Deposition behavior and photoelectrochemical characteristics of chlorophylla Langmuir-Blodgett films

The deposition behavior and photoelectric response characteristics of chlorophylla (Chla) monolayers and multilayers were investigated under various film fabrication conditions. Chla LB films were deposited onto quartz and pretreated ITO glass substrates under several fabrication conditions, including surface pressure and number of layers. The absorption spectra of Chla in a solution state and solid-like state (LB films) were fairly consistent with each other, and two absorption peaks were found at 678 and 438 nm, respectively. The prepared Chla LB films were set into an electrochemistry cell equipped with a Pt plate as the counter electrode, and the photoelectric response characteristics were obtained and analyzed relative to the light illumination. By considering the resulting photocurrents, the optimal fabrication conditions for Chla LB films were determined as 20 mN/m of surface pressure and 20 layers. The action spectrum of the Chla LB films was obtained in the visible region, and was found to be in good agreement with the absorption spectrum. The possible application of the proposed system as a constituent of an artificial color recognition device was suggested based on combining with the photoelectric conversion property of another lightsensitive biological pigment.     

Unusual photoelectrochemical behaviour of nanocrystalline TiO2 films

Although photooxidation of water and numerous other species which are part of reversible redox couples is poorly efficient at nanocrystalline TiO₂, conversely high photocurrent efficiencies are observed for the oxidation of various organic molecules.This is associated with the fact that in most cases photooxidation of organic molecules does not produce species able to act as electron scavengers. The behaviour of nanocrystalline TiO₂ photoelectrodes is clearly dominated by the indirect recombination or redox cycling where intermediates or products of the hole transfer act in turn as electron scavengers. These processes occur whatever the applied anodic bias showing that the actual potential in most of the nanocrystalline TiO₂ film is disconnected from that imposed to the conducting substrate.     

The biocatalytic effect of Halobacterium halobium on photoelectrochemical hydrogen production

Hydrogen gas can be produced electrochemically by leading a current through two electrodes immersed in a NaCl solution. Bacteriorhodopsin (BR) a protein found in the purple membrane of Halobacterium halobium, is known to pump protons across the membrane upon illumination. In this study, the effect of BR on photoelectrochemical hydrogen production was investigated. A batch type bio-photoelectrochemical reactor was designed and constructed. The photoelectrochemical hydrogen production experiments were performed with free H. halobium packed cells or immobilised H. halobium cells. The cells were either immobilised in polyacrylamide gel (PAG) or on cellulose acetate membrane (CAM). Experiments were also performed with purple membrane fragments of H. halobium immobilised on cellulose acetate membrane. It was found that the presence of bacteriorhodopsin (BR) in the reactor enhances the hydrogen production rate upon illumination. Immobilisation increased the amount of hydrogen produced per mole of BR. Compared to control experiments without BR, the power requirement of the photoelectrochemical reactor per amount of hydrogen produced decreased fourfold when purple membrane fragments immobilised on CAM were used. The presence of BR regulates the pH of the system, increases the hydrogen production rate and causes light-induced proton dissociation, which lowers the electrical power requirement for the electrochemical conversion.     

Conduction and photoelectrochemical properties of monomeric and electropolymerized tetraruthenated porphyrin films.

The influence of the preparation method on the structure, conduction and photoelectrochemical properties of monomeric and polymeric tetraruthenated porphyrin films on ITO glass and nanocrystalline TiO2 has been investigated. The films were characterized by STM, MAC mode SFM, cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and combined electro-/photoelectrochemical techniques. The electronic diffusion coefficient D(e)C(m)2 of the films differed by three to four orders of magnitude depending on the procedure employed for the deposition process. The photoelectrochemical properties were evaluated either: by depositing the films directly on transparent ITO electrodes, under an applied bias potential and presence of O2 as electron acceptor; or by depositing the porphyrin material on nanocrystalline TiO2 in a Gr?tzel-type cell. In the first case the porphyrin films exhibited a typical p-type semiconductor behavior described by a Schottky junction model, while in the second the films behaved as a sensitizer of an n-type semiconductor. The photoelectrochemical properties of the porphyrin films and their performance as sensitizer in Gr?tzel-type cells were found to be strongly dependent on the conductivity and packing characteristics of the material. Semi-empirical calculations were performed by modified MM2 and ZINDO/S methods, in order to simulate the packing and electronic structures of the tetraruthenated porphyrin.     

Optical and photoelectrochemical properties of Langmuir films of a Zn-complex of ethioporphyrin II

The optical and photoelectrochemical properties of Zn ethioporphyrin II (ZnEP) Langmuir films deposited on an SnO2-optically transparent electrode were investigated. Absorption and fluorescence spectra were utilized to control the film structure. The main three factors, in our opinion, act on the photovoltage, namely, film thickness, ZnEP aggregate formation and the total ZnEP concentration in the monolayer. It was shown that the photopotential decreases as the amount of ZnEP aggregates in the film decreases, and the photopotential increases with surface pressure transferred to the SnO2 layer; the maximum photopotential is registered in films consisting of three and five layers.     

Photovoltaic effect in pigment films in contact with an electrolytes. V. Theory of the Becquerel photovoltaic effect in porous films of phthalocyanine]

In accordance with literature and our experimental data a theoretical analysis of the model system metal-porous film of the pigment-electrolyte was carried out at stationary illumination in the regimes of photocurrent and photopotential. The main properties and positions of the model are supported experimentally. Specific behaviour of the photovoltaic system considered resides in the discovered dependence of the transfer mechanism on the value of catode potential of the electrode.     

Electrostriction and dynamics of solid supported lipid films

This review reports the significance of bilayer lipid membranes on a solid support (sBLM) for the construction of biosensors. The methods of formation of lipid membranes on different solid supports including different metals (silver, gold, stainless steel), agar and conducting polymers are presented. Several examples of the application of electrostriction and dielectric relaxation methods for the study of mechanical properties and dynamics of solid supported bilayers have been shown. We demonstrated that these methods are useful for determination of the binding of enzymes and antibodies to sBLM, for the study of hybridization of nucleic acids on membrane surfaces and for the study of physical properties of modified supported membranes.     

Dynamic mechanical properties of solid films of deoxyribonucleic acid

Solid films of deoxyribonucleic acid (DNA) from salmon testes were prepared by a solvent-casting method. The thermal molecular motion of the DNA film was examined by dynamic mechanical analysis (DMA). Four absorption peaks and one shoulder of the loss modulus were observed in the temperature domain from approximately 150 to 490 K. To assign these, thermal analysis employing thermogravimetry (TG) and differential thermal analysis (DTA) was used in conjunction with ultraviolet (UV)-visible and Fourier-transform infrared (FT-IR) spectroscopy. It seems most likely that, in order of increasing temperature, they are a B(I)→B(II) conformational transition, a relatively large-scale movement associated with water molecules, water evaporation, thermal denaturation of DNA, and a glass transition.     

The effect of potentiating factors on the bradykinine effect in vitro]

Bradykinin potentiating factors from the venom of Bothrops jajaraca and Agkistrodon halys blomhoffii potentiate the action of bradykinin at several smooth muscles. This potentiation is specific for bradykinin and has to be distinguished from an unspecific potentiation. The potentiation induced by BPF is not due to an indirect cholinergic mechanism or to a kininase inhibition in vitro. The results suggest that there would be an allosteric transition of the bradykinin receptor.     

The effect of plasmin on kallikreinogen]

The effect of purified plasmin preparation on kallikreinogen isolated from rat blood plasma was studied by chromatography on DEAE-Sephadex. Plasmin was shown to affect kallikreinogen to form an active enzyme--kallikrein. The dependence of the activation degree on the plasmin activity and incubation time was studied. Evidence was found for the absence of Hagemann factor in the reaction medium, which excludes the possibility of indirect action of plasmin on kallikreinogen through the Hagemann factor fragments formed.     

Tyrosine hydroxylase activity in two-dimensional monomolecular films]

The activity of a neurospecific enzyme of tyrosine hydroxylase (TH) in monomolecular films formed onto solid surface was studied. The data obtained show that the formation of two-dimensional films onto negative-charge surfaces by the Langmuir-Schafer technology does not lead to the inactivation of the enzyme. Neuroleptic trifluoperazine increased the activity of TH. Monomolecular films of TH may be used as a sensitive element of biosensors for primary monitoring of neuroleptic-like compounds.     

The extracorporeal immunostimulating effect of terrilytin in staphylococcal infection]

The intravenous injection of terrilytin-treated lymphocytes into rats infected with staphylococci enhances the formation of staphylococcal alpha antitoxin in the animals and the development of immune response to T-dependent antigen, such as sheep red blood cells (SRBC), but produces no effect on the development of immune response induced by T-independent antigen (lipopolysaccharide). Terrilytin-treated lymphocytes induce the release of the factor promoting the development of immune response to staphylococcal antigens and SRBC by spleen cells, incapable of adherence to plastic, but have no influence on the development of immune response to lipopolysaccharide in rats infected with staphylococci. At the same time in such rats spleen cells adhering to plastic take part in the transfer of signals from terrilytin-treated lymphocytes to nonadhering spleen cells of recipients.     

Controlling the reflection wavelength of iridescent solid films of nanocrystalline cellulose

Nanocrystalline cellulose (NCC) self-assembles in suspension to form iridescent chiral nematic films upon drying that can reflect circularly polarized light at specific wavelengths. Ultrasound treatment has now been found to increase the chiral nematic pitch in suspension and red-shift the reflection wavelength of NCC films as the applied energy increases. Sonication and electrolyte addition combined allow the reflective properties of the film to be predictably tuned. The effects of sonicating an NCC suspension are cumulative and permanent. Suspensions sonicated with different energy inputs may be mixed to give an NCC film having a reflection band intermediate between those obtained from the individual suspensions. The data suggest that the ultrasound-induced red-shift is electrostatic in nature.     

The effect of electric fields on brain cephalin and lecithin films

Summary The effect of a direct-current electric field on cephalin and lecithin films was measured using infrared spectral techniques. The intensities of the spectral bands assigned to the vibrations of the phosphate and the fatty acid chain increased to a maximum as the applied potential was increased. These changes were observed only with brain cephalin and brain lecithin films and not with synthetic lipid films. These observations may be due to changes in the alignments of the phosphate and base dipoles in the lipid molecule as the applied field is changed. The electric field strengths at which the maximum intensities of the spectral bands are observed increase as the thickness decreases. Extrapolation to the thickness of the nerve membrane yields a value of the field strength that is much larger than is to be expected in the neuron. This suggests that only the phosphate group and the hydrocarbon chain change conformation during the passage of the nerve impulse.Presented in part at the First Meeting of the International Society for Neurochemistry, 1967, and the 156th Meeting of the American Chemical Society, 1968.     

The photosynthetic partial reactions involved in photoelectrochemical current generation by thylakoid membranes

Summary A thylakoids containing photoelectrochemical cell was used to monitor the photocurrent under photentiostatic mode using specific electron donnors and acceptors, and inhibitors of electron transfer. It is shown that both photosystem I and II can generate a photocurrent under the appropriate conditions. The photocurrent was also monitored in the absence of oxygen evolution thus suggesting a possible application for hydrogenase catalysed hydrogen production.Abbreviations Chl chlorophyll - DCIP 2,6-dichlorophenol-indophenol - DCBQ 2,3-dichlorobenzoquinone - DCMU 3-(3,4-dichlorophenyl)-1, 1-dimethylurea - DPC p-diphenylcarbazide - FeCN potassium ferricyanide