Temperature Dependent Near Infrared Spectroscopy for Understanding the Hydrogen Bonding of Amines

Abstract

Temperature dependent near-infrared (NIR) spectroscopy has been developed for structural analyses, especially for the study of hydrogen bonding, due to the distinct influence of temperature on both intra-and inter-molecular interactions. In this work, the hydrogen bonding of primary aliphatic amines (amylamine, hexylamine and heptylamine) were studied using the NIR spectra measured from 25 to 80 ℃ with a step of 5 ℃. Continuous wavelet transform (CWT) was applied to enhance the resolution of the NIR spectra, and independent component analysis (ICA) was adopted for analyzing the temperature effect. High resolution spectra were obtained by CWT, from which the peaks of free and hydrogen-bonded NH groups can be identified. The results obtained by ICA show that three independent components (ICs) can be obtained, corresponding to the spectral information of the free, linearly and cyclically hydrogen-bonded NH groups, respectively. Therefore, with the reconstructed spectra from the three ICs, the variation of the three forms of NH groups with temperature can be analyzed. When temperature increases, the hydrogen-bonded NH groups transform into the free form, and the cyclic form dissociates through the linear form. Furthermore, NIR spectra of the amines in carbon tetrachloride (CCl 4 ) solution were measured at 25 ℃ in the concentration range of 0.1～1.0 mol/L. The three ICs can also be obtained by ICA from the spectra after CWT. From the variation of the ICs with concentration, it was shown that NH groups in the amines prefer to be linearly aggregated at low concentration, but the cyclic aggregation increases with the increase of concentration. In addition, a comparison was performed on the results obtained by ICA from the spectra of the three amines measured at different temperatures. The result shows that there is no obvious difference for the temperature effect of the three amines, the variation of the three forms of NH groups with temperature, however, is different. With the increase of the carbon chain length, the variation of free and cyclically hydrogen-bonded NH group slows down, but there is a slight increase for the change rate of linearly hydrogen-bonded NH group. Therefore, temperature dependent near-infrared (NIR) spectroscopy may provide a new tool for studying the hydrogen bonding in liquid and solution samples with the help of chemometric calculations. The method may be promising for analyzing the complicated interactions in bio-systems, particularly the hydrogen bonding or inter-and intramolecular interactions.

Rapid and Nondestructive Detection of Proline in Serum Using Near-Infrared Spectroscopy and Partial Least Squares

“…Shao Xueguang carried out a series of research work in this methodological field. With the changes in “disturbance factors,” a quantitative and qualitative analysis method of the solution system was established [ 35 ], which is an important theoretical basis for the detection of proline in blood in this study. It is precisely because of the advantages of near-infrared spectroscopy technology, such as simple operation, fast analysis speed, low cost of detection, and nondestructive samples, making near-infrared spectroscopy an ideal alternative method for proline detection.…”