Quantitative Analysis Of The Chemical And Physical Structures Using Solid-State NMR

Two new experiment schemes are proposed in this thesis to achieve quantitative analysis of cross polarization.They are QCP/QCP_RCmethods (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 QCP_RCmethods 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 T_1p.And QCP_RC method is more precise and suitable for molecules having short ¹H T_1pand mixtures.Because the experimental error cause by ¹H T_1prelaxation is compensated in QCP_RC.Furthermore,it has been proved by the computer simulation that QCP/QCP_RCmethods 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 T_1p,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.