Dynamic NMR: A new intensity ratio for evaluation of lifetime in paripartite A ⇌ B systems

Dimitrov, Valentin

doi:10.1002/mrc.1270080306

Cited by 7 publications

(3 citation statements)

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“…Conditions for NMR spectra are as described in the legend to Table 1. pH = 7.0. sity at the frequency of the conjugate acid, vP, to the intensity at the center of the coalescing peaks, (PI + v2)/2 at 470.5 MHz, (Dimitrov, 1976;Martin et al, 1980). This calculation assumes that there are two equally populated exchange sites, no strong coupling between the two sites, and T2 (or T *) of site 1 equals that of site 2.…”

Section: Resultsmentioning

confidence: 99%

New class of 19F pH indicators: fluoroanilines

Deutsch

Taylor

1989

Biophysical Journal

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The pH dependence of the 19F chemical shift has been characterized for a number of fluorine-substituted aniline derivatives. These compounds constitute a new class of 19F nuclear magnetic resonance (NMR) pH indicators, characterized by single 19F resonance lines with sensitivities ranging from 2 to 7 ppm/pH unit near the aniline pKa; total shifts between conjugate acid and base of 5-15 ppm; and pKas ranging from 1 to 7. One compound, N,N-(methyl-2-carboxyisopropyl)-4-fluoroaniline, has a pKa of 6.8 and a sensitivity of 5 ppm/pH unit. This compound displays significant broadening of its 19F resonance near the aniline pKa (6.8), due to a decreased rate of exchange between conjugate acid and base species. Our results are consistent with slow dissociation of an intramolecular hydrogen bond in the zwitterionic species that limits the exchange rate between protonated and unprotonated forms for N,N-(methyl-2-carboxyisopropyl)-4-fluoroaniline.

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Section: Resultsmentioning

confidence: 99%

New class of 19F pH indicators: fluoroanilines

Deutsch

Taylor

1989

Biophysical Journal

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“…(For other sensitivity measures compare [30] or [311). As, is called the sensitivity of the parameter pr.…”

Section: =$6pk/(i Qk 1 I Dpk 1);mentioning

confidence: 99%

ChemInform Abstract: ITERATIVE LEAST‐SQUARES LINESHAPE FITTING OF 1H‐DECOUPLED CARBON‐13 DNMR SPECTRA

Heinzer¹,

Oth²

1981

Chemischer Informationsdienst

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SummaryIterative least-squares lineshape fitting of 'H-decoupled I3C-DNMR. spectra is advantageously used for the investigation of symmetrical or asymmetrical intramolecular (two-structure) exchange processes. The least-squares procedure adopted allows the following parameters to be either optimized by computer or kept constant (according to experimental conditions): the nuclei populations (taking into account line intensity effects resulting from differences in spin-lattice relaxation times and/or Overhauser enhancements), the corresponding chemical shifts and natural linewidths (characterizing the sites undergoing exchange), the fractional population of one structure (in the case of asymmetrical exchange), one of the chemical rates, the base-line position, and the base-line tilt. The relative sensitivity of the lineshape with respect to the fitted parameters as well as the importance of correlations among these parameters have been investigated and tested with examples. The reliability of the kinetic parameters as obtained by the iterative leastsquares lineshape fitting procedure is discussed.

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“…4 If we could satisfactorily estimate the values of the relaxation times, it would then be possible to fit only the rate constants.…”

Section: Introductionmentioning

confidence: 99%

Dynamic NMR: combined use of 1D selective EXSY and complete lineshape analysis of spectra subjected to reference deconvolution and linear prediction or the maximum entropy method

Vassilev

Dimitrov

2001

Magnetic Reson in Chemistry

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In dynamic NMR lineshape analysis and in handling other curve-fitting problems, the quality of the adjusted parameters improves if the iterative procedure is constrained by introducing additional conditions. It is demonstrated on a simple model of a two-site exchange system that in the complete lineshape analysis of spectra subjected to reference deconvolution and linear prediction or the maximum entropy method in combination with 1D EXSY experiments, the unknown parameters can be reduced to only one, the rate constant. This approach ensures excellent results for the activation parameters. It is also shown that 1D selective EXSY (1D SEXSY) experiments using E-BURP pulses could successfully be used as a substitute to the more (experimentally) demanding 2D EXSY measurements.

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Dynamic NMR: A new intensity ratio for evaluation of lifetime in paripartite A ⇌ B systems

Cited by 7 publications

References 7 publications

New class of 19F pH indicators: fluoroanilines

New class of 19F pH indicators: fluoroanilines

ChemInform Abstract: ITERATIVE LEAST‐SQUARES LINESHAPE FITTING OF 1H‐DECOUPLED CARBON‐13 DNMR SPECTRA

Dynamic NMR: combined use of 1D selective EXSY and complete lineshape analysis of spectra subjected to reference deconvolution and linear prediction or the maximum entropy method

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