用遗传算法优化灵敏度增强的定量^(13)C NMR实验

Optimizing Sensitivity-enhanced Quantitative^(13)C NMR Experiment by Genetic Algorithm

定量核磁共振(qNMR)是NMR分析的重要组成部分,在组分分析、化合物结构鉴定等方面发挥着重要作用.碳原子组成了有机物的框架,而^(13)C NMR具有化学位移分布范围宽、谱峰窄、可宽带去耦等优点,因此^(13)C NMR在有机物分析中具有独特优势.但^(13)C核天然丰度低、旋磁比小、纵向弛豫时间较长,阻碍了定量^(13)C NMR的更广泛应用.在此前的工作中,我们提出了Q-DEPT^(+)脉冲序列,设计了读脉冲翻转角和极化转移时间双重循环,使得CH、CH_(2)、CH_(3)三种碳核在较宽的^(1)J_(CH)范围内获得均匀的灵敏度增强,并可用于定量^(13)C NMR实验.在本文中,我们利用遗传算法进一步优化了Q-DEPT^(+)实验的极化转移时间和读取脉冲的脉宽,并将^(13)C通道的180°硬脉冲改为对频偏效应有补偿作用的G5组合脉冲,优化后的序列称为Q-DEPT^(++).对胆固醇乙酸酯的氘代氯仿溶液分别使用常规反门控去耦(zgig)、Q-DEPT^(+)和Q-DEPT^(++)脉冲序列进行了定量实验,并将三者的定量准确性和灵敏度进行了对比.结果显示Q-DEPT^(++)脉冲序列在定量准确性和灵敏度两方面均有明显提高.

Quantitative NMR experiments are an essential part of NMR analysis,which play a critical role in component analysis and compound structure identification.Carbon atoms form the framework of organic compounds,and^(13)C NMR has unique advantages in organic analysis due to its wide chemical shift range,narrow spectral peaks,and broadband decoupling capability.However,the low natural abundance,low gyromagnetic ratio,and long longitudinal relaxation time of^(13)C nuclei hinder its wider application in quantitative experiments.In our previous work,we proposed the Q-DEPT^(+)pulse sequence and designed a double loop of pulse flip angle and polarization transfer time,which allows for uniform sensitivity enhancement for the three types of carbon nuclei,CH,CH_(2),and CH_(3),within a wide^(1)J_(CH)range,making it suitable for quantitative^(13)C NMR.In this study,we further optimized the polarization transfer time and read pulse width ofthe Q-DEPT^(+)experiment by using a genetic algorithm,and replaced the 180°hard pulse in the^(13)C channel with a G5 composite pulse that compensates for the frequency offset effect.The optimized pulse sequence was named Q-DEPT^(++).Quantitative experiments were performed on cholesterol acetate in CDCl_(3)by using the reverse-gated decoupling pulse sequence(zgig),Q-DEPT^(+),and Q-DEPT^(++)respectively,and the quantification accuracy and sensitivity of the three pulse sequences were compared.The results showed that Q-DEPT^(++)has obvious improvement in both quantification accuracy and sensitivity.