New, stable β‐phosphorus‐labelled pyrrolidine nitroxides from nitrones for magnetometry: an ESR investigationHaire, D. Lawrence; Janzen, Edward G.; Chen, Guoman; Robinson, Valerie J.; Hrvoic, Ivan
doi: 10.1002/(SICI)1097-458X(199904)37:4<251::AID-MRC406>3.0.CO;2-Mpmid: N/A
The present study was devoted to the design and synthesis
of new, prototypical nitroxides for use in dynamic nuclear
polarization (DNP) magnetometers. Specifically, eight
β‐phosphorylated pyrrolidine nitroxides were synthesized.
Their large (ca. 5.0 mT) β‐31
P hyperfine splittings render them desirable for magnetometry
applications. Seven of these free radicals are
2‐dialkylphosphityl‐2,5,5‐trialkyl‐ or
2‐diarylphosphityl‐2,5,5‐trialkylpyrrolidine
nitroxides. Structural and solvent effects on the ESR spectra of
these nitroxides were explored. Hydrolysis of a phosphityl group
creates a remarkable eighth nitroxide. It exhibits an extremely
pH‐dependent ESR spectrum. Other nitroxides (e.g.
β‐aminyls) are known to show pH‐dependent ESR
spectra (ΔaN≈0.15 mT), and these
have been proposed by Keana et al. as novel, sensitive pH
indicators. Whereas they operate by changes in the nitroxide nitrogen
hyperfine splitting, the present special nitroxide displays little
change in the nitroxide nitrogen splitting (Δa
N≈0.03 mT). A very robust variation in the
β‐31P hyperfine splitting (Δa
N≈0.35 mT), however, is observed. Hence it may
be a much more sensitive pH probe molecule than Keana et al
.'s. It is proposed that this ESR variation for the present
nitroxide is due to conformational changes that are pH dependent.
Copyright © 1999 John Wiley & Sons, Ltd.
NMR of enaminones. part 6—17O and 13C NMR study of tautomerization in Schiff bases Zhuo, Jin‐Cong
doi: 10.1002/(SICI)1097-458X(199904)37:4<259::AID-MRC442>3.0.CO;2-6pmid: N/A
13C and 17O NMR spectra are
reported for three series of Schiff bases:
2‐(aminomethylene)cyclohexanones (1),
salicylideneamines (2) and N‐(2‐hydroxy‐1‐naphthalenylmethylene)amines (3). The 13C and 17O NMR data show that Schiff bases 1 exist in ketoenamine form, 2 in enolimine form and 3 as an equilibrium mixture of both forms. The tautomeric composition of Schiff base 3 was estimated. Alkylamines slightly favoured the ketoenamine form; aromatic amines favoured the enolimine form. The tautomeric equilibria are shifted towards the enolimine form in non‐polar solvents and with increase in temperature. Copyright © 1999 John Wiley & Sons, Ltd.
NMR spectroscopic diffusion, chemical shift and linewidth measurements of low‐affinity binding of ibuprofen enantiomers to human serum albuminMa, Yuehong; Liu, Maili; Mao, Xi‐an; Nicholson, Jeremy K.; Lindon, John C.
doi: 10.1002/(SICI)1097-458X(199904)37:4<269::AID-MRC446>3.0.CO;2-Upmid: N/A
The binding of racemic, (R)(−) and (S)(+)‐ibuprofen (IBP) to human
serum albumin (HSA) was studied using NMR spectroscopy.
Having saturated the tight binding sites, the extent of weak binding
was then investigated. The molecular diffusion coefficients of IBP in
HSA solution at different concentration ratios indicate that there is
no significant difference in binding capacity of the two enantiomers
of IBP to HSA at high IBP: HSA ratios. However, there are chemical
shift and linewidth changes in the 1NMR spectrum of IBP in
the presence of HSA induced by the binding and this suggests that the
major binding interaction involves the sec‐butyl chain
of the IBP molecule binding to HSA in hydrophobic pockets. Copyright
© 1999 John Wiley & Sons, Ltd.
1H and 13C NMR study of paramagnetic chiral macrocyclic lanthanide complexesLisowski, Jerzy
doi: 10.1002/(SICI)1097-458X(199904)37:4<287::AID-MRC455>3.0.CO;2-#pmid: N/A
The chiral macrocyclic complexes obtained in a template
condensation of (R,R
)‐1,2‐diaminocyclohexane and
2,6‐diformylpyridine, [LnL](NO3
)3 , Ln=La(III),
Ce(III), Eu(III) and Yb(III), were
studied by 1Hand 13C NMR spectroscopy. The
signal assignment was based on COSY, NOESY and HMQC measurements and
the isotropic shifts of the paramagnetic complexes were analysed. The
spectra of the investigated compounds in methanol–chloroform
solution indicate a D2‐symmetrical, helical
conformation of the ligand. The chiral [LnL](NO3
)3 complexes are able to form diastereoisomeric
adducts with D‐ and L‐aminoacids that
can be distinguished by 1H NMR spectroscopy. Copyright
© 1999 John Wiley & Sons, Ltd.
14N NMR single‐crystal study of hexamethylenetetramineKye, Young‐Sik; Harbison, Gerard S.
doi: 10.1002/(SICI)1097-458X(199904)37:4<299::AID-MRC454>3.0.CO;2-Wpmid: N/A
The 14N NMR spectrum of hexamethylenetetramine
(HMT) is dominated by the very large electric quadrupole
coupling constant of 4.412 MHz at room temperature. Nonetheless, by
carefully accounting for this interaction one can subtract its
first‐ and second‐order effects on the spectrum,
leaving the much smaller anisotropic chemical shift interaction. The
chemical shielding anisotropy of HMT is −8.3±3.2 ppm,
small but different from zero, with an isotropic chemical shift in
good agreement with the value in aqueous solution. This study
illustrates how even very tiny chemical shift tensors can be
extracted from the NMR spectra of quadrupolar nuclei using
appropriate techniques. Copyright © 1999 John Wiley & Sons,
Ltd.
Complete assignment of the 13C NMR spectra of a series of 5,8‐disubstituted 4,4‐dimethylanthracene‐1,9,10(4H)‐trionesAraya‐Maturana, Ramiro; Cassels, Bruce K.; Delgado‐Castro, Tomás; Hurtado‐Guzmán, Claudio; Jullian, Carolina
doi: 10.1002/(SICI)1097-458X(199904)37:4<312::AID-MRC443>3.0.CO;2-Ppmid: N/A
The regiosomeric quinones
5‐acetyloxymethyl‐4,4,8‐trimethyl‐
(5) and
8‐acetyloxymethyl‐4,4,5‐trimethylanthracene‐1,9,10(4H)‐trione (6) were synthesized and their regiochemistry was assigned on the basis of the unambiguous structure elucidation of 9,10‐dihydroxy‐5‐acetyloxymethyl‐4,4,8‐trimethyl‐5,8‐dihydroanthracen‐1(4H)‐one (2), the precursor of 5. The 1H and 13C NMR spectra of these compounds were assigned completely using two‐dimensional techniques. These interpretations were used for the total assignment of the NMR spectra of the closely related 5‐hydroxymethyl‐ and 5‐formyl‐4,4,8‐trimethylanthracene‐1,9,10(4H)‐triones (7 and 8, respectively). Copyright © 1999 John Wiley & Sons, Ltd.