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Structure/function relationships in heterogeneous catalysis play an important role in catalyst design strategies. The combination of chemisorption of suitable probe molecules alongside application of infrared spectroscopy is an established technique for providing information on the metal crystallite morphology of supported metal catalysts. Following a review of key literature on this topic, a variety of experimental arrangements that may be adopted for this task are examined. Specifically, the adsorption of CO over a 5wt% Pd/Al2O3 catalyst is investigated using transmission and diffuse reflectance sampling options and two research grade spectrometers. Although comparable spectra are obtained on all the platforms examined, differences are noted. In particular, temperature-programmed IR spectroscopy on one platform enables resolution of two features assigned to linear CO bound to the Pd particles. The relevance of this sub-division of terminal sites with respect to selective hydrogenation reactions is briefly considered.

We have investigated the severity of interferences in the determination of lutetium in neutron activation analysis. The preferred reaction makes use of the large radiative capture cross section of 2090 b for 176Lu(n,γ)177Lu, which emits a 208.4 keV gamma emission (t1/2 = 6.73 days). Activation of 176Lu simultaneously produces 177mLu, which also emits at 208.4 keV (t1/2 = 160.4 days). We found that these convolutions did not produce significant error in lutetium analysis for a sample of NIST 1633c, even for longer decay times used to reduce the 239Np interference at 209.8 keV.

Author(s): Grimaldo, Lenny; Burns, Jillian; Miller, Robert E.; Kalmbach, Andrew; Smith, April; Hassrick, Jason; Brennan, Colin | Abstract: Recruitment of estuarine organisms can vary dramatically from year to year with abiotic and biotic conditions. The San Francisco Estuary (California, USA) supports a dynamic ecosystem that receives freshwater flow from numerous tributaries that drain one of the largest watersheds in western North America. In this study, we examined distribution and habitat use of two forage fish larvae of management interest, Longfin Smelt Spirinchus thaleichthys and Pacific Herring Clupea pallasii, during a low-flow and a high-flow year to better understand how their rearing locations (region and habitat) may affect their annual recruitment variability. During the low-flow year, larval and post-larval Longfin Smelt were distributed landward, where suitable salinity overlapped with spawning habitats. During the high-flow year, larval Longfin Smelt were distributed seaward, with many collected in smaller tributaries and shallow habitats of San Francisco Bay. Local spawning and advection from seaward habitats were speculated to be the primary mechanisms that underlie larval Longfin Smelt distribution during the high-flow year. Larval Pacific Herring were more abundant seaward in both years, but a modest number of larvae were also found landward during the low-flow year. Larval Pacific Herring abundance was lower overall in the high-flow year, suggesting advection out of the area or poor recruitment. Future monitoring and conservation efforts for Longfin Smelt and Pacific Herring should recognize that potential mechanisms underlying their recruitment can vary broadly across the San Francisco Estuary in any given year, which suggests that monitoring and research of these two species expand accordingly with hydrologic conditions that are likely to affect their spawning and larval rearing distributions.

The styrene hydrogenation over Pd/C in a three-phase dead-end stirred tank reactor has been simulated. The mass transfer coefficients were calculated based on experimental data. The fast intrinsic reaction kinetics did not allow the effects of the gas–liquid and liquid–solid mass transfer to be ignored. A rigorous model is described which includes all mass transfer steps with a Langmuir–Hinshelwood model of the surface chemical reaction. The adsorption constants of hydrogen, styrene and ethylbenzene on catalyst active sites were estimated from a single experimental reaction profile. The parameterised model was validated against 6 further sets of experimental data which were not included in the parameters' estimation procedure. Results indicate the ethylbenzene, styrene and hydrogen adsorption to have an equilibrium constant of 148.34 L mol−1, 847.72 L mol−1 and 19 984 L mol−1, respectively. The intrinsic rate constant for the 4.63% Pd/C catalyst is 0.0542 mol gcat−1 s or 1.17 mol gPd−1 s−1. This work demonstrates that the analysis of the whole hydrogenation reaction profile in combination with detailed mass transfer resistance evaluation can provide fundamental system properties.

The liquid-phase hydrogenation of the aromatic cyanohydrin mandelonitrile (MN, C6H5CH(OH)CN) over a carbon-supported Pd catalyst to produce the primary amine phenethylamine (PEA, C6H5CH2CH2NH2) is investigated with respect to the transition from operation in single-batch mode to repeat-batch mode. While a single-batch reaction returns a complete mass balance, product analysis alongside mass balance measurements for a six-addition repeat-batch procedure shows an attenuation in the rate of product formation and an incomplete mass balance from the fourth addition onward. This scenario potentially hinders possible commercial operation of the phenethylamine synthesis process, so it is investigated further. With reference to a previously reported reaction scheme, the prospects of sustained catalytic performance are examined in terms of acid concentration, stirrer agitation rate, catalyst mass, and hydrogen availability. Gas-liquid mass transfer coefficient measurements indicate efficient gas → liquid transfer kinetics within the experimental constraints of the Henry's law limitation on hydrogen solubility in the process solvent (methanol). Deviations from the optimized product selectivity are attributed to mass transport constraints, specifically the H2(solv) → 2H(ads) transition, which is ultimately restrained by the availability of H2(solv). Finally, in an attempt to better understand the deactivation pathways, inelastic neutron scattering measurements on a comparable industrial-grade catalyst operated in an analogous reaction in fed-batch mode indicate the presence of an oligomeric overlayer postreaction. This overlayer is thought to be formed via oligomerization of hydroxyimine or imine species via specific pathways that are identified within a postulated global reaction scheme.

Acetic acid is an important organic solvent for the chemical industry, such as in catalytic hydrogenation and for electrosynthesis reactions generally. In this work, the adsorption and electrochemical oxidation of several sulfur-containing anions (S2−, S2O4 2−, S2O5 2− and SO3 2−) over Pt electrodes in a mixture of sulfuric acid/acetic acid was investigated by using cyclic voltammetry. Electrochemical oxidation provides a means of regenerating Pt catalysts and the sulfur-containing anions studied are examples of species that might be produced under synthetic conditions or could be present as impurities in industrial feedstock. To determine the oxidation reaction mechanism and its surface-structure sensitivity, Pt polycrystalline and single-crystal electrodes are implemented in this study. It is found that the oxidation of the sulfur-containing species on Pt polycrystalline electrode takes place at higher potentials in comparison to the same reactions in aqueous media. This is attributed to the low coverage of surface oxide, owing to the low concentration of water and the adsorption of acetate at the surface. Experiments on the Pt basal planes and stepped surfaces reveal a strong surface-structure dependence for the oxidation of all the sulfur-containing species. These results provide valuable information that will aid the engineering of nanocatalysts with specific crystalline structure less prone to contamination during catalytic process in mixtures of sulfuric/acetic acid.

The selective production of primary amines is a problem that plagues heterogeneously catalysed nitrile hydrogenation reactions. Whilst the target amine tyramine (HOC6H4CH2CH2NH2) is biochemically available through the action of enzymes, synthetic routes to this species are not widely reported. Here, a heterogeneously catalysed method is proposed that utilises a Pd/C catalyst to effect the selective hydrogenation of 4-hydroxybenzyl cyanide within a three-phase reactor. The aforementioned selectivity issues are overcome by adjustment of various experimental parameters (hydrogen supply, agitation rate, temperature, use of an auxiliary agent) that result in improved catalytic performance, such that the desired tyramine salt (tyramine hydrogen sulphate) can be produced in quantitative yield. Accordingly, through consideration of the interconnectivity of hydrogenation and hydrogenolysis processes, a selective synthetic strategy is achieved with the findings suitable for extension to other substrates of this nature.

A carbon supported Pd catalyst is used in the liquid phase hydrogenation of the aromatic cyanohydrin mandelonitrile (C6H5CH(OH)CH2CN) to afford the primary amine phenethylamine (C6H5CH2CH2NH2). Employing a batch reactor, the desired primary amine is produced in 87% selectivity at reaction completion. Detection of the by-product 2-amino-1-phenylethanol (C6H5CH(OH)CH2NH2) accounts for the remaining 13% and closes the mass balance. The reaction mechanism is investigated, with a role for both hydrogenation and hydrogenolysis processes established.

The liquid phase hydrogenation of benzonitrile over a 5wt% Pd/C catalyst using a stirred autoclave is investigated. The reaction conforms to a consecutive reaction sequence: firstly benzonitrile is hydrogenated to produce benzylamine, which subsequently undergoes a hydrogenolysis step to form toluene. Benzonitrile hydrogenation obeys first order kinetics with an activation energy of 27.6 kJ mol−1. In contrast, the benzylamine hydrogenolysis stage obeys zero order kinetics and exhibits an activation energy of 80.1 kJ mol−1. A 1wt% Pd/Al2O3 catalyst is additionally examined, which is also seen to support hydrogenolysis activity alongside the hydrogenation pathway. Gas phase transmission infrared spectroscopic measurements of the hydrogenation of benzonitrile and benzylamine over the 1wt% Pd/Al2O3 catalyst utilising hydrogen and deuterium are undertaken, which enable reaction schemes incorporating adsorption geometries of intermediate adsorption complexes to be proposed.

Experimental studies on the mechanism of copper-catalyzed amination of aryl halides have been undertaken for the coupling of piperidine with iodobenzene using a Cu(I) catalyst and the organic base tetrabutylphosphonium malonate (TBPM). The use of TBPM led to high reactivity and high conversion rates in the coupling reaction, as well as obviating any mass transfer effects. The often commonly employed O,O-chelating ligand 2-acetylcyclohexanone was surprisingly found to have a negligible effect on the reaction rate, and on the basis of NMR, calorimetric, and kinetic modeling studies, the malonate dianion in TBPM is instead postulated to act as an ancillary ligand in this system. Kinetic profiling using reaction progress kinetic analysis (RPKA) methods show the reaction rate to have a dependence on all of the reaction components in the concentration range studied, with first-order kinetics with respect to [amine], [aryl halide], and [Cu]total. Unexpectedly, negative first-order kinetics in [TBPM] was observed...

Heterogenous hydrogenations of high value chemicals are a widely used class of reaction that potentially benefit from the advantages continuous processing possesses. Trickle bed reactors offer a viable alternative to batch manufacture, however further understanding of the interplay between hydrogen mass transfer and catalytic reaction is required to facilitate the uptake of such technologies. To isolate the transport processes, the hydrogenation of styrene was conducted with a single 1% palladium on carbon pellet immobilized within glass beads with a liquid feed either hydrogen saturated or hydrogen free and the liquid flow rate was varied. The transfer rate of hydrogen was found to be significantly affected by the hydrogen content in the feed. The observations are well described by a new model in which the pellet film is treated as a plug flow reactor, with mass transfer from the gas phase to the film modelled as diffusion through a stagnant film, and mass transfer from the film to the catalyst surface and the subsequent reaction modelled as resistances in series. Our findings indicate that the provision of inert mass transfer area to saturate the fluid with hydrogen can significantly increase the productivity per unit mass of catalyst. In addition, by controlling the ratio of catalytic and inert surface the hydrogen concentration close to the catalyst surface can be tuned. This could be utilised to adjust both the activity and selectivity of the system and therefore, give trickle bed reactors an advantage in chemical manufacturing processes.

This research describes the method of neutron activation analysis (NAA) and Compton suppression for determination of some toxic elements in red mud (collected from Eti Seydisehir Aluminium Plant in Turkey). Furthermore, short-term leaching tests of elements were undertaken on red mud to evaluate in terms of the environmental impact. Morphological characterizations and qualitative element composition of red mud were also performed by SEM–EDX analysis. Fe, Al, Na, Ti and Ca contents in red mud were found significantly high. It can be concluded that some toxic elements may not easily mobile under the environmental conditions.

A mechanistic exploration of the liquid phase hydrogenation of the aromatic cyanohydrin mandelonitrile (C6H5CH(OH)CH2CN) over a carbon supported Pd catalyst to produce the primary amine, phenethylamine (C6H5CH2CH2NH2) is conducted. Prior examination showed the reaction to involve the production of the ketone intermediate 2-aminoacetophenone (C6H5C(O)CH2NH2), formed as a consequence of the presence of an acid catalysed tautomeric side reaction. The corresponding deuteration reaction, reported here and analysed by multinuclear NMR spectroscopy and mass spectrometry, is employed to further investigate accessible pathways. Examination of the resultant product distribution of the deuteration, and the location of deuterium incorporation establishes the role of a hydroxy-imine species as a key reaction intermediate. In addition, the acid catalysed tautomerism to the ketone is shown to be a reversible side reaction, but also a contributor to desired product formation. Moreover, an order for the three critical hydrogen consuming steps in phenethylamine formation is established. Hydrogenation of the nitrile functionality to afford the hydroxy-imine precedes hydrogenolysis of the hydroxyl group, with the final step being hydrogenation of the imine to form the target product, phenethylamine.

The selective production of primary amines is a problem that plagues heterogeneously catalysed nitrile hydrogenation reactions. Whilst the target amine tyramine (HOC

Many areas like smart buildings, crowd flow, action recognition, and assisted living rely on occupancy information. Although the use of smart cameras can alleviate the problem and provide accurate occupancy information, at the same time it can be cost prohibitive, invasive and not easy to scale or generalize to different environments. An alternative solution should bring similar accuracy while minimizing the previous problems. This work presents a candidate wireless sensor network for indirect occupancy measurements in a smart building. A prototype was built, that consists of CO 2 , temperature and humidity sensors. The prototype was placed in a complex indoor environment to collect data for a week. Then, the data was analyzed to examine potential correlation between sensor data and occupancy information. According to experimental results, CO 2 can be used for indirect occupancy measurements.

The use of a Pd/C catalyst in the liquid phase hydrogenation of various aromatic nitriles (benzonitrile, benzyl cyanide, 3-phenyl propionitrile and cinnamonitrile) has been studied in order to assess the effectiveness of this type of catalyst for this class of reaction. On modifying the nitrile substituent and upon introducing conjugation, varying degrees of conversion are observed. For benzyl cyanide and 3-phenylpropionitrile, incomplete mass balance profiles are linked to spill-over to the carbon support. In the case of benzonitrile hydrogenation, a hydrogenolytic step leads to a loss of selectivity to the primary amine to yield toluene with, ultimately, complete selectivity. Co-hydrogenation measurements on mixtures of benzonitrile and benzylamine indicate the presence of site-selective chemistry. Co-hydrogenation studies on mixtures of benzonitrile and benzyl cyanide highlight the competitive nature of the reaction system and, indirectly, establish a contribution from adsorbed imine species.

A series of copper(I) alkylamide complexes have been synthesised; copper(I) dicyclohexylamide (1), copper(I) 2,2,6,6-tetramethylpiperidide (2), copper(I) pyrrolidide (3), copper(I) piperidide (4), and copper(I) benzylamide (5). Their solid-state structures and structures in [D6 ]benzene solution are characterised, with the aggregation state in solution determined by a combination of DOSY NMR spectroscopy and DFT calculations. Complexes 1, 2 and 4 are shown to exist as tetramers in the solid state by X-ray crystallography. In [D6 ]benzene solution, complexes 1, 2 and 5 were found by using (1) H DOSY NMR to exist in rapid equilibrium between aggregates with average aggregation numbers of 2.5, 2.4 and 3.3, respectively, at 0.05 M concentration. Conversely, distinct trimeric, tetrameric and pentameric forms of 3 and 4 were distinguishable by one-dimensional (1) H and (1) H DOSY NMR spectroscopy. Complexes 3-5 are found to react stoichiometrically with iodobenzene, in the presence or absence of 1,10-phenanthroline as an ancillary ligand, to give arylamine products indicative of their role as potential intermediates in the modified Ullmann reaction. The role of phenanthroline has also been explored both in the stoichiometric reaction and in the catalytic Ullmann protocol.

A quantitative study of the hydrolytic dissolution of solid p-chloranil at alkaline pH using a combination of the channel flow cell and in situ atomic force microscopy measurements shows that the dissolution is driven by reaction of the substrate with hydroxide ions at, or very close to, the dissolving surface. The dissolution rate equation, deduced from the channel flow cell for single crystals of p-chloranil, is rate/mol cm-2 s-1 = 3.8 × 10-7[OH-]0 where [OH-]0/M is the hydroxide ion concentration adjacent to the solid surface. An analogous rate law is derived for pressed pellet substrates. The novel application of the atomic force microscope to make absolute measurements of surface averaged dissolution rates is described. Comparison with the independent channel flow cell data reveals good mechanistic agreement and consistency of rate constants provided it is recognised that a thick stagnant diffusion layer can be present under the usual conditions employed for AFM. © 1997 Elsevier Science S.A.

The kinetics of the dyeing of a dichlorotriazinyl-reactive dye, Procion Blue MX-R, with knitted cotton fabrics have been studied using a versatile technique based on a spectrochemical channel flow cell. A mechanism is derived where the simultaneous hydrolysis of the dye molecules, the physical binding of the hydrolyzed form, and the chemical fixation of the active form onto the fabric are taken into account. It is shown that the dye fixation to the fabric is controlled by a solid-liquid interfacial process that is first order with respect to the surface concentration of dye; however, the rate of this reaction is governed by the availability of sites for the adsorption of dye molecules on the fabric surface. Dyeing experiments are performed over a wide range of initial dye concentrations; supporting electrolyte concentrations and the kinetic parameters are reported. Atomic force microscopic studies indicate that mercerization pretreatment provides a disordered fiber surface which may offer additional sites for dye adsorption.

The mechanism of the dyeing of cotton and nylon cloth by the azo dyes Orange G and Sunset Yellow FCF was investigated using a channel flow cell. The variation in dyeing with flow rate was found to proceed via a mechanism in which the flux of dye entering the cloth relative to the flux of dye to the cloth surface decreased with increasing flow rate. A mechanism is deduced in which the dye passes from bulk solution, through a porous surface layer within the cloth, before passing into the bulk cloth. Adsorption onto surface sites in this porous layer blocks the passage of further dye into the cloth. Kinetic parameters for such a mechanism are given.

The kinetics of dissolution of benzoic acid into aqueous solution are studied using the channel flow cell method. In contrast to alternative experimental approaches the method is shown to provide interfacial rate data permitting mechanistic insight. Kinetic parameters are reported. © 1993 American Chemical Society.

Reversible partitioning of a portion of the catalyst away from the active cycle provides a mechanistic rationalization of the anomalous reaction orders observed in the presence of additives. The concept of stable reservoir species leads to a practical protocol for maintaining a robust catalyst system that may be particularly useful for development of reactions under harsh conditions likely to lead to catalyst deactivation and incomplete turnover. Probing Pd-catalyzed amination reactions in the presence of competitive binding events reveals the key role that reservoir species connected reversibly to the catalytic cycle can play.

The article describes a numerical and experimental investigation of the voltammetric response observed within small-scale electrochemical reactors, where reagents are directed to a sensor electrode using hydrodynamic focusing. A microelectrochemical reactor was developed, fabricated and tested for electrochemical sensitivity. The studies presented examine the influence of stream velocity, lead-in length and focusing stream ratios on the electrolytic current induced. The numerical models reveal a regime where the finely focused stream of reagent responds in an identical manner to a cell completely full of reagent and also to a regime where diffusional broadening of the reagent stream into the carrier stream becomes significant with a resulting loss in voltammetric sensitivity. In addition at higher focusing ratios, where the reagent occupies a much smaller portion of the channel, full electrochemical depletion of the species is possible at substantially greater throughput rates than is feasible without the focusing arrangement. Experimental studies show qualitative agreement with numerical predictions.

Healthy competition: The Pd(binap)-catalyzed amination of aryl halides demonstrates how the results from competitive reactions can be strikingly different from those obtained from study of the separate reactions. We show how the competitive network provides mechanistic information not accessible from study of the reactions separately.

A novel microfluidic approach for the quantification of reaction kinetics is presented. A three-dimensional finite difference numerical simulation was developed in order to extract quantitative kinetic information from fluorescence lifetime imaging experimental data. This approach was first utilized for the study of a fluorescence quenching reaction within a microchannel; the lifetime of a fluorophore was used to map the diffusion of a quencher across the microchannel. The approach was then applied to a more complex chemical reaction between a fluorescent amine and an acid chloride, via numerical simulation the bimolecular rate constant for this reaction was obtained.

A surface-controlled dissolution of cylindrical solid particles model is applied to potassium carbonate, sodium bicarbonate and sodium carbonate in dimethylformamide at elevated temperatures. Previously published data for the dissolution of potassium carbonate is interpreted assuming a cylindrical rather than a spherical shape of the particles, the former representing a closer approximation to the true shape of the particles as revealed by scanning electron microscopy. The dissolution kinetics of sodium carbonate and sodium bicarbonate in dimethylformamide at 100 degrees C were investigated via monitoring of the deprotonation of 2-cyanophenol with dissolved solid to form the 2-cyanophenolate anion that was detected with UV-visible spectroscopy. From fitting of experimental results to theory, the dissolution rate constant, k, for the dissolutions of potassium carbonate, sodium bicarbonate and sodium carbonate in dimethylformamide at 100 degrees C were found to have the values of (1.0 +/- 0.1) x 10(-7) mol cm(-2) s(-1), (5.5 +/- 0.3) x 10(-9) mol cm(-2) s(-1) and (9.7 +/- 0.8) x 10(-9) mol cm(-2) s(-1), respectively.

In this paper we present a mathematical model for the surface-controlled dissolution of cylindrical solid particles. This is employed to interpret experimental data published previously for the dissolution of potassium bicarbonate in dimethylformamide at elevated temperatures. Significant kinetic differences in assuming cylindrical rather than spherical shapes are reported with the former representing a closer approximation to the true shape of the particles as revealed by scanning electron microscopy. From the fits of experimental data to the cylindrical model for the surface-controlled dissolution, the dissolution rate constant, k, for the dissolution of KHCO(3) in DMF was found to be (9.6 +/- 1.6) x 10(-9) mol cm(-2) s(-1) at 100 degrees C, and the activation energy for the dissolution was 34.5 kJ mol(-1) over the temperature range of 60-100 degrees C. Comparison between cylindrical and spherical dissolution theory highlights the importance of considering the particle shapes for realistic modeling of surface-controlled dissolution kinetics.

This paper describes the gelation of symmetric dendrimers based on building blocks constructed from L-lysine. These dendrimers form gel-phase materials in nonpolar organic solvents. The thermal properties and concentration dependence of the gelation were investigated, and it was found that there was a clear dendritic effect on the behavior of the soft materials formed, with higher generation dendrimers giving rise to more thermally stable gels. Variable temperature 1H NMR studies indicated that this behavior was probably a consequence of more extensive interdendrimer hydrogen bonding occurring between the peptidic groups in the higher generation dendrimers. The supramolecular aggregates were found to have a fibrillar structure, with the dimensions and alignment of the fibers being dependent on dendritic generation. Circular dichroism measurements confirmed that these fibers possessed chiral organization of the peptidic groups on the supramolecular (nano) scale, assigned as helicity. This paper indicates that dendritic functionalization provides a useful way of tuning gel-phase materials properties, with clear dendritic effects on gel formation being quantified for the first time, hence illustrating the way dendritic functionalization can play a positive role in the formation of highly functional organic materials with desirable properties.

A new hydrodynamic microelectrochemical reactor design is presented for the voltammetric sensing of chemical species contained within two immiscible liquid streams flowing within rectangular ducts, in direct contact. This article describes the design, fabrication and experimental characterisation of the device. A microfabricated rectangular duct (of typical dimensions: height 75μm, width 500μm and length 3 cm) was constructed using FOTURAN glass and standard photolithographic procedures. Microelectrode sensors were positioned on one internal duct wall with a geometry to permit separate voltammetric monitoring of the two solvent phases. Reagent solutions containing N,N,N′,N′-tetramethyl-1,4-phenylene diamine in 1,2-dichloroethane and hexaamineruthenium(III)chloride in water were pumped through the device under laminar flow conditions. Linear sweep voltammetric measurements were performed separately on the two electrolyte streams and the variation of the transport limited current as a function of volume flow rate through the cell monitored. Under conditions where stable flow was obtained the current flow rate relationship was observed to follow analogous voltammetric behaviour to that observed in macroscopic flow cell devices. Keywords: Hydrodynamic voltammetry, Immiscible liquid/liquid flow, Microreactors

The reaction between solid cyanuric chloride and an aromatic amine, N,N-dimethyl-p-phenylendiamine (DMPA) in aqueous solution is studied using the channel flow cell method in which a constant geometric area of solid is exposed to solution. It is shown that reaction occurs via the dissolution of the solid (with a constant flux of material being released into solution) followed by homogeneous coupling to the amine in parallel with hydrolysis of cyanuric chloride. Kinetic parameters for the process are reported and the value of the approach used for the determination of mechanisms for interfacial processes at insulator solid/liquid interfaces noted

We describe the application of wide-field frequency domain Fluorescence Lifetime Imaging Microscopy (FLIM) to imaging in microfluidic devices. FLIM is performed using low cost, intensity modulated Light Emitting Diodes (LEDs) for illumination. The use of lifetime imaging for quantitative analysis within such devices is demonstrated by mapping the molecular diffusion of iodide ions across a microchannel.

We report the synthesis of a family of gelators in which alkyl chains are connected to the amino groups of L-lysine methyl ester using a range of different hydrogen bonding linking groups (carbamate, amide, urea, thiourea and diacylhydrazine) using simple synthetic methodology based on isocyanate or acid chloride chemistry. The ability of these compounds to gelate organic solvents such as toluene or cyclohexane can be directly related to the ability of the linking group to form intermolecular hydrogen bonds. In general terms, the ability to structure solvents can be considered as: thiourea

This paper describes the synthesis of gold nanoparticles stabilized by two series of new dendritic disulfide ligands with alkene groups at their peripheries. Intraparticle cross-linking of the alkene groups around the periphery of each nanoparticle was achieved by Grubbs' metathesis. It was demonstrated that cross-linking of the organic ligand has no effect on the size or morphology of the inorganic gold core as determined by TEM and UV-vis measurements. However, the introduction of cross-linking at the surface of the ligand enhances the stability of the gold nanocore toward chemical etchant agents (NaCN) and thermal treatment. The impact of cross-linking on nanoparticle stability is greater when the cross-linking is closer to the nanoparticle surface (i.e., using lower generation dendritic ligands). Attempts to perform further synthetic transformation on the hybrid materials in order to remove the gold core led to insoluble products composed predominantly of the dendritic ligand.

Understanding the mechanisms of solid-liquid systems is fundamental to the development and operation of processes for the production of agrochemicals and pharmaceuticals. The use of a strong inorganic base in an organic solvent, typically, potassium carbonate in dimethylformamide, is often used to facilitate the formation of a required anionic organic nucleophile. In this paper, the dissolution kinetics of potassium carbonate in dimethylformamide at elevated temperatures is studied in the presence of ultrasound, as revealed via monitoring of the deprotonation of 2-cyanophenol by dissolved K2CO3. Two independent experimental methods were employed; the loss of 2-cyanophenol was detected electrochemically at a platinum microdisk working electrode, and the formation of the 2-cyanophenolate anion was monitored via UV/visible spectroscopic analysis. The results were modeled by fitting the experimental data to a theoretical model for the surface-controlled dissolution of solid particles. The dissolution rate constant, k, for the dissolution of K2CO3 in DMF was found to have a value of (1.3 +/- 0.2) x 10(-7) mol cm(-2) s(-1) at 100 degrees C, and the activation energy for the dissolution was 44.2 +/- 0.4 kJ mol(-1) over the temperature range of 70-100 degrees C studied.

A series of gold nanoparticles stabilised by ‘Newkome-type’ dendritic branching has been synthesised and fully characterised. In particular, the properties and behaviour of these hybrid materials are compared with those of a previously reported set of nanoparticles stabilised by dendrons constructed using l -lysine building blocks. The rates of cyanide-induced nanoparticle decomposition were determined, and it was found that the rate of decomposition increased on the introduction of dendritic branching. Furthermore, ‘Newkome-type’ dendrons were significantly more effective at protecting the encapsulated gold nanoparticle than the l -lysine based dendrons. It is proposed that this observation can be explained on the basis of more effective packing and surface coverage by the ‘Newkome-type’ dendrons. Importantly, this study therefore demonstrates that the organic chemical structure of dendritic ligands plays a crucial role in controlling the reactivity of self-assembled hybrid nanostructures.

Gold nanoparticles with diameters of ca. 13 nm were synthesised by UV irradiation of a supramolecular organogel into which HAuCl4 and tetraoctylammonium bromide had been diffused—the gel network plays an essential role in nanoparticle stabilisation.

We present a mathematical model for the surface-controlled dissolution of solid particles. This is applied to the dissolution of a solid having different particle size distribution functions: those of a monodispersed solid containing particles of all one size, a two-size-particle distribution, and a Gaussian distribution of the particle sizes. The dissolution of potassium bicarbonate in dimethylformamide is experimentally studied indirectly at elevated temperatures. We monitor the dissolution via the homogeneous deprotonation of 2-cyanophenol by dissolved KHCO3. The loss of 2-cyanophenol was detected electrochemically at a platinum microdisk electrode, and separately, the formation of the 2-cyanophenolate anion was monitored via UV-visible spectroscopic analysis. The results presented show that the kinetics of the loss of 2-cyanophenol behaves on one hand as a homogeneous chemical process and on the other hand as a dissolution-rate-controlled process. Initially, predissolved KHCO3 in solution deprotonates the 2-cyanophenol and homogeneous reaction dominates the observed kinetics, and at longer times, the observed kinetics is controlled by the rate of KHCO3 dissolution. Modeling of the experimental results for the surface-controlled dissolution of KHCO3 in dimethylformamide (DMF) yielded a mean value for the dissolution rate constant, k, at elevated temperatures; k was found to have a value of (1.1 +/- 0.3) x 10(-8) mol cm(-2) s(-1) at 100 degrees C, and the activation energy for the dissolution was 34.4 +/- 0.4 kJ mol(-1) over the temperature range 60-100 degrees C.

A novel “flow injection” channel flow cell is described which enables transient phenomena at the solid−liquid interface to be investigated. In the cell the solution reactant is injected into the main channel of a flow cell upstream from, and through the opposite wall from, the solid substrate. A detector electrode is positioned downstream of the latter so that current−time transients can be used to infer the kinetics and mechanism of processes at the solid−liquid interface. The performance of the cell was theoretically modeled using FLOTRAN. It was shown that the “injection” of reactant causes only very minor disturbance to the main channel flow. This facilitates the assumption of Poiseuille flow in the channel so as to enable the numerical interpretation of the current−time transients.

The reaction between solid cyanuric chloride and an aromatic amine, N,N-dimethyl-p-phenylenediamine (DMPA) in aqueous solution is studied using the channel flow cell method in which a constant geometric area of solid is exposed to solution. It is shown that reaction occurs via the dissolution of the solid (with a constant flux of material being released into solution) followed by homogeneous coupling to the amine in parallel with hydrolysis of cyanuric chloride. Kinetic parameters for the process are reported and the value of the approach used for the determination of mechanisms for interfacial processes at insulator solid/liquid interfaces noted. In particular the site of the chemical coupling reaction between DMPA and cyanuric chloride is found to be located in homogeneous solution rather than proceeding via an interfacial process although the rate of the reaction is effectively controlled by the speed at which solid can enter the solution. © 1993 American Chemical Society.

This paper reports the synthesis of dendrons containing a spermine unit at their focal point. The dendritic branching is based on L-lysine building blocks, and has terminal oligo(ethyleneglycol) units on the surface. As a consequence of the solubilising surface groups, these dendrons have high solubility in solvents with widely different polarities (e.g., dichloromethane and water). The protonated spermine unit at the focal point is an effective anion binding fragment and, as such, these dendrons are able to bind to polyanions. This paper demonstrates that polyanions can be bound in both dichloromethane (using a dye solubilisation assay) and in water (competitive ATP binding assay). In organic media the dendritic branching appears to have a pro-active effect on the solubilisation of the dye, with more dye being solubilised by higher generations of dendron. On the other hand, in water the degree of branching has no impact on the anion binding process. We propose that in this case, the spermine unit is effectively solvated by the bulk solvent and the dendritic branching does not need to play an active role in assisting solubility. Dendritic effects on anion binding have therefore been elucidated in different solvents. The dendritic branching plays a pro-active role in providing the anion binding unit with good solubility in apolar solvent media.