Preparation And Application Of Nuclear Spin Singlet States In Different Spin Systems

This paper focuses on the preparation of singlet states in liquid nuclear magnetic resonance?NMR?systems.This singlet state has a lifetime far greater than its longitudinal relaxation time,which can break the limitation of T₁ relaxation on magnetic resonance technology to some extent.Moreover,successfully applied to many areas such as molecular diffusion constant measurement,slow chemical exchange.We first studied the preparation of nuclear spin singlet states in two spin systems,and then extended the research object to the three-spin system.Next,the life of the spin singlet states are measured.In addition,according to the particularity of the preparation process of nuclear spin singlet,we propose a method to measure the J-coupling value of the strong coupling system.The experimental results show that the method has good accuracy.In order to understand the influence of the external environment on the conversion rate and lifetime of nuclear spin singlet state,we studied the effects of concentration,temperature,RF center,system J-coupling value and magnetic field inhomogeneity on long-lived singlet state.The experimental results show that the preparation efficiency and lifetime of the singlet state are not affected by the sample concentration and the magnetic field inhomogeneity,but sensitive to the change of temperature,RF center and system J-coupling value.Finally,we propose a new filtering method based on the nuclear spin singlet state,which can filter the non-single state signal because it is not affected by the gradient field,thus achieving high selectivity detection of specific signals.The experimental results show that the method can overcome the limitation of peak accumulation and has good selectivity for single signal detection of complex systems.