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A promising replacement for the radioactive sources commonly encountered in ion mobility spectrometers is a miniaturized, energy-efficient photoionization source that produce the reactant ions via soft X-radiation (2.8 keV). In order to successfully apply the photoionization source, it is imperative to know the spectrum of reactant ions and the subsequent ionization reactions leading to the detection of analytes. To that end, an ionization chamber based on the photoionization source that reproduces the ionization processes in the ion mobility spectrometer and facilitates efficient transfer of the product ions into a mass spectrometer was developed. Photoionization of pure gasses and gas mixtures containing air, N-2, CO2 and N2O and the dopant CH2Cl2 is discussed. The main product ions of photoionization are identified and compared with the spectrum of reactant ions formed by radioactive and corona discharge sources on the basis of literature data. The results suggest that photoionization by soft X-radiation in the negative mode is more selective than the other sources. In air, adduct ions of O-2 - with H2O and CO2 were exclusively detected. Traces of CO2 impact the formation of adduct ions of O-2 - and Cl -(upon addition of dopant) and are capable of suppressing them almost completely at high CO2 concentrations. Additionally, the ionization products of four alkyl nitrates (ethylene glycol dinitrate, nitroglycerin, erythritol tetranitrate and pentaerythritol tetranitrate) formed by atmospheric pressure chemical ionization induced by X-ray photoionization in different gasses (air, N-2 and N2O) and dopants (CH2Cl2, C2H5Br and CH3I) are investigated. The experimental studies are complemented by density functional theory calculations of the most important adduct ions of the alkyl nitrates (M) used for their spectrometric identification. In addition to the adduct ions [M + NO3](-) and [M + Cl](-), adduct ions such as [M + N2O2](-), [M + Br](-) and [M+ I](-) were detected, and their gas-phase structures and energetics are investigated by density functional theory calculations. Copyright (C) 2016 John Wiley & Sons, Ltd.
Apart from their central role during 3D structure determination of proteins the backbone chemical shift assignment is the basis for a number of applications, like chemical shift perturbation mapping and studies on the dynamics of proteins. This assignment is not a trivial task even if a 3D protein structure is known and needs almost as much effort as the assignment for structure prediction if performed manually. We present here a new algorithm based solely on 4D [H-1, N-15]-HSQC-NOESY-[H-1, N-15]-HSQC spectra which is able to assign a large percentage of chemical shifts (73-82 %) unambiguously, demonstrated with proteins up to a size of 250 residues. For the remaining residues, a small number of possible assignments is filtered out. This is done by comparing distances in the 3D structure to restraints obtained from the peak volumes in the 4D spectrum. Using dead-end elimination, assignments are removed in which at least one of the restraints is violated. Including additional information from chemical shift predictions, a complete unambiguous assignment was obtained for Ubiquitin and 95 % of the residues were correctly assigned in the 251 residue-long N-terminal domain of enzyme I. The program including source code is available at https://github.com/thomasexner/4Dassign.
Catalytic amounts of a weak base are sufficient to induce the decomposition of anthracene endoperoxides to anthraquinone. The mechanism has been elucidated by isolation of intermediates in combination with DFT calculations. The whole process is suitable for the convenient generation of hydrogen peroxide under very mild conditions.
Materials based on biodegradable polyesters, such as poly(butylene terephthalate) (PBT) or poly(butylene terephthalate-co-poly(alkylene glycol) terephthalate) (PBTAT), have potential application as pro-regenerative scaffolds for bone tissue engineering. Herein, the preparation of films composed of PBT or PBTAT and an engineered spider silk protein, (eADF4(C16)), that displays multiple carboxylic acid moieties capable of binding calcium ions and facilitating their biomineralization with calcium carbonate or calcium phosphate is reported. Human mesenchymal stem cells cultured on films mineralized with calcium phosphate show enhanced levels of alkaline phosphatase activity suggesting that such composites have potential use for bone tissue engineering.
The high potential of bottom-up fabrication strategies for realizing sophisticated optical sensors combining the high sensitivity of a surface plasmon resonance with the exceptional properties of stimuli-responsive hydrogel is demonstrated. The sensor is composed of a periodic hole array in a gold film whose holes are filled with gold-capped poly(N-isoproyl-acrylamide) (polyNIPAM) microspheres. The production of this sensor relies on a pure chemical approach enabling simple, time-efficient, and cost-efficient preparation of sensor platforms covering areas of cm(2). The transmission spectrum of this plasmonic sensor shows a strong interaction between propagating surface plasmon polaritons at the metal film surface and localized surface plasmon resonance of the gold cap on top of the polyNIPAM microspheres. Computer simulations support this experimental observation. These interactions lead to distinct changes in the transmission spectrum, which allow for the simultaneous, sensitive optical detection of refractive index changes in the surrounding medium and the swelling state of the embedded polyNIPAM microsphere under the gold cap. The volume of the polyNIPAM microsphere located underneath the gold cap can be changed by certain stimuli such as temperature, pH, ionic strength, and distinct molecules bound to the hydrogel matrix facilitating the detection of analytes which do not change the refractive index of the surrounding medium significantly.
Three-dimensional (3D) Bragg coherent x-ray diffractive imaging (CXDI) with a nanofocused beam was applied to quantitatively map the internal strain field of a single indium phosphide nanowire. The quantitative values of the strain were obtained by pre-characterization of the beam profile with transmission ptychography on a test sample. Our measurements revealed the 3D strain distribution in a region of 150 nm below the catalyst Au particle. We observed a slight gradient of the strain in the range of +/- 0.6% along the [111] growth direction of the nanowire. We also determined the spatial resolution in our measurements to be about 10 nm in the direction perpendicular to the facets of the nanowire. The CXDI measurements were compared with the finite element method simulations and show a good agreement with our experimental results. The proposed approach can become an effective tool for in operando studies of the nanowires.
Polyplexes between Salmon DNA and non-modified hyperbranched poly(ethyleneimines) of varying molar mass, i.e., PEI(5 k) with 5000 g/mol and PEI(25 k) with 25,000 g/mol, and modified PEI(5 k) with maltose units (PEI-Mal) were investigated in dependence on the molar N/P ratio by using dynamic light scattering (DLS), zeta potential measurements, micro differential scanning calorimetry (mu-DSC), scanning-transmission electron microscopy (STEM), and cryo-scanning electron microscopy (cryo-SEM). A reloading of the polyplexes can be observed by adding the unmodified PEI samples of different molar mass. In excess of PEI a morphological transition from core-shell particles (at N/P 8) to loosely packed onion-like polyplexes (at N/P 40) is observed. The shift of the DSC melting peak from 88 degrees C to 76 degrees C indicates a destabilization of the DNA double helix due to the complexation with the unmodified PEI. Experiments with the maltose-modified PEI show a reloading already at a lower N/P ratio. Due to the presence of the sugar units in the periphery of the polycation electrostatic interactions between DNA become weaker, but cooperative H-bonding forces are reinforced. The resulting less-toxic, more compact polyplexes in excess of the PEI-Mal with two melting points and well distributed DNA segments are of special interest for extended gene delivery experiments. (C) 2015 Elsevier B.V. All rights reserved.
The interaction of water with a-alumina (i.e. alpha-Al2O3) surfaces is important in a variety of applications and a useful model for the interaction of water with environmentally abundant aluminosilicate phases. Despite its significance, studies of water interaction with alpha-Al2O3 surfaces other than the (0001) are extremely limited. Here we characterize the interaction of water (D2O) with a well defined alpha-Al2O3(1 (1) over bar 02) surface in UHV both experimentally, using temperature programmed desorption and surface-specific vibrational spectroscopy, and theoretically, using periodic-slab density functional theory calculations. This combined approach makes it possible to demonstrate that water adsorption occurs only at a single well defined surface site (the so-called 1-4 configuration) and that at this site the barrier between the molecularly and dissociatively adsorbed forms is very low: 0.06 eV. A subset of OD stretch vibrations are parallel to this dissociation coordinate, and thus would be expected to be shifted to low frequencies relative to an uncoupled harmonic oscillator. To quantify this effect we solve the vibrational Schrodinger equation along the dissociation coordinate and find fundamental frequencies red-shifted by more than 1500 cm(-1). Within the context of this model, at moderate temperatures, we further find that some fraction of surface deuterons are likely delocalized: dissociatively and molecularly absorbed states are no longer distinguishable.
The past two decades witnessed tremendous progress in the field of creation of different types of responsive materials. Cholesteric polymer networks present a very promising class of smart materials due to the combination of the unique optical properties of cholesteric mesophase and high mechanical properties of polymer networks. In the present work we demonstrate the possibility of fast and reversible photocontrol of the optical properties of cholesteric polymer networks. Several cholesteric photopolymerizable mixtures are prepared, and porous cholesteric network films with different helix pitches are produced by polymerization of these mixtures. An effective and simple method of the introduction of photochromic azobenzene-containing nematic mixture capable of isothermal photoinducing the nematic isotropic phase transition into the porous polymer matrix is developed, It is found that cross-linking density and degree of polymer network filling with a photochromic nematic mixture strongly influence the photo-optical behavior of the obtained composite films. In particular, the densely cross-linked films are characterized by a decrease in selective light reflection bandwidth, whereas weakly cross-linked systems display two processes: the shift of selective light reflection peak and decrease of its width. It is noteworthy that the obtained cholesteric materials are shown to be very promising for the variety applications in optoelectronics and photonics.
The competitive extraction of Cr(III) onto Nauclea diderrichii seed epicarp doped with MnO2 nanoparticles (MnO2 nano-bioextractant (MNB)) in a single and binary batch system was studied. For validity of experimental data, chi square test, root mean square error, sum of the square errors, hybrid fractional error function, Marquart’s percent standard deviation and standard absolute error were used. Among the kinetic models used, pseudo-second-order and Langmuir equations gave the best fits for the experimental data, with qe (mg g) for the uptake of Cr(III) in single metal system onto MNB, then Cr(III) with Cd(II), Pb(II), Hg(II), KCl and CaCl2 in binary metal systems onto MNB were 2.611, then 1.989, 1.016, 2.208, 1.249 and 1.868 from kinetic standpoint, respectively. The initial sorption rates, h (mg/g/min), and half lives, t1/2 (min), for the uptake of Cr(III) in single metal system onto MNB, then Cr(III) with Cd(II), Pb(II), Hg(II), KCl and CaCl2 in binary metal system onto MNB were 3.497, then 2.311, 2.274, 0.242, 2.956, 45.568 and 0.747, then 5.769, 1.766, 12.144, 1.762, and 2.415, respectively. Physicochemical surface analyses such as pH of point of zero charge, Brunauer–Emmett–Teller single point and multi-point techniques for surface area analyses, scanning electron microscopy and transmission electron microscopy were done on MNB and MnO2 nanoparticles in order to understand their surface microstructures. Desorption study showed that MNB can be recycled and used for future study. Hence, MNB showed good potential to remediate Cr(III) from wastewaters and polluted water.