Investigation Of New Spectroscopic Technique And Exploration Of Its Potential Application On Macromolecules

The present study investigates some new spectroscopic technique and demonstrates their potential application on some macromoles systems.The use of a novel spectral interconversion scheme to probe weak molecular interactions of a polymer system is investigated. Based on the multivariate regression model, such as, partial least squares (PLS2) and principal component analysis (PCA), the thermally induced changes in the weak interaction of poly(n-isopropylacrylamide) (PNIPA) film was studied by the interconversion between middle infrared (MIR) and near IR (NIR) spectra measured at temperatures between 40 and 220 oC. It was demonstrated that not only NIR spectra but also well-resolved MIR spectra of PNIPA film, either in narrow or wide spectral ranges, can be predicted from each other based on the proposed scheme. The thermally induced weak interaction changes of PNIPA, expressed as either the band shift or intensity changes at a specific region, can be probed properly. This study provides a novel method for the analysis of weak interactions in complex systems. For a better PCA-based prediction, it is suggested that the samples whose spectra to be predicted should be as similar as possible to those used in the model. The robustness of the spectral prediction is also compared with that achieved by partial least square (PLS2) model in detail, illustrating its advantages in predicting more subtle structural changes as C-H groups.A new application of generalized two-dimensional (2D) correlation spectroscopy called"concatenated"2D correlation analysis is proposed, which is useful in identifying the presence of strict similarity or very subtle difference between two spectral data sets having a similar origin. In this study, the detailed examination of process reversibility is explored. Concatenated 2D correlation analysis can extract more detailed information, such as the comparison of effects of two different perturbations or different systems. We describe the principle of the"mirror image concatenation"in 2D correlation analysis, which is applied to demonstrate its reliability and efficiency on three spectral models. The concatenated 2D correlation analysis shows its power in revealing the irreversibility of thermally induced conformation transition of RNase A as well as the comparison of different species of TCM.The study demonstrates an application of"concatenated"2D correlation analysis in semi-quantitative examination of the reversibility of the temperature-induced hydration variation of PNIPMA in water solution. Hydration reversibility of hydrophilic amide group and hydrophobic CH group are compared in different temperature ranges. The contribution of different factors to the 2D asynchronous spectrum could be separated by selecting the range of the spectral dataset for concatenation. The hydration variation of PNIPMA manifests significant irreversibility in the phase separation stage. The irreversibility of CH groups is not as strong as that of amide group during the round trip.