Multifield Saturation Magnetization

Superseding the older techniques referred to as magnetic susceptibility measurements, Dr. Day is the leading international expert on the application of this technique to metallobiomolecules. Available as a satellite facility, this technique provides detailed electronic spin and site-symmetry information (from zero-field splitting and g-value determinations) for all the paramagnetic centers in the sample. It can also be used to determine absolute amounts of paramagnetic sites in metallobiomolecules [Edmund (Tad) Day, Emory].

Acronyms, synonyms

• Multifield Saturation Magnetization
• Susceptibility
• Magnetic Susceptibility

Measured physical quantities

• Magnetic moment in the direction of the applied magnetic field

Information available

• Spin, S
• Amount of spin, [S]
• Zero-field splittings and g-values, D, E/D, g
• Exchange coupling, J

Information NOT available, limitations

• It is difficult to resolve magnetically complex samples
• It is not possible to resolve spin S=1 with large g from spin S=2 with g=2

Examples of questions that can be answered

• Is that S=9/2 EPR signal due to 1% or 100% of the protein?
• Is that Ni(II) site spin S=1 or spin S=0 (or both)?
• Is there an integer-spin paramagnetic center present? How much?
• What is the exchange coupling of the diferrous state of a dinuclear iron protein?

Major advantages

• All paramagnetism is detected - there is no "silent" magnetization
• The amount of paramagnetism is reliably measured
• Exchange coupling can be accurately measured even when it is smaller than the zero-field splitting

Major disadvantages

• Requires a magnetically pure and well-characterized sample

Sample constraints

• Sample volume is ca. 0.2 mL
• Concentration is 0.5 mM or higher
• Magnetic purity is important (e.g., the g=4.3 EPR signal of impurity high-spin Fe(III) must be negligible)
• Oxygen must be removed from the sample
• The sample must be deuterated
• A matched control is required