Anomalous equilibrium and kinetic. cap alpha. -deuterium secondary isotope effects accompanying hydride transfer from reduced nicotinamide adenine dinucleotide

Journal Article · Wed Jun 04 00:00:00 EDT 1980 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00532a035· OSTI ID:6873771

Kurz, L C; Frieden, C

The kinetic ..cap alpha..-deuterium secondary isotope effect on the second-order rate constant has been measured for the nonenzymatic direct hydride transfer reduction of 4-cyano-2,6-dinitrobenzenesulfonate by NADH (deuterium substitution of the hydrogen bonded to the 4 carbon of NADH which is not transferred to the acceptor). Values of 1.156 +- 0.018 and 1.1454 +- 0.0093 were obtained using direct and intramolecular competition methods, respectively. The corresponding (enzyme catalyzed) equilibrium isotope effects were found to be 1.013 +- 0.020 and 1.0347 +- 0.0087 as determined by direct and intermolecular competition methods, respectively. Thus, the value of the kinetic effect is significantly greater than that on the equilibrium. It is suggested that this may arise either from participation of the ..cap alpha.. hydrogen in a hyperconjugative stabilization of an early transition state or from its participation in the reaction coordinate motion of a nonlinear activated complex. The values of the equilibrium effect allow calculation of a fractionation factor (relative to acetylene) for hydrogen bonded to the 4 carbon of NAD/sup +/ of 1.448 +- 0.028 or 1.418 +- 0.020. This is larger than expected based on comparison with hydrogen bound to sp/sup 2/ carbon in propene (1.336) or benzene (1.368) but is consistent with the decreased aromatic character of pyridinium vibrational spectra. The lack of a significant inverse value for the equilibrium ..cap alpha..-dueterium effect suggests complications in the interpretation of reported kinetic secondary effects of 0.85 and 1.2 for the forward (sp/sup 3/ ..-->.. sp/sup 2/) and reverse (sp/sup 2/ ..-->.. sp/sup 3/) rate constants for the nonenzymatic transhydrogenation of N-benzyl-1,4-dihydronicotinamide and its nicotinamide salt.

• Research Organization: Washington Univ. School of Medicine, St. Louis, MO
• OSTI ID: 6873771
• Journal Information: J. Am. Chem. Soc.; (United States), Vol. 102:12
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
59 BASIC BIOLOGICAL SCIENCES
DEUTERIUM
ISOTOPE EFFECTS
NAD
CHEMICAL REACTIONS
HYDROGEN TRANSFER
EXPERIMENTAL DATA
COENZYMES
DATA
HYDROGEN ISOTOPES
INFORMATION
ISOTOPES
LIGHT NUCLEI
NUCLEI
NUCLEOTIDES
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
STABLE ISOTOPES
400302* - Organic Chemistry- Isotope Effects- (-1987)
550201 - Biochemistry- Tracer Techniques