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Volumn 125, Issue 5, 2003, Pages 1334-1351

Mechanistic studies on the interaction of reduced cobalamin (vitamin B12r) with nitroprusside

Author keywords

[No Author keywords available]

Indexed keywords

CHEMICAL REACTIONS; CYANIDES; SODIUM COMPOUNDS; SPECTROSCOPIC ANALYSIS;

EID: 0037419880     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja0210852     Document Type: Article
Times cited : (24)

References (60)
  • 5
  • 6
    • 0037029510 scopus 로고    scopus 로고
    • and references therein
    • Zheng, D.; Birke, R. Inorg. Chem. 2002, 41, 2548 and references therein.
    • (2002) Inorg. Chem. , vol.41 , pp. 2548
    • Zheng, D.1    Birke, R.2
  • 23
    • 0346522496 scopus 로고    scopus 로고
    • note
    • Due to the strong absorption bands of the corrin ring in the UV-vis region, cobalamin is a much more distinctive chromophore compared to the nitroprusside ion. The intraligand electronic transitions of cobalamin are very sensitive to the oxidation state of the cobalt centre and nature of the ligands present in the axial positions. Consequently, UV-vis spectroscopy provides a good way to characterize the cobalamin reaction products, but not those of the cyanonitrosylferrate species.
  • 27
    • 0347782943 scopus 로고    scopus 로고
    • note
    • 2 by nitroprusside or its coordination at the vacant α position, thus leading to the formation of β-and α-substituted products, respectively. Indeed, the time-resolved UV-vis spectral changes and the respective absorbance/time plots obtained at pH ≤ 3 indicated the occurrence of two processes which exhibited a similar pattern of spectral changes (as shown in Figure S2, Supporting Information), but occurred at noticeably different rates. The contribution of the slower process to the overall reaction could be clearly observed at pH < 2, but became negligible at pH > 3, i.e., when the dimethylbenzimidazole ligand occupies the α position in Cbl(II). It is, therefore, reasonable to assume that the slower process reflects the formation and subsequent electronic stabilisation of the α-substituted cyano-bridged species. However, due to the fact that this reaction path occurs only at low pH and is of little relevance to the present study, its nature was not studied in more detail.
  • 34
    • 0346522495 scopus 로고    scopus 로고
    • note
    • 27). This suggests similar nucleophilic reactivity of axial and equatorial cyanides toward coordination to the cobalt center, such that the product distribution will mainly be determined by the statistics of the substitution process.
  • 36
    • 0347152824 scopus 로고    scopus 로고
    • note
    • At pH 2 very weak signals were also observed at ca. 9.2, 7.6, 7.5, and 6.65 ppm. Although these signals clearly indicate formation of the base-off dimethylbenzimidazole-protonated cobalamin species, the low intensity and broad features of the signals do not allow their unambiguous assignment.
  • 38
    • 0346522492 scopus 로고    scopus 로고
    • note
    • 2- as the other reaction product was confirmed by EPR spectroscopy.
  • 39
    • 0345891696 scopus 로고    scopus 로고
    • note
    • 4), were in general similar to those observed for the reaction in water. The overall reaction time, however, and in particular the induction periods preceding the formation of cyanocobalamin, were significantly longer, such that this reaction step could be conveniently studied by conventional EPR spectroscopy. Significant deceleration of the reaction observed in methanolic medium can at least in part be ascribed to a decrease in driving force for the electron-transfer reaction due to a negative shift of the redox potential of the iron center on going from water to methanol.
  • 43
    • 0345891694 scopus 로고    scopus 로고
    • note
    • a = 2.9 in Cbl(II)).
  • 46
    • 0347782938 scopus 로고
    • and references therein
    • (d) Brown, K. L. J. Am. Chem. Soc. 1987, 26, 2034 and references therein.
    • (1987) J. Am. Chem. Soc. , vol.26 , pp. 2034
    • Brown, K.L.1
  • 48
    • 0347152825 scopus 로고    scopus 로고
    • note
    • 3OD was confirmed by a characteristic increase in absorbance in the range 580-600 nm of the UV-vis spectrum.
  • 49
    • 0347782912 scopus 로고    scopus 로고
    • note
    • These mainly include the high extinction coefficients of Cbl(II), and formation of cyano-bridged polynuclear species, such as Co-Fe-Co trimers.
  • 50
    • 0347152823 scopus 로고    scopus 로고
    • note
    • - was employed as the competing nucleophile
  • 54
    • 0347152820 scopus 로고    scopus 로고
    • note
    • Differential pulse voltammetry offers a better resolution of poorly separated redox waves compared to cyclic voltammetry, and for that reason is mainly used in the discussion of the reductive processes observed for compex 2. Cyclic voltammograms recorded in the corresponding potential range (compare Figure S10, Supporting Information) provided additional information on the reoxidation processes from reverse anodic scans. Detailed discussion of these data, however, is beyond the scope of the present study.
  • 56
    • 0347152821 scopus 로고    scopus 로고
    • note
    • 2-. This facilitates observation of changes in the electrochemical properties of the metal centres resulting from the formation of cyano-bridged species.
  • 57
    • 0347152822 scopus 로고    scopus 로고
    • note
    • 2- (which is expected as the predominant process occurring at the second reduction potential under our conditions) is included in the discussion.
  • 58
    • 0347152782 scopus 로고    scopus 로고
    • note
    • No significant dependence on pH was observed for the peak ascribed to the one-electron reduction of the trans isomer of 2 in the studied pH range.
  • 59
    • 0345891661 scopus 로고    scopus 로고
    • note
    • Concentrations of nitric oxide were monitored for ca. 2 h after mixing of the reactants.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.