One-bond carbon-proton coupling constants: angular dependence in alpha-linked oligosaccharides.

Area of Science:

• Carbohydrate Chemistry
• Computational Chemistry
• Structural Biology

Background:

• Oligosaccharides are crucial in biological processes.
• Understanding their structure-property relationships is vital.
• Carbon-13 to proton coupling constants (1JC,H) provide structural insights.

Purpose of the Study:

• To investigate the angular dependence of 1JC,H in alpha-linked oligosaccharide models.
• To elucidate the effect of HO-2 orientation on 1JC,H.
• To compare calculated and experimental 1JC,H values for validation.

Main Methods:

• Semi-empirical INDO calculations using FPT formulation.
• Analysis of angular dependence using a trigonometric function.
• DEPT (Distortionless Enhancement by Polarization Transfer) NMR spectroscopy for experimental data.
• Thermodynamic averaging of 1JC,H values based on conformer abundance.

Main Results:

• Established the angular dependence of 1JC,H on glycosidic dihedral angles (phi H and psi H).
• Validated computational methods by comparing with experimental DEPT data.
• Determined solvent effects on 1JC,H values.
• Calculated averaged 1JC,H values for maltose and isomaltose, showing good agreement with experimental data.

Conclusions:

• The study provides a reliable method for predicting 1JC,H values in oligosaccharides.
• Accurate 1JC,H analysis aids in determining carbohydrate conformation and linkage.
• This work contributes to a deeper understanding of carbohydrate structure and dynamics.