1. State Key Laboratory of Applied Organic ChemistryKey Laboratory of Nonferrous Metal Chemistry andResources Utilization of Gansu ProvinceCollege of Chemistry and Chemical EngineeringLanzhou University Lanzhou 730000 P. R. China
2. Key Laboratory of Magnetic Resonance in Biological SystemsState Key Laboratory of Magnetic Resonance and Atomic andMolecular PhysicsWuhan Institute of Physics and MathematicsChinese Academy of Sciences Wuhan 430071 P. R. China