Spin-spin coupling edition in chiral liquid crystal NMR solvent

The application of the G-SERFph pulse sequence is presented on enantiomeric mixtures dissolved in a chiral liquid crystal. It aims at editing, within one single 2D spectrum, every proton coupling which is experienced by a given proton site in the molecule, and leads to real phased T-edited spectroscopy (T=J+2D). This NMR experiment is based on the combination of homonuclear semi-selective refocusing techniques with a spatial frequency encoding of the sample. This approach, which consists in handling selectively each coupling in separate cross sections of the sample, is applied to the visualization of enantiomers dissolved in a chiral liquid crystalline phase. Advantages and limits of this methodology are widely discussed.     

Synthesis of Atom‐Precise Chiral Ag14 Clusters Protected by Penicillamine Ligands

A pair of atom‐precise chiral silver(I) nanocluster enantiomers ( Ag₁₄‐d and Ag₁₄‐l ) protected by d ‐ and l ‐penicillamine ligands is reported. Crystallographic structures reveal that the nanoclusters consist of a S^2? template and a chiral Ag₁₄ core stabilized by 12 penicillamine ligands. The penicillamine ligands show two binding fashions: (i) only thiolate coordination, and (ii) thiolate and carboxylate co‐coordination. Meanwhile, the two enantiomers show strong circular dichroism with opposite signals (mirror image relationship) owing to the chiral metallic core induced by chiral ligands, suggesting that the nanoclusters have well‐defined stereostructures as common chiral molecules do. The proton conductivity is also explored due to the existence of both amino groups and carboxylate groups from the penicillamine ligands, which is beneficial to construct H‐bond network for proton transfer.     

Partial Wave Analysis of Chiral NN Interactions

We analyze chiral interactions to N2LO in the light of proton–proton and neutron–proton scattering data published from 1950 to 2013 and discuss under which conditions the chiral constants can be extracted.     

Proton Spin and Chiral Dynamics

 Recent successful chiral models for the spin fractions of the proton rely on parametrizations that are inconsistent with deep inelastic lepton scattering unless the quark masses are neglected and inconsistent with chiral quark models based on constituent quarks, because only chiral spinflip transitions are considered. Non-spinflip transitions are important for constituent quarks as they depend on the quark masses. Therefore, the models are valid at a scale of about 0.63 GeV to Λ_χ, where dynamical quark masses are expected to be close to current quark masses, rather than Λ_QCD. When constituent quark masses are properly included, chiral quark models generate spin fractions that disagree with the proton spin data. Received July 1, 1998; accepted for publication January 30, 1999     

Resolution enhancement in spectra of natural products dissolved in weakly orienting media with the help of 1H homonuclear dipolar decoupling during acquisition: application to 1H-13C dipolar couplings measurements

In weakly orienting media such as poly-gamma-benzyl-L-glutamate (PBLG) a polymer that forms a chiral liquid crystal in organic solvents, the spectral resolution for embedded molecules is usually poor because of numerous (1)H, (1)H dipolar couplings that generally broaden proton spectra. Therefore (1)H, (13)C dipolar couplings are difficult or impossible to measure. Here, we incorporate Flip-Flop decoupling during detection into an HSQC experiment. Flip-Flop removes the (1)H, (1)H dipolar couplings and scales the chemical shifts of the protons as well as the (1)H, (13)C dipolar couplings during detection. A resolution gain by a factor 1.5-4.2 and improved signal intensity by an average factor of 1.6-1.7 have been obtained. This technique is demonstrated on (+)-menthol dissolved in a PBLG/CDCl(3) phase.     

η-Photoproduction in a gauge-invariant chiral unitary framework

We analyze photoproduction of η mesons off the proton in a gauge-invariant chiral unitary framework. The interaction kernel for meson-baryon scattering is derived from the leading order chiral effective Lagrangian and iterated in a Bethe-Salpeter equation. The recent precise threshold data from the Crystal Ball at MAMI can be described rather well and the complex pole corresponding to the S₁₁(1535) is extracted. An extension of the kernel is also discussed.     

SERF-filtered experiments: new enantio-selective tools for deciphering complex spectra of racemic mixtures dissolved in chiral oriented media

The use of chiral liquid crystals as NMR solvent is a powerful tool to visualize and quantify enantiomers. This technique is much more robust than traditional liquid state techniques. Recent developments have been performed to simplify proton spectra obtained in these solvents which are usually complex to analyze. In the different published sequences the enantiomeric differentiation can be visualized but none of them rely the different (1)H-(1)H couplings to have a coherent set for each enantiomer especially in cases of racemic mixtures. In this work to overcome such limitations, we present a new NMR pulse sequence using semi-selective pulses to assign for each enantiomer the different (1)H-(1)H couplings. The aim is to obtain the signal of only one enantiomer, through a first Selective ReFocussing (SERF) filtering block implemented for the enantio-selection followed by a second SERF block for measuring a chosen coupling. The whole sequence is called (1)H SERF-filtered-SERF. These techniques permit for the first time to assign all dipolar couplings to each enantiomer of racemic mixtures dissolved in chiral oriented media. We demonstrate that using this experiment it is possible to visualize enantio-differentiation even in the case where the multiplets are not resolved in the SERF experiments, pushing back the limits of the enantiomeric visualization.     

η − η′ photoproduction and the axial isoscalar neutral current coupling

We show that coherentη andη′ photoproduction by means of the Primakoff Effect on the proton depends on the strange component of the neutral axial current coupling. We construct polarization asymmetries that are sensitive to this coupling through theγ?Z interference. Theη′ is not a Goldstone boson of a spontaneously broken chiral symmetry, but a phenomenological analysis of theη andη′ production through chiral perturbation theory allows to calculate the observables of interest. The polarized proton or polarized photon asymmetries are predicted to be close to 10^?4 for ?q ²～0.1?0.5 GeV².     

Probing the QCD chiral cross-over transition in heavy ion collisions

We argue that by measuring higher moments of the net proton number fluctuations in heavy ion collisions (HIC) one can probe the QCD chiral cross-over transition experimentally. We discuss the properties of fluctuations of the net baryon number in the vicinity of the chiral cross-over transition within the Polyakov loop extended quark-meson model at finite temperature and baryon density. The calculation includes non-perturbative dynamics implemented within the functional renormalization group approach. We find a clear signal for the chiral cross-over transition in the fluctuations of the net baryon number. We address our theoretical findings to experimental data of the STAR Collaboration on energy and centrality dependence of the net proton number fluctuations and their probability distributions in HIC.     

Dynamical symmetry breaking in the sea of the nucleon

We derive the nonanalytic chiral behavior of the flavor asymmetry d - u. Such behavior is a unique characteristic of Goldstone boson loops in chiral theories, including QCD, and establishes the unambiguous role played by the Goldstone boson cloud in the sea of the proton. Generalizing the results to the SU(3) sector, we show that strange chiral loops require that the s - s distribution be nonzero.     

Electroweak Structure of Light Nuclei Within Chiral Effective Field Theory

We review the results of the most recent calculations for the electromagnetic structure of light nuclei, the weak muon capture on deuteron and ³He and the weak proton–proton capture reaction at energies of astrophysical interest, performed within the chiral effective field theory framework.     

Modified z-gradient filtering as a mean to obtain phased deuterium autocorrelation 2D NMR spectra in oriented solvents

We describe a modified z-gradient filter scheme specifically designed to obtain pure absorption mode deuterium 2D NMR spectra recorded in oriented solvents. The proposed technique is investigated by analysing the evolution of the density operator for a spin I=1. The method is applied to the recently designed Q-COSY and Q-resolved 2D experiments to simplify the analysis of chiral molecules dissolved in weakly orienting chiral liquid crystals. The efficiency of this z-gradient filtering technique is illustrated using the perdeuterated 1-butanol, a prochiral molecule of average Cs symmetry, dissolved in an organic solution of poly-gamma-benzyl-L-glutamate (PBLG). The experimental results as well as the advantages of the new experiments compared with the previous ones are described and discussed.     

Homo- and heteronuclear 2D NMR approaches to analyse a mixture of deuterated unlike/like stereoisomers using weakly ordering chiral liquid crystals

We describe several homo- and heteronuclear 2D NMR strategies dedicated to the analysis of anisotropic (2)H spectra of a mixture of dideuterated unlike/like stereoisomers with two remote stereogenic centers, using weakly orienting chiral liquid crystals. To this end, we propose various 2D correlation experiments, denoted "D(H)(n)D" or "D(H)(n)C" (with n=1, 2), that involve two heteronuclear polarization transfers of INEPT-type with one or two proton relays. The analytical expressions of correlation signals for four pulse sequences reported here were calculated using the product-operators formalism for spin I=1 and S=1/2. The features and advantages of each scheme are presented and discussed. The efficiency of these 2D sequences is illustrated using various deuterated model molecules, dissolved in organic solutions of polypeptides made of poly-gamma-benzyl-L-glutamate (PBLG) or poly-epsilon-carbobenzyloxy-L-lysine (PCBLL) and NMR numerical simulations.     

Doubly charged Higgs from e–γ scattering in the 3-3-1 Model

The solution of the Dirac equation with a generalized harmonic oscillator potential is used to extract the constituent bare parton densities. The results are firstly in spatial space which are converted to momentum space, using the Fourier transformation. The final results are presented in terms of the Bjorken x-variable. Employing the effective chiral quark model and the related convolutions, the parton densities inside the proton are obtained. Choosing an appropriate radius of proton, they indicate reasonable behavior. Although the initial framework is completely theoretical, the results for the sea and valence quark densities and also the ratio of d to u valence quarks inside the proton are in good agreement with the available experimental data and some theoretical models.     

NMR studies of water compartmentation in carrot parenchyma tissue during drying and freezing

An analysis is presented of the effect of drying and freezing on the distribution and pulse spacing dependence of water proton transverse relaxation times in carrot parenchyma tissue. The relaxation behaviour can be interpreted by treating the effects of changing subcellular morphology with a numerical cell model and combining this with a two-site proton exchange model to take account of solutes dissolved in the vacuolar fluid. In this way it is shown that drying removes water primarily from the vacuolar compartment, causing cell shrinkage and concentration of dissolved solutes, with little change in the volume of intercellular air spaces. Freezing causes initial ice crystal formation in the vacuolar compartment which concentrates the dissolved solutes. However, even at 248 K substantial quantities of nonfreezing water are associated with the cell walls and dissolved biopolymers. Comparison is made with previous studies on apple tissue.     

New method of 1H NMR diffusion measurements in chiral liquid crystals

A novel method for diffusion measurements in chiral liquid crystals by means of ¹H NMR is proposed. The proton NMR signal caused by a special preparation pulse sequence is computed. We determine the component of the diffusion tensor in the direction of the cholesteric helix by fitting the calculated to corresponding experimental lineshapes. A time-resolved study is possible.     

To old and new PDF and PFF

A short review of problems with parton distribution functions in nucleons, non-polarized and polarized, is given. The main part is devoted to the T-odd Collins fragmentation function and to the proton transversity distribution its possible measurements and its first experimental probe via spin asymmetries in semi-inclusive DIS. It is argued that the proton transversity distribution is close to the prediction of chiral quark soliton model could be successfully measured in future DIS experiments with longitudinally polarized target and the Collins analyzing power is linearly growing with z.     

Study of Ratio of Proton Momentum Distributions with a Chiral Quark Model

The ratio between the anomalous magnetic moments of proton and neutron has recently been suggested to be connected to the ratio of proton momentum fractions carried by the valence quarks inside it. This moment fraction ratio is respectively evaluated by using constituent quark model and chiral quark model in order to check meson cloud effect. Our results show that the meson cloud effect is remarkable to the ratio of the proton momentum fractions, and therefore, this ratio is a sensitive test for the meson cloud effect as well as for the SU(6) symmetry breaking effect.     

Leading chiral contributions to the spin structure of the proton

The leading chiral contributions to the quark and gluon components of the proton spin are calculated using heavy-baryon chiral perturbation theory. Similar calculations are done for the moments of the generalized parton distributions relevant to the quark and gluon angular momentum densities. These results provide useful insight into the role of pions in the spin structure of the nucleon and can serve as a guide for extrapolating lattice QCD calculations at large quark masses to the chiral limit.     

Chiral hyperbags

We construct and studySU (3) chiral bags (called chiral hyperbags) in the scheme of collective-coordinate quantization with chiral symmetry breaking treated as perturbation. We show how the Wess-Zumino constraint arises from the quark-bag sector, complementing the soliton sector, in a manner analogous to what happens in (1+1) dimensional chiral bags. Due to the Wess-Zumino term, all the quantum numbers — baryon charge, isopin, angular momentum, hypercharge etc. are fractionized in a prescribed manner. One notable aspect of the fractionization is that for all ranges of bag radius, there is alwaysmore angular momentum lodged in the soliton sector than in the quark sector. It is shown thatwithin the scheme we have adopted, the symmetry breaking termobstructs the Cheshire Cat principle and that consequently when strange quarks are present, the baryons (i.e. hyperons) favor a bigger bag (say R ? 1 fm) than non-strange baryons; this confirms a phenomenological argument put forward some time ago by Brown, Klimpt, Rho and Weise (at least in the collective-coordinate scheme). Our approach allows us to calculate the strangeness content of the proton — a highly topical issue — and we find that while a perturbative treatment of the symmetry breaking term can be made to work (for a big bag) for hyperon spectroscopy, the strangeness content of the proton is insensitive to the bag radius; for relevant ranges of bag radius, the ¯ss admixture stays significant, say, ?19%. This result is in stark contrast to the Callan-Klebanov Skyrmion — a remarkably successful model for hyperons — which predicts only about 3%. A subtle role of the Wess-Zumino term is suggested.