323,149 research outputs found
Nuclear spin singlet states as magnetic on/off probes in self-assembling systems
No full textSelf-assembling processes occur in a variety of compounds such as peptides, proteins and DNA. These processes have been linked to pathologies and have as well been exploited for designing responsive contrast agents for disease detection. Novel methods to investigate and detect self-assembly therefore hold promise to obtain more insights into disease progression or open pathways to the design of novel self-assembling materials. In this article we are introducing nuclear singlet states to probe self-assembly in the dipeptide isoleucine–phenylalanine (IF) as a thermoresponsive on/off switch for nuclear magnetic resonance (NMR). We have investigated the relaxation and singlet state properties of the β-protons of phenylalanine in the IF dipeptide in aqueous solutions. At IF concentrations of 2 wt% and above 308 K, a long lived nuclear singlet state, as compared to the longitudinal relaxation, was observed. At 308 K the dipeptide starts forming a gel and no singlet state is accessible at lower temperatures. Upon heating, the gel disassembles and an isotropic liquid forms making the singlet state accessible again. This demonstrates the thermoresponsive on–off character of the nuclear spin singlet state in the IF dipeptide
Over 50 %1H and 13C polarization for generating hyperpolarized metabolites—A para‐hydrogen approach.
No full textpara‐Hydrogen‐induced polarization (PHIP) is a method to rapidly generate hyperpolarized compounds, enhancing the signal of nuclear magnetic resonance (NMR) experiments by several thousand‐fold. The hyperpolarization of metabolites and their use as contrast agents in vivo is an emerging diagnostic technique. High degrees of polarization and extended polarization lifetime are necessary requirements for the detection of metabolites in vivo. Here, we present pulsed NMR methods for obtaining hyperpolarized magnetization in two metabolites. We demonstrate that the hydrogenation with para‐hydrogen of perdeuterated vinyl acetate allows us to create hyperpolarized ethyl acetate with close to 60 % 1H two‐spin order. With nearly 100 % efficiency, this order can either be transferred to 1H in‐phase magnetization or 13C magnetization of the carbonyl function. Close to 60 % polarization is experimentally verified for both nuclei. Cleavage of the ethyl acetate precursor in a 20 s reaction yields ethanol with approximately 27 % 1H polarization and acetate with around 20 % 13C polarization. This development will open new opportunities to generate metabolic contrast agents in less than one minute
Diario del dolore. Feriti e crocerossine nella Prima guerra mondiale attraverso le loro scritture
No full textHyperpolarization of15N in an amino acid derivative
No full textHyperpolarization is a nuclear magnetic resonance (NMR) technique which can be used to significantly enhance the signal in NMR experiments. In recent years, the possibility to enhance the NMR signal of heteronuclei by the use of para-hydrogen induced polarization (PHIP) has gained attention, especially in the area of possible applications in magnetic resonance imaging (MRI). Herein we introduce a way to synthesize a fully deuterated, 15N labelled amino acid derivative and the possibility to polarize the 15N by means of hydrogenation with para-hydrogen to a polarization level of 0.18%. The longevity of the polarization with a longitudinal relaxation time of more than a minute can allow for the observation of dynamic processes and metabolic imaging in vivo. In addition, we observe the phenomenon of proton–deuterium exchange with a homogeneous catalyst leading to signal enhanced allyl moeities in the precursor
Orientational Sampling Schemes Based on Four Dimensional Polytopes
No full textThe vertices of regular four-dimensional polytopes are used to generate sets of uniformly distributed three-dimensional rotations, which are provided as tables of Euler angles. The spherical moments of these orientational sampling schemes are treated using group theory. The orientational sampling sets may be used in the numerical computation of solid-state nuclear magnetic resonance spectra, and in spherical tensor analysis procedures
Pulsed magnetic resonance to signal‐enhance metabolites within seconds by utilizing para‐hydrogen
No full textDiseases such as Alzheimer's and cancer have been linked to metabolic dysfunctions, and further understanding of metabolic pathways raises hope to develop cures for such diseases. To broaden the knowledge of metabolisms in vitro and in vivo, methods are desirable for direct probing of metabolic function. Here, we are introducing a pulsed nuclear magnetic resonance (NMR) approach to generate hyperpolarized metabolites within seconds, which act as metabolism probes. Hyperpolarization represents a magnetic resonance technique to enhance signals by over 10 000‐fold. We accomplished an efficient metabolite hyperpolarization by developing an isotopic labeling strategy for generating precursors containing a favorable nuclear spin system to add para‐hydrogen and convert its two‐spin longitudinal order into enhanced metabolite signals. The transfer is performed by an invented NMR experiment and 20 000‐fold signal enhancements are achieved. Our technique provides a fast way of generating hyperpolarized metabolites by using para‐hydrogen directly in a high magnetic field without the need for field cycling
Molecular precursors to produce para-hydrogen enhanced metabolites at any field
No full textEnhancing magnetic resonance signal via hyperpolarization techniques enables the real-time detection of metabolic transformations even in vivo. The use of para-hydrogen to enhance 13C-enriched metabolites has opened a rapid pathway for the production of hyperpolarized metabolites, which usually requires specialized equipment. Metabolite precursors that can be hyperpolarized and converted into metabolites at any given field would open up opportunities for many labs to make use of this technology because already existing hardware could be used. We report here on the complete synthesis and hyperpolarization of suitable precursor molecules of the side-arm hydrogenation approach. The better accessibility to such side-arms promises that the para-hydrogen approach can be implemented in every lab with existing two channel NMR spectrometers for 1H and 13C independent of the magnetic field
Symmetry-breaking in the endofullerene H2O@C60revealed in the quantum dynamics of ortho and para-water: a neutron scattering investigation
No full textInelastic neutron scattering (INS) has been employed to investigate the quantum dynamics of water molecules permanently entrapped inside the cages of C60 fullerene molecules. This study of the supramolecular complex, H2O@C60, provides the unique opportunity to study isolated water molecules in a highly symmetric environment. Free from strong interactions, the water molecule has a high degree of rotational freedom enabling its nuclear spin isomers, ortho-H2O and para-H2O to be separately identified and studied. The INS technique mediates transitions between the ortho and para spin isomers and using three INS spectrometers, the rotational levels of H2O have been investigated, correlating well with the known levels in gaseous water. The slow process of nuclear spin conversion between ortho-H2O and para-H2O is revealed in the time dependence of the INS peak intensities over periods of many hours. Of particular interest to this study is the observed splitting of the ground state of ortho-H2O, raising the three-fold degeneracy into two states with degeneracy 2 and 1 respectively. This is attributed to a symmetry-breaking interaction of the water environment
Nuclear singlet multimers (NUSIMERs) with long-lived singlet states
No full textMagnetic resonance (NMR) is a powerful tool in chemical analysis, structure determination and in medical diagnostics. Developing novel biological sensors for this field holds promise to better investigate protein structures or target diseases more efficiently. Herein, we explore nuclear spin singlet states in dendritic macromolecules as a platform molecule to develop stimuli responsive probes. We have developed a nuclear singlet multimer (NUSIMER) based on a generation 5 poly(amidoamine) dendrimer (PAMAM) which contains on average about 90 accessible nuclear spin singlet states with lifetimes up to 10-fold longer than the T1 relaxation times (up to 10 seconds Tsvs. T1 < 0.5 seconds) in a single molecule. We demonstrate little influence on the singlet lifetime in phosphate buffer (H2O) and a high viscosity gel environment in the presence of paramagnetic oxygen. Additionally, we demonstrate an increase in singlet lifetime upon the release of a protective chemical moiety from the NUSIMER following a stimulus, whereby no change in longitudinal relaxation time is observed. The robustness and change in singlet lifetime of the NUSIMER holds promise for the development of a novel type of biosensors
Infrared spectroscopy of endohedral HD and D2 in C60
No full textWe report on the dynamics of two hydrogen isotopomers, D2 and HD, trapped in the molecular cages of a fullerene C60 molecule. We measured the infrared spectra and analyzed them using a spherical potential for a vibrating rotor. The potential, vibration-rotation Hamiltonian, and dipole moment parameters are compared with previously studied H2@C 60 parameters [M. Ge, U. Nagel, D. Hvonen, T. Rm, S. Mamone, M. H. Levitt, M. Carravetta, Y. Murata, K. Komatsu, J. Y.-C. Chen, and N. J. Turro, J. Chem. Phys. 134, 054507 (2011)10.1063/1.3535598]. The isotropic part of the potential is similar for all three isotopomers. In HD@C60, we observe mixing of the rotational states and an interference effect of the dipole moment terms due to the displacement of the HD rotation center from the fullerene cage center. © 2011 American Institute of Physics
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