ABSTRACTA theoretical approach to Optical Nuclear Polarisation (ONP) is described, which is based on the analysis of Level Anti-Crossings (LACs) in triplet states. Here we consider ONP formed in molecular crystals doped with suitable guest molecules and ONP generated in diamond crystals containing negatively charged nitrogen-vacancy (NV–) centres. In both cases, electron spin polarisation of triplet states generated by light excitation is transferred to nuclei giving rise to ONP. Polarisation transfer is most efficient at LACs; for this reason, we consider in detail crossings of electron–nuclear energy levels and the role of different perturbation terms (coming from isotropic and anisotropic hyperfine coupling, zero-field splitting and sample orientation), which turn these crossings into LACs and give rise to ONP. Analytical results are supported by numerical calculations of the ONP field dependences. Thus, the outlined LAC analysis is a useful approach for interpreting the ONP magnetic field dependence. 相似文献
In the hyperpolarisation method known as dynamic nuclear polarisation (DNP), a small amount of unpaired electron spins is added to the sample containing the nuclear spins and the polarisation of these unpaired electron spins is transferred to the nuclear spins by means of a microwave field. Traditional DNP uses weak continuous wave (CW) microwave fields, so perturbation methods can be used to calculate the polarisation transfer. A much faster transfer of the electron spin polarisation is obtained with the integrated solid effect (ISE) which uses strong pulsed microwave fields. As in nuclear orientation via electron spin locking, the polarisation transfer is coherent, similar to the coherence transfer between nuclear spins. This paper presents a theoretical approach to calculate this polarisation transfer.
ISE is successfully used for a fast polarisation transfer from short-lived photo-excited triplet states to the surrounding nuclear spins in molecular crystals. These triplet states are strongly aligned in the photo-excitation process and do not require the low temperatures and strong magnetic fields needed to polarise the electron spins in traditional DNP. In the following paper, the theory is applied to the system naphthalene-h8 doped with pentacene-d14 which provides the photo-excited triplet states, and compared with experimental results. 相似文献
In dynamic nuclear polarisation (DNP), also called hyperpolarisation, a small amount of unpaired electron spins is added to the sample containing the nuclear spins, and the polarisation of these unpaired electron spins is transferred to the nuclear spins by means of a microwave field. Traditional DNP polarises the electron spin of stable paramagnetic centres by cooling down to low temperature and applying a strong magnetic field. Then weak continuous wave microwave fields are used to induce the polarisation transfer. Complicated cryogenic equipment and strong magnets can be avoided using short-lived photo-excited triplet states that are strongly aligned in the optical excitation process. However, a much faster transfer of the electron spin polarisation is needed and pulsed DNP methods like nuclear orientation via electron spin locking (NOVEL) and the integrated solid effect (ISE) are used.
To describe the polarisation transfer with the strong microwave fields in NOVEL and ISE, the usual perturbation methods cannot be used anymore. In the previous paper, we presented a theoretical approach to calculate the polarisation transfer in ISE. In the present paper, the theory is applied to the system naphthalene-h8 doped with pentacene-d14 yielding the photo-excited triplet states and compared with experimental results. 相似文献
Fentanyl, also known as ‘jackpot’, is a synthetic opiate that is 50–100 times more potent than morphine. Clandestine laboratories produce analogues of fentanyl, known as fentalogues to circumvent legislation regarding its production. Three pyridyl fentalogues were synthesized and then hyperpolarized by signal amplification by reversible exchange (SABRE) to appraise the forensic potential of the technique. A maximum enhancement of -168-fold at 1.4 T was recorded for the ortho pyridyl 1H nuclei. Studies of the activation parameters for the three fentalogues revealed that the ratio of ligand loss trans to hydride and hydride loss in the complex [Ir(IMes)(L)3(H)2]+ (IMes=1,3-bis(2,4,6-trimethylphenyl)imidazole-2-ylidene) ranged from 0.52 to 1.83. The fentalogue possessing the ratio closest to unity produced the largest enhancement subsequent to performing SABRE at earth's magnetic field. It was possible to hyperpolarize a pyridyl fentalogue selectively from a matrix that consisted largely of heroin (97 : 3 heroin:fentalogue) to validate the use of SABRE as a forensic tool. 相似文献
ABSTRACTA method is proposed to manipulate electron spin order of spin-correlated radical pairs. As radical pairs are often born in a well-defined spin state, e.g. in the singlet state, they acquire Chemically Induced Dynamic Electron Polarisation (CIDEP). In the case of singlet-state preparation CIDEP is of the multiplet (or anti-phase) type resulting in reduction of EPR (electron paramagnetic resonance) signals due to overlap of absorptive and emissive lines in the spectrum. Here we propose to convert the singlet spin order into net magnetisation of the radical pair by applying a microwave field, with its amplitude slowly (adiabatically) reduced to zero. We demonstrate that by properly choosing the microwave frequency one can completely convert the singlet order into net polarisation of the radical pair with significant enhancement of the signal as compared to multiplet CIDEP. Calculations show that the technique is operative for both weakly coupled and strongly coupled spin pairs. Potential applications of the method are discussed. 相似文献
This perspective article describes the concept of a long-lived nuclear spin state and some of its applications. Classes of molecular environments for which nuclear spin order can be stored for extended periods of time are described, and applications to studies of molecular dynamics and interactions, diffusion NMR and hyperpolarisation are presented. Some of the opportunities and challenges in the field are discussed. 相似文献
Proton pulse NMR, established as a versatile method in Solid State Physics, Chemistry, Biology and Medical Science, requires
on the order of 1018 nuclei to detect an electromagnetic signal in a free induction decay (FID). The main cause for this small sensitivity is
the low polarisation in the order of a few ppm due to the Boltzmann distribution in the magnetic field. Thus, NMR experiments
on hydrogen are limited to metals with extremely high hydrogen solubility like Pd near room temperature. Using a polarised
proton beam, a NMR signal is possible with as few as 1013 implanted nuclei. For the first time spin–spin and spin–lattice relaxation times were measured in Au and W with this technique
at the Bonn cyclotron. 相似文献
The (+) and ( ? ) enantiomers for a cryptophane-7-bond-linker-benzenesulfonamide biosensor (C7B) were synthesised and their chirality was confirmed by electronic circular dichroism spectroscopy. Biosensor binding to carbonic anhydrase II (CAII) was characterised for both enantiomers by hyperpolarised (HP) 129Xe NMR spectroscopy. Our previous study of the racemic ( ± ) C7B biosensor–CAII complex [Chambers, J.M.; Hill, P.A.; Aaron, J.A.; Han, Z.H.; Christianson, D.W.; Kuzma, N.N.; Dmochowski, I.J. J. Am. Chem. Soc.2009, 131, 563–569] identified two ‘bound’ 129Xe@C7B peaks by HP 129Xe NMR (at 71 and 67 ppm, relative to ‘free’ biosensor at 64 ppm), which led to the initial hypothesis that (+) and ( ? ) enantiomers produce diastereomeric peaks when coordinated to Zn2+ at the chiral CAII active site. Unexpectedly, the single enantiomers complexed with CAII also identified two ‘bound’ 129Xe@C7B peaks: (+) 72, 68 ppm and ( ? ) 68, 67 ppm. These results are consistent with X-ray crystallographic evidence for benzenesulfonamide inhibitors occupying a second site near the CAII surface. As illustrated by our studies of this model protein–ligand interaction, HP 129Xe NMR spectroscopy can be useful for identifying supramolecular assemblies in solution. 相似文献