Enhanced Solubilisation of Six PAHs by Three Synthetic Cyclodextrins for Remediation Applications: Molecular Modelling of the Inclusion Complexes

Abstract

Solubilisation of six polycyclic aromatic hydrocarbons (PAHs) (acenaphthene, anthracene, fluoranthene, fluorene, phenanthrene and pyrene) by three synthetic cyclodextrins (CDs) (2-hydroxypropyl-β-CD, hydroxypropyl-γ-CD and ramdomly methylated-β-CD) was investigated in order to select the CD which presents the greatest increase in solubility and better complexation parameters for its use in contaminated scenarios. The presence of the three cyclodextrins greatly enhanced the apparent water solubility of all the PAHs through the formation of inclusion complexes of 1∶1 stoichiometry. Anthracene, fluoranthene, fluorene and phenanthrene clearly presented a higher solubility when β-CD derivatives were used, and especially the complexes with the ramdomly methylated-β-CD were favoured. On the contrary, pyrene presented its best solubility results when using 2-hydroxypropyl-γ-CD, but for acenaphthene the use of any of the three CDs gave the same results. Complementary to experimental phase-solubility studies, a more in-depth estimation of the inclusion process for the different complexes was carried out using molecular modelling in order to find a correlation between the degree of solubilisation and the fit of PAH molecules within the cavity of the different CDs and to know the predominant driving forces of the complexation.

Efficient extraction and detection of aromatic toxicants from crude oil and tar balls using multiple cyclodextrin derivatives

“…The addition of cyclodextrin to the aqueous solutions has the potential to alter this partitioning between the aqueous and oil layers, because cyclodextrins have been shown to bind PAHs and other aromatic analytes with high efficiencies. 40,41 For the motor oil-buffer solutions, the addition of γ -cyclodextrin and 2-HPCD led to a substantial increase in the amount of photophysically active compounds extracted into the aqueous layer (from 24.0% in PBS to 33.6% and 34% for 2-HPCD and γ -cyclodextrin respectively), which is consistent with the known ability of these cyclodextrins to bind PAHs. Other cyclodextrin derivatives, including β-cyclodextrin, methyl-β-cyclodextrin, and α-cyclodextrin, have cavity sizes that are too small to bind many PAHs, and their addition had no effect on the oil-water fluorescence ratios (Table 1).…”

Effect of contact time and the use of hydroxypropyl-β-cyclodextrin in the removal of fluorene and fluoranthene from contaminated soils

“…It must be taken into 29 account that loss due to FLU biodegradation in the soil is not possible because all the 30 experiments were carried out in the presence of an HgCl 2 solution to prevent microbial 31 degradation of the PAH. 32 These results indicate that there are few advantages in using HPBCD as the extractant 33 an ageing period subsequent to contamination, which is what usually occurs in real 1 contaminated soils. However, the advantage of the observed behaviour of FLU in aged 2 soils is that it will present very few problems for subsequent desorption, such as 3 leaching, runoff or damage for the microbial population.…”

Assisted attenuation of a soil contaminated by diuron using hydroxypropyl-β-cyclodextrin and organic amendments

“…These molecules posses a hydrophobic cavity and an exterior that is strongly hydrophilic. This peculiar structure allows organic molecules to be included in the cavity via non-covalent bonds to form inclusion complexes (Morillo et al, 2012). In previous studies, complexes between diuron and different CDs were successfully obtained in solution, where the most successful complexation parameters and the highest solubility increment were obtained for HPBCD .…”