5. The polarization studies in DMSO were only carried out at higher temperatures because it was difficult to transfer the sample when it is too viscous, which occurs at a temperature close to the freezing point of the solvent (DMSO, 19 °C). Compared to methanol-d4, the enhancements in methanol were reduced to a half and in ethanol to a quarter, while those in DMSO were an order of magnitude smaller and thus less suitable to polarize pyrazinamide. In the case of isoniazid, the enhancements of the Ipilimumab datasheet two protons again showed a “V-curve”

dependency on polarization magnetic field (Fig. 6). Interestingly, at 0 G, the polarization of proton 2 was negative while that of proton 3 was positive. The optimal magnetic field for both protons was again very similar, namely around 60–65 G. A magnetic field

of 65 G was therefore again chosen to study the temperature dependence. At this field strength, the polarization of protons was almost twice of that of proton 3, probably due to proton 2 being closer to the nitrogen atom, which directly bonds to iridium upon ligation. The polarization of isoniazid in methanol-d4 at a magnetic field of 65 G was measured over the temperature range 4.7–54.4 °C (Fig. 7). The signal enhancements observed for both protons increased with temperature until reaching a maximum enhancements of −220 and −150 fold at 46.1 °C. At higher temperature (54.4 °C), the enhancements were Ganetespib slightly decreased. The polarization of isoniazid in the other three solvents was also investigated for a polarization transfer magnetic field (-)-p-Bromotetramisole Oxalate of 65 G (Fig. 9), even though this magnetic field was not optimal for the polarization in ethanol at room temperature (Fig. 8). The best enhancements were always at 46.1 °C. The SABRE enhancement of isoniazid shows similar solvents

dependence as that of pyrazinamide. Compared to methanol-d4, the enhancements in methanol were slightly lower, in ethanol about a half, and in DMSO about one fifth, making it a less suitable solvent in which to polarize isoniazid via SABRE. According to SABRE theory [22], polarization transfer, binding kinetics and spin relaxation determine the size of the enhancement. The polarization of parahydrogen is transferred to the substrate through J coupling networks, the strength of which is determined by the chemical structure and bonding strength of the substrate-metal complex. Since the multi-bond J couplings between the parahydrogen and the substrate are small, a relative long residence time on the metal (in the order of 100 ms to s) is required for effective transfer. Thus, in the case of fast binding kinetics, the short lifetime of the substrate-metal complex will decrease SABRE enhancements. On the other hand, since the concentration of the substrate is much larger than that of the catalyst precursor, polarization of all of the substrate molecules requires relative fast exchange between the substrate in free form and metal bound form.