Chemical rescue of active site mutants of S. pneumoniae surface endonuclease EndA and other nucleases of the HNH family by imidazole

The His-Asn-His (HNH) motif characterizes the active sites of a large number of different nucleases such as homing endonucleases, restriction endonucleases, structure-specific nucleases and, in particular, nonspecific nucleases. Several biochemical studies have revealed an essential catalytic function for the first amino acid of this motif in HNH nucleases. This histidine residue was identified as the general base that activates a water molecule for a nucleophilic attack on the sugar phosphate backbone of nucleic acids. Replacement of histidine by an amino acid such as glycine or alanine, which lack the catalytically active imidazole side chain, leads to decreases of several orders of magnitude in the nucleolytic activities of members of this nuclease family. We were able, however, to restore the activity of HNH nuclease variants (i.e., EndA (Streptococcus pneumoniae), SmaNuc (Serratia marcescens) and NucA (Anabaena sp.)) that had been inactivated by His→Gly or His→Ala substitution by adding excess imidazole to the inactive enzymes in vitro. Imidazole clearly replaces the missing histidine side chain and thereby restores nucleolytic activity. Significantly, this chemical rescue could also be observed in vivo (Escherichia coli). The in vivo assay might be a promising starting point for the development of a high-throughput screening system for functional EndA inhibitors because, unlike the wild-type enzyme, the H160G and H160A variants of EndA can easily be produced in E. coli. A simple viability assay would allow inhibitors of EndA to be identified because these would counteract the toxicities of the chemically rescued EndA variants. Such inhibitors could be used to block the nucleolytic activity of EndA, which as a surface-exposed enzyme in its natural host destroys the DNA scaffolds of neutrophil extracellular traps (NETs) and thereby allows S. pneumoniae to escape the innate immune response.     

Bright two-photon emission and ultra-fast relaxation dynamics in a DNA-templated nanocluster investigated by ultra-fast spectroscopy

Metal nanoclusters have interesting steady state fluorescence emission, two-photon excited emission and ultrafast dynamics. A new subclass of fluorescent silver nanoclusters (Ag NCs) are NanoCluster Beacons. NanoCluster Beacons consist of a weakly emissive Ag NC templated on a single stranded DNA ("Ag NC on ssDNA") that becomes highly fluorescent when a DNA enhancer sequence is brought in proximity to the Ag NC by DNA base pairing ("Ag NC on dsDNA"). Steady state fluorescence was observed at 540 nm for both Ag NC on ssDNA and dsDNA; emission at 650 nm is observed for Ag NC on dsDNA. The emission at 550 nm is eight times weaker than that at 650 nm. Fluorescence up-conversion was used to study the dynamics of the emission. Bi-exponential fluorescence decay was recorded at 550 nm with lifetimes of 1 ps and 17 ps. The emission at 650 nm was not observed at the time scale investigated but has been reported to have a lifetime of 3.48 ns. Two-photon excited fluorescence was detected for Ag NC on dsDNA at 630 nm when excited at 800 nm. The two-photon absorption cross-section was calculated to be ～3000 GM. Femtosecond transient absorption experiments were performed to investigate the excited state dynamics of DNA-Ag NC. An excited state unique to Ag NC on dsDNA was identified at ～580 nm as an excited state bleach that related directly to the emission at 650 nm based on the excitation spectrum. Based on the optical results, a simple four level system is used to describe the emission mechanism for Ag NC on dsDNA.     

High-temperature strength behavior of tantalum diboride to 2000°C

This study investigated the high-temperature strength of spark plasma sintered tantalum diboride (TaB₂) for the first time. TaB₂ exhibited a unique elastic fracture behavior below 1900°C, unlike other transition metal diborides. The consolidation process involved spark plasma sintering at 2000–2200°C yielding dense TaB₂ samples. The flexural strength was measured at elevated temperatures up to 2000°C, showing a quite high flexural strength of 400 ± 20 MPa at 1900°C. These findings provide valuable insights into the high-temperature behavior of TaB₂, highlighting its potential for advanced applications.     

New Refractories Developed by the Ukrainian Research Institute of Refractories Named after A.S. Berezhnoy

The article gives an introduction to the Ukrainian Research Institute of Refractories and especially its R D and refractory products for the industries of iron and steel,nonferrous,glass and chemistry etc.     

Low-Temperature Processing and Mechanical Properties of Zirconia and Zirconia–Alumina Nanoceramics

The 1.5- to 3-mol%-Y₂O₃-stabilized tetragonal ZrO₂ (Y-TZP) and Al₂O₃/Y-TZP nanocomposite ceramics with 1 to 5 wt% of alumina were produced by a colloidal technique and low-temperature sintering. The influence of the ceramic processing conditions, resulting density, microstructure, and the alumina content on the hardness and toughness were determined. The densification of the zirconia (Y-TZP) ceramic at low temperatures was possible only when a highly uniform packing of the nanoaggregates was achieved in the green compacts. The bulk nanostructured 3-mol%-yttria-stabilized zirconia ceramic with an average grain size of 112 nm was shown to reach a hardness of 12.2 GPa and a fracture toughness of 9.3 MPa·m^1/2. The addition of alumina allowed the sintering process to be intensified. A nanograined bulk alumina/zirconia composite ceramic with an average grain size of 94 nm was obtained, and the hardness increased to 16.2 GPa. Nanograined tetragonal zirconia ceramics with a reduced yttria-stabilizer content were shown to reach fracture toughnesses between 12.6–14.8 MPa·m^1/2 (2Y-TZP) and 11.9–13.9 MPa·m^1/2 (1.5Y-TZP).     

Concentration effects in the base-catalyzed hydrolysis of oligo(ethylene glycol)- and amine-containing methacrylic monomers

Concentration effects in the base-catalyzed hydrolysis of water-soluble methacrylates (3-(N,N-dimethylaminoethyl) methacrylate (DMAEMA), 2-hydroxyethyl methacrylate (HEMA) and oligo(ethylene glycol) methacrylates (OEGMAs)) have been studied. These monomers are rapidly hydrolyzed in the presence of bases at the room temperature in dilute aqueous solutions, but the reaction rate decreases sharply in highly concentrated solutions. A clear correlation was found between a form of the viscosity isotherm for DMAEMA solutions and the concentration dependence of the autocatalytic hydrolysis rate which indicates the connection of process kinetics with the structure of solutions. These data should be considered when carrying out homo- and copolymerization of the previously mentioned monomers in aqueous solutions.     

Evaluation of Mass Transfer Resistances from Drying Experiments

A new approach to experimental evaluation of mass transfer resistances from drying experiments is proposed. A composite model of ginseng root mass transfer, based on one-dimensional treatment of diffusive and convective resistances as additive components of radial mass transfer, was developed. Mass transfer resistance was evaluated from a linear relationship between measured flux and thermodynamic driving force. Partitioning of mass transfer resistance into diffusive (core and skin) and convective (air boundary layer) resistances was done by modification of boundary conditions: (a) high (3 m/s) and low (1 m/s) air velocity; (b) skin removal. Total radial mass transfer resistance was evaluated as (146 ± 6) ? 10⁶ s/m at 38°C, significantly decreasing to (48 ± 1.5) ? 10⁶ s/m at 50°C. Boundary resistance was evaluated as (54 ± 5) ? 10⁶ s/m at 38°C and (26 ± 3) ? 10⁶ s/m at 50°C in the entire range of moisture contents. Core and skin resistances were both moisture dependent: core resistance increased from initial value of (6 ± 1) ? 10⁶ s/m to (61 ± 6) ? 10⁶ s/m toward the end of drying, whereas skin resistance decreased from initial value of (92 ± 5) ? 10⁶ s/m to (25 ± 5) ? 10⁶ s/m at the endpoint of drying. However, the sum of core and skin resistances, which represents composite diffusive resistance of intact ginseng root, was constant and independent of moisture content: (91 ± 4.6) ? 10⁶ s/m at 38°C and (22 ± 1.6) ? 10⁶ s/m at 50°C. The relationship between mass transfer resistance R and drying rate factor k = 1/RC was used for verification of the composite model.     

Enhancement of the Performance of Low-Efficiency HVAC Filters Due to Continuous Unipolar Ion Emission

Our novel concept utilizing continuous emission of unipolar ions, which has been recently proven to enhance the efficiency of facepiece respirators, was applied to conventional HVAC filters. Laboratory study demonstrated that the air ion emission in the vicinity of a low-efficiency HVAC filter significantly improves its performance. For example, the collection efficiency of two commercial HVAC filters challenged with 1μm PSL particles jumped from 5–15% (measured with no ion emission) to 40–90% (when the ion output rate was ～ 10¹² e^?/sec). The enhancement effect depends on the filter type and, generally, on the distance from the ion emitter to the filter surface. The results were explained as follows. The air ions with high mobility are deposited on the fibers forming a macroscopic electric field, which shield out some incoming unipolarly charged particles due to repelling forces. The field estimate has shown that this explanation is feasible. The enhancement effect seems to have a good potential to be employed in industrial and residential ventilation systems as it enhances the aerosol collection efficiency of a low-efficiency HVAC filter while not affecting its pressure drop.     

Bioaerosol Contamination of Ambient Air as the Result of Opening Envelopes Containing Microbial Materials

Mailing envelopes containing pathogenic spores of bacillus anthraxes, which have recently been used by terrorists to infect humans, calls for a new investigation to identify a level of possible contamination of ambient air as a result of the opening of such envelopes. Here we show that opening an envelope and unfolding a letter aerosolize microbial particles located inside and create their cloud with the diameter equivalent to the length of the letter side along which it was folded. With no motion of an envelope recipient (first case study presented in this paper), the front of the cloud moves due to forced convection caused by the impulse at opening and reaches a human face (approximately 50 cm from the opening zone) in about 6 sec. The concentration of particles at that distance is about three times lower compared to the concentration in the source. Further spread of the cloud brings its front to the distances of 1 and 1.5 meters within 25 and 55 seconds with the corresponding concentrations of around 10% and 5% compared to the source respectively. The second case study presents the results for a more realistic scenario when an envelope recipient, after observing a dust cloud appearing as the result of the opening of the envelope, recoils in fright creating additional air flows significantly disturbing the aerosol propagation described in the former study. It was found theoretically and verified by experiments that the amount of particles captured by the letter recipient varies significantly depending on the geometrical characteristics of the human, distance to the opening zone, reaction time, and recoil velocity.