Mid-Infrared Optical Frequency Combs based on Difference Frequency Generation for Molecular Spectroscopy

Mid-infrared femtosecond optical frequency combs were produced by difference frequency generation of the spectral components of a near-infrared comb in a 3-mm-long MgO:PPLN crystal. We observe strong pump depletion and 9.3 dB parametric gain in the 1.5 \mu m signal, which yields powers above 500 mW (3 \mu W/mode) in the idler with spectra covering 2.8 \mu m to 3.5 \mu m. Potential for broadband, high-resolution molecular spectroscopy is demonstrated by absorption spectra and interferograms obtained by heterodyning two combs.Comment: 11 pages, 8 figure

Supernova Light Curves Powered by Young Magnetars

We show that energy deposited into an expanding supernova remnant by a highly magnetic (B ~ 5 x 10^14 G) neutron star spinning at an initial period of P ~ 2-20 ms can substantially brighten the light curve. For magnetars with parameters in this range, the rotational energy is released on a timescale of days to weeks, which is comparable to the effective diffusion time through the supernova remnant. The late time energy injection can then be radiated without suffering overwhelming adiabatic expansion losses. The magnetar input also produces a central bubble which sweeps ejecta into an internal dense shell, resulting in a prolonged period of nearly constant photospheric velocity in the observed spectra. We derive analytic expressions for the light curve rise time and peak luminosity as a function of B, P and the properties of the supernova ejecta that allow for direct inferences about the underlying magnetar in bright supernovae. We perform numerical radiation hydrodynamical calculations of a few specific instances and compare the resulting light curves to observed events. Magnetar activity is likely to impact more than a few percent of all core collapse supernovae, and may naturally explain some of the brightest events ever seen (e.g., SN 2005ap and SN 2008es) at L > 10^44 ergs/s.Comment: 5 pages, submitted to Ap

Including Protons in Solid-State NMR Resonance Assignment and Secondary Structure Analysis: The Example of RNA Polymerase II Subunits Rpo4/7

International audience1 H-detected solid-state NMR experiments feasible at fast magic-angle spinning (MAS) frequencies allow accessing 1 H chemical shifts of proteins in solids, which enables their interpretation in terms of secondary structure. Here we present 1 H and 13 C-detected NMR spectra of the RNA polymerase subunit Rpo7 in complex with unlabeled Rpo4 and use the 13 C, 15 N, and 1 H chemical-shift values deduced from them to study the secondary structure of the protein in comparison to a known crystal structure. We applied the automated resonance assignment approach FLYA including 1 H-detected solid-state NMR spectra and show its success in comparison to manual spectral assignment. Our results show that reasonably reliable secondary-structure information can be obtained from 1 H secondary chemical shifts (SCS) alone by using the sum of 1 H α and 1 H N SCS rather than by TALOS. The confidence, especially at the boundaries of the observed secondary structure elements, is found to increase when evaluating 13 C chemical shifts, here either by using TALOS or in terms of 13 C SCS

Two-Dimensional Distance Correlation Maps from Pulsed Triple Electron Resonance (TRIER) on Proteins with Three Paramagnetic Centers

Pribitzer S, Ibanez LF, Gmeiner C, et al. Two-Dimensional Distance Correlation Maps from Pulsed Triple Electron Resonance (TRIER) on Proteins with Three Paramagnetic Centers. APPLIED MAGNETIC RESONANCE. 2018;49(11):1253-1279

Dark Photocatalysis: Storage of Solar Energy in Carbon Nitride for Time-Delayed Hydrogen Generation

While natural photosynthesis serves as the model system for efficient charge separation and decoupling of redox reactions, bio-inspired artificial systems typically lack applicability owing to synthetic challenges and structural complexity. We present herein a simple and inexpensive system that, under solar irradiation, forms highly reductive radicals in the presence of an electron donor, with lifetimes exceeding the diurnal cycle. This radical species is formed within a cyanamide- functionalized polymeric network of heptazine units and can give off its trapped electrons in the dark to yield H-2, triggered by a co-catalyst, thus enabling the temporal decoupling of the light and dark reactions of photocatalytic hydrogen production through the radical's longevity. The system introduced here thus demonstrates a new approach for storing sunlight as long-lived radicals, and provides the structural basis for designing photocatalysts with long-lived photo-induced states

Sequence-specific recognition of methylated DNA by human zinc-finger proteins

DNA methylation is an essential epigenetic mark. Three classes of mammalian proteins recognize methylated DNA: MBD proteins, SRA proteins and the zinc-finger proteins Kaiso, ZBTB4 and ZBTB38. The last three proteins can bind either methylated DNA or unmethylated consensus sequences; how this is achieved is largely unclear. Here, we report that the human zinc-finger proteins Kaiso, ZBTB4 and ZBTB38 can bind methylated DNA in a sequence-specific manner, and that they may use a mode of binding common to other zinc-finger proteins. This suggests that many other sequence-specific methyl binding proteins may exist