Figure S1: 1D 13 C DARR spectra of HETs(218 289) at various -1 H SAFR flip angle using pulse sequence in Fig. 2 (b) in the main text (1200 MHz).Acquisition parameters (128 scans, 64 dummy scans, relaxation delay 2.7 s), experimental time (8 min 49 s), and processing parameters (no apodization, common phase correction, automatic fifth-order polynomial baseline correction) of each spectrum were otherwise the same.All spectra were run immediately one after another from top to bottom.(a) A reference spectrum with no SAFR pulse.(b) Difference spectra between 1D 13 C DARR spectra after 1 H SAFR pulse with flip angle varying from 0.5° to 20.0° and the reference spectrum in (a).(c) Difference spectrum between another 1D DARR after 0.5° SAFR and the reference.(d) Difference between a control spectrum with identical parameters as in (a) and the reference spectrum in (a).The difference spectra in (b), (c), and (d) are scaled 50 times up relative to (a).Figure S2: Comparison of 2D hNH experiments of dASC recorded with various options of the pulse program safr-hNH (850 MHz).Acquisition parameters (400 t1 increments, 16 scans per FID, SAFR flip angle 0.5°) and experimental time (2 h 35 min 8 s) of each spectrum were otherwise the same.No drift correction was applied.(a) The effect of SAFR while 13 C decoupling was turned off: a spectrum with SAFR switched off (top) and two spectra with SAFR on (control 1 and control 2 shown in Fig. S11 as well) were recorded in order to show possible differences caused by SAFR as well as random changes.(b) 13 C decoupling turned on: SAFR off (top) and on (bottom).(c) 1D traces along the horizontal dashed lines in (a) and (b).
Abstract. With the advent of faster magic-angle spinning (MAS) and higher magnetic fields, the resolution of biomolecular solid-state nuclear magnetic resonance (NMR) spectra has been continuously increasing. As a direct consequence, the always narrower spectral lines, especially in proton-detected spectroscopy, are also becoming more sensitive to temporal instabilities of the magnetic field in the sample volume. Field drifts in the order of tenths of parts per million occur after probe insertion or temperature change, during cryogen refill, or are intrinsic to the superconducting high-field magnets, particularly in the months after charging. As an alternative to a field–frequency lock based on deuterium solvent resonance rarely available for solid-state NMR, we present a strategy to compensate non-linear field drifts using simultaneous acquisition of a frequency reference (SAFR). It is based on the acquisition of an auxiliary 1D spectrum in each scan of the experiment. Typically, a small-flip-angle pulse is added at the beginning of the pulse sequence. Based on the frequency of the maximum of the solvent signal, the field evolution in time is reconstructed and used to correct the raw data after acquisition, thereby acting in its principle as a digital lock system. The general applicability of our approach is demonstrated on 2D and 3D protein spectra during various situations with a non-linear field drift. SAFR with small-flip-angle pulses causes no significant loss in sensitivity or increase in experimental time in protein spectroscopy. The correction leads to the possibility of recording high-quality spectra in a typical biomolecular experiment even during non-linear field changes in the order of 0.1 ppm h−1 without the need for hardware solutions, such as stabilizing the temperature of the magnet bore. The improvement of linewidths and peak shapes turns out to be especially important for 1H-detected spectra under fast MAS, but the method is suitable for the detection of carbon or other nuclei as well.
This work reports the results of EPR and NMR study of the Ce3+ incorporation in LaAlO3 single crystals grown by the micro-pulling-down method in the range of the Ce concentrations in the solid solution La1-xCexAlO3 from x=0.001 up to x=1.0. From EPR measurements, Ce3+ g tensor parameters were determined as a function of Ce concentration. The g tensor has an orthorhombic symmetry even in the trigonal phase (x < 0.1) suggesting that the incorporation of Ce at La site lowers the lattice symmetry near this ion. The local properties of the La1-xCexAlO3 crystals were further studied by 27Al and 139La high-resolution NMR measurements. It was found that 139La chemical shift has the Fermi contact interaction origin. It linearly increases with the Ce concentration from 0 ppm up to 165 ppm at x = 0.5. Due to this strong Fermi contact interaction, separated peaks corresponding to different Ce-O-La spin transfer passways are resolved in the 139La NMR spectra. On the other hand, no Fermi contact interaction is visible in 27Al NMR spectra. However, these spectra contain a satellite peak whose intensity linearly increases with an increase of the Ce concentration leaving position of this peak unchanged. This was interpreted as manifestation of the crystal structure modification in the vicinity of Ce ions in agreement with EPR data. Thus, optical properties of Ce3+ in LaAlO3 will be determined namely by the local crystal structure near this ion.
Effect of cytosine methylation on DNA duplexes was studied by using a model system of three self-complementary DNA octamers containing central CpG motif surrounded by a couple of AT base pairs, CAACGTTG, CATCGATG, and CTTCGAAG, and their analogues with the central cytosine methylated at C5 position. Temperature dependences of 1 H NMR, UV absorption, and Raman scattering spectra measured for aqueous solutions at concentrations of different orders of magnitude were subjected to a joint analysis that allowed an accurate determination of the enthalpy and entropy of duplex formation. It was revealed that the changes of the enthalpy and entropy contributions are strongly dependent on the base composition in the vicinity of the CpG motif.
