19075-26-4Relevant academic research and scientific papers
Differences in proton-proton coupling constants of N+-CH2-CH2 protons of some betaines, N+-(CH2)2-3-COO-, and their complexes in aqueous solution
Szafran, Miroslaw,Dega-Szafran, Zofia,Nowak-Wydra, Barbara,Pietrzak, Mariusz
, p. 555 - 564 (2007/10/03)
Synthesis and 1H NMR spectra in D2O of 4 betaines and 19 betaine complexes with mineral acids containing 2 or 3 CH2 groups in the tether, N+-(CH2)n-COO-, n=2,3, and diverse volume of the positively charged groups are reported. In compounds containing three CH2 groups in the tether and three substituents at the nitrogen atom or α, α′-disubstituted pyridine ring, a characteristic multiplet for an AA′MM′X2 spin system is observed. This is consistent with preference for trans conformation (68-85%). In the spectra of compounds with two CH2 groups in the tether or three CH2 groups and unsubstituted pyridine ring, the multiplet changes to a triplet and gives apparent A2X2 and A2M2X2 spectra, respectively, consistent with no significant conformational preference. Both the number of CH2 groups in tether and the bulkiness of the charged groups are responsible for the observed differences of N+CH2 multiplicity and reflect changes in conformational preferences. According to the PM3 calculations, in the gas phase a gauche-like conformer is more stable than the trans, but in aqueous solution it is reverse.
Intercharge Distance of Flexible Zwitterionic Molecules in Solution
Chevalier, Yves,Perchec, Pierre Le
, p. 1768 - 1774 (2007/10/02)
The conformation of flexible zwitterionic molecules in solutions of polar solvents is studied by means of a NMR chemical shift method.This method makes use of chemical shift changes of NMR lines, induced by the electrostatic field caused by the electrical charges of the zwitterion.The electrostatic field at the observed nucleus is calculated, taking distances of zwitterionic (trimethylammonio)alkanoates in aqueous and methanolic solutions are then deduced from the 13C NMR chemical shift data as a function of the number of methylenes linking the cationic and anionic groups of the zwitterion.The comparison of experimental data with the end to end distances predicted by the rotational isomerism state theory shows that the polymethylene chain has a more folded conformation than the free chain.Electrostatic attraction between the two zwitterionic charges is thus important, although it could be expected that it could be offset by steric hindrance, i.e., by the bulkiness of terminal charged groups.
