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ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 24, Number 3
BKCSDE 24(3)
March 20, 2003 |
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Title |
The Mechanism of the Decomposition of a Bronchodilator, S-Nitroso-N-acetyl-D,Lpenicillamine (SNAP), by a Bronchoconstrictor, Aqueous Sulfite: Detection of the N-Nitrosohydroxylamine-N-sulfonate ion
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Author |
Alvin A. Holder, Sophia C. Marshall, Peng George Wang, Chee-Hun Kwak
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Keywords |
S-Nitrosothiols, Bronchoconstrictor, Bronchodilator, Aqueous sulfite, S-Nitroso-N-acetyl-D,Lpenicillamine
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Abstract |
The mechanism of the decomposition of a bronchodilator, S-nitroso-N-acetyl-D,L-penicillamine (SNAP) by a bronchoconstrictor, aqueous sulfite, has been investigated in detail. The decomposition was studied using a conventional spectrophotometer at 336 nm over the ranges: 0.010 [SIV]T 0.045 mol dm-3, 3.96 pH 6.80 and 15.0 q 30.0 oC, 0.60 I 1.00 mol dm-3, and at ionic strength 1.00 mol dm-3 (NaCl). The rate of reaction is dependent on the total sulfite concentration and pH in a complex manner, i.e., kobs = k1K2[SIV]T/ ([H+] + K2). At 25.0 °C, the second order rate constant, k1, was determined as 12.5 ± 0.15 mol-1 dm3 s-1. DH¹ = +32 ± 3 kJ mol-1 and DS ¹ = -138 ± 13 J mol-1K-1. The N-nitrosohydroxylamine-N-sulfonate ion was detected as an intermediate before the formation of any of the by-products, namely, N-acetyl-D,Lpenicillamine. The effect of concentration of aqueous copper(II) ions on this reaction was also examined at pH 4.75, but there was no dependence on [Cu2+]. In addition, the pKa of SNAP was determined as 3.51 ± 0.06 at 25.4 °C [I = 1.0 mol dm-3 (NaCl)].
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350 - 356 |
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