Dynamic Nuclear Polarization Fast Field Cycling Method for the Selective Study of Molecular Dynamics in Block Copolymers

Abstract

Dynamic nuclear polarization (DNP) is one of the most useful methods to increase sensitivity in NMR spectroscopy. It is based on the transfer of magnetization from an electron to the nuclear spin system. Based on previous work that demonstrated the feasibility of integrating DNP with fast field cycling (FFC) relaxometry and the possibility to distinguish between different mechanisms, such as the Overhauser effect (OE) and the solid effect (SE), the first FFC study of the differential relaxation properties of a copolymer is presented. For this purpose, concentrated solutions of the polystyrene-block-polybutadiene-block-polystyrene (SBS) triblock copolymer and the corresponding homopolymers were investigated. T -T relaxation data are discussed in terms of molecular mobility and the presence of radicals. The DNP selective data indicate a dominant SE contribution to the enhancement of the NMR signal for both blocks of the triblock copolymer and for the homopolymer solutions. The enhancement factors are different for both polymer types and in the copolymer, which is explained by the individual H T relaxation times and different electron-nucleus coupling strength. The T relaxation dispersion measurements of the SE enhanced signal were performed, which led to improved signal-to-noise ratios that allowed the site-specific separation of relaxation times and their dependence on the Larmor frequency with a higher accuracy.

Progress in low-field benchtop NMR spectroscopy in chemical and biochemical analysis

“…Moreover, in solution, DNP has been shown to increase sensitivity up to ten thousand times under standard conditions, opening up a variety of applications for lower frequency spectrometers [19]. DNP in compact, LF-NMR analysis has been applied to successfully study numerous processes such as lactate dehydrogenase activity in prostate carcinomas through hyperpolarisation of [1- 13 C] pyruvate [22], as well as mouse brain metabolism [23], together with molecular dynamics in block copolymers [24]. In addition to DNP, signal amplification by reversible exchange (SABRE) is considered a rapid and efficient method of NMR hyperpolarisation that can enhance the sensitivity of proton and heteronuclear experiments [25].…”

Molecular Dynamics in the Lyophases of Copolymer P123 Investigated with FFC NMR Relaxometry

“…Furthermore, our recent DNP FFC NMR coupled with CPMG is showing promising results in improving the resolution and sensitivity enhancements in low fields which enabled monitoring differential relaxation behavior of polystyrene (PS) and polybutadiene (PB) blocks of the triblock copolymer PS−PB−PS. 34 We strongly believe that such NMR methodologies are beneficial in the lyophases of P123 to discern sitespecific relaxation and further validate the data using Rouse and other relaxation models (such as BPP) pertinent to the treatment of polymer dynamics. Another complication in proton relaxation is that it involves contributions from interand intramolecular dipolar interactions.…”

“…Recently, Gizatullin et al exploited the power of the dynamic nuclear polarization FFC NMR method coupled with the Carr−Purcell−Meiboom−Gill (CPMG) spin echo sequence, for sensitivity and resolution enhancements toward assessing the differential relaxation behavior of polystyrene (PS) and polybutadiene (PB) blocks of the triblock copolymer PS−PB−PS. 34 The present investigations aim at reporting the dynamics of various lyotropic phases of block copolymer P123 employing 1 H relaxation data sampled at various Larmor frequencies (10 kHz−30 MHz), subjected to the formulation of a judicious choice of a hybrid relaxation model due to Rouse modes 17 and order fluctuation modes 25 available in the literature. To the best of our knowledge, such systematic variable-temperature 1 H FFC NMR data on associative block copolymers exhibiting lyotropic liquid crystalline polymorphism combined with a suitable analysis have not been presented in the literature before.…”

Progress in Low Field Benchtop NMR Spectroscopy in Chemical and Biochemical Analysis

“…DNP in compact, LF-NMR analysis has been applied to successfully study numerous processes such as lactate dehydrogenase activity in prostate carcinomas through hyperpolarisation of [1-13 C] pyruvate [22], as well as mouse brain metabolism [23], together with molecular dynamics in block copolymers [24]. In addition to DNP, signal amplification by reversible exchange (SABRE) is considered a rapid and efficient method of NMR hyperpolarisation that can enhance the sensitivity of proton and heteronuclear experiments [25].…”