Spectroscopic Characterization of 3-Aminoisoxazole, a Prebiotic Precursor of Ribonucleotides

Abstract

The processes and reactions that led to the formation of the first biomolecules on Earth play a key role in the highly debated theme of the origin of life. Whether the first chemical building blocks were generated on Earth (endogenous synthesis) or brought from space (exogenous delivery) is still unanswered. The detection of complex organic molecules in the interstellar medium provides valuable support to the latter hypothesis. To gather more insight, here we provide the astronomers with accurate rotational frequencies to guide the interstellar search of 3-aminoisoxazole, which has been recently envisaged as a key reactive species in the scenario of the so-called RNA-world hypothesis. Relying on an accurate computational characterization, we were able to register and analyze the rotational spectrum of 3-aminoisoxazole in the 6–24 GHz and 80–320 GHz frequency ranges for the first time, exploiting a Fourier-transform microwave spectrometer and a frequency-modulated millimeter/sub-millimeter spectrometer, respectively. Due to the inversion motion of the −NH2 group, two states arise, and both of them were characterized, with more than 1300 lines being assigned. Although the fit statistics were affected by an evident Coriolis interaction, we were able to produce accurate line catalogs for astronomical observations of 3-aminoisoxazole.

Toward Accurate yet Effective Computations of Rotational Spectroscopy Parameters for Biomolecule Building Blocks

“…In addition to energy evaluations, different ChS variants have been employed and tested for geometry optimizations [ 19 , 51 , 62 , 63 ]. For conventional QC methods, ChS and junChS are defined analogous to Equations ( 1 ) and ( 2 ), whereas the extrapolation to the CBS limit (but not the CV correction) can be avoided (and sometimes introduces non-negligible oscillations) for approaches exploiting explicitly-correlated methods.…”

“…As mentioned above, the largest contribution to rotational constants comes from their equilibrium value, which is related to the corresponding equilibrium geometry. In this connection, ChS, junChS and junChSF12 have proven to provide very accurate results [ 19 , 63 ], with the former two models being rather well tested [ 83 ]. When employing explicitly-correlated methods, the computational cost of the ChS methodology can be further reduced by omitting the CBS extrapolation step.…”

Barrier to Methyl Internal Rotation and Equilibrium Structure of 2-Methylthiophene Determined by Microwave Spectroscopy

“…To accurately determine the molecular structure and methyl internal rotation parameters of 2MTP, in the present study, we applied a state-of-the-art molecular jet Fourier-transform microwave (MJ-FTMW) spectroscopy technique combined with modern quantum chemical calculations. This theory-experiment joint-venture has become the method of choice to investigate many small molecular systems similar to 2MTP [11][12][13][14][15]. The high sensitivity and resolution of the experimental setup also enabled the observation of the 34 S and 13 C isotopologues in natural abundance, allowing the determination of the structure of 2MTP in the gas phase for the heavy atom backbone.…”