The Regeneration of Visual Purple in Solution

Abstract

INTRODUCXION Regeneration of visual purple in solution was originally observed by Kiihne (Ewald and Kiihne, 1878). It was not until recently that it was again reported by Hecht, Chase, Shlaer, and Halg (1936). They found by measuring density changes at 500 mt~ with Shlaer's photoelectric spectro- photometer (Shlaer, 1938) that regeneration occurred only after about 85 per cent of the visual purple originally present had been bleached and that it was maximal in solutions of pH about 7.7. Hosoya (1938) has reported that under certain conditions visual purple can be made to regen~te in solution after only a relatively small percentage of it has been bleached. It is known that at ~eutral and acid pH's the photic decomposition of visual purple results in the appearance of other colored compounds (Weigert and Nakashima, 1930; Chase, 1936; Lythgoe, 1937), one or more of which become colorless at a rate dependent upon the temperature (Hosoya, 1933; Wald, 1937; Lythgoe, 1937). Since visual purple regeneration is measured optically, the presence of such additional color changes would complicate and perhaps mask the changes of visual purple itself at these pH's. Because this effect becomes greater in more acid solutions, it was apparent that pH 7.7 might not be the true maximum for regeneration. We have extended the investigations already reported by examining in detail the effect of pH on regeneration, taking into consideration the forma- tion and disappearance of colored decomposition products, and making the measurements in such a way as to minimize the complicating factors that are present in neutral and slightly acid solutions. We have also investi- gated the effect of wave length of the bleaching light, as well as that of temperature during extraction. We have secured data which give information about the course of the regeneration reaction in solution by measuring the absorption spectrum of solutions during regeneration, and have made some investigations into the kinetics of the chemical reaction which controls the process. * This work was aided by a grant from The Rockefeller Foundation. 21