Atomic Layer Deposition of Aluminum-Free Silica onto Patterned Carbon Nanotube Forests in the Preparation of Microfabricated Thin-Layer Chromatography Plates

JPC – Journal of Planar Chromatography – Modern TLC - We describe the direct, conformal, atomic layer deposition (ALD) of silica onto carbon nanotubes (CNTs) in the microfabrication of...     

Quantification of Structural Integrity and Stability Using Nanograms of Protein by Flow-Induced Dispersion Analysis

In the development of therapeutic proteins, analytical assessment of structural stability and integrity constitutes an important activity, as protein stability and integrity influence drug efficacy, and ultimately patient safety. Existing analytical methodologies solely rely on relative changes in optical properties such as fluorescence or scattering upon thermal or chemical perturbation. Here, we present an absolute analytical method for assessing protein stability, structure, and unfolding utilizing Taylor dispersion analysis (TDA) and LED-UV fluorescence detection. The developed TDA method measures the change in size (hydrodynamic radius) and intrinsic fluorescence of a protein during in-line denaturation with guanidinium hydrochloride (GuHCl). The conformational stability of the therapeutic antibody adalimumab and human serum albumin were characterized as a function of pH. The simple workflow and low sample consumption (40 ng protein per data point) of the methodology make it ideal for assessing protein characteristics related to stability in early drug development or when having a scarce amount of sample available.     

Electronic and optical properties of defect chalcopyrite HgAl2Se4

The structural, electronic and optical properties of HgAl₂Se₄ are investigated using the full potential linear augmented plane wave method based on density functional theory. The calculated structural parameters using LDA are in excellent agreement with the available experimental result. The obtained energy band gap (2.24 eV) using EV-GGA approximation is in excellent agreement with experimental data (2.20 eV). Variation in the energy band gap as a function of the unit cell lattice parameter has been studied. The optical properties show a considerable anisotropy, which makes this compound very useful for various linear–nonlinear optical devices.     

Prolonged bone marrow T1-relaxation in patients with polycythemia vera

In vitro as well as in vivo studies have shown prolonged T1 relaxation times in patients with acute leukemia. The mechanism behind this finding is not known. In order to evaluate if this was specific for leukemia we examined eight patients with polycythemia vera, representing a condition with a rather benign bone marrow neoplasia. In this group of patients we found prolonged T1 relaxation times but normal T2 relaxation times. This may indicate that the prolonged T1 relaxation time seen in leukemic bone marrow is not due to the malignant cell per se.     

DIY XES—development of an inexpensive,versatile, and easy to fabricate XES analyzer and sample delivery system

The application of X-ray emission spectroscopy (XES) has grown substantially with the development of X-ray free-electron lasers, third and fourth generation synchrotron sources, and high-power benchtop sources. By providing the high X-ray flux required for XES, these sources broaden the availability and application of this method of probing electronic structure. As the number of sources increase, so does the demand for X-ray emission detection and sample delivery systems that are cost effective and customizable. Here, we present a detailed fabrication protocol for von Hamos X-ray optics and give details for a 3D-printed spectrometer design. Additionally, we outline an automated, externally triggered liquid sample delivery system that can be used to repeatedly deliver nanoliter droplets onto a plastic substrate for measurement. These systems are both low cost, efficient, and easy to recreate or modify depending on the application. A low cost multiple X-ray analyzer system enables measurement of dilute samples, whereas the sample delivery limits sample loss and reproducibly replaces spent sample with fresh sample in the same position. While both systems can be used in a wide range of applications, the design addresses several challenges associated specifically with time-resolved XES (TRXES). As an example application, we show results from TRXES measurements of photosystem II, a dilute, photoactive protein.     

Thermodynamics of Dipolar Chain Systems

The thermodynamics of a quantum system of layers containing perpendicularly oriented dipolar molecules is studied within an oscillator approximation for both bosonic and fermionic species. The system is assumed to be built from chains with one molecule in each layer. We consider the effects of the intralayer repulsion and quantum statistical requirements in systems with more than one chain. Specifically, we consider the case of two chains and solve the problem analytically within the harmonic Hamiltonian approach which is accurate for large dipole moments. The case of three chains is calculated numerically. Our findings indicate that thermodynamic observables, such as the heat capacity, can be used to probe the signatures of the intralayer interaction between chains. This should be relevant for near future experiments on polar molecules with strong dipole moments.     

Disjoint Paths in Decomposable Digraphs

The k‐linkage problem is as follows: given a digraph and a collection of k terminal pairs such that all these vertices are distinct; decide whether D has a collection of vertex disjoint paths such that is from to for . A digraph is k‐linked if it has a k‐linkage for every choice of 2k distinct vertices and every choice of k pairs as above. The k‐linkage problem is NP‐complete already for [11] and there exists no function such that every ‐strong digraph has a k‐linkage for every choice of 2k distinct vertices of D [17]. Recently, Chudnovsky et al. [9] gave a polynomial algorithm for the k‐linkage problem for any fixed k in (a generalization of) semicomplete multipartite digraphs. In this article, we use their result as well as the classical polynomial algorithm for the case of acyclic digraphs by Fortune et al. [11] to develop polynomial algorithms for the k‐linkage problem in locally semicomplete digraphs and several classes of decomposable digraphs, including quasi‐transitive digraphs and directed cographs. We also prove that the necessary condition of being ‐strong is also sufficient for round‐decomposable digraphs to be k‐linked, obtaining thus a best possible bound that improves a previous one of . Finally we settle a conjecture from [3] by proving that every 5‐strong locally semicomplete digraph is 2‐linked. This bound is also best possible (already for tournaments) [1].     

Substrates and Cyclic Peptide Inhibitors of the Oligonucleotide-Activated Sirtuin 7**

The sirtuins are NAD⁺-dependent lysine deacylases, comprising seven isoforms (SIRT1–7) in humans, which are involved in the regulation of a plethora of biological processes, including gene expression and metabolism. The sirtuins share a common hydrolytic mechanism but display preferences for different ϵ-N-acyllysine substrates. SIRT7 deacetylates targets in nuclei and nucleoli but remains one of the lesser studied of the seven isoforms, in part due to a lack of chemical tools to specifically probe SIRT7 activity. Here we expressed SIRT7 and, using small-angle X-ray scattering, reveal SIRT7 to be a monomeric enzyme with a low degree of globular flexibility in solution. We developed a fluorogenic assay for investigation of the substrate preferences of SIRT7 and to evaluate compounds that modulate its activity. We report several mechanism-based SIRT7 inhibitors as well as de novo cyclic peptide inhibitors selected from mRNA-display library screening that exhibit selectivity for SIRT7 over other sirtuin isoforms, stabilize SIRT7 in cells, and cause an increase in the acetylation of H3 K18.     

Highly selective micro-sequential injection lab-on-valve (μSI-LOV) method for the determination of ultra-trace concentrations of nickel in saline matrices using detection by electrothermal atomic absorption spectrometry

A highly selective procedure is proposed for the determination of ultra-trace level concentrations of nickel in saline aqueous matrices exploiting a micro-sequential injection Lab-On-Valve (μSI-LOV) sample pretreatment protocol comprising bead injection separation/pre-concentration and detection by electrothermal atomic absorption spectrometry (ETAAS). Based on the dimethylglyoxime (DMG) reaction used for nickel analysis, the sample, as contained in a pH 9.0 buffer, is, after on-line merging with the chelating reagent, transported to a reaction coil attached to one of the external ports of the LOV to assure sufficient reaction time for the formation of Ni(DMG)₂ chelate. The non-ionic coordination compound is then collected in a renewable micro-column packed with a reversed-phase copolymeric sorbent [namely, poly(divinylbenzene-co-N-vinylpyrrolidone)] containing a balanced ratio of hydrophilic and lipophilic monomers. Following elution by a 50-μL methanol plug in an air-segmented modality, the nickel is finally quantified by ETAAS. Under the optimized conditions and for a sample volume of 1.8 mL, a retention efficiency of 70 % and an enrichment factor of 25 were obtained. The proposed methodology showed a high tolerance to the commonly encountered alkaline earth matrix elements in environmental waters, that is, calcium and magnesium, and was successfully applied for the determination of nickel in an NIST standard reference material (NIST 1640-Trace elements in natural water), household tap water of high hardness and local seawater. Satisfying recoveries were achieved for all spiked environmental water samples with maximum deviations of 6 %. The experimental results for the standard reference material were not statistically different to the certified value at a significance level of 0.05.