Determination of the optical bandgap and disorder energies of thin amorphous SiC and AlN films produced by radio frequency magnetron sputtering

Amorphous aluminum nitrite and silicon carbide (a-AlN and a-SiC) thin films were prepared by radio frequency magnetron sputtering. Due to the deposition method and production conditions the deposited films grown in amorphous state. We systematically measure the optical bandgap through optical transmission spectroscopy and its change with a cumulative thermal annealing. The results show a linear relation between the Tauc-gap and the Tauc-slope for both AlN and SiC films, which can be explained analytically from the existence of an Urbach focus, and therefore can be used to determine the Urbach focus or to ensure the correct usage of the bandgap determination methods

Molecular Evolution of the Neuropeptide S Receptor

The neuropeptide S receptor (NPSR) is a recently deorphanized member of the G protein-coupled receptor (GPCR) superfamily and is activated by the neuropeptide S (NPS). NPSR and NPS are widely expressed in central nervous system and are known to have crucial roles in asthma pathogenesis, locomotor activity, wakefulness, anxiety and food intake. The NPS-NPSR system was previously thought to have first evolved in the tetrapods. Here we examine the origin and the molecular evolution of the NPSR using in-silico comparative analyses and document the molecular basis of divergence of the NPSR from its closest vertebrate paralogs. In this study, NPSR-like sequences have been identified in a hemichordate and a cephalochordate, suggesting an earlier emergence of a NPSR-like sequence in the metazoan lineage. Phylogenetic analyses revealed that the NPSR is most closely related to the invertebrate cardioacceleratory peptide receptor (CCAPR) and the group of vasopressin-like receptors. Gene structure features were congruent with the phylogenetic clustering and supported the orthology of NPSR to the invertebrate NPSR-like and CCAPR. A site-specific analysis between the vertebrate NPSR and the well studied paralogous vasopressin-like receptor subtypes revealed several putative amino acid sites that may account for the observed functional divergence between them. The data can facilitate experimental studies aiming at deciphering the common features as well as those related to ligand binding and signal transduction processes specific to the NPSR

Orientation selective 2D-SIFTER experiments at X-band frequencies

Frequency-correlated 2D SIFTER with broadband pulses at X-band frequencies can be used to determine the inter-spin distance and relative orientation of nitroxide moieties in macromolecules when the flexibility of the spin-labels is restricted. At X-band frequencies the EPR spectrum of nitroxides is governed by the strongly anisotropic nitrogen hyperfine coupling. For rigid spin-labels, where the orientation of the inter-connecting vector R correlates to the relative orientations of the nitroxide labels, the dipolar oscillation frequency varies over the EPR spectral line shape. Broadband shaped pulses allow excitation of the complete nitroxide EPR spectra. In this case, Fourier transform of the echo signal gives both fast and direct access to the orientation dependent dipole coupling. This allows determination of not only the inter-spin distance R, but also their mutual orientation. Here, we show the application of the frequency-correlated 2D SIFTER experiment with broadband pulses to a bis-nitroxide model compound and to a double stranded DNA sample. In both molecules, there is restricted internal mobility of the two spin-labels. The experimental results are compared to orientation selective pulsed electron double resonance (PELDOR) experiments and simulations based on a simple geometrical model or MD simulations describing the conformational flexibility of the molecules. Fourier transformation of the SIFTER echo signal yields orientation selective dipolar time traces over the complete EPR-spectral range. This leads to an improved frequency resolution and either to a reduced experimental measurement time or a larger span of frequency offsets measured compared to orientation selective PELDOR experiments. The experimental potential and limitations of the 2D SIFTER method for samples containing rigid spin-labels will be discussed

Dynamics of Nucleic Acids at Room Temperature Revealed by Pulsed EPR Spectroscopy

The investigation of the structure and conformational dynamics of biomolecules under physiological conditions is challenging for structural biology. Although pulsed electron paramagnetic resonance (like PELDOR) techniques provide long‐range distance and orientation information with high accuracy, such studies are usually performed at cryogenic temperatures. At room temperature (RT) PELDOR studies are seemingly impossible due to short electronic relaxation times and loss of dipolar interactions through rotational averaging. We incorporated the rigid nitroxide spin label Ç into a DNA duplex and immobilized the sample on a solid support to overcome this limitation. This enabled orientation‐selective PELDOR measurements at RT. A comparison with data recorded at 50 K revealed averaging of internal dynamics, which occur on the ns time range at RT. Thus, our approach adds a new method to study structural and dynamical processes at physiological temperature in the <10 μs time range with atomistic resolution

High-resolution EPR distance measurements on RNA and DNA with the non-covalent Ǵ spin label

Pulsed electron paramagnetic resonance (EPR) experiments, among them most prominently pulsed electron-electron double resonance experiments (PELDOR/DEER), resolve the conformational dynamics of nucleic acids with high resolution. The wide application of these powerful experiments is limited by the synthetic complexity of some of the best-performing spin labels. The recently developed Ǵ (G-spin) label, an isoindoline-nitroxide derivative of guanine, can be incorporated non-covalently into DNA and RNA duplexes via Watson-Crick base pairing in an abasic site. We used PELDOR and molecular dynamics (MD) simulations to characterize Ǵ, obtaining excellent agreement between experiments and time traces calculated from MD simulations of RNA and DNA double helices with explicitly modeled Ǵ bound in two abasic sites. The MD simulations reveal stable hydrogen bonds between the spin labels and the paired cytosines. The abasic sites do not significantly perturb the helical structure. Ǵ remains rigidly bound to helical RNA and DNA. The distance distributions between the two bound Ǵ labels are not substantially broadened by spin-label motions in the abasic site and agree well between experiment and MD. Ǵ and similar non-covalently attached spin labels promise high-quality distance and orientation information, also of complexes of nucleic acids and proteins

Differentiating the influence of sedentary behavior and physical activity on brain health in late adulthood

Public health messaging calls for individuals to be more physically active and less sedentary, yet these lifestyle behaviors have been historically studied independently. Both physical activity (PA) and sedentary behavior (SB) are linked through time-use in a 24-hour day and are related to health outcomes, such as neurocognition. While the benefits of PA on brain health in late adulthood have been well-documented, the influence of SB remains to be understood. The purpose of this paper was to critically review the evolving work on SB and brain health in late adulthood and emphasize key areas of consideration to inform potential research. Overall, the existing literature studying the impact of SB on the components and mechanisms of brain health are mixed and inconclusive, provided largely by cross-sectional and observational work employing a variety of measurement techniques of SB and brain health outcomes. Further, many studies did not conceptually or statistically account for the role of PA in the proposed relationships. Therefore, our understanding of the way in which SB may influence neurocognition in late adulthood is limited. Future efforts should include more prospective longitudinal and randomized clinical trials with intentional methodological approaches to better understand the relationships between SB and the brain in late adulthood, and how these potential links are differentiated from PA

Evolving the lock to fit the key to create a family of G protein-coupled receptors potently activated by an inert ligand

We evolved muscarinic receptors in yeast to generate a family of G protein-coupled receptors (GPCRs) that are activated solely by a pharmacologically inert drug-like and bioavailable compound (clozapine-N-oxide). Subsequent screening in human cell lines facilitated the creation of a family of muscarinic acetylcholine GPCRs suitable for in vitro and in situ studies. We subsequently created lines of telomerase-immortalized human pulmonary artery smooth muscle cells stably expressing all five family members and found that each one faithfully recapitulated the signaling phenotype of the parent receptor. We also expressed a G(i)-coupled designer receptor in hippocampal neurons (hM(4)D) and demonstrated its ability to induce membrane hyperpolarization and neuronal silencing. We have thus devised a facile approach for designing families of GPCRs with engineered ligand specificities. Such reverse-engineered GPCRs will prove to be powerful tools for selectively modulating signal-transduction pathways in vitro and in vivo