Two-step one-electron transfer reaction of chromium(III) complex containing levodopa and uridine with N-bromosuccinimide

[Cr-III(LD)(Urd)(H2O)(4)](NO3)(2) center dot 3H(2)O (LD = Levodopa; Urd = uridine) was prepared and characterized. The product of the oxidation reaction was examined using HPLC. Kinetics of the oxidation of [Cr-III(LD)(Urd)(H2O)(4)](2+) with N-bromosuccinimide (NBS) in an aqueous solution was studied spectrophotometrically, with 1.0-5.0 x 10(-4) mol dm(-3) complex, 0.5-5.0 x 10(-2) mol dm(-3) NBS, 0.2-0.3 mol dm(-3) ionic strength (I), and 30-50 degrees C. The reaction is first order with respect to [Cr-III] and [NBS], decreases as pH increases in the range 5.46-6.54 and increases with the addition of sodium dodecyl sulfate (SDS, 0.0-1.0 x 10(-3) mol dm(-3)). Activation parameters including enthalpy, Delta H*, and entropy, Delta S*, were calculated. The experimental rate law is consistent with a mechanism in which the protonated species is more reactive than its conjugate base. It is assumed that the two-step one-electron transfer takes place via an inner-sphere mechanism. A mechanism for this reaction is proposed and supported by an excellent isokinetic relationship between Delta H* and Delta S* for some Cr-III complexes. Formation of [Cr-III(LD)(Urd)(H2O)(4)](2+) in vivo probably occurs with patients who administer the anti-Parkinson drug (Levodopa), since Cr-III is a natural food element. This work provides an opportunity to identify the nature of such interactions in vivo similar to that in vitro.