Dataset Information

NMR investigation of chloromethane complexes of cryptophane-A and its analogue with butoxy groups.

ABSTRACT: Host-guest complexes between cryptophane-A as host and dichloromethane and chloroform as guests are investigated using (1)H and (13)C NMR spectroscopy. Moreover, a related cryptophane, with the methoxy groups replaced by butoxy units (cryptophane-But), and its complexes with the same guests were also studied. Variable temperature spectra showed effects of chemical exchange between the free and bound guests, as well as of conformational exchange of the host. The guest exchange was studied quantitatively by exchange spectroscopy or line shape analysis. Extraction of kinetic and thermodynamic parameters led to the characterization of the affinity between guests and hosts. On the other hand, the host exchange was investigated by means of (13)C Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion which aims at the determination of the transverse relaxation rate R2, the inverse of the transverse relaxation time T2, as a function of the repetition of the ? pulses in a CPMG train. The variation of the measured transverse relaxation rate with the repetition rate ?CPMG indicated conformational exchange occurring on the microsecond-millisecond time scale. Structural information was obtained through measurements of cross-relaxation rates, both within the host and between the host and the guest protons. The NMR results were supported by DFT calculations.

SUBMITTER: Takacs Z

PROVIDER: S-EPMC3963437 | biostudies-literature | 2014 Feb

REPOSITORIES: biostudies-literature

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NMR investigation of chloromethane complexes of cryptophane-A and its analogue with butoxy groups.

Takacs Z Z Steiner E E Kowalewski J J Brotin T T

The journal of physical chemistry. B 20140212 8

Host-guest complexes between cryptophane-A as host and dichloromethane and chloroform as guests are investigated using (1)H and (13)C NMR spectroscopy. Moreover, a related cryptophane, with the methoxy groups replaced by butoxy units (cryptophane-But), and its complexes with the same guests were also studied. Variable temperature spectra showed effects of chemical exchange between the free and bound guests, as well as of conformational exchange of the host. The guest exchange was studied quantit ...[more]

PMID: 24472055

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Project description:Hyperpolarized (129)Xe chemical exchange saturation transfer ((129)Xe Hyper-CEST) NMR is a powerful technique for the ultrasensitive, indirect detection of Xe host molecules (e.g., cryptophane-A). Irradiation at the appropriate Xe-cryptophane resonant radio frequency results in relaxation of the bound hyperpolarized (129)Xe and rapid accumulation of depolarized (129)Xe in bulk solution. The cryptophane effectively "catalyzes" this process by providing a unique molecular environment for spin depolarization to occur, while allowing xenon exchange with the bulk solution during the hyperpolarized lifetime (T(1) ? 1 min). Following this scheme, a triacetic acid cryptophane-A derivative (TAAC) was indirectly detected at 1.4 picomolar concentration at 320 K in aqueous solution, which is the record for a single-unit xenon host. To investigate this sensitivity enhancement, the xenon binding kinetics of TAAC in water was studied by NMR exchange lifetime measurement. At 297 K, k(on) ? 1.5 × 10(6) M(-1) s(-1) and k(off) = 45 s(-1), which represent the fastest Xe association and dissociation rates measured for a high-affinity, water-soluble xenon host molecule near rt. NMR line width measurements provided similar exchange rates at rt, which we assign to solvent-Xe exchange in TAAC. At 320 K, k(off) was estimated to be 1.1 × 10(3) s(-1). In Hyper-CEST NMR experiments, the rate of (129)Xe depolarization achieved by 14 pM TAAC in the presence of radio frequency (RF) pulses was calculated to be 0.17 ?M·s(-1). On a per cryptophane basis, this equates to 1.2 × 10(4)(129)Xe atoms s(-1) (or 4.6 × 10(4) Xe atoms s(-1), all Xe isotopes), which is more than an order of magnitude faster than k(off), the directly measurable Xe-TAAC exchange rate. This compels us to consider multiple Xe exchange processes for cryptophane-mediated bulk (129)Xe depolarization, which provide at least 10(7)-fold sensitivity enhancements over directly detected hyperpolarized (129)Xe NMR signals.

Dataset Information

NMR investigation of chloromethane complexes of cryptophane-A and its analogue with butoxy groups.

Publications

NMR investigation of chloromethane complexes of cryptophane-A and its analogue with butoxy groups.

Similar Datasets

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