Verdazyls and Related Nitrogen‐Containing Free Radicals

Abstract

acids, and b) to differentiate between primary, secondary, and tertiary monohydric alcohols and for the quantitative analysis of binary and ternary mixtures of these alcohols. The three types of monobasic acids can be distinguished by the multiplet structure and intensity ratio of the a-CH2 and a-CH proton resonance signals, provided that these do not overlap with the P-proton multiplets. The intensities of the signals are determined relative to that of the carboxylic proton resonance signal. For quantitative analysis of binary mixtures, the intensity ratio can be used. For the analysis of alcohols, the preparation of the sample constitutes an important part of the procedure, for it must ensure that any exchange of the hydroxyl protons comes to a standstill [7]. The three types of alcohol then show differences in the multiplicity of the hydroxyl signal and in its chemical shift. This depends on the solvent and the temperature. A second procedure, based on comparison of peak heights gives results of similar absolute accuracy (is %) in suitable cases.Relations between Structure and Rate Constants for the Dissociation and Recombination of Carboxylic Acids

Dynamic Nuclear Polarization for Sensitivity Enhancement in Biomolecular Solid-State NMR

“…In verdazyl radical, , the electron spin is not stringently centered at a carbon site, but is largely delocalized over a conjugated system of four nitrogens and a central carbon which is carrying negative spin density via the mechanism of spin polarization of its atomic orbitals. , Verdazyl-ribose is well water-soluble and highly biocompatible, and may feature better stability than nitroxide-based radicals under biologically relevant conditions . Its MAS DNP performance is close to that of a nitroxide (see Section ) at 9.4 T, however, best performance is expected at lower fields because the dominating broadening mechanism is (field-independent) HFI to the four 14 N nuclei …”

“…In verdazyl radical, 251,252 the electron spin is not stringently centered at a carbon site, but is largely delocalized over a conjugated system of four nitrogens and a central carbon which is carrying negative spin density via the mechanism of spin polarization of its atomic orbitals. 253,254 Verdazyl-ribose is well water-soluble and highly biocompatible, and may feature better stability than nitroxide-based radicals under biologically relevant conditions.…”

Verdazyls and Related Radicals Containing the Hydrazyl [R2N‐NR] Group

“…79 The localized electronic structure attenuates the "communication" of verdazyl radicals with other covalently-linked chromophores. Experimental and computational 52,73,80 -82 studies on a variety of C3-linked verdazyl di-(or tri-or tetra-) radicals 32 or their N-linked 19,27,83 counterparts 33 show the two radicals to invariably be fairly weakly electronically coupled, irrespective of whether the diradical in question is based on a Kuhn 19,[24][25][26]28,84 or 6-oxoverdazyl 42,49 -52 structure. Even the 6-oxoverdazyl diradical, in which the two radicals are directly linked, remains an open shell singlet diradical in its ground state, with the triplet excited state some 760 cm −1 higher in energy.…”

Verdazyl-ribose: A new radical for solid-state dynamic nuclear polarization at high magnetic field

“…1) [15]. Verdazyl radicals were discovered in 1963 [16, 17], and can be very stable in the solid-state and in solution. Under some conditions, verdazyl-ribose is more stable than nitroxide radicals.…”