Biomedical subjects

Daniel Canet

Publications and source records attributed to Daniel Canet.

4 recordsLinked to original sources

PubMed2006

Chemical shift imaging (CSI) by precise object displacement.

A mechanical device (NMR lift) has been built to displace vertically an object (typically an NMR sample tube) inside the NMR probe with an accuracy of 1 microm. A series of single pulse experiments are performed for incremented vertical positions of the sample. With a sufficiently spatially selective radio-frequency (r.f.) field, one obtains chemical shift information along the displacement direction (one-dimensional chemical shift imaging (CSI)). Knowing the vertical r.f. field profile (the amplitude of the r.f. field along the vertical direction), one can reconstruct the spectrum associated with all the slices corresponding to consecutive sample positions and improve the spatial resolution, which is simply related to the accuracy of the displacement device. Beside tests performed on phantoms, the method has been applied to solvent penetration in polymers and to benzene diffusion in a heterogeneous zeolite medium.

Journal Article↗

PubMed2005

Polarization transfer from para-hydrogen to heteronuclei: effect of H/D substitution. The case of AA'X and A2A2'X spin systems.

Upon hydrogenation from para-hydrogen (p-H(2)), hyperpolarization transfer toward a heteronucleus may be possible even if the two protons are chemically equivalent in the final product (but not magnetically equivalent), provided that J couplings with the heteronucleus exist. It is however shown (theoretically and experimentally) that this transfer effectively occurs if the spin system in the hydrogenated molecule is of the type AA'X (A and A' denoting the two protons originating from p-H(2) and X the heteronucleus) but does not occur for a spin system of the A(2)A(2)(')X type. A theory has been worked out for assessing the details of the X spectrum (multiplet patterns) in the case of ALTADENA and PASADENA experiments. Experimental verifications are provided.

Journal Article↗

PubMed2005

HMBC-like experiment based on longitudinal csa/dipolar cross-correlation.

A gradient-based sequence is proposed for efficiently filtering out all quantities except the longitudinal two-spin order, created by csa/dipolar cross-correlation rates. The dipolar interaction is between a proton and a heteronucleus, the csa being generally the one of the heteronucleus. Proton detection is carried out to benefit from maximum sensitivity. The resulting two-dimensional spectrum has the same aspect as an HMBC spectrum, implying the existence of a J coupling between the two considered nuclei, but here cross-peaks indicate the strength of the relevant csa/dipolar cross-correlation rate. The method is especially interesting in the case of medium-sized molecules where a given heteronucleus is subjected to several csa/dipolar cross-correlation effects, along with the corresponding J couplings.

Carbon Isotopes↗

PubMed2004

Measurement of 15N csa/dipolar cross-correlation rates by means of Spin State Selective experiments.

We propose a method for the determination of (15)N csa/dipolar cross-correlation rates based on the measurement of the two apparent transverse (or longitudinal) relaxation rates associated with each component of the nitrogen doublet (N(alpha) and N(beta)). This is achieved by inserting a spin state selective scheme in conventional inverse Carr-Purcell-Meiboom-Gill (or inversion-recovery) pulse sequence which allows for the edition of a HSQC-type spectrum for each of the spin states. Transverse cross-correlation rates necessitate two independent sets of measurements (for N(alpha) and N(beta), respectively), whereas for longitudinal cross correlation rates, besides N(alpha) and N(beta) measurements, the method requires the knowledge of both the (15)N longitudinal auto-relaxation rate and the longitudinal two-spin order (2NzHz) auto-relaxation rate. These additional parameters are mandatory because of the non-exponential behavior of the N(alpha) and N(beta) longitudinal decays. Conversely, the present method does not require any complex manipulation of 2D spectra, the cross-correlation rates being obtained from the difference of the two (N(alpha) and N(beta)) apparent relaxation rates. This approach is applied to (15)N-labelled ubiquitin at two different magnetic fields (9.4 T and 14.1 T).

Magnetics↗