V. N. Zaitsev

Modeling of heavy metal ion binding by phosphoric acid activated carbon

Abstract The adsorption of heavy metal ions (Cu, Cd, Co and Pb) onto oxidized synthetic activated carbon SP800-Ox modified with phosphoric acid has been investigated. It has been shown that metal adsorption order depends on solution pH and metal ion concentration. Metal ion adsorption was modeled by the surface complexation model (DDL) where carbon is represented as four independent monoprotic acid sites (super-acidic, phosphorus-containing, carboxylic and phenolic). Initial estimation of the surface group density and acidity were made on the base of single ion binding data (proton binding) analysis by a continuous distribution approach. Calculated metal ion binding constants suggest formation of only monodentate charged complex with composition (SOMe+), where SO− is deprotonated phosphoric, carboxylic or phenolic group. No other surface complexes were found to be significant. Super-acidic group did not participate in metal ion binding at all.

Chromium(VI) removal via reduction–sorption on bi-functional silica adsorbents

Organically-modified silica gels bearing mercaptopropyl and ethylenediaminetriacetate groups (SiO2-SH/ED3A) have been used for reduction and subsequent sequestration of Cr(VI) species. The uptake mechanism involves Cr(VI) reduction by thiol groups (SH) and further immobilization of the so-generated Cr(III) species via complexation to the ethylenediaminetriacetate moieties (ED3A). The most appropriate pH range (1-3) for complete Cr(VI) reduction-sorption by SiO2-SH/ED3A originates from the balance between full reduction of Cr(VI) by SH, requiring low pH values, and quantitative complexation of Cr(III) by ED3A, which is favored in less acidic media. Such bi-functional adsorbents are considerably more effective at removal of Cr(VI) than those simply modified with thiol groups alone. The whole reduction-sorption process was characterized by fast kinetics, thus permitting efficient use of the SiO2-SH/ED3A adsorbent in dynamic conditions (column experiments). Monitoring the amount of immobilized chromium species on the solid was achieved using X-ray fluorescence spectroscopy and UV-vis spectroscopy. Studying the influence of ionic strength and presence of heavy metals revealed few interference on Cr(VI) removal.

Cobalt phthalocyanine tetracarboxylic acid modified reduced graphene oxide: a sensitive matrix for the electrocatalytic detection of peroxynitrite and hydrogen peroxide

The quantification of peroxynitrite (ONOO−, PON) and hydrogen peroxide (H2O2) is intrinsically difficult as both species show similar oxidative features located within a narrow potential. The sub-second lifetime of ONOO− at neutral pH further complicates the analysis. In this paper, we examine the electrocatalytic activity of cobalt phthalocyanine tetracarboxylic acid (CoPc–COOH) loaded reduced graphene oxide (rGO) films towards peroxynitrite and hydrogen peroxide detection. The rGO/CoPc–COOH matrix is synthesized by the reaction of graphene oxide (GO) and CoPc–COOH at 90 °C for 5 h under ultrasonication. The integration of CoPc–COOH and the reduction of GO to rGO was confirmed by X-ray photoelectron spectroscopy, FTIR, Raman, UV-vis spectroscopy and electrochemistry. The rGO/CoPc–COOH film showed high electrocatalytic activity and specificity for ONOO− at anodic potential with a sensitivity of ≈11.5 ± 1 nA nM−1 and a peroxynitrite detection limit of ≈1.7 nM. The rGO/CoPc–COOH films further exhibited electrocatalytic reduction of H2O2 with a sensitivity of 14.5 μA mM−1 and a detection limit of ≈60 μM for H2O2.

Insulin loaded iron magnetic nanoparticle–graphene oxide composites: synthesis, characterization and application for in vivo delivery of insulin

One of the focal subjects in insulin delivery is the development of insulin formulations that protect the native insulin from degradation under acidic pH in the stomach. In this work we show, for the first time, that a graphene oxide (GO) based matrix can ensure the stability of insulin at low pH. GO and GO modified with 2-nitrodopamine coated magnetic particle (GO–MPdop) matrices loaded with insulin were prepared and the pH triggered release of the insulin was studied. The loading of insulin on the GO nanomaterials proved to be extremely high at pH < 5.4 with a loading capacity of 100 ± 3% on GO and 88 ± 3% on GO–MPdop. The insulin-containing GO matrices were stable at acidic pH, while insulin was released when exposed to basic solutions (pH = 9.2). Using Xenopus laevis oocytes as a model we showed that the meiotic resumption rate of GO and GO–MPdop remained unaltered when pre-treated in acidic conditions, while pre-incubated insulin (without GO nanomaterials) has lost almost entirely its maturation effect. These results suggest that GO based nanomatrices are promising systems for the protection of insulin.

Chemically modified porous silicon for laser desorption/ionization mass spectrometry of ionic dyes.

Desorption/ionization on silicon (DIOS) mass spectra of model ionic dyes methylene blue (MB+Cl-) and methyl orange (Na+MO-) were studied using p+ type-derived porous silicon (PS) free layers. As-prepared PS (PS-H), the PS thermally oxidized at 300 degrees C (PS-OX), PS with chemically grafted cation-exchanging alkylsulfonic acid (PS-SO(3)H) and anion-exchanging propyl-octadecyldimethylammonium chloride (PS-ODMA+Cl-) groups was tested as ionization platforms. Two mechanisms of the methylene blue desorption/ionization were found: (1) the formation of [MB + H]+* ion due to the reduction/protonation of MB+, which is predominant for PS-H and PS-OX platforms and (2) direct thermal desorption of the MB+ cation, prevailing for PS-SO3H. The fragmentation of the cation is significantly suppressed in the latter case. The samples of PS-SO3H and PS-ODMA+ Cl- efficiently adsorb the dyes of the opposite charge from their solutions via the ion-exchange. Consequent DIOS MS studies allow to detect only low fragmented ions (MB+ and MO-, respectively), demonstrating the potential of the ion-exchange adsorption combined with DIOS MS for the analysis of ionic organic compounds in solutions.

An impedimetric immunosensor based on diamond nanowires decorated with nickel nanoparticles

Nanostructured boron-doped diamond has been investigated as a sensitive impedimetric electrode for the detection of immunoglobulin G (IgG). The immunosensor was constructed in a three-step process: (i) reactive ion etching of flat boron-doped diamond (BDD) interfaces to synthesize BDD nanowires (BDD NWs), (ii) electrochemical deposition of nickel nanoparticles (Ni NPs) on the BDD NWs, and (iii) immobilization of biotin-tagged anti-IgG onto the Ni NPs. Electrochemical impedance spectroscopy (EIS) was used to follow the binding of IgG at different concentrations without the use of any additional label. A detection limit of 0.3 ng mL(-1) (2 nM) with a dynamic range up to 300 ng mL(-1) (2 μM) was obtained with the interface. Moreover, the study demonstrated that this immunosensor exhibits good stability over time and allows regeneration by incubation in ethylenediaminetetraacetic acid (EDTA) aqueous solution.

Quantitative physicochemical analysis of equilibria on chemically modified silica surfaces

Quantitative physicochemical analysis (QPCA) enables the determination of the stoichiometric compositions and physicochemical parameters of species in equilibrium systems proceeding from the composition-property dependencies. The paper discusses modifications to the routine QPCA procedures required to characterize properties of reagents fixed on surfaces of silica-organic hybrid materials. The cooperative effects and the energetic heterogeneity of fixed reagents are especially important in this context. It follows that the main peculiarities of silica surfaces chemically modified by aliphatic amines are (a) the pronounced energetic heterogeneity of reagents caused by the non-random surface topography, (b) the decrease of the bacisity of amines induced by their interactions with residual surface silanols, and (c) the expressed sensibility of reactions in the near-surface layer to the state of its hydration. The interaction of grafted organic bases with metal ions results in the preferred formation of bis metal-ligand coordination compounds. Stability constants of complexes are decreased as a consequence of fixation and depend on not only donor but also acceptor ability of a solvent. Also, the denticity of polydentate ligands may decrease as a result of grafting. The changes of protolytic and complexing properties in the case of grafting of weak acids and phosphorus-containing complexons are due to their interactions with other surface groups and the influence of hydration effects in the near-surface layer.

Controlled electrochemically-assisted deposition of sol-gel biocomposite on electrospun platinum nanofibers.

The modification of platinum nanofibers by silica using the electrochemically-assisted deposition is reported here. Pt nanofibers are obtained by electrospinning and deposited on a glass substrate. The electrochemically-assisted deposition of the sol-gel material then gives the unique possibility to finely tune the silica film thickness around these nanofibers. It also allows the successful encapsulation of a biomolecule (glucose oxidase was chosen here as a model) while retaining its biological activity, as pointed out via the electrochemical monitoring of H(2)O(2) produced upon addition of glucose in the medium. This silica-glucose oxidase composite offers the possibility of comparing systematically the influence of the deposition time on the bioelectrode response and to compare it with the particular features of the deposits. It was found that the film first grew uniformly around the nanofibers and then started to deposit between them, covering the whole sample (fibers and glass substrate), and tended to fully embed the nanofibers for prolonged deposition. The thickness of the silica film is critical for the electroactivity of the biocomposite, the best response being obtained for a silica layer thickness in the range of the fiber diameter (∼50 nm).

Plasmonic photothermal cancer therapy with gold nanorods/reduced graphene oxide core/shell nanocomposites

Gold nanorods (Au NRs) are known for their efficient conversion of photon energy into heat, resulting in hyperthermia and suppression of tumor growth in vitro and in vivo. Au NRs are thus of great promise for photothermal therapy (PTT) of different cancers. From the point of cancer therapy, low laser powers are essential (≤1 W cm−2) to ensure minimal side effects such as skin burning. Herein, we investigate the potential of polyethylene glycol functionalized reduced graphene oxide (rGO-PEG) enrobed Au NRs for the photothermal destruction of human glioblastoma astrocytoma (U87MG) cells in mice. We show that Au NRs@rGO-PEG are ideal multifunctional theranostic nanostructures that can exert efficient photothermal destruction of tumors in mice upon low doses of NIR light excitation and can act as fluorescent cellular markers due to the presence of a NIR dye integrated onto the rGO shell. Due to the specific interaction between Tat protein modified Au NRs@rGO-PEG nanostructures with the human glioblastoma astrocytoma (U87MG) cells, selective targeting of the tumor is achieved. In vivo experiments in mice show that upon irradiation of the tumor implanted in mice at 800 nm under low doses (0.7 W cm−2), U87MG tumor growth gets suppressed. The study demonstrates that the novel nanomaterials allow for an efficient destruction of solid tumors and might thus serve as an excellent multi-functional theranostic agent in photothermal therapeutic applications.

Preconcentration by solid-phase microextraction

The review is devoted to a new method of sample preparation, solid-phase microextraction. Its advantages are miniaturization; considerable reduction or even complete elimination of the use of toxic solvents; high concentration factors; low cost; simplicity of coupling with instrumental methods of analysis; and possibility of automation. The main versions of solid-phase microextraction and the parameters of their optimization are considered, such as the chemical composition of the adsorbent, the thickness of the adsorbing coating, pH, the nature and concentration of the salting-out agent, extraction time, stirring intensity, temperature, desorption conditions, and analyte derivatization. Examples of using solid-phase microextraction in the analysis of environmental samples, biological samples, and foodstuffs are presented.