Chiroptical detection. Novel possibilities of its application to enantiomers

Mannschreck, Albrecht; Andert, Doris; Eiglsperger, A.; Gmahl, E.; Buchner, Hans

doi:10.1007/bf02316442

Cited by 52 publications

(21 citation statements)

References 25 publications

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“…1), the other one should be taken to be equal except for sign, i.e., C + = −C − . On the basis of these ratios and the experimental chromatograms A() and ␣(), our general computer program 7,11 SEPP for Windows 12,13 calculates the deconvolved curves A + (), A − (), a + (), and ␣ − (). The procedure described here for photometry/polarimetry is identical for photometry/ circular dichroism.…”

Section: Procedures For the Determination Of Ratios And The Deconvolumentioning

confidence: 99%

“…The ratios C + and C − represent this additional information, needed for solving the four equations for the four wanted values at many elution volumes. 7 In circular dichroic detection, Equations 1 and 5 require the ratios g + and g − as additional information.Therefore, the aim of the present study is to describe and discuss in detail the methods for obtaining such ratios and for deconvolving overlapped peaks of enantiomers. In addition, results of the determination of optical purity and peak purity as well as for the study of the interconversion of enantiomers, using novel examples, are given and discussed.…”

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Chiroptical detection during liquid chromatography: Deconvolution of overlapping peaks of enantiomers and its applications

et al. 2003

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The peaks of enantiomers in liquid chromatography (LC) frequently overlap for different reasons. The experimental curve can be deconvolved, i.e., transformed into the two curves of the enantiomers, without any assumption concerning their peak shapes. Besides the usual photometric UV detection, resulting in absorbance A, polarimetric or circular dichroic detection is required, providing the rotation 90 degree angle alpha or the differential absorbance DeltaA, respectively. The accuracy of the ratio alpha/A or DeltaA/A for the pure enantiomers is essential for the quality of the deconvolution. The determination of these ratios, using the overlapping peaks, and the subsequent computer deconvolution of the latter are discussed in more detail than in the earlier publications, e.g. Ref. 1 concerning this particular method. The computer program developed for this purpose is characterized. A condition is given which limits the availability of ratios and, therefore, the possibility of deconvolution. Several novel examples are described which stem from the following fields of application of deconvolved peaks: actual optical purities during LC (on-line analysis), overall optical purity of a sample, purities of chromatographic peaks, and, finally, enantiomerization during LC.

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Section: Procedures For the Determination Of Ratios And The Deconvolumentioning

confidence: 99%

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confidence: 99%

Chiroptical detection during liquid chromatography: Deconvolution of overlapping peaks of enantiomers and its applications

et al. 2003

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“…This process has been studied by a peak deconvolution procedure [14,15] or more often by computer simulation [1,3]. Peak areas of enantiomers determined by these methods were used to calculate apparent rate constants, which are weighted means of the different enantiomerization rates in the mobile and the stationary phase [3].…”

Section: Theoreticalmentioning

confidence: 99%

“…The peak areas of enantiomers were determined directly from the chromatogram detected by the selective polarimetric detector. Deconvoluted peak areas of enaniomers were used to determine rate constants and energy barrier to enantiomerization [14,15]. However, a deconvolution method for the determination of peak areas in a peak cluster obtained by dynamic chromatography with non-selective detection has not been published to our knowledge.…”

Section: Introductionmentioning

confidence: 99%

On the use of a peak deconvolution procedure for the determination of energy barrier to enantiomerization in dynamic chromatography

et al. 2000

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The term enantiomerization characterizes a process in which the enantiomers undergo inversion of their respective conformations during a chromatographic separation [1]. Enantiomerization of enantiomers A and B can be described by a scheme:where k 1 and k -1 are the rate constants.The A→B enantiomerization is the first order kinetic reaction which is described by following differential equation:(1) The B→A enantiomerization is described by the similar equation:where c is concentration of a considered enantiomer and t is time.Equations 1 and 2 describe interconversion of individual enantiomers in a static system where enantiomers A and B are in a contact. Direct chromatographic separation of enantiomers is, however, a dynamic system, and therefore interconverted enantiomers A* and B* will be separated from the "original ones". A peak cluster composed of a peak of interconverted enantiomers (A*B*) between the two peaks of enantiomers is formed as a consequence of this separation [2].Energy barriers to enantiomerization of enantiomers can be determined by several methods. While the isolation of single enantiomers followed by classical racemization kinetics using chiroptical methods is cumbersome and time-consuming, dynamic [1,[3][4][5] and stopped-flow [6,[8][9][10] chromatographic techniques are more straightforward since enantiomers are separated and analyzed on-line, thus requiring only minute amounts of the racemic or enriched mixture of enantiomers. The lower energy barrier to interconversion of enantiomers (around 70-100 kJ mol -1 ) can be determined by dynamic HPLC (DHPLC) [11]. Higher energy barriers to interconversion of enantiomers (around 70-200 kJ mol -1 ) can be determined by dynamic gas chromatography (DGC) [9]. DHPLC and DGC has been shown to produce rate constants and energy barriers to enantiomerization in good agreement with those obtained by independent techniques [12] except for the rare case when the stationary phase shows high catalytic activity [13]. Mannschreck with co-workers have used simultaneous photometric ad polarimetric detectors for aOn the use of a peak deconvolution procedure for the determination of energy barrier to enantiomerization in dynamic chromatography Abstract. Manual or computer assisted peak deconvolution on chromatograms of the racemate of 1-chloro-2,2-dimethylaziridine enantiomers GC was used to determine the peak areas of enantiomers in the racemate prior (A A,0 , A B,0 ) and after the separation (A A, A B ). These peak areas were used in the determination of apparent rate constants and apparent energy barrier to enantiomerization. Comparison of apparent energy barriers determined using deconvolution of chromatograms with data published in literature showed differences within 7 % rel.

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“…The present significance of liquid chromatography (LC) for many areas of science requires adequate possibilities of detection.2 As far as the substrate consists of chiral molecules, chiroptical detectors [2][3][4] are particularly valuable because they provide a unique, selective information which, for fundamental reasons, cannot be obtained by other instruments: positive and negative signs. Apparently, chiroptical detection is not applied in all cases where it might be advantageous.…”

Section: Introductionmentioning

confidence: 99%

Chiroptical detection during liquid chromatography: Applications to stereoanalysis and stereodynamics

Mannschreck

1992

Chirality

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Qualitative and quantitative use of polarimetry at one wavelength for detection during liquid chromatography is briefly reviewed. Acquisition of circular dichroism spectra by stopped-flow and nonstop measurements has been further developed. Reasons are given why the angle of rotation, i.e., the polarimeter, is preferred for monochromatic use and differential absorbance, i.e., the dichrograph, for polychromatic requirements. Both methods are demonstrated by novel applications, mainly to enantiomers which interconvert thermally via intramolecular processes.

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Chiroptical detection. Novel possibilities of its application to enantiomers

Cited by 52 publications

References 25 publications

Chiroptical detection during liquid chromatography: Deconvolution of overlapping peaks of enantiomers and its applications

Chiroptical detection during liquid chromatography: Deconvolution of overlapping peaks of enantiomers and its applications

On the use of a peak deconvolution procedure for the determination of energy barrier to enantiomerization in dynamic chromatography

Chiroptical detection during liquid chromatography: Applications to stereoanalysis and stereodynamics

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