Infrared spectra of complex organic molecules in astronomically relevant ice mixtures

Context. Complex organic molecules (COMs) have been largely identified through their characteristic rotational transitions in the gas of interstellar and circumstellar regions. Although these species are formed in the icy mantles that cover dust grains, the most complex species that has been unambiguously identified in the solid-phase to date is methanol (CH3OH). With the upcoming launch of the James Webb Space Telescope (JWST), this situation may change. The higher sensitivity, spectral and spatial resolution of the JWST will allow for the probing of the chemical inventory of ices in star-forming regions. In order to identify features of solid-state molecules in astronomical spectra, laboratory infrared spectra of COMs within astronomically relevant conditions are required. This paper is part of a series of laboratory studies focusing on the infrared spectra of frozen COMs embedded in ice matrices. These reflect the environmental conditions in which COMs are thought to be found. Aims. This work is aimed at characterizing the infrared features of acetone mixed in ice matrices containing H2O, CO2, CO, CH4, and CH3OH for temperatures ranging between 15 K and 160 K. Changes in the band positions and shapes due to variations in the temperature, ice composition, and morphology are reported. This work also points out the IR features that are considered the best promising tracers when searching for interstellar acetone-containing ices. Methods. Acetone-containing ices were grown at 15 K under high-vacuum conditions and infrared (IR) spectra (500–4000 cm−1/20–2.5 μm, 0.5 cm−1 resolution) in transmission mode were recorded using a Fourier transform infrared spectrometer. Spectra of the ices at higher temperatures are acquired during the heating of the sample (at a rate of 25 K h−1) up to 160 K. The changes in the infrared features for varying conditions were analyzed. Results. A large set of IR spectra of acetone-containing ices is presented and made available as a basis for interpreting current and future infrared astronomical spectra. The peak position and full width at half maximum of selected acetone bands have been measured for different ice mixtures and temperatures. The bands that are best suitable for acetone identification in astronomical spectra are: the C=O stretch mode, around 1710.3 cm−1 (5.847 μm), that lies in the 1715–1695 cm−1 (5.83–5.90 μm) range in the mixed ices; the CH3 symmetric deformation, around 1363.4 cm−1 (7.335 μm) that lies in the 1353–1373 cm−1 (7.28–7.39 μm) range in the mixed ices; and the CCC asymmetric stretch, around 1228.4 cm−1 (8.141 μm), that lies in the 1224–1245 cm−1 (8.16–8.03 μm) range in the mixed ices. The CCC asymmetric stretch band also exhibits potential as a remote probe of the ice temperature and composition; this feature is the superposition of two components that respond differently to temperature and the presence of CH3OH. All the spectra are available through the Leiden Ice Database

Laboratory data in support of JWST observations of interstellar ices

Laboratory astrophysics and astrochemistr

Folding properties of the hepatitis B core as a carrier protein for vaccination research

The hepatitis B core (HBc) protein has been used successfully in numerous experiments as a carrier for heterologous peptides. Folding and capsid formation of the chimeric proteins is not always achieved easily. In silico analyses were performed to provide further comprehension of the feasibility for predicting successful capsid formation. In contrast to previous work, we show that common in silico predictions do not ensure assembly into particles. We included new considerations regarding capsid formation of HBc fusion proteins. Not only the primary sequence and the length of the inserts seem important, also the rigidity, the distance between the N and the C-terminus and the presence of cysteines, which could form disulphide bonds, could influence proper capsid formation. Furthermore, new conformational insights were formulated when linkers were added to create extra flexibility of the chimeric particles. Different hypotheses were suggested to clarify the obtained results. To this extent, the addition of glycine-rich linkers could lower high rigidity of the insert, removal of the strain of the core protein or ease interaction between the HBc and the insert. Finally, we observed specific changes in capsid formation properties when longer linkers were used. These findings have not been reported before in this and other virus-like particle carriers. In this study, we also propose a new high-yield purification protocol for fusion proteins to be used in vaccination experiments with the carrier protein or in comparative studies of particulate or non-particulate HBc fusion proteins

Optically stimulated luminescence from quartz measured using the linear modulation technique

Mucosal Associated Invariant T (MAIT) cells are abundant in humans and recognise bacterial ligands. Here we demonstrate that MAIT cells are also activated during human viral infections in vivo. MAIT cells activation was observed during infection with Dengue virus, Hepatitis C virus, and Influenza Virus. This activation – driving cytokine release and Granzyme B upregulation - is TCR-independent but dependent on IL-18 in synergy with IL-12, IL-15 and/or interferon-α/β. IL-18 levels and MAIT cell activation correlate with disease severity in acute Dengue infection. Furthermore, HCV treatment with interferon-α leads to specific MAIT cell activation in vivo in parallel with an enhanced therapeutic response. Moreover, TCR- independent activation of MAIT cells leads to a reduction of HCV replication in vitro mediated by IFN-γ. Together these data demonstrate MAIT cells are activated following viral infections, and suggest a potential role in both host defence and immunopathology