Transition Metal Complexes of a Salen–Fullerene Diad: Redox and Catalytically Active Nanostructures for Delivery of Metals in Nanotubes

A covalently‐linked salen–C₆₀ (H₂L) assembly binds a range of transition metal cations in close proximity to the fullerene cage to give complexes [M(L)] (M=Mn, Co, Ni, Cu, Zn, Pd), [MCl(L)] (M=Cr, Fe) and [V(O)L]. Attaching salen covalently to the C₆₀ cage only marginally slows down metal binding at the salen functionality compared to metal binding to free salen. Coordination of metal cations to salen–C₆₀ introduces to these fullerene derivatives strong absorption bands across the visible spectrum from 400 to 630 nm, the optical features of which are controlled by the nature of the transition metal. The redox properties of the metal–salen–C₆₀ complexes are determined both by the fullerene and by the nature of the transition metal, enabling the generation of a wide range of fullerene‐containing charged species, some of which possess two or more unpaired electrons. The presence of the fullerene cage enhances the affinity of these complexes for carbon nanostructures, such as single‐, double‐ and multiwalled carbon nanotubes and graphitised carbon nanofibres, without detrimental effects on the catalytic activity of the metal centre, as demonstrated in styrene oxidation catalysed by [Cu(L)]. This approach shows promise for applications of salen–C₆₀ complexes in heterogeneous catalysis.     

Application of ultra-performance liquid chromatography-tandem mass spectrometry for the determination of steroid oestrogens in wastewaters

An ultra-performance liquid chromatography method using a triple quadrupole mass spectrometer was developed and validated for the determination of steroid oestrogens in wastewater matrices. To date, analytical methods established in the literature for 17α-ethinylestradiol have been unable to achieve the proposed predicted no effect concentration of 0.1?ng?l^?1. The extensive sample pretreatment and analytical methodology proposed herein enable 17α-ethinylestradiol to be determined at very low background concentrations with a theoretical method detection limit of 0.06?ng?l^?1 which has been applied in real environmental matrices. During the validation process, a trickling filter wastewater treatment works was monitored to demonstrate the method's application. Oestrogen removal across the filters demonstrated good removals of natural free oestrogens (≥62.0%) with lower removals of the synthetic oestrogen 17α-ethinylestradiol (29.2%) from wastewaters at 10°C. The method's application illustrates its capability of detecting oestrogen concentrations in real wastewater samples comprising complex organics of comparatively high concentration. Furthermore, a complete process mass balance for 17α-ethinylestradiol is now attainable which has previously posed a challenge owing to the low environmental concentrations typically exhibited, but more significantly as a result of the lower sensitivity inherent in previously reported analytical methods.     

Convenient preparations of racemic and enantiopure methyl 6-oxopipecolate

Short, convenient syntheses of racemic and enantiopure methyl 6-oxopipecolate are described, starting from either pipecolic acid or (S)-lysine respectively. The sequence for the latter compound relies upon improved methodology for the oxidation of C-6 of lysine.     

Sulfur-linked cyanobiphenyl-based liquid crystal dimers and the twist-bend nematic phase

ABSTRACT

The synthesis and characterisation of two series of cyanobiphenyl-based liquid crystal dimers containing sulfur links between the spacer and mesogenic units, the 4?-[1,ω-alkanediylbis(thio)]bis-[1,1?-biphenyl]-4-carbonitriles (CBSnSCB), and 4?-({ω-[(4?-cyano[1,1?-biphenyl]-4-yl)oxy]alkyl}thio)[1,1?-biphenyl]-4-carbonitriles (CBSnOCB) are described. The odd members of both series show twist-bend nematic and nematic phases, whereas the even members exhibit only the nematic phase. An analogous cyanoterphenyl-based dimer, 3⁴-{6-[(4?-cyano[1,1?-biphenyl]-4-yl)thio]-hexyl}[1¹,2¹:2⁴,3¹-terphenyl]-1⁴-carbonitrile (CT6SCB), is also reported and shows enantiotropic N_TB and N phases. The transitional properties of these dimers are discussed in terms of molecular curvature, flexibility and biaxiality. The same molecular factors also influence the birefringence of nematic phases. Resonant X-ray scattering studies of the twist-bend nematic phase at both the carbon and sulfur absorption edges were performed, which allowed for the determination of critical behaviour of the helical pitch at the transition to the nematic phase, the behaviour was found to be independent of molecular structure. It was also observed that despite the different molecular bending angle and flexibility, in all compounds the helical pitch length far from the N-N_TB transition corresponds to 4 longitudinal molecular distances.     

5‐Butyl‐4‐(4,4,5,5‐tetra­methyl‐1,3,2‐dioxaborolan‐2‐yl)‐3‐(2,4,6‐tri­methyl­phenyl)­isoxazole

A novel [3+2]‐cyclo­addition reaction of alkynyl­boronates and nitrile oxides gave the title compound, C₂₂H₃₂BNO₃, as a single regioisomer. The X‐ray crystal structure analysis of this compound shows two independent mol­ecules in the asymmetric unit, each with approximately coplanar isoxazole and boronate rings.     

A [2 + 2] cycloaddition route to dimethylaminomethylene vinamidinium salts

[reaction: see text] Trifluoropropanoic acid reacts with 1 equiv of POCl3 in DMF to generate the trifluoromethyl enamine (7). At this stage, two reaction manifolds are available. The expected reaction with additional POCl3 generates the 2-trifluoromethyl vinamidinium salt (3c). However, thermally driven loss of fluoride generates an iminium ion, which sets the stage for a [2 + 2] cycloaddition to ultimately generate the dimethylaminomethylene vinamidinium salt (1).     

A vibrational spectroscopic study of the adsorption of 4,4′-bipyridyl by sepiolite and smectite group clay minerals from Anatolia (Turkey)

The adsorption of 4,4-bipyridyl by natural sepiolite and smectite group clay minerals (bentonite, hectorite and saponite) from Anatolia (Turkey) has been studied using vibrational spectroscopy. Investigation of Fourier-transform infrared and Fourier-transform Raman spectra of adsorbed 4,4-bipyridyl indicate the presence of chemisorbed species. However, any evidence for the generation of anionic species on the surface of the phyllosilicates has not been detected. It is proposed that the adsorbed bipyridyl molecules on sepiolite are centrosymmetric and H-bonded to the surface hydroxyls through both the nitrogen lone pairs as bidentate ligands. The adsorbed bipyridyl molecules on the smectite group clays are coordinated to exchangeable cations both directly and also indirectly through water as monodentate ligands. XRD patterns of the clays studied are also recorded.     

Non-linear dielectric spectroscopy: antifouling and stabilisation of electrodes by a polymer coating

Non-linear dielectric spectroscopy (NLDS) has previously been shown to produce quantitative information that is indicative of the metabolic state of various organisms, by modeling the non-linear effects of their membranous enzymes on an applied oscillating electromagnetic field using supervised multivariate analysis methods. However, the instability of the characteristics of the measuring apparatus rendered the process temperamental at best in the laboratory and impractical for field use. The main practical problem, of the non-stationarity of the electrode-solution interface and the ease with which the electrode surfaces are subject to protein fouling. It is addressed by applying a thin, electrically transparent antifouling coat to the electrodes. This reduces the interminable cleaning procedures previously required to prepare the electrodes for use, increases their usable lifetime before recleaning, and also improves the precision and linearity of multivariate models on NLDS data.     

Palladium catalysed cyclisation-carbonylation of enynes to give cyclic gamma,delta-unsaturated acids

In the presence of acetic acid, trifurylphosphine and CO (2 atm), palladium catalyses the conversion of a range of enynes to cyclic delta,gamma-unsaturated carboxylic acids in good yield.