3 research outputs found
Carbon-13 longitudinal relaxation time measurements and DFT-GIAO NMR computations for two ammonium ions of a tetraazamacrocyclic scorpiand system
Spin-lattice relaxation times, T1s, for 13C nuclei in two cations Hn1n+ (n
= 1, 5)of N-(2-amino-ethyl)-cyclam (1, scorpiand) were determined by means
of 13C{1H} NMR experiments in aqueous solution at pH 11.5 and 0.2. The
theoretical study [modeling with OPLS-AA, B3LYP/6-31G(d) geometry
optimizations, dispersion-corrected energies (DFT-D3), and DFT-GIAO
predictions of the NMR chemical shifts (including an IEF-PCM simulation of
hydration)] was also done for several conformers of the tautomer iso-H414+
not investigated before. The binding directions in protonated polyamino
receptors necessary for efficient complexation of the nitrate anion(s)
were briefly outlined, as well. All these results were discussed in terms
of 'abnormal' 13C chemical shift changes found previously for the
side-chain carbons of amine 1 in strongly acidic solution (HNO3). In
conclusion, an earlier proposal of its association with NO3- at pH=1 was
rejected. Instead, the participation of small amounts of a microspecies
iso-H414+Dhydr under such conditions can be proposed.Publikacja w ramach programu Springer Open Choice/Open Access finansowanego przez Ministerstwo Nauki i Szkolnictwa Wyższego i realizowanego w ramach umowy na narodową licencję akademicką na czasopisma Springer w latach 2010-2013