PyrroTriPol: a semi-rigid trityl-nitroxide for high field dynamic nuclear polarization

Abstract

Magic angle spinning (MAS) dynamic nuclear polarization (DNP) has significantly broadened the scope of solid-state NMR to study biomolecular systems and materials. In recent years, the advent of very high...

AsymPol-TEKs as efficient polarizing agents for MAS-DNP in glass matrices of non-aqueous solvents

“…The 240 GHz spectrum were measured under the same conditions as previously described. 33,49,54,74 The field modulation was set to 0.3 mT and the mw power was reduced in order to avoid signal saturation. The calibration of the magnetic field allows the determination of the g-values with a global uncertainty of 2 Â 10 À4 .…”

“…However, further improvements remain mandatory to fully unlock the potential of MAS-DNP especially for challenging samples, and at high magnetic fields and fast MAS frequencies. This has triggered the continuous development of PAs for MAS-DNP, from the introduction of improved bis-nitroxides [45][46][47][48][49] to hetero-biradicals such as tritylnitroxides [50][51][52][53][54][55] and BDPA-nitroxides. 56,57 PAs are designed for use in either aqueous matrices or in organic solvents, depending on the systems studied.…”

Exploiting solid-state dynamic nuclear polarization NMR spectroscopy to establish the spatial distribution of polymorphic phases in a solid material

“…Interestingly, recent advances in dynamic nuclear polarization (DNP) NMR, 20–27 in which polarization from the electron spin of an exogenous polarizing agent 28–32 is transferred to nuclear spins through microwave irradiation, can significantly enhance the ability of NMR to detect small amounts of solid phases in heterogenous materials by enhancing the sensitivity of solid-state NMR measurements by several orders of magnitude. Furthermore, DNP NMR may also generate large polarization gradients, allowing domain sizes between ca .…”

Role of Protons in and around Strongly Coupled Nitroxide Biradicals for Cross-Effect Dynamic Nuclear Polarization

“…Instead, an increase in R CE can equivalently be achieved by using biradicals with correct relative orientations (which increases the number of CE rotor events) or by using heterobiradicals, ,, i.e., molecules made of two different radical types with different EPR line widths. The latter impacts Δω a + Δω b in eq .…”

“…42,44 It is possible that the presence of electron−electron cross-relaxation limits the performance of the AsymPols and other biradicals with large e−e couplings. 42,44 Instead, an increase in R CE can equivalently be achieved by using biradicals with correct relative orientations (which increases the number of CE rotor events) 36 or by using heterobiradicals, 42,76,77 i.e., molecules made of two different radical types with different EPR line widths. The latter impacts Δω a + Δω b in eq 1.…”