Looking at SO2

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Science  14 Oct 2005:
Vol. 310, Issue 5746, pp. 199
DOI: 10.1126/science.310.5746.199b

Optical sensors for SO2, a colorless pollutant, have relied on secondary indicators, such as those that detect pH changes or detect byproducts of SO2 reactions. Leontiev and Rudkevich have focused on a long-known but apparently little-used aspect of SO2 chemistry: its ability to form adducts with amines by accepting their lone-pair electrons. Binding of amines such as piperidine or diethylamine to Zn-tetraphenylporphyrin in chloroform solution shifts its color from red to dark green. Addition of SO2 displaces the amine and turns the solution back to red. Because of the specificity of adduct formation, molecules such as CO, CO2, H2O, or N2O had no effect on the indicator, which is sensitive down to the low millimolar range. — PDS

J. Am. Chem. Soc. 10.1021/ja053260v (2005).

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