spectroscopy Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectro ...

, a Soret peak or Soret band is an intense peak in the blue wavelength region of the

visible spectrum The visible spectrum is the spectral band, band of the electromagnetic spectrum that is visual perception, visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' (or simply light). The optica ...

. The peak is named after its discoverer, Jacques-Louis Soret. The term is commonly used in absorption spectroscopy, corresponding to a

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

of maximum absorption (electromagnetic radiation) ranging around 400 nm in the blue region.

Examples

The Soret band arises primarily due to an electron dipole movement that allows π-π* transitions; most common in porphyrin compounds. Most analytical studies of porphyrincontaining moiety can be done using ultraviolet–visible spectroscopy and exciting wavelength at the respective Soret band wavelength. For example, the "Soret peak" is used to describe the absorption of vividly-pigmented

heme Heme (American English), or haem (Commonwealth English, both pronounced /Help:IPA/English, hi:m/ ), is a ring-shaped iron-containing molecule that commonly serves as a Ligand (biochemistry), ligand of various proteins, more notably as a Prostheti ...

-containing moieties, such as various cytochromes. For example, the cytochromes P450, a diverse class of monooxygenase

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s, exhibit a Soret peak at 450 nm in their reduced form when saturated with

carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

. This is called a CO difference spectrum assay: the absorbance spectrum of the solution is subtracted from the spectrum after saturation with

. If the P450 has been denatured, for example due to bad handling, the peak shifts to 420 nm. It is possible to see both 420 nm and 450 nm peaks on the same spectrum if only a portion of the P450 has been denatured.

References

{{Reflist Biochemistry detection methods Absorption spectroscopy