13C chemical shifts of polyacetylene chains with charged conformational defects: A GIAO–DFT study

Benchmarking quantum mechanical calculations with experimental NMR chemical shifts of 2-HADNT

“…The DFT methods are more cost-effective approaches because that in those methods electron correlation is treated at a more affordable semiempirical level. The C-13 chemical shift calculated from DFT methods such as GIAO and B3LYP can provide structural information for different charge states [29]. On the other hand, the experimental C-13 chemical shifts can be well reproduced using B3LYP for monomeric bilirubin molecule [30].…”

Molecular dynamic simulations, GIAO‐NMR and TD‐DFT spectroscopy analyze for zwitterionic isoleucine (ILE)N, 1 ≤ N ≤ 6, in water solution

“…That way, they would show the same magnetic response and the averages of the two values for observed would be close to 0.9, 10.9, 12.3, 10.2, 11.2, and 10.4 ppm, respectively for N = 1 − 6. Previous studies 25,26 show that there is evidence of strong dependence on the magnetic shielding constant with the distribution of atomic charges to organic structures. In our simulations, this dependence can also be associated with the fact that in all (ILE) N structures, the charge distribution of these electrically charged regions are always the same, configuring an exposure similar to the solvent medium and independent of the number of amino acids.…”

“…This difference is observed by the fact that the CHARMM36 model addresses a standardized repeating mechanics for amino acids as N grows and therefore does not consider interactions that can reshape the electronic distribution. In this sense, it is important to highlight that polarized charge models in solution tend to better describe spectroscopic properties as can be seen in several previous works 29,31,43,44,53 , especially for NMR spectroscopy which is strongly related to the electronic distribution of the structure 25,26 , as observed for neutral and charged polymers. Despite these modifications, the CHARMM36 description for the dipole moment is very similar to that observed in DFT calculations (treating the solvent as point charges).…”

“…Special emphasis is given to the magnetic shielding constant and the optical absorption spectrum where we observe fundamental characteristics that characterize the absorption bands of each compound. NMR spectroscopy is a very powerful technique for determining fundamental characteristics of isolated molecules, such as neutral or charged polymers determining isomeric characteristics or even behavior in the distribution of atomic charges 25,26 . In solution, it characterize interactions between solute‐solvent and have been applied in conjunction with Monte Carlo 27 or MD 28 simulation techniques for the inclusion of solvent effects on this nuclear property 29–31 .…”

“…NMR spectroscopy is a very powerful technique for determining fundamental characteristics of isolated molecules, such as neutral or charged polymers determining isomeric characteristics or even behavior in the distribution of atomic charges. 25,26 In solution, it characterize interactions between solutesolvent and have been applied in conjunction with Monte Carlo 27 or MD 28 simulation techniques for the inclusion of solvent effects on this nuclear property [29][30][31] . Allied to this technique, the absorption spectrum is able to determine electrical characteristics that are strongly influenced by solute-solvent interactions, especially for polar and protic solvents such as water 32,33 .…”