Novel Phenyl-Based Bis-quaternary Ammonium Compounds as Broad-Spectrum Biocides

Herein we report the synthesis and microbiological evaluation of novel phenyl based bis-quaternary ammonium compounds (bis-QACs). Using a simple 2-step synthetic route from dibromo- and dihydroxybenzenes, we obtained a structurally diverse broad panel of bis-QACs with topologically distinct bridging connections between pyridinium heads. Selected analogs possessed potent broad-spectrum biocidal activity against both bacterial and fungal pathogens: methicillin-resistant Staphylococcus aureus (ATCC 43300); Escherichia coli (ATCC 25922), Klebsiella pneumonia (ATCC 700603), Acinetobacter baumannii (ATCC 19606), Pseudomonas aeruginosa (ATCC 27853), Candida albicans (ATCC 90028), Cryptococcus neoformans var. grubii (ATCC 208821). Promising compounds displayed minimum inhibitory concentrations (MIC) values ≤0.25 μg/mL alongside improved cytotoxicity and hemolytic profiles compared to modern antiseptics. Thus, synthesized bis-QACs represent a promising class of biocides with the potential to replace existing household sanitizers.     

Quantum chemistry behind bioimaging: insights from ab initio studies of fluorescent proteins and their chromophores

The unique properties of green fluorescent protein (GFP) have been harnessed in a variety of bioimaging techniques, revolutionizing many areas of the life sciences. Molecular-level understanding of the underlying photophysics provides an advantage in the design of new fluorescent proteins (FPs) with improved properties; however, because of its complexity, many aspects of the GFP photocycle remain unknown. In this Account, we discuss computational studies of FPs and their chromophores that provide qualitative insights into mechanistic details of their photocycle and the structural basis for their optical properties. In a reductionist framework, studies of well-defined model systems (such as isolated chromophores) help to understand their intrinsic properties, while calculations including protein matrix and/or solvent demonstrate, on the atomic level, how these properties are modulated by the environment. An interesting feature of several anionic FP chromophores in the gas phase is their low electron detachment energy. For example, the bright excited ππ* state of the model GFP chromophore (2.6 eV) lies above the electron detachment continuum (2.5 eV). Thus, the excited state is metastable with respect to electron detachment. This autoionizing character needs to be taken into account in interpreting gas-phase measurements and is very difficult to describe computationally. Solvation (and even microsolvation by a single water molecule) stabilizes the anionic states enough such that the resonance excited state becomes bound. However, even in stabilizing environments (such as protein or solution), the anionic chromophores have relatively low oxidation potentials and can act as light-induced electron donors. Protein appears to affect excitation energies very little (<0.1 eV), but alters ionization or electron detachment energies by several electron volts. Solvents (especially polar ones) have a pronounced effect on the chromophore's electronic states; for example, the absorption wavelength changes considerably, the ground-state barrier for cis-trans isomerization is reduced, and fluorescence quantum yield drops dramatically. Calculations reveal that these effects can be explained in terms of electrostatic interactions and polarization, as well as specific interactions such as hydrogen bonding. The availability of efficient computer implementations of predictive electronic structure methods is essential. Important challenges include developing faster codes (to enable better equilibrium sampling and excited-state dynamics modeling), creating algorithms for properties calculations (such as nonlinear optical properties), extending standard excited-state methods to autoionizing (resonance) states, and developing accurate QM/MM schemes. The results of sophisticated first-principle calculations can be interpreted in terms of simpler, qualitative molecular orbital models to explain general trends. In particular, an essential feature of the anionic GFP chromophore is an almost perfect resonance (mesomeric) interaction between two Lewis structures, giving rise to charge delocalization, bond-order scrambling, and, most importantly, allylic frontier molecular orbitals spanning the methine bridge. We demonstrate that a three-center Hückel-like model provides a useful framework for understanding properties of FPs. It can explain changes in absorption wavelength upon protonation or other structural modifications of the chromophore, the magnitude of transition dipole moment, barriers to isomerization, and even non-Condon effects in one- and two-photon absorption.     

Modeling of the residual kinematic errors of coordinate measuring machines using LaserTracer system

It is complex and divergent for the conventional motion controllers to process various G codes using different interpolation algorithms. This impairs programming efficiency and robustness of the controller. In this paper, we propose the universal non-uniform rational B-splines (NURBS)-based interpolator which can simplify the architecture of interpolation in spite of interpreting different kinds of inputs. Direct conversion of long G01 and G02/G03 numerical control (NC) segments to NURBS segment is first implemented. The fitting of multiple short segments into a continuous and smooth NURBS segment is then carried out. More importantly, the universal NURBS-based interpolator utilizes the Cox–de Boor algorithm which is highly efficient and can take advantage of the parallel computing scheme to accelerate the processing speed. Furthermore, due to the construction of real-time environment, the proposed algorithm enables interpretation, look-ahead functions, and motion control to work simultaneously. A 2D NC program possessing hundreds of short G01 segments and long segments (i.e., G02, G03, and long G01) is tested on an in-house developed XY-table with a PC-based motion controller. The results have shown the effectiveness and feasibility of the proposed real-time NURBS-based interpolator.     

Ultrasmall Dispersible Crystalline Nickel Oxide Nanoparticles as High‐Performance Catalysts for Electrochemical Water Splitting

Ultrasmall, crystalline, and dispersible NiO nanoparticles are prepared for the first time, and it is shown that they are promising candidates as catalysts for electrochemical water oxidation. Using a solvothermal reaction in tert‐butanol, very small nickel oxide nanocrystals can be made with sizes tunable from 2.5 to 5 nm and a narrow particle size distribution. The crystals are perfectly dispersible in ethanol even after drying, giving stable transparent colloidal dispersions. The structure of the nanocrystals corresponds to phase‐pure stoichiometric nickel(ii ) oxide with a partially oxidized surface exhibiting Ni(iii ) states. The 3.3 nm nanoparticles demonstrate a remarkably high turn‐over frequency of 0.29 s^–1 at an overpotential of g = 300 mV for electrochemical water oxidation, outperforming even expensive rare earth iridium oxide catalysts. The unique features of these NiO nanocrystals provide great potential for the preparation of novel composite materials with applications in the field of (photo)electrochemical water splitting. The dispersed colloidal solutions may also find other applications, such as the preparation of uniform hole‐conducting layers for organic solar cells.     

Ultrasmall Co3O4 Nanocrystals Strongly Enhance Solar Water Splitting on Mesoporous Hematite

The synthesis of crystalline, nonagglomerated, and perfectly dispersible Co₃O₄ nanoparticles with an average size of 3–7 nm using a solvothermal reaction in tert‐butanol is reported. The very small size and high dispersibility of the Co₃O₄ nanoparticles allow for their homogeneous deposition on mesoporous hematite layers serving as the photoactive absorber in the light‐driven water splitting reaction. This surface treatment leads to a striking photocurrent increase. While the enhancement of hematite photoanode performance by cobalt oxides is known, the preformation and subsequent application of well‐defined cobalt oxide nanoparticles are novel and allow for the treatment of arbitrarily complex hematite morphologies. Photoelectrochemical and transient absorption spectroscopy studies show that this enhanced performance is due to the suppression of surface electron–hole recombination on time scales of milliseconds to seconds.     

Rolled-up tubes and cantilevers by releasing SrRuO3-Pr0.7Ca0.3MnO3 nanomembranes

ABSTRACT: Three-dimensional micro-objects are fabricated by the controlled release of inherently strained SrRuO3/Pr0.7Ca0.3MnO3/SrRuO3 nanometer-sized trilayers from SrTiO3(001) substrates. Freestanding cantilevers and rolled-up microtubes with a diameter of 6 to 8 μm are demonstrated. The etching behavior of the SrRuO3 film is investigated, and a selectivity of 1:9,100 with respect to the SrTiO3 substrate is found. The initial and final strain states of the rolled-up oxide layers are studied by X-ray diffraction on an ensemble of tubes. Relaxation of the sandwiched Pr0.7Ca0.3MnO3 layer towards its bulk lattice parameter is observed as the major driving force for the roll-up of the trilayers. Finally, μ-diffraction experiments reveal that a single object can represent the ensemble proving a good homogeneity of the rolled-up tubes.PACS: 81.07.-b; 68.60.-p; 68.37.Lp; 81.16.Dn.     

Properties of silicon dioxide layers with embedded metal nanocrystals produced by oxidation of Si:Me mixture

A two-dimensional layers of metal (Me) nanocrystals embedded in SiO₂ were produced by pulsed laser deposition of uniformly mixed Si:Me film followed by its furnace oxidation and rapid thermal annealing. The kinetics of the film oxidation and the structural properties of the prepared samples were investigated by Rutherford backscattering spectrometry, and transmission electron microscopy, respectively. The electrical properties of the selected SiO₂:Me nanocomposite films were evaluated by measuring C-V and I-V characteristics on a metal-oxide-semiconductor stack. It is found that Me segregation induced by Si:Me mixture oxidation results in the formation of a high density of Me and silicide nanocrystals in thin film SiO₂ matrix. Strong evidence of oxidation temperature as well as impurity type effect on the charge storage in crystalline Me-nanodot layer is demonstrated by the hysteresis behavior of the high-frequency C-V curves.     

CRISPR/Cas9-RNA interference system for combinatorial metabolic engineering of Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae is widely used in industrial biotechnology for the production of fuels, chemicals, food ingredients, food and beverages, and pharmaceuticals. To obtain high-performing strains for such bioprocesses, it is often necessary to test tens or even hundreds of metabolic engineering targets, preferably in combinations, to account for synergistic and antagonistic effects. Here, we present a method that allows simultaneous perturbation of multiple selected genetic targets by combining the advantage of CRISPR/Cas9, in vivo recombination, USER assembly and RNA interference. CRISPR/Cas9 introduces a double-strand break in a specific genomic region, where multiexpression constructs combined with the knockdown constructs are simultaneously integrated by homologous recombination. We show the applicability of the method by improving cis,cis-muconic acid production in S. cerevisiae through simultaneous manipulation of several metabolic engineering targets. The method can accelerate metabolic engineering efforts for the construction of future cell factories.     

Wind Turbine of the Savonius–Magnus Type with Conical Blades: Dynamics and Control

Journal of Computer and Systems Sciences International - We consider a mathematical model of a horizontal-axis wind-energy unit in which Savonius rotors are used instead of classical blades. The...     

In Vitro Toxicity Testing of Food Contact Materials: State‐of‐the‐Art and Future Challenges

Currently, toxicological testing of food contact materials (FCMs) is focused on single substances and their genotoxicity. However, people are exposed to mixtures of chemicals migrating from food contact articles (FCAs) into food, and toxic effects other than genotoxic damage may also be relevant. Since FCMs can be made of more than 8 thousand substances, assessing them one‐by‐one is very resource‐consuming. Moreover, finished FCAs usually contain non‐intentionally added substances (NIAS). NIAS toxicity can only be tested if a substance's chemical identity is known and if it is available as a pure chemical. Often, this is not the case. Nonetheless, regulations require safety assessments for all substances migrating from FCAs, including NIAS, hence new approaches to meet this legal obligation are needed. Testing the overall migrate or extract from an FCM/FCA is an option. Ideally, such an assessment would be performed by means of in vitro bioassays, as they are rapid and cost‐effective. Here, we review the studies using in vitro bioassays to test toxicity of FCMs/FCAs. Three main categories of in vitro assays that have been applied include assays for cytotoxicity, genotoxicity, and endocrine disruption potential. In addition, we reviewed studies with small multicellular animal‐based bioassays. Our overview shows that in vitro testing of FCMs is in principle feasible. We discuss future research needs and FCM‐specific challenges. Sample preparation procedures need to be optimized and standardized. Further, the array of in vitro tests should be expanded to include those of highest relevance for the most prevalent human diseases of concern.