Microwave Spectroscopy of Biomolecular Building Blocks

Abstract

Microwave spectroscopy, considered as the most definitive gas phase structural probe, is able to distinguish between different conformational structures of a molecule, because they have unique spectroscopic constants and give rise to distinct individual rotational spectra.Previously, application of this technique was limited to molecular specimens possessing appreciable vapor pressures, thus discarding the possibility of studying many other molecules of biological importance, in particular those with high melting points, which had a tendency to undergo thermal reactions, and ultimately degradation, upon heating.Nowadays, the combination of laser ablation with Fourier transform microwave spectroscopy techniques, in supersonic jets, has enabled the gas-phase study of such systems. In this chapter, these techniques, including broadband spectroscopy, as well as results of their application into the study of the conformational panorama and structure of biomolecular building blocks, such as amino acids, nucleic bases, and monosaccharides, are briefly discussed, and with them, the tools for conformational assignation - rotational constants, nuclear quadrupole coupling interaction, and dipole moment.

Diving for Accurate Structures in the Ocean of Molecular Systems with the Help of Spectroscopy and Quantum Chemistry

“…This technique thus paves the way toward the determination of the molecular structure for biomolecules and metalcontaining compounds (see, for example, Refs. [19][20][21][22][23][24] ).…”

Isolated Neutral Peptides

“…In this spirit, the classical gas-phase methods of the physicist, inherited from atomic or small molecule spectroscopy, namely optical absorption, either in the microwave, IR/Raman or UV spectral range, have been mobilised to tackle these issues. First, microwave experiments, carried out in supersonic expansions, remain devoted to relatively small molecules, from models of biomolecules to more recently investigated natural and capped amino-acids and sugars [21]. The advantage of this approach stems from its direct sensitivity to the structure, through the rotational constant, allowing it to provide stringent tests to the theoretical structures calculated.…”

The Shape of the Simplest Non‐proteinogenic Amino Acid α‐Aminoisobutyric Acid (Aib)

“…[8] In contrast, much less is known about the conformational behavior of these building blocksa si ndividualn eutrals pecies. [9] The difficultiese ncountered in these studiesc ome from variouss ources. Amino acids in condensed phasese xist as zwitterionic bipolar species, and moreover,t he intermoleculari nteractions presenti ns uch mediaa re ad rawback to investigating the intrinsic structural properties of such flexible molecules.…”

“…Fortunately,l aser ablation (LA) has emerged as as erious alternative to overcome those limitations. In this context, we have successfully appliedt his technique in combinationw ith molecularbeam and Fourier transform microwaves pectroscopy (MB-FTMW) [9,10] to analyze the conformational landscapeso fc oded a-amino acids, [10][11][12][13] which were limited to glycine and alanine vaporized by conventional heating methods [14][15][16][17][18] before our investigations. The implementation of laser ablation (LA) in the latest generation of Fourier transform microwaves pectrometers based on chirped-pulse excitation (CP-FTMW) [19,20] has recentlya llowedt he study of the dipeptide glycine-glycine in our laboratory.…”