From Molecular to Cluster Properties: Rotational Spectroscopy of 2-Aminopyridine and of Its Biomimetic Cluster with Water

Adam Kraśnicki,Jean-Claude Guillemin,Zbigniew Kisiel

doi:10.3390/molecules26226870

Abstract

We report the observation and analysis of the rotational spectrum of a 1:1 cluster between 2-aminopyridine and water (AMW) carried out with supersonic expansion Fourier transform microwave spectroscopy at 4.7–16.5 GHz. Measurements of the 2-aminopyridine monomer (AMP) were also extended up to 333 GHz for the room-temperature rotational spectrum and to resolved hyperfine splitting resulting from the presence of two 14N quadrupolar nuclei. Supersonic expansion measurements for both AMP and AMW were also carried out for two synthesized isotopic species with single deuteration on the phenyl ring. Nuclear quadrupole hyperfine structure has also been resolved for AMW and the derived splitting constants were used as an aid in structural analysis. The structure of the AMW cluster was determined from the three sets of available rotational constants and the hydrogen bonding configuration is compared with those for clusters with water of similarly sized single-ring molecules. Experimental results aided by quantum chemistry computations allow the conclusion that the water molecule is unusually strongly bound by two hydrogen bonds, OH...N and O...HN, to the NCNH atomic chain of AMP with the potential to replace hydrogen bonds to the identical structural segment in cytosine and adenine in CT and AT nucleic acid base pairs.

Highlights

Hydrogen bonding is a fundamental interaction found in many biochemical systems
One area highlighting its importance is the structure of deoxyribonucleic acid (DNA) [1]
Its two helical component chains are connected by hydrogen bonds between the coding nucleic acid residues, which allows their relatively low-energy separation. 2aminopyridine (AMP, C5H6N2) is a biomimetic molecule of particular significance since its –NC(NH2)– ring segment is identical to those in adenine and cytosine, which is responsible in the latter for two of the three bridging hydrogen bonds in the GC nucleic acid base pair, and for the two bridging bonds in the AT base pair

Summary

Introduction

Hydrogen bonding is a fundamental interaction found in many biochemical systems. One area highlighting its importance is the structure of deoxyribonucleic acid (DNA) [1]. N, subtended by the water moiety in AMW, is a clear hydrogen bond, similar to that in pyrrole-water [2] In this way, AMW differs from the previously studied complexes between water and heteroaromatic molecules, such as those with pyrimidine [3], pyrrole [2], or pyrazine [4] in all of which there is only one bona fide hydrogen bond, sometimes augmented by a peripheral dispersive interaction (see further below). The AMW cyclic complex is more successful at mimicking the situation in more complicated biological systems and may offer detailed molecular insight into the solvation of nucleic acid bases.

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Conclusion