CE07 - Chimie moléculaire, Chimie durable et procédés associés

Crystalline product assisted by intensified CO2 process – CYPRES

Crystallinity and chirality assisted by CO2

The project evaluates the possibility of controlling the structural and enantiomeric purity of compounds of pharmaceutical interest possibly formulated in cocrystals via the use of compressed CO2. CO2 should allow access to metastable equilibria favourable to co-crystallization, chiral resolution, or both. The development of CO2-assisted processes could thus meet the industrial demand for rapid and efficient selective crystallization.

Supercritical CO2: antisolvent or solvent for the precipitation of new crystalline forms?

The solid state of drugs is a major issue in the pharmaceutical field. On the one hand, the isolation of new crystalline forms of an active ingredient (polymorphs, hydrates) with specific properties can have a significant impact on the marketing of the drug concerned, including the publication of new patents. On the other hand, since the majority of new pharmaceutical substances discovered are chiral, access to pure enantiomers is achieved by resolving the racemic mixture via crystallization and requires an advanced knowledge of the solid state.<br />Recently, research on co-crystals of active ingredients has accelerated. Indeed, the existence of new stoichiometric phases between target molecules and co-formers presents different advantages: new intellectual property, improved pharmacokinetic properties or access to conditions favorable to chiral resolution.<br /><br />In this context, the challenges and objectives of the CYPRES project are :<br />- to diversify methods to access new co-crystals through the use of supercritical CO2.<br />- To develop and improve crystallization control under supercritical conditions.<br />- to evaluate the ability of supercritical CO2 to allow access to metastable equilibria during crystallization.<br />- to formulate a stereoselective crystallization process under supercritical conditions.

In order to meet the challenges proposed by the CYPRES project, three complementary experimental approaches are being implemented: (i) classical crystallization with in-situ X-ray diagnostics, (ii) supercritical CO2-assisted crystallization in a microfluidic reactor, (iii) supercritical CO2-assisted crystallization in a 'macro' reactor.
The approach consists in first identifying and studying the behavior of chiral molecules and co-crystals under classical crystallization conditions. Each system that will be selected for sc-CO2 testing will be fully characterized from the point of view of its thermal behavior (phase diagram establishment), in particular to know if the system crystallizes as a conglomerate or as a racemic compound. When a conglomerate is detected, a preferential crystallization process will be established under classical conditions and will serve as a reference for scCO2 crystallization tests. The development of an in situ X-ray diffraction analysis will be developed in the next steps of the project and will support this classical preferential crystallization method.
The CO2 crystallization, mainly conducted here in the antisolvent mode, consists in adding CO2 to a mother liquor to decrease the solubility of the species and cause their precipitation or co-precipitation. The major challenge of this semi-continuous process is the control of crystalline purity and enantiomeric excess, two characteristics that depend on the reactor homogeneity in space and time and on thermodynamics. The use of microfluidic-type microreactors should allow a better control of the mixing between CO2 and the solvent while the larger volume reactor will give access to a higher productivity necessary for phase identification.

- Identification of 2 chiral molecules (A, B) crystallizing as stable racemic compounds and having the possibility to form a metastable conglomerate. For these two molecules, preferential crystallisation processes in the classical solvent route were established.
- Elaboration of new racemic co-crystals (CC) with A or B, and of an enantiopure co-crystal of A not described in the literature, by conventional (dry or solvent-assisted grinding) methods.
- The screening of co-crystal production by antisolvent CO2 crystallisation led to the effective formation of 4 co-crystals out of the 12 systems tested, 2 of which are not described in the literature.
- The co-crystallisation under CO2 of one of the chiral molecules led to the formation of a different and unique phase. This specificity has rarely been observed before with organic molecules and a fortiori with cocrystals.
- This new phase is produced with 3 variants of the process from different partners, eliminating any risk of artefact. The three options allow the production of pure cocrystal powders, but in which the new phase and the conventional phase can coexist depending on the operating conditions.
- A second system based on chiral API is being developed for co-crystallization by CO2. The cocrystals obtained from the S or the RS molecule have the same crystalline characteristics as those produced by conventional means. It should be noted, however, that the speed of the process (about 4 hours to obtain pure and dry cocrystals from a solution), combined with the low temperatures, help to promote CO2 as an eco-friendly alternative.
- Construction of a high-pressure microfluidic platform for the in situ monitoring of diffusion and nucleation phenomena of crystal growth by supercritical anti-solvent effect.Placed under a microscope, it allows the acquisition of images and video of the crystallization events in real time. Applied to chiral molecules, crystallization on the high pressure microchip gives results on the precipitation time of the RS and S forms of the active ingredient. The processing of the obtained images allows to trace the growth kinetics of the active ingredient crystals.

- The description of chiral systems including the establishment of form stabilities, which is necessary to consider preferential crystallization.
- The new form of CO2-produced cocrystal is a racemic cocrystal; it corresponds to the most difficult option of enantiomeric separation. It is envisaged to select a system known to give a stable conglomerate in order to increase the chances of successful CO2-assisted preferential crystallization.
- The CO2 investigations of the second racemic system will be extended to consider preferential crystallization by conglomerate formation.
- The microfluidic device will be applied to different systems in order to validate the developed design which should allow 'slow' mixing of CO2 and solvent and thus allow in-situ monitoring of the crystallization. Raman microscopy is implemented to monitor local concentration gradients.
- The modelling of the crystallization in a microfluidic reactor is in progress in order to couple experimental observation and numerical simulation, giving thus access to growth rate in real time.

F. Ercicek, O. Nguyen, C. Harscoat-Schiavo, M. Marchivie, A. Erriguible, P. Subra-Paternault, S. Marre, Microchip co-crystallization with supercritical CO2, European Meeting on Supercritical Fluids, poster session, May, 2021, online.

Léa Nimod, Isabelle Ziri, Olivier Monnier. “CYPRES project – Enantiomeric resolution by using supercritical CO2 co-crystallization”, Sanofi internal «R&D week« Sanofi Montpellier, 2 décembre 2021.

F. Ercicek, O. Nguyen, A. Erriguible, C. Harscoat-Schiavo, P. Subra-Paternault, S. Marre. On-chip in-situ observations of crystallization events under supercritical CO2. Oral presentation. ISSF 2022, 13 th International Symposium on Supercritical Fluids, Montréal 15-18 may 2022.

F. Ercicek, M. Marchivie, C. Harscoat-Schiavo, S. Marre, P. Subra-Paternault. Cocristallisation d’actifs pharmaceutiques en milieu supercritique. Présentation orale. CRISTAL 10, 9-10 juin 2022, Lyon

F. Ercicek, C. Harscoat-Schiavo, M.Marchivie, S. Marre and P. Subra-Paternault. Investigations of pharmaceutical compounds co-crystallization for application to chiral resolution assisted by supercritical CO2. Présentation orale. BIWIC 2022, 27th International Workshop on Industrial Crystallization, 31st august – 2nd september 2022, Espoo Finland

«Cristallisation préférentielle d’un cocristal chiral ; une voie originale pour la séparation d’énantiomères.«, Chrystal LOPES, Nino PATRY, Clément BRANDEL, Yohann CARTIGNY, Congrès CRISTAL 10 Lyon, juin 2022. Poster presentation


Teaching at ENSIC Engineering School, Nancy: «Aspects fondamentaux et appliqués du polymorphisme des composés moléculaires et pharmaceutiques« Y. CARTIGNY juin 2022

Fatma Ercicek, Christelle Harscoat-Schiavo, Patrick Layrisse, Mathieu Marchivie, Yohann Cartigny, et al.. Naproxen-bipyridine cocrystallization assisted by pressurized carbon dioxide. Journal of Supercritical Fluids, 2023, 200, pp.105976. ?10.1016/j.supflu.2023.105976?. ?hal-04098643?

Fatma Ercicek, Christelle Harscoat-Schiavo, Patrick Layrisse, Mathieu Marchivie, Yohann Cartigny, et al. Cocrystallization of Naproxen and Bipyridine assisted by supercritical CO2.
CO2 solvent or CO2 antisolvent, what is the best process?
présentation orale. European Meeting on Supercritical Fluids, May 2023, Budapest
Yohann Cartigny. STUDIES ON SOLID-VAPOR EQUILIBRIA TO DEVELOP NEW SOLID MATERIALS: THE CASE OF HYDRATES. Congrès Société Chimique de France, Nantes 25 au 27 juin 2023

In the context of sustainable crystallization and process intensification, the overall objective of the CYPRES project is to evaluate the performances of supercritical CO2 at controlling the crystal purity through a better understanding of CO2-mediated crystallization mechanisms with special insight into time-related aspects. The targets considered here cover (i) the fabrication of co-crystals pure powders and (ii) chiral resolution, both implying to manage a selective crystallization. Though supercritical CO2 technology is increasingly proposed as medium in advanced manufacturing processes for simple and composite products, the control of the crystal phase and its purity of organic materials is far less investigated than particle generation whereas it is of vital importance to assure the desired effect specially for pharmaceutical active ingredient. Since selective crystallization is controlled by the interplay of phase equilibria and kinetics, the use of CO2 is foreseen here as a different way to manage those factors through the unique flexibility of varying conditions via pressure, the modality of contacting species with CO2 and the adaptable composition of the CO2:solvent mixture that are likely to impact the structural and purity of products.
To achieve the objectives, CYPRES relies onto five complementary partners’ expertises and three technologies that will contribute to the rationalisation of key parameters of the CO2-based process. Diagrams of phase co-existence and conventional crystallization monitored by in-situ X-Rays diffraction (XRD) at atmospheric conditions will provide the fundamental grounds for selected systems. Microfluidics in scCO2, undeveloped for organic molecules, will provide temporal and spatial informations of crystallization in CO2 media thanks to a better control of local conditions whilst numerical simulation will help at understanding the contribution of the involved phenomena. CO2 crystallization will optimize the production of the relevant crystals based on both conventional and microfluidic outcomes. The project aims at developing in-situ techniques for the CO2-based set-ups ( Raman, UV, RX) to get access to real time monitoring of crystallization events.

Project coordination

Christelle HARSCOAT-SCHIAVO (Institut Chimie et Biologie des Membranes et des Nano-objets)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.


CBMN Institut Chimie et Biologie des Membranes et des Nano-objets
ITUN Technische Universität Bergakademie Freiberg / Institut für Thermische Verfahrenstechnik, Umwelt und Naturstoffverfahrenstechnik

Help of the ANR 428,188 euros
Beginning and duration of the scientific project: June 2019 - 48 Months

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