Chiroptical Spectroscopies


Our department is specialized in the characterization of chiral molecules and more particularly, in the   determination of absolute configuration by chiroptical spectroscopies. We perform Vibrational Circular Dichroism (VCD), Electronic Circular Dichroism (ECD) and Optical Rotation Dispersion (ORD) analyses.

We offer also the classical qualitative spectral analysis (structure characterization) in the domains near UV (190-390nm) and visible (390-750nm), the near-infrared (4000-13400 cm-1), middle-infrared (400-4000 cm-1) and far-infrared (30-400 cm-1) regions.

We analyze the samples received from academic or industrial research laboratories working in various fields of chemistry: pharmaceutical, materials, food industry...

Our Means

Spectroscopies IR & VCD

PMA50 (Bruker)

VCD module associated with a VERTEX70 spectrometer. The module is equipped with a HgCdTe D316 detector (InfraRed associates, inc.) and an autonomy of 24h for the realization of experiments over several days. Measurements can be performed in the 800-3800 cm-1 spectral range.


VERTEX 70 (Bruker) :

Fourier transform spectrometer (FTIR) used for routine analysis or advanced experiments. The VERTEX70 has a large choice of parameters. It can be configured to work in the 3 infrared spectral ranges: near IR (12000-4000 cm-1), middle IR (4000-400 cm-1) and far IR (400-30 cm-1).

TENSOR 27 (Bruker) :

Fourier transform spectrometer (FTIR), this instrument is used for routine analysis in the mid-infrared (400-4000 cm-1).

Preparation of samples for IR & VCD analysis

The samples analyzed can be liquids, gels or solids. We do not analyze gases. For measurements of solutions or gels, we have several removable cells equipped with windows covering a wide spectral range: NaCl (700-28000 cm-1), CaF2 (1200-66000 cm-1), BaF2 (900-50000 cm-1). Solids measurements can be performed:

- Using pellets obtained by compressing a mixture of the product to be analyzed with KBr or PET.
- Using a mixture of the product to be analyzed with Nujol.

For routine infrared measurements on pure products, we dispose a total attenuated reflection accessory (ATR) single reflection with platinum diamond crystal (Bruker). This accessory is adaptable on the spectrometers TENSOR 27 and VERTEX 70. It can be used in the spectral range 30-8000 cm-1.


Spectroscopies UV-vis, ECD, ORD & MCD


J815 (Jasco) :

Spectrometer dedicated to the measurement of ECD and ORD spectra. It is configured to work in a wide spectral range: 180-1000 nm. The instrument is equipped with a Peltier system for precise temperature control.   ORD spectra are measured with the ORDE402 accessory (Jasco). The J815 spectrometer can be equipped with a 1.6 Tesla permanent magnet for MCD spectra measurements.

V670 (Jasco) :

Dual beam spectrometer used for routine analysis or more complex experiments. This instrument can work in a wide spectral range from near UV to near IR: 190-2700 nm. It can be equipped with different accessories:

  • Peltier system ETCS-761 (Jasco) : Working temperature 0 to 100 °C
  • 60 mm horizontal integrating sphere (Jasco) for the analysis of powders, gels or liquids

Products can be analyzed in different forms: pure or diluted liquids, gels or solids.


Preparation of samples for UV-vis, ECD & ORD analysis

The samples analyzed can be liquids, gels or solids. We do not analyze gases. For the measurements of solutions or gels, we have several quartz cells with several possible optical paths (0.1mm to 10 cm). For measurements in the solid state, we can, as in infrared, make pellets or use the integrating sphere for the measurement in reflection on powders.


Determination of absolute configuration by CD spectroscopies

The determination of the absolute configuration by VCD and ECD requires 3 steps:

1. Measurement of the CD spectra of both enantiomers, when available. The circular dichroism is the ability of a molecule to absorb differently the left (LCP) and right (RCP) circularly polarized light. For optimal results, it is preferable that each sample analyzed is chemically pure and has an enantiomeric excess (ee) as close to 100% as possible. When both enantiomers are not available, the measurement can be performed with a single enantiomer. The samples are usually measured in solution. Although more delicate, it is also possible to analyze samples in the solid state. The quantities necessary for the CD analysis of a product depend on its nature: they can vary from a few mg to several tens of mg. The solvents used are the standard solvents of infrared spectroscopy for VCD and UV-vis for ECD.

2. Modeling of the spectra by quantum chemistry methods (DFT, TD-DFT) for a chosen absolute configuration. This step requires to correctly describe the measured solution. Especially in VCD, environmental effects such as solute-solvent interactions can have important consequences on the shape of the spectrum. Our service has a long experience in this field and can bring assistance in the realization of this step. It should be noted that this step is generally the one that will determine the duration of the analysis: from a few days to several months.

3. 3. Determination of absolute configuration by comparison of measured and calculated spectra.


Measurement of ORD spectra

Rotational power dispersion (ORD) spectra (optical rotatory dispersion (ORD)), also called circular birefringence spectra, give the evolution of the rotatory power in a spectral range. They allow a more reliable characterization of enantiomers and should be preferred to a simple rotatory power measurement.

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