NMR studies of proton transfer in 1∶1 tris(trimethoxyphenyl)phosphine oxide–phenol complexes

Lagier, Claudia M.; Olivieri, Alejandro C.; Harris, Robin K.

doi:10.1039/a802219d

Cited by 9 publications

(5 citation statements)

References 18 publications

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“…The anion 6 was chosen to compare with its isomer 3 to test whether the anion's chelating ability is an important feature in stabilizing the lipophilic G-quadruplex. 6 (the conjugate acid has p K a = 5.22) is more basic than 3 (the conjugate acid has p K a = 3.96), but 6 cannot form the same bifurcated hydrogen bonds with the inner G 4 -quartets as 3 .…”

Section: Resultsmentioning

confidence: 99%

Lipophilic G-Quadruplexes Are Self-Assembled Ion Pair Receptors, and the Bound Anion Modulates the Kinetic Stability of These Complexes

et al. 2003

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With an eye toward the eventual selective modification of noncovalent structures, we used ESI-MS, X-ray crystallography, and NMR spectroscopy to study the anion's influence on the structure and dynamics of self-assembled ion pair receptors formed from guanosine G 1. We compared five complexes of formula (G 1)(16).2Ba(2+).4A(-) containing different organic anions: 2,4,6-trinitrophenolate (2), 2,6-dinitrophenolate (3), 4-methyl-2,6-dinitrophenolate (4), 4-methoxy-2,6-dinitrophenolate (5), and 2,5-dinitrophenolate (6). Crystallography reveals that anion-nucleobase hydrogen bond geometry is sensitive to both phenolate basicity and structure. For the 2,6-substituted anions 2-5, progressive shortening of anion-nucleobase hydrogen bonds is correlated with increased phenolate basicity. Lipophilic G-quadruplexes with different anions also have much different kinetic stabilities in CD(2)Cl(2) solution. Proton NMR shows that free 6 exchanges faster with G-quadruplex-bound anion than do the 2,6-dinitrophenolates 2-5. The increased lability of 6 is probably because, unlike the 2,6-dinitrophenolates, this anion cannot effectively chelate separate G(8).M(2+) octamers via anion-nucleobase hydrogen bonds. In addition to these structural effects, the anion's basicity modulates the anion exchange rate between its free and bound states. 2D EXSY NMR shows that 3 and 5 exchange about 7 times slower than the less basic picrate (2). The use of 3, a relatively basic dinitrophenolate that hydrogen bonds with the amino groups of the two "inner" G(4)-quartets, resulted in extraordinary kinetic stabilization of the G-quadruplex in CD(2)Cl(2). Thus, no isomerization product (G 1)(8).Ba(2+).(G 1)(8).Sr(2+).4(3) was observed even 2 months after the separate G-quadruplexes (G 1)(16).2Ba(2+).4(3) and (G 1)(16).2Sr(2+).4(3) were combined in CD(2)Cl(2). In sharp contrast, G-quadruplexes containing the isomeric 6 anion have isomerization half-lives of approximately t(1/2) = 30 min under identical conditions. All the evidence indicates that the structure and electronics of the organic anions, bound to the assembly's periphery, are crucial for controlling the kinetic stability of these cation-filled G-quadruplexes.

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Section: Resultsmentioning

confidence: 99%

Lipophilic G-Quadruplexes Are Self-Assembled Ion Pair Receptors, and the Bound Anion Modulates the Kinetic Stability of These Complexes

et al. 2003

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“…The information available from previous NMR studies on phosphine oxides, their complexes, and their derivatives has generally been restricted to the determination of isotropic 31 P and 17 O chemical shifts (CS), δ iso , and isotropic J coupling constants from solution NMR spectroscopy, − as well as δ iso ( 31 P) from 31 P magic-angle spinning (MAS) NMR spectroscopy in the solid state. − Some information on the 31 P ( I = 1/2) CS tensor is also available. − In contrast, results from 17 O ( I = 5/2) NMR spectroscopy of phosphine oxides in the solid state are lacking. The range of oxygen isotropic chemical shifts in solution is on the order of 2500 ppm with phosphine oxides generally falling in the range of 20−100 ppm. − Overviews of 17 O nuclear quadrupolar coupling constants ( C Q ), which are very sensitive to the electric field gradient (EFG) about the 17 O nucleus, are available. − Values of C Q ( 17 O) range from less than 1.0 MHz (e.g., MoO 4 2- ) to greater than 15 MHz (e.g., H 2 O 2 ).…”

Section: Introductionmentioning

confidence: 99%

“…[12][13][14][15] Some information on the 31 P (I ) 1/2) CS tensor is also available. [16][17][18][19][20][21][22][23][24][25] In contrast, results from 17 chemical shifts in solution is on the order of 2500 ppm with phosphine oxides generally falling in the range of 20-100 ppm. [26][27][28] Overviews of 17 O nuclear quadrupolar coupling constants (C Q ), which are very sensitive to the electric field gradient (EFG) about the 17 O nucleus, are available.…”

Section: Introductionmentioning

confidence: 99%

An ¹⁷O NMR and Quantum Chemical Study of Monoclinic and Orthorhombic Polymorphs of Triphenylphosphine Oxide

2003

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Solid-state (17)O NMR spectroscopy is employed to characterize powdered samples of known monoclinic and orthorhombic modifications of (17)O-enriched triphenylphosphine oxide, Ph(3)PO. Precise data on the orientation-dependent (17)O electric field gradient (EFG) and chemical shift (CS) tensors are obtained for both polymorphs. While the (17)O nuclear quadrupolar coupling constants (C(Q)) are essentially identical for the two polymorphs (C(Q) = -4.59 +/- 0.01 MHz (orthorhombic); C(Q) = -4.57 +/- 0.01 MHz (monoclinic)), the spans (Omega) of the CS tensors are distinctly different (Omega = 135 +/- 3 ppm (orthorhombic); Omega = 155 +/- 5 ppm (monoclinic)). The oxygen CS tensor is discussed in terms of Ramsey's theory and the electronic structure of the phosphorus-oxygen bond. The NMR results favor the hemipolar sigma-bonded R(3)P(+)-O(-) end of the resonance structure continuum over the multiple bond representation. Indirect nuclear spin-spin (J) coupling between (31)P and (17)O is observed directly in (17)O magic-angle-spinning (MAS) NMR spectra as well as in (31)P MAS NMR spectra. Ab initio and density-functional theory calculations of the (17)O EFG, CS, and (1)J((31)P,(17)O) tensors have been performed with a variety of basis sets to complement the experimental data. This work describes an interesting spin system for which the CS, quadrupolar, J, and direct dipolar interactions all contribute significantly to the observed (17)O NMR spectra and demonstrates the wealth of information which is available from NMR studies of solid materials.

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“…The Brønsted basicity of phosphine oxides has been studied via their interactions with phenols, which can complex with phosphine oxides to form isolable H-bonded adducts. [36][37][38][39][40] Proton transfer from substituted phenols to triphenylphosphine oxide was assessed by monitoring the deshielding of relevant nuclei using solution and solid-state NMR spectroscopy. 38 In general, decreases in pK a of the phenol were correlated to increased proton transfer to triphenylphosphine oxide, but intramolecular H-bonding and steric effects can obscure these trends.…”

Section: Introductionmentioning

confidence: 99%

Variation in pnictogen–oxygen bonding unlocks greatly enhanced Brønsted basicity for the monomeric stibine oxide

Wenger,

Getahun,

Johnstone

2023

Dalton Trans.

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NMR studies of proton transfer in 1∶1 tris(trimethoxyphenyl)phosphine oxide–phenol complexes

Cited by 9 publications

References 18 publications

Lipophilic G-Quadruplexes Are Self-Assembled Ion Pair Receptors, and the Bound Anion Modulates the Kinetic Stability of These Complexes

Lipophilic G-Quadruplexes Are Self-Assembled Ion Pair Receptors, and the Bound Anion Modulates the Kinetic Stability of These Complexes

An ¹⁷O NMR and Quantum Chemical Study of Monoclinic and Orthorhombic Polymorphs of Triphenylphosphine Oxide

Variation in pnictogen–oxygen bonding unlocks greatly enhanced Brønsted basicity for the monomeric stibine oxide

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NMR studies of proton transfer in 1∶1 tris(trimethoxyphenyl)phosphine oxide–phenol complexes

Cited by 9 publications

References 18 publications

Lipophilic G-Quadruplexes Are Self-Assembled Ion Pair Receptors, and the Bound Anion Modulates the Kinetic Stability of These Complexes

Lipophilic G-Quadruplexes Are Self-Assembled Ion Pair Receptors, and the Bound Anion Modulates the Kinetic Stability of These Complexes

An 17O NMR and Quantum Chemical Study of Monoclinic and Orthorhombic Polymorphs of Triphenylphosphine Oxide

Variation in pnictogen–oxygen bonding unlocks greatly enhanced Brønsted basicity for the monomeric stibine oxide

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An ¹⁷O NMR and Quantum Chemical Study of Monoclinic and Orthorhombic Polymorphs of Triphenylphosphine Oxide