Reactivity of bi- and monometallic trifluoroacetates towards amorphous SiO2.

The reactivity of alkali-manganese(II) and alkali trifluoroacetates towards amorphous SiO2 (a-SiO2) was studied in the solid-state. K4Mn2(tfa)8, Cs3Mn2(tfa)7(tfaH), KH(tfa)2, and CsH(tfa)2 (tfa = CF3COO-) were thermally decomposed under vacuum in fused quartz tubes. Three new bimetallic fluorotrifluoroacetates of formulas K4Mn3(tfa)9F, Cs4Mn3(tfa)9F, and K2Mn(tfa)3F were discovered upon thermolysis at 175 °C. K4Mn3(tfa)9F and Cs4Mn3(tfa)9F feature a triangular-bridged metal cluster of formula [Mn3(µ3-F)(µ2-tfa)6(tfa)3]4-. In the case of K2Mn(tfa)3F, fluoride serves as an inverse coordination center for the tetrahedral metal cluster K2Mn2(µ4-F). Fluorotrifluoroacetates may be regarded as intermediates in the transformation of bimetallic trifluoroacetates to fluoroperovskites KMnF3, CsMnF3, and Cs2MnF4, which crystallized between 250 and 600 °C. Decomposition of these trifluoroacetates also yielded alkali hexafluorosilicates K2SiF6 and Cs2SiF6 as a result of the fluorination of fused quartz. The ability to fluorinate fused quartz was observed for monometallic alkali trifluoroacetates as well. Hexafluorosilicates and heptafluorosilicates K3SiF7 and Cs3SiF7 were obtained upon thermolysis of KH(tfa)2 and CsH(tfa)2 between 200 and 400 °C. This ability was exploited to synthesize fluorosilicates under air by simply reacting alkali trifluoroacetates with a-SiO2 powder.

Synthesis, Structure, and Luminescence of Mixed-Ligand Lanthanide Trifluoroacetates.

A series of new mixed-ligand lanthanide trifluoroacetates of formula Ln(4-cpno)(tfa)3(H2O)·H2O (Ln = Sm, Eu, Gd, Tb, Dy; 4-cpno = 4-cyanopyridine N-oxide; tfa = trifluoroacetate) is reported. Trifluoroacetates were synthesized as chemically pure polycrystalline solids and their crystal structures were probed using single-crystal and powder X-ray diffraction. Ln(4-cpno)(tfa)3(H2O)·H2O solids make up an isostructural series in which LnO8 polyhedra are bridged by 4-cpno to form edge-sharing dimers. Trifluoroacetato connects these dimers to yield chains whose three-dimensional packing is governed by hydrogen bonds established between 4-cpno, trifluoroacetato, and water. 4-cpno serves as an efficient sensitizer of lanthanide-centered luminescence. UV excitation of its singlet manifold and subsequent energy transfer to the 4f levels of the lanthanides yield orange (Sm), red (Eu), green (Tb), and yellow (Dy) emissions. Sensitization efficiencies reach 81 and 64% for Eu and Tb hybrids, respectively. Tb(4-cpno)(tfa)3(H2O)·H2O displays a quantum yield of 52%, which coupled to the high absorptivity of 4-cpno, makes it a bright-green emitter under 292 nm excitation. Lanthanide trifluoroacetates may therefore serve as hybrid solid-state light emitters provided that adequate sensitizers are identified.

Permanganate Oxidation of Microcystin-LA: Kinetics, Quantification, and Implications for Effective Drinking Water Treatment.

Permanganate pretreatment of drinking water is effective in transforming dissolved, noxious contaminants and in reducing halogenated by-products. Permanganate targets specific compounds such as taste and odor compounds, disinfection precursors, manganese, and natural organic contaminants that are not removed readily by conventional treatment alone. Cyanobacterial blooms (cHABs) can increase disinfection by-product precursors as well as the cyanotoxin, microcystin (MC), a potent liver toxin. MC toxicity is conferred by a unique, conserved amino acid, Adda, that inhibits protein phosphatase 1 and 2A. Although over 150 MC congeners have been reported, thousands of MCs are statistically possible. Over the last ten years, one congener, MC-LA, has been reported with increasing frequency, making it one of the most common cyanotoxins identified in North American freshwater systems; yet its oxidation has not been widely studied. Frequently, Adda specific enzyme-linked immunosorbent assay (ELISA) and protein phosphatase inhibition assay (PPIA) are used to quantitate total MCs to evaluate treatment efficiency and exposure. Anecdotal reports suggest that MC degradation products can cause interference with the Adda-ELISA. MC-LA was used as the model MC compound in this study. PPIA quantitation of MC-LA in water agreed with liquid chromatography high resolution mass spectrometry (LC/HRMS), whereas the ELISA quantitation did not agree with LC/HRMS quantitation. We determined the second order rate constant for MC-LA as 118 ± 9 M-1 s-1, the activation energy to be 21.2 kJ mol-1, and the rate to be independent of pH between pH 6 and 9. Ten oxidation products (OPs) were observed by LC/HRMS and three primary reaction pathways are proposed. The reaction pathways were used to explain differences in the quantification by Adda-ELISA, HRMS, and PPIA. The oxohydroxylation of MC-LA produced two major OPs, C46H67N7O14 [M+H] + = 942.4819 and C46H69N7O15 [M+H]+ =960.4925. Major OPs may contain an unmodified Adda and are the likely cause of interference with the Adda-ELISA. Several governmental agencies recommend the use of the Adda-ELISA to determine the MC quantitation for treatment efficiency and customer exposure; yet our results suggest that these or other OPs interfere with the Adda-ELISA causing artificially high values for total MCs.

Rubidium-Alkaline-Earth Trifluoroacetate Hybrids as Self-Fluorinating Single-Source Precursors to Mixed-Metal Fluorides.

Three novel bimetallic hybrid crystals featuring rubidium-alkaline-earth metal pairs and trifluoroacetato ligands were synthesized, and their utility as self-fluorinating single-source precursors to the corresponding mixed-metal fluorides was demonstrated. Rb2Mg2(tfa)6(tfaH)2·3H2O, RbCa(tfa)3, and RbSr2(tfa)5 (tfa = CF3COO-; tfaH = CF3COOH) were synthesized in both single-crystal and polycrystalline forms via solvent evaporation. Their crystal structures were solved using single-crystal X-ray diffraction (XRD), and chemical purity was confirmed using thermal analysis (TGA/DTA). Metal-oxygen-metal connectivity in Rb2Mg2(tfa)6(tfaH)2·3H2O was restricted to four-metal building blocks. In contrast, RbCa(tfa)3 and RbSr2(tfa)5 were found to be extended inorganic hybrids ( Cheetham et al. Chem. Commun. 2006 , 0 , 4780 - 4795 ) exhibiting infinite metal connectivity in three and two dimensions, respectively. Systematic analysis of the coordination modes of the trifluoroacetato ligand revealed its ability to bridge alkali and alkaline-earth metals. Rietveld analysis of powder X-ray diffraction data (PXRD) showed that thermal decomposition of Rb2Mg2(tfa)6(tfaH)2·3H2O and RbCa(tfa)3 under inert atmosphere yielded crystalline RbMgF3 and RbCaF3, respectively. This solid-state transformation occurred without the need for an external fluorinating agent because the trifluoromethyl group acted as a built-in fluorine source. Solid-state and solution thermolysis of Rb2Mg2(tfa)6(tfaH)2·3H2O provided access to the hexagonal and cubic polymorphs of the fluoroperovskite RbMgF3, respectively. Findings reported in this article highlight that bimetallic trifluoroacetates offer unique features from the standpoint of both crystal lattice topology and reactivity.

Low-Symmetry Mixed Fluorinated Subphthalocyanines as Fluorescence Imaging Probes in MDA-MB-231 Breast Tumor Cells.

Boron subphthalocyanines (SPcs) are aromatic macrocycles that possess a combination of physical and optical properties that make them excellent candidates for application as fluorescent imaging probes. These molecules have intense electronic absorption and emission, and structural versatility that allows for specific tuning of physical properties. Herein, we report the synthesis of a series of low-symmetry fluorinated SPcs and compare them to analogous compounds with varying numbers of peripheral fluorine atoms and varied aromaticity. Across the series, with increasing addition of fluorine atoms to the periphery of the ring, a downfield chemical shift in 19F NMR and a bathochromic shift of electronic absorption were observed. Expanding the size of the aromatic ring by replacing peripheral benzo- groups with naphtho- groups prompted a far more drastic bathochromic shift to absorption and emission. Fluorescence quantum yields (Φf) proved to be sufficiently high to observe intracellular fluorescence from MDA-MB-231 breast tumor cells in vitro by epifluorescence microscopy; fluorination proved vital for this purpose to improve solubility. This report lays the groundwork for the future development of these promising SPcs for their ultimate application as near-infrared (NIR) fluorescent imaging probes in biological systems.