Determination of enantiomeric compositions of analytes using novel fluorescent chiral molecular micelles and steady state fluorescence measurements

Abstract

Novel fluorescent chiral molecular micelles (FCMMs) were synthesized, characterized, and employed as chiral selectors for enantiomeric recognition of non-fluorescent chiral molecules using steady state fluorescence spectroscopy. The sensitivity of the fluorescence technique allowed for investigation of low concentrations of chiral selector (3.0 x 10(-5) M) and analyte (5.0 x 10(-6) M) to be used in these studies. The chiral interactions of glucose, tartaric acid, and serine in the presence of FCMMs poly(sodium N-undecanoyl-L-tryptophanate) [poly-L-SUW], poly(sodium N-undecanoyl-L-tyrosinate) [poly-L-SUY], and poly(sodium N-undecanoyl-L-phenylalininate) [poly-SUF] were based on diastereomeric complex formation. Poly-L-SUW had a significant fluorescence emission spectral difference as compared to poly-L-SUY and poly-L-SUF for the enantiomeric recognition of glucose, tartaric acid, and serine. Studies with the hydrophobic molecule alpha-pinene suggested that poly-L-SUY and poly-L-SUF had better chiral discrimination ability for hydrophobic analytes as compared to hydrophilic analytes. Partial-least-squares regression modeling (PLS-1) was used to correlate changes in the fluorescence emission spectra of poly-L-SUW due to varying enantiomeric compositions of glucose, tartaric acid, and serine for a set of calibration samples. Validation of the calibration regression models was determined by use of a set of independently prepared samples of the same concentration of chiral selector and analyte with varying enantiomeric composition. Prediction ability was evaluated by use of the root-mean-square percent relative error (RMS%RE) and was found to range from 2.04 to 4.06%.

Fig. 1

Molecular structures of a poly-L-SUW; b poly-L-SUY; c poly-L-SUF; d glucose; e tartaric acid; f serine; g α-pinene

Fig. 2

Circular dichroism spectra of a poly-D-SUW and poly-L-SUW; b poly-D-SUY and poly-L-SUY; c poly-D-SUF and poly-L-SUF

Fig. 3

Fluorescence emission spectra and mean-centered spectral plots of 3.0×10⁻⁵ M a poly-L-SUW [λ_ex =280 nm]; b poly-L-SUY [λ_ex= 280 nm]; c poly-L-SUF [λ_ex =260 nm] in the presence of 5.0×10⁻⁶ M enantiomers of 1 Glucose; 2 Tartaric acid; 3 Serine

Fig. 4

Fluorescence emission spectra and mean-centered spectral plots of 3.0×10⁻⁵ M a Poly-L-SUY [λ_ex =280 nm]; b Poly-L-SUF [λ_ex= 260 nm] in the presence of 5.0×10⁻⁶ M enantiomers of α-pinene

Fig. 5

Fluorescence emission spectra and mean-centered spectral plots of 3.0×10⁻⁵ M Poly-L-SUW [λ_ex=280 nm] in the presence of 5.0×10⁻⁶ M enantiomers of a Glucose; b Tartaric acid; c Serine with varied mole fractions: (1) 1.0 D; (2) 0.9 D; (3) 0.8 D; (4) 0.7 D; (5) 0.6 D; (6) 0.5 D; (7) 0.4 D; (8) 0.3 D; (9) 0.2 D; (10) 0.1 D; (11) 0.0 D

Scheme 1

Synthetic scheme for FCMMs