A. V. Koshkin

Microwave-assisted solvent-free synthesis of the substituted spiroindolinonaphth[2,1-b][1,4]oxazines

Abstract The synthesis of the substituted spiroindolinonaphth[2,1-b][1,4]oxazines 3a–e is developed through the condensation of 2-methylene-1,3,3-trimethylindoline derivatives and 1-nitroso-2-naphthol under microwave irradiation. In the same conditions, in presence of morpholine the 6′-morpholinosubstituted compounds 4a, b, d, e are formed. The main advantages of the method are the short reaction time, solvent-free reaction condition, cleaner reaction products and the higher product yields in comparison with known methods of synthesis.

Vibronic structure of electronic absorption and fluorescence spectra of pyrene in the complex with β-cyclodextrin in the presence of nonpolar and polar solvents

The feasibility of using pyrene as a fluorescent probe in complexes cyclodextrin-pyrene-analyte in aqueous solutions was studied for several analytes (A) of different polarity. Bands that prove the formation of the complex Py2βCD were found for the first time in the UV-VIS spectrum of an aqueous solution of pyrene in the presence of β-cyclodextrin. A characteristic of a fluorescent probe is the ratio I3/I1 in the fluorescence spectrum, where I3 is the intensity of the third vibronic line at ∼800 cm−1, and I1 is the intensity of the 0-0 transition. The value of I3/I1 for Py2βCD is highly sensitive to the addition of an analyte with a concentration of several μM/L to the aqueous solution. Dependences of (I3/I1)/C on the function of the dielectric constant ɛ of the analyte fɛ= (ɛ − 1)/(2ɛ + 1) are divided into two straight lines with different slopes for nonpolar and polar solvents. Energies of insertion of analytes into Py2βCD were calculated by the quantumchemical PM3 method. An increase in (I3/I1)/C corresponds to the more thermodynamically stable complex 2APy2βCD.

Characteristic features of nile red fluorescence in transparent xerogels

A procedure for preparing transparent silica gels and xerogels has been developed and samples of these materials have been fabricated to investigate the effect of microenvironment on spectral and sensor properties of the Nile Red dye. Spectral properties of the dye in modified and unmodified gels and xerogels have been investigated using fluorescence spectroscopy. It has been found that these xerogels are permeable to volatile organic substances, and their potential use as fluorescent sensor material has been demonstrated.

Naphthalene vapor sorption by polymer nanoparticles with molecularly imprinted shells

The process of naphthalene adsorption from the gas phase by layers of core-shell polymer nanoparticles obtained with the use of molecular imprinting methods is studied by the fluorescent analysis method. Within the pseudo-second-order kinetic model of sorption, data on the rate constants of fluorescence change are obtained, primary regularities of the sorption process are determined, and the presence of selective recognition sites in the shells of nanoparticles is proven.

EPR and fluorescence study of molecular dynamics of lipids in bilayers adsorbed on porous silica gel

Lipid bilayers immobilized on highly porous silica gel monoliths (SLBs) have been proposed as templates for chemosensors. Procedures for preparation and characterization of SLBs have been developed and applied. Rotational dynamics and orientational ordering at different depths in a SLB membrane and, for comparison, in bilayer liposomes have been studied for the first time using n-PC phospholipid spin labels.

Sorption processes of styryl dyes dications with N-ammonioalkyl substituent of varying length on the surface of polystyrene submicroparticles

We have investigated the multilayer adsorption isotherms of styryl dyes (SDs) of pyridine series (dications) with active centers (COOH) of the surface of polystyrene colloidal particles in an aqueous solution, depending on the length of N-substituent and the particle diameter. A proposed model of sorption takes into account both the ion-exchange sorption mechanism (exchange of H+ ions to SD dications) and a phase equilibrium shift of SD solution to multilayer ionic condensate in the ionic diffusive layer near the electric charged surface of the particles if the concentration of the SD solution is high enough. Modeled sorption isotherms are in agreement with the experimental data.

Investigation of volatile aliphatic and aromatic amine detection using a fluorescent pH indicator ethyl eosin in polymer matrices

Changes in the fluorescence spectra (F) of ethyl eosin (EE) embedded into polymer matrices of different compositions, gas permeability, and polarity under the action of gaseous aliphatic and aromatic amines (dimethylamine (DMA), trimethylamine (TMA), and pyridine (Pyr)), depending on the pH and the structure of polymer matrix, were investigated. Organic methanesulfonic acid was used to adjust pH in a polymer matrix. Cellulose acetate-propionate (CAP), polyvinyl trimethylsilane (PVTMS), polyethylene oxide (PEO), and polyvinylpyrrolidone (PVP), as well as mesoporous silica gel microspheres, were used as polymer matrices. Absorption and fluorescence maxima of EE in solution and in most polymers are in the region of 505 nm and 550 nm, respectively. The maximum of EE fluorescence intensity increases in all polymer matrices except for PVP in the presence of amines, while the F decreases in the PVP matrix and silica gel microspheres. The fluorescence response to DMA is higher than to TMA and Pyr for all the polymers; the F response is two-phase in the case of Pyr: an increase in F followed by a decrease. Characteristic response times for different matrices change in a sequence: CAP < PVP < PEO < MS < PVTMS. These differences are probably due to the different contributions to the process of the analyte diffusion, its affinity to the polymer, and the internal polarity of the polymer matrix for different polymers.

Model of absorption of gaseous naphthalene by ordered layers of polymer submicroparticles with nanostructured shells

A new model describing the kinetics of absorption of naphthalene vapor from the atmosphere in three-ordered layers of polymer submicroparticles (400–450 nm) with both simple and porous (modified) shells and an impenetrable core was proposed. The experiment examined the layers of polymer particles made of poly(ethylene glycol dimethacrylatå) (PEGDM) containing various amounts of monolayers (2, 5, 10, and 20). The processing of the experiment using a physical model allowed one to obtain the rate constants of the naphthalene absorption by the polymer and the template pores of the particle shell. Based on these results, the effective thickness of the particle shell (about 15 nm) was estimated; the effective diffusion coefficient of the naphthalene in the polymer is D ≈ 0.2 nm2 s−1. The effective value of the energy barrier of the naphthalene sorption by the particle surface (about 4–5 kcal/mol) was calculated, which approximately corresponds to unsaturated hydrogen bond energy and may indicate the role of the adsorption layer of moisture on the particle surface. The efficiency of the model in describing the two-stage absorption of the analyte by the layers of submicroparticles with nanoporous shells was shown.