title: Chiroptical spectroscopy of natural products: avoiding the aggregation effects of chiral carboxylic acids.
abstract: Determination of the absolute configurations and predominant conformations of chiral natural products, occurring as carboxylic acids, using chiroptical spectroscopic methods becomes challenging due to the formation of solute aggregates (in the form of dimers, etc.) and/or solute-solvent complexes resulting from intermolecular hydrogen bonding with solvent. A hypothesis that such aggregation effects can be avoided by using corresponding sodium salts or acid anhydrides for chiroptical spectroscopic measurements has been tested. For this purpose, vibrational circular dichroism, electronic circular dichroism, and optical rotatory dispersion spectra for disodium salts of two natural products, hibiscus acid and garcinia acid, and the anhydride of acetylated garcinia acid have been measured. These experimental spectra are analyzed in combination with quantum chemical calculations of corresponding spectra. The spectral analysis for sodium salts and anhydride turned out to be simpler, suggesting that the conversion of carboxylic acids to corresponding salts or anhydride can be advantageous for the application of chiroptical spectroscopy.
authors.affiliation: Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA. Prasad.L.Polavarapu@Vanderbilt.edu
authors.forename: Prasad L
authors.initials: PL
authors.lastname: Polavarapu
authors.forename: Emily A
authors.initials: EA
authors.lastname: Donahue
authors.forename: Karissa C
authors.initials: KC
authors.lastname: Hammer
authors.forename: Vijay
authors.initials: V
authors.lastname: Raghavan
authors.forename: Ganesh
authors.initials: G
authors.lastname: Shanmugam
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Ibnusaud
authors.forename: Divya S
authors.initials: DS
authors.lastname: Nair
authors.forename: Chithra
authors.initials: C
authors.lastname: Gopinath
authors.forename: Deenamma
authors.initials: D
authors.lastname: Habel
mesh_terms: D001688:Biological Products / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry*; D002942:Circular Dichroism / Q000379:methods*; D002951:Citrates / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure; D012492:Salts; D013237:Stereoisomerism
chemical_list: D001688:Biological Products; D002264:Carboxylic Acids; D002951:Citrates; D012492:Salts; C007999:hydroxycitric acid