Chelating tendencies in the rows of polymeric sorbents and their copper(II) and lead(II) complexes

The physicochemical properties of chelating polymer sorbents (CPSs), derivatives of poly(styrene-2-hydroxy-〈1-azo-1′〉-2′-hydroxybenzene), are studied with respect to copper and lead ions. The following sorption parameters are determined: the optimum acidity, temperature, and duration; the sorption capacity of the sorbent (SCS); and stability constants of polychelates. Quantitative correlations are found between the dissociation constants (pK′ _a) of the analytical functional group (AFG) of the sorbent, and the pH₅₀ of chelation of the tested metals; between p K′ _a and the stability of the complexes (logβ); and between pK′_a and the charge of the oxygen atom of the complexing group (z); these correlations are intended for use in elucidating the effect of the structural features and acid-base properties of the AFG on the chemisorption parameters of copper(II) and lead(II). These correlations predict the physical-chemical properties of sorbents and the sorption parameters of trace elements for preconcentrating and separating them from biological, natural, and technical objects     

A physicochemical study of the sorption of lead: Correlations in a series of chelating polymer sorbents

The sorption properties of chelating polymer sorbents (CPSs), the derivatives of poly(styrene-2-oxy-azo-2′-oxybenzene), with respect to the lead ion are studied. The parameters of the sorption processes—optimum conditions of sorption (acidity, temperature, and time), the sorption capacities of sorbents, the possibility of desorption, and the stability constants of the chelated polymers—are determined. Quantitative correlations between p K′_OH of the functional analytical group (FAG) of the sorbent and σ _{o + p(p)} for ortho-and para-substituents, between p K′_OH and pH₅₀ for the formation of chelate complexes of lead, between p K′_OH and the stability of lead complexes (logβ), and between σ _{o + p(p)} and pH₅₀ for the formation of chelate complexes of lead are established with the aim of studying regularities of the influence of the structure and acid-base properties of FAGs on parameters of chemisorption of Pb²⁺. It is shown that the established correlations provide a means for quantitatively predicting physicochemical parameters of sorbents and the process of sorption of lead with the aim of targeted synthesis of CPSs and their use in the chemistry of polymer compounds and in the process of concentrating.     

Study of the chemical structures of the photo-cross-linking products between Tyr and the 5-azido-2-nitrobenzoyl residue

Irradiation of N-(tyrosyl)-N'-(5-azido-2-nitrobenzoyl)-1,2-diaminoethane (I) initiates chemical reactions that lead to different products depending on the experimental conditions. All of these products are attributed to the reactions of triplet 4-nitrobenzoyl nitrene (4NBN). The reactions of triplet 4NBN with the tyrosyl residue result in the formation of two distinct products: compound II, which is unstable in aqueous solution, and the stable compound cyclo-[1-(4'-nitro-3'-benzoyl)-2-(aminotyrosyl)-N,N'-ethylenediami ne] (III). The formation of II is detected only in aerobic conditions. The unstable photoproduct II converts almost completely into compound III when its solution is concentrated. The photoproducts II and III have absorption spectra that are close to those of the photolabelled peptides. This finding is important for speculating about the chemical nature of the photomodification products of protein tyrosyl residues by the arylazide group.     

Quenching of tryptophan fluorescence of firefly luciferase by substrates

The interaction of firefly luciferase with substrates (luciferin and MgATP) by steady-state and time-resolved fluorescence is studied. The efficient quenching of tryptophan fluorescence of the active enzyme takes place upon its binding with substrates. In the presence of ATP the quenching is of dynamic type and is caused by structural changes in the protein molecule upon ATP binding. A model is proposed in which the complex has smaller fluorescence quantum yield than the free enzyme because of partial quenching of tryptophan fluorescence by the new microenvironment. Quenching of tryptophan fluorescence by luciferin due to the efficient energy transfer from tryptophan to luciferin is discussed. The calculated distance between Trp-419 and luciferin for the L. mingrelica luciferase in the enzyme-substrate complex is less than 12 A.     

Adsorption of zinc on polymeric chelating adsorbents in the analysis of natural water

The physicochemical and analytical properties of polymeric chelating adsorbents, polystyrene-2-hydroxy-(1-azo-1′)-2′-hydroxybenzene derivatives, to zinc ions were studied. A possible chemical mechanism of the complexation process was based by a number of parameters. A procedure was proposed for the preconcentration of zinc followed by its stripping voltammetric determination in natural water. The detection limit of the proposed procedure (0.1 μg/L) ensures reliable ecological control of natural waters; the relative standard deviation was 1–4% at a concentration level of n × 10^?5%.     

Optical properties of Eu(fod)3-doped polymers using supercritical carbon dioxide

X-ray diffraction pattern of solvated Eu(fod)₃(H₂O)_1,5(i-PrOH)_0,5 form of Eu(fod)₃ complex (fod=6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) is presented. The photoluminescence (PL) spectra of Eu³⁺ ions in polycrystalline powder Eu(fod)₃ and also in Eu(fod)₃-doped polymethylmethacrylate (PMMA), polypropylene (PP) and polydimethylsiloxane (PDMS) were investigated. It is revealed that the matrix influences the temperature quenching of PL intensity in the range 20-100 °C. A polycrystalline powder Eu(fod)₃ and Eu(fod)₃-doped PP are the most effective materials for PL quenching. It is shown that water molecules in the first coordinating sphere of Eu³⁺ ions increase PL intensity temperature quenching.     

Photosensitivity and thermosensitivity of polymers doped with Eu(fod)<Subscript>3</Subscript> molecules

We have studied the photoluminescence (PL) spectra of Eu³⁺ ions and the decay kinetics for the photoluminescence intensity on exposure to temperature and UV radiation in polypropylene and oligo(urethane methacrylate) (OUM) doped with Eu(fod)₃ molecules (fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octadione) by soaking in a supercritical CO₂ solution. We have established that the decay kinetics for the photoluminescence intensity on exposure to UV radiation depends on the temperature of the sample and the concentration of the dopant in it. Based on studies of the spectral characteristics of doped OUM samples, we suggest that this material can be used as a two-color luminescent temperature sensor. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 104-111, January-February, 2009.     

Frustrations in polymer conformation in gels and their minimization through molecular imprinting

We report an experimental realization of a gel system in which frustrations exist and can be minimized, thus meeting two crucial criteria predicted to enable memory of conformations in polymers. The gels consist of a thermosensitive major monomer component and two minor components. One minor component is positively charged and will form complexes around negatively charged target molecules placed in solution. The complexes can be imprinted into the gel by then cross-linking the second minor component, which will form cross-links additional to those in the major polymer matrix. The complexes are destroyed and reformed upon swelling and reshrinking of the gels, showing that memorization has been achieved.