Tuning and dissecting electronic and steric effects in ammonium receptors: nonactin vs artificial receptors.
Ion selective electrodes (ISE) based on three different tripodal receptors (5, 6, and 7) have been investigated for sensing ammonium ion. Each receptor is based on three pyrazole groups that can accept three H-bonds from the bound ammonium ion. The receptor based on 4-bromo-3,5-dimethylpyrazole (6) is the most sensitive with a detection limit for ammonium ion of 2.5 x 10(-5) M at pH 8. The detection limits for the receptors based on 2,3-dimethylpyrazole (5) and unsubstitued pyrazole (7) are 1.0 x 10(-4) and 2.0 x 10(-4) M, respectively. The selectivities of the receptors 5, 6, and 7 for sensing ammonium ion over potassium ion (logK(NH)4+(/K)+) are -2.8, -2.3, and -1.7, respectively. In contrast, the detection limit and the selectivity of a nonactin-based ISE are 2.2 x 10(-5) M and -1.3, respectively. Crystallographic studies reveal that 6 accepts three H-bonds from the bound ammonium and singly protonated receptor 5 forms three H-bonds with the bound water molecule.
Chin
Jik
J
Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada. jchin@chem.utoronto.ca
Oh
Jinho
J
Jon
Sang Yong
SY
Park
Sang Hyun
SH
Walsdorff
Christian
C
Stranix
Brent
B
Ghoussoub
Assaad
A
Lee
Seok Jong
SJ
Chung
Hyun Jei
HJ
Park
Su-Moon
SM
Kim
Kimoon
K
D000900:Anti-Bacterial Agents / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004566:Electrodes; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D018942:Macrolides / Q000737:chemistry*; D015394:Molecular Structure; D011720:Pyrazoles / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D011955:Receptors, Drug / Q000737:chemistry*; D013237:Stereoisomerism
D000900:Anti-Bacterial Agents; D018942:Macrolides; D011720:Pyrazoles; D000644:Quaternary Ammonium Compounds; D011955:Receptors, Drug; C050476:nonactin