Excited-State Dynamics of Melamine and Its Lysine Derivative Investigated by Femtosecond Transient Absorption Spectroscopy.

Yuyuan Zhang,Ashley Beckstead,Xijun Piao,Bern Kohler,Dennis Bong,Yuesong Hu

doi:10.3390/molecules21121645

Yuyuan Zhang, Ashley Beckstead + Show 4 more

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https://doi.org/10.3390/molecules21121645

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Abstract

Melamine may have been an important prebiotic information carrier, but its excited-state dynamics, which determine its stability under UV radiation, have never been characterized. The ability of melamine to withstand the strong UV radiation present on the surface of the early Earth is likely to have affected its abundance in the primordial soup. Here, we studied the excited-state dynamics of melamine (a proto-nucleobase) and its lysine derivative (a proto-nucleoside) using the transient absorption technique with a UV pump, and UV and infrared probe pulses. For melamine, the excited-state population decays by internal conversion with a lifetime of 13 ps without coupling significantly to any photochemical channels. The excited-state lifetime of the lysine derivative is slightly longer (18 ps), but the dominant deactivation pathway is otherwise the same as for melamine. In both cases, the vast majority of excited molecules return to the electronic ground state on the aforementioned time scales, but a minor population is trapped in a long-lived triplet state.

Highlights

The 1,3,5-triazines, or s-triazines, represent an important class of prebiotic molecules that may have been building blocks of the primitive informational polymers that preceded RNA
We investigated the excited-state dynamics of the lysine derivative of melamine in which the amino groups (Figure 1)
Prior studies studies discussed above make it plausible that the lowest singlet state could be an nπ* state. Discussed above make it plausible that the lowest singlet state could be an nπ* state. Such a such a state could possibly be a long-lived trap for the excited-state population, our results clearly state could possibly be a long-lived trap for the excited-state population, our results clearly indicate indicate that most excited states return to the electronic ground state on a time scale of 13 ps

Summary

Introduction

The 1,3,5-triazines, or s-triazines, represent an important class of prebiotic molecules that may have been building blocks of the primitive informational polymers that preceded RNA. Along with some amino acids and pyrimidines, several s-triazines, i.e., melamine, ammeline, ammelide, and cyanuric acid (structures shown in Figure 1), can be synthesized in an icy urea solution under a reductive N2 /H2 /CH4 atmosphere [1]. It is known that melamine and cyanuric acid form a supramolecular assembly via hydrogen bonding [2], demonstrating the molecular recognition ability of s-triazines. Oligodipeptides tagged with diamino-triazine derivatives form duplex hybrids with oligo-T/U DNA or RNA [3]. Mono-derivatized triaminotriazine, or melamine, has two thymine recognition faces. Bifacial peptide nucleic acid (bPNA), which displays melamine on peptide side chains, can dock two oligothymidine strands to form a highly stable triplex hybrid with high selectivity over other oligonucleotides [4,5]

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Discussion

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