Analysis of HMQC experiments applied to a spin ½ nucleus subject to very large CSA
PBN-AR
Instytucja
Centrum Badań Molekularnych i Makromolekularnych Polskiej Akademii Nauk
Informacje podstawowe
Główny język publikacji
EN
Czasopismo
SOLID STATE NUCLEAR MAGNETIC RESONANCE
ISSN
0926-2040
EISSN
Wydawca
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI
URL
Rok publikacji
2019
Numer zeszytu
Strony od-do
11-25
Numer tomu
100
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+ 4
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Język
EN
Treść
The acquisition of solid-state NMR spectra of “heavy” spin I = 1/2 nuclei, such as 119 Sn, 195 Pt, 199 Hg or 207 Pb can often prove challenging due to the presence of large chemical shift anisotropy (CSA), which can cause significant broadening of spectral lines. However, previous publications have shown that well-resolved spectra can be obtained via inverse 1 H detection using HMQC experiments in combination with fast magic angle spinning. In this work, the efficiencies of different 195 Pt excitation schemes are analyzed using SIMPSON numerical simulations and experiments performed on cis- and transplatin samples. These schemes include: hard pulses (HP), selective long pulses (SLP) and rotor-synchronized DANTE trains of pulses. The results show that for spectra of species with very large CSA, HP is little efficient, but that both DANTE and SLP provide efficient excitation profiles over a wide range of CSA values. In particular, it is revealed that the SLP scheme is highly robust to offset, pulse amplitude and length, and is simple to set up. These factors make SLP ideally suited to widespread use by “non-experts” for carrying out analyses of materials containing “heavy” spin I = 1/2 nuclei that are subject to very large CSAs. Finally, the existence of an “intermediate” excitation regime, with an rf-field strength in between those of HP and SLP, which is effective for large CSA, is demonstrated. It must be noted that in some samples, multiple sites may exist with very different CSAs. This is the case for 195 Pt species with either square-planar or octahedral structures, with large or small CSA, respectively. These two types of CSAs can only be excited simultaneously with DANTE trains, which scale up the effective rf-field. Another way to obtain all the information is to perform two different experiments: one with SLP and the second with HP to excite the sites with moderate/large and small/moderate CSAs, respectively. These two complementary experiments, recorded with two different spinning speeds, can also be used to discriminate the center-band resonances from the spinning sidebands.
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Oryginalny artykuł naukowy
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System-identifier
PX-5ca5bb93d5de2bd4962e64b7
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