Development of stopped-flow hyper-CEST NMR method on recirculating hyperpolarization system as applied to void space...

Area of Science:

• Polymer Science
• Analytical Chemistry
• Spectroscopy

Background:

• 129Xe NMR spectroscopy is valuable for analyzing polymer void spaces (free volume).
• Low sensitivity of traditional 129Xe NMR limits its application in research and industry.
• Developing methods to enhance signal detection is crucial for polymer characterization.

Purpose of the Study:

• To overcome the sensitivity limitations of 129Xe NMR spectroscopy for polymer analysis.
• To introduce and validate an enhanced hyper-CEST NMR method incorporating recirculation and subtraction modes.
• To accurately detect and analyze void spaces in polymer films like cellulose nanofiber (CNF) and silk fibroin (SF).

Main Methods:

• Utilized a hyper-CEST (Chemical Exchange Saturation Transfer) method combined with hyperpolarization.
• Incorporated recirculation and subtraction modes alongside a stopped-flow technique for signal enhancement.
• Analyzed saturation frequency dependence at 100 Hz increments to determine chemical shifts of weak signals.

Main Results:

• The enhanced hyper-CEST method successfully detected very weak hidden signals in CNF and SF films.
• Void space sizes in CNF and SF were determined by analyzing the chemical shifts of these hidden peaks.
• The subtraction mode proved efficient in identifying the presence or absence of specific signals.
• The method's applicability was further supported by analysis of thermoplastic polyurethane film.

Conclusions:

• The developed hyper-CEST NMR method with recirculation and subtraction modes significantly enhances the detection of weak signals in polymers.
• This technique provides accurate insights into polymer void spaces, overcoming previous sensitivity limitations.
• The method holds promise for future exploratory studies involving the detection of very weak signals in various materials.