Sergei Yu. Zaitsev

Supramolecular assemblies of photochromic benzodithia-18-crown-6 ethers in crystals, solutions, and monolayersElectronic supplementary information (ESI) available: crystal data, data collection, and structure solution and refinement parameters. See http://www.rsc.org/suppdata/nj/b1/b110630a/

We studied the assembly of dithiacrown ether styryl dye (CSD) molecules in crystals, solutions, and films in the presence of metal cations. X-Ray diffraction data allowed us to conclude that the anion affects the supramolecular architecture of CSDs in the crystal, specifically, the type of stacking of the dye molecules. In solution, in the presence of Pb2+, CSD molecules with the betaine structure spontaneously form dimeric complexes consisting of two dye molecules and two metal cations, with a fixed mutual arrangement of the double bonds. The dimer complex is stable due to coordination between the anion substituent of one molecule and the metal cation located in the crown ether cavity of the other molecule. Irradiation of the dimer complexes leads to regio- and stereoselective [2 + 2]-cycloaddition, giving only one cyclobutane derivative of the eleven theoretically possible products. The other photoreaction studied for CSDs is reversible Z–E isomerization. Due to its specific structure, the betaine-type CSD is able to form the ‘anion-capped’ Z-isomer. Intramolecular coordination in the ‘anion-capped’ isomer enhances its stability and causes a sharp deceleration of its dark Z–E isomerization. The amphiphilic CSD forms relatively stable monolayers on distilled water and various aqueous salt subphases. The results obtained indicate that it is possible to distinguish between two types of the dye monolayer structures based on the presence of alkali or heavy metal cations in the aqueous subphase.

Thin films and assemblies of photosensitive membrane proteins and colloidal nanocrystals for engineering of hybrid materials with advanced properties

The development and study of nano-bio hybrid materials engineered from membrane proteins (the key functional elements of various biomembranes) and nanoheterostructures (inorganic colloidal nanoparticles, transparent electrodes, and films) is a rapidly growing field at the interface of materials and life sciences. The mainspring of the development of bioinspired materials and devices is the fact that biological evolution has solved many problems similar to those that humans are attempting to solve in the field of light-harvesting and energy-transferring inorganic compounds. Along this way, bioelectronics and biophotonics have shown considerable promise. A number of proteins have been explored in terms of bioelectronic device applications, but bacteriorhodopsin (bR, a photosensitive membrane protein from purple membranes of the bacterium Halobacterium salinarum) and bacterial photosynthetic reaction centres have received the most attention. The energy harvesting in plants has a maximum efficiency of 5%, whereas bR, in the absence of a specific light-harvesting system, allows bacteria to utilize only 0.1-0.5% of the solar light. Recent nano-bioengineering approaches employing colloidal semiconductor and metal nanoparticles conjugated with biosystems permit the enhancement of the light-harvesting capacity of photosensitive proteins, thus providing a strong impetus to protein-based device optimisation. Fabrication of ultrathin and highly oriented films from biological membranes and photosensitive proteins is the key task for prospective bioelectronic and biophotonic applications. In this review, the main advances in techniques of preparation of such films are analyzed. Comparison of the techniques for obtaining thin films leads to the conclusion that the homogeneity and orientation of biomembrane fragments or proteins in these films depend on the method of their fabrication and increase in the following order: electrophoretic sedimentation < Langmuir-Blodgett and Langmuir-Schaefer methods < self-assembly and layer-by-layer methods. The key advances in the techniques of preparation of the assemblies or complexes of colloidal nanocrystals with bR, purple membranes, or photosynthetic reaction centres are also reviewed. Approaches to the fabrication of the prototype photosensitive nano-bio hybrid materials with advanced photovoltaic, energy transfer, and optical switching properties and future prospects in this field are analyzed in the concluding part of the review.

Photosensitive supramolecular systems based on amphiphilic crown ethers

Abstract An amphiphilic crown-ether styryl dye was synthesized and its properties at the interfaces were investigated. This dye, which in monolayers interacts with some cations and shows reversible changes of the light reflection after photoactivation near the absorption maximum, is an excellent component of functional organized systems.

Polymer ultrathin films with immobilized photosynthetic reaction center proteins

Mixed monolayers of lipids with photosynthetic reaction center proteins (RCs) from Rb. sphaeroides and C. aurantiacus were studied and the optimum conditions for stable films fabrication were determined. The following synthetic: ACPE, TDA, PDA, DODL and natural lipids: PE, PC were used. The rate of polymerization of the mixed ACPE-RC and TDA-RC monolayers is lower than those for pure lipid-like monomers on the air/water interface but high enough for the fast preparation of the polymer films. The optical and photoelectrical measurements provide evidence for an orientation of RCs (from Rb. sphaeroides) on interface. Hydrophilic H-subunit in the mixed ACPE-RCs and DODL-RCs monolayers is preferentially oriented towards water as in the pure RC monolayers. Opposite orientation was found with TDA-RCs and PDA-RCs films. No preferential orientation was found for lipid-RCs (C. aurantiacus) monolayers probably because of the low asymmetry of hydrophobic subunits (M and L) of these RCs.

Functional Langmuir films with glucose oxidase

Abstract Adsorbed layers of glucose oxidase on an air—water interface were prepared and investigated. The enzyme is more strongly adsorbed on positively charged lipid monolayers than on zwitterionic ones and only slightly adsorbed on negatively charged monolayers of stearic acid, probably because of the total negative charge of the protein molecule in buffer solution at pH 7.0. It is found that the amount of protein at the air—water interface is two times higher than in the subphase solution and that glucose oxidase retains its enzymatic activity in adsorbed layers. The transfer of between one and ten lipid—protein monolayers onto Pt electrodes under 20–40 mN m −1 surface pressure by the Langmuir—Blodgett method was performed. As a result the biosensor was obtained with a measuring range of 0.5–5.0 mM glucose. The best electrode characteristics were found with glucose oxidase adsorbed on mixed monolayers of phosphatidylcholine/cetyltrimethylammonium bromide. The amperometric response was found to depend on the number of transferred lipid—protein monolayers and on the surface pressure at which the transfer was carried out.

Dynamic surface tension measurements as general approach to the analysis of animal blood plasma and serum.

Abstract This review summarizes a current state of knowledge regarding surface tension methods of the analysis of animal blood plasma and serum as the major biological liquids. The fundamental information on general properties of the biological liquids (animal blood, urea, milk, etc.) is important in many aspects: animal nutrition, health assessment, physiological control, quality of livestock production, etc. The comparison of the major methods of the static and dynamic surface tension (DST) measurements of various liquids is presented. The comprehensive analysis of some colloid properties of animal biological liquids, including the study of the DST parameters (surface tension values at particular time intervals, tilts of the tensiograms) and the protein–lipid–salt content, is proposed. Strong or medium positive (negative) correlations between DST and biochemical parameters (content of total and particular proteins, lipids, etc.) are obtained and discussed for a few animal groups (fillies, mares, stallions, bulls, heifers, pregnant and lactating cows) for the first time. The data obtained highlight the importance of the particular balances and vital functions of the main components in such an important biological liquid as blood plasma. The reliability of the correlations between the DST and the biochemical parameters of animal blood samples under normal and particular physiological conditions (age, gender, pregnancy, lactation period, etc.) is shown. The database of the DST values will be useful in fundamental areas (colloid and physical chemistry, bioorganic and biological chemistry, animal biology, and ecology), as well as in practice (animal medicine and biotechnology, dairy and meat production, etc.).

Study of biochemical reactions in thin organic films by means of evanescent optical wave

Abstract An optical biosensor has been developed for detection of pesticides, based on the evanescent optical wave technique. The concentration of the pesticide was measured in liquid. We specially originated a core complex of photosystem II film on a cheap disposable element. A setup on the basis of the Kretschmann arrangement was improved by using a computer-controlled angular scanning system. The detection concentration limits were 10−11 M for dinitrophenole and 10−10 M for paraoxon. The results obtained show the perspective of the integral method for detection of different kinds of pesticides at extremely low concentration levels of 0.1 ppb.

X-ray reflectivity analysis of Langmuir-Blodgett films of reaction center proteins from photosynthetic bacteria

Langmuir-Blodgett (LB) films of the reaction center protein-pigment complexes (RCs) isolated from photosynthetic bacteria Chloroflexus aurantiacus, Rhodobacter sphaeroides and Rhodopseudomonas viridis were prepared and investigated by small-angle X-ray reflectivity. The patterns obtained for the eight-monolayer (LB) films of the RCs from Rb. sphaeroides and Rps. viridis show well defined Kiessig fringes. This confirms the preparation of molecularly smooth (roughness less than 1.5 nm), flat RC films and allows us to estimate their thickness as 30.5 and 34.0 nm respectively. Well ordered RC deposition took place only onto the “front” side of the substrate, which faces the moving barrier in the Langmuir trough. X-ray reflectivity measurements of LB films of RCs from C. aurantiacus show no Kiessig fringes, independent of the side of the glass plate; this can be explained due to the formation of an unordered protein film during LB deposition. These effects are due to the high asymmetry of the RCs from Rb. sphaeroides and, especially, Rps. viridis in comparison with the RCs from C. aurantiacus.

Polymeric Langmuir films with glucose oxidase as prototype biosensors

Abstract Adsorbed layers of glucose oxidase on monolayers of specially synthesized N,N-dimethyl-N-cetylacetyl,methacryloylethyl ammonium bromide have been prepared and investigated. The enzyme is strongly adsorbed on a positively charged lipid monolayer and retains its enzymatic activity. The polymerization of the lipid layer by soft UV illumination at the interface increases the stability of the lipid-protein film and the reproducibility of the response measurements. A prototype biosensor is obtained by Langmuir-Blodgett transfer of one to ten lipid-protein monolayers onto Pt electrodes (at 20–40 mN m−1) with a measurement range of 0.4–4.0 mM glucose.

Mixed monolayers of valinomycin and dipalmitoylphosphatidic acid

The interactions of mixed monolayers of the hydrophobic peptide valinomycin and the negatively charged phospholipid dipalmitoylphosphatidic acid (DPPA) with alkali metal cations in the aqueous subphase were investigated. For this purpose, the isotherms of surface pressure, surface potential and Brewster reflectivity versus molecular area were measured for the mixed monolayers (valinomycin-DPPA) in the absence and presence of Na+ and K+ ions, respectively, in the aqueous subphase. Complete miscibility of the components in the monolayers is deduced from Brewster angle microscopy. Two additional states of valinomycin-DPPA monolayers were observed when K+ ions were present instead of Na+ ions in the aqueous subphase. This phenomenon correlates with the strong complexation between the valinomycin and K+ ions in the bulk. The negatively charged phospholipid (DPPA) influences the ability of valinomycin to bind cations at the interface.