Raman excess spectroscopy vs. principal component analysis: probing the intermolecular interactions between chiral molecules and imidazolium-based ionic liquids

Abstract

Raman spectroscopy is a very sensitive and specific measurement tool for probing intermolecular interaction structures. As imidazolium-based ionic liquids can favorably be used for enantioseparation, in

Vibrational Spectroscopy of Ionic Liquids

“…405,406 However, this approach is undermined when the reference spectrum cannot be obtained. In this context, Koch et al 407 discussed a multivariate approach for quaternary mixtures of [C 2 C 1 im][C 2 SO 4 ], water, and D-and L-glucose. A word of caution is in order since not all multivariate analysis methods will provide meaningful information in the first approach, a careful choice being fundamental for the employed method and proper data pre and post processing.…”

“…In Raman excess spectroscopy, or other excess spectroscopies, the deviation of the experimental spectrum of the mixture from the ideal counterpart, which is the weighted average of pure samples spectra, may provide chemical information about interactions in the mixture. , However, this approach is undermined when the reference spectrum cannot be obtained. In this context, Koch et al discussed a multivariate approach for quaternary mixtures of [C 2 C 1 im]­[C 2 SO 4 ], water, and d - and l -glucose. A word of caution is in order since not all multivariate analysis methods will provide meaningful information in the first approach, a careful choice being fundamental for the employed method and proper data pre and post processing …”

Direct Readout of Homo- vs Heterochiral Ligand Shell of Quantum Dots

“…The chiroptical activity of QDs is typically tested using electronic circular dichroism, , or circularly polarized luminescence. , In turn, Raman spectroscopy has been used as a powerful method to investigate different properties of nanocrystalline materials (including ZnO) such as composition, crystallite size distribution, , disorder and thickness of the ligand shell, and changes associated with doping or to calculate the surface and interface parameters. , However, to the best of our knowledge, this technique has not been used to differentiate between QDs coated exclusively by single enantiomers and QDs possessing the organic shell composed of a racemic mixture of these enantiomers, even though number of studies of various chiral biologically important entities (e.g., sugars, DNA, proteins, molecules) have demonstrated that Raman spectroscopy (including surface-enhanced Raman spectroscopy, , which provides a way to detect smaller quantities) is a very promising and powerful technique, offering rapid sample screening to distinguish the respective enantiomeric forms. − A critical part of the differentiation strategy based on Raman spectroscopy is the identification of both significant bands and a proper algorithm that can analyze the measured data set. − In this regard, principal component analysis (PCA), as a statistical method, is useful for finding a pattern in Raman data of high dimensions. The efficiency of PCA relies on the ability to transform high-complexity Raman data into a new coordinate principal component (PC) system using an orthogonal linear transformation with the axes oriented to show the maximal variation in the data set. , A dozen scientific papers show the value of PCA, especially in hyperspectral mapping, characterization, detection, identification, and distribution approaches. − As we have mentioned before, the introduction of chiral ligands has been regarded as an effective strategy to obtain nanoclusters with optical purity.…”

“… 36 , 37 However, to the best of our knowledge, this technique has not been used to differentiate between QDs coated exclusively by single enantiomers and QDs possessing the organic shell composed of a racemic mixture of these enantiomers, even though number of studies of various chiral biologically important entities (e.g., sugars, DNA, proteins, molecules) have demonstrated that Raman spectroscopy (including surface-enhanced Raman spectroscopy, 38 , 39 which provides a way to detect smaller quantities) is a very promising and powerful technique, offering rapid sample screening to distinguish the respective enantiomeric forms. 40 − 42 A critical part of the differentiation strategy based on Raman spectroscopy is the identification of both significant bands and a proper algorithm that can analyze the measured data set. 43 − 45 In this regard, principal component analysis (PCA), as a statistical method, is useful for finding a pattern in Raman data of high dimensions.…”