Synthesis and Photophysics of a New Family of Fluorescent 9‐Alkyl‐Substituted Xanthenones

9‐Alkyl xanthenones with different aliphatic pendant groups have been easily prepared by means of nucleophilic addition of the corresponding Grignard derivative to a tert‐butyldimethylsilyl ether (TBDMS)‐protected 3,6‐dihydroxy‐xanthenone. The photophysical behavior of the new dyes has been explored by using absorption, steady‐state‐, and time‐resolved fluorescence measurements. We determined the equilibrium constants, visible spectral characteristics, fluorescence quantum yield, and decay times. Remarkably, they retain similar fluorescent properties of fluorescein including the characteristic phosphate‐mediated excited‐state proton‐transfer (ESPT) reaction. 6‐Hydroxy‐9‐isopropyl‐3H‐xanthen‐3‐one ( 5 ) was investigated in living cells; it presented a good permeability and efficient accumulation inside the cytosol. For the first time, we reported that the requirement of an aryl group at C‐9 is no longer needed and new fluorescent sensors can be therefore easily developed.     

Coordination Chemistry of Cyclopropenylidene‐Stabilized Phosphenium Cations: Synthesis and Reactivity of Pd and Pt Complexes

A straightforward synthesis of cyclopropenylidene‐stabilized phosphenium cations 1 a – g through the reaction of [(iPr₂N)₂C₃⁺Cl]BF₄ with secondary phosphines is described. Their donor ability was evaluated by analysis of the CO stretching frequency in Rh complexes [RhCl(CO)L₂](BF₄)₂ and electrochemical methods. The cyclopropenium ring induces a phosphite‐type behavior that can be tuned by the other two substituents attached to the phosphorus atom. Despite of the positive charge that they bear, phosphenium cations 1 a – g still act as two‐electron donor ligands, forming adducts with Pd^II and Pt^II precursors. Conversely, in the presence of Pd⁰ species, an oxidative insertion of the Pd atom into the C_carbene–phosphorus bond takes place, providing dimeric structures in which each Pd atom is bonded to a cyclopropenyl carbene while two dialkyl/diaryl phosphide ligands serve as bridges between the two Pd centers. The catalytic performance of the resulting library of Pt^II complexes was tested; all of the cationic phosphines accelerated the prototype 6‐endo‐dig cyclization of 2‐ethynyl‐1,1′‐biphenyl to afford pentahelicene. The best ligand 1 g was used in the synthesis of two natural products, chrysotoxene and epimedoicarisoside A.     

Experimental and Theoretical Studies on Arene‐Bridged Metal–Metal‐Bonded Dimolybdenum Complexes

The bis(hydride) dimolybdenum complex, [Mo₂(H)₂{HC(N‐2,6‐iPr₂C₆H₃)₂}₂(thf)₂], 2 , which possesses a quadruply bonded Mo₂^II core, undergoes light‐induced (365 nm) reductive elimination of H₂ and arene coordination in benzene and toluene solutions, with formation of the Mo^I₂ complexes [Mo₂{HC(N‐2,6‐iPr₂C₆H₃)₂}₂(arene)], 3?C₆H₆ and 3?C₆H₅Me , respectively. The analogous C₆H₅OMe, p‐C₆H₄Me₂, C₆H₅F, and p‐C₆H₄F₂ derivatives have also been prepared by thermal or photochemical methods, which nevertheless employ different Mo₂ complex precursors. X‐ray crystallography and solution NMR studies demonstrate that the molecule of the arene bridges the molybdenum atoms of the Mo^I₂ core, coordinating to each in an η² fashion. In solution, the arene rotates fast on the NMR timescale around the Mo₂‐arene axis. For the substituted aromatic hydrocarbons, the NMR data are consistent with the existence of a major rotamer in which the metal atoms are coordinated to the more electron‐rich C?C bonds.     

Isolation and Immobilization of Influenza Virus-Specific N-SA-α-2,3-Gal Receptors Using Magnetic Nanoparticles Coated with Chitosan and Maackia amurensis Lectin

Avian influenza viruses preferentially bind to sialic acid alpha-2,3-galactose (N-SA-α-2,3-Gal) receptors on epithelial cells. Herein, we describe a procedure we have developed for isolation of N-SA-α-2,3-Gal receptors from porcine trachea using magnetic nanoparticles (NPs) coated with chitosan (NP-Ch) and functionalized with Maackia amurensis lectin (NP-lectin). Magnetic nanoparticles were coated with chitosan in a one-step co-precipitation, and then M. amurensis lectin was immobilized covalently using glutaraldehyde. Lectin coated nanoparticles were incubated with sialic acid enriched fraction of tracheal homogenate, and N-SA-α-2,3-Gal receptor was extracted under magnetic field in two cycles. The presence of 66.4 kDa protein was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The interaction of immobilized receptor (NP-Ch-R) with M. amurensis lectin (NP-Ch-R-L) was demonstrated by Fourier transform infrared spectrometry (FTIR) and thermogravimetric analysis (TGA).     

Synthesis of a truncated tetradenolide

The enantiopure synthesis of a truncated tetradenolide is presented. Starting from the versatile Chiron 7,3-lactone-xylofuranose derivative (7,3-LXF), the enantiomerically pure synthesis of the title compound is obtained in six steps with a 40% overall yield.     

Distance-Dependent Electron Transfer Kinetics in Axially Connected Silicon Phthalocyanine-Fullerene Conjugates

The effect of donor-acceptor distance in controlling the rate of electron transfer in axially linked silicon phthalocyanine-C₆₀ dyads has been investigated. For this, two C₆₀-SiPc-C₆₀ dyads, 1 and 2 , varying in their donor-acceptor distance, have been newly synthesized and characterized. In the case of C₆₀-SiPc-C₆₀ 1 where the SiPc and C₆₀ are separated by a phenyl spacer, faster electron transfer was observed with k_cs equal to 2.7×10⁹ s⁻¹ in benzonitrile. However, in the case of C₆₀-SiPc-C₆₀ 2 , where SiPc and C₆₀ are separated by a biphenyl spacer, a slower electron transfer rate constant, k_cs=9.1×10⁸ s⁻¹, was recorded. The addition of an extra phenyl spacer in 2 increased the donor-acceptor distance by ∼4.3 Å, and consequently, slowed down the electron transfer rate constant by a factor of ∼3.7. The charge separated state lasted over 3 ns, monitoring time window of our femtosecond transient spectrometer. Complimentary nanosecond transient absorption studies revealed formation of ³SiPc* as the end product and suggested the final lifetime of the charge separated state to be in the 3–20 ns range. Energy level diagrams established to comprehend these mechanistic details indicated that the comparatively high-energy SiPc^.+-C₆₀^.− charge separated states (1.57 eV) populated the low-lying ³SiPc* (1.26 eV) prior returning to the ground state.     

Dissipation of the herbicide active ingredient glyphosate in natural water samples in the presence of biofilms

Dissipation of the herbicide active ingredient glyphosate was investigated in natural waters. To assess combined effects, glyphosate was applied in its pure form (glyphosate isopropylammonium salt) and in preparation Roundup Classic® formulated with polyethoxylated tallowamines (POEA). Standing and running surface water samples originated from Lake Balaton and River Danube between early May and mid-June of 2015. The kinetics of dissipation of glyphosate, measured by high-performance liquid chromatography combined with UV-VIS absorbance detection or tandem mass spectrometry, was investigated under laboratory conditions in aquaria with or without the presence of biofilms. The quantity and the biofilm structure of algal biomass were determined by in vivo fluorimetry and scanning electron microscopy. The presence of POEA affected the dissipation of glyphosate, and dissipation profiles differed in the investigated natural waters. Significantly higher initial concentrations of glyphosate were measured in River Danube for treatment with formulated glyphosate (101.4 ± 6.2 µg L^?1), than with glyphosate alone (79.9 ± 6.6 µg L^?1), and dissipation to a residual level (57.6 ± 1.4 µg L^?1) consequently took longer (approximately by 1 day). Degradation of glyphosate from the initial level (91.24 ± 5.9 µg L^?1) in Lake Balaton was not detected. Phytotoxic effects of glyphosate, particularly if enhanced by a formulant on algal biomass, were observed. Thus, 5–18% and 11–33% of algal biomass reduction was determined in River Danube upon treatments with glyphosate and Roundup Classic®, respectively. Corresponding biomass decreases in Lake Balaton were 1.3–13% and 9–14%, respectively, accompanied by an overall decay in the algal biofilms. In River Danube, treatments resulted in the occurrence of 1.4–5.8% of green algae in the algal biomass in 28 days, while green algae were not detected in the untreated control. The results indicate that glyphosate is capable of modifying the structure of the algal community and to induce increased secretion of extracellular polymeric substances matrix in the biofilms assessed.     

Mechanically Interlocked Single‐Wall Carbon Nanotubes

Extensive research has been devoted to the chemical manipulation of carbon nanotubes. The attachment of molecular fragments through covalent‐bond formation produces kinetically stable products, but implies the saturation of some of the C? C double bonds of the nanotubes. Supramolecular modification maintains the structure of the SWNTs but yields labile species. Herein, we present a strategy for the synthesis of mechanically interlocked derivatives of SWNTs (MINTs). In the key rotaxane‐forming step, we employed macrocycle precursors equipped with two π‐extended tetrathiafulvalene SWNT recognition units and terminated with bisalkenes that were closed around the nanotubes through ring‐closing metathesis (RCM). The mechanically interlocked nature of the derivatives was probed by analytical, spectroscopic, and microscopic techniques, as well as by appropriate control experiments. Individual macrocycles were observed by HR STEM to circumscribe the nanotubes.