Sophie Fourmentin

Remediation technologies using cyclodextrins: an overview

Nowadays, the human activity and the modern way of life are responsible for the increase of the environmental pollution. Industrial processes generate a variety of molecules that may pollute air, water, and soils due to negative impacts for ecosystems and humans. The development of innovative remediation technologies has thus emerged as a significant environmental priority. Within this scope, supramolecular chemistry, which is a recent discipline, could provide solutions. In particular, cyclodextrins (CDs) are a family of cyclic oligosaccharides having a low-polarity cavity in which organic compounds of appropriate shape and size can form inclusion complexes. This unique property makes them suitable for application in environmental protection. Here, we review the use of cyclodextrins and cyclodextrin derivatives in remediation technologies. Accordingly, the present review shows the advantages of using CDs in soil, groundwater, wastewater, and atmosphere remediation. Resulting processes are highly versatile, since the complexing ability of CD is applicable to a wide range of pollutants. They may also been referred to green processes, according to the CD innocuity. Moreover, as inclusion phenomena correspond to reversible equilibriums, a major trend in the CD environmental application field is to develop methods, which combine supramolecular chemistry and irreversible processes, as advanced oxidation or biodegradation. Such processes might lead to a complete remediation of pollutants and eventually to the CD recycling.

Analytical Improvement in Measuring Formation Constants of Inclusion Complexes between β-Cyclodextrin and Phenolic Compounds

Inclusion complex formation betweensixteen para-substituted phenols andβ-cyclodextrin have been investigated in orderto establish Quantitative Structure AffinityRelationships. An analytical methodology is proposed,in order to obtain reliable evaluation of bindingaffinities. Potentiometry and circular dichroism havebeen applied to define experimental conditions and toconfirm postulated equilibriums. In addition, the useof algorithmic treatments and concentrationoptimisation to determine formation constants leads tocoherent values between 1H NMR, direct UVSpectroscopy and the spectral displacement method. Theresults emphasise the contribution of van der Waalsinteractions, provided that no significant differencein the dipole of the molecule arises from thepara-substituent.

Fenton degradation assisted by cyclodextrins of a high molecular weight polycyclic aromatic hydrocarbon benzo[a]pyrene.

This paper investigates the effect of native beta-cyclodextrin (beta-CD) and its CD derivatives, such as hydroxypropyl-beta-cyclodextrin (HPBCD) and randomly methylated-beta-cyclodextrin (RAMEB), on the solubilization of a high molecular weight polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP) and on its degradation by Fentons reaction. The results show that BaP apparent solubility was significantly increased in the presence of cyclodextrin (CD) in the following order: beta-CD<RAMEB<HPCD. BaP Fenton degradation was strongly dependent on the capacity of cyclodextrin to solubilize BaP. In the presence of a radical scavenger (mannitol), BaP Fenton degradation was inhibited with RAMEB but not in the presence of HPCD. Molecular modelisation was used to visualize the steric complementarity of these host-guest systems. No significant difference of encapsulation between the two modified CDs was observed. Nevertheless, the results suggest a probable existence of a ternary complex HPCD-BaP-iron permitting the generation of hydroxyl radicals in close proximity to BaP. On the basis of these results, it appears that HPCD may be useful for developing targeted BaP degradation system.

Fluorescent Indolizine-β-Cyclodextrin Derivatives for the Detection of Volatile Organic Compounds

This paper presents the synthesis, the structural determination and the sensing capabilities toward Volatile Organic Compounds (VOCs) of a new class of fluorescent indolizine-cyclodextrin sensors. Two different pathways, both involving bipyridinium ylides and 6-amino-b-cyclodextrin, have been used to carry out the synthesis of these sensors. The macrocycle structures were dominantly established by 1H-NMR spectra and systematically studied by molecular modelling (MM3, AM1, AM1-COSMO methods). The sensing capabilities of the sensors were evaluated by emission of fluorescence, during the inclusion of the guest (adamantanol or aromatic derivatives) into the cyclodextrin (CD) host cavity. The host/guest complex formation was investigated by formation constant determinations, using experimental methods, coupled with theoretical calculations of formation energies using a specific docking procedure. Both experimental and theoretical results suggest that some compounds would make very attractive sensors for VOC detection. Some compounds could also be taken into consideration as biological markers.

Complexation of estragole as pure compound and as main component of basil and tarragon essential oils with cyclodextrins

Inclusion complexes of estragole (ES) as pure compound and as main component of basil and tarragon essential oils (EOs) with α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD), randomly methylated-β-cyclodextrin (RAMEB), a low methylated-β-cyclodextrin (CRYSMEB) and γ-cyclodextrin (γ-CD) were characterized. Formation constants (Kf) of the complexes were determined in aqueous solution by nonlinear regression analysis using static headspace gas chromatography (SH-GC) and UV-visible spectroscopy. Solid inclusion complexes were prepared by the freeze-drying method for different CD:ES molar ratios and were characterized by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR). Inclusion complexes formation allowed the controlled release of ES. Moreover, increased DPPH radical scavenging activity and photostability of ES and ES containing EOs (ESEOs) were observed in the presence of CDs. These findings suggest that encapsulation with CDs could be an efficient tool to improve the use of ES and ESEOs in aromatherapy, cosmetic and food fields.

Retention of aroma compounds from Mentha piperita essential oil by cyclodextrins and crosslinked cyclodextrin polymers

In this paper, the controlled release of aroma compounds from cyclodextrins (CDs) and CD polymers was studied by multiple headspace extraction (MHE) experiments. Mentha piperita essential oil was obtained by Soxhlet extraction and identification of the major compounds was performed by GC-MS analysis. Menthol, menthone, pulegone and eucalyptol were identified as the major components. Retention of standard compounds in the presence of different CDs and CD polymers has been realised by static headspace gas chromatography (SH-GC) at 25 °C in the aqueous or gaseous phase. Stability constants for standard compounds and for compounds in essential oil have been also determined with monomeric CD derivatives. The obtained results indicated the formation of a 1:1 inclusion complex for all the studied compounds. Molecular modelling was used to investigate the complementarities between host and guest. This study showed that β-CDs were the most versatile CDs and that β-CD polymers could perform the controlled release of aroma compounds.

Cyclodextrin, an efficient tool for trans-anethole encapsulation: chromatographic, spectroscopic, thermal and structural studies.

Inclusion complexes of trans-anethole (AN) with α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD), randomly methylated-β-cyclodextrin (RAMEB) and a low methylated-β-cyclodextrin (CRYSMEB) were investigated in aqueous solution by static headspace gas chromatography (SH-GC), phase solubility study, UV-Visible, (1)H NMR and (2D) ROESY NMR spectroscopies. The obtained results indicated the formation of 1:1 inclusion complex for all the studied CDs. Water solubility of AN was significantly improved upon complexation with CDs as demonstrated by phase solubility and retention studies. Solid inclusion complexes were prepared by the freeze-drying method and the encapsulation of AN was confirmed by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) studies. Moreover, the degradation of AN, induced by UVC irradiation, was markedly reduced by the formation of CD inclusion complexes. Results showed that encapsulation in CDs was an efficient way to increase solubility and stability of AN, thereby making it valuable for food or pharmaceutical applications.

Effect of cyclodextrin complexation on phenylpropanoids' solubility and antioxidant activity.

Summary The complexation abilities of five cyclodextrins (CDs) with seven phenylpropanoids (PPs) were evaluated by UV–visible spectroscopy, phase solubility studies and molecular modeling. Formation constants (K f), complexation efficiency (CE), PP:CD molar ratio, increase in formulation bulk and complexation energy were assessed. All complexes exhibited a 1:1 stoichiometry but their stability was influenced by the nature and the position of the phenyl ring substituents. A relationship between the intrinsic solubility of guests (S 0) and the solubilizing potential of CD was proposed. Molecular modeling was used to investigate the complementarities between host and guest. Finally, the antioxidant activity of encapsulated PPs was evaluated by scavenging of the stable DPPH radical.

Investigation of monoterpenes complexation with hydroxypropyl-β-cyclodextrin

In this study, we investigated the inclusion complexation of 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) and eight monoterpenes (eucalyptol, geraniol, limonene, linalool, α-pinene, β-pinene, pulegone, and thymol) in aqueous solution and solid state. The formation constants (Kf) of inclusion complexes were determined using fluorescence spectroscopy and static headspace gas chromatography. The results indicated the formation of 1:1 inclusion complexes between HP-β-CD and all studied guests. A linear relationship was found between Kf values and the hydrophobic character of the monoterpenes expressed as logP. Solid complexes were prepared by the freeze-drying method in a 1:1 (HP-β-CD:monoterpene) molar ratio. Physicochemical characterization of solid inclusion complexes was carried out using Fourier transform infrared spectroscopy and differential scanning calorimetry. Finally, the encapsulation efficiency (EE%) of HP-β-CD was determined using HPLC analysis. Noticeable difference in the EE% was observed between monoterpene hydrocarbons and oxygenated monoterpenes. These results suggested that complexation with HP-β-CD could be a promising strategy to enlarge the application of monoterpenes in cosmetic, pharmaceutical and food industries.

Experimental and Theoretical Study on the Inclusion Compounds of Aroma Components with β-Cyclodextrins

Inclusion equilibria between four aroma components suspected to be allergen and various β-cyclodextrins were investigated. The association constants of inclusion complexes were measured in aqueous solution by UV/VIS spectroscopy by competition method with methyl orange and direct titration. The data indicated the formation of 1:1 inclusion compounds. In addition, a theoretical study using MM3 force field was conducted and the computed formation energy, e.g. the stability of the complexes, were in good agreement with the calculated formation constants.