Showing papers by "Vadim G. Kessler published in 2019"

Self-assembly of plant protein fibrils interacting with superparamagnetic iron oxide nanoparticles.

Abstract: In situ fibrillation of plant proteins in presence of the superparamagnetic iron oxide nanoparticles (NP) promoted formation of a hybrid nanocomposite. The morphology of NP-fibril composite was revealed using ex-situ atomic force microscopy (AFM) in air. The NP-fibrils were associated into extended multi-fibril structures, indicating that the addition of NPs promoted protein association via β-sheet assembly. Real-time movement of NPs attached to fibrils under an external magnetic field was visualized using in-situ AFM in liquid, revealing that composite structures were stable at low pH, and displaying dipolar property of the NPs in the composite at high pH. Changes in magnetic properties of NPs when interacting with protein fibrils were quantitatively mapped using magnetic force microscopy (MFM). The magnetic moment of the NPs in composite was increased by co-existing with protein at low pH, while their dipolar nature was maintained at high pH. Self-assembly of the protein into fibrils is accelerated with increasing NP concentration within an optimal range, which is attributed to a fibrillation-competent conformation of the peptides. The latter was explained by the formation of favorable hydrogen bonds, electrostatic interactions, and efficient surface energy transfer between NPs and proteins.

Optically Active Hybrid Materials Based on Natural Spider Silk.

Abstract: Spider silk is a natural material possessing unique properties such as biocompatibility, regenerative and antimicrobial activity, and biodegradability. It is broadly considered an attractive matrix for tissue regeneration applications. Optical monitoring and potential control over tissue regrowth are attractive tools for monitoring of this process. In this work, we show upconversion modification of natural spider silk fibers with inorganic nanoparticles. To achieve upconversion, metal oxide nanoparticles were doped with low concentrations of rare-earth elements, producing potentially biocompatible luminescent nanomaterials. The suggested approach to spider silk modification is efficient and easy to perform, opening up sensing and imaging possibilities of biomaterials in a noninvasive and real-time manner in bio-integration approaches.

Phase Control in Hafnia: New Synthesis Approach and Convergence of Average and Local Structure Properties.

Abstract: Technologically relevant tetragonal/cubic phases of HfO2 can be stabilized at room temperature by doping with trivalent rare earths using various approaches denoted generically as bulk coprecipitation. Using in situ/ex situ X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy, and in situ/ex situ site-selective, time-gated luminescence spectroscopy, we show that wet impregnation of hafnia nanoparticles with 10% Eu oxide followed by mild calcination in air at 500 °C produces an efficient stabilization of the cubic phase, comparable to that obtained by bulk precipitation. The physical reasons behind the apparently conflictual data concerning the actual crystallographic phase and the local symmetry around the Eu stabilizer and how these can be mediated by luminescence analysis are also discussed. Apparently, the cubic crystal structure symmetry determined by XRD results in a pseudocubic/tetragonal local structure around Eu determined by luminescence. Considering the recent findings on wet impregnated CeO2 and ZrO2, it is concluded that CeO2, ZrO2, and HfO2 represent a unique case of a family of oxides that is extremely tolerant to heavy doping by wet impregnation. In this way, the same batch of preformed nanoparticles can be doped with different lanthanide concentrations or with various lanthanides at a fixed concentration, allowing a systematic and reliable investigation of the effect of doping, lanthanide type, and lanthanide concentration on the various functionalities of these technologically relevant oxides.

Formation of mesoporous structure in Al2O3–NaAlO2-based materials produced by template synthesis

Abstract: Mesoporous alumina and γ-Al2O3–NaAlO2 composites with different morphology were produced by soft chemistry methods using polyethylenimine (PEI), pluronic P123 (P123), and polymer–colloid complex (PCC) derived from them as templates in solution. Sodium aluminate was applied as an additive for production of the mesoporous γ-Al2O3–NaAlO2 composite. The obtained samples were characterized by scanning and transmission electron microscopy, atomic force microscopy, Fourier transform IR spectrometry, X-ray diffraction analysis, and low-temperature N2 adsorption–desorption analysis. The effect of sodium aluminate introduction on the morphological features of the obtained samples was investigated. Mesostructured aluminum oxide obtained using individual templates such as P123 and PEI possesses cylindrical pores, whereas applying PCC resulted in the formation slit-shaped pores. The produced mesoporous aluminum oxide and γ-Al2O3–NaAlO2 composite had a narrow pore size distribution and large surface area. This approach was demonstrated to allow for the control of pore sizes and shapes.

Hierarchically porous zirconia through precursor-directed large-scale synthesis

Abstract: Two new precursors, produced by modification of zirconium t-butoxide with 1-dimethylamino-propanol-2 (HDMAP), solid Zr2(DMAP)3(OtBu)5 (1), and liquid Zr2(DMAP)4(OtBu)4 (2), were obtained by reaction of 1.5 and 2 equivalents of HDMAP, respectively, in toluene on Zr(OtBu)4. The produced compounds were characterized by Fourier-transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance (NMR), and thermogravimetric analysis (TGA) to estimate their stability and volatility. Action of traces of water in solvents or contact with humid air transforms 1 and 2 into less soluble crystalline Zr2(DMAP)3(OtBu)4(OH) (3). Molecular structures of compounds 1 and 3 were established using single-crystal X-ray studies and for 2, they were elucidated by applying 2D 1H–13C-correlated NMR spectra. The crystals of 1 were subjected to hydrolysis via either storage in ambient atmosphere or immersion into boiling water and the resulting products were characterized by X-ray powder diffraction, TGA, scanning electron microscopy, and atomic force microscopy techniques. The product of hydrolysis in air, ZrO2-1, is essentially nonporous, while hydrolysis in boiling water results in ZrO2-2 with hierarchical macro-, meso-, and microporosity. Both materials are essentially X-ray amorphous with diffraction patterns appearing as oblique curves, resembling unresolved profiles of the monoclinic baddeleyite structure of ZrO2. Heat treatment at 200 and 400 °C does not affect essentially the morphology or porosity and leaves the phase composition unchanged, while that at 600 °C converts both samples into a tetragonal ZrO2 phase. The ZrO2-2 material is via this treatment losing microporosity and becoming macro–mesoporous with a well-defined pore size of about 3 nm. Heat treatment at 900 °C results in collapse of pores and transformation into a well-defined monoclinic baddeleyite structure for both materials.

Silica and titania nanoadsorbents for application in molecular recognition technology

Abstract: The warming climate leads globally to increased acidity and increased organic and biological pollution of freshwater sources. The augmented acidity is associated additionally with enhanced release of metals from the mineral bed in rivers and lakes. Development of adsorbents for rapid cleaning of water, possessing a principally new broad spectrum of action is required. New adsorbents are exploiting both metal cation binding functions and immobilized enzymatic functions to permit using them for complex cleaning procedures in one step. Molecular recognition technology was used for achieving specific affinity to rare earth elements cations as a models of radioactive pollutants. The latter approach has also been applied for hydrometallurgy purpose and for the recycling of valuable metals. Specific immobilization of enzymes allows to improve and stabilize their activity over time. Combining metal cation binding and enzymatic functions opens possibility to avoid the otherwise practically inevitable poisoning of the enzymes. Adsorbents were provided with magnetic components to make them easily removable and simplify technically the water cleaning and remediation procedures.

Chemical and Biochemical Approaches for the Synthesis of Substituted Dihydroxybutanones and Di- and Tri-Hydroxypentanones.

Abstract: Polyhydroxylated compounds are building blocks for the synthesis of carbohydrates and other natural products. Their synthesis is mainly achieved by different synthetic versions of aldol-coupling reactions, catalyzed either by organocatalysts, enzymes, or metal-organic catalysts. We have investigated the formation of 1,4-substituted 2,3-dihydroxybutan-1-one derivatives from para- and meta-substituted phenylacetaldehydes by three distinctly different strategies. The first involved a direct aldol reaction with hydroxyacetone, dihydroxyacetone, or 2-hydroxyacetophenone, catalyzed by the cinchona derivative cinchonine. The second was reductive cross-coupling with methyl- or phenylglyoxal promoted by SmI2, resulting in either 5-substituted 3,4-dihydroxypentan-2-ones or 1,4 bis-phenyl-substituted butanones, respectively. Finally, in the third case, aldolase catalysis was employed for synthesis of the corresponding 1,3,4-trihydroxylated pentan-2-one derivatives. The organocatalytic route with cinchonine generated distereomerically enriched syn-products (de = 60-99%), with moderate enantiomeric excesses (ee = 43-56%) but did not produce aldols with either hydroxyacetone or dihydroxyacetone as donor ketones. The SmI2-promoted reductive cross-coupling generated product mixtures with diastereomeric and enantiomeric ratios close to unity. This route allowed for the production of both 1-methyl- and 1-phenyl-substituted 2,3-dihydroxybutanones at yields between 40-60%. Finally, the biocatalytic approach resulted in enantiopure syn-(3 R,4 S) 1,3,4-trihydroxypentan-2-ones.