High-resolution solid-state NMR structure of Alanyl-Prolyl-Glycine

We present a de novo high-resolution structure of the peptide Alanyl-Prolyl-Glycine using a combination of sensitive solid-state NMR techniques that each yield precise structural constraints. High-quality ¹³C–¹³C distance constraints are extracted by fitting rotational resonance width (R²W) experiments using Multimode Multipole Floquet Theory and experimental chemical shift anisotropy (CSA) orientations. In this strategy, a structure is first calculated using DANTE-REDOR and torsion angle measurements and the resulting relative CSA orientations are used as an input parameter in the ¹³C–¹³C distance calculations. Finally, a refined structure is calculated using all the constraints. We investigate the effect of different structural constraints on structure quality, as determined by comparison to the crystal structure and also self-consistency of the calculated structures. Inclusion of all or subsets of these constraints into CNS calculations resulted in high-quality structures (0.02 Å backbone RMSD using all 11 constraints).     

1H and 13C NMR Chemical Shifts and N-Substituent Effects of Some Unsymmetrically N,N-Disubstituted Acetamides

The ¹H and ¹³C NMR chemical shift assignments of a series of (E) - and (Z)-N,N-Dialkylacetamides [CH₃C(O)NR¹R², with R¹/R²=Me/Et (1), Me/n-Bu (2), Et/n-Bu (3), Et/t-Bu (4), Me/Hydrcxyethyl (5)., Et/Hydroxyethyl (6), Et/Acetylhydroxyethyl (7)] are reported. The ¹H chemical shifts for the N-substituents of the amides 1–7 recorded in benzene-d₆ and in chloroform-d₁ are in agreement with the Hatton and Richards (ASIS) and Paulsen-Todt models, respectively. The ¹³C chemical shifts for the N-substituents of compounds 1–3 were compared with data of the corresponding symmetrical amides, and the results can be explained by the reciprocal steric compression effect of one N-substituent on the other. The validity of this explanation is confirmed by ¹³C spin-lattice relaxation time (T₁) measurements.     

Broad-band homo-nuclear correlations assisted by 1H irradiation for bio-molecules in very high magnetic field at fast and ultra-fast MAS frequencies

We propose a new broadband second-order proton-assisted ¹³C–¹³C correlation experiment, SHANGHAI. The ¹³C–¹³C magnetization transfer is promoted by ¹H irradiation with interspersed four phases super-cycling. This through-space homo-nuclear sequence only irradiates on the proton channel during the mixing time. SHANGHAI benefits from a large number of modulation sidebands, hence leading to a large robustness with respect to chemical shift differences, which permits its use in a broad MAS frequency range. At ultra-fast MAS (ν_R ? 60 kHz), SHANGHAI is only efficient when the amplitude of ¹H recoupling rf-field is close to half the spinning speed (ν₁ ≈ ν_R/2). However, at moderate to fast MAS (ν_R = 20–35 kHz), SHANGHAI is efficient at any rf-power level larger than ν₁ ≈ 10 kHz, which simultaneously permits avoiding excessive heating of bio-molecules, and using large sample volumes. We show that SHANGHAI can be employed at the very high magnetic field of 23.5 T and then allows the observation of correlation between ¹³C nuclei, even if their resonance frequencies differ by more than 38 kHz.     

<Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>) Cosmology from <Emphasis Type="Italic">q</Emphasis>-theory

From a macroscopic theory of the quantum vacuum in terms of conserved relativistic charges (generically denoted by q ^(a) with label a), we have obtained, in the low-energy limit, a particular type of f(R) model relevant to cosmology. The macroscopic quantum-vacuum theory allows us to distinguish between different phenomenological f(R) models on physical grounds. The text was submitted by the authors in English.     

Study of Different Forms of Density Distributions in Proton–Nucleus Total Reaction Cross Section and the Effect of Phase in NN Amplitude

Proton total-reaction cross-section (σR), measurements for about five nuclei in the range ¹²C to ²⁰⁸Pb at beam energies spanning 40–800 MeV have been analyzed in a systematic way by using the optical limit approximation of the Coulomb-modified Glauber multiple scattering theory. Two different phenomenological nuclear density distributions of the target nucleus in addition to the realistic one have been used in the present analysis. By applying the energy dependence in the slope parameter of nucleon–nucleon (NN) scattering amplitude, it is found that in general, the predictions of σ _R with the phenomenological Gambhir and Patil density distribution agree fairly well with the experimental data. The inclusion of phase in the NN amplitude improves the theoretical results. Our analysis shows that the calculated total reaction cross sections closely reproduce the measured data over the whole range of energy considered in this work. To validate our analyses, we have also obtained a fairly good representation of elastic p-nucleus differential scattering cross section data. The effect of a Coulomb energy shift in the proton beam has also been studied.     

Charge asymmetry and rovibrational excitations of HD+

Average values of the interparticle distances for rovibrationally excited HD⁺ are calculated using a method where the Born–Oppenheimer (BO) approximation is not assumed. The difference between the proton–electron and deuteron–electron distances is used to describe the charge asymmetry in the system. All-particle one-centre explicitly correlated Gaussian functions are used in the calculations of the HD⁺ rovibrational states. In this work, the non-BO method is extended to calculate the rovibrational states corresponding to the total rotational quantum number of two (N = 2). The algorithms for calculating the Hamiltonian and overlap matrix elements, and the matrix elements of the analytical energy gradient determined with respect to the exponential parameters of the Gaussians, are presented. The gradient is employed in the variational optimisation of the parameters, which is key in obtaining very accurate rovibrational energies in the calculations. The algorithm for calculating the average interparticle distances is also shown. The charge asymmetry of HD⁺ near the dissociation limit occurs, as expected, with the electron preferentially being near to the deuteron. The asymmetry for a particular vibrational level increases with rotational excitations. The rovibrational transition energies are also calculated and compared with available experimental data.     

3D 13C–13C–13C correlation NMR for de novo distance determination of solid proteins and application to a human α-defensin

The de novo structure of an antimicrobial protein, human α-defensin 1 (HNP-1), is determined by combining a 3D ¹³C–¹³C–¹³C (CCC) magic-angle spinning (MAS) correlation experiment with standard resonance assignment experiments. Using a short spin diffusion mixing time to assign intra-residue cross peaks and a long mixing time to detect inter-residue correlation peaks, we show that the 3D CCC experiment not only reduces the ambiguity of resonance assignment, but more importantly yields two orders of magnitude more long-range distances without recourse to existing crystal structures. Most of these distance constraints could not be obtained in a de novo fashion from 2D correlation spectra due to significant resonance overlap. Combining the distance constraints from the 3D CCC experiment and the chemical-shift-derived torsion angles, we obtained a de novo high-resolution NMR structure of HNP-1, with a heavy-atom RMSD of 3.4 Å from the crystal structure of the analogous HNP-3. The average energy of the minimum-energy ensemble is less than of 40 kcal/mol. Thus, the 3D CCC experiment provides a reliable means of restraining the three-dimensional structure of insoluble proteins with unknown conformations.     

The Observation and Dynamics of 1H NMR Spin Noise in Methanol

The observation of ¹H spin noise in relation to prior established magnetization and radiation damping has revealed a correlated dynamics. The spin noise of methyl satellites in ¹³C-enriched methanol was observed in the presence of an antiphase magnetization, created by the combination of ¹H–¹³C J coupling evolution and radiofrequency (RF) pulses. A gradient pulse was applied to remove residue spin coherence coming from the RF pulses, and as a result spin noise phenomena were uncovered. While magnetization was in an inverted metastable state, the spin–spin relaxation time was shortened to prevent a super radiation burst. The relation between magnetization, radiation damping, and absorption or emission of the spin noise of methyl satellites has been studied. In relation to magnetization and radiation damping, spin noise bump and dip have been observed simultaneously in the same molecule. Both can be created through a proper inversion of magnetization. The revealed spin noise dynamics of spin system coupling to the probe circuit via radiation damping allows performance of a transformation from dip into bump by proper application of pulses combined with ¹H–¹³C J coupling evolution.     

Measuring the string susceptibility in 2D simplicial quantum gravity using the Regge approach

We use Monte Carlo simulations to study pure 2D Euclidean quantum gravity with R²-interaction on spherical topologies, employing Regge's formulation. We attempt to measure the string susceptibility exponent γ_str by using a finite-size scaling Ansatz in the expectation value of R², as has been done in a previous study by Bock and Vink (Nucl. Phys. B 438 (1995) 320). By considerably extending the range and statistics of their study we find that this Ansatz is plagued by large systematic errors. The R² specific string susceptibility exponent γ_str^′ is found to agree with theoretical predictions, but its determination also is subject to large systematic errors and the presence of finite-size scaling corrections. To circumvent this obstacle we suggest a new scaling Ansatz which in principle should be able to predict both, γ_str and γ_str^′. First results indicate that this requires large system sizes to reduce the uncertainties in the finite-size scaling Ansätze. Nevertheless, our investigation shows that within the achievable accuracy the numerical estimates are still compatible with analytic predictions, contrary to the recent claim by Bock and Vink.     

Combined solid state NMR and ONIOM studies of reversible crystalline phase reaction for nickel coordination compounds

Ni(II) with bis(acetylacetone)ethylenediamine ligand forms complexes which crystallizes as semi-hydrate with C2/c space group in monoclinic system and anhydrous form with Pna2(1) space group in orthorhombic system. ¹³C and ¹⁵N CP/MAS experiments were employed for structural characterization of both forms and searching of process of reversible water exchange in the crystal lattice. Comparative analysis of ¹³C and ¹⁵N principal elements of chemical shift tensors for ligand and complexes showed the sensitivity of δ_ii elements both for complexation and phase reaction processes. Theoretical ¹³C and ¹⁵N NMR shielding parameters σ_ii were computed employing ONIOM approach and correlated with experimental δ_ii data. The applicability of ONIOM in structural analysis of coordination compounds (CC) is discussed.     

Carbon isotopic signature reveals the geographical trend in methane consumption and production pathways in alpine ecosystems over the Qinghai–Tibetan Plateau

On the Qinghai–Tibetan Plateau, isotopic signatures in soil–atmosphere CH₄ fluxes were investigated in nine grasslands and three wetlands. In the grasslands, the fractionation factor for soil CH₄ uptake, α_soil, was much smaller than the usually reported value of 0.9975–1.0095. Stepwise multiple variation analysis indicates that α_soil is higher for higher soil water contents but is lower for higher C/N ratios of soil surface biomass. In the three wetlands, the soil-emitted δ¹³C–CH₄ was similar (?55.3?±?5.5?‰ and ?53.0?±?5.5?‰) in two bogs separated by >1000?km but was lower (?63.4?±?6.3?‰) in a marsh. Environmental factors related to intrasite variations in soil-emitted δ¹³C–CH₄ include the soil C/N ratio, oxidation–reduction potential, soil C concentration and soil water contents. Geographical isotopic surveys revealed environmental constraints on the CH₄ consumption pathways in grasslands and the biome type-specific consistency in CH₄ production pathways in wetlands.     

Towards an understanding of heavy baryon spectroscopy

The recent observation at CDF and D0 of Σ _b , Σ _b ^* and Ξ _b baryons opens the door to the advent of new states in the bottom baryon sector. The states measured provide sufficient constraints to fix the parameters of phenomenological models. One may therefore consistently predict the full bottom baryon spectra. For this purpose we have solved exactly the three-quark problem by means of the Faddeev method in momentum space. We consider our guidance may help experimentalists in the search for new bottom baryons and their findings will help in constraining further the phenomenological models. We identify particular states whose masses may allow to discriminate between the dynamics for the light quark pairs predicted by different phenomenological models. Within the same framework we also present results for charmed, doubly charmed, and doubly bottom baryons. Our results provide a restricted possible assignment of quantum numbers to recently reported charmed-baryon states. Some of them are perfectly described by D-wave excitations with J ^P = 5/2⁺, as the Λ _c (2880), Λ _c (3055), and Λ _c (3123). Communicated by V. Vento     

Kernradien von12C,13C,14N und16O aus Elektronenstreuung zwischen 30 und 60 MeV

Elastic electron scattering cross sections of¹²C,¹⁴N and¹⁶O relative to the proton, and of¹³C relative to¹²C have been measured. Using harmonic oscillator wave functions the followingrms charge radiiR _m were deduced by phaseshift calculations: 2.395 (28) fm for¹²C, 2.384 (47) fm for¹³C, 2.492 (33) fm for¹⁵N, 2.666 (33) fm for¹⁶O. The ratioR _m (¹³C)/R _m (¹²C) is 0.995±0.008. The errors given do not include uncertainties from the model dependence of the evaluation which may be of the same magnitude.     

Effect of the frequency of intramolecular motions on the NMR relaxation in liquid state temperature regime

Equations for the spectral densities of complex motion of a spin pair undergoing internal motion and isotropic/anisotropic overall rotation have been considered. The fluctuations of the interproton distances, caused by internal motion, have been taken into account in the theoretical equations. A method allowing a distinction between the isotropic and the anisotropic overall rotation of molecules has been proposed. The effect of the activation parameters of internal motions (known from the solid state study) on the measured T ₁ relaxation of the ¹³C and ¹H–¹H cross-relaxation rates has been analysed for methyl-β-D-galactopyranoside in DMSO-d6 solution. The conformational trans-gauche jumps of the methylene group are not fast enough to affect the T ₁ value of carbon C6 in the liquid state temperatures regime. Only the methyl group rotation is a very fast internal motion. This motion influences the carbon C7 relaxation and methyl protons–anomeric proton cross-relaxation. The values of interatomic distances between anomeric H(C1) and H(C5) as well as the three methyl protons H(C7) have been calculated from the cross-relaxation rates. The distance H(C1)–H(C7) fluctuates due to the rotation of methyl group. The application of the ‘model-free approach’ to study molecular dynamics in solutions is discussed.     

General models of Einstein gravity with a non-Newtonian weak-field limit

We investigate Einstein theories of gravity, coupled to a scalar field j{\varphi} and point-like matter, which are characterized by a scalar field-dependent matter coupling function e^H(j){e^{H(\varphi)}} . We show that under mild constraints on the form of the potential for the scalar field, there are a broad class of Einstein-like gravity models—characterized by the asymptotic behavior of H—which allow for a non-Newtonian weak-field limit with the gravitational potential behaving for large distances as ln r. The Newtonian term GM/r appears only as sub-leading. We point out that this behavior is also shared by gravity models described by f (R) Lagrangians. The relevance of our results for the building of infrared modified theories of gravity and for modified Newtonian dynamics is also discussed.     

Determination of 13C Enrichment by Conventional GC-MS and GC-(MS)-C-IRMS

Abstract

Isotopic enrichment of branched-chain L-amino acids (BCAA) and branched-chain 2-oxo acids (BCOA) in standard preparations and in human plasma samples withdrawn after oral loads with 1-¹³C labelled BCAA were measured on a conventional GC-MS system and an on-line GC-C-IRMS employing O-TMS quinoxalinol derivatives. It was concluded that the recently introduced GC-C-IRMS, owing to its high sensitivity, is the adequate analytical tool when tracer doses of stable isotope labelled compounds of low enrichment are to be used in biomedical in vivo studies.     

The 13C bicarbonate method: an inverse end product method for measuring CO2 production and energy expenditure

We reconsider the principle of the ¹³C bicarbonate (NaH¹³CO₃) method (¹³C-BM) for the determination of the CO₂ production to obtain an estimate of energy expenditure (EE). Its mathematical concept based on a three-compartmental model is related to the [¹⁵N]glycine end product method. The CO₂ production calculated by the ¹³C-BM, R_aCO₂(¹³C) is compared to the result from the indirect calorimetry, RCO₂(IC). In an interspecies comparison (dog, goat, horse, cattle, children, adult human; body mass ranging from 15 to 350?kg, resting and fasting conditions) we found an excellent correlation between the results of ¹³C-BM and IC with RCO₂(IC)?=?0.703?×?R_aCO₂(¹³C), (R²?=?0.99). The slope of this correlation corresponds to the fractional ¹³C recovery (RF(¹³C)) of ¹³C in breath CO₂ after administration of NaH¹³CO₃. Significant increase in RF(¹³C) was found in physically active dogs (0.95?±?0.14; n?=?5) vs. resting dogs (0.71?±?0.10, n?=?17; p?=?.015). The ¹³C recovery in young bulls was greater in blood CO₂ (0.81?±?0.05) vs. breath CO₂ (0.73?±?0.05, n?=?12, p?<?.001) and in ponies with oral (0.76?±?0.03, n?=?8) vs. intravenous administration of NaH¹³CO₃ (0.69?±?0.07; n?=?8; p?=?.026). We suggest considering the ¹³C-BM as a ‘stand-alone’ method to provide information on the total CO₂ production as an index of EE.     

Z′ search in e+e− annihilation

Expectations for constraints on extra Z bosons are derived for LEP2 and future linear e⁺e^? colliders. For typical GUTs, a Z′ with M_Z′ ≤ 3 to $6sqrt {s}$ may cause observable effects. The Z′ discovery limits are dominated by statistical errors. However, if a Z′ signal is observed, the discrimination between different models becomes much worse if systematic errors are taken into account. Discrimination between models is possible for $M_{Z^{?ime}} < 3sqrt {s}$. A determination of Z′ff couplings independently of models becomes attractive with future colliders. Anticipated bounds are determined.     

Lepton flavor violation: Constraints from the exotic μ−-eμ− conversion

The exotic neutrinoless μ^? → e ^? conversion is studied within conventional extensions of the standard model as well as in minimal supersymmetric models with R-parity-conserving and R-parity-violating mechanisms. The dependence on the nucleon and nuclear structure of the μ-e conversion rates is consistently taken into account. From the available experimental data on the branching ratio $R_{\mu e^ - }$ for the currently interesting nuclei ⁴⁸Ti and ²⁰⁸Pb, and from the experimental sensitivity for ²⁷Al, which has been employed as a target in MECO experiment at Brookhaven, we extract very severe constraints for the flavor violation parameters with our calculated transition matrix elements. We especially emphasize the constraints resulting for SUSY R-parity-violating parameters.     

Interionic potentials for alkali halide crystals derived by the hybrid Thomas-Fermi-Dirac method

The first results of a systematic study of interatomic potentials in sixteen alkali halides derived using the hybrid Thomas-Fermi-Dirac method are presented. Both the basic method and modifications to (a) correct the exchange energy to exclude the self-exchange part and (b) scale the kinetic and exchange energy terms are employed. The interactions between ion pairs are calculated at a set of interionic distances in a range corresponding to ± 30% deviations from the appropriate measured equilibrium separation. In this way a tabular function for the lattice energy/ion pair is constructed and predicted values of the equilibrium nearest neighbour interionic distance, the equilibrium lattice energy/ion pair and the Smith stiffness parameter are found numerically. The derived short-range interactions between ion pairs are fitted over the whole range to the analytic form A exp($\text{?R}\text{ρ}$) + CR^?6. It is shown that the use of an expression for the lattice energy/ion pair involving these analytic forms introduces significant errors in the predicted physical parameters.