Nonactin Ammonium ionophore

Ammonium ionophore I (Nonactin) [6833-86-7] M 736.9, m 147-148 , [a] g 0 (c 1.2, CHCI3). Crystallise it from MeOH (colourless needles), and it is dried at 20 in high a vacuum. It is a selectophore with high sensitivity for NH + ions. [Corbaz et al. Helv Chim Acta 38 1445 1955, Domingues et al. Helv Chim Acta 45 129 1962, Nawata Ando Helv Chim Acta 55 1371 1972, Beilstein 19/12 V 751.]... 

Although rum ammonia levels are not routinely measured, it is a useful indicator of Reye s syndrome and should be monitored in newborns at risk of developing hyperammonemia Ammonia is produced in many analytically useful enzyme reactions and the ammonium ISE has been used as the base sensor in several enzyme electrodes (see next section). In addition to valinomycin, other antibiotics such as the nonactin homalogs and gramicidins also behave as ionophores. The nonactin homolo were originally studied for their ability to selectively bind potassiiun ions It was then discovered that ammonium ions were preferred over potassium ions, and the selectivity coefficient Knh+ = 0.12 was reported. Since ammonia is present at fairly low levels in serum, this selectivity is not sufficient to to accurately measure NH4 in the presence of K. An extra measure of selectivity can be gained by using a gas permeable membrane to separate the ammonia gas from the sample matrix... 

Nonactine and nigericin are two ionophores used to collapse the liposomal transmembrane ammonium and pH gradients, respectively. Nonactine is an... 

Important cation binding systems in Nature are, for example, a class of macro-cyclic compounds termed ionophores and proteins that bind quaternary ammonium ions such as acetylcholine. The ionophores valinomycin 1, nonactin, the ennia-tines, and baeuvericin are cation binders that are structurally quite diverse, yet... 

Ion selective electrodes can also be used as transducers in potentiometric biosensors. An example is a biosensor for urea (blood urea nitrogen, BUN) based on a polymembrane ISE (vinyl chloride) for ammonium ion (Figure 4-14). The enzyme urease is immobilized at the surface of the ammonium selective ISE based on the antibiotic nonactin (see structure of ionophore in Figure 4-3), and catalyzes the hydrolysis of urea to NH3 and CO2. 

The ammonia produced dissolves to form NH, which is sensed by the ISE. The signal generated by the NH4 produced is proportional to the logarithm of the concentration of urea in the sample. The response may be either steady state or transient. Typically, correction for background potassium is required, since the nonactin ionophore has limited selectivity for ammonium over potassium (Knh4/k = 0.1). Potassium is measured simultaneously with urea and used to correct the output of the urea sensor using the Nicolslcy-Eisenman equation. 

Liquid, plasticized PVC matrix, nonactin/monactin Liquid, plasticized PVC matrix, valinomycin and quaternary ammonium salt in dioctylphthalate Liquid, plasticized PVC matrix, an acyclic, lipophilic neutral ionophore... 

The transducer can be an ammonium ISE ionophore (nonactin-based), a gas sensor for ammonia or carbon dioxide, and an iodide-selective sensor. The latter can be coupled with the enzymes L-aminooxidase (l-AOx) and peroxidase (e.g., coimmobilized in a polyacrylamide gel), which catalyses reactions [V] and [VI] ... 

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