Figure 1.

Photoreduction of the ferric haem of AXCP crystals by excitation with a 405 nm laser. (a, b) No photoreduction is observed at low laser power densities from 1.6 to 4.0 mW mm⁻² at the start of (blue spectra) and after (red spectra) the kinetic series. (c) Higher laser density powers (>4.0 mW mm⁻²) result in clear photoreduction of the Fe, as shown by the split of the ν₄ marker at 1368 cm⁻¹ and interconversion into the 1351 cm⁻¹ peak, which is evidence for the ferrous state of the haem Fe. (d) This interconversion and the presence of only the 1351 cm⁻¹ band are strong evidence of complete reduction and occur more rapidly at higher power densities such as 9.8 mW mm⁻². The blue spectrum represents the first spectrum of the first kinetic series and the red spectrum represents the last spectrum of the last kinetic series.