¹³C shielding scale for MAS NMR spectroscopy

Abstract

We have performed the direct measurements of (13)C magnetic shielding for pure liquid TMS, solution of 1% TMS in CDCl3 and solid fullerene. The measurements were carried out in spherical ampoules exploring the relation between the resonance frequencies, shielding constants and magnetic moments of (13)C and (3)He nuclei. Next the (13)C shielding constants of glycine, hexamethylbenzene and adamantane were established on the basis of appropriate chemical shifts measured in the solid state. All the new results are free from susceptibility effects and can be recommended as the reference standards of (13)C shielding scale in the magic angle spinning NMR experiments.

A Brief Review on Bioactive Compounds from Species

“…The measurement of shielding can be easily extended on MAS nuclear MR experiments as it was already shown for 13 C spectra [16]. All the above conclusions are true and vital for the method of shielding measurements.…”

Calculations of NMR properties for sI and sII clathrate hydrates of methane, ethane and propane

“…The 13 C and 1 H shielding constants for encaged and gaseous guest molecules are presented in Tables 1 and 2 together with available experimental results. The 13 C experimental data are rescaled to absolute values using recent benchmark results for pure liquid TMS (183.20 ppm) and 1 % solution of TMS in CDCl 3 (183.94 ppm) by Jackowski and Makulski [ 68 ]. The 1 H shielding constants are referenced to benchmark values for gaseous molecules by Garbacz et al [ 69 ], obtained with extrapolation to zero density, giving results characterizing single, non-interacting molecules.…”

A simple graphical approach to predict local residue conformation using NMR chemical shifts and density functional theory

“…The gauge‐invariant atomic orbital (GIAO) condition was applied to calculate the NMR shielding tensors. Chemical shifts of each carbon were referred to the experimental value of absolute shielding of carbon in pure liquid tetramethylsilane, TMS, (183.94 ppm) . Since there was no experimental value for absolute shielding of proton for TMS, 1 H chemical shifts of each proton were referred to calculated isotropic shielding constant using B3LYP/6‐311 + G(d,p) and B3LYP/6‐311G(d,p) (31.99 and 32.00 ppm, respectively) .…”

“…Chemical shifts of each carbon were referred to the experimental value of absolute shielding of carbon in pure liquid tetramethylsilane, TMS, (183.94 ppm). [27] Since there was no experimental value for absolute shielding of proton for TMS, 1 H chemical shifts of each proton were referred to calculated isotropic shielding constant using B3LYP/ 6-311 1 G(d,p) and B3LYP/6-311G(d,p) (31.99 and 32.00 ppm, respectively). [28,29] The Spartan software [30] was applied to carry out the conformational analysis of the structures and the Gaussian 09 package [31] was used to perform the optimization of the structures and the shielding constant calculations.…”