In the standard theory of DNP, a two-spin model is used while the nuclei near the electron are treated as 'anomalous' nuclei to differenciate the bulk nuclei outside a diffusion barrier.

The role of the core nucleu of nitroxide radicals in enhancing NMR signals by means of DNP is reexamined. Prelimilary analysis reveals that double resonance can be achieved by equalizing the Larmor frequency of the bulk nuclei and one of the ENDOR (electron nuclear double resonanc) frequencies.

[Related publication] Dowload the PDF.

Adiabatic rapid passage (ARP) conditions were originally formulated in solids. In liquids, the correlation time of molecular motion could become compariable with or shorter than the electron spin-lattice relaxation time. As a result, the adiabatic rapid passage conditions should be modified accordingly (Zhong and PilbrowJ. Magn. Reson. 97, 111 1992). This allows to characterize molecular motions, both isotropic and anisotropic, as slow as miliseconds. In essence, it theoretically predicts that the product of the measured correlation time and the magnetic field modulation amplitude equal to a constant. Alternative experimental methods are being investigated in conjuction with conventional saturation-transfer EPR setups. Recently, the adiabatic rapid passage principle has been used in realizing spacially-encoded single-scan 2D NMR by Prof. Frydman's group.

[Related publication] Dowload the PDF.

In August 1993, a new type of the electron spin echo was unexpectedly observed in a coal sample at Monash EPR Lab. As shown in Fig. a, the position of the spin echo is determined by the interpulse separation of the two long pulses but independent of the their pulse lengths. By reducing the first pulse length to a short pi/2 pulse (See Fig. b), one obtains the spin-locked echo first described by Hartmann and Hahn in 1962 at the end of their paper on nuclear double resonance in the rotating frame. Hence we denoted the new type of the electron spin echo as the electron spin-locked echo (ESLE).

The ESLE was initially applied by us in the ESEEM (electron spin echo evelope modulation) experiments by monitoring the dependence of the ESLE amplitude on the pulse length. Sharp proton NMR signals were detected which show resonant effects when the electron Rabi nutation frequency is made to match the protong Larmore frequency. No sum ESEEM frequency was observed as it always shows up using the two-short-pulse Hahn echo. Before 1993, all ESEEM experiments were conducted using relatively short microwave pulses compared with the phase memory time T2. Spin-locking and its inevitable consequence, decoupling, have been frequently applied in pulse NMR, but remained a sleeping beauty in pulsed EPR studies. In essence, the electron spin-lattice relaxation in the rotating frame was not considered in developing new pulsed EPR spectroscopy by then. Several ESLE-related pulsed EPR methods have been subsequently developed in light of our report since the manuscript was submitted. Further investigations of ESLE are being carried out in relation to qubits and other new research topics.

[Related publication] Dowload the PDF.

Despite many sophisticated magnetic resonance techniques have been developed over the part 60 years, some basic issues in theory and experimental modeling remain to be further explored. For example, detection of single electron spin would appear completely impossible ten years ago. Many formula used in EPR and NMR textbooks are based on the "high-temperature" approximation, but care should be taken in high-fields studies. Recoupling approach has provided new insights into the structural modeling of proteins, while paramagnetic spin labeling at sites of interest may facilitate and refine NMR studies of biochemical systems. Moreover, integrated magnetic resonance investigation (IMRI) seems of practical importance for combining NMR and EPR knowledge and making rational choice of aquiring new instruments at low cost.

One of basic issues we have studied is to consistently describe the magnetic resonance spectra and their dependence on the field and frequency.

[Related publication] Dowload the PDF.

[Innovative Methods of 1D&2D ESEEM] Dowload the PDF.

We are currently studying several drugs possessing potent anti-neoplastic activity based on our early EPR and NMR studies. This research project is carried out in collaboration with several leading biochemistry groups.

[Related publication] Dowload the PDF.