Alexander I. Petrov

Porous calcium carbonate microparticles as templates for encapsulation of bioactive compounds

The paper describes the preparation and characterisation of porous calcium carbonate microparticles with an average size of 5 µm and their use for encapsulation of biomacromolecules. The average pore size of about 30–50 nm enables size selective and time-dependent permeation of different macromolecules. Layer-by-layer adsorption of polyelectrolytes into these particles followed by core dissolution leads to formation of interconnecting networks (matrix-like structure) made of polyelectrolyte complexes. The structure can be used for accumulation of bio-macromolecules, mainly proteins. Besides the inter-polyelectrolyte structure templated on porous CaCO3 microparticles the microgel particles (“ghost”) can also be made inside by complexing alginate and calcium. The adsorption of biomacromolecules inside the porous calcium carbonate particles is presumably regulated by electrostatic interactions on the microparticle surface within pores and protein–protein interactions. Protein adsorption into CaCO3 microparticle voids together with layer-by-layer assembly of biopolymers provide a way for fabrication of completely biocompatible microcapsules envisaging their use as biomaterials.

Protein-calcium carbonate coprecipitation: A tool for protein encapsulation

A new approach of encapsulation of proteins in polyelectrolyte microcapsules has been developed using porous calcium carbonate microparticles as microsupports for layer‐by‐layer (LbL) polyelectrolyte assembling. Two different ways were used to prepare protein‐loaded CaCO3 microparticles: (i) physical adsorption – adsorption of proteins from the solutions onto preformed CaCO3 microparticles, and (ii) coprecipitation – protein capture by CaCO3 microparticles in the process of growth from the mixture of aqueous solutions of CaCl2 and Na2CO3. The latter was found to be about five times more effective than the former (∼100 vs ∼20 μg of captured protein per 1 mg of CaCO3). The procedure is rather mild; the revealed enzymatic activity of α‐chymotrypsin captured initially by CaCO3 particles during their growth and then recovered after particle dissolution in EDTA was found to be about 85% compared to the native enzyme. Core decomposition and removal after assembly of the required number of polyelectrolyte layers resulted in release of protein into the interior of polyelectrolyte microcapsules (PAH/PSS)5 thus excluding the encapsulated material from direct contact with the surrounding. The advantage of the suggested approach is the possibility to control easily the concentration of protein inside the microcapsules and to minimize the protein immobilization within the capsule walls. Moreover, it is rather universal and may be used for encapsulation of a wide range of macromolecular compounds and bioactive species.

Carbonate microparticles for hollow polyelectrolyte capsules fabrication

Calcium, cadmium and manganese carbonate crystals were used as core material for fabrication of hollow polyelectrolyte capsules by means of the Layer-by-Layer assembly. The use of inorganic templates is a way of fabrication of clean capsules, which is essential for basic research and is a significant step towards their biocompatibility. The ways of particle and capsule fabrication and characterization are described. Scanning electron microscopy (SEM)-Energy dispersive X-ray spectroscopy (EDX) measurements proved the purity of the hollow capsules from the core material. The capsules obtained were characterized by scanning force microscopy, and confocal fluorescence microscopy.

Multilayer films containing immobilized nucleic acids. Their structure and possibilities in biosensor applications

Langmuir-Blodgett (LB) and film technologies based on electrostatic attraction self-assembly (SA) are shown to be useful for immobilization of nucleic acids (DNA, polynucleotides) onto solid supports in sensor devices. The nucleic acids were immobilized in complexes with cationic surfactants (for LB) and polycations (for SA). Infrared spectral studies showed that DNA unfolds in multilayer LB films with octadecylamine and conserves its double helical structure in the LB films with dioctadecyldimethylammonium and in the SA films with polyallylamine, polyethylenimine and poly-L-lysine. Atomic groups and the types of interactions determining the complex formation of these films have been identified. The hydration of LB and SA films was studied to find out binding sites of water molecules and to evaluate the flexibility of nucleic acid compounds in the multilayer films. The possibilities of biosensor applications of these LB and SA films were monitored on binding of specific reagents for DNA by DNA-containing films and mononucleotides by a complementary single-stranded polynucleotide immobilized on a positively charged solid support.

Spectroscopic study of thin multilayer films of the complexes of nucleic acids with cationic amphiphiles and polycations: their possible use as sensor elements

Abstract Two types of multilayer films of DNA complexes with amphiphilic molecules of dioctadecyldimethylammonium (DODA) and polycations: polyallylamine, polyethylenimine and poly- l -lysine were obtained using Langmuir-Blodgett (LB) technique and successive alternating adsorption method (SA films) correspondingly. Structure and affinity properties of the films were studied by IR, UV-VIS and CD spectroscopy. IR spectral criteria of polynucleotide conformation [M. Ghomi, R. Lettelier, J. Liquier, E. Taillandier, Int. J. Biochem., 22 (1990) 691–699] show DNA conserves its double helical structure in all the films. Low frequency shift of IR absorption bands of DNA in the films indicates electrostatic interaction between PO 2 - groups of DNA and positively charged groups of polycations or polar heads of DODA molecules. Water molecules were found to penetrate into all types of the films and to bind with DNA hydration centers (phosphatic groups). In contrast to usual DNA films, the hydration in the LB and SA films does not initiate B-to-A conformational transition of double helix. The binding of DNA-contained films with different DNA-intercalated molecules, including antitumor drug—daunomycin, has been also studied.

Mechanism of Nitric Oxide Oxidation Reaction (2NO + O2 → 2NO2) Revisited.

The reaction between molecular oxygen and two nitric oxide(II) molecules is studied with high-level ab initio wave function methods, including geometry optimizations with coupled cluster (CCSD(T,full)/cc-pCVTZ) and complete active space with second order perturbation theory levels (CASPT2/cc-pVDZ). The energy at the critical points was refined by calculations at the CCSD(T,full)/aug-cc-pCVTZ level. The controversies found in the previous theoretical studies are critically discussed and resolved. The best estimate of the activation energy is 6.47 kJ/mol.

The role of NH3 and hydrocarbon mixtures in GaN pseudo-halide CVD: a quantum chemical study

The prospects of a control for a novel gallium nitride pseudo-halide vapor phase epitaxy (PHVPE) with HCN were thoroughly analyzed for hydrocarbons–NH3–Ga gas phase on the basis of quantum chemical investigation with DFT (B3LYP, B3LYP with D3 empirical correction on dispersion interaction) and ab-initio (CASSCF, coupled clusters, and multireference configuration interaction including MRCI+Q) methods. The computational screening of reactions for different hydrocarbons (CH4, C2H6, C3H8, C2H4, and C2H2) as readily available carbon precursors for HCN formation, potential chemical transport agents, and for controlled carbon doping of deposited GaN was carried out with the B3LYP method in conjunction with basis sets up to aug-cc-pVTZ. The gas phase intermediates for the reactions in the Ga-hydrocarbon systems were predicted at different theory levels. The located π-complexes Ga…C2H2 and Ga…C2H4 were studied to determine a probable catalytic activity in reactions with NH3. A limited influence of the carbon-containing atmosphere was exhibited for the carbon doping of GaN crystal in the conventional GaN chemical vapor deposition (CVD) process with hydrocarbons injected in the gas phase. Our results provide a basis for experimental studies of GaN crystal growth with C2H4 and C2H2 as auxiliary carbon reagents for the Ga-NH3 and Ga-C-NH3 CVD systems and prerequisites for reactor design to enhance and control the PHVPE process through the HCN synthesis.

Integrability Conditions, Income Distribution, and Social Structures

Integrability conditions are the most important characteristics of the structure of consumer demand. The situation where the conditions are violated is discussed. The origin of the conditions is analyzed in the framework of the neoclassical theory of consumer demand. It is proved that the integrability of consumer demand functions is related to the existence of a Bergsonian welfare function for an appropriate distribution of income.

The Numerical Scheme for the Basset Type Integro-Differential Equation in Hydrodynamics

A high-order precision numerical scheme was proposed for the Basset kernel integrals and the Basset type integro-differential equations that often arise in hydrodynamics. The scheme was tested on a model integral and on a real problem of particle focusing in a standing acoustic wave in liquid. The scheme showed around 2 orders higher speed of integral estimation compared with the existing analogs. The obtained results show that the integral can be approximated with high order of precision and the real problem is simulated well by the proposed scheme. A variable step technique was used to increase the precision of integro-differential equation simulation even more by eliminating the discrepancy at the very start of the simulation. The proposed numerical scheme may found its applications in many biological and medical problems related to acoustophoresis or in particle sedimentation simulations.

Aluminum derivative peroxides in the (t-BuO)3Al–2t-BuOOH catalytic system as a source of electron-excited dioxygen: a quantum chemical study on a model

The quantum chemical study of the MeOOH/(MeO)3Al model system has been carried out in order to predict the mechanism of the catalytic decomposition of t-BuOOH under mild conditions for the t-BuOOH/(t-BuO)3Al system being a powerful synthetic tool for selective oxidation. To elucidate the chemical excitation of O2 eliminated in the catalytic reaction and to predict the electronic state of O2, the topology of the potential energy surface (PES), the structures of intermediates and transition states, the activation and reaction energies were obtained at the B3LYP/cc-pVTZ theory level. It was shown that the peroxide, (MeO)2AlOOMe, corresponding to the experimentally obtained (t-BuO)2AlOOBu-t, is formed in the first step of the reaction. After that, in the main pathway, the aluminum-containing peroxide reacts with the second MeOOH molecule through the nucleophilic substitution of the second methoxy group forming the MeOAl(OOMe)2 diperoxide. The diperoxide rearranges to aluminum-containing ozonide MeOAlOOOMe. The ozonide isomerizes in the mononuclear-metal dioxygen intermediate (MeO)3Al·O2. The latter decomposes through the adiabatic ((MeO)3Al + O2(b1Σ+g)) and non-adiabatic ((MeO)3Al + O2(X3Σ−g)) pathways, which corresponds to experimental data about the incomplete conversion of O2 to O2(b1Σ+g). The generation of O2(b1Σ+g) was revealed by the analysis of the energy diagram calculated with the CCSD(T), CCSDT(Q), and CASSCF methods. It was suggested that the η1-(MeO)3Al·O2 and, thus, (t-BuO)3Al·O2 complexes are new sources of O2(b1Σ+g).