Two-photon fluorescent probe for hydrogen sulfide based on a red-emitting benzocoumarin dye

Hydrogen sulfide (H₂S) is an endogenous gasotransmitter and plays intriguing biological roles. To study the biological role of H₂S, efficient fluorescent probes are in great demand. For imaging of H₂S in deep-tissue, a two-photon probe that emits in the red wavelength region is of choice to avoid the autofluorescence from intrinsic biomolecules. Here, we disclose such a probe, which, developed based on an acetyl benzocoumarin fluorophore, can be excited at 900?nm under two-photon excitation and emit in the red region. The probe shows high reactivity, selectivity, and sensitivity in in vitro assays. Two-photon microscopic imaging of H₂S in HeLa cells aided by the probe demonstrates that it is potentially useful to study H₂S level changes in cells and tissues influenced by external stimuli.     

Sol-Gel Formation of Reticular Methyl-Silicate Materials by Hydrogen Peroxide Decomposition

A new method for the formation of reticular silicate and organically modified silicate is introduced. Monoliths were prepared by incorporating a few percent hydrogen peroxide in the sol-gel starting solution. For example, incorporation of 6–10% (v) hydrogen peroxide in base catalyzed sol-gel precursors of methyl-Ormosil yielded macroporous monoliths with a bi-modal pore size distribution. The average characteristic pore diameters were approximately 1.2 nm and 0.7 m, depending on the sol-gel precursors used and the preparation protocol. The specific surface area was approximately 160 m2/g, contributed mainly by the microporous structure. A similar preparation procedure without hydrogen peroxide yielded only fractured or powdery materials. Presumably, the decomposition of the hydrogen peroxide yielded microbubbles, which formed templates for the polycondensation reaction. SEM, nitrogen adsorption isotherms and small angle X-ray spectroscopy were used to characterize the reticular materials.     

Electrospray Ionization Mass Spectrometric Analysis of Aqueous Polysulfide Solutions

The speciation of polysulfides in aqueous solutions was investigated by electrospray – ion trap and electrospray – time of flight mass spectrometry. The pH dependence of the observed total dissolved polysulfides concentration followed the trend calculated based on reported thermodynamic constants. However, the observed species distributions were substantially different from those calculated based on thermodynamic coefficients derived by UV spectroscopy. Notably, large abundances of heptasulfide, octasulfide and nonasulfide species were observed throughout the pH range 6 to 11. The large molecular weight anions had not been reported before in aqueous solutions although indirect evidence had suggested their existence.     

Effect of the composition and structure of titanosilicas on their photocatalytic activity in the decomposition of methylene blue

A comparison is made of the catalytic activity of the titanosilicas produced by pyrogenic synthesis and by the deposition of TiO₂ on pyrogenic SiO₂ in the photocatalytic decomposition of methylene blue (MB). The deposited titanosilicas exhibit high catalytic activity in the decomposition of MB as a result both of textural features and of the presence mainly of the anatase phase in the deposited TiO₂ compared with the pyrogenic titanosilicas. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 1, pp. 23–28, January–February, 2006.     

Direct Electrical Wiring of Oxidoreductase Enzymes to Silicate Based Electrodes

Three types of reagentless glucose biosensor based on composite graphite-ormosil materials are described: (1) a redox modified silicate-graphite electrode doped with glucose oxidase, (2) a methyl silicate-graphite material doped with redox modified glucose oxidase, and (3) a methyl silicate and redox modified graphite composite material doped with glucose oxidase.     

Sol-gel derived ceramic-carbon enzyme electrodes: Glucose oxidase as a test case

Several types of amperometric biosensors comprised of immobilized glucose oxidase in chemically-modified ceramic-carbon matrices are compared. The electrodes are comprised of several building blocks each performing a specific function. Glucose oxidase is used to catalyze the bio-oxidation of glucose; carbon powder imparts conductivity and favorable electrochemical characteristics; the Ormosil network provides rigidity and porosity; and the organic modification of the Ormosil imparts controlled surface polarity. Additionally, hydrophilic chemical modifiers are incorporated in order to control the size of the wetted, electroactive layer; high dispersion of inert metal catalysts is used to enhance hydrogen peroxide oxidation and redox mediators may be co-immobilized when oxygen independent response is desirable. The electrodes can be prepared either in the form of thick supported film, useful for disposable electrodes or as bulk-modified, disk shape electrodes, which can be used as renewable surface electrodes.     

Lipase-catalysed stereoselective esterifications using gelatin-based hydrogels

A hydrogel stable in an organic solvent has been developed. This pseudo-solid aqueous gel (PAG) consists of only native gelatin and water, and has been used for immobilization of enzymes. A relatively high amount of gelatin is required in order to obtain stable gels. PAGs containing the enzyme Candida antarctica lipase (SP 525) were successfully used in catalysing the esterification of R/S-(±)-2-octanol and hexanoic acid in hexane. The conversions as well as the enantiomeric excess values of the product, R-(−)-2-octyl hexanoate, were high and comparable to those obtained with microemulsion-based gels. The PAGs containing immobilized lipase gave reproducible results and may be re-used several times. The gels are easy to prepare and use, non-toxic and biocompatible. The PAGs retain their integrity in organic solvents and may be used in preparative-scale synthesis of organic compounds.     

Stability of Colloidal Silica Modified by Macromolecular Polyacrylic Acid (PAA) – Application of Turbidymetry Method

The effect of anionic polyacrlic acid (PAA) adsorption on fumed silica (SiO₂) surface on suspension stability was studied. The turbidymetry method was applied to monitor the changes in the suspension stability (using apparatus Turbiscan Lab^Expert with cooling module TLAb Cooler). PAA macromolecules contain dissociable carboxyl groups, therefore, all measurements were carried out at three pH values: 3, 6 and 9. Analysis of obtained transmission and backscattering curves and Turbiscan Stability Indexes (TSI) allowed determination of the most probable mechanism of the stability of the studied systems. The PAA adsorption has the greatest impact on the silica suspension stability at pH 3 (significant improvement of its stability). On the other hand, the presence of polyacrylic acid at pH 6 causes a noticeable deterioration of system stability conditions. At pH 9, polymer minimally influences the stability of SiO₂ suspension.     

A Method for Estimating the Functionality of TiO2/Quantum Dot Multilayer Hybrid Structures Based on the Generation of Reactive Oxygen Species

Optics and Spectroscopy - A new technique for estimating the efficiency of electron transfer from a CdSe/ZnS quantum dot (QD) to TiO2 nanoparticles based on the generation of reactive oxygen...