Intramolecular hydrolysis of glycinamide and glycine dipeptides coordinated to cobalt(III). [Part II]: reactions of the cis-[Co(en)₂(OH₂/OH)(glyNHR)]³⁺/²⁺ ions (R = H, CH₂CO₂C₃H₇, CH₂CO₂⁻) and the effect of buffer species

Boreham, C.J., Buckingham, D.A., and Keene, F. R. (1979) Intramolecular hydrolysis of glycinamide and glycine dipeptides coordinated to cobalt(III). [Part II]: reactions of the cis-[Co(en)₂(OH₂/OH)(glyNHR)]³⁺/²⁺ ions (R = H, CH₂CO₂C₃H₇, CH₂CO₂⁻) and the effect of buffer species. Journal of the American Chemical Society, 101 (6). pp. 1409-1421.

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Abstract

The intramolecular addition of cobalt(III) bound H₂0 and OH⁻ to glycinamide, glycylglycine isopropyl ester, and glycylglycine also coordinated to Co(III) in the cis-[Co(en)₂(OH₂/OH)(glyNHR)]³⁺/²⁺ ions (R = H, CH₂CO₂C₃H₇, CH₂CO₂⁻) has been investigated both in the absence and presence of buffers. For the dipeptide complex (R = CH₂CO₂C₃H₇) both the aqua and hydroxo species form [Co(en)₂(glyO)]²⁺, but loss of hydroxide also occurs resulting in the chelated amide [Co(en)₂(glyNHR)]³⁺. A combination of rate and product analysis data suggests that the initial cyclization is rate determining under all conditions. Buffer species act as general bases in this rate-determining process, but they also enhance the formation of the hydrolysis product. Coordinated water is more reactive than coordinated hydroxide owing largely to a more positive δS≠.

Item ID: 22761
Item Type: Article (Refereed Research - C1)
ISSN: 1520-5126
Date Deposited: 04 Oct 2012 06:43
FoR Codes: 03 CHEMICAL SCIENCES > 0302 Inorganic Chemistry > 030207 Transition Metal Chemistry @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970103 Expanding Knowledge in the Chemical Sciences @ 100%
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