Enantioselective transformation of fluoxetine in water and its ecotoxicological relevance.

European legislation focusing on water quality is expected to broaden to encompass several pharmaceuticals as priority hazardous substances. This manuscript aims to challenge current regulatory approaches that do not recognize stereochemistry of chiral pharmaceuticals by testing the hypothesis that environmental transformation and effects of chiral pharmaceuticals are stereoselective. Our experiments revealed that, while degradation of chiral fluoxetine (FL) in river water occurs via non-enantioselective photochemical and mildly-enantioselective microbial processes favoring the (R)-enantiomer, a pronounced enantioselectivity favoring (S)-FL (leading to the formation of (S)-NFL (norfluoxetine)) is observed during activated sludge treatment. Toxicity tests proved strong enantiomer-specific toxicity in the case of Tetrahymena thermophila, protozoa that are utilized during activated sludge treatment ((R)-FL is 30× more toxic than (S)-FL; (S)-NFL is 10× more toxic than (S)-FL). This is of paramount importance as preferential degradation of (S)-FL in activated sludge microcosms leads to the enrichment of FL with 30× more toxic (R)-FL and formation of 10× more toxic (S)-NFL. It is commonly assumed that a decreased concentration of FL leads to decreased biological impact. Our study proves that despite the overall decrease in FL concentration, accumulation of toxic (R)-FL and formation of toxic (S)-NFL leads to much higher than presumed toxicological effects.

Langmuir monolayers composed of single and double tail sulfobetaine lipids.

HYPOTHESIS: Owing to structural similarities between sulfobetaine lipids and phospholipids it should be possible to form stable Langmuir monolayers from long tail sulfobetaines. By modification of the density of lipid tail group (number of carbon chains) it should also be possible to modulate the two-dimensional phase behaviour of these lipids and thereby compare with that of equivalent phospholipids. Potentially this could enable the use of such lipids for the wide array of applications that currently use phospholipids. The benefit of using sulfobetaine lipids is that they can be synthesised by a one-step reaction from cheap and readily available starting materials and will degrade via different pathways than natural lipids. The molecular architecture of the lipid can be easily modified allowing the design of lipids for specific purposes. In addition the reversal of the charge within the sulfobetaine head group relative to the charge orientation in phospholipids may modify behaviour and thereby allow for novel uses of these surfactants. EXPERIMENTS: Stable Langmuir monolayers were formed composed of single and double tailed sulfobetaine lipids. Surface pressure-area isotherm, Brewster Angle Microscopy and X-ray and neutron reflectometry measurements were conducted to measure the two-dimensional phase behaviour and out-of-plane structure of the monolayers as a function of molecular area. FINDINGS: Sulfobetaine lipids are able to form stable Langmuir monolayers with two dimensional phase behaviour analogous to that seen for the well-studied phospholipids. Changing the number of carbon tail groups on the lipid from one to two promotes the existence of a liquid condensed phase due to increased Van der Waals interactions between the tail groups. Thus the structure of the monolayers appears to be defined by the relative sizes of the head and tail groups in a predictable way. However, the presence of sub-phase ions has little effect on the monolayer structure, behaviour that is surprisingly different to that seen for phospholipids.