Axial and Equatorial Hydrogen Bonds in Pentamethylene Sulfide⋅⋅⋅Hydrogen Chloride Complex

Sanz, M. Eugenia; López, Juan C.; Alonso, José L.

doi:10.1002/(sici)1521-3765(19991105)5:11<3293::aid-chem3293>3.0.co;2-#

Cited by 34 publications

(8 citation statements)

References 14 publications

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“…It has been proposed (45) that this is a consequence of collisional relaxation at the onset of the supersonic expansion, which causes higher-energy forms to collapse to the preferred lower-energy ones due to collisions with the carrier gas. The extent of conformational relaxation depends on several factors, most significantly barrier heights between conformers (46-48) and the carrier gas (49)(50)(51)(52). 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).…”

Section: Resultsmentioning

confidence: 94%

Revealing the multiple structures of serine

Blanco

Sanz

López

et al. 2007

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

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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: 94%

Revealing the multiple structures of serine

Blanco

Sanz

López

et al. 2007

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

Self Cite

117

141

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“…Very recently, axial and equatorial hydrogen bonds have been observed for the first time in the prototypical systems tetrahydropyran´´´HCl [1] and pentamethylene sulfide´´´HCl [2] using molecular beam Fourier transform microwave (MB-FTMW) spectroscopy. The six-membered rings of tetrahydropyran and pentamethylene sulfide carry two nonbonding electron pairs at the O or S atoms that turn out to be nonequivalent due to the chair conformation of the rings.…”

Section: Introductionmentioning

confidence: 99%

Conformation and Stability of the Hydrogen-Bonded Complex 6-Oxabicyclo[3.1.0]hexane⋅⋅⋅HCl

et al. 2000

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The hydrogen-bonded complex between 6-oxabicyclo[3.1.0]hexane and hydrogen chloride was investigated by microwave spectroscopy in a supersonic jet. A dual flow pulsed valve was used to preclude chemical reaction between the monomers. Only the equatorial conformer was observed and the spectra of three isotopomers, (C5H8O, H35Cl), (C5H8O, H37Cl) and (C5H8O, D35Cl), were measured. The derived structure of the complex has Cs symmetry with the hydrogen chloride pointing to the domain of the equatorial lone pair of electrons at the oxygen atom. The three atoms involved in the hydrogen bond adopt a bent arrangement with a O...H distance of 1.77(4) A, a (O...H-Cl) angle of 115(4)degrees, and a deviation of 15.4(14)degrees of the hydrogen bond from collinearity. In agreement with the experimental results, ab initio calculations predict the equatorial form to be the most stable one.

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“…The assignment of both conformers was completed with the measurement of b type transitions. The spectra of several isotopic species were also detected and assigned for both forms.Recently, axial and equatorial hydrogen bond complexes have been also reported for tetrahydropyran´´´HCl, [7] thiane´´´HCl, [8] and tetrahydropyran´´´HF. [9] In these cases, the existence of two nonequivalent pairs of lone electrons at the oxygen or sulfur atoms is a consequence of the structure of the acceptor molecule itself.…”

mentioning

confidence: 99%

“…These deviations can be attributed to the existence of secondary hydrogen bonds between the chlorine atom and the nearest H atoms of the methylene groups. [6,8,13] The calculated distances r(Cl´´´H b ) 3.20 and r(Cl´´´H a ) 3.26 for the axial and the equatorial conformers, respectively, lie in the range reported for related complexes. [6,8,13,15] An interesting fact is the relaxation from the equatorial to the axial conformer observed in the supersonic expansion.…”

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confidence: 99%

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Hydrogen Bond in Molecules with Large-Amplitude Motions: A Rotational Study of Trimethylene Sulfide⋅⋅⋅HCl

Sanz

Lesarri

López

et al. 2001

Angew. Chem. Int. Ed.

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Axial and Equatorial Hydrogen Bonds in Pentamethylene Sulfide⋅⋅⋅Hydrogen Chloride Complex

Abstract: Axial and equatorial hydrogen bonds have been observed in the heterodimer formed between pentamethylene sulfide and hydrogen chloride in a pulsed supersonic expansion by using Fourier transform microwave spectroscopy. The ground-state rotational spectra of the isotopic species (C 5 H 10 32

Cited by 34 publications

References 14 publications

Revealing the multiple structures of serine

Revealing the multiple structures of serine

Conformation and Stability of the Hydrogen-Bonded Complex 6-Oxabicyclo[3.1.0]hexane⋅⋅⋅HCl

Hydrogen Bond in Molecules with Large-Amplitude Motions: A Rotational Study of Trimethylene Sulfide⋅⋅⋅HCl

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