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A synchrotron-based vacuum ultraviolet absorption spectrum (VUV) of quadricyclane (QC) is reported with energies up to 10.8 eV. Extensive vibrational structure has been extracted from the broad maxima by fitting short energy ranges of the VUV spectrum to high level polynomial functions and processing the regular residuals. Comparison of these data with our recent high-resolution photoelectron spectral (PES) of QC showed that this structure must be attributed to Rydberg states. Several of these appear before the valence states at higher energies. Both types of states have been calculated by configuration interaction (CI), including symmetry-adapted cluster studies (SAC-CI), and time dependent density functional theoretical methods (TDDFT). There is a close correlation between the SAC-CI vertical excitation energies (VEE) and both B3LYP and especially CAM-B3LYP determined ones. The VEE for several low-lying s-, p-, d- and f-Rydberg states (RS), have been determined by SAC-CI and adiabatic excitation energies (AEE) by TDDFT methods. Searches for equilibrium structures for 11,3A2, and 11B1 states for QC led to rearrangement to a norbornadiene structure. Determination of the experimental 00 band positions, which show very low cross-sections, has been assisted by matching features in the spectra with Franck-Condon fits. Herzberg-Teller vibrational profiles for the Rydberg states are relatively more intense than the FC ones, but only at high energy, and are attributed to up to 10 quanta. The vibrational fine structure of the RS calculated by both FC and HT procedures, gives an easy route into generating HT profiles for ionic states, which usually require non-standard procedures. Postprint

International audience; Electronic circular dichroism (ECD) and anisotropy spectra carry information on differential absorption of left- and right-circularly polarized light (LCPL and RCPL) by optically active compounds. This makes them powerful tools for the rapid determination of enantiomeric excesses (ee) in asymmetric synthetic and pharmaceutical chemistry, as well as for predicting the ee inducible by ultraviolet (UV) CPL. The ECD response of a chiral molecule is, however, critically dependent on the properties of the surrounding medium. Here, we report on the first ECD/anisotropy spectra of aqueous solutions of the calcium salt dihydrate of glyceric acid. A systematic study of the effect of the salt concentration and pH on the chiroptical response revealed significant changes and the appearance of a new ECD band of opposite sign. Based on the literature, this can be rationalized by the increase in the relative proportion of free glyceric acid/glycerate to Ca2+ complexes with glycerate with decreasing salt concentration or pH. Glyceric acid can be readily produced under astrophysical conditions. The anisotropy spectra of the solution containing prevalently the free form of this dihydroxy carboxylic acid resemble the ones of previously investigated aliphatic chain hydroxycarboxylic acids and proteinogenic amino acids. This indicates possible common handedness of stellar CPL-induced asymmetry in the potential comonomers of primitive proto-peptides.

Funding Information: This work was supported by Fundação para a Ciência e Tecnologia, Ministério da Ciência, Tecnologia e Ensino Superior (FCT-MCTES), through the grant number PTDC/QUI/64248/2006 (to A.S.P.), the Radiation Biology and Biophysics Doctoral Training Programme—RaBBiT (PD/00193/2012), Applied Molecular Biosciences Unit—UCIBIO (UIDP/04378/2020, i4HB—Institute for Health and Bioeconomy (LA/P/0140/2020) and CEFITEC (UIDB/00068/2020). A.V.A. (PD/BD/135477/2017 and COVID/BD/152498/2022) is supported by the RaBBiT programme. This work benefited from STSM funding by COST Action (CA15126 MOBIEU) and by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. Publisher Copyright: © 2022 by the authors. Encapsulins are protein nanocages capable of harboring smaller proteins (cargo proteins) within their cavity. The function of the encapsulin systems is related to the encapsulated cargo proteins. The Myxococcus xanthus encapsulin (EncA) naturally encapsulates ferritin-like proteins EncB and EncC as cargo, resulting in a large iron storage nanocompartment, able to accommodate up to 30,000 iron atoms per shell. In the present manuscript we describe the binding and protection of circular double stranded DNA (pUC19) by EncA using electrophoretic mobility shift assays (EMSA), atomic force microscopy (AFM), and DNase protection assays. EncA binds pUC19 with an apparent dissociation constant of 0.3 ± 0.1 µM and a Hill coefficient of 1.4 ± 0.1, while EncC alone showed no interaction with DNA. Accordingly, the EncAC complex displayed a similar DNA binding capacity as the EncA protein. The data suggest that initially, EncA converts the plasmid DNA from a supercoiled to a more relaxed form with a beads-on-a-string morphology. At higher concentrations, EncA self-aggregates, condensing the DNA. This process physically protects DNA from enzymatic digestion by DNase I. The secondary structure and thermal stability of EncA and the EncA−pUC19 complex were evaluated using synchrotron radiation circular dichroism (SRCD) spectroscopy. The overall secondary structure of EncA is maintained upon interaction with pUC19 while the melting temperature of the protein (Tm) slightly increased from 76 ± 1 °C to 79 ± 1 °C. Our work reports, for the first time, the in vitro capacity of an encapsulin shell to interact and protect plasmid DNA similarly to other protein nanocages that may be relevant in vivo. publishersversion published