Selective C-C coupling at a Pt(IV) centre : 100% preference for sp2-sp3 over sp3-sp3

The oxidative addition of three different organic halides to the non-symmetric platinum(II) mer coordinated dicyclometallated C^N^C complex 1 yielded short-lived six-coordinate platinum(IV) complexes 2(R), with the incoming groups trans across the platinum centre. A spontaneous reductive coupling reaction then occurred with, in each case, a completely chemoselective sp2-sp3 coupling, and exclusively gave R-3, with the newly introduced R group bonded to the previously cyclometallated aryl ring. Following a recyclometallation reaction, the oxidative addition/reductive elimination cycle was repeated and gave the same selectivity. A one-pot route to doubly alkylating the aryl ring was developed. The observed selectivity might have been predicted on the normal basis of a steric barrier associated with non-flat sp3 hybridised groups, but we suggest that it arises from the stereochemistry at the metal, and the orientation of the ligands

One-step grafting of polymers to graphene oxide

The direct grafting of poly(N-isopropylacrylamide) to the basal plane of graphene oxide has been achieved in a single step: cleavage of the terminal thiocarbonylthio group on RAFT grown poly(N-isopropylacrylamide) reveals a reactive thiol that attacks the epoxides present across the surface of graphene oxide. The new composite material was characterised by a combination of SSNMR, FTIR, Raman, EDX, XPS, TGA and contact angle measurement; it shows enhanced thermal stability and solubility in water

Controlled electrochemical and electroless deposition of noble metal nanoparticles on graphene

Electrodeposition of nanoparticles on graphene is described, providing a convenient approach for making graphene–nanoparticle composites as well as insight into the electrochemical activity of graphene. To avoid complications due to surface contamination, chemical vapour deposition grown graphene was used directly on its copper growth substrate. We identify and isolate two nanoparticle growth processes for both silver and palladium deposition: electroless deposition that appears to occur preferentially at defects and edges next to the underlying copper, and conventional electrodeposition that occurs uniformly across the graphene surface. We show that control over electrodeposited nanoparticle size and number density can be achieved through varying electrodeposition conditions. The resultant nanoparticles are homogeneously dispersed across the graphene surface, suggesting that here both edge-plane and basal-plane graphene sites are electroactive. These results demonstrate that, as with other carbon nanostructures, electrodeposition is a powerful and flexible tool for forming functional composites with graphene

Impact of sequential surface-modification of graphene oxide on ice nucleation

Base-washed graphene-oxide which has been sequentially modified by thiol-epoxy chemistry, results in materials with ice nucleation activity. The role of hydro-philic/phobic grafts and polymers was evaluated with the most potent functioning at just 0.25 wt %. These 2-D hybrid materials may find use in cryopreservation and fundamental studies on ice formation

Trapping five-coordinate platinum(IV) intermediates

The oxidation of three different complexes of the doubly cycloplatinated 2,6-di(4-fluorophenyl)pyridine ligand (namely DMSO, PPh3 and PPr3 derivatives, 1a, 1b and 1c, respectively) with the electrophilic oxidant iodobenzenedichloride was studied. In each case oxidation can yield a simple trans-dichloro platinum(IV) complex (2(t)), which subsequently isomerises to the cis isomer (2(c)). However, by changing the solvent, or performing the reaction in the presence of an additional ligating species, a five-coordinate intermediate can be trapped out and isolated. Thus, cationic species with additional DMSO or pyridine coordinated could be collected for the DMSO and PPh3 derivatives. The PPr3 derivative traps out the reactive five-coordinate species with an agostic interaction that subsequently induces a transcyclometallation reaction to give a complex with a singly cyclometallated pyridine and a cyclometallated phosphine, which was characterised crystallographically

Concerted reductive coupling of an alkyl chloride at Pt(IV)

Oxidation of a doubly cyclometallated platinum(II) complex results in two isomeric platinum(IV) complexes. Whereas the trans isomer is robust, being manipulable in air at room temperature, the cis isomer decomposes at −20 °C and above. Reductive coupling of an alkyl chloride at the cis isomer gives a new species which can be reoxidised. The independence of this coupling on additional halide rules out the reverse of an SN2 reaction, leaving a concerted process as the only sensible reaction pathway

Non-covalent functionalization of graphene with a hydrophilic self-limiting monolayer for macro-molecule immobilization

Two different pyrene-substituted ions were used to render the surface of graphene hydrophilic. Self-limiting monolayers of ammonium and sulfonate substituted pyrenes were used to give, respectively, an overall positive and negative charge to the surface. Both pyrenes gave a stable hydrophilic surface and were used to selectively immobilise negatively or positively charged macro-molecules. This simple and versatile non-covalent approach can be used on graphene on a variety of substrates (e.g. copper, SiO2), suspended graphene, and also for graphite

Stir bar sorptive extraction coupled with GC/MS applied to honey: optimization of method and comparative study with headspace extraction techniques

The stir bar sorptive extraction (SBSE) techniques, coupled with gas chromatography–mass spectrometry, were successfully applied to the study of Eucalyptus honey’s for the determination of volatile organic compounds (VOCs). An optimization of the extraction method was carried out and the variables, NaCl concentration (used as matrix modifier), and the concentration of honey solution were studied targeting the whole VOCs composition. After the evaluation of the experiments, the best condition for the extraction of honey volatile components was 2 mol/L of NaCl and the more concentrated honey solution (0.5 g of honey per mL of water). Additionally, the results were compared with those obtained by two headspace (HS) techniques, namely solid-phase microextraction (SPME) and dynamic headspace (DHS). SBSE volatiles differ qualitatively and quantitatively from those obtained by the SPME and DHS methods. In any event, the chemical composition of Eucalyptus honey volatiles extracted by all three techniques shows the presence of some typical floral markers. Our results confirm a general trend reported in the literature, which show the higher sensitivity of SBSE in the extraction of less volatile compounds in comparison with HS methods

Identification and quantification of glucosinolates in different tissues of Raphanus raphanistrum by liquid chromatography tandem-mass spectrometry

This study aims to identify and quantify the glucosinolates from different parts of wild radish R. raphanistrum (leaves, flowers, fruits, roots) using liquid chromatography-tandem mass spectrometry. Glucoraphenin is the predominant compound, accounting for about 87% (w/w) of total glucosinolate content, followed by glucobrassicin, glucoraphasatin and glucoraphanin (153 mg 100 g−1, 149 mg 100 g−1 and 141 mg 100 g−1 FW, respectively) in fruits; followed by glucoraphasatin (3 mg 100 g−1 FW) in flowers and by glucobrassicin, 4-hydroxyglucobrassicin and glucoraphasatin (145 mg 100 g−1, 27 mg 100 g−1 and 24 mg 100 g−1 FW, respectively) in leaves. In roots the major glucosinolate is glucoraphasatin (56 mg 100 g−1 FW) followed by the glucoraphenin and methoxyglucobrassicin (16 mg 100 g−1 and 7 mg 100 g−1 FW, respectively). Principal component analysis allowed the discrimination of fruit samples from other parts of the plant for the majority of glucosinolates and the fruits are highlighted as sources of glucosinolates. The results are interesting given that wild radish is one of the most important weeds of crops in the Mediterranean region and is popular for home vegetable production and for its employment in human nutrition both as a food as well as for medicinal purposes

Acclimatization study of Tagetes lucida L. in Egypt and the chemical characterization of its essential oils

Seeds of Tagetes lucida were imported to Egypt from Canada and propagated under greenhouse conditions in peat moss media. Soil was sandy in texture and the irrigation system was dripping irrigation. The growth parameters were determined at five successive plant ages, fresh and dry weights of herb were determined at three successive plant ages. The yield of aerial parts after 175 days, was about 7.5 Mg/ha. The essential oil (EO) was extracted by hydro-distillation for three hours with a yield of about 0.5% (w/v). The EO of each sample was subjected to gas-chromatography/mass spectrometry analyses to study the chemical composition. The main component of the EO was identified as methyl chavicol which matched over 90% of the whole composition. Chlorophyll a and carotenes increased with increasing plant age in both sites and seasons. Flavonoids decreased with the development of plant age, while the opposite was true with coumarines content