title: NMR probing of structural peculiarities in ionic solutions close to critical point.
abstract: (1)H, (23)Na, (35)Cl, (79)Br, and (81)Br NMR chemical shifts (delta) and signal half widths (Delta(12)) have been measured in aqueous electrolyte mixtures [tetrahydrofuran/H(2)ONaCl and 3-methylpyridine (3MP)H(2)ONaBr] at different mass fractions of salt (X) in the one-phase region, close to their lower critical solution points (T(CL)). Discontinuous changes in slope of delta=f(X) and Delta(12)=f(X) have been found in (23)Na and (81)Br NMR spectra of 3MP/water/NaBr solution at X approximately 0.1 and T=301 K. The dependency of (1)H NMR signals of 3MP is continuous over the whole investigated range of X=0.002-0.2, whereas changes in the slope of H(2)O chemical shifts are hardly noticeable. In the two-phase region, i.e., at T>T(CL), a doubling of all NMR signals has been observed. The sensitivity of NMR parameters depends more on composition of solution for anions (Cl(-) and Br(-)) than for cations (Na(+)). A very strong relaxation effect for (81)Br nuclei with relaxation rates reaching 14 000 s(-1) was observed. The results are interpreted in terms of ion-molecular clustering and changes in coherency of dipole configurations of water molecules during supramolecular restructuring of solutions.
authors.affiliation: Faculty of Physics, Vilnius University, Sauletekio al. 9-3, bld.3, LT-10222 Vilnius, Lithuania. vytautas.balevicius@ff.vu.lt
authors.forename: Vytautas
authors.initials: V
authors.lastname: Balevicius
authors.forename: Zofia
authors.initials: Z
authors.lastname: Gdaniec
authors.forename: Hartmut
authors.initials: H
authors.lastname: Fuess
mesh_terms: D000838:Anions; D001966:Bromine / Q000737:chemistry; D002627:Chemistry, Physical / Q000379:methods*; D002713:Chlorine / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D008027:Light; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008968:Molecular Conformation; D011522:Protons; D012492:Salts / Q000737:chemistry; D012542:Scattering, Radiation; D012964:Sodium / Q000737:chemistry; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D000838:Anions; D011522:Protons; D012492:Salts; D014867:Water; D002713:Chlorine; D006859:Hydrogen; D012964:Sodium; D001966:Bromine