η1-Allylpalladium complexes with a tridentate PNP ligand with different phosphino groups

The iminodiphosphine 2-(PPh2)C6H4-1-CHvNC6H4-2-(PPh2) (P–N–P′) is used for the preparation of the complexes [Pd(η1-CHR1–CHvCR2R3)(P–N–P′)]BF4 [R1 = R2 = R3 = H: (1); R1 = R2 = Ph, R3 = H: (2); R1 = R3 = H, R2 = Ph: (3); R1 = H, R2 = R3 = Me: (4)]. The P–N–P′ tridentate coordination and the η1-allyl bonding mode in the solid are confirmed by the X-ray structural analysis of 1. In solution, the complexes 1 and 2 undergo an η1–η3–η1 rearrangement at 298 K interconverting the bonding site of the allyl group. A five-coordinate structure with the phosphine ligands in the axial position is proposed for the η3-allyl intermediate. For the dynamic process, a ΔG≠ value of 53.8 kJ mol−1 is obtained from 1H NMR data of 2. In 3 and 4, the allyl ligand is rigidly bound to the metal through the less substituted terminus, in line with the higher free energy content of the corresponding isomers: [Pd(η1-CHPh– CHvCH2)(P–N–P′)]+ +48.78 kJ mol−1; [Pd(η1-CMe2–CHvCH2)(P–N–P′)]+ +69.35 kJ mol−1. The complexes react with secondary amines in the presence of fumaronitrile at different rates yielding allylamines and the palladium(0) derivative [Pd(η2-fn)(P–N–P′)] (5). On the basis of charge distribution on the allylic carbon atoms and of steric factors, the difference in rate and the regioselectivity in the amination of 1–3 are better rationalized by a mechanism with nucleophilic attack at the η3-intermediate rather than by an SN2 mechanism with nucleophilic attack at the Pd–CHR1 carbon atom. The high regioselectivity in the reaction of 4 with piperidine implies an SN2′ mechanism with nucleophilic attack at the CMe2 allyl carbon. A dynamic process occurs also for the 18-electron complex 5 consisting in a dissociation–association equilibrium of the olefin

[PdCl2{8-(di-tert-butylphosphinooxy)quinoline)}]: a highly efficient catalyst for Suzuki-Miyaura reaction

The complex [PdCl2(P-N)] containing the basic and sterically demanding 8-(di-tert-butylphosphinooxy)quinoline ligand (P-N) is a highly efficient catalyst for the coupling of phenylboronic acid with aryl bromides or aryl chlorides. The influence of solvent and base has been investigated, the highest rates being observed at 110 C in toluene with K2CO3 as the base. With aryl bromides the reaction rates are almost independent on the electronic properties of the para aryl substituents, on the contrary, reduced reaction rates are observed when bulky substituents are present on the substrate. Nevertheless the coupling of 2-bromo-1,3,5-trimethylbenzene with phenylboronic acid can be carried out to completion in 2 h using a catalyst loading of 0.02 mol %. Under optimized reaction conditions, turnover frequencies as high as 1900 h(-1) can be obtained in the coupling of 4-chloroacetophenone with phenylboronic acid: lower reaction rates are obtained with Substrates bearing EDG substituents on the aryl group. (C) 2009 Elsevier Ltd. All rights reserved

Colorimetric and fluorescent sensing of copper ions in water through o-phenylenediamine-derived carbon dots

Fluorescent nitrogen and sulfur co-doped carbon dots (NSCDs) were synthesized using a simple one-step hydrothermal method starting from o-phenylenediamine (OPD) and ammonium sulfide. The prepared NSCDs presented a selective dual optical response to Cu(II) in water through the arising of an absorption band at 660 nm and simultaneous fluorescence enhancement at 564 nm. The first effect was attributed to formation of cuprammonium complexes through coordination with amino functional groups of NSCDs. Alternatively, fluorescence enhancement can be explained by the oxidation of residual OPD bound to NSCDs. Both absorbance and fluorescence showed a linear increase with an increase of Cu(II) concentration in the range 1-100 mu M, with the lowest detection limit of 100 nM and 1 mu M, respectively. NSCDs were successfully incorporated in a hydrogel agarose matrix for easier handling and application to sensing. The formation of cuprammonium complexes was strongly hampered in an agarose matrix while oxidation of OPD was still effective. As a result, color variations could be perceived both under white light and UV light for concentrations as low as 10 mu M. Since these color changes were similarly perceived in tap and lake water samples, the present method could be a promising candidate for simple, cost-effective visual monitoring of copper onsite

Two different acid oxidation syntheses to open C60 fullerene for heavy metal detection

Graphene oxide quantum dots (GOQDs) can be synthesized through a large variety of synthesis methods starting from different carbon allotropes such as nanotubes, graphite, C60 and exploiting various synthesis and reactions. These different approaches have great influence on the properties of the obtained materials, and, consequently, on the potential applications. In this work, Buckminster C60 fullerene has been used to prepare unfolded fullerene nanoparticles (UFNPs) via two distinct synthesis methods namely: Hummer and H2 SO4 + HNO3 solution. The different characteristics of the final materials and the different response in the presence of heavy metal ions have been investigated in view of sensing applications of water contamination

Exogenous Control over Intracellular Acidification: Enhancement via Proton Caged Compounds Coupled to Gold Nanoparticles

The pH regulation has a fundamental role in several intracellular processes and its variation via exogenous compounds is a potential tool for intervening in the intracellular processes. Proton Caged Compounds (PPCs) release protons upon UV irradiation and may efficiently provoke intracellular on-command acidification. Here, we explore the intracellular pH variation, when purposely synthesized PCCs are coupled to gold nanoparticles (AuNPs) and dosed to HEK-293 cells. We detected the acidification process caused by the UV irradiation by monitoring the intensity of the asymmetric stretching mode of the CO2 molecule at 2343 cm-1. The comparison between free and AuNPs functionalized proton caged compound demonstrates a highly enhanced CO2 yield, hence pH variation, in the latter case. Finally, PCC functionalized AuNPs were marked with a purposely synthesized fluorescent marker and dosed to HEK-293 cells. The corresponding fluorescence optical images show green grains throughout the whole cytoplasm

Characterization for biofilm-forming cyanobacteria for biomass and lipid production

Aims: This work reports on one of the first attempts to use biofilm-forming cyanobacteria for biomass and lipid production. Methods and Results: Three isolates of filamentous cyanobacteria were obtained from biofilms at different Italian sites and characterized by a polyphasic approach, involving microscopic observations, ecology and genetic diversity (studying the 16S rRNA gene). The isolates were grown in batch systems and in a semi-continuous flow incubator, specifically designed for biofilms development. Culture system affected biomass and lipid production, but did not influence the fatty acid profile. The composition of fatty acids was mainly palmitic acid (>50%) and less amounts of other saturated and monounsaturated fatty acids. Only two isolates contained two polyunsaturated fatty acids. Conclusions: Data obtained from the flow-lane incubator system would support a more economical and sustainable use of the benthic microorganisms for biomass production. The produced lipids contained fatty acids suitable for a high-quality biodiesel production, showing high proportions of saturated and monounsaturated fatty acids. Significance and Impact of the Study: Data seem promising when taking into account the savings in cost and time derived from easy procedures for biomass harvesting, especially when being able to obtain the co-production of other valuable by-products

Phosphorus and metal removal combined with lipid production by the green microalga Desmodesmus sp.: An integrated approach

This work focused on the potential of Desmodesmus sp. to be employed for wastewater 15 bioremediation and biodiesel production. The green microalga was grown in a culture medium with a phosphorus (P) content of 4.55 mg L-1 16 simulating an industrial effluent; it was also exposed to a bimetal solution of copper (Cu) and nickel (Ni) for 2 days. P removal was between 94 and 100%. After 2 days of exposure to metals, 94% of Cu and 85% of Ni were removed by Desmodesmus sp. Adsorption tests showed that the green microalga was able to remove up to 90% of Cu and 43% of Ni in less than 30 minutes. The presence of metals decreased the lipid yield, but biodiesel quality from the biomass obtained from metal exposed samples was higher than that grown without metals. This result revealed that this technology could offer a new alternative solution to environmental pollution and carbon-neutral fuel generation

Kinetic Studies of the Oxidative Addition and Transmetallation Steps Involved in the Cross-Coupling of Alkynyl Stannanes with Aryl Iodides Catalysed by teta2-(Dimethyl fumarate)(iminophosphane)palladium(0) Complexes

The complexes [Pd(eta(2)-dmfu)(P-N)] {dmfu = dimethyl fumarate; P-N = 2-(PPh2)C6H4-1-CH=NR, R = C6H4OMe-4 (1a), CHMe2 (2a), C6H3Me2-2,6 (3a), C6H3(CHMe2)(2)-2,6 (4a)} undergo dynamic processes in solution which consist of a P-N ligand site exchange through initial rupture of the Pd-N bond at lower energy and an olefin dissociation-association at higher energy. According to equilibrium constant values for olefin replacement, the complex [Pd(eta(2)-fn)(P-N)] (fn = fumaronitrile, 1b) has a greater thermodynamic stability than its dmfu analogue 1a. The kinetics of the oxidative addition of ArI (Ar = C6H4CF3-4) to 1a and 2a lead to the products [PdI(Ar)(P-N)] (1c, 2c) and obey the rate law, k(obs) = k(1A) + k(2A)[ArI]. The k(1A) step involves oxidative addition to a reactive species [Pd(solvent)(P-N)] formed from dmfu dissociation. The k2A step is better interpreted in terms of oxidative addition to a species [Pd(eta(2) -dmfu) (solvent) (kappa(1)-P-N)] formed in a pre-equilibrium step from Pd-N bond breaking. The complexes 1c and 2c react with PhCequivalent toCSnBu(3) in the presence of an activated olefin (ol = dmfu, fn) to yield the palladium(0) derivatives [Pd(eta(2)-ol)(P-N)] along with lSnBu(3) and PhCequivalent toCAr. The kinetics of the transmetallation step, which is rate-determining for the overall reaction, obey the rate law: k(obs) = k(2T)[PhCequivalent toCSnBu(3)]. The k(2T) values are markedly enhanced in more polar solvents such as CH3CN and DMF. The solvent effect and the activation parameters suggest an associative S(E)2 mechanism with substantial charge separation in the transition state. The kinetic data of the above reactions in various solvents indicate that, for the cross-coupling of PhCequivalent toCSnBu(3) with ArI catalysed by 1a or 2a, the rate-determining step is represented by the oxidative addition and that CH3CN is the solvent in which the highest rates are observed. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004

Mechanistic understanding of chromium-based oligomerisation catalysts : an EPR and ENDOR investigation

Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR) spectroscopies have been used to study the fundamental nature of chromium-based selective oligomerisation catalysts. A series of 'pre-catalyst' complexes were fully characterised CW-EPR revealed each complex to possess an axial g matrix (g > ge > g ) and superhyperfine coupling to two equivalent 31P nuclei, consistent with a low-spin cf species of approximate Cjv symmetry, where the metal contribution to the SOMO is primarily dxy. The isotropic component to the 31P coupling was of a larger magnitude in those Cr(I) complexes bearing PNP ligands than those bearing PCP, indicating that the phosphorus 3s character in the SOMO was higher for the former. CW-ENDOR demonstrated that subtle structural differences in the complexes, namely in the phenyl ring conformations, occurred as a function of ligand type. Pulsed experiments proved that the technique is valid and viable for further work on the activated system. Upon activation of the pre-catalyst with an alkylaluminium, four distinct paramagnetic centres were identified. A Cr(I) bis-arene complex was firstly detected it was found to form either via intramolecular co-ordination of the ligand phenyl groups, or preferentially via solvent-based arene co-ordination, if such groups were available. Two further species (I and III) were subsequently observed at low temperatures the spin Hamiltonian parameters extracted for both showed that a significant modification to the structure of the pre-catalyst had occurred. Half-field transitions indicated the possibility of a dimeric nature to Species III. ENDOR measurements detected an exceptionally large proton coupling in the activated system, possibly due to the co ordination of alkyl fragments to the metal centre. A final, fourth paramagnetic centre (Species IV), was detected and classed as an intermediate species, due to the greater similarity between its g and A matrices with those of the parent complex, than the other activated species. Finally, a preliminary investigation into analogous pre-catalyst complexes bearing N-heterocyclic carbene ligands was performed, due to their similar employment in oligomerisation catalysis CW-EPR spectra revealed information on both their electronic and structural natures.EThOS - Electronic Theses Online ServiceGBUnited Kingdo