Structure and charge-state dependence of the gas-phase ionization energy of proteins

Photoionization of protein ions: The ionization energy of polyprotonated protein cations in the gas phase measured using VUV synchrotron radiation appears to be correlated with the charge state z of the protein and its tertiary structure. A simple electrostatic model accounts for the results and also shows predictive capabilities to derive a mean radius R(m) of the protein ion from the ionization energy, and vice versa.     

The Free Energy of the Quantum Heisenberg Ferromagnet at Large Spin

We consider the spin-S ferromagnetic Heisenberg model in three dimensions, in the absence of an external field. Spin wave theory suggests that in a suitable temperature regime the system behaves effectively as a system of non-interacting bosons (magnons). We prove this fact at the level of the specific free energy: if S???? and the inverse temperature ????0 in such a way that ??S stays constant, we rigorously show that the free energy per unit volume converges to the one suggested by spin wave theory. The proof is based on the localization of the system in small boxes and on upper and lower bounds on the local free energy, and it also provides explicit error bounds on the remainder.     

Network Dynamics in Elemental Assimilation and Metabolism

Metabolism and physiology frequently follow non-linear rhythmic patterns which are reflected in concepts of homeostasis and circadian rhythms, yet few biomarkers are studied as dynamical systems. For instance, healthy human development depends on the assimilation and metabolism of essential elements, often accompanied by exposures to non-essential elements which may be toxic. In this study, we applied laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to reconstruct longitudinal exposure profiles of essential and non-essential elements throughout prenatal and early post-natal development. We applied cross-recurrence quantification analysis (CRQA) to characterize dynamics involved in elemental integration, and to construct a graph-theory based analysis of elemental metabolism. Our findings show how exposure to lead, a well-characterized toxicant, perturbs the metabolism of essential elements. In particular, our findings indicate that high levels of lead exposure dysregulate global aspects of metabolic network connectivity. For example, the magnitude of each element’s degree was increased in children exposed to high lead levels. Similarly, high lead exposure yielded discrete effects on specific essential elements, particularly zinc and magnesium, which showed reduced network metrics compared to other elements. In sum, this approach presents a new, systems-based perspective on the dynamics involved in elemental metabolism during critical periods of human development.     

Ab initio and experimental study of the K-shell spectra of 2,5-dihydrofuran

The K-shell spectra of gaseous 2,5-dihydrofuran at the carbon and oxygen thresholds are reported for the first time. They have been measured using the inner-shell electron energy loss spectroscopy (ISEELS) method. Ab initio Configuration Interaction calculations have been carried out to assign the observed bands. The O1s spectrum is similar to that of tetrahydrofuran and the assignments of the bands are close to those obtained in the case of furan, excepting the furan first π* band. At the C1s edge, the spectrum differs from the furan case, because of the different chemical environment of one of the non-equivalent carbon atoms: due to the presence of hydrogen atoms out of the carbon–oxygen ring plane, several Rydberg core excited states have an important valence character, leading to large intensities in the experimental spectrum.