Intermolecular double-quantum coherences in gases

R. H. ACOSTA; P.P. ZÄNKER; L. AGULLES-PEDRÓS; J. SCHMIEDESKAMP; H.W. SPIESS

Tarragona, España

Congreso; EUROMAR Magnetic Resonance Meeting; 2007

Since the discovery of intermolecular multiple-quantum coherences (iMQCs) in solution NMR due to the distant dipolar field (DDF) of spins [1], great attention has been paid to this subject, resulting in several novel applications in biomedical spectroscopy and imaging [2,3]. Numerous works have been published concerning the effect of diffusion on the iMQCs [4,5,6]. As diffusion coefficients in liquids are small and cannot be varied easily, studying iMQCs in the gas phase is relevant, as the diffusivity is much higher than in liquids and additionally can be changed over several orders of magnitude. In order to detect iMQCs in gases, hyperpolarized (HP) gases were employed, in combination with the awareness of the influence of fast diffusion on echo signals (see contribution of Zänker et al.). By this means the first measurements of intermolecular double-quantum coherences (iDQCs) in the gas phase were accomplished and are presented here.   The signals were obtained from HP 3He (provided by the Physics Department of the University of Mainz [7]), which was admixed with a buffer gas (SF6) to lower and control the diffusion coefficient, by applying a CRAZED pulse sequence [1]. The sequence consists of two RF pulses and two gradient pulses, which work as a DQ-filter. The time domain signal was measured with a high SNR in HP 3He, while the remaining SQ signal was suppressed by an appropriate phase cycle. The CRAZED sequence was repeated with varying flip angles of the second RF pulse and the expected maximum at 120° was obtained.   In conclusion, iDQC signals in gases were detected for the first time. The high sensitivity of these iDQCs to diffusion and spatial restrictions opens the way to new applications, e.g. in structure determination of porous materials or human lungs, similar to studies that have been performed on model systems for liquids [8].   -------- [1] W.S. Warren, W. Richter, A.H. Andreotti and S. Farmer, Science 267:2005-2009 (1993). [2] W. S. Warren, S. Ahn, M. Mescher, M. Garwood, K. Ugurbil, W. Richter, R. R. Rizi, J. Hopkins, and J. S. Leigh. Science, 281:247–251, 1998. [3] J. Zhong, Z. Chen, and S. D. Kennedy. Recent Res. Devel. Chem. Physics, 5:23–55, 2004. [4] W. Barros Jr., J. C. Gore, and D. F. Gochberg. J. Magn. Reson. 178:166–169, 2006. [5] I. Ardelean and R. Kimmich. J. Chem. Phys. 112(12):5275–5280, 2000. [6] Z. Chen and J. Zhong. J. Chem. Phys. 114(13):5642–5653, 2001. [7] E. Ottten Europhysics News 35 No. 1 (2004) [8] L.-S. Bouchard and W.S. Warren J. Magn. Reson. 170:299-309 (2004).   E-mail: racosta@famaf.unc.edu.ar