Synthesis of poly(methyl methacrylate)-block-poly(L-histidine) and its use as a hybrid silver nanoparticle conjugate

Poly[(methyl methacrylate)-block-poly(L-histidine)] (PMMA-b-PHIS) was synthesized by combining atom transfer radical polymerization and living ring-opening polymerization of alpha-amino acid-N-carboxyanhydride. The resulting hybrid block copolymer forms reverse micelles in the mixture solution of water and N,N-dimethylformamide (DMF) and self-assembles into PHIS/PMMA core/shell spheres with controllable size in the range of 80 to 250 nm depending on the micellization temperature. The self-assembly of PMMA-b-PHIS was carried out in H2O/DMF (3/7) mixture in the presence of AgNO3. Reduction of the resulting Ag ions encapsulated inside of the reverse micelles yielded an attractive Ag nanoparticle core/polymer shell conjugate system.     

Reinforcing of a calcium phosphate cement with hydroxyapatite crystals of various morphologies

A series of biocomposite materials was successfully prepared by reinforcing advanced calcium phosphate cement with hydroxyapatite fibrous and elongated plate-like particles. Powder X-ray diffraction showed that ball-milled biocomposite precursors (dicalcium and tetracalcium phosphates) entirely transform to a single phase hydroxyapatite end product within 7 h at 37 °C. Electron microscopy showed that the resultant biocomposites are constituted of nanoscaled cement particles intimately associated with the reinforcement crystals. The influence of shape, size, and concentration of the hydroxyapatite filler on the compression strength of reinforced cements is discussed. The best compression strength of 37 ± 3 MPa (enhancement of ～50% compared to pure cement) was achieved using submicrometer-sized hydroxyapatite crystals with complementary shapes. Nanoindentation revealed that averaged elastic modulus and hardness values of the cements are consistent with those reported for trabecular and cortical human bones, indicating a good match of the micromechanical properties for their potential use for bone repair. The stiffness of the biocomposites was confirmed to gradate-compliant cement matrix, cement-filler interface, and stiff filler-as a result of the structuring at the nanometer-micrometer level. This architecture is critical in conditioning the final mechanical properties of the functional composite biomaterial. In vitro cell culture experiments showed that the developed biomaterial system is noncytotoxic.     

Aggregation of experiments for estimation of hydrogen permeability parameters

The study of the hydrogen permeability of materials employs a variety of methods with their own specific features, advantages and drawbacks. The penetration method allows determining the diffusion coefficient from so-called lag time. The accuracy of the estimation depends on the degree of proximity to the DLR (diffusion limited regime) mode. The method of ‘communicating vessels’ is more sensitive to surface processes. ‘Separate’ application of these methods leads to a situation where the materials studied are in fact somewhat different (for example, due to different impacts on the surface), and significant differences in parameter estimates ensue. This paper suggests and implements a cascade experiment technique and the corresponding mathematical toolkit. The informative capacity of experimental studies and the accuracy of the estimation of hydrogen permeability parameters (diffusion, absorption, desorption) are thus enhanced.     

Progress in Development of Russian National Measurement Standards in the Field of Mass Concentration Measurement of Suspended Particles

Aerodisperse system (ambient aerosol) is a dynamic system, thus its physical and chemical properties change continuously in the atmosphere. In addition to the changing characteristic of atmospheric aerosols, their accurate and precise measurements are a challenging task because these measurements depend on several parameters for which the traceable standards/calibration are essentially required. In Russia, the traceability for these measurements is provided in accordance with the recommendations of the Russian national regulatory standard “State hierarchy scheme for the instruments deployed for the measurements of the disperse parameters of aerosols, suspensions and powdered materials.” The State primary standard for the units of disperse parameters of aerosols, suspensions and powdered materials (GET-163) and the State primary special standard for the unit of mass concentration of particles in aerodispersed media (GET-164) are placed at the top of the hierarchy scheme. This paper describes the State primary special standard GET-164 and the specificity of ensuring the traceability in disseminating the unit realized by this primary special standard to working measurement instruments. Methods used to generate aerodispersed media with desired properties are validated and the problem for achieving the highest accuracy in the measurements related to the primary special standard GET-164 is discussed. The SI unit of mass concentration of particulate matter is disseminated from the State primary special standard GET-164 to the working instruments through a set of working standards. The methods, which are used to generate aerodispersed media in disseminating the unit of mass concentration, provided for carrying out investigations and calibration of measurement instruments over a wide range of the mass concentration of suspended particles of different disperse composition. The main ways of improving the standard facilities in the field of measurements of the mass concentration of suspended particles are (i) related to the improvement of the method used to measure concentrations by means of a beta-ray analyzer-comparator (included in the composition of the State primary special standard GET-164) by reducing the uncertainty of the approximation of the conversion characteristics and (ii) due to implementation of methods providing for accurately controlled dilution of aerosols to extend the ranges in which the mass concentration values of suspended particles are reproduced. In order to develop a procedure for international comparisons of such standards, the corresponding investigations of the State primary special standard GET-164 were carried out.     

Reorganization of perylene bisimide J-aggregates: from delocalized collective to localized individual excitations

Water-induced reorganization of individual one-dimensional J-aggregates of perylene bisimide (PBI) dyes was observed by fluorescence microscopy. Fluorescence spectra and decay kinetics of individual J-aggregates immobilized on glass surfaces were measured under a dry nitrogen atmosphere and under humid conditions. The fluorescence properties of PBI J-aggregates arisen from collective excitons under dry nitrogen atmosphere were changed to those of non-interacting dye monomers when water vapor was introduced into the environment (sample chamber). Time-dependent changes of the fluorescence spectra and lifetimes upon exposure to water vapor suggest an initial coordination of water molecules at defect sites leading to the formation of H-type dimer units that act as exciton quenchers, and a subsequent slower disintegration of the hydrogen-bonded J-aggregate into monomers that lack resonance coupling. Our present studies resulted in a direct demonstration of how drastically the optical properties of molecular ensembles and characteristics of their excited states can be changed by delicate reorganization of dye molecules at nanometre scales.     

Small-angle neutron scattering characterization of the structure of nanoporous carbons for energy-related applications

We used small-angle neutron scattering (SANS) and neutron contrast variation to study the structure of four nanoporous carbons prepared by thermo-chemical etching of titanium carbide TiC in chlorine at 300, 400, 600, and 800 °C with pore diameters ranging between ∼4 and ∼11 Å. SANS patterns were obtained from dry samples and samples saturated with deuterium oxide (D₂O) in order to delineate origin of the power law scattering in the low Q domain as well as to evaluate pore accessibility for D₂O molecules. SANS cross section of all samples was fitted to Debye-Anderson-Brumberger (DAB), DAB-Kirste-Porod models as well as to the Guinier and modified Guinier formulae for cylindrical objects, which allowed for evaluating the radii of gyration as well as the radii and lengths of the pores under cylindrical shape approximation. SANS data from D₂O-saturated samples indicate that strong upturn in the low Q limit usually observed in the scattering patterns from microporous carbon powders is due to the scattering from outer surface of the powder particles. Micropores are only partially filled with D₂O molecules due to geometrical constraints and or partial hydrophobicity of the carbon matrix. Structural parameters of the dry carbons obtained using SANS are compared with the results of the gas sorption measurements and the values agree for carbide-derived carbons (CDCs) obtained at high chlorination temperatures (>600 °C). For lower chlorination temperatures, pore radii obtained from gas sorption overestimate the actual pore size as calculated from SANS for two reasons: inaccessible small pores are present and the model-dependent fitting based on density functional theory models assumes non-spherical pores, whereas SANS clearly indicates that the pore shape in microporous CDC obtained at low chlorination temperatures is nearly spherical.     

UV radiation induces genome-mediated, site-specific cleavage in viral proteins

Much research has been dedicated to understanding the molecular basis of UV damage to biomolecules, yet many questions remain regarding the specific pathways involved. Here we describe a genome-mediated mechanism that causes site-specific virus protein cleavage upon UV irradiation. Bacteriophage MS2 was disinfected with 254 nm UV, and protein damage was characterized with ESI- and MALDI-based FT-ICR, Orbitrap, and TOF mass spectroscopy. Top-down mass spectrometry of the products identified the backbone cleavage site as Cys46-Ser47 in the virus capsid protein, a location of viral genome-protein interaction. The presence of viral RNA was essential to inducing backbone cleavage. The similar bacteriophage GA did not exhibit site-specific protein cleavage. Based on the major protein fragments identified by accurate mass analysis, a cleavage mechanism is proposed by radical formation. The mechanism involves initial oxidation of the Cys46 side chain followed by hydrogen atom abstraction from Ser47 C(α). Computational protein QM/MM studies confirmed the initial steps of the radical mechanism. Collectively, this study describes a rare incidence of genome-induced protein cleavage without the addition of sensitizers.     

Carboxyethylated polyaminostyrene for selective copper removal

In order to prepare copper selective chelating resin, β-alanine functionality was introduced into polystyrene matrix by the aza-Michael addition of poly(4-aminostyrene) to acrylic acid. The resin was characterized by elemental analysis and pH potentiometric titration in terms of the degree of carboxyethylation (DS = 1.3) and protonation constant of the amine group (log K _H = 7.48). The optimum pH for Cu²⁺ adsorption was found to be 7–8 (0.1 M ammonium acetate buffer) and the contact time required to achieve the equilibrium was about 1 h. The adsorption kinetics follows a pseudo-second order reaction rate, where the initial stage is governed by intraparticle diffusion. The adsorption isotherm data are in good agreement with the Langmuir model. The resin shows high adsorption capacity (1.26 mmol/g) and exhibits high selectivity toward Cu²⁺ ions with no affinity to Zn²⁺, Co²⁺, Cd²⁺ ions and only weak affinity to Ni²⁺ ions.     

Multifunctional carbon-nanotube cellular endoscopes

Glass micropipettes, atomic force microscope tips and nanoneedles can be used to interrogate cells, but these devices either have conical geometries that can damage cells during penetration or are incapable of continuous fluid handling. Here, we report a carbon-nanotube-based endoscope for interrogating cells, transporting fluids and performing optical and electrochemical diagnostics at the single organelle level. The endoscope, which is made by placing a multiwalled carbon nanotube (length, 50-60?μm) at the tip of a glass pipette, can probe the intracellular environment with a spatial resolution of ～100?nm and can also access organelles without disrupting the cell. When the nanotube is filled with magnetic nanoparticles, the endoscope can be remotely manoeuvered to transport nanoparticles and attolitre volumes of fluids to and from precise locations. Because they are mounted on conventional glass micropipettes, the endoscopes readily fit standard instruments, creating a broad range of opportunities for minimally invasive intracellular probing, drug delivery and single-cell surgery.     

Carbon nanotube-tipped endoscope for in situ intracellular surface-enhanced Raman spectroscopy

Gold nanoparticle-decorated carbon nanotubes (CNTs) are used to study intracellular environments in situ using surface-enhanced Raman spectroscopy (SERS). CNTs are decorated with gold nanoparticles and assembled onto the tips of pulled glass capillaries to form a SERS-enabled endoscope. The sub-micrometer size and high mechanical strength of the endoscope make it possible to penetrate the cell membrane for intracellular probing and remain positioned inside during lengthy SERS measurements without causing damage to the cell. Using the SERS-enabled endoscope, DNA and other biomolecules are detected in situ within the nucleus of a single human cervical carcinoma cell in a minimally invasive manner. The SERS-enabled endoscopes exhibit high selectivity and sensitivity for detecting trace amounts of analytes (≈1 pM) in biofluid environments, highlighting their capabilities as label-free, biological sensors for real-time in situ cellular diagnostics, biological detection, and pharmaceutical research.