Influence of magic angle spinning on T1H of SBR studied by solid state 1H NMR

Abstract

We have investigated the influence of the high centrifugal pressure caused by fast magic-angle spinning (MAS) on the molecular motion of styrene-butadiene rubbers (SBR) filled with SiO 2 (SBR/Si composite) though solid-state magic-angle spinning nuclear magnetic Resonance ( 1 H MAS NMR) measurements. Because the 1 H-1 H dipolar interaction of elastomers is weak compared with that of glassy polymers, a narrower 1 H linewidth is observed under fast MAS. The temperature dependence of the 1 H spin-lattice relaxation time (T 1 H ) revealed that the T 1 H minimum increases with the MAS rate. Furthermore, we observed a difference in the temperature dependence of T 1 H between end-chain-modified SBR and normal (unmodified) SBR in the SBR/Si composites. The temperature dependence of T 1 H is described by the Bloembergen-Purcell-Pound theory, with the assumption that the correlation time obeys the Williams-Landel-Ferry empirical theory. The fitting showed that the molecular motion does not change significantly until a MAS rate of 20 kHz, with the motional mode changing considerably at a MAS rate of 25 kHz. The motion of SBR in the unmodified SBR/Si composite was greatly affected by the fast MAS rates. Furthermore, the plot of the estimated centrifugal pressure versus the T 1 H minimum resembled the stress-strain curve. This result enables the detection of macroscopic physical deformation by the microscopic parameter INTRODUCTIONSolid-state NMR is useful for the investigation of the molecular motion of the functional groups of elastomers and polymers. In particular, the recent development of the magic-angle spinning (MAS) technique allows a sample rotor to be spun much faster than 20 kHz. Thus, we can detect the high-resolution 1 H signals of rubbers and elastomers under the fast rates that are possible in MAS because these fast MAS rates effectively reduce the signal broadening that arises from the relatively weak 1 H-1 H dipolar interaction of elastomers (in comparison with that of glassy solid polymers).Generally, spin-lattice relaxation time (T 1 ) is observed to study molecular motion. In the case of rare spins such as 13 C, however, it is time-consuming to observe the signals and measure an accurate T 1 with a good signal-to-noise ratio. In contrast, proton signals are intense enough to allow quick analysis of molecular motion through the T 1 measurement. However, for a glassy solid polymer, the strong 1 H-1 H dipolar interaction obscures the individual functional group signals, even with fast MAS. For rubbers and elastomers under fast MAS, in contrast, each peak assigned to a respective functional group can be detected because of the weak 1 H-1 H dipolar interaction. Furthermore, it is easy to detect 1 H-T 1 ( 1 H spin-lattice relaxation time (T 1 H )) accurately. In contrast, it is well known that MAS causes the temperature of the inner sample to increase because of friction between the MAS and the air. In addition, it has recently been reported that fast MAS causes

Sedimentation Yields Long-Term Stable Protein Samples as Shown by Solid-State NMR

“…However, the maximal centrifugal pressure in an NMR rotor acts on the ZrO 2 rotor wall during MAS (∼1,500 bar at 17.0 kHz MAS in a 3.2 mm rotor, F. Engelke, lecture notes of EBSA solid-state NMR school 2014). The pressure value acting on the protein is even lower and is estimated between 60 and 91 bars (Kawamura et al, 2007;Asano et al, 2012). Consequently no pressure-induced protein degradation is expected (where this would, for example, occur at the 2,500 bar for ubiquitin (Charlier et al, 2018), 3,000 bar for PHS SNase (Roche et al, 2012), or 1,000 bar for spinach photosystem II (Tan et al, 2005)).…”

Change in local dynamics of bacteriorhodopsin with retinal isomerization under pressure as studied by fast magic angle spinning NMR

“…Pressure-induced protein structure, cell-volume changes, pharmaceutical samples and rubbers have all been characterized using fast MAS techniques. [20][21][22][23][24][25] In this study, we demonstrated that the significant changes in the dynamics of protein induced by fast sample spinning occur in the vicinity of retinal. In our previous studies, we assigned the major signals observed for bR by analyzing the associated local conformation and dynamics using a site-directed solid-state NMR approach.…”

Chapter 2. Solid‐State NMR in Drug Discovery and Development

“…42 For example, in a recent study of styrene-butadiene rubbers, a 3.2 mm outer diameter rotor with an inner diameter of 2 mm was predicted to exert a pressure of 9.5 MPa with n r ¼ 25 kHz, a much higher value than the pressure of 1.0 MPa exerted with a slower n r ¼ 10 kHz. 43 Cryogenic cooling of probe electronics to reduce thermal noise is widely employed in solution-state NMR and is used extensively in applications to drug discovery and development. Cooling of the probe coil and electronics to 25 K, or in some cases higher temperatures, while maintaining the sample at room temperature, yields signal-to-noise ratio (SNR) enhancements on the order of 2 to 4 times that of a conventional probe by reducing thermal electronic noise (see also Chapter 5 for in vivo applications of a cryogenic coil).…”