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Two step one-electron transfer reaction of chromium(III) complex containing carbidopa and inosine with N-bromosuccinimide
| Content Provider | Semantic Scholar |
|---|---|
| Author | Abdel-Khalek,, Ahmed A. Abdel-Hafeez, Mahmoud M. |
| Copyright Year | 2012 |
| Abstract | H + to form succinimide (RH) and R • is an unstable radical, and hence, two succinimidyl radical may dimerize to form bisuccinimidyl (R-R) 30, 31 . Our suggestion that the NBS acts as oxidant by a free radical path involving the homolytic dissociation of NBS with reducing metal ions (Cr III ) to yield R • and Br • as intermediates is in good agreement with the theoretical results on calculated bond dissociation energies (BDEs) involving the formation of the Br • , Br + and Br − of the N-Br bond. It has been reported that the N-Br BDE of the Br • formation is lower 32 than that of Br + or Br − . From the above mechanism, the rate of the reaction can be described by Eq. (14): In oxidation of the binary and ternary complexes, [Cr III (Ino)(H2O)5] 3+ and [Cr III (CD)(Ino)(H2O)4] 2+ , by NBS at T = 35 °C and I = 0.2 mol dm -3 , the hydroxy complexes, [Cr III (Ino)(H2O)4(OH)] 2+ and [Cr III (CD)(Ino)(H2O)4(OH)] + , are significantly more reactive than their conjugate acids 17 . The rate of Table 3 – Values of ∆Η and ∆S for the oxidation of some Cr complexes by NBS Cr complexes ∆ Η (kJ mol) ∆S (J K mol) Ref. [CrIII(CD)(Ino)(H2O)4] 2+ 22.328 -339.87 Present work [CrIII(H2O)6] 3+ 37.8 -148.8 34 [CrIII(Ino)(Gly)(H2O)5] 2+ 59.3 -79.6 17 [CrIII(LD)(Urd)(H2O)4] 2+ 59.57 26.57 33 oxidation of [Cr III (CD)(Ino)(H2O)4] 2+ is much slower than that of [Cr III (Ino)(H2O)5] 3+ , as evidenced by the values of intramolecular electron transfer rate constant. For [Cr III (CD)(Ino)(H2O)4] 2+ it is 1.43 × 10 -7 s -1 and for [Cr III (Ino)(H2O)5] 3+ it is 6.90 × 10 -4 s -1 , which can be explained on the basis of crystal field theory. The crystal field stabilization energy (∆0) between t 3 2g and e 0 g orbitals of Cr III in the ternary complex will increase due to the electrostatic field of the conjugate base of CD. Therefore, in [Cr III (CD)(Ino)(H2O)4] 2+ , losing the three t 3 2g electrons from the central Cr III ion, during the oxidation reaction becomes more difficult. Values of enthalpies and entropies of activation for the oxidation of some Cr III complexes, viz., [Cr III (CD)(Ino)(H2O)4] 2+ , [Cr III (LD)(Urd)(H2O)4] 2+ , [Cr III (H2O)6] 3+ and [Cr III (Ino)(Gly)(H2O)5] 2+ (where LD = levodopa , Urd = uridine and Gly = glycine), with NBS are collected in Table 3. There is a similar change in ∆H * and ∆S * values, leading to an excellent linear relationship. This indicates a common mechanism for the oxidation of these Cr III complexes by NBS, in which NBS ion coordinates to the Cr III -complexes in the step preceeding the rate determining intra-molecular electron transfer within the precursor complex. Similar behaviour has been observed for a large number of redox reactions 14 . |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://nopr.niscair.res.in/bitstream/123456789/14533/1/IJCA%2051A(8)%201073-1079.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
