Deuterium isotope effects in constrained tryptophan derivatives: Implications for tryptophan photophysics

Journal Article · Wed Oct 21 04:00:00 EDT 1992 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja00048a014· OSTI ID:457059

McMahon, L P; Colucci, W J; McLaughlin, M L ^[1]

---

1. Ethyl Corp., Baton Rouge, LA (United States); and others

The deuterium isotope effect on the fluorescence quantum yield and lifetime of the constrained tryptophan derivative 3-carboxy-1,2,3,4-tetrahydro-2-carboline, W(1), was determined as a function of pH and temperature. The isotope effect between pH 3.5 and 11 is attributed to a temperature-dependent quenching process common to all indoles. At room temperature the quantum yield ratio in D{sub 2}O and H{sub 2}O is 1.05 for W(1) zwitterion and 1.7 for W(1) anion. The temperature dependence of the fluorescence lifetime was determined for the zwitterion and the anion in H{sub 2}O and D{sub 2}. The frequency factors A and activation energies E{sup *} in H{sub 2}O are A = 6 x 10{sup 16} s{sup -1}, E{sup *} = 12.6 kcal/mol for W(1) anion, and N-methylindole The frequency factors A of these compounds are 2- to 3-fold larger in H{sub 2}O than in D{sub 2}O. The large deuterium isotope effect W(1) anion at room temperature compared to W(1) zwitterion results from two factors: a smaller temperature-independent nonradiative rate and a larger isotopically sensitive temperature-dependent rate. Several mechanisms for the intrinsic deuterium isotope effect are discussed. Two mechanisms are consistent with available data for indoles: {open_quotes}invisible{close_quotes} or incomplete proton transfer from water to indole and formation of a water-indole charge-transfer exciplex. 57 refs., 8 figs., 4 tabs.

• Sponsoring Organization: USDOE
• OSTI ID: 457059
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 22 Vol. 114; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

55 BIOLOGY AND MEDICINE
BASIC STUDIES
CHEMICAL REACTION KINETICS
DECAY
DEUTERIUM
ELECTRON TRANSFER
FLUORESCENCE
ISOTOPE EFFECTS
TRYPTOPHAN