Free Fructose Is Conformationally Locked

Abstract

Fructose has been examined under isolation conditions using a combination of UV ultrafast laser vaporization and Fourier-transform microwave (FT-MW) spectroscopy. The rotational spectra for the parent, all (six) monosubstituted (13)C species, and two single D species reveal unambiguously that the free hexoketose is conformationally locked in a single dominant β-pyranose structure. This six-membered-chair skeleton adopts a (2)C(5) configuration (equivalent to (1)C(4) in aldoses). The free-molecule structure sharply contrasts with the furanose form observed in biochemically relevant polysaccharides, like sucrose. The structure of free fructose has been determined experimentally using substitution and effective structures. The enhanced stability of the observed conformation is primarily attributed to a cooperative network of five intramolecular O-H···O hydrogen bonds and stabilization of both endo and exo anomeric effects. Breaking a single intramolecular hydrogen bond destabilizes the free molecule by more than 10 kJ mol(-1). The structural results are compared to ribose, recently examined with rotational resolution, where six different conformations coexist with similar conformational energies. In addition, several DFT and ab initio methods and basis sets are benchmarked with the experimental data.

Microwave Spectroscopy of Biomolecular Building Blocks

“…The low-temperature environment of a supersonic expansion provides the ideal medium for preparing individual conformers of sugars in virtual isolation conditions, ready to be interrogated by a short burst of microwave radiation. To date, rotational investigations of monosaccharides have been carried out for C 4 sugars [222], C 5 sugars [62,223,224], and C 6 sugars [225][226][227]. All factors contributing to stabilization of the observed species are given in the next sections.…”

“…2) OH (5) Á Á ÁOH (4) Á Á ÁOH (3) Á Á ÁOH (2) Á Á ÁOH (1) Á Á ÁO (ring) , with a counterclockwise arrangement of the OH groups. This hydrogen bond cooperative interaction is a form of intramolecular solvation which reinforces the C 5 gÀ has also been examined by LA-MB-FTMW spectroscopy [227] and its structure has been determined from the rotational spectra of parent and monosubstituted isotopic species.…”

FructationIn Vivo: Detrimental and Protective Effects of Fructose

“…Generally, glucose is the least reactive monosaccharide and this characteristic can be considered to the emergence of glucose as the primary metabolic fuel [36, 81, 82]. Fructose also forms both pyranose and furanose structures [83] but exists to a greater extent in the open-chain active form than does glucose. The proportion of acyclic forms of glucose and fructose in aqueous solution accounts for 0.001–0.002% and 0.7%, respectively [48, 84].…”

Iterative design of a helically folded aromatic oligoamide sequence for the selective encapsulation of fructose

“…Unlike the furanose forms of fructose, the stabilization of β-7a is uncommon. Indeed, only four protein structures are reported in the Protein Data Bank that sequester this form 39 .…”