Nuclear magnetic resonance and calorimetric studies on the solvation of cryptand C221 and its sodium(+) and potassium(+) ion complexes in nonaqueous solvents

1983 ◽  
Vol 105 (26) ◽  
pp. 7563-7566 ◽  
Author(s):  
Emmanuel Schmidt ◽  
Alexander I. Popov ◽  
Jean Pierre Kintzinger ◽  
Jean-Michel Tremillon
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Potassium Ion ◽  
Nonaqueous Solvents ◽  
Calorimetric Studies ◽  
Sodium And Potassium ◽  
Nuclear Magnetic

Carbon-13 nuclear magnetic resonance study of potassium and thallium ion binding to the Gramicidin A transmembrane channel

1985 ◽  
Vol 63 (7) ◽  
pp. 1976-1981 ◽  
Author(s):  
D. W. Urry ◽  
T. L. Trapane ◽  
C. M. Venkatachalam ◽  
K. U. Prasad
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Binding Constants ◽  
Potassium Ion ◽  
Gramicidin A ◽  
Ion Concentration ◽  
Ion Binding ◽  
Carbonyl Carbon ◽  
Nuclear Magnetic

By means of carbon-13 nuclear magnetic resonance, carbonyl carbon ion-induced chemical shifts of the Gramicidin A channel are determined at 70 °C and analyzed as a function of potassium ion concentration and as a function of thallium ion concentration. In both cases two binding processes are observed. The estimated binding constants for potassium ion binding are 28/M and 2.4/M for the tight (single ion occupancy) and weak (double ion occupancy) sites, respectively, and for thallium ion binding are of the order of 103/M for the tight site and approximately 70/M for the weak site. These studies, which utilize a 90% enriched carbonyl carbon within the binding site of the channel to monitor ion interaction, argue for the presence of two ions in the channel for conditions under which planar bilayer transport studies are commonly carried out.

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