Radiative alpha capture on 7-Be with DRAGON at energies relevant to the νp-process

The origin of about 35 neutron-deficient stable isotopes with mass number A >74, known as the <i>p</i>-nuclei, has been a long-standing puzzle in nuclear astrophysics. The <i>νp</i>-process is a candidate for the production of the light <i>p</i>-nuclei, but it presents high sensitivity to both supernova dynamics and nuclear physics [1,2]. It has been recently shown that the breakout from <i>pp</i>-chains through the ⁷Be(α,γ)¹¹C reaction, which occurs prior to <i>νp</i>-process, can significantly influence the reaction flow, and subsequently the production of <i>p</i>-nuclei in the 907Be(α,γ)¹¹C reaction with unknown strengths using DRAGON [3] was recently performed at TRIUMF. The reaction was studied in inverse kinematics using a radioactive ⁷Be (t_1/2= 53.24 d) beam provided by ISAC-I and two resonances above the ¹¹C α--separation energy - Q_α = 7543.62 keV - were measured. The experimental details, in particular how the recoil transmission and BGO efficiencies were accounted for considering the large cone angle for this reaction, will be presented and discussed alongside some preliminary results. <br><br><br><b>References</b><br><br>[1] C. Frohlich <i>et al.</i>, Phys. Rev. Lett. <b>96</b>, 142502 (2006). <br><br>[2] S. Wanajo, H.-T. Janka and S. Kubono, Astrophys. J. <b>729</b>, 46 (2011).<br><br>[3] D.A. Hutcheon <i>et al.</i>, Nucl. Instr. Meth. Phys. Res. A <b>498</b>, 190 (2003).<br><div><br></div><div>Poster presented at the 15^th International Symposium on Nuclei in the Cosmos (June 24-29, 2018 Assergi, L'Aquila, Italy)<br></div><br

Nature’s Selection of Geranyl Group as a tRNA Modification: The Effects of Chain Length on Base-Pairing Specificity

The recently discovered geranyl modification on the 2-thio position of wobble U34 residues in tRNA^Glu, tRNA^Lys, and tRNA^Gln in several bacteria has been found to enhance the U:G pairing specificity and reduce the frameshifting error during translation. It is a fundamentally interesting question why nature chose a C10 terpene group in tRNA systems. In this study, we explore the significance of the terpene length on base-paring stability and specificity using a series of 2-thiouridine analogues containing different lengths of carbon chains, namely, methyl- (C1), dimethylallyl- (C5), and farnesyl-modified (C15) 2-thiothymidines in a DNA duplex. Our thermal denaturation studies indicate that the relatively long chain length of ≥ C10 is required to maintain the base-pairing discrimination of thymidine between G and A. The results from our molecular dynamics simulations show that in the T:G-pair-containing duplex, the geranyl and farnesyl groups fit into the minor groove and stabilize the overall duplex stability. This effect cannot be achieved by the shorter carbon chains such as methyl and dimethylallyl groups. For a duplex containing a T:A pair, the terpene groups disrupt both hydrogen bonding and stacking interactions by pushing the opposite A out of the helical structure. Overall, as the terpene chain length increases, the xT:G pair stabilizes the duplex, whereas the xT:A pair causes destabilization, indicating the evolutionary significance of the long terpene group on base-pairing specificity and codon recognition

Cu(II)-Based Paramagnetic Probe to Study RNA–Protein Interactions by NMR

Paramagnetic NMR techniques allow for studying three-dimensional structures of RNA–protein complexes. In particular, paramagnetic relaxation enhancement (PRE) data can provide valuable information about long-range distances between different structural components. For PRE NMR experiments, oligonucleotides are typically spin-labeled using nitroxide reagents. The current work describes an alternative approach involving a Cu­(II) cyclen-based probe that can be covalently attached to an RNA strand in the vicinity of the protein’s binding site using “click” chemistry. The approach has been applied to study binding of HIV-1 nucleocapsid protein 7 (NCp7) to a model RNA pentanucleotide, 5′-ACGCU-3′. Coordination of the paramagnetic metal to glutamic acid residue of NCp7 reduced flexibility of the probe, thus simplifying interpretation of the PRE data. NMR experiments showed attenuation of signal intensities from protein residues localized in proximity to the paramagnetic probe as the result of RNA–protein interactions. The extent of the attenuation was related to the probe’s proximity allowing us to construct the protein’s contact surface map

Construction and structure studies of DNA-bipyridine complexes as versatile scaffolds for site-specific incorporation of metal ions into DNA

<p>The facile construction of metal–DNA complexes using ‘Click’ reactions is reported here. A series of 2′-propargyl-modified DNA oligonucleotides were initially synthesized as structure scaffolds and were then modified through ‘Click’ reaction to incorporate a bipyridine ligand equipped with an azido group. These metal chelating ligands can be placed in the DNA context in site-specific fashion to provide versatile templates for binding various metal ions, which are exchangeable using a simple EDTA washing-and-filtration step. The constructed metal–DNA complexes were found to be thermally stable. Their structures were explored by solving a crystal structure of a propargyl-modified DNA duplex and installing the bipyridine ligands by molecular modeling and simulation. These metal–DNA complexes could have wide applications as novel organometallic catalysts, artificial ribonucleases, and potential metal delivery systems.</p