Concerning the origin of 19F-19F NMR COSY and NOESY connections in the spectra of perfluorooctanoic acid, R(F)-palmitic acid-F13 and diethyl perfluorosuberate

A rationally designed perfluorinated host for the extraction of PFOA from water utilising non-covalent interactions

Three hosts for the encapsulation of perfluorooctanoic acid have been synthesized. The host:guest complexes have been characterized by multinuclear NMR spectroscopy in solution and the solid state.

Parahydrogen-induced polarization transfer to 19F in perfluorocarbons for 19F NMR spectroscopy and MRI

Fluorinated substances are important in chemistry, industry, and the life sciences. In a new approach, parahydrogen-induced polarization (PHIP) is applied to enhance (19)F MR signals of (perfluoro-n-hexyl)ethene and (perfluoro-n-hexyl)ethane. Unexpectedly, the end-standing CF3 group exhibits the highest amount of polarization despite the negligible coupling to the added protons. To clarify this non-intuitive distribution of polarization, signal enhancements in deuterated chloroform and acetone were compared and (19)F-(19)F NOESY spectra, as well as (19)F T1 values were measured by NMR spectroscopy. By using the well separated and enhanced signal of the CF3 group, first (19)F MR images of hyperpolarized linear semifluorinated alkenes were recorded.

Efficient photocatalytic decomposition of perfluorooctanoic acid by indium oxide and its mechanism

Perfluorooctanoic acid (C(7)F(15)COOH, PFOA) has increasingly attracted worldwide concerns due to its global occurrence and resistance to most conventional treatment processes. Though TiO(2)-based photocatalysis is strong enough to decompose most organics, it is not effective for PFOA decomposition. We first find that indium oxide (In(2)O(3)) possesses significant activity for PFOA decomposition under UV irradiation, with the rate constant about 8.4 times higher than that by TiO(2). The major intermediates of PFOA were C(2)-C(7) shorter-chain perfluorocarboxylic acids, implying that the reaction proceeded in a stepwise manner. By using diffuse reflectance infrared Fourier transform spectroscopy, (19)F magic angle spinning nuclear magnetic resonance, and electron spin resonance, we demonstrate that the terminal carboxylate group of PFOA molecule tightly coordinates to the In(2)O(3) surface in a bidentate or bridging configuration, which is beneficial for PFOA to be directly decomposed by photogenerated holes of In(2)O(3) under UV irradiation, while PFOA coordinates to TiO(2) in a monodentate mode, and photogenerated holes of TiO(2) preferentially transform to hydroxyl radicals, which are inert to react with PFOA. PFOA decomposition in wastewater was inhibited by bicarbonate and other organic matters; however, their adverse impacts can be mostly avoided via pH adjustment and ozone addition.

Aggregation of perfluoroctanoate salts studied by 19F NMR and DFT calculations: counterion complexation, poly(ethylene glycol) addition, and conformational effects

The aggregation of perfluoroctanoate salts in H(2)O is studied by (19)F NMR on solutions of LiPFO, NaPFO, and CsPFO, without and with the addition of two poly(ethylene glycol) (PEG) oligomers of molecular weight 1500 and 3400 Da, respectively, and with the addition of suitable crown ethers. The (19)F chemical shift (cs) trends are monitored, at 25 °C, in a concentration range including the critical micellar concentration (cmc) or, in the presence of PEG, the critical aggregation concentration (cac). The cac values in the samples with PEG are lower than the cmc values of the corresponding samples without PEG; moreover, the (19)F cs trends above the cac and above the polymer saturation concentration reveal and help to explain some peculiarities of the aggregation process of PEG on PFO micelles, which, in the first step, seems to occur while the surfactant concentration in water is still increasing. Also in LiPFO/H(2)O or NaPFO/H(2)O solutions containing 12-crown-4 or 15-crown-5 ethers, suitable to complex Li(+) or Na(+) ions, respectively, the cmc decreases. On the other hand, the micellization process in the presence of crown ethers does not show other peculiarities. The prevailing conformations of the PFO chain are discussed on the basis of quantum-mechanical calculations. The theoretical chemical shifts were computed at the DFT level of theory, taking into account the effects of the environment by means of the IEF-PCM method. The helical structure is the most stable one, but anti conformations are easily accessible, in both the aqueous and fluorinated environment. The comparison between computed and experimental chemical shifts indicates that anti conformations are more important in the micelles than in water and in CsPFO micelles than in LiPFO or NaPFO ones.

Determining the molecular interactions of perfluorinated carboxylic acids with human sera and isolated human serum albumin using nuclear magnetic resonance spectroscopy

Perfluorooctanoate (PFOA) is ubiquitous in North American human sera and has a serum half-life of 3.5 years in humans. The molecular interactions that lead to the bioaccumulation of these hydrophobic and lipophobic molecules in human blood are not well understood. Perfluorohexanoic acid (PFHxA) and PFOA were used as model perfluorinated carboxylic acids (PFCAs) to characterize the major site of PFCA interaction in human sera. Using novel heteronuclear saturation transfer difference nuclear magnetic resonance spectroscopy experiments, human serum albumin (HSA) was identified as the major site of interaction for both PFHxA and PFOA in human sera. Heteronuclear single quantum coherence nuclear magnetic resonance experiments were then performed to interrogate site-specific interactions of PFHxA and PFOA with isolated HSA. Perfluorohexanoic acid was found to bind specifically to Sudlow's drug-binding site II, whereas PFOA interacted preferentially with Sudlow's drug-binding site I at the lower concentration, with additional interactions developing at the higher concentration. These experiments highlight the utility of nuclear magnetic resonance spectrometry as a tool to observe the in situ interactions of chemical contaminants with biological systems. Both PFCAs displaced the endogenous HSA ligand oleic acid at concentrations lower than observed for the drugs ibuprofen and phenylbutazone, which are established HSA ligands. Interactions between PFCAs and HSA may affect the pharmacokinetics and distribution of fatty acids and certain drugs in the human body and warrant further investigation.

Binding of perfluorocarboxylates to serum albumin: a comparison of analytical methods

Perfluorochemicals are globally pervasive contaminants that are persistent, bioaccumulative, and toxic. Perfluorocarboxylic acids (PFCAs) with 8-13 carbons accumulate in the liver and blood of aquatic organisms; PFCA-protein interactions may explain this accumulation pattern. Here, the interactions between PFCAs with 8-11 carbons and serum albumin are examined using three experimental approaches: surface tension titrations, (19)F NMR spectroscopy, and fluorescence spectroscopy. Surface tension titrations indicate complex formation at high (mM) PFCA concentrations. Secondary association constants ranging from 10(2) to 10(4) M(-1) were determined from (19)F NMR titrations at high PFCA:albumin mole ratios. Fluorescence measurements indicate that PFCA-albumin interactions alter the protein conformation at low PFCA:albumin mole ratios (up to 5:1) and suggest two binding classes with association constants around 10(5) and 10(2) M(-1). While (19)F NMR and fluorescence provide both qualitative and quantitative information about PFCA-albumin interactions, surface tension provides only qualitative information. Limitations associated with instrumentation and methods require high PFCA concentrations in both surface tension and (19)F NMR experiments; in contrast, fluorescence allows for analysis of a wider range of PFCA concentrations and PFCA:albumin mole ratios. Results from this study indicate that fluorescence, though an indirect method, offers a more comprehensive picture of the nature of PFCA-albumin interactions.

Structure and orientation of small molecules dissolved in the liquid crystalline phases of CsPFO/water system by multinuclear NMR

Pyridine, L-alanine and L-phenylalanine dissolved in the liquid crystalline phases of the lyotropic system CsPFO/water are studied by means of (2)H, (13)C and (1)H NMR. The orientational order parameters of the solutes are determined in a wide temperature range, together with some relevant geometrical parameters. In particular, a prevailing conformation for L-phenylalanine interacting with the micelle is suggested and, for all solutes, convincing representations of their specific interactions with the micelle surface are inferred. From (19)F and (13)C NMR spectra in the nematic phase, the orientational order parameters for the perfluorooctanoate chain inside the micelles are estimated.