model of the Atom
Abstract. The finite size effect of electron and nucleus is accounted for in the model of atom. Due to their hard sphere repulsion the energy of the 1s orbital decreases and the corrections amount up to 8% in Uranium. Several models for boundary conditions on the atomic nucleus surface are discussed as well.
Keywords: atom model, hard spheres, nuclei boundary conditions
R. TsekovLog in to read the full text
Complex Systems for Drug Transport across Cell Membranes
Abstract. Targeted drug delivery to specific tissues or cell compartments in the human organism is an advantageous route to overcoming multidrug resistance or reducing undesired side effects of pharmaceutics. Efficient specific targeting requires associating the drug with a carrier molecule. A multitude of compounds and assemblies have been tested as transporting moieties. This review summarizes the various classes of nanocarrier constructs, which have been proposed for transferring a class of potent chemotherapeutic agents, namely, anthracycline antibiotics through cell membranes. The building principles of the delivery systems are outlined and their pros and cons are discussed. Wherever available, the results from molecular simulations are presented. Special attention is paid to peptide-based systems in general and to a special type of peptides in particular â€“ the cell-penetrating peptides, which may be used as building blocks of new systems for targeted drug delivery.
Keywords: drug delivery systems, anthracycline antibiotics, doxorubicin, cell-penetrating peptides, nanoparticles, biodegradable polymers
N. Ivanova, Y. Tsoneva, N. Ilkova, A. IvanovaLog in to read the full text
Surface Functionalization of Silica Sol-Gel Microparticles with Europium Complexes
Abstract. The present contribution is focused on the relation preparation â€“ structure â€“ optical properties of hybrid silica powders containing Eu(III) complexes: SiO2:[Eu(ntac)3][pphendcn] and SiO2:[Eu(phen)2](NO3)3. New methods for surface functionalization of silica microparticles, based on adsorption of 1,10-phenantroline and [Eu(ntac)3][pphendcn], are proposed in the framework of preparation of red emitting hybrid composites with quantum efficiency 20 â€“ 50 %. The optical properties of rare earth ions incorporated in silica composites are used to explore the site symmetry (D2, C2v or lower) of the Eu3+ optical centers in the hybrid composites. Quantum yields of the investigated sol-gel micropowders and quantification of their optical spectra are presented. X-Ray diffraction patterns of the investigated hybrid composites are presented. A short overview of sol-gel technology as a method for preparation of functional nanomaterials is presented.
Keywords: silica, europium complexes, luminescence, sol-gel
N. Danchova, G. Ahmed, M. Bredol, S. GutzovLog in to read the full text
Study of Protein Modified Gold Nanoparticles in Bulk Phase and at Air/Water Interface
Abstract. The colorimetric assay based on the surface plasmon resonance of metal nanoparticles receives significant attention because of its simplicity, sensitivity and low cost. The preparation of stable suspensions of gold nanoparticles (GNPs) modified with proteins is a prerequisite for their use as an analytical tool for the colorimetric spectral analysis. A convenient experimental procedure for reproducible production of functionalized with Bovine serum albumin (BSA) GNPs is proposed. The functionalized GNPs were morphologically characterized by means of Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) and their properties were determined by UV-Vis spectroscopy. The Langmuir monolayers of GNPs/BSA were also studied by measuring the surface pressure-area (ï°-A) isotherms and the conditions for transferring the Langmuir â€“ Blodgett (LB) films on mica solid supports were found. The LB films were further characterized by AFM and TEM. The reported experimental protocols and procedures have potential for further applications for the development of biosensors for detection of enzyme activity.
Keywords: gold nanoparticles (GNPs), atomic force microscopy (AFM), transmission electron microscopy (TEM), bovine serum albumin (BSA), protein modified nanoparticles
A. Chanachev, P. Georgiev, Tz. Ivanova, K. BalashevLog in to read the full text
Parallel Stability Analysis of Membrane Lamellar Structures and Foam Films
Abstract. In the frames of the DLVO theory the root mean square amplitude of capillary waves in a thin liquid film is calculated and its dependence on some important physical parameters is unveiled. Two important models are considered: films with classical interfaces and films between lipid bilayers. The performed numerical analysis demonstrates essential difference in their behavior due to the different elastic properties of the film surfaces. It is shown that the film lifetime is significantly long at some â€˜magicâ€™ film radii.
Keywords: thin liquid films, lamellar structures, thickness fluctuations
N.G. Ivanova, R. TsekovLog in to read the full text
Interfacial Reorganization of Molecular Assemblies Used as Drug Delivery Systems
Abstract. The number of potential applications of nanosized molecular assemblies such as vesicles, nanocapsules, biodegradable polyester matrix and more complex structures in drug research and nanomedicine is rapidly increasing with the developed technologies to tune and control their bulk and mainly surface properties. For a better understanding of nanoparticle behavior at the membrane interfaces an in vitro study of the mechanisms of loss of mechanical stability and their reorganization on various membrane systems seems indispensable. By using the simplest convenient monolayer models the mechanisms of destabilization and reorganization of various classical or modified nanosized molecular assemblies spread or adsorbed on pure air/water interface or at the preformed model membrane were studied.
Keywords: vesicles, lipid nanocapsules, lung surfactants, spreading, model membrane monolayer
I. Panaiotov, Tz. Ivanova, K. Balashev, N. Grozev, I. Minkov, K. MirchevaLog in to read the full text
Anomalous Drainage of Nanofilms from Concentrated NaCl Solutions of Tetraethylene Glycol Octyl Ether (C8E4)
Abstract. The drainage of planar foam nanofilms, stabilized by tetraethylene glycol octyl ether (C8E4) in aqueous solutions of NaCl was studied. The experiments on foam nanofilm drainage were performed at three different NaCl concentrations â€“ 0.02 M, 0.2 M and 2 M. In each one of these salt solutions the variation of the surfactant (C8E4) concentration was within the range of 10-6 â€“ 10-3 M. It was established that at 0.02 M NaCl the nanofilms drain in accord with Reynolds equation. At 0.2 M NaCl small deviations from the theoretical predictions were observed in some cases. At 2 M NaCl the nanofilms drain substantially slower than the prediction of the Reynolds equation. In addition, it was found that the overall dependence nanofilm thickness versus time became linear instead of exponential one at 10-4 M and 10-3 M C8E4. The latter is unexpected results because it shows change in the very regime of drainage of the foam nanofilm.
Keywords: nanofilms, foam film drainage, thin liquid films, salt solutions, non-ionic surfactants
S.I. KarakashevLog in to read the full text
Kinetics of the Osmotic Process and the Polarization Effect
Abstract. Osmosis, i.e. the transport of fluids through a semipermeable membrane, has been investigated for more than a century, using open and closed osmotic devices. We have developed now a novel operative experimental approach, based on a controlled volume variation, to modify the rate of the osmotic process. The new method has been applied for the experimental studies of the evolution of osmotic pressure in aqueous solutions of low molecular weight solutes. Quantitative data about the solvent osmotic rate dependence on the relative solution volume variation have been generated. The dynamic aspects of the process frequently exhibit new specific effects. Such non-trivial effects are the maxima in the rates of solvent transfer established in the experiments. The attempt to interpret such maxima brought in the concept of a polarization effect in the near-membrane space: local dilution of solution, due to the influx of solvent, which in its turn raises a diffusion flux from the bulk. We consider the effects established here by using artificial semipermeable membranes to be of relevance for the biological processes, taking place in the real living cells and tissues.
Keywords: osmotic pressure, osmotic kinetics, concentration polarization
B.P. Radoev, I.L. Minkov, E.D. ManevLog in to read the full text
Wetting Behavior of Natural and Synthetic Therapeutic Pulmonary Surfactants
Abstract. The wetting properties of aqueous solutions of two therapeutic pulmonary surfactants (TPS) with respect to solid surfaces with different degree of hydrophobicity ï±w have been studied. A special procedure for hydrophobization of the SiO2-glass hydrophilic surface allows the preparation of hydrophobic solid surfaces with different ï±w. The contact angles of drops from a TPS solution onto SiO2-glass surfaces have been measured as a function of their ï±w. The completely hydrophilic SiO2-glass surface is essentially hydrophobized by the animal-derived TPS Curosurf as well as by the synthetic TPS CHF 5633. The hydrophobization depends on the surfactant concentration – the contact angles increase with increasing the Curosurf concentration C in the low concentration range, but they remain almost constant in a wide range of C > 90 Âµg/ml. Similar are the ï± (ï±w) curves for aqueous solutions of both TPS. The thickness h of the wetting thin liquid films from aqueous solutions of Curosurf as well as of CHF 5633 on SiO2-glass surfaces depends on ï±w of the solid surface. The h(ï±w) curves always pass a minimum. The h-values, as well as the h(ï±w) curve, are mainly determined by the balance of the positive (repulsive) steric and negative (attractive) hydrophobic disjoining pressures, which depend on the orientations and conformations of the molecules adsorbed on the wetting film surfaces from the very complicated multi-component aqueous solutions. Practically no significant difference in the wetting behaviour of the aqueous solutions of the natural TPS Curosurf and the synthetic TPS CHF 5633 has been established, however about 25% less Curosurf than CHF 5633 was needed to achieve almost the same wetting behaviour.
Keywords: pulmonary surfactant, therapeutic surfactant preparation, wetting behavior, contact angle, wetting liquid film
L. Alexandrova, M. Nedyalkov, D. PlatikanovLog in to read the full text