Theoretical Prediction of ¹³C NMR Chemical Shifts of Polymers Using Oligomeric Approach

Abstract

Combined density functional theoretical (DFT) and ab initio methods have been used for the calculation of 13 C NMR chemical shifts of some hydrogen-terminated oligomers of ethylene, propylene, isobutylene, ethylene oxide, vinyl alcohol, and acrylonitrile. The 13 C isotropic chemical shift (δiso) values are calculated with respect to theoretical isotropic shielding constant (σiso) value of the tetramethylsilane (TMS). The average unsigned error in δiso values of the various oligomers varies between 2 and 5 ppm. The error of ca. 5.22 ppm for acrylonitrile arises mainly due to the cyano carbon. Oligomeric approach has been employed to calculate the δ iso values of the corresponding polymers. This approach is validated by the excellent correlation obtained for the linear fits. These calculated δiso values for the polymers are in good agreement with the experimental values.

Quantum Mechanical Calculation of NMR Parameters in the Stereostructural Determination of Natural Products

“…In order to determine which adenine was responsible for nucleophilic attack on the cyclopropane ring of the ligand, a new faster and easier method was devised as an alternative to the full collection of experimental restraints necessary to obtain the 3D experimental structure of the covalent complex. In particular, an approach based on integrated NMR experimental data with GIAO 1 H NMR DFT calculated values was proposed to study ligand-macromolecule interactions, going well over the successful application of 1 H and 13 C NMR chemical shift calculations in the structure elucidation of organic molecules, [8a,9b,28] in the interpretation of polymer spectra [28d] and in the conformational analysis of peptides, [91][92][93] oligosaccharides, [94] and calixarenes. [95] Thus, two 3D models were built where 36 was covalently bound to A5 or A6 (model A or B, respectively; Figure 11a,b), and starting from the NMR structure of duocarmycin SA covalently linked to the DNA duplex (PDB [96] archive code 1DSA) [97] 36 was built and docked in the minor groove.…”

Nuclear factor kappa B activation is a potential target for preventing pancreatic carcinoma by aspirin

“…Several investigations have employed ab initio methods to interpret NMR spectra, almost exclusively chemical shifts, of polymers. Because of substantial computational needs, most of these studies are quite recent 5–11. They are based on the important methodological developments for estimating chemical shifts and coupling constants with high accuracy 12–15.…”

“…Although helpful, these studies neglect possible long‐range effects on the NMR chemical shifts. A recent theoretical study by Asirvatham et al 10 tackled the chain length dependence of the chemical shifts. However, although these investigators consider a broad range of polymers under their isotactic form, the evaluations are limited to trimers (except for polyethylene where the tetramer is also considered).…”

Structural Features of the (+)‐Yatakemycin/d(GACTAATTGAC)‐(GTCAATTAGTC) Complex – Quantum Mechanical Calculation of NMR Parameters as a Tool for the Characterization of Ligand/DNA Interactions

“…[43,44] So far, the use of 1 H and 13 C chemical shifts calculations has been shown to be efficient in the elucidation of organic molecules, [45][46][47][48][49][50] in the interpretation of polymer spectra, [50] and in the conformational analysis of peptides, [51][52][53] oligosaccharides, [54] and calixarenes. [55] Here we propose a QM-NMR integrated approach for the characterization of a larger and more complex system, involving a ligand-receptor system and in particular a nucleic acid structure.…”