Effect of Urea on Phase Transition of Poly(N-isopropylacrylamide) and Poly(N,N-diethylacrylamide) Hydrogels: A Clue for Urea-Induced Denaturation

Abstract

spectroscopy has been applied to study the urea effect on phase transition of two similar thermosensitive polymer hydrogels: poly(N-isopropylacrylamide) (PNIPAM) and poly(N,N-diethylacrylamide) (PDEA). It is found that urea influences the phase transition of the hydrogels in opposite ways: lowering the lower critical solution temperature (LCST) of PNIPAM and hence stabilizing its globular structure, whereas raising the LCST of PDEA and destabilizing the globular structure. The selfdiffusion coefficient and urea−polymer nuclear Overhauser effect (NOE) measurement reveal that urea has a stronger interaction with PNIPAM than with PDEA. Moreover, the enhanced positive water−PNIPAM NOE suggests that urea not only interacts directly with PNIPAM via hydrogen bond but also intensifies the hydrogen bonding interaction between water and PNIPAM. We suggest that different urea−polymer hydrogen bonding interaction due to the presence or absence of amide hydrogen is correlated with the distinct LCST variation of PNIPAM and PDEA.

A new thermoresponsive polymer of poly(N-acryloylsarcosine methyl ester) with a tunable LCST

“…[19][20][21][22][23][24][25][26][27][28][38][39][40][41][42][43][44][45] Figure 4A shows the temperature-dependent transmittance of PNASME at different polymer concentration. It indicates that the LCST-type soluble-to-insoluble phase transition of the diluted PNASME 170 solution (0.10-0.20 wt%) occurs within a broad temperature range, whereas with the polymer concentration increasing above 0.30 wt% a very sharp soluble-to-insoluble phase transition takes place within a narrow temperature window of ~1 o C. This sharp soluble-toinsoluble phase transition of PNASME suggests that the PNASME is a qualified candidate of thermoresponsive sensors.…”

“…The similar phenomenon has been observed in the cases of PDEAM and polypeptides. 21,44,45 Phenol, a Lewis acid, is also employed to understand the hydrogen bonding interaction between PNASME and water. As summarized in Figure 7 (black solid circle), a contrary trend of the T cp decreasing with the increase in the phenol concentration has been found.…”

“…45,59,60 By choosing a suitable mixing time, the magnetization may transfer between the dipolar and coupled spin pair and therefore increases the strength of cross-peaks in the spectra. In this study, we employ this technology to assess the direct hydrogen bonding between PNASME 170 , and urea or phenol.…”

“…21, 22 Ye et al employed differential scanning calorimetry (DSC) to study the effect of urea on the LCST of PNIPAM, and a similar result also was reported. 23 Poly(N,N-diethylacrylamide) (PDEAM), another thermoresponsive N-alkyl-substituted polyacrylamides containing a tertiary amide in the pendant (Scheme 1), exhibits an LCST at 35 o C. [38][39][40][41][42][43][44][45] Both static/dynamic light scattering and high-resolution magic angle spinning (HRMAS) NMR spectroscopy have revealed the tertiary amide groups of PDEAM still have the ability to interact with water or urea via hydrogen bonding by accepting the proton from them. 44,45 As such, all these results indicate that the amide groups, no matter the secondary amide group or the tertiary amide group, are the crucial component for the thermoresponse of polyacrylamides, and can be powerful tools for designing new thermoresponsive polymers.…”

Quantification of solvent water and hydration dynamic of thermo‐sensitive microgel by dielectric spectroscopy

“…Due to the complex structure of biomacromolecules, some alternatives are often used as model molecules to study some biological processes. Poly( N ‐isopropylacrylamide) (PNIPAM), which is a typical thermosensitive polymer with the lower critical solution temperature (LCST) of 32 °C [for PNIPAM gel, it is called volume phase transition temperature (VPTT)], is often used as a model molecule because of its similar structure with amino acid which is the basic unit of some biomacromolecules such as protein and enzyme . In microgel aqueous solution, there are two forms of water, that is, the bound and free water.…”