A neutral water-soluble broadening agent for spin-label studies.

Cr(maltolate)3 is proposed as a neutral water-soluble reagent for the broadening of accessible nitroxyl spin labels or spin probes in biological experiments. For situations in which the molecular charge is important, it supplements Cr(oxalate)3(3-), which is somewhat more effective on a molar basis. The interaction of the two reagents with spin-labeled creatine kinase is an example of a case in which the charge of the broadening agent is important.