Water soluble, chiral, verdazyl radicals derived from aldoses

Le, Thanh‐Ngoc; Grewal, Harjot S; Changoco, Victor; Truong, Vinhly; Brook, David J. R.

doi:10.1016/j.tet.2016.08.035

Cited by 14 publications

(14 citation statements)

References 38 publications

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“…Owed to the in general lower toxicity of TMI free compounds, many of these applications are related to the increasingly important field of biochemistry. Similar developments with respect to their application of verdazyl radicals are conceivable, and first results have been obtained in some of the aforementioned fields [ 38 , 107 , 108 , 109 , 110 , 111 , 112 ].…”

Section: Discussionmentioning

confidence: 79%

Verdazyls as Possible Building Blocks for Multifunctional Molecular Materials: A Case Study on 1,5-Diphenyl-3-(p-iodophenyl)-verdazyl Focusing on Magnetism, Electron Transfer and the Applicability of the Sonogashira-Hagihara Reaction

et al. 2018

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This work explores the use of Kuhn verdazyl radicals as building blocks in multifunctional molecular materials in an exemplary study, focusing on the magnetic and the electron transfer (ET) characteristics, but also addressing the question whether chemical modification by cross-coupling is possible. The ET in solution is studied spectroscopically, whereas solid state measurements afford information about the magnetic susceptibility or the conductivity of the given samples. The observed results are rationalized based on the chemical structures of the molecules, which have been obtained by X-ray crystallography. The crystallographically observed molecular structures as well as the interpretation based on the spectroscopic and physical measurements are backed up by DFT calculations. The measurements indicate that only weak, antiferromagnetic (AF) coupling is observed in Kuhn verdazyls owed to the low tendency to form face-to-face stacks, but also that steric reasons alone are not sufficient to explain this behavior. Furthermore, it is also demonstrated that ET reactions proceed rapidly in verdazyl/verdazylium redox couples and that Kuhn verdazyls are suited as donor molecules in ET reactions.

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Section: Discussionmentioning

confidence: 79%

Verdazyls as Possible Building Blocks for Multifunctional Molecular Materials: A Case Study on 1,5-Diphenyl-3-(p-iodophenyl)-verdazyl Focusing on Magnetism, Electron Transfer and the Applicability of the Sonogashira-Hagihara Reaction

et al. 2018

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“…The 45 μl NMR samples contained 40 mM of radicals, either verdazyl-ribose or 4-hydroxy-TEMPO, and 150 mM 15 N, 13 C 3 -L-alanine in partially protonated glycerol/water (60/30/10 volume% d 8 -glycerol/D 2 O/H 2 O). The radical concentration is determined by measuring the optical absorption [15, 25]. For the verdazyl radical, the optical absorption at the 382 nm peak in the glycerol/water solvent was 1100 cm −1 M −1 .…”

Section: Experimental Methodsmentioning

confidence: 99%

“…This paper reports high field solid-state DNP experiments testing a recently synthesized water-soluble verdazyl radical molecule, verdazyl-ribose (Fig. 1) [15]. Verdazyl radicals were discovered in 1963 [16, 17], and can be very stable in the solid-state and in solution.…”

Section: Introductionmentioning

confidence: 99%

“…Under some conditions, verdazyl-ribose is more stable than nitroxide radicals. For example, ascorbic acid rapidly reacts with nitroxide radicals, but does not react significantly with the verdazyl [15]. Verdazyl radicals have been used successfully for liquid-state DNP at relatively low magnetic field (up to 1.4 T) [18, 19], but to our knowledge have not been previously used for high magnetic field DNP.…”

Section: Introductionmentioning

confidence: 99%

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

Thurber

Changcoco

et al. 2018

Journal of Magnetic Resonance

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Solid-state dynamic nuclear polarization (DNP) using the cross-effect relies on radical pairs whose electron spin resonance (ESR) frequencies differ by the nuclear magnetic resonance (NMR) frequency. We measure the DNP provided by a new water-soluble verdazyl radical, verdazyl-ribose, under both magic-angle spinning (MAS) and static sample conditions at 9.4 T, and compare it to a nitroxide radical, 4-hydroxy-TEMPO. We find that verdazyl-ribose is an effective radical for cross-effect DNP, with the best relative results for a non-spinning sample. Under non-spinning conditions, verdazyl-ribose provides roughly 2× larger C cross-polarized (CP) NMR signal than the nitroxide, with similar polarization buildup times, at both 29 K and 76 K. With MAS at 7 kHz and 1.5 W microwave power, the verdazyl-ribose does not provide as much DNP as the nitroxide, with the verdazyl providing less NMR signal and a longer polarization buildup time. When the microwave power is decreased to 30 mW with 5 kHz MAS, the two types of radical are comparable, with the verdazyl-doped sample having a larger NMR signal which compensates for its longer polarization buildup time. We also present electron spin relaxation measurements at Q-band (1.2 T) and ESR lineshapes at 1.2 and 9.4 T. Most notably, the verdazyl radical has a longer T than the nitroxide (9.9 ms and 1.3 ms, respectively, at 50 K and 1.2 T). The verdazyl electron spin lineshape is significantly affected by the hyperfine coupling to four N nuclei, even at 9.4 T. We also describe 3000-spin calculations to illustrate the DNP potential of possible radical pairs: verdazyl-verdazyl, verdazyl-nitroxide, or nitroxide-nitroxide pairs. These calculations suggest that the verdazyl radical at 9.4 T has a narrower linewidth than optimal for cross-effect DNP using verdazyl-verdazyl pairs. Because of the hyperfine coupling contribution to the electron spin linewidth, this implies that DNP using the verdazyl radical would improve at lower magnetic field. Another conclusion from the calculations is that a verdazyl-nitroxide bi-radical would be expected to be slightly better for cross-effect DNP than the nitroxide-nitroxide bi-radicals commonly used now, assuming the same spin-spin coupling constants.

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“…10 However, in contrast to the nitronyl nitroxides, methodologies to incorporate chirality into the vd unit have not been explored, with only one example reported in the literature to-date. 11 In the current paper we describe the versatile synthesis and characterization of two isomeric series of enantiopure N,N′-chelate vd radical ligands bearing (−)-pinene-pyridyl functionality, i.e. the (−)-5,6 series, 1a-1c and the (−)-4,5 series, 2a-2c, bearing different substituents at the 1,5 positions of the oxoverdazyl radical in order to modify the stereo-electronics, (Fig.…”

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confidence: 99%

Versatile synthesis of chiral 6-oxoverdazyl radical ligands – new building blocks for multifunctional molecule-based magnets

et al. 2018

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A versatile synthetic methodology to access the first family of chiral verdazyl N,N'-chelate ligands is described and exemplified by N,N'-dimethyl-, N,N'-di-isopropyl-and N,N'-diphenyl oxoverdazyls bearing two isomers of the pinene-pyridine functional group. Their physical properties were probed by X-band EPR spectroscopy, cyclic voltammetry and DFT calculations. Preliminary reactivity studies show they can act as N,N'-chelate ligands affording a chiral 1 : 1 complex (3b) with CuCl 2 , which was characterized by single-crystal X-ray diffraction. Variable temperature EPR studies on (3b) confirm the presence of antiferromagnetic interactions between the spins of the Cu(II) ion and the verdazyl radical.The unique properties associated with chiral molecules and their interaction with light inter alia has a rich history that today plays a central role in many areas of chemistry that include organometallic, coordination compounds, metal nanoparticles and molecule-based materials.1 The marriage of chirality with free radical chemistry has also found applications in diverse fields ranging from enantioselective catalysis 2 to the development of chiral radicals as building blocks for chiral organic, or hybrid organic/inorganic magnets. 3 In the latter case, crystallization of chiral molecules into non-centrosymmetric space groups can confer unique physical phenomena that include ferroelectric, piezoelectric, second harmonic generation (SHG) and/or non-linear optical (NLO) properties. 4 Furthermore, in select examples, when magnetic chirality coexists with nuclear chirality, the spatial and temporal symmetry is simultaneously broken affording a range of magneto-optical properties that includes magneto-chiral dichroism (MChD).5

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Water soluble, chiral, verdazyl radicals derived from aldoses

Cited by 14 publications

References 38 publications

Verdazyls as Possible Building Blocks for Multifunctional Molecular Materials: A Case Study on 1,5-Diphenyl-3-(p-iodophenyl)-verdazyl Focusing on Magnetism, Electron Transfer and the Applicability of the Sonogashira-Hagihara Reaction

Verdazyls as Possible Building Blocks for Multifunctional Molecular Materials: A Case Study on 1,5-Diphenyl-3-(p-iodophenyl)-verdazyl Focusing on Magnetism, Electron Transfer and the Applicability of the Sonogashira-Hagihara Reaction

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

Versatile synthesis of chiral 6-oxoverdazyl radical ligands – new building blocks for multifunctional molecule-based magnets

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