Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 112, Issue 14, Pages 4218-4220Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1503739112
Keywords
formose reaction; quantum tunneling; hydride shift; prebiotic reactions
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Funding
- NASA [NNX12AD89G]
- National Science Foundation [CHE-1213976]
- Extreme Science and Engineering Discovery Environment Grant [TG-CHE090070]
- NASA [53370, NNX12AD89G] Funding Source: Federal RePORTER
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1213976] Funding Source: National Science Foundation
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Hydrogen atom transfer reactions between the aldose and ketose are key mechanistic features in formose chemistry by which formaldehyde is converted to higher sugars under credible prebiotic conditions. For one of these transformations, we have investigated whether hydrogen tunneling makes a significant contribution to the mechanism by examining the deuterium kinetic isotope effect associated with the hydrogen transfer during the isomerization of glyceraldehyde to the corresponding dihydroxyacetone. To do this, we developed a quantitative HPLC assay that allowed us to measure the apparent large intrinsic kinetic isotope effect. From the Arrhenius plot of the kinetic isotope effect, the ratio of the preexponential factors A(H)/A(D) was 0.28 and the difference in activation energies E-a(D) - E-a(H) was 9.1 kJ.mol(-1). All these results imply a significant quantum-mechanical tunneling component in the isomerization mechanism. This is supported by multidimensional tunneling calculations using POLYRATE with small curvature tunneling.
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