Studies on cardiotonic steroids from the skin of Japanese toad.

Abstract

<p>A roll-to-roll high-current diffuse dielectric barrier discharge at atmospheric pressure was operated in air and Ar/N<sub>2</sub>/O<sub>2</sub> gas mixtures. The exhaust gas from the discharge was studied using a high-resolution Fourier-transform infrared spectrometer in the range from 3000 to 750 cm<sup>-1</sup> to unravel the plasma-polymer interactions. The absorption features of H<sub>x</sub>N<sub>y</sub>O<sub>z</sub>, CO<sub>x</sub>, and HCOOH (formic acid) were identified, and the relative densities were deduced by fitting the absorption bands of the detected molecules. Strong interactions between plasma and polymer (Polyethylene-2,6-naphthalate, or PEN) in precursor-free oxygen-containing gas mixtures were observed as evidenced by a high CO<sub>x</sub> production. The presence of HCOOH in the gas effluent, formed through plasma-chemical synthesis of CO<sub>x</sub>, turns out to be a sensitive indicator for etching. By adding tetraethylorthosilicate precursor in the plasma, dramatic changes in the CO<sub>x</sub> production were measured, and two distinct deposition regimes were identified. At high precursor flows, a good agreement with the precursor combustion and the CO<sub>x</sub> production was observed, whereas at low precursor flows an etching-deposition regime transpires, and the CO<sub>x</sub> production is dominated by polymer etching.</p>