Using MOS-500 for Magnetic Circular Dichroism – MOS-500 – Spectroscopy – Application Note 22

Abstract

MOS-500. Magnetic circular dichroism. MCD. Circular Dichroism. Magnetic field. Metalloproteins. Cytochrome c. Permanent magnet. The principle of Magnetic Circular Dichroism (MCD) is to run CD measurements in the presence of a controlled magnetic field to determine the oxidation and spin state of metal electrons. The main applications of this technique due to the presence of metals with degenerate energy levels contained in proteins result in strong MCD signals as is observed in Metallo and ferric heme proteins is in biology and biochemistry. This application note illustrates the capabilities of a MOS-500 with an MCD accessory containing a permanent 1.4T magnet to determine oxidation and spin state of the iron in horse heart cytochrome c. Hardware reconfiguration is done within minutes and spectra can be obtained without the need to purge the optics down to 200 nm while taking advantage of the incredible wavelength resolution of grating monochromators in the visible region.

Introduction

The principle of Magnetic Circular dichroism is to run CD measurements (steady-state mode) under a controlled magnetic field. MCD is capable of determining both oxidation and spin state. Main applications are in biology and biochemistry, for example metalloproteins and ferric heme proteins are the most likely candidates for MCD measurements, as the presence of metals with degenerate energy levels lead to strong MCD signals. In this note we illustrate capabilities of MCD accessory using horse heart cytochrome c. However proteins can also show some MCD signal without metal centers, MCD being capable of stoichiometrically measuring the tryptophan content of proteins assuming there are no other
competing absorbers in the spectroscopic system.

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