23Na exchange

Competition for binding to heparin (in essentially salt-free solutions) has been studied for most physiological cations, by ion-exchange,372 equilibrium dialysis,373 c.d.,365 and 23Na-n.m.r. spectroscopy.370 The following order of affinity was generally observed Na+ < K+ < Mg2+ < Ca2+. 

NaB (C6H5 )4/l 8-crown-6/dioxolane systems the exchange was found to be slow on the nmr timescale two 23Na resonances were observed for solutions containing an excess of the sodium salt. 

Na 2.58 y P e" 1.39 23Na(n,y)24Na Exchangeable sodium measurements... 

Cation flux rates were assessed for 10 directly in phospholipid vesicles using a dynamic 23Na NMR method. In this procedure, addition of a Dy3+ shift reagent to an aqueous vesicle solution prepared in the presence of Na+ results in an external Na+ signal shifted with respect to internal Na+. With the incorporation of a channel former, the line width broadens, reflecting dynamic exchange between internal and external Na+ through the membrane channel. Consequently, the linewidth varies directly with cation flux and a plot of [channel] versus linewidth permits determi-... 

In a recent publication (184), alkali metal (7Li and 23Na) NMR spectroscopy confirmed that in solution as well as in the crystalline state, [LiTi(0-/-Pr)5]2 exists as a dimer with a rapid isopropoxide exchange, whereas a tight ion pair exists between Na+ and the Ti(0-/-Pr)5- anion. 

In Table V is the temperature dependence of the 23Na linewidths of Nafion-Na+ for a number of equivalent weights. At all equivalent weights the resonance narrows with increasing temperatures. This behavior is indicative of exchange which is fast on the NMR time scale. With two exceptions (27° and 47°C at 1347 and 1500 equiv wt), the linewidth... 

Analysis of Cation Position in Ion-Exchanged Y Zeolites by 23Na NMR... 

Lin and Chao (1991) studied the variation of the cation distribution with the lanthanum exchange level in hydrated La,Na-Y zeolites by two-dimensional 23Na nutation NMR spectra in which the chemical shift and the quadrupole interaction could be separated. They proposed that the mobility of both water molecules and sodium ions can be reduced by lowering the temperature of the sample, and the migration of lanthanum ions from supercages to small cages causes the redistribution of sodium after dehydration... 

The possible combinations of electronic, rotational, and nuclear spin states can now be compiled [10] as shown in Table 4.6. The total wave function P must be (s) and (a) under the nuclear exchange for boson and fermion nuclei, respectively. Fermion nuclei exhibit half-integral spin I = j ( H, He, C), 1 = 1 (23Na), J = I ( O), etc. Bosons include integral-spin nuclei, such as He, (I = 0) and (/ = 1). 

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