Understanding the effect of urea on the phase transition of poly(N-isopropylacrylamide) in aqueous solution by temperature-dependent near-infrared spectroscopy
“…S 2 water species acts as a bridge to connect the polymer chains in the loose hydrophobic structure, and the dissociation of the S 2 at high temperatures leads to the formation of the micelle. Furthermore, the effect of urea on the interaction of water and the polymer poly(N-isopropyl acrylamide) (PNIPAM) was studied by NPCA for understanding the denaturation in aqueous environments [51]. The results indicate that the water species with three hydrogen bonds (S 3 ) plays an important role in the stabilization of PNIPAM, which may connect the NH and CO groups in the polymer.…”
Section: Structural Change Of Water In the Aggregation Of Proteins An...mentioning
Temperature-dependent near-infrared (NIR) spectroscopy has been developed and taken as a powerful technique for analyzing the structure of water and the interactions in aqueous systems. Due to the overlapping of the peaks in NIR spectra, it is difficult to obtain the spectral features showing the structures and interactions. Chemometrics, therefore, is adopted to improve the spectral resolution and extract spectral information from the temperature-dependent NIR spectra for structural and quantitative analysis. In this review, works on chemometric studies for analyzing temperature-dependent NIR spectra were summarized. The temperature-induced spectral features of water structures can be extracted from the spectra with the help of chemometrics. Using the spectral variation of water with the temperature, the structural changes of small molecules, proteins, thermo-responsive polymers, and their interactions with water in aqueous solutions can be demonstrated. Furthermore, quantitative models between the spectra and the temperature or concentration can be established using the spectral variations of water and applied to determine the compositions in aqueous mixtures.
“…S 2 water species acts as a bridge to connect the polymer chains in the loose hydrophobic structure, and the dissociation of the S 2 at high temperatures leads to the formation of the micelle. Furthermore, the effect of urea on the interaction of water and the polymer poly(N-isopropyl acrylamide) (PNIPAM) was studied by NPCA for understanding the denaturation in aqueous environments [51]. The results indicate that the water species with three hydrogen bonds (S 3 ) plays an important role in the stabilization of PNIPAM, which may connect the NH and CO groups in the polymer.…”
Section: Structural Change Of Water In the Aggregation Of Proteins An...mentioning
Temperature-dependent near-infrared (NIR) spectroscopy has been developed and taken as a powerful technique for analyzing the structure of water and the interactions in aqueous systems. Due to the overlapping of the peaks in NIR spectra, it is difficult to obtain the spectral features showing the structures and interactions. Chemometrics, therefore, is adopted to improve the spectral resolution and extract spectral information from the temperature-dependent NIR spectra for structural and quantitative analysis. In this review, works on chemometric studies for analyzing temperature-dependent NIR spectra were summarized. The temperature-induced spectral features of water structures can be extracted from the spectra with the help of chemometrics. Using the spectral variation of water with the temperature, the structural changes of small molecules, proteins, thermo-responsive polymers, and their interactions with water in aqueous solutions can be demonstrated. Furthermore, quantitative models between the spectra and the temperature or concentration can be established using the spectral variations of water and applied to determine the compositions in aqueous mixtures.
“…The increase of the former shows the possibility to obtain the quantity of water from the spectra and the profile change of the latter indicates that the hydration of NH and CH may be reflected in the spectra. 12,18,31,33,41 Figure 2.NIR spectra of water and hydrogels with different water contents measured at 30 °C.…”
Section: Resultsmentioning
confidence: 99%
“…In our previous work, the quantitative spectra–temperature relationship (QSTR) model was established and applied to the quantitative analysis of aqueous mixtures. 24,25 The structures and function of water in an anti-freezing system 26 and the chemical transformations of oligopeptides, 27 proteins, 28,29 and temperature-sensitive polymers 30,31 were obtained from the change in the NIR spectra of water with concentration and temperature. Furthermore, with the help of molecular simulation, nine water structures with different hydrogen bonding were proposed and described by the form of AmDn, in which m and n are the number of proton acceptors and donors in a water molecule.…”
Analysis of the confined water in hydrogels is essential for understanding the chemical and physical properties. Methods to quantify the content and study the structure of water in hydrogel using near-infrared (NIR) spectroscopy were proposed. The NIR spectra of poly-N,N,-dimethylacrylamide (PDMAA) hydrogel with different water contents were measured at different temperatures. A partial least squares (PLS) model was established using the spectra of the samples with water content (wh) from 4.0% to 387.6%. Continuous wavelet transform (CWT) was adopt to calculate the resolution enhanced spectra, from which the spectral features of water species with free OH (S0) and with one or two hydrogen bonds (S1, S2) was obtained. The variation of these water species with water content suggests the existence of the water molecules bonding to NH groups by one hydrogen bond (S1NH), the water-cage directly hydrating the CH groups of the polymer network and bulk-like water. Moreover, the variation of water structures with temperature shows that the release of bulk-like water occurs in the phase transition of the hydrogel, but the S1NH and cage water keep unchanged. The former explains the sudden volume shrinkage for the phase transition and the latter may be the reason for the shape memory effect in the repeated swelling and deswelling of hydrogels.
“…Although there is a peak around 7120 cm À1 in Figure 3(b), which indicates the existence of the free water in the system, the two peaks at 6968 and 6783 cm À1 suggest that IC2 w should be the spectral information of bonded water, because the peaks of hydrogen-bonded water molecules appear at a lower wavenumber than that of free water molecules in NIR spectrum. [25][26][27][28][29]37,41,44 Therefore, the main information in IC2 w should come from the bound water. Comparing IC3 w with the reference spectrum in Figure 3(c), it is clear that the IC is the spectral feature of core water, which is known as much similar with the bulk water.…”
Section: Spectral Analysismentioning
confidence: 99%
“…Besides, the variation of water structures during the aggregation of thermosensitive polymers was also analyzed. 28,29 The water species with two hydrogen bonds (S 2 ) and three hydrogen bonds (S 3 ) were found to play an important role in the phase transition.…”
Confined water has an important effect on the structural stability and biological activity of biomolecules. Reverse micelles (RM) are a good system for investigating the structure of water in confined environment. In this work, the structure of water in RMs with different water content ( w0) was studied using near infrared spectra measured at different temperature. Independent component analysis was used to extract the spectral features changing with the w0 and temperature. Three independent components representing the spectral features of trapped water, bound water, and core water were obtained. Furthermore, through the variation of the trapped water and bound water with temperature, an increase of the former and a reduction of the latter were found, revealing that the two water structures play an important role for the mobility of the RM’s shell.
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