For isoniazid, the best enhancements in methanol-d4, methanol, ethanol and DMSO were −230, −140, −120 and selleck −34 respectively in a magnetic field of 65 G. The enhancement of proton 3 was only 50–70% of that of proton 2. Both systems show a similar temperature profile where 37.5–46.1 °C seems to reflect the optimum temperature and hence lifetime of the polarization transfer catalyst. It would therefore appear that

the J-coupling framework in the pyrazinamide system is more suited for optimal transfer. Considering the solvent effects, the SABRE enhancement can be increased by minimizing the spin relaxation of the substrate-metal complex, namely using less viscous solvent and deuterated solvent. The authors would like to thank the University of York for financial assistance and Bruker Biospin for a parahydrogen polarizer. KDA would like to thank the MRC for a studentship, SBD, GGRG and REM would like to thank the EPSRC (Grant no. EP/G009546/1) and the Wellcome Trust (awards WT092506MA and WT098335MA). “
“Diffusion-ordered spectroscopy (DOSY) is a family of NMR experiments used in mixture analysis to allow signals belonging to a given species to be correlated FG-4592 through their rate of diffusion. The technique is widely used [1], [2], [3], [4], [5], [6], [7], [8], [9] and [10] but is well-known to give misleading results when applied to systems undergoing chemical exchange [11]. While such effects can be put to good use [12] and [13],

when using DOSY to identify mixture components they are a serious nuisance [14]. Thus, for example, where hydroxyl signals are seen in DOSY spectra they routinely appear at higher diffusion coefficients than non-exchanging signals Baf-A1 clinical trial from the same species, because of exchange with residual water [15] and other labile protons. Almost all

DOSY pulse sequences in common use, such as the Oneshot45 [16] and [17] sequence used to acquire the spectrum of Fig. 1a, use the stimulated echo (STE). The primary reason is to minimise J-modulation: the STE stores spatially-encoded magnetization along the z-axis for most of the diffusion time, minimising the time for which J acts. Any exchange of magnetization during this storage period, whether by chemical exchange [18], [19] and [20] or nuclear Overhauser effect (NOE) [21], will affect the attenuation as a function of gradient pulse area for the signals involved. This changes the apparent diffusion coefficients and complicates analysis. The practical effect is that DOSY spectra show peaks with apparent diffusion coefficients intermediate between those of the exchanging sites, with the exact positions determined by the interplay between experimental parameters and the rate(s) of exchange, making it appear that more different species are present than is actually the case. The effects of exchange are particularly frustrating in analysis problems such as mixtures of flavonoids [23], and in general in samples containing glycans [15].