Molecular structure of a conformer of glycine by microwave spectroscopy

McGlone, Shane J.; Elmes, Patricia S.; Brown, R. D.; Godfrey, Peter D.

doi:10.1016/s0022-2860(99)00181-7

Cited by 79 publications

(67 citation statements)

References 27 publications

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“…Type III conformers are ''missing'' in the supersonic expansion for all ␣-amino acids with nonpolar side chains studied up to now (19-25, 27-30, 34-36). This has been attributed to relaxation to configuration I, which is supported by the relatively small III 3 I interconversion barriers determined for glycine and alanine (19)(20)(21)(22)(23)(24)27). Contrary to the previously described experimental behavior, type III conformers have been observed in serine.…”

Section: Resultsmentioning

confidence: 52%

Revealing the multiple structures of serine

Blanco

Sanz

López

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

117

141

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We explored the conformational landscape of the proteinogenic amino acid serine [CH2OHOCH(NH2)OCOOH] in the gas phase. Solid serine was vaporized by laser ablation, expanded in a supersonic jet, and characterized by Fourier transform microwave spectroscopy. In the isolation conditions of the jet there have been discovered up to seven different neutral (non-zwitterionic) structures of serine, which are conclusively identified by the comparison between the experimental values of the rotational and quadrupole coupling constants with those predicted by ab initio calculations. These seven forms can serve as a basis to represent the shape of serine in the gas phase. From the postexpansion abundances we derived the conformational stability trend, which is controlled by the subtle network of intramolecular hydrogen bonds formed between the polar groups in the amino acid backbone and the hydroxy side chain. It is proposed that conformational cooling perturbs the equilibrium conformational distribution; thus, some of the lower-energy forms are ''missing'' in the supersonic expansion.amino acids ͉ conformations ͉ laser ablation ͉ microwave spectroscopy ͉ supersonic expansion A mino acids are distinguished by an outstanding conformational flexibility originating from multiple torsional degrees of freedom, which makes folding and functionality of proteins possible (1). Whereas covalent forces determine the molecular skeleton, conformational isomerism is controlled by weaker nonbonded interactions within the molecule, especially hydrogen bonding. Amino acids are also very sensitive to the chemical medium chosen for their study. In traditional studies in the condensed phase, the extensive intermolecular hydrogen bond interactions fix amino acids as doubly charged zwitterions (2, 3), wiping out the conformational variety of these molecules. The intrinsic structural preferences of amino acids can be revealed only when they are studied as free species in the gas phase, where neutral forms (present in polypeptide chains) are the most stable in detriment of ionic or zwitterionic forms. Levy and coworkers (4) were the first to measure highly resolved electronic spectra of amino acids in the gas phase by seeding tryptophan in a supersonic expansion. Since then, different experimental methods have been used to investigate the electronic spectrum of amino acids and a variety of biological molecules in the gas phase (5-7). The electronic spectrum is interpreted with the help of theoretical calculations to identify different conformations with a high degree of confidence. However, the use of electronic spectroscopy is limited to favorable cases that present aromatic chromophores. Only three of the 20 natural amino acids have aromatic side chains that meet this criterion: phenylalanine, tyrosine, and tryptophan (4,(8)(9)(10)(11)(12)(13)(14).Microwave spectroscopy, often considered the most definitive gas-phase structural probe, can distinguish unambiguously between different conformational structures and provide accurate structural inform...

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Section: Resultsmentioning

confidence: 52%

Revealing the multiple structures of serine

Blanco

Sanz

López

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

117

141

View full text Add to dashboard Cite

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“…[19][20][21][22][23] A weakness of this standard approach is that no special consideration is given to large-amplitude motion(s). Third, the experimental ground-state rotational constants of all the isotopologues 3,5 are corrected to yield empirically-based equilibrium rotational constants. Fourth, guided weighted least-squares refinements are performed with various ab initio structural constraints to determine the r BO e parameters in best agreement with the available zero-point corrected experi- mental rotational constants.…”

Section: Computational Detailsmentioning

confidence: 99%

“…For Gly-II, it remained unclear whether its equilibrium structure was planar or not. The determination of an extensive set of rotational constants of several isotopologues of Gly-IIn 5 was aided by the substantial dipole moments of this conformer. The empirical rotational constants of Gly-II indicated that the effective structure in the ground vibrational state is planar, because the amino hydrogens were indistinguishable in the partially deuterated [OH, NDH] and [OD, NDH] MW spectra.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, neither the gas electron diffraction (GED), 4 as detailed before, 5,8 nor the MW 5 and millimeterwave (MMW) 6 experimental studies yielded an accurate vibrationally averaged molecular structure of Gly-Ip. Application of the computational strategy of equilibrium structure determination of this study, outlined below, offers no difficulties for Gly-Ip, and the resulting r BO e structure should be highly reliable.…”

mentioning

confidence: 99%

“…For Gly-IIn both substitution (r s ) and least-squares structures have been determined based on effective ground-state rotational constants of 12 isotopologues. 5 The r s structure seemed to be suspect 5 due to ''the small b-axis coordinates associated with both the nitrogen and carbonyl carbon atoms.'' The least-squares structural fit assumed 5 that in the ground vibrational state Gly-IIn has C s point-group symmetry.…”

mentioning

confidence: 99%

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Molecular structures of the two most stable conformers of free glycine

et al. 2007

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The equilibrium molecular structures of the two lowest-energy conformers of glycine, Gly-Ip and Gly-IIn, have been characterized by high-level ab initio electronic structure computations, including all-electron cc-pVTZ CCSD(T) geometry optimizations and 6-31G* MP2 quartic force fields, the latter to account for anharmonic zero-point vibrational effects to isotopologic rotational constants. Based on experimentally measured vibrationally averaged effective rotational constant sets of several isotopologues and our ab initio data for structural constraints and zero-point vibrational shifts, least-squares structural refinements were performed to determine improved Born-Oppenheimer equilibrium (r(e)) structures of Gly-Ip and Gly-IIn. Without the ab initio constraints even the extensive set of empirical rotational constants available for 5 and 10 isotopologues of Gly-Ip and Gly-IIn, respectively, cannot satisfactorily fix their molecular structure. Excellent agreement between theory and experiment is found for the rotational constants of both conformers, the rms residual of the final fits being 7.8 and 51.6 kHz for Gly-Ip and Gly-IIn, respectively. High-level ab initio computations with focal point extrapolations determine the barrier to planarity separating Gly-IIp and Gly-IIn to be 20.5 +/- 5.0 cm(-1). The equilibrium torsion angle tau(NCCO) of Gly-IIn, characterizing the deviation of its heavy-atom framework from planarity, is (11 +/- 2) degrees. Nevertheless, in the ground vibrational state the effective structure of Gly-IIn has a plane of symmetry.

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Multiphoton Resonance Spectroscopy of Biological Molecules

Häber

Kleinermanns

2011

Handbook of High‐resolution Spectroscopy

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High‐resolution gas‐phase spectroscopy of biomolecules allows us to distinguish between the intrinsic properties of biomolecules and those properties that are induced by solvation or by the geometrical restrictions of the environment. In the gas phase, we can study the isolated biomolecules and their water clusters under size‐controlled conditions. Comparison with experiments in solution then provides information about the specific role of the biological environment, like solvent effects or geometric constraints of nucleic acids and peptides. However, gas‐phase studies are often complicated by the thermal instability of many biomolecules, which often prevents the use of conventional thermal sources for vaporizing them. This obstacle has been overcome by applying laser desorption techniques to biomolecules as a gentle alternative to thermal heating in combination with very sensitive detection schemes like resonance‐enhanced multiphoton ionization, double resonance methods, and dispersed fluorescence.

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Molecular structure of a conformer of glycine by microwave spectroscopy

Cited by 79 publications

References 27 publications

Revealing the multiple structures of serine

Revealing the multiple structures of serine

Molecular structures of the two most stable conformers of free glycine

Multiphoton Resonance Spectroscopy of Biological Molecules

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