Millimeter wave spectrum of glycine. A new conformer

Alparone

et al. 2008

Biophysical Chemistry

The geometries, relative energies, gas-phase static and dynamic dipole polarizabilities of the two most stable neutral forms and of the zwitterionic form of the twenty naturally occurring amino acids have been obtained by Density Functional and conventional ab initio HatreeFock theories using correlation consistent basis sets. Mean electronic polarizabilities (<α e >s) are encompassed in the 40-160 a.u. range and are little dependent on the amino acid framework conformation, structure and conformation. The relation between <α e > and the number of electrons in the molecule makes to classify the amino acids as one of the most polarizable family of compounds. Calculated <α e > values of the neutral forms linearly relate to the molecular volume and molecular hardness as well as, rather unexpectedly, with the experimental values in water solution, where amino acids are known to be in a zwitterionic form. Vibrational polarizabilities amount to 15-45 a.u.. They come essentially from the lowfrequency angular deformation modes of the -OH and -NH 2 groups.

Section: Geometries and Relative Energiessupporting

confidence: 80%

Electronic and vibrational polarizabilities of the twenty naturally occurring amino acids

Alparone

et al. 2008

Biophysical Chemistry

J. Am. Soc. Mass Spectrom.

“…Millimeter wave spectroscopy has shown that Gly is not in the zwitterionic form in the gas phase [15], consistent with much earlier results using ion/molecule reactions [34]. Infrared (IR) cavity ringdown spectroscopy of jet-cooled arginine (Arg) showed two peaks corresponding to the neutral Arg.…”

supporting

confidence: 82%

Zwitterion formation in gas-phase cyclodextrin complexes

Ahn

Cong

Lebrilla

et al. 2005

Protonated complexes of amino acids and underivatized ␤-cyclodextrin, produced by electrospray ionization and trapped in the Fourier transform mass spectrometer, undergo formation of ternary complexes when reacted with alkyl amine. Based on the reactivities of the protonated amino acid complexes with alkylamines, the reactivities of the corresponding amino acid esters, and partially derivatized ␤-cyclodextrin hosts, we conclude that the ternary complexes are salt-bridge zwitterionic species composed of amino acid zwitterions and protonated alkylamine all interacting with the hydroxyl groups on the narrow rim of the cyclodextrin. Molecular modeling calculations and experimental results suggest that the interactions of the amino acids with the rims contribute greatly to the formation of the zwitterionic species. (J Am Soc Mass Spectrom 2005, 16, 166 -175)

“…The first spectrum observed in the laboratory (Brown et al 1978;Suenram & Lovas 1978) was that of a higher conformer (later referred to as conformer II) because its dipole moment of ∼5.6 Debye is much higher than that of the most stable isomer (∼1.2 Debye). Conformer I was later characterized (Suenram & Lovas 1980) and the energy difference estimated to be ∼2 kcal/mol together with dipole moments of 0.9 and 5.4 debye for comformers I and II, respectively (Lovas et al 1995). Seven conformers of glycine can be found within ∼7 kcal/mol of conformer I; the relative energies and structures of five, with whom the present calculations agree, were reported by Holtom et al (2005).…”

Section: Neutral Glycine and Isomerssupporting

confidence: 54%

About the detectability of glycine in the interstellar medium

Lattelais

Pauzat

Pilmé

et al. 2011

A&A

Context. Glycine, the simplest of aminoacids, has been found in several carbonaceous meteorites. It remains unclear, however, wether glycine is formed in the interstellar medium (ISM) and therefore available everywhere in the Universe. For this reason, radioastronomers have searched for many years unsuccessfully to detect glycine in the ISM. Aims. We provide possible guidelines to optimize the return of these searches. Since, for most of the species observed so far in the ISM, the most abundant isomer of a given generic chemical formula is the most stable one (minimum energy principle (MEP)), we assess whether neutral glycine is the best molecule to search for or whether one of its isomers/conformers or ionic, protonated, or zwitterionic derivatives would have a higher probability of being detected. Methods. The question of the relative stability of these different species is addressed by means of quantum density functional theory (DFT) simulations within the hybrid B3LYP formalism. Each fully optimized structure is verified as a stationary point by means of a vibrational analysis. A comprehensive screening of 32 isomers/conformers of the C 2 H 5 O 2 N chemical formula (neutral, negative, and positive ions together with the corresponding protonated species and the possible zwitterionic structures) is carried out. In the sensitive case of the neutral compounds, more accurate relative energies were obtained by means of high level post Hartree-Fock coupled cluster calculations with large basis sets (CCSD(T)/cc-pVQZ). Results. We find that neutral glycine is not the most stable isomer and, therefore, probably not the most abundant one, which might explain why it has escaped detection so far. We find instead that N-methyl carbamic acid and methyl carbamate are the two most stable isomers and, therefore, probably the two most abundant ones. Among the non-neutral forms, we found that glycine is the most stable isomer only if protonated or zwitterionic if present in interstellar ices. Conclusions. Assuming that MEP can be applied to optimize our search for glycine, our conclusion is that this search will remain extremely difficult with the present instruments and we propose searching instead for other examples among the most stable isomers.