Chapter 6
Other Methods for the Elucidation
of Molecular Structures and Mechanistic
Details of Enantiomers
As outlined earlier, the notorious lack of well-validated standards of highest optical
purity is still a considerable drawback for reliable peak assignments and quantitation
(Landagaray et al. 2016; Naile et al. 2016; Hasan et al. 2017; Ulrich et al. 2018).
Furthermore, enantioselective analyses today are an integrated part of toxicological
and mechanistic studies aiming at enzyme/pollutant interactions and at deepened
insight into the effects of chiral drugs and other bioactive chemicals (Joseph et al.
1986; Nikolic et al. 2009; Newmeyer et al. 2014; Christoffersen et al. 2015; Chai
et al. 2016; McTier et al. 2016; Hambuchen et al. 2017; Bedewy et al. 2018). The
absolute structure information of enantiomeric pure target substances is an important
information for the identification of retention properties, elution sequence for the
chromatographic separation and consequently for the evaluation of potential biological effects and toxicity. Therefore, the preparation or separation, as well as the
determination of the absolute configuration of enantiomeric pure compounds, is a
crucial prerequisite of such complex scientific endeavours. Very powerful methods,
although with limited sensitivity, can be employed absolute structure elucidations
and/or mechanistic studies. These elucidation methods include X-ray crystallography, nuclear magnetic resonance (NMR), mass spectrometry, refractive index and
vibrational circular dichroism.
6.1 X-Ray Crystallography
The condition for the application of this experimental approach is the separation of a
pure enantiomer in optimal crystalline form, which may have been achieved by
separating a sufficient amount of the enantiopure compound by enantioselective
HPLC (Karle and Karle 1989; Stahlberg et al. 2001; Scriba 2016) or preparative cGC
(Schmidt et al. 2000; Heeb et al. 2007; Riddell et al. 2016). As an example for this
experimental approach, the determination of the absolute structure of (+)-α-HCH is
described (Möller et al. 1993, 1994): the HPLC separation of the (+)-α-HCH
© Springer Nature Switzerland AG 2021
R. Kallenborn et al., Chiral Environmental Pollutants,
https://doi.org/10.1007/978-3-030-62456-9_6
89
Other Methods for the Elucidation
of Molecular Structures and Mechanistic
Details of Enantiomers
As outlined earlier, the notorious lack of well-validated standards of highest optical
purity is still a considerable drawback for reliable peak assignments and quantitation
(Landagaray et al. 2016; Naile et al. 2016; Hasan et al. 2017; Ulrich et al. 2018).
Furthermore, enantioselective analyses today are an integrated part of toxicological
and mechanistic studies aiming at enzyme/pollutant interactions and at deepened
insight into the effects of chiral drugs and other bioactive chemicals (Joseph et al.
1986; Nikolic et al. 2009; Newmeyer et al. 2014; Christoffersen et al. 2015; Chai
et al. 2016; McTier et al. 2016; Hambuchen et al. 2017; Bedewy et al. 2018). The
absolute structure information of enantiomeric pure target substances is an important
information for the identification of retention properties, elution sequence for the
chromatographic separation and consequently for the evaluation of potential biological effects and toxicity. Therefore, the preparation or separation, as well as the
determination of the absolute configuration of enantiomeric pure compounds, is a
crucial prerequisite of such complex scientific endeavours. Very powerful methods,
although with limited sensitivity, can be employed absolute structure elucidations
and/or mechanistic studies. These elucidation methods include X-ray crystallography, nuclear magnetic resonance (NMR), mass spectrometry, refractive index and
vibrational circular dichroism.
6.1 X-Ray Crystallography
The condition for the application of this experimental approach is the separation of a
pure enantiomer in optimal crystalline form, which may have been achieved by
separating a sufficient amount of the enantiopure compound by enantioselective
HPLC (Karle and Karle 1989; Stahlberg et al. 2001; Scriba 2016) or preparative cGC
(Schmidt et al. 2000; Heeb et al. 2007; Riddell et al. 2016). As an example for this
experimental approach, the determination of the absolute structure of (+)-α-HCH is
described (Möller et al. 1993, 1994): the HPLC separation of the (+)-α-HCH
© Springer Nature Switzerland AG 2021
R. Kallenborn et al., Chiral Environmental Pollutants,
https://doi.org/10.1007/978-3-030-62456-9_6
89