Tautomeric equilibria of nucleobases in the hachimoji expanded genetic alphabet

Evolution has yielded biopolymers that are constructed from exactly four building blocks and are able to support Darwinian evolution. Synthetic biology aims to extend this alphabet, and we recently showed that 8-letter (hachimoji) DNA can support rule-based information encoding. One source of replicative error in non-natural DNA-like systems, however, is the occurrence of alternative tautomeric forms, which pair differently. Unfortunately, little is known about how structural modifications impact free-energy differences between tautomers of the non-natural nucleo¬bases used in the hachimoji expanded genetic alphabet. Determining experimental tautomer ratios is technically difficult and so strategies for improving hachimoji DNA replication efficiency will benefit from accurate computational predictions of equilibrium tautomeric ratios. We now report that high-level quantum-chemical calculations in aqueous solution by the embedded cluster reference interaction site model (EC-RISM), benchmarked against free energy molecular simulations for solvation thermodynamics, provide useful quantitative information on the tautomer ratios of both Watson-Crick and hachimoji nucleobases. In agreement with previous computational studies, all four Watson-Crick nucleobases adopt essentially only one tautomer in water. This is not the case, however, for non-natural nucleobases and their analogs. For example, although the enols of isoguanine and a series of related purines are not populated in water, these heterocycles possess N1-H and N3-H keto tautomers that are similar in energy thereby adversely impacting accurate nucleobase pairing. These robust computational strategies offer a firm basis for improving experimental measurements of tautomeric ratios, which are currently limited to studying molecules that exist only as two tautomers in solution

Probing exotic phenomena at the interface of nuclear and particle physics with the electric dipole moments of diamagnetic atoms: A unique window to hadronic and semi-leptonic CP violation

The current status of electric dipole moments of diamagnetic atoms which involves the synergy between atomic experiments and three different theoretical areas -- particle, nuclear and atomic is reviewed. Various models of particle physics that predict CP violation, which is necessary for the existence of such electric dipole moments, are presented. These include the standard model of particle physics and various extensions of it. Effective hadron level combined charge conjugation (C) and parity (P) symmetry violating interactions are derived taking into consideration different ways in which a nucleon interacts with other nucleons as well as with electrons. Nuclear structure calculations of the CP-odd nuclear Schiff moment are discussed using the shell model and other theoretical approaches. Results of the calculations of atomic electric dipole moments due to the interaction of the nuclear Schiff moment with the electrons and the P and time-reversal (T) symmetry violating tensor-pseudotensor electron-nucleus are elucidated using different relativistic many-body theories. The principles of the measurement of the electric dipole moments of diamagnetic atoms are outlined. Upper limits for the nuclear Schiff moment and tensor-pseudotensor coupling constant are obtained combining the results of atomic experiments and relativistic many-body theories. The coefficients for the different sources of CP violation have been estimated at the elementary particle level for all the diamagnetic atoms of current experimental interest and their implications for physics beyond the standard model is discussed. Possible improvements of the current results of the measurements as well as quantum chromodynamics, nuclear and atomic calculations are suggested.Comment: 46 pages, 19 tables and 16 figures. A review article accepted for EPJ

Coulomb dissociation reactions on proton-rich Ar isotopes

5 pags., 3 figs., 1 tab. -- 11th Symposium on Nuclei in the Cosmos, 19-23 July 2010, Heidelberg, GermanyA Coulomb dissociation experiment on the proton-rich 32Ar and 34Ar isotopes was performed at the ALADIN-LAND setup at GSI in Darmstadt. Recent RQRPA calculations show a low-lying E1 soft-vibrational mode at an excitation energy Ex ≈ 9 MeV for proton-rich argon isotopes at the dripline. In a macroscopic picture, this can be understood as an out-of-phase oscillation of a thin proton skin against the isospin-saturated core, similar to the neutron pygmy resonance at the neutron dripline. On the other hand, the measured (γ, p) reactions are interesting for the calculation of reaction cross-sections and radiative proton capture rates for the rp-process. In this hydrogen burning process a lot of nuclear structure inputs are still missing. Especially in the argon region a bottleneck for the reaction flow is assumed at 30S and 34Ar. The impact of the predicted proton pygmy resonance on the reaction flow is not yet clear. The experimental motivation and the experiment itself are described. Identification plots for incoming and outgoing particles are shown and a tracking algorithm is applied and shows to work succesfully.This project is supported by the HGF Young Investigators Project VH-NG-327.Peer reviewe