Balevicius Vytautas, Gdaniec Zofia, Fuess Hartmut
Faculty of Physics, Vilnius University, Sauletekio al. 9-3, bld.3, LT-10222 Vilnius, Lithuania.
J Chem Phys. 2005 Dec 8;123(22):224503. doi: 10.1063/1.1989312.
(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.
已在接近其下临界溶解点（(T_{CL})）的单相区域中，在不同盐质量分数（(X)）的水电解质混合物[四氢呋喃/水/氯化钠和3 - 甲基吡啶（3MP）/水/溴化钠]中测量了（1）氢、（23）钠、（35）氯、（79）溴和（81）溴的核磁共振化学位移（(\delta)）和信号半高宽（(\Delta_{1/2})）。在(X)约为0.1且(T = 301K)的3MP/水/溴化钠溶液的（23）钠和（81）溴核磁共振谱中，发现(\delta = f(X))和(\Delta_{1/2}= f(X))的斜率存在不连续变化。3MP的（1）氢核磁共振信号在整个研究的(X = 0.002 - 0.2)范围内是连续的，而水化学位移斜率的变化几乎不明显。在两相区域中，即(T>T_{CL})时，观察到所有核磁共振信号加倍。核磁共振参数的灵敏度对阴离子（(Cl^-)和(Br^-)）溶液组成的依赖性比对阳离子（(Na^+)）的更强。观察到（81）溴核具有非常强的弛豫效应，弛豫速率达到(14000 s^{-1})。结果根据离子 - 分子簇以及溶液超分子重组过程中水分子偶极构型相干性的变化进行了解释。
