Electronic structure of strongly correlated d-wave superconductors

We study the electronic structure of a strongly correlated d-wave superconducting state. Combining a renormalized mean field theory with direct calculation of matrix elements, we obtain explicit analytical results for the nodal Fermi velocity upsilon(F), the Fermi wave vector k(F), and the momentum distribution n(k) as a function of hole doping in a Gutzwiller projected d-wave superconductor. We calculate the energy dispersion E(k) and spectral weight of the Gutzwiller-Bogoliubov quasiparticles and find that the spectral weight associated with the quasiparticle excitation at the antinodal point shows a nonmonotonic behavior as a function of doping. Results are compared to angle resolved photoemission spectroscopy of the high-temperature superconductors.     

Improved sample preparation for MALDI–MSI of endogenous compounds in skin tissue sections and mapping of exogenous active compounds subsequent to ex-vivo skin penetration

Localization of endogenous and exogenous compounds directly in tissue sections is a challenging task in skin research. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) is a powerful label-free technique that enables determination of the distribution of a large range of biomolecules directly in tissue sections. Nevertheless, its application in this field is limited in large part by the low adhesion of skin tissue sections to indium–tin oxide-coated (ITO) glass slides. For the first time corona discharge (CD) treatment was used to modify the glass slide surface for improved adhesion. Localization of endogenous cholesterol sulfate was performed directly in human skin tissue sections. A spatial resolution of approximately 30 μm was sufficient for assignment of mass signals to skin structure morphology. Furthermore, imaging of an exogenous model compound, Nile red, was performed directly in skin tissue sections after ex-vivo penetration into porcine skin, enabling determination of the pathway and depth of penetration. Finally, the ion density map of Nile red was compared with its high resolution fluorescence micrograph. This work provides new insights into the application of MALDI–MSI in skin research.     

Low-temperature transport in Heisenberg chains

A technique to determine accurately transport properties of integrable and nonintegrable quantum-spin chains at finite temperatures by quantum Monte Carlo is presented. The reduction of the Drude weight by interactions in the integrable gapless regime is evaluated. Evidence for the absence of Drude weight in the gapless regime of a nonintegrable system with longer-ranged interactions is presented. We estimate the effect of the nonintegrability on the transport properties and compare with recent experiments on one-dimensional quantum-spin chains.     

High-throughput backbone resonance assignment of small 13C,15N-labeled proteins by a triple-resonance experiment with four sequential connectivity pathways using chemical shift-dependent, apparent 1J(1H,13C): HNCACBcodedHAHB

The proposed three-dimensional triple-resonance experiment HNCACBcodedHAHB correlates sequential 15N, 1H moieties via the chemical shifts of 13Calpha, 13Cbeta, 1Halpha, and 1Hbeta. The four sequential correlation pathways are achieved by the incorporation of the concept of chemical shift-coding [J. Biomol. NMR 25 (2003) 281] to the TROSY-HNCACB experiment. The monitored 1Halpha and 1Hbeta chemical shifts are then coded in the line shape of the cross-peaks of 13Calpha, 13Cbeta along the 13C dimension through an apparent residual scalar coupling, the size of which depends on the attached hydrogen chemical shift. The information of four sequential correlation pathways enables a rapid backbone assignment. The HNCACBcodedHAHB experiment was applied to approximately 85% labeled 13C,15N-labeled amino-terminal fragment of Vaccinia virus DNA topoisomerase I comprising residues 1-77. After one day of measurement on a Bruker Avance 700 MHz spectrometer and 8 h of manual analysis of the spectrum 93% of the backbone assignment was achieved.     

Detection of soy proteins in processed foods: literature overview and new experimental work

Several tests for the detection of soy proteins in foods have been described in the literature, and some are commercially available. This article gives an overview of these methods and discusses the advantages and disadvantages of each individual method. Based on the conclusions of this inventory, an experimental approach was designed to improve the sensitivity of measuring soy protein in processed foods. The aimed sensitivity is 10 ppm (10 microg soy protein in 1 g solid sample), which is over 100-fold lower than presently available tests. The aimed sensitivity is this low because levels of food allergens at 10 ppm and above may provoke reactions in food allergic persons. Native soybean meal, soy protein isolate, soy protein concentrate, and textured soy flakes were used as test materials. Several extraction procedures were compared and a new method using high pH was selected. Polyclonal antibodies were raised in rabbits and goats, and immunopurified antibodies were used in sandwich and inhibition enzyme-linked immunosorbent assay (ELISA). Extraction at pH 12 resulted in good yields for all tested samples, both quantitatively (Bradford) and qualitatively by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Immunopurified rabbit antibodies against this extract used in a competition ELISA format resulted in a sensitive test with a detection limit of 0.02 microg/mL, corresponding to 0.4 microg/g (0.4 ppm) in food samples. Cross-reactivity with some main food ingredients was measured and appeared to be negative in all cases. The presently developed test is applicable for soy ingredients and soy-containing foods that are processed in different ways. The limit of quantitation is 1 ppm, which is an enormous improvement over earlier described methods.     

Pseudomultidimensional NMR by spin-state selective off-resonance decoupling

An alternate technique for accurately monitoring the chemical shift in multidimensional NMR experiments using spin-state selective off-resonance decoupling is presented here. By applying off-resonance decoupling on spin S during acquisition of spin I, we scaled the scalar coupling J(I,S) between the spins, and the residual scalar coupling turns out to be a function of the chemical shift of spin S. Thus, the chemical shift information of spin S is indirectly retained, without an additional evolution period and the accompanying polarization transfer elements. The detection of the components of the doublet using spin-state selection enables an accurate measurement of the residual scalar coupling and a precise value for the chemical shift, concomitantly. The spin-state selection further yields two subspectra comprising either one of the two components of the doublet and thereby avoiding the overlap problems that arise from off-resonance decoupling. In general, spin-state selective off-resonance decoupling can be incorporated into any pulse sequence. Here, the concept of spin-state selective off-resonance decoupling is applied to 3D (13)C or (15)N-resolved [(1)H,(1)H]-NOESY experiments, adding the chemical shift of the heavy atom attached to the hydrogen ((13)C or (15)N nuclei) with high resolution resulting in a pseudo-4D. These pseudo-4D heavy-atom resolved [(1)H, (1)H]-NOESY experiments contain chemical shift information comparable to that of 4D (13)C or (15)N-resolved [(1)H,(1)H]-NOESY, but with an increase in chemical shift resolution by 1-2 orders of magnitude.     

Fragment Screening and Fast Micromolar Detection on a Benchtop NMR Spectrometer Boosted by Photoinduced Hyperpolarization

Fragment-based drug design is a well-established strategy for rational drug design, with nuclear magnetic resonance (NMR) on high-field spectrometers as the method of reference for screening and hit validation. However, high-field NMR spectrometers are not only expensive, but require specialized maintenance, dedicated space, and depend on liquid helium cooling which became critical over the recurring global helium shortages. We propose an alternative to high-field NMR screening by applying the recently developed approach of fragment screening by photoinduced hyperpolarized NMR on a cryogen-free 80 MHz benchtop NMR spectrometer yielding signal enhancements of up to three orders in magnitude. It is demonstrated that it is possible to discover new hits and kick-off drug design using a benchtop NMR spectrometer at low micromolar concentrations of both protein and ligand. The approach presented performs at higher speed than state-of-the-art high-field NMR approaches while exhibiting a limit of detection in the nanomolar range. Photoinduced hyperpolarization is known to be inexpensive and simple to be implemented, which aligns greatly with the philosophy of benchtop NMR spectrometers. These findings open the way for the use of benchtop NMR in near-physiological conditions for drug design and further life science applications.     

Structure Elucidation and Spectroscopic Analysis of Chromophores Produced by Oxidative Psilocin Dimerization

Psilocin ( 1 ) is the dephosphorylated and psychotropic metabolite of the mushroom natural product psilocybin. Oxidation of the phenolic hydroxy group at the C-4 position of 1 results in formation of oligomeric indoloquinoid chromophores responsible for the iconic blueing of bruised psilocybin-producing mushrooms. Based on previous NMR experiments, the hypothesis included that the 5,5’-coupled quinone dimer of 1 was the primary product responsible for the blue color. To test this hypothesis, ring-methylated 1 derivatives were synthesized to provide stable analogs of 1 dimers that could be completely characterized. The chemically oxidized derivatives were spectroscopically analyzed and compared to computationally derived absorbance spectra. Experimental evidence did not support the original hypothesis. Rather, the blue color was shown to stem from the quinoid 7,7’-coupled dimer of 1 .