Efficiency of heteronuclear dipolar decoupling schemes in solid-state NMR: Investigation of effective transverse relaxation times

Rationalising Heteronuclear Decoupling in Refocussing Applications of Solid‐State NMR Spectroscopy

“…Here, we focus on understanding what are the limiting factors determining decoupling performance under different experimental conditions. Table compiles the peak values observed here with previous literature results …”

“…The relative complexity of SPINAL‐64 has hindered its theoretical analysis, but its mode of operation is assumed to be essentially the same as TPPM and so might be expected to have a similar dependence. Although the detrimental effects of increasing upon can be inferred from previously published data on glycine, and poorer values of at 600 MHz compared with 300 MHz have been noted for XiX and RS‐HEPT decoupling, the field dependence has not been explicitly explored. Figures S6 and S7 in the Supporting Information collate results from Ref.…”

“…Moreover,u nlike TPPM,t he SPINAL-64 parameter map, Figure 3b,c hanges shape with B 0 ,a nd so it may be more difficult to observe consistent trends for more complex sequences. This may explain, for example, why SPINAL-64 appeared to perform better at 700 MHz compared with 500 MHz in ap revious study, [21] whereas all the other results show the opposite trend. The linewidthu nder XiX decoupling,a nd relateds equences such as PISSARRO-5,i sd ominated by proximity to resonance conditions as well as second-order cross-terms between the heteronuclear and homonuclear dipolar couplings, [60] and so is not expected to show as trong magnetic field dependence.…”

“…As originally defined, the different phase angles in SPINAL-64 were fixed (108,1 5 8 and 208), but have subsequently been optimised, either in the fixed ratio 1:1.5:2 with as ingle optimisation parameter 0,o ra dditionally optimising the angles a and b. [21,45] Here, asingle phase optimisation was used.…”

“…[28,29] Hence T 0 2 continues increasing as the decoupling efficiency increases even thought he spectral resolution has plateaued. [30] It has been noted previously when comparing different decoupling sequences, [21,27] or different parameters under the same sequence, [31] that the optimal T 0 2 values tend to vary significantly even though the differencesi ns pectrall inewidthsa tt he same conditions are small. So while optimising spectralr esolution is relevant for many applications, T 0 2 provides more insightw hen trying to understand the factors determining decoupling performance, and is directly relevant to the challenging experiments discussed above.T he T 0 2 values observed here suggest that Jc ouplingsa ss mall as af ew Hz are measurable andt hat J-based 13 Cc orrelation experiments should be viable form ost systemswithout the need for isotopic enrichment.…”