Functionalization of polystyrene. III. Synthesis of polymeric thiol reagents

The synthesis of polymer-bound thiol reagents, supported on macroporous 4% divinylbenzene co-polymer (Amberlite XE-305), via three synthetic approaches is described: (i) Alkylation or acylation of XE-305 with 3-nitro-4-halogen-substituted benzyl chloride or benzoyl halide yielding 3-nitro-4-halobenzene-bound species, followed by substitution of the activated polymeric halogen atom with sulfur (see Scheme 1). (ii) Formation of a thiol ether by a direct substitution of an active polymeric halogen by reaction with benzylthiol, followed by chlorination, thiolation, and reduction (see Scheme 2). (iii) Attachment of a prepared tailor-made disulfide to aminomethyl function of a polymeric support, followed by reduction (see Scheme 3). The polymers were tested for their free-thiol content by 5, 5′-dithiobis(2-nitrobenzoic acid) (Ellman's reagent¹²) in DMF. Their thiolytic activity was investigated in the removal of 2-nitrophenylsulphenyl (Nps) group from Nps-protected amino acid (Scheme 4). Site-site interaction between the polymer-bound thiol with its activated halide precursor to yield polymeric sulfide during displacement reaction, and the interconversion of the polymeric thiols into polymeric disulfides at equilibrium or during reaction with Nps-amino acids, observed, and is attributed to the flexibility of the polymeric matrices.     

The dependence of the electronic conductivity of carbon molecular sieve electrodes on their charging states

The dependence of the electronic conductivity of activated carbon electrodes on their potential in electrolyte solutions was examined. Kapton polymer films underwent carbonization (1000 degrees C), followed by a mild oxidation process (CO(2) at 900 degrees C) for various periods of time, to obtain carbons of different pore structures. A specially designed cell was assembled in order to measure the conductivity of carbon electrodes at different potentials in solutions. When the carbon electrodes possessed molecular sieving properties, a remarkable dependence of their conductivity on their charging state was observed. Aqueous electrolyte solutions containing ions of different sizes were used in order to demonstrate this phenomenon. As the average pore size of the activated carbons was larger, their molecular sieving ability was lower, and the dependence of their conductivity on their charging state regained its classical form. This behavior is discussed herein.     

Modal series solution for an epidemic model

In this article, we generalize a recently proposed method to obtain an exact general solution for the classical Susceptible, Infected, Recovered and Susceptible (SIRS) epidemic mathematical model. This generalization is based upon the nonlinear coupling of two frequencies in an infinite modal series solution. It is shown that these series provide a nonstandard approach in order to obtain an accurate analytical solution for the classical SIRS epidemic model. Numerical results of the SIRS epidemic model for real and complex frequencies are included in order to test the validity and reliability of the method. This method could be applied to a wide class of models in physics, chemistry or engineering.     

Acousto-optical spectrum analysis of ultra-high-frequency radio-wave analogue signals with an improved resolution exploiting the collinear acoustic wave heterodyning

This article is devoted to the problem of improving the frequency resolution inherent in a parallel acousto-optical spectrum analysis via involving an additional nonlinear phenomenon into the data processing. In so doing, we examine possible application of the wave heterodyning to the real-time scale acousto-optical analysis of the frequency spectrum belonging to ultra-high-frequency radio-wave signals peculiar, for example, for radio-astronomy. The nonlinear process of wave heterodyning is realized through providing a co-directional collinear interaction of the longitudinal acoustic waves of finite amplitudes. This process, which is beforehand studied theoretically and investigated experimentally via the acousto-optical technique as well, allows us either to improve the frequency resolution of spectrum analysis at a given frequency range or to increase by a few times the current frequencies of radio-wave signals under processing. The first step along this way is connected with the experimental modeling of the acoustic wave heterodyning in solids via exploitation of the specific acousto-optical cell based on a liquid, which allows the simplest realization of a cell with the needed properties. Then, these theoretical and practical findings are used in our experimental studies aimed at creating a new type of acousto-optical cells, which are able to improve the resolution inherent in acousto-optical spectrum analyzer operating over ultra-high-frequency radio-wave signals. In particular, the possibility of upgrading the frequency resolution through the acoustic wave heterodyning is experimentally demonstrated using the cell made of lead molybdate crystal. The obtained results demonstrate practical efficiency of the novel approach presented.     

Silica-coated CdTe quantum dots functionalized with thiols for bioconjugation to IgG proteins

Quantum dots (QDs) have been increasingly used in biolabeling recently as their advantages over molecular fluorophores have become clear. For bioapplications QDs must be water-soluble and buffer stable, making their synthesis challenging and time-consuming. A simple aqueous synthesis of silica-capped, highly fluorescent CdTe quantum dots has been developed. CdTe QDs are advantageous as the emission can be tuned to the near-infrared where tissue absorption is at a minimum, while the silica shell can prevent the leakage of toxic Cd(2+) and provide a surface for easy conjugation to biomolecules such as proteins. The presence of a silica shell of 2-5 nm in thickness has been confirmed by transmission electron microscopy and atomic force microscopy measurements. Photoluminescence studies show that the silica shell results in greatly increased photostability in Tris-borate-ethylenediaminetetraacetate and phosphate-buffered saline buffers. To further improve their biocompatibility, the silica-capped QDs have been functionalized with poly(ethylene glycol) and thiol-terminated biolinkers. Through the use of these linkers, antibody proteins were successfully conjugated as confirmed by agarose gel electrophoresis. Streptavidin-maleimide and biotinylated polystyrene microbeads confirmed the bioactivity and conjugation specificity of the thiolated QDs. These functionalized, silica-capped QDs are ideal labels, easily synthesized, robust, safe, and readily conjugated to biomolecules while maintaining bioactivity. They are potentially useful for a number of applications in biolabeling and imaging.     

Development of Methods to Measure Carbon Isotope Ratios of Bacterial Biomarkers in the Environment

Abstract

The δ¹³C value of bacterial carbon is an important parameter in microbial ecology for studying the carbon flow within a microbial community and for the identification of ecological important strains involved in the mineralization of certain carbon pools in the environment. In our study, biomarkers were isolated from bacteria from a microbial consortium derived from two chemostats and δ¹³C values were measured. Similar isotope ratios between biomarkers such as fatty acids and outer membrane protein, biomass and substrate were observed. The δ¹³C analyses of outer membrane protein F of Pseudomonas and biomarker fatty acids were combined to follow bacterial assimilation of ¹³C labelled 4-chlorocatechol. This new approach was also used in the environment where soil samples were cultivated with different ¹³C traced substrates.

The isotopic analyses of bacterial biomarkers indicated that carbons of histidine were widely incorporated into bacterial biomarkers, in contrast to 4-chlorocatechol which was less often used as a substrate. Results indicate that by isolating bacterial biomarkers and measuring their δ¹³C values, activities of microbial communities in a complex environmental sample can be determined. This new method has the potential to elucidate individual carbon sources for individual bacterial taxa in microbial ecology.