SOXS: a wide band spectrograph to follow up transients

SOXS (Son Of X-Shooter) will be a spectrograph for the ESO NTT telescope capable to cover the optical and NIR bands, based on the heritage of the X-Shooter at the ESO-VLT. SOXS will be built and run by an international consortium, carrying out rapid and longer term Target of Opportunity requests on a variety of astronomical objects. SOXS will observe all kind of transient and variable sources from different surveys. These will be a mixture of fast alerts (e.g. gamma-ray bursts, gravitational waves, neutrino events), mid-term alerts (e.g. supernovae, X-ray transients), fixed time events (e.g. close-by passage of minor bodies). While the focus is on transients and variables, still there is a wide range of other astrophysical targets and science topics that will benefit from SOXS. The design foresees a spectrograph with a Resolution-Slit product ~ 4500, capable of simultaneously observing over the entire band the complete spectral range from the U- to the H-band. The limiting magnitude of R~20 (1 hr at S/N~10) is suited to study transients identified from on-going imaging surveys. Light imaging capabilities in the optical band (grizy) are also envisaged to allow for multi-band photometry of the faintest transients. This paper outlines the status of the project, now in Final Design Phase.Comment: 12 pages, 14 figures, to be published in SPIE Proceedings 1070

Son of X--Shooter: a multi--band instrument for a multi--band universe

Son Of X-Shooter (SOXS) will be a new instrument designed to be mounted at the Nasmyth--A focus of the ESO 3.5 m New Technology Telescope in La Silla site (Chile). SOXS is composed of two high-efficiency spectrographs with a resolution slit product 4500, working in the visible (350 -- 850 nm) and NIR (800 -- 2000 nm) range respectively, and a light imager in the visible (the acquisition camera usable also for scientific purposes). The science case is very broad, it ranges from moving minor bodies in the solar system, to bursting young stellar objects, cataclysmic variables and X-ray binary transients in our Galaxy, supernovae and tidal disruption events in the local Universe, up to gamma-ray bursts in the very distant and young Universe, basically encompassing all distance scales and astronomy branches. At the moment, the instrument passed the Preliminary Design Review by ESO (July 2017) and the Final Design (with FDR in July 2018).Comment: 23 pages, 10 Figures, accepted to be published in Frontier Research in Astrophysics 2018 Conference proceedings in Proceeding of Science. arXiv admin note: text overlap with arXiv:1807.0882

Slow Dissociation of a Charged Ligand: Analysis of the Primary Quinone QA Site of Photosynthetic Bacterial Reaction Centers

Reaction centers (RCs) are integral membrane proteins that undergo a series of electron transfer reactions during the process of photosynthesis. In the QA site of RCs from Rhodobacter sphaeroides, ubiquinone-10 is reduced, by a single electron transfer, to its semiquinone. The neutral quinone and anionic semiquinone have similar affinities, which is required for correct in situ reaction thermodynamics. A previous study showed that despite similar affinities, anionic quinones associate and dissociate from the QA site at rates ≈104 times slower than neutral quinones indicating that anionic quinones encounter larger binding barriers (Madeo, J.; Gunner, M. R. Modeling binding kinetics at the QA site in bacterial reaction centers. Biochemistry2005, 44, 10994–11004). The present study investigates these barriers computationally, using steered molecular dynamics (SMD) to model the unbinding of neutral ground state ubiquinone (UQ) and its reduced anionic semiquinone (SQ–) from the QA site. In agreement with experiment, the SMD unbinding barrier for SQ– is larger than for UQ. Multi Conformational Continuum Electrostatics (MCCE), used here to calculate the binding energy, shows that SQ– and UQ have comparable affinities. In the QA site, there are stronger binding interactions for SQ– compared to UQ, especially electrostatic attraction to a bound non-heme Fe2+. These interactions compensate for the higher SQ– desolvation penalty, allowing both redox states to have similar affinities. These additional interactions also increase the dissociation barrier for SQ– relative to UQ. Thus, the slower SQ– dissociation rate is a direct physical consequence of the additional binding interactions required to achieve a QA site affinity similar to that of UQ. By a similar mechanism, the slower association rate is caused by stronger interactions between SQ– and the polar solvent. Thus, stronger interactions for both the unbound and bound states of charged and highly polar ligands can slow their binding kinetics without a conformational gate. Implications of this for other systems are discussed

Regulating STING in health and disease.

The presence of cytosolic double-stranded DNA molecules can trigger multiple innate immune signalling pathways which converge on the activation of an ER-resident innate immune adaptor named "STimulator of INterferon Genes (STING)". STING has been found to mediate type I interferon response downstream of cyclic dinucleotides and a number of DNA and RNA inducing signalling pathway. In addition to its physiological function, a rapidly increasing body of literature highlights the role for STING in human disease where variants of the STING proteins, as well as dysregulated STING signalling, have been implicated in a number of inflammatory diseases. This review will summarise the recent structural and functional findings of STING, and discuss how STING research has promoted the development of novel therapeutic approaches and experimental tools to improve treatment of tumour and autoimmune diseases

Spectral hole burning: examples from photosynthesis

The optical spectra of photosynthetic pigment–protein complexes usually show broad absorption bands, often consisting of a number of overlapping, ‘hidden’ bands belonging to different species. Spectral hole burning is an ideal technique to unravel the optical and dynamic properties of such hidden species. Here, the principles of spectral hole burning (HB) and the experimental set-up used in its continuous wave (CW) and time-resolved versions are described. Examples from photosynthesis studied with hole burning, obtained in our laboratory, are then presented. These examples have been classified into three groups according to the parameters that were measured: (1) hole widths as a function of temperature, (2) hole widths as a function of delay time and (3) hole depths as a function of wavelength. Two examples from light-harvesting (LH) 2 complexes of purple bacteria are given within the first group: (a) the determination of energy-transfer times from the chromophores in the B800 ring to the B850 ring, and (b) optical dephasing in the B850 absorption band. One example from photosystem II (PSII) sub-core complexes of higher plants is given within the second group: it shows that the size of the complex determines the amount of spectral diffusion measured. Within the third group, two examples from (green) plants and purple bacteria have been chosen for: (a) the identification of ‘traps’ for energy transfer in PSII sub-core complexes of green plants, and (b) the uncovering of the lowest k = 0 exciton-state distribution within the B850 band of LH2 complexes of purple bacteria. The results prove the potential of spectral hole burning measurements for getting quantitative insight into dynamic processes in photosynthetic systems at low temperature, in particular, when individual bands are hidden within broad absorption bands. Because of its high-resolution wavelength selectivity, HB is a technique that is complementary to ultrafast pump–probe methods. In this review, we have provided an extensive bibliography for the benefit of scientists who plan to make use of this valuable technique in their future research