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Martin Goez

Publications and source records attributed to Martin Goez.

6 recordsLinked to original sources
PubMed2005

Photo-CIDNP experiments with an optimized presaturation pulse train, gated continuous illumination, and a background-nulling pulse grid.

Methods to record chemically induced dynamic nuclear polarization (CIDNP) spectra that are virtually free from background magnetization and avoid the sensitivity loss and subtraction artifacts of difference spectroscopy have been developed. Presaturation by a string of composite pi/2 pulses, each followed by a defocussing field gradient, is analyzed, and guidelines for the optimization of pulse phases and gradient strengths are derived. Subsequent gated illumination during a grid of pi pulses with a prescribed timing causes the background magnetization to vanish at those moments of a pulse sequence when CIDNP magnetization is to be sampled or transferred. By shifting the illumination intervals within such a grid, the sign of the polarizations can be inverted without influencing the development of the background magnetization, allowing a further strong suppression of residual background by a phase cycle. Experimental examples for the application of these methods to more complex CIDNP experiments (1D-CIDNP-COSY, 1D-CIDNP-TOCSY, CIDNP-induced heteronuclear Overhauser effects, water suppression in protein CIDNP) are given.

Animals↗
PubMed2005

Increasing the sensitivity of time-resolved photo-CIDNP experiments by multiple laser flashes and temporary storage in the rotating frame.

Pulse sequences have been developed that add up time-resolved photo-CIDNP signals from n successive laser flashes not in the acquisition computer of the NMR spectrometer but in the experiment itself, resulting in a greatly improved signal-to-noise ratio. For this accumulation, CIDNP is first stored in the transverse plane and then on the z axis, and finally superimposed on CIDNP produced by the next flash. These storage cycles also result in a very efficient background suppression. Because only one free induction decay is acquired for n flashes, the noise is digitized only once. The signal gain is demonstrated experimentally and analyzed theoretically. Losses are mostly due to nuclear spin relaxation, and to a small extent to instrument imperfections. With 10 laser flashes, a signal increase by a factor of about 7.5 was realized. As their main advantage compared to signal averaging in the usual way, these sequences yield the same signal-to-noise ratio with fewer laser flashes; the theoretical improvement is by a factor of n.

Journal Article↗