Abstract

Photodissociation of ligands has made important contributions to the understanding of function and structure of heme proteins. Here we present a theory for photochemical dissociation that is not limited by the assumption of previous analyses of optically thin samples, and apply it to interpretation of the photodissociated state of carboxymyoglobin (Mb⋆CO). Equations are derived and presented in terms of the effects of absorbance, [log₁₀(<i>I</i>₀/<i>I</i>) = <i>A</i>, the probability of absorption of light quanta per unit surface area], and the potential for dissociation, <i>D</i> (maximum probability of photodissociation per unit surface area; a linear function in time of photolysis), for both monochromatic and polychromatic light sources. When monochromatic light is used, we show that for large absorbances (<i>A</i> > 2) the fractional photolysis increases as (log <i>D</i>)/<i>A</i>, and may appear to "saturate" even though well below completion. For polychromatic light intensities and absorbances, the theory predicts that the near-infrared tail of the absorbance band of carboxymyoglobin should be sufficiently transparent to allow the radiation to penetrate the sample, yet still have a significant absorptivity such that complete photodissociation is possible. An optically thick myoglobin-CO sample illuminated with a tungsten lamp was observed to behave somewhere between these two theories. These theoretical relations may be useful in the analysis of photolysis data from optically dense solutions and as a guide for future experimental design.

Picosecond time-resolved vibrational spectroscopy using a regenerative amplifier

T. M. Jedju, M. W. Roberson, and L. Rothberg
Appl. Opt. 31(15) 2684-2691 (1992)

Enhancement of ligand binding to myoglobin by far-infrared excitation from a free-electron laser

Bernard Gerstman, Mark Roberson, and Robert Austin
J. Opt. Soc. Am. B 6(5) 1050-1057 (1989)

Picosecond circular dichroism spectroscopy: a Jones matrix analysis

Xiaoliang Xie and John D. Simon
J. Opt. Soc. Am. B 7(8) 1673-1684 (1990)

Photochemical reflective optical fiber sensor for selective detection of phenol in aqueous solutions

Zhengkun Wang, Nianbing Zhong, Ming Chen, Haixing Chang, Dengjie Zhong, Yongwu Wu, Huimin Liu, Xin Xin, Mingfu Zhao, Bing Tang, Tao Song, and Shenghui Shi
Appl. Opt. 58(8) 2091-2099 (2019)

Mammalian complex III heme dynamics studied with pump-probe spectroscopy and red light illuminations

Sean P. O’Connor, Samantha M. Powell, John M. Rickman, Nathaniel J. Pope, Gary D. Noojin, Marlan O. Scully, Michael L. Denton, and Vladislav V. Yakovlev
Biomed. Opt. Express 12(11) 7082-7091 (2021)