Intramolecular Fluorocyclizations of Unsaturated Carboxylic Acids with a Stable Hypervalent Fluoroiodane Reagent

A new class of fluorinated lactones was prepared by the intramolecular fluorocyclizations of unsaturated carboxylic acids by using the stable fluoroiodane reagent in combination with AgBF₄. This unique reaction incorporates a cyclization, an aryl migration, and a fluorination all in one step. The fluoroiodane reagent, prepared easily from fluoride, can also be used without a metal catalyst to give moderate yields within just 1 hour, thus demonstrating that it is a suitable reagent for developing new ¹⁸F‐labelled radiotracers for PET imaging.     

Supramolecular self-assembly of water-soluble cavitands: investigated by molecular dynamics simulation

In this study, we have examined supramolecular self-assembly process of a hydrophobic guest with a water-soluble host known by the trivial name octa acid (OA). Two octa acids form a capsular assembly only in presence of a nonpolar guest(s). Size and shape of the guest control the stoichiometry of the capsular complex. Here, all atom molecular dynamics simulation has been utilized to investigate complex formation mechanisms of a nonpolar guest (nonylbenzene) with two OA cavitands. Nonylbenzene was encapsulated into the nonpolar cavity of OA capsule owing to solvophobic interactions. Upon encapsulation it was twisted and bent due to lack of free space within the capsule. These unusual forms obtained from the simulation study were in accord with experimental findings. The post-complexation attributes of the guest were regulated by the available free space within the OA and favorable non-covalent interactions between the guest and the walls of the OA capsule. In the identical simulation condition two OA cavitands did not form a capsule without a guest, thus indicating requirement of a guest during the self-assembly of OA cavitands.     

Mechanically induced scission and subsequent thermal remending of perfluorocyclobutane polymers

Perfluorocyclobutane (PFCB) polymer solutions were subjected to pulsed ultrasound, leading to mechanically induced chain scission and molecular weight degradation. (19)F NMR revealed that the new, mechanically generated end groups are trifluorovinyl ethers formed by cycloreversion of the PFCB groups, a process that differs from thermal degradation pathways. One consequence of the mechanochemical process is that the trifluorovinyl ether end groups can be remended simply by subjecting the polymer solution to the original polymerization conditions, that is, heating to >150 °C. Stereochemical changes in the PFCBs, in combination with radical trapping experiments, indicate that PFCB scission proceeds via a stepwise mechanism with a 1,4-diradical intermediate, offering a potential mechanism for localized functionalization and cross-linking in regions of high stress.     

Factors that affect quantification of diode array data in comprehensive two-dimensional liquid chromatography using chemometric data analysis

There has been a tremendous increase in research on comprehensive two dimensional LC (LC×LC); however, to date, the central analytical issue, quantification, has received only minimal attention. It is vital to the further development of LC×LC that a greater understanding of the specific factors affecting peak quantification in LC×LC be attained. This work focuses on the following factors: data complexity, retention time shifting, dynamic range issues, chromatographic and spectral peak overlap and difficulties related to background signal removal. The above mentioned factors that affect peak quantification are investigated using fourteen replicate analyses of a urine sample, representing the effects of such factors when analyzing samples in complex matrices. We demonstrate that quantification of LC×LC data is improved following implementation of chemometric techniques that minimized the deleterious effects on quantification due to chromatographically overlapped peaks, retention time shifting and background signal interference. The chemometrically resolved data shows a 2.5-fold increase in precision of quantification over the quantification of the raw data. It is also demonstrated that the method quantifies sixteen peaks that were not visually evident prior to chemometric analysis. The purpose of this paper is to determine the impact of these issues on the effectiveness of LC×LC as a technique for the quantitative analysis of complex samples.     

The solubility of oxygen in aqueous fluorocarbon emulsions

The solubility of oxygen in aqueous fluorocarbon emulsions has been measured directly for several perfluorocarbons and monobromo or monoiodo-perfluorocarbons. The measured oxygen solubilities are consistent with results for the solubility of oxygen in neat liquid perfluorinated organic compounds.     

The influence of Al(III) supersaturation and NaOH concentration on the rate of crystallization of Al(OH)3 precursor particles from sodium aluminate solutions

The growth kinetics of colloidal Al(III)-containing particles (diameter<1000 nm), nucleated in optically clear, supersaturated sodium aluminate solutions as a precursor to Al(OH)(3) crystals, has been studied using dynamic light scattering. Two series of solutions were examined at 22 degrees C to determine the influence of Al(III) supersaturation and NaOH concentration on the initial particle growth behavior. One solution series consisted of solutions with constant Al(III) absolute supersaturation (DeltaC) of 1.48 M and [NaOH] range 1.83-4.00 M ([NaOH]/[Al(III)]=1.13-2.15) and Al(III) relative supersaturation (sigma)=3.86-10.36. The other solution series had a constant sigma of 7.55 and [NaOH] range of 1.50-4.27 M ([NaOH]/[Al(III)]=1.18-1.54) and DeltaC=0.86-3.19. The correlation between the initial particle growth rates and supersaturation (DeltaC or sigma) revealed marked anomalies over the entire supersaturation range studied. The growth rate remained substantially constant in the DeltaC range 0.86-2.55 M (for the constant sigma solution series), before increasing sharply upon a further increase of DeltaC beyond 2.55 M. The variation of the growth rate with sigma in the range 3.86-9.00 (for the constant DeltaC solution series) was remarkably weak, contrary to expectation. At higher sigma (>9.00), however, a marked increase in growth rate with increasing sigma was displayed. At constant DeltaC or sigma, the growth rate showed a strong variation with NaOH concentration, indicating that Na(+) and OH(-) species play a pivotal role in the Al(OH) precursor particles (nuclei) growth process. Furthermore, the kinetics of growth displayed by these nanosized particles are an order of magnitude slower than those observed for macroscopic gibbsite (gamma-Al(OH)(3)) crystals at similar supersaturations and temperature. The difference may be rationalized in terms of particle size and Al(OH)(3) dimorphic phase dependent solubility effects. An empirically adequate growth kinetics modeling was achieved when the growth rates were correlated with the Al(III) supersaturation (DeltaC or sigma) and the excess (free) NaOH concentration, rather than the former alone, as is commonly the case. A critical [NaOH]/[Al(III)] molar ratio of 1.27-1.35, below which the particle growth rate increased markedly and above which the rate was significantly reduced, was observed. This behavior is believed to be linked to solution speciation change that occurs at certain Al(III) and NaOH compositions.