The Axial and Equatorial Hydrogen Bonds in the Tetrahydropyran⋅⋅⋅HF Complex

Antolı́nez, Sonia; López, Juan C.; Alonso, José L.

doi:10.1002/1439-7641(20010216)2:2<114::aid-cphc114>3.0.co;2-c

Cited by 37 publications

(4 citation statements)

References 22 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: 99%

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: 99%

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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“…For example, in saturated cyclic ethers, such as tetrahydropyran, two different lone pairs (axial and equatorial) are available at the ether oxygen atom to accept a proton. Alonso and collaborators could assign the supersonic-jet Fourier-transform microwave (FTMW) spectra of both axial and equatorial complexes in the case of tetrahydropyran···HCl, [13] tetrahydropyran···HF, [14] and pentamethylene sulfide···HF, [15] thus characterizing relative energies and structural differences. Three conformers have been observed for formamide···water, [4] and six conformers in the molecular recognition study of the self-aggregation of propylene oxide.…”

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confidence: 99%

Adducts of NH₃ with the Conformers of Glycidol: A Rotational Spectroscopy Study

et al. 2009

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Two locks accept the same master key: Two different complexes of ammonia with two different conformers of glycidol have been characterized by Fourier transform microwave spectroscopy (see picture; gray C, blue N, red O, white H). In both complexes NH3 is linked to the alcohol molecule through an OH⋅⋅⋅N (stronger) and an NH⋅⋅⋅O (weaker) hydrogen bond. Structural and energetic features of the hydrogen bonds are given.

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“…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. In the present case, the equivalence of the nonbonding pairs at sulfur is broken by effect of complexation.…”

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confidence: 99%