节点文献
固体核磁共振对化学与物理结构的定量表征
Quantitative Analysis of the Chemical and Physical Structures Using Solid-State NMR
【作者】 舒婕;
【导师】 陈群;
【作者基本信息】 华东师范大学 , 无线电物理, 2009, 博士
【副题名】对几种新方法的研究
【摘要】 本文首先针对固体核磁共振中交叉极化(CP)的定量问题,提出了两种新的实验方法:QCP/QCPRC(Quantitative Cross Polarization andQuantitative Cross Polarization with Relaxation Compensation)方法和SACP(Successive Adiabatic Cross Polarization)方法。实验以几种氨基酸小分子及其混合物为研究体系,通过对两种实验方法的特点与实用性的研究,得到如下结论:1)QCP/QCPRC方法成功实现固体小分子样品基团的定量分析及混合物的成分分析,其测量的百分误差可以达到5%以下。对于氢T1p较长的样品,可使用QCP方法进行分析测量;而在对氢T1p较短的样品及混合物的成分分析时,可使用QCPRC方法。与QCP方法相比,QCPRC方法具有更高的测量精度。此外,通过计算机模拟可以证明,该方法在高速魔角旋转的条件下同样适用。2)实验以丙氨酸样品为研究体系对SACP方法的特点进行了深入的讨论。证明在适当的参数组合下,该测试方法的百分误差可低至5%以下,达到了理想的定量效果。此外,通过在不同实验条件下的测试,发现SACP实验方法存在自反馈机制,这使该方法对参数设置的要求很低。在与丙氨酸相同的实验条件下,甘氨酸的定量结果的百分误差仅为0.86%。最后,结合信噪比与实验耗时的分析,发现SACP方法在实现交叉极化定量的同时,仅需使用与普通交叉极化相当甚至更短的实验时间,实验数据的处理也大为简化。本文的第二部分以一种可作为智能磁共振造影剂载体的聚离子高分子共混体系为研究对象,对魔角旋转(MAS)条件下的NMR相容性测试方法进行了研究。实验首先在5kHz的MAS转速下,使用传统的相容性研究方法,通过CP/MAS,弛豫时间的测量等实验对该造影剂的工作机理进行了研究。实验结果表明,聚离子的共混体系中,两种组分的相容尺度受到了溶液体系的pH值的影响,在pH为7.4的条件下,共混体系的相容尺度为3-4nm,而pH为4.0的条件下,相容尺度为60-70nm。两种聚离子高分子间的距离发生了纳米级的变化,这种变化影响了络合在Gd离子上的水分子与自由水分子间的交换速率,从而实现了酸敏感的聚离子造影剂造影性能的pH可调控性。为了研究MAS对传统相容性测量方法的影响,实验在5-15kHz几个不同MAS转速下,对共混体系的弛豫时间进行了测量。发现MAS对共混体系的组分的1H T1具有明显的调制作用。随着MAS转速的提高,弛豫时间所反映的体系的空间尺度逐渐变小,使共混物各组分所表现出的弛豫行为逐渐向各自纯净物体系的弛豫行为接近。不同MAS转速下弛豫时间的变化影响了相容性测量结果的准确性。这说明NMR相容性测量方法需要结合MAS转速进行分析。因而MAS下,对于相容性NMR分析方法的开发与完善十分必要。综上所述,本论文首次提出了两种新的交叉极化定量方法,并证明了其具有理想的应用前景。首次通过固体NMR方法研究酸敏感造影剂,揭示了其造影性能pH可调控性的工作机理;同时,通过变MAS转速实验,首次发现了MAS对体系相容性测试结果的影响,提出了发展相容性测试方法的必要性。
【Abstract】 Two new experiment schemes are proposed in this thesis to achieve quantitative analysis of cross polarization.They are QCP/QCPRCmethods (quantitative cross polarization and quantitative cross polarization with relaxation compensation)and SACP(successive adiabatic cross polarization) experiment.These new methods are applied successively to several amino acids and a mixture of alanine and glycine.The advantages are illustrated below.1.QCP and QCPRCmethods can quantitatively analyze the groups of small molecules and the component contents of mixtures.The percentage errors can be below 5%.QCP method is proper for molecules having long 1H T1p.And QCPRC method is more precise and suitable for molecules having short 1H T1pand mixtures.Because the experimental error cause by 1H T1prelaxation is compensated in QCPRC.Furthermore,it has been proved by the computer simulation that QCP/QCPRCmethods can be used under high MAS rates.2.SACP method is evaluated by applying it to an alanine powder sample.It is found that with a proper set of parameters,this method can give a reliable quantitative result,with a percentage error below 5%.It is also found that there is a self-feedback effect in the SACP experiment.This effect makes the parameter settings very tolerable.With the same parameter settings,the percentage errors for alanine and glycine are 3.9%and 0.86%,respectively. Compared to the conventional cross polarization experiment,SACP can achieve both the singnal enhancement and quantitative analysis with a single experiment.The second part of the thesis describes on NMR method for the miscibility research under the MAS condition.First,a pH sensitive MRI contrast agent is studied by the traditional NMR miscibility method.Through the CP/MAS experiments and T1p,T1 measurements,the mechanism of this kind of contrast agent is discovered.For this polymer blend,the miscibility scale is different under different pH conditions.This affects the exchange between the free water molecules and the water molecules in conjuction with the Gadolinium ions.So, these kinds of contrast agents display different contrast properties under different pH conditions.In order to find the effect of MAS on the traditional method,1H T1 measurements are carried out under different MAS rates.It is found that,as the MAS rate increases,the volume of sample decreases.Spin diffusion becomes less efficient.This leads to the T1 of each component obtained at higher spin rate aprroaching to its intrinsic relaxation time.The change of relaxation rate under different MAS rate leads to different miscibility results.This indicates that it is necessary to develop new NMR methods for miscibility research.In this thesis,we present two new cross polarization schemes for quantitative analysis.Both methods are accurate and qualified for further application.For the first time,we applied solid-state NMR on the study of a pH sensitive contrast agent and discovered its mechanism.It is also the first time that we found the effect of MAS rate on the miscibility research and proposed the necessity of developing NMR methods for miscibility study.
【Key words】 Solid-State NMR; Cross Polarization; Cross Depolarization; Reciprocity Relation; CP Enhancement factor; Quantification; MAS; Miscibility;