Ab initio study of lowest-energy conformers of lewis X (Lex) trisaccharide

G. Csonka, Carlos P. Sosa, I. Csizmadia

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

This paper presents the first ab initio conformational study of the Gal-β,4-[Fuc-α-1,3]-GlcNAc-β-OCH3 and Gal-β-1,4-[Fuc-α-1,3]-GlcNAc-β-OH trisaccharides (Lewis x) in the gas phase. Their lowest-energy conformers were selected first by the MM2*-SUMM conformational search technique. MM2* relative energies do not follow the same order for the two similar compounds. The molecular geometries and energies of the lowest-energy rotamers (7 of the acetal and 11 of the hemiacetal) were further analyzed at the HF/6-31G(d) level of theory. The ab initio method yields the same energetic order for the rotamers of the two molecules with considerably larger energetic differences for the first 7 rotamers: the MM2* method provides 0.3-0.5 kcal/mol, whereas the HF/6-31G(d) method provides 4.5 kcal/mol. In the most stable MM2* structures the hydrogen-bonded chains of galactose (in counterclockwise direction) and fucose (in clockwise direction) are not connected. The Gal(O6H) is a hydrogen bond donor (in clockwise direction) to the O3 glycosidic oxygen of GlcNAc. The Fuc(O2H)→(O=C)GlcNAc interaction connects the fucose and GlcNAc. In contrast, the most stable HF/6-31G(d) structure has a long chain of seven ordered hydrogen bonds including a Gal(O6H)→(O3)Fuc interaction (with clockwise hydrogen-bonded chain in galactose and fucose). The torsion angles for Fuc-α-1,3-GlcNAc and Gal-β,4-GlcNAc glycosidic bonds agree well in the solid, liquid, and gas phases. For example there is a rather good overlap between the GlcNAc moiety of one of the X-ray structures and the most similar HF/6-31G(d) structure. The stacking of the fucose and galactose moieties is similar. The orientations of the hydroxyl groups are usually different, as they are influenced by intramolecular hydrogen bonding in the gas-phase Hartree-Fock structure versus intermolecular hydrogen bonding in the solid-phase X-ray structure.

Original languageEnglish
Pages (from-to)3381-3390
Number of pages10
JournalJournal of Physical Chemistry A
Volume104
Issue number15
Publication statusPublished - Apr 20 2000

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Fucose
galactose
Hydrogen bonds
Galactose
hydrogen
vapor phases
Gases
solid phases
hydrogen bonds
Hydrogen
acetals
energy
Trisaccharides
X rays
Acetals
torsion
liquid phases
x rays
Hydroxyl Radical
Torsional stress

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Ab initio study of lowest-energy conformers of lewis X (Lex) trisaccharide. / Csonka, G.; Sosa, Carlos P.; Csizmadia, I.

In: Journal of Physical Chemistry A, Vol. 104, No. 15, 20.04.2000, p. 3381-3390.

Research output: Contribution to journalArticle

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abstract = "This paper presents the first ab initio conformational study of the Gal-β,4-[Fuc-α-1,3]-GlcNAc-β-OCH3 and Gal-β-1,4-[Fuc-α-1,3]-GlcNAc-β-OH trisaccharides (Lewis x) in the gas phase. Their lowest-energy conformers were selected first by the MM2*-SUMM conformational search technique. MM2* relative energies do not follow the same order for the two similar compounds. The molecular geometries and energies of the lowest-energy rotamers (7 of the acetal and 11 of the hemiacetal) were further analyzed at the HF/6-31G(d) level of theory. The ab initio method yields the same energetic order for the rotamers of the two molecules with considerably larger energetic differences for the first 7 rotamers: the MM2* method provides 0.3-0.5 kcal/mol, whereas the HF/6-31G(d) method provides 4.5 kcal/mol. In the most stable MM2* structures the hydrogen-bonded chains of galactose (in counterclockwise direction) and fucose (in clockwise direction) are not connected. The Gal(O6H) is a hydrogen bond donor (in clockwise direction) to the O3 glycosidic oxygen of GlcNAc. The Fuc(O2H)→(O=C)GlcNAc interaction connects the fucose and GlcNAc. In contrast, the most stable HF/6-31G(d) structure has a long chain of seven ordered hydrogen bonds including a Gal(O6H)→(O3)Fuc interaction (with clockwise hydrogen-bonded chain in galactose and fucose). The torsion angles for Fuc-α-1,3-GlcNAc and Gal-β,4-GlcNAc glycosidic bonds agree well in the solid, liquid, and gas phases. For example there is a rather good overlap between the GlcNAc moiety of one of the X-ray structures and the most similar HF/6-31G(d) structure. The stacking of the fucose and galactose moieties is similar. The orientations of the hydroxyl groups are usually different, as they are influenced by intramolecular hydrogen bonding in the gas-phase Hartree-Fock structure versus intermolecular hydrogen bonding in the solid-phase X-ray structure.",
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N2 - This paper presents the first ab initio conformational study of the Gal-β,4-[Fuc-α-1,3]-GlcNAc-β-OCH3 and Gal-β-1,4-[Fuc-α-1,3]-GlcNAc-β-OH trisaccharides (Lewis x) in the gas phase. Their lowest-energy conformers were selected first by the MM2*-SUMM conformational search technique. MM2* relative energies do not follow the same order for the two similar compounds. The molecular geometries and energies of the lowest-energy rotamers (7 of the acetal and 11 of the hemiacetal) were further analyzed at the HF/6-31G(d) level of theory. The ab initio method yields the same energetic order for the rotamers of the two molecules with considerably larger energetic differences for the first 7 rotamers: the MM2* method provides 0.3-0.5 kcal/mol, whereas the HF/6-31G(d) method provides 4.5 kcal/mol. In the most stable MM2* structures the hydrogen-bonded chains of galactose (in counterclockwise direction) and fucose (in clockwise direction) are not connected. The Gal(O6H) is a hydrogen bond donor (in clockwise direction) to the O3 glycosidic oxygen of GlcNAc. The Fuc(O2H)→(O=C)GlcNAc interaction connects the fucose and GlcNAc. In contrast, the most stable HF/6-31G(d) structure has a long chain of seven ordered hydrogen bonds including a Gal(O6H)→(O3)Fuc interaction (with clockwise hydrogen-bonded chain in galactose and fucose). The torsion angles for Fuc-α-1,3-GlcNAc and Gal-β,4-GlcNAc glycosidic bonds agree well in the solid, liquid, and gas phases. For example there is a rather good overlap between the GlcNAc moiety of one of the X-ray structures and the most similar HF/6-31G(d) structure. The stacking of the fucose and galactose moieties is similar. The orientations of the hydroxyl groups are usually different, as they are influenced by intramolecular hydrogen bonding in the gas-phase Hartree-Fock structure versus intermolecular hydrogen bonding in the solid-phase X-ray structure.

AB - This paper presents the first ab initio conformational study of the Gal-β,4-[Fuc-α-1,3]-GlcNAc-β-OCH3 and Gal-β-1,4-[Fuc-α-1,3]-GlcNAc-β-OH trisaccharides (Lewis x) in the gas phase. Their lowest-energy conformers were selected first by the MM2*-SUMM conformational search technique. MM2* relative energies do not follow the same order for the two similar compounds. The molecular geometries and energies of the lowest-energy rotamers (7 of the acetal and 11 of the hemiacetal) were further analyzed at the HF/6-31G(d) level of theory. The ab initio method yields the same energetic order for the rotamers of the two molecules with considerably larger energetic differences for the first 7 rotamers: the MM2* method provides 0.3-0.5 kcal/mol, whereas the HF/6-31G(d) method provides 4.5 kcal/mol. In the most stable MM2* structures the hydrogen-bonded chains of galactose (in counterclockwise direction) and fucose (in clockwise direction) are not connected. The Gal(O6H) is a hydrogen bond donor (in clockwise direction) to the O3 glycosidic oxygen of GlcNAc. The Fuc(O2H)→(O=C)GlcNAc interaction connects the fucose and GlcNAc. In contrast, the most stable HF/6-31G(d) structure has a long chain of seven ordered hydrogen bonds including a Gal(O6H)→(O3)Fuc interaction (with clockwise hydrogen-bonded chain in galactose and fucose). The torsion angles for Fuc-α-1,3-GlcNAc and Gal-β,4-GlcNAc glycosidic bonds agree well in the solid, liquid, and gas phases. For example there is a rather good overlap between the GlcNAc moiety of one of the X-ray structures and the most similar HF/6-31G(d) structure. The stacking of the fucose and galactose moieties is similar. The orientations of the hydroxyl groups are usually different, as they are influenced by intramolecular hydrogen bonding in the gas-phase Hartree-Fock structure versus intermolecular hydrogen bonding in the solid-phase X-ray structure.

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