The Broken Ring: Reduced Aromaticity in Lys-Trp Cations and High pH Tautomer Correlates with Lower Quantum Yield and Shorter Lifetimes
نویسندگان
چکیده
Several nonradiative processes compete with tryptophan fluorescence emission. The difficulty in spectral interpretation lies in associating specific molecular environmental features with these processes and thereby utilizing the fluorescence spectral data to identify the local environment of tryptophan. Here, spectroscopic and molecular modeling study of Lys-Trp dipeptide charged species shows that backbone-ring interactions are undistinguished. Instead, quantum mechanical ground state isosurfaces reveal variations in indole π electron distribution and density that parallel charge (as a function of pK(1), pK(2), and pK(R)) on the backbone and residues. A pattern of aromaticity-associated quantum yield and fluorescence lifetime changes emerges. Where quantum yield is high, isosurfaces have a charge distribution similar to the highest occupied molecular orbital (HOMO) of indole, which is the dominant fluorescent ground state of the (1)L(a) transition dipole moment. Where quantum yield is low, isosurface charge distribution over the ring is uneven, diminished, and even found off ring. At pH 13, the indole amine is deprotonated, and Lys-Trp quantum yield is extremely low due to tautomer structure that concentrates charge on the indole amine; the isosurface charge distribution bears scant resemblance to the indole HOMO. Such greatly diminished fluorescence has been observed for proteins where the indole nitrogen is hydrogen bonded, lending credence to the association of aromaticity changes with diminished quantum yield in proteins as well. Thus tryptophan ground state isosurfaces are an indicator of indole aromaticity, signaling the partition of excitation energy between radiative and nonradiative processes.
منابع مشابه
1,N2-deoxyguanosine adducts of acrolein, crotonaldehyde, and trans-4-hydroxynonenal cross-link to peptides via Schiff base linkage.
DNA-protein cross-links (DPCs) are formed upon exposure to a variety of chemical and physical agents and pose a threat to genomic integrity. In particular, acrolein and related aldehydes produce DPCs, although the chemical linkages for such cross-links have not been identified. Here, we report that oligodeoxynucleotides containing 1,N(2)-deoxyguanosine adducts of acrolein, crotonaldehyde, and t...
متن کامل1,N-Deoxyguanosine Adducts of Acrolein, Crotonaldehyde, and trans-4-Hydroxynonenal Cross-link to Peptides via Schiff Base Linkage*
DNA-protein cross-links (DPCs) are formed upon exposure to a variety of chemical and physical agents and pose a threat to genomic integrity. In particular, acrolein and related aldehydes produce DPCs, although the chemical linkages for such cross-links have not been identified. Here, we report that oligodeoxynucleotides containing 1,N-deoxyguanosine adducts of acrolein, crotonaldehyde, and tran...
متن کاملAnion˗π and Intramolecular Hydrogen Bond Interactions in the Various Complexes of 1,3,5-Triamino-2,4,6-trinitrobenzene with H-, F-, Cl- and Br- Anions
The quantum chemical calculations were performed to investigate the interplay between the anion˗π and intramolecular hydrogen bond (IMHB) interactions in the various complexes of 1,3,5-triamino-2,4,6-trinitrobenzene (ANB) with Hˉ, Fˉ, Clˉ and Brˉ anions. For better understanding the cooperative effects, the parent molecules (ANB) and the corresponding complexes of 1,3,5˗trinitrobenzene with the...
متن کاملInvestigating the Effect of Changes of Halogenated Compounds on the Aromaticity Flow (NICS) of Composite Rings 5-fluorophenyl-1, 3, 7, 9-tetra methylpyrido [2,3-: d [d-5,6 dipyrimidine -2, 4, 6 and 8 tetron
In the combination of 5-fluorophenyl-1, 3, 7, 9-tetra methylpyrido [2, 3, d, d, 5, 6 dipyrimidine -2, 4, 6, and 8 tetron, there are 4 rings, respectively, ring that is attached to the halogen ring A and, respectively, a ring The lower and the right to the left of the ring A are called C, B, and D. Calculations and studies show that the amount of aromatics in halogen-ring A in all cases has the ...
متن کاملA Theoretical Study on the Aromaticity of 5-methylcytosine tautomers in the gas phase
The armaticity of 5 methylcytosine tautomers in the gas phase has been studied and the chemical structures of related tautomers are investigated . The electronic energy, enthalpy and free energy of each tautomer are also estimated at the B3LYP/6-31 G* // B3LYP/6-31 G* and MP2 / 6-31 G* // MP2 / 6-31 G* Levels
متن کامل