Prototropic Interactions of Pyrimidine Nucleic Acid Bases with Acridine: A Spectroscopic Investigation

Abstract

In this article, we have investigated the interactions of three pyrimidine nucleic acid bases, cytosine (C), thymine (T), and uracil (U) with acridine (Acr), an N-heterocyclic DNA intercalator, through the changes in photophysics of Acr inside SDS micelles. Fluorescence of AcrH(+)* at 478 nm and its lifetime are quenched on addition of C, T, and U, while a concomitant increment of Acr* is observed only with C. However, the relative amplitude of Acr* increases with a simultaneous decrease in AcrH(+)* only with C. The fluorescence quenching of AcrH(+)* is explained by photoinduced electron transfer (PET), while changes in the relative contributions of Acr* and AcrH(+)* with C are due to associated excited-state proton transfer (ESPT). The rate of electron transfer (kET) is maximum for T, followed by U and C. The associated ESPT from AcrH(+)* is the reason behind the reduced efficiency of PET with C. The lack of proton transfer with T and U as well as the higher kET for T compared to U are explained by keto-enol tautomerization and subtle changes in the structure and geometry of the pyrimidine bases.

Surface Charge Alteration in Carbon Dots Governs the Interfacial Electron Transfer and Transport

“…This is probably due to the solubilization of the organic molecule in the hydrophobic portion of the micelle bringing close contact between the substrate and borohydride. The confinement effect often results in uncommon photophysics and charge transfer phenomena. − Recently, we have found that the electrostatic interactions between the micelle and CDs influence their ET ability . We anticipate similar effects to be operating here with the highly negatively charged surface of the anionic RCDs interacting strongly with the cationic CTAB micellar surface by electrostatic attraction.…”

Redox Modifications of Carbon Dots Shape Their Optoelectronics

“…Time-resolved emission spectra are detected by using a picosecond pulsed diode laser-based TCSPC spectrometer and MCP-PMT as a detector [43][44][45] . The emission from the sample is collected at a right angle to the direction of the excitation beam, maintaining the magic angle polarization with a bandpass of 4 nm.…”

“…A concomitant decrease in the lifetime of 1.81 μs for U CDs at 360 nm (peak-I, triplet π-π*) is observed, while the lifetimes for O CDs and R CDs are enhanced to 2.25 and 2.18 μs respectively. This is a clear indication of alteration of the dynamics of the multiple excited transition states for the >C=C< and >C=O bonds, and the isosbestic point at 375 nm establishes the equilibrium between the two forms in the triplet states, due to keto-enol tautomerism in the CDs upon surface modification 45,49,[54][55][56] . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 12 Scheme-1: The proposed mechanism between singlet and triplet inter system crossing based on possible allowed transitions.…”

Origin of Spectral Features and Acid–Base Properties of 3,7-Dihydroxyflavone and Its Monofunctional Derivatives in the Ground and Excited States

“…[5][6][7][8][9][10][11] The use of the compounds in this role emerges from their ability to occur in the electronically excited state in various structural forms (tautomeric, rotameric, protolytic) each of which have different fluorescent features (emission wavelengths, lifetimes) which depend on the properties of the medium (such as polarity, acidity/basicity, hydrogenbonding ability) or biological environment. One group of compounds that are widely used as ESPT fluorophores are hydroxyflavones (hydroxy-2-phenyl-4H-chromen-4-ones), 12 …”