Electron spin resonance of FeVO4

We report on electron spin resonance (ESR) investigations of a FeVO₄ single crystal. Temperature and angular dependences of ESR resonance positions were measured and calculated in temperature range of 35–100 K. The spectra show rich angular dependences of the linewidth, the shape and the resonance field. They consist of a single broad line with asymmetric distortion. Due to the low symmetry of the crystal lattice this distortion can be explained by taking into account the influence of non diagonal dynamic susceptibility.     

Carbon electrode fabrication from pyrolyzed parylene C

Carbon electrodes coupled with electrochemical detection have been used extensively for the investigation of biogenic amines. Herein we report the fabrication and characterization of carbonaceous electrodes prepared from pyrolyzed parylene C (PPC) films. High-aspect ratio carbonaceous microelectrodes have been prepared by masking PPC coated pipets with an insulating parylene C film. PPC thin film electrodes were characterized electrochemically, spectroscopically, and with electron microscopy. The procedures described here offer a route to fabrication of thin film carbon electrodes that can be patterned and produced in parallel. These electrodes are similar to carbon electrodes derived from pyrolyzed photoresist films but do not require spin-coating or lithography and can readily coat three-dimensional surfaces.     

Visual perception of Fourier rainbow holographic display

The rainbow hologram provides views of reconstruction with rainbow color within a large viewing zone. In our recent paper, a Fourier rainbow holographic display using diffraction grating and a white‐light LED source was introduced. In this technique, the rainbow effect is realized by the dispersion of white‐light source on diffraction grating, while the slit is implemented numerically by reducing the demands of the space‐bandwidth product of the display. This paper presents a novel analysis on the visual perception of the Fourier rainbow holographic display using Wigner distribution. The view‐dependent appearance of the image, including multispectral field of view and viewing zone, is investigated considering the observer and the display parameters. The resolution of the holographic view is also investigated. For this, a new quantitative assessment for image blur is introduced using Wigner distribution analysis. The analysis is supported with numerical simulations and experimentally captured optical reconstructions for the holograms of the computer model and real object generated with different slit size, reconstruction distance, and different observation conditions.     

The HP1a disordered C terminus and chromo shadow domain cooperate to select target peptide partners

Drosophila melanogaster heterochromatin protein 1a (HP1a) is essential for compacted heterochromatin structure and the associated gene silencing. Its chromo shadow domain (CSD) is well known for binding to peptides that contain a PXVXL motif. Heterochromatin protein 2 (HP2) is a non-histone chromosomal protein that associates with HP1a in the pericentric heterochromatin, telomeres, and the fourth chromosome. Using NMR spectroscopy, fluorescence polarization, and site-directed mutagenesis, we identified an LCVKI motif in HP2 that binds to the HP1a CSD. The binding affinity of the HP2 fragment is approximately two orders of magnitude higher than that of peptides from PIWI (with a PRVKV motif), AF10 (with a PLVVL motif), or CG15356 (with LYPLL and LSIVA motifs). To delineate differential interactions of the HP1a CSD, we characterized its structure, backbone dynamics, and dimerization constant. We found that the dimerization constant is bracketed by the affinities of HP2 and PIWI, which dock to the same HP1a homodimer surface. This suggests that HP2, but not PIWI, interaction can drive the homodimerization of HP1a. Interestingly, the integrity of the disordered C-terminal extension (CTE) of HP1a is essential for discriminatory binding, whereas swapping the PXVXL motifs does not confer specificity. Serine phosphorylation at the peptide binding surface of the CSD is thought to regulate heterochromatin assembly. Glutamic acid substitution at these sites destabilizes HP1a dimers, but improves the interaction with both binding partners. Our studies underscore the importance of CSD dimerization and cooperation with the CTE in forming distinct complexes of HP1a.     

Net.Create: Network Visualization to Support Collaborative Historical Knowledge Building

Students across disciplines struggle with sensemaking when they are faced with the need to understand and analyze massive amounts of information. This is particularly salient in the disciplines of both history and data science. Our approach to helping students build expertise with complex information leverages activity theory to think about the design of a classroom activity system integrated with the design of a collaborative open-source network-analysis software tool called Net.Create. Through analysis of network log data as well as video data of students’ collaborative interactions with Net.Create, we explore how our activity system helped students reconcile common contradictions that create barriers to dealing with complex datasets in large lecture classrooms. Findings show that as students draw on details in a historical text to collaboratively construct a larger network, they begin to move more readily between small detail and aggregate overview. Students at both high and low initial skill levels were able to increase the complexity of their historical analyses through their engagement with the Net.Create tool and activities. Net.Create transforms the limitation of large class sizes in history classrooms into a resource for students’ collaborative knowledge building, and through collaborative data entry it supports the historiographic practices of citation and revision and helps students embed local historical actors into a larger historical context.

     

Towards NO-free Regulation of sGC: Design and Synthesis of trans-AB-porphyrins

The pathogenesis of the cardiovascular system is often associated with dysfunction of soluble guanylate cyclase (sGC), which can be stimulated in both an NO-dependent and -independent manner. It was previously reported that PPIX and its amphiphilic derivatives markedly activate the enzyme. To date, all porphyrins studied are naturally occurring compounds or their derivatives, possessing substituents at β-positions. Such porphyrins are of limited abundance and their derivatives or analogues are difficult to synthesize, while synthetic meso-substituted porphyrins are easy to prepare. Thus, we have decided to study their effect on guanylate cyclase. To this end, a series of trans-AB-porphyrins, bearing both hydrophilic and hydrophobic groups at the opposite ends of the macrocycle, loosely mimicking the arrangement of the substituents in PPIX, was design and synthesized. Their synthesis involves preparation of suitable building blocks – dipyrromethanes, starting from aldehydes or acetals and following an acid-catalyzed [2+2]-dipyrromethane condensation. Biological properties of synthesized porphyrins with regard to sGC activation were tested. meso-Substituted porphyrins do interact with sGC, though they are poor activators, indicating that further optimization of their structure is required.     

Optical Fourier Transforms of Birefringent Fibres

Abstract

A cylindrical birefringent fibre orientated diagonally between two crossed polarizers can be regarded as a single-, double- or multiple-slit source of light, depending on the refractive index of the medium which surrounds the fibre. When normally trans-illuminated by monochromatic light and observed through a polarizing microscope fitted with a condenser-slit diaphragm, the fibre produces specific interference patterns in the exit pupil of the microscope objective. These patterns manifest themselves as optical Fourier transforms. Their properties and possible applications are discussed. The experiments were performed using polymeric textile fibres.     

Substrate Stiffness Mediates Formation of Novel Cytoskeletal Structures in Fibroblasts during Cell–Microspheres Interaction

It is well known that living cells interact mechanically with their microenvironment. Many basic cell functions, like migration, proliferation, gene expression, and differentiation, are influenced by external forces exerted on the cell. That is why it is extremely important to study how mechanical properties of the culture substrate influence the cellular molecular regulatory pathways. Optical microscopy is one of the most common experimental method used to visualize and study cellular processes. Confocal microscopy allows to observe changes in the 3D organization of the cytoskeleton in response to a precise mechanical stimulus applied with, for example, a bead trapped with optical tweezers. Optical tweezers-based method (OT) is a microrheological technique which employs a focused laser beam and polystyrene or latex beads to study mechanical properties of biological systems. Latex beads, functionalized with a specific protein, can interact with proteins located on the surface of the cellular membrane. Such interaction can significantly affect the cell’s behavior. In this work, we demonstrate that beads alone, placed on the cell surface, significantly change the architecture of actin, microtubule, and intermediate filaments. We also show that the observed molecular response to such stimulus depends on the duration of the cell–bead interaction. Application of cytoskeletal drugs: cytochalasin D, jasplakinolide, and docetaxel, abrogates remodeling effects of the cytoskeleton. More important, when cells are plated on elastic substrates, which mimic the mechanical properties of physiological cellular environment, we observe formation of novel, “cup-like” structures formed by the microtubule cytoskeleton upon interaction with latex beads. These results provide new insights into the function of the microtubule cytoskeleton. Based on these results, we conclude that rigidity of the substrate significantly affects the cellular processes related to every component of the cytoskeleton, especially their architecture.