Experimental investigation of low lying excited states in201Hg

Zeitschrift für Physik A Hadrons and nuclei - The decay of201Tl to201Hg has been investigated withγ- and conversion electron spectroscopic methods. The 26 keV level in201Hg, proposed...     

Proton-detected scalar coupling based assignment strategies in MAS solid-state NMR spectroscopy applied to perdeuterated proteins

Assignment of proteins in MAS (magic angle spinning) solid-state NMR relies so far on correlations among heteronuclei. This strategy is based on well dispersed resonances in the ¹⁵N dimension. In many complex cases like membrane proteins or amyloid fibrils, an additional frequency dimension is desirable in order to spread the amide resonances. We show here that proton detected HNCO, HNCA, and HNCACB type experiments can successfully be implemented in the solid-state. Coherences are sufficiently long lived to allow pulse schemes of a duration greater than 70 ms before incrementation of the first indirect dimension. The achieved resolution is comparable to the resolution obtained in solution-state NMR experiments. We demonstrate the experiments using a triply labeled sample of the SH3 domain of chicken α-spectrin, which was re-crystallized in H₂O/D₂O using a ratio of 1/9. We employ paramagnetic relaxation enhancement (PRE) using EDTA chelated Cu^II to enable rapid data acquisition.     

The structure of 113Sn from proton and alpha- particle induced reactions

The results of in-beam investigations of ¹¹³ Sn using the (p,n), (p,3n), (α,n) and (α,2n) reactions are summarized. Excited states have been identified until E _x = 4715 MeV and J ^π = (27/2^{t -}). For a large number of levels mean lifetimes τ have been determined with the DSA method. For the J ^k = 25/2⁺ state at E _x = 4059 MeV, τ = 1.0(4) ns has been measured with the γ-RF method. The experimental results are compared with the predictions of shell-model calculations. Most of the positive-parity states may be considered as one-or three-quasiparticle neutron excitations of the 2d_5/2, 1_g7/2, 3_s1/2 and 2d_3/2 shells, the negative-parity states as the coupling of one 1h_11/2 neutron to the two- or four-quasiparticle neutron excitations in the even-mass ¹¹²Sn core. For the 25/2⁺ isomer the three-quasiparticle neutron configuration ν(h ₁₁ ^2/2 g ₇ ^2/?1 ) has been proposed on the basis of a shell-model analysis using the mass-formula formalism. The experimentally observed yrast states in ₅₀ ¹¹³ Sn₆₃ are compared with the corresponding states in the valence mirror nucleus ₆₃ ¹⁴⁵ Eu82 giving remarkable similarities although the parameters for the shell-model calculations differ considerably. The analysis of nearest-neighbour spacing distributions of experimentally obtained 5/2⁺ states in ¹¹³Sn does not allow definite conclusions about regularity or chaos.     

Rapid approximate calculation of water binding free energies in the whole hydration domain of (bio)macromolecules

The evaluation of water binding free energies around solute molecules is important for the thermodynamic characterization of hydration or association processes. Here, a rapid approximate method to estimate water binding free energies around (bio)macromolecules from a single molecular dynamics simulation is presented. The basic idea is that endpoint free‐energy calculation methods are applied and the endpoint quantities are monitored on a three‐dimensional grid around the solute. Thus, a gridded map of water binding free energies around the solute is obtained, that is, from a single short simulation, a map of favorable and unfavorable water binding sites can be constructed. Among the employed free‐energy calculation methods, approaches involving endpoint information pertaining to actual thermodynamic integration calculations or endpoint information as exploited in the linear interaction energy method were examined. The accuracy of the approximate approaches was evaluated on the hydration of a cage‐like molecule representing either a nonpolar, polar, or charged water binding site and on α‐ and β‐cyclodextrin molecules. Among the tested approaches, the linear interaction energy method is considered the most viable approach. Applying the linear interaction energy method on the grid around the solute, a semi‐quantitative thermodynamic characterization of hydration around the whole solute is obtained. Disadvantages are the approximate nature of the method and a limited flexibility of the solute. © 2016 Wiley Periodicals, Inc.     

Quantitative measurement of differential 15N-H(alpha/beta)T2 relaxation rates in a perdeuterated protein by MAS solid-state NMR spectroscopy

Dynamic parameters become more and more accessible in the study of uniformly isotopically enriched proteins by MAS solid-state NMR. We demonstrate that T(2)-related relaxation properties can quantitatively be determined in a sample of a perdeuterated microcrystalline protein by the measurement of (15)N,(1)H dipole, (15)N CSA cross-correlated relaxation rates. We find that the measured cross-correlated relaxation rates are independent of the MAS rotation frequency, and therefore reflect local dynamic fluctuations of the protein structure.     

Extrapolation methods for approximating arc length and surface area

A well-known method of estimating the length of a parametric curve in is to sample some points from it and compute the length of the polygon passing through them. In this paper we show that for uniform sampling of regular smooth curves, Richardson extrapolation can be applied repeatedly giving a sequence of derivative-free length estimates of arbitrarily high orders of accuracy. A similar result is derived for the approximation of the area of parametric surfaces.