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The solid-state behaviour of five ionophore-encapsulated TCNQ complexes: (18-crown-6)K(TCNQ)2.5 (1), ([2.2.2]-cryptand)K(TCNQ)2.5 (2), (benzo-18-crown-6)K(TCNQ)2 (3), (dibenzo-18-crown-6)K(TCNQ)2 (4), and (dicyclohexano-18-crown-6)K(TCNQ)3 (5) has been explored. For both 1 and 2, the TCNQ components assemble as a pentameric repeat unit within infinite TCNQ columns with the cation complex sitting in a cavity between the columns; whereas for 3 and 4, neighbouring (crown ether)K+ complexes form dimers involving K+–π interactions which further assemble into one-dimensional columns sitting between infinite TCNQ stacks. In the solid-state complex 5, the crown ether adopts a chair conformation with the resulting (crown ether)K+ complex assembling into a one-dimensional ladder. Pairs of TCNQ dimers separated by an isolated TCNQ unit form infinite TCNQ columns. IR and Raman spectroscopy reveal the presence of partially charged TCNQ units within all five TCNQ complexes (1–5) and resistivity studies indicate that all five TCNQ complexes (1–5) are more conductive than the corresponding simple KTCNQ salts. Preliminary EPR studies of 1 and 2 indicate typical behaviour of complex TCNQ salts (containing both TCNQ0 and TCNQ˙−).

An investigation of the solid-state behaviour of five 12-crown-4 alkali metal TCNQ complexes, (12-crown-4)2LiTCNQ (1), (12-crown-4)2NaTCNQ (2), (12-crown-4)2Li(TCNQ)2 (3), (12-crown-4)2Na(TCNQ)2 (4), and (12-crown-4)2K(TCNQ)2 (5), reveals an unusual “cross-stitch” packing motif with the extended face-to-face π-stacked TCNQ˙− columns present in complexes 1 and 2. The effect of the presence of additional neutral TCNQ0 has also been explored.

The solid-state behaviour of four alkali metal TCNQ complexes: (15-crown-5)LiTCNQ (1), (15-crown-5)NaTCNQ (2), (15-crown-5)Li(TCNQ)2.H2O (3.H2O) and (15-crown-5)Na(TCNQ)2.H2O (4.H2O) has been explored by single crystal X-ray diffraction, Infrared (IR), Raman and Electron Paramagnetic Resonance (EPR) measurements. The presence of a small cation and ionophore leads to subtle changes in behaviour compared with their larger alkali metal analogues and in the hydrated salts water bridges form links between the crown-encapsulated cations and neighbouring TCNQ stacks.

A detailed study of the ability of pyridine-2,6-dicarboxylic acid (1) and its 4-mono- and 3,4,5-tri-substituted analogues to sensitize emission from Pr3+, Nd3+, Gd3+, Dy3+ and Er3+ is presented. Sensitization of Ln3+ emission was demonstrated via the ligands in all complexes, excluding Gd3+, with emission covering the spectral range from 500 nm to 1850 nm obtained with variation of the Ln3+ ion. From the study of the ligand-based photoluminescence obtained from Gd3+-complexes, and the relative ligand and Ln3+ emission obtained from the other complexes, the singlet and triplet state energies of complexes of (1) are estimated to be at 3.1 eV and 2.6 eV respectively whilst for the 3,5-dibromo-substituted complexes (4) they are at 2.9 eV and 2.3 eV. Hypersensitivity of the Er3+ 4I15/2 → 2H11/2 and 4I15/2 → 4G11/2 intra-atomic transitions is also observed in the 4-chloro-substituted (3) complex. Enhanced sensitization of Nd3+ (ca. 5-fold) and Er3+ (ca. 2-fold) near-infrared emission is demonstrated for complexes of (3) and (4) respectively in comparison with those of (1).

Electrospun fibrous matrices prepared from methacrylate-based copolymers are investigated as a tool for retinal pigment epithelium (RPE) transplantation in the treatment of degenerative retinal diseases. Human RPE cells were used to probe the cell–surface interactions on these copolymer matrices. For the first time, simple changes in chemical functionality have been found to induce gel formation of these methacrylate backbone copolymers in vitro. This effect is shown to significantly improve RPE cell adhesion and survival.

Engineering tissue structures that mimic those found in vivo remains a challenge for modern biology. We demonstrate a new technique for engineering composite structures of cells comprising layers of heterogeneous cell types. An acoustofluidic bioreactor is used to assemble epithelial cells into a sheet-like structure. On transferring these cell sheets to a confluent layer of fibroblasts, the epithelial cells cover the fibroblast surface by collective migration maintaining distinct epithelial and fibroblast cell layers. The collective behaviour of the epithelium is dependent on the formation of cell-cell junctions during levitation and contrasts with the behaviour of mono-dispersed epithelial cells where cell-matrix interactions dominate and hinder formation of discrete cell layers. The multilayered tissue model is shown to form a polarised epithelial barrier and respond to apical challenge. The method is useful for engineering a wide range of layered tissue types and mechanistic studies on collective cell migration.

As supramolecular chemistry evolves, from the design of interactions in the solution and the solid state to applications at surfaces, there is a need for the development of analytical techniques capable of directly interrogating surface-localised supramolecular interactions. We present a proof-of-concept integrated optical Bragg grating sensor, capable of evanescently detecting small changes in refractive index at infrared wavelengths within a microfluidic system. The high spectral fidelity of the Bragg gratings combined with precise thermal compensation enables direct monitoring of the surface throughout the experiment, enabling the sensor to probe changes in situ and in real-time during surface preparation and chemical modification, and then to follow the progress of a dynamic surface-localised supramolecular interaction. In this study the sensor is assessed through the investigation of a photo-switchable inclusion complex between an azobenzene-functionalised surface and cyclodextrin in aqueous solution. The ability to investigate supramolecular interactions directly in real-time upon a planar surface via refractive index offers a valuable new tool in the understanding of complex dynamic supramolecular systems.

Development of synthetic surfaces that are highly reproducible and biocompatible for in vitro cell culture offers potential for development of improved models for studies of cellular physiology and pathology. They may also be useful in tissue engineering by removal of the need for biologically-derived components such as extracellular matrix proteins. We synthesised four types of 2-alkyl-2-oxazoline polymers ranging from the hydrophilic poly(2- methyl-2-oxazoline) to the hydrophobic poly(2-n-butyl-2-oxazoline). The polymers were terminated using amine-functionalised glass coverslips, enabling the synthetic procedure to be reproducible and scaleable. The polymer-coated glass slides were tested for biocompatibility using human epithelial (16HBE 14o-) and fibroblastic (MRC5) cell lines. Differences in adhesion and motility of the two cell types was observed, with the poly(2- isopropyl-2-oxazoline) polymer equally supporting the growth of both cell types, whereas poly(2-n-butyl-2-oxazoline) showed selectivity for fibroblast growth. In summary, 2-alkyl-2- oxazoline polymers may be a useful tool for building in vitro model cell culture models with preferential adhesion of specific cell types.

Chemical scientists’ experiences with LabTrove., Electronic Laboratory Notebooks (ELNs) are progressively replacing traditional paper books in both commercial research establishments and academic institutions. University researchers require specific features from ELNs, given the need to promote cross-institutional collaborative working, to enable the sharing of procedures and results, and to facilitate publication. The LabTrove ELN, which we use as our exemplar, was designed to be researcher-centric (i.e., not only aimed at the individual researcher's basic needs rather than to a specific institutional or subject or disciplinary agenda, but also able to be tailored because it is open source). LabTrove is being used in a heterogeneous set of academic laboratories, for a range of purposes, including analytical chemistry, X-ray studies, drug discovery and a biomaterials project. Researchers use the ELN for recording experiments, preserving data collected, and for project coordination. This perspective article describes the experiences of those researchers from several viewpoints, demonstrating how a web-based open source electronic notebook can meet the diverse needs of academic researchers.

We report the photosensitization of crystalline silicon via energy transfer using covalently attached protoporphyrin IX (PpIX) derivative molecules at different distances via changing the diol linker to the surface. The diol linker molecule chain length was varied from 2 carbon to 10 carbon lengths in order to change the distance of PpIX to the Si(111) surface between 6 A and 18 A. Fluorescence quenching as a function of the PpIX-Si surface distance showed a decrease in the fluorescence lifetime by almost two orders of magnitude at the closest separation. The experimental fluorescence lifetimes are explained theoretically by a classical Chance-Prock-Silbey model. At a separation below 2 nm, we observe for the first time, a Forster like dipole-dipole energy transfer with a characteristic distance of R-o = 2.7 nm.

Highly branched polyamidoamine (PAMAM) dendrimers presenting biological activities have been envisaged as non-viral gene delivery vectors. They are known to associate with nucleic acid (DNA) in non-covalent complexes via electrostatic interactions. Although their transfection efficiency has been proved, PAMAMs present a significant cytotoxicity due to their cationic surface. To overcome such a drawback, different chemical modifications of the PAMAM surface have been reported such as the attachment of hydrophobic residues. In the present work, we studied the complexation of DNA duplexes with different low-generation PAMAM, ammonia-cored G0(N) and G1(N) PAMAM, native or chemically modified with aromatic residues, i.e., phenyl-modified-PAMAM G0(N) and phenylalanine-modified-PAMAM G1(N). To investigate the interactions involved in the PAMAM/DNA complexes, also called dendriplexes, we used electrospray ionization (ESI) coupled to ion mobility spectrometry-mass-spectrometry (IM-MS). ESI is known to allow the study of non-covalent complexes in native conditions while IM-MS is a bidimensional separation technique particularly useful for the characterization of complex mixtures. IM-MS allows the separation of the expected complexes, possible additional non-specific complexes and the free ligands. Tandem mass spectrometry (MS/MS) was also used for the structural characterization. This work highlights the contribution of IM-MS and MS/MS for the study of small dendriplexes. The stoichiometries of the complexes and the equilibrium dissociation constants were determined. The [DNA/native PAMAM] and [DNA/modified-PAMAM] dendriplexes were compared.

There have been significant recent developments in the field of integrated optical Bragg grating sensors for use in the biological domain, where changes in the thickness of a surface layer upon specific binding of biological targets allows quantitative detection. However in the chemical domain less work has been reported. We present here an integrated optical Bragg grating sensor, capable of evanescently detecting small changes in refractive index down to 10(-6) RIU at infrared wavelengths, within a microfluidic system. The high spectral fidelity of the Bragg gratings combined with precise thermal compensation enables direct monitoring of the surface throughout the experiment. This allows the sensor to probe surface changes in situ and in real-time, from preparation through to chemical modification of the surface, so that the progress of dynamic surface-localized interactions can be followed. Here we describe confirmatory studies to validate this approach, including a comparison with the modelled optical system, before assessing the ability to detect binding of Group I cations at a crown ether-functionalised supramolecular surface. Unlike larger biological entities, for these small chemical species, simple additive changes in film-thickness no longer prevail.

The intriguing twist-bend nematic (NTB) phase is formed, primarily, by liquid crystal dimers having odd spacers. Typically, the phase is preceded by a nematic (N) phase via a weak first-order transition. Our aim is to obtain dimers where the NTB phase is formed directly from the isotropic (I) phase via a strong first-order phase transition. The analogy between such behaviour and that of the smectic A (SmA)–N–I sequence suggests that this new dimer will require a short spacer. This expectation is consistent with the prediction of a molecular field theory, since the decrease in the spacer length results in an increase in the molecular curvature. A vector of odd dimers based on benzoyloxybenzylidene mesogenic groups with terminal ethoxy groups has been synthesised with spacers composed of odd numbers of methylene groups. Spacers having 5, 7, 9 and 11 methylene groups are found to possess the conventional phase sequence NTB–N–I; surprisingly, for the propane spacer, the NTB phase is formed directly from the I phase. The properties of these dimers have been studied with care to ensure that the identification of the NTB phase is reliable.

Age-related macular degeneration is the most common cause of blindness in the UK. Cellular replacement of retinal pigment epithelium cells is a potential therapeutic option to treat the cellular loss and dysfunction which is characteristic of age-related macular degeneration and other progressive retinopathies. A supportive scaffold, natural or artificial, may be required to facilitate cell delivery to the eye. Research to improve the biomimetic properties of such scaffolds, in order to optimise cell attachment and functionality following implantation, is ongoing. This short review will focus on the potential of biomaterials for ocular tissue engineering and how surface modification and the physical properties of these scaffolds can be tailored to help realise the full clinical potential of retinal pigment epithelium cell transplantation.

An exposed Bragg grating incorporated into a planar waveguide forms an optical device that acts as a refractive index sensor. The exposed evanescent field causes the Bragg peak to be sensitive to the refractive index of its surroundings and can be used to detect changes in this environment. The method reported is able to provide accurate temperature compensation by applying a scaling factor derived from measurement of the birefringence of the transverse electric (TE) and transverse magnetic (TM) modes of the Bragg reflection. For a fluid sensor, fluctuations in ambient temperature can be both accounted for and compensated to produce a temperature-insensitive sensor.

2,7-Disubstituted-1,8-naphthyridine derivatives have been found to self-assemble into infinite 1-D tapes in the solid state in a manner similar to that seen previously for their 2,6-disubstituted pyridine analogues.

An integrated study of the organic-inorganic framework material zinc cyclohexane trans-1,2-dicarboxylate involving synthesis, structure elucidation, computer simulation, and calorimetry shows that the chiral R,R form (right in picture) is less stable than its racemic R,R/S,S analogue (left) and adopts a layered structure with a fundamentally different topology. The results point to the possibility that the structural diversity of racemic frameworks and their homochiral analogues may be much greater than has hitherto been suspected.

A novel dihydrate structure of pyridine-2,6-dicarboxylic (dipicolinic) acid is reported, found to demonstrate a different solid-state architecture to that of the previously published monohydrate crystal. In addition, we report the crystal structure of a monohydrate of 4-chloro pyridine-2,6-dicarboxylic acid, which is also compared to the known dipicolinic acid monohydrate.

The effect of substitution at the 4 and 3,5 positions in the pyridine ring of europium(III) pyridine-2,6-dicarboxylate complexes has been investigated with particular emphasis on sensitization of the Eu3+ ion. Sensitization of the Eu3+ 615-nm emission was achieved through excitation of the ligands in which the 4 substituent was -H, -OH, and -Cl and the 3,5 position was -H. In these cases, the ligand-to-Eu3+ ratio was confirmed as being 3:1. The sensitization was found to increase following substitution of the 4 position in the order ClHOH. This is attributed to energy transfer occurring from the ligands into different Eu3+ intra-atomic energy levels, with spin selection rules governing the efficiency of this process. The Eu3+ luminescence lifetime was measured and found to vary from 1.16 to 2.90 ms depending on the excitation energy, ligand, and solvent. For the case of the 3,5-dibromo-4-hydroxy derivative, no sensitization was observed and a ligand-to-Eu3+ ratio of 1:1 was found. The solubility of these complexes in water and their long emission lifetime make them attractive for use as probes in biological systems.

Solid-state structural studies of three isomeric bis-(chlorocarbonyl) pyridines (the 2,6; 2,5 and 3,5 regiosiomers), indicate that the tape-assembly observed previously in the corresponding 2,6-, some 3,5-diesters and, in the present study, the 3,5-bis-chlorocarbonyl isomer is perturbed by the presence of chlorine-mediated interactions in the 2,6-and 2,5-bis acid chlorides

Photo-switchable calixarenes consisting of a stilbene or azobenzene bridge, spanning the narrow rim as a switching unit, were synthesized through reductive coupling of o-, m- and p-bis-benzaldehyde and bis-nitrobenzene-substituted calix[4]arenes. Both cis- and trans-stilbenes were produced from the reductive coupling of the o- and m-bis-benzaldehyde with the cis isomer being predominant for both regioisomers, whilst the coupling of p-bis-benzaldehyde gave only cis product. On the other hand, the only isolable product obtained from the reductive coupling of bis-o- and bis-m-nitrobenzene was the corresponding trans-azobenzene and the coupling product from bis-p-nitrobenzene was not stable. Each of the synthesized compounds showed a photostationary state in their cis–trans isomerization. The complexation of alkali metal ions was observed for only the o-azobenzene derivative suggesting that the lone pair of N-atom in the azo bridge participates in this process.

When the novel pyridine-2,6-dicarboxylic acid bis[(quinolin-8-ylmethyl)amide] (PDQA) is treated with CoCl2 a 1:1 complex [(PDQAH2)][CoIICl4] (2), is formed. Treatment of 2 with NaNO2 results in oxidation of the to CoIII affording [(PDQA-H)CoIII(NO2)2] (3) whereas under basic conditions a 2:1 (ligand:CoIII) paddle-like structure [CoIII(PDPA-2H)2K(H2O)2(CH3OH)1]·(H2O)2 (1) is obtained.

The solid-state behavior of six novel 6-substituted PnAO (propylene amine oxime) complexes (6-11) involving Tc(V), Co(III), and Cu(II) salts is reported. Each of the Tc complexes 6-8 has the C6-substituent located equatorially in a six-membered chelate ring involving a Tc=O unit which has the expected boat geometry. The C6-substituent therefore has little effect on the conformational behavior of the PnAO complex and thus provides an attractive site for further modification. The Co(III) complex 9 has the expected octahedral geometry, while the Cu(II) complexes 10 and 11 form square-based pyramids capped by water molecules. One Cu(II) system (10) contains two unique complexes in the asymmetric unit which are associated via multiple hydrogen bonds to a BF(4) anion, the remaining BF(4) anion being loosely hydrogen bonded to a coordinating water molecule. The cobalt and copper complexes 9-11 each exhibit a chair conformation for the six-membered chelate ring.

A new organic polymer as positive electrode material is presented. Poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (PDBM) has oxocarbon cycles which are part of the polymer backbone and exhibit redox properties. Composite materials with acetylene black were investigated as positive electrodes for rechargeable lithium batteries. A specific capacity of 150 mAh g −1 was reached with 40% acetylene black. The composite electrodes showed moderately good cyclability with less than 10% degradation in the first 100 cycles.

Single crystal X-ray diffraction structures of two simple bis(guanidinium) sulfates that have previously been shown to recognise oxoanions in solution are reported. Comparison of these solid state structures with previous data suggests a relationship between increasing ligand planarity (preorganisation) and internal sulfate complexation, the greatest degree of preorganisation resulting in formation of a discrete 1 ∶ 1 host–guest complex.

Poly(methyl methacrylate/2-methacryloylethyl methacrylate)-based copolymers of varying composition have been synthesized and characterized. Free-radical polymerization of hydroxyethyl methacrylate and methyl methacrylate over a range of monomer feed ratios gives an ideal random copolymer series which has been functionalized by further methacryloylation of the pendant hydroxyl group. The resulting polymers have been cross-linked both thermally and by UV exposure, as evidenced by infrared and solid-state NMR spectroscopy. After thermal cross-linking the polymers remain stable up to 200 °C. Variation of polymer composition has allowed the refractive index to be tuned between 1.497 and 1.518, a range suitable for waveguide applications, and channel waveguides have been fabricated by UV writing. The propagation loss of these channel waveguides is less than 1 dB/cm at a range of near-IR wavelengths.

International audience; Polyamidoamine (PAMAM) are synthetic dendrimers which present attractive properties for the biolog- ical and biomedical fields, as they proved to be efficient drug and gene carriers. In order to increase their transfection efficiency, chemical modifications of the amino end-groups had been reported. In this work, the synthesis of the ammonia-cored G1(N) PAMAM and the consecutive chemical modification with glycine or phenylalanine amino-acids were monitored using the coupling of thin layer chromatography (TLC) with matrix–assisted laser desorption ionization–mass spectrometry (MALDI–MS). Thus, the moni- toring of the PAMAM synthesis included the identification of the by-products such as defective structures of PAMAM dendrimers as well as the study of phenylalanine-grafted PAMAM oligomer distribution.

We present here the preparation and the structural characterization of first-generation ammonia-cored polyamidoamine (PAMAM) dendrimers modified with glycine residues. Chemical modification of the dendrimer was done to increase the biocompatibility of these compounds, known to be effective delivery agents for drugs or genes. Fully modified PAMAM [Gly6G1(N)] on the one hand and partially modified [GlynG1(N), with n = 0 to 6)] on the other hand were obtained depending on the experimental conditions. The resulting modified PAMAM dendrimers have to be cautiously characterized to understand and interpret their physico-chemical and biochemical properties as well as to control their chemical design. The structural characterization was carried out using ion mobility spectrometry-mass spectrometry (IM-MS), multistage tandem mass spectrometry (MSn), accurate mass measurements by high resolution–mass spectrometry (HR-MS), two dimensional nuclear magnetic resonance (NMR) and capillary electrophoresis (CE). Characteristic fragmentation patterns for these compounds were obtained from ESI/MSn (with n = 2 to 4) experiments. IM-MS and CE analysis showed that a single component was mainly obtained for the complete grafting experimental conditions while a distribution of oligomers was produced for partially grafted products. The physical separation of GlynG1(N) oligomer ions was achieved in the gas phase (IM-MS) as well as in the condensed phase (CE). Besides, the collision cross sections (CCS) were estimated by IM-MS and compared to theoretical values. Then, the glycine grafting yield for GlynG1(N) PAMAM was determined by both NMR and IM-MS experiments.

Acylation of benzyl ferrocenecarboxylate 3 with benzoyl chloride affords the known ferrocene keto-acid 5 in one step and provides a convenient entry to a variety of unsymmetrical 1,1′-substituted ferrocene derivatives. Similar acylation procedures have been employed to bridge two ferrocene units leading to a series of rigid bis-ferrocene derivatives, which are precursors to more elaborate receptor architectures.

Reaction of 1-chlorocarbonyl-ferrocene or -ruthenocene with aza-15-crown-5 (1,4,7,10-tetraoxa-13-azacyclopentadecane) afforded the respective amide-linked metallocene crowns. Nucleophilic displacement of trimethylamine from trimethylammoniomethyl-ferrocene or -ruthenocene iodides with aza-15-crown-5 yielded the corresponding methylene-linked crowns. Variable-temperature 13C NMR investigation of the hindered rotation about the amide links of the amide-linked crowns in the presence of guest cations indicated that cation complexation occurs exclusively within the crown ring. Extraction experiments with a range of metal-cation dye salts revealed a favourable binding capacity for the methylene-linked crowns. Detailed 13C NMR analysis of sodium and potassium ion binding by these systems suggests the presence of a stabilising interaction between the metallocene π system and the crown-bound cation. Cyclic voltammetric analysis of metal-ion binding by the amine-linked crowns revealed cation-induced shifts of the appropriate redox couple comparable with those reported for related systems.

We have demonstrated that a planar integrated optical Bragg grating sensor chip, fabricated using a direct UV-writing approach, can perform as an all-optically accessed relative humidity sensor. Using a simple mesoporous silica thin film enabled operation across the range 0–100%RH, however a thickness decrease of 25% caused by hydrolytic degradation of the silica thin film resulted in a permanent decrease in sensitivity after 1–2 weeks use. Grafting the thin-film with aluminium oxide is shown here to prevent hydrolytic degradation with long-term sensitivity maintained. Aluminium oxide grafting offers the additional benefit of enhanced sensitivity, up to 3.5 times that of the silica analogue; the sensitivity of the aluminium oxide modified thin film device = 0.69 ± 0.05%RH/pm, in the range 0–60%RH within a gas flow system, whilst the sensitivity of the silica thin film sensor device = 2.47 ± 0.18%RH/pm. Long-term measurements, in static ambient lab conditions, were in excellent agreement with a commercial humidity sensor and also indicated that the thermal compensation afforded by the on-chip reference gratings was sufficient to prevent any drift in calibration. As with all humidity sensors, contamination of the sensor occurred. But for the aluminium oxide device, this was easily removed by rinsing with common organic solvents and the sensitivity was repeatedly and reproducibly restored. The device is accessed using optical fibre technology and is intrinsically safe in flammable environments.

We report the determination of the surface recombination velocity of electron-hole pairs for silicon samples passivated with organic monolayers using the Kelvin probe. The recombination velocity was determined from the surface photovoltage and incident photon flux. By scanning of the Kelvin probe tip over the sample, the change in surface recombination velocity can be measured allowing recombination lifetime mapping. Organic monolayers with different chain lengths and exhibiting various recombination lifetimes were synthesized through a two-step chlorination-alkylation technique. The estimated recombination lifetimes were compared against those obtained from an industrial standard technique and were found to be in good agreement.

The Kelvin probe is a very powerful and versatile tool, allowing the extraction of data such as diffusion length, surface photovoltage and impurity concentrations. This paper investigates the extraction of surface recombination velocities (and assuming a bulk lifetime, the surface recombination lifetime) from the I-V type dependence of the sample. By using an X-Y stage, the surface recombination lifetime can be imaged for entire wafers, instead of obtaining an average value of lifetime similar to that obtained from the Sinton WCT-120 lifetime tool. This is useful in determining where further improvements in the surface passivation can be obtained, by observing problem areas in the passivation layer.

Crystals of (15-crown-5)2KTCNQ adopt a solid-state architecture built up from isolated TCNQ•- dimer units surrounded by crown-encapsulated cation “barrels” with no evidence for direct counterion interaction. The structural and spectroscopic behavior of this material therefore provides a valuable model for the solid-state behavior of an isolated TCNQ•- dimer.

Whilst the use of FABMS in the analysis of ligand-cation interactions has become widespread, there are a number of experimental variables associated with the use of this technique, the effects of which have not previously been addressed. The interactions of 12-crown-4, 15-crown-5 and 18-crown-6 with the alkali metal cations reveal two important observations: (i) that the matrix employed for the FAB studies has a dramatic effect on the observed binding behaviour and (ii) that the observed relative intensities of protonated ions ([M + H]+) and metallated ions ([M + Metal]+) differ enormously. Determination of the ratios of these signals would allow quantitative arguments to be applied to experiments of this type. Accordingly, previous reports of the use of FABMS for the quantitative study of ligand–cation interactions must be viewed with caution.

A planar Bragg grating device has been developed that is capable of detecting changes in the refractive index of a wide range of fluids including solvents, acids and bases. The integration of this high precision refractive index sensor within a chemically resistant microfluidic flow system has enabled the investigation of diverse fluid interactions. By cycling between different solvents, both miscible and immiscible, within the microfluidic system it is shown that the previous solvent determines the nature of the refractive index profile across the transition in composition. This solvent dispersion effect is investigated with particular attention to the methanol–water transition, where transients in refractive index are observed that are an order of magnitude larger in amplitude than the difference between the bulk fluids. The potential complications of such phenomenon are discussed together with an example of a device that exploits this effect for the unambiguous composition measurement of a binary solvent system.

International audience

With the drive for ever more efficient photovoltaics, the passivating layer becomes of greater importance. Currently, two main passivating mechanisms have been widely investigated; removal of surface states by organic layers and charging of surfaces to invert the surface bands. Our paper aims to increase the knowledge of this area by combining the removal of surface states with charging, in an attempt to build ever more efficient passivation layers. It was found that upon immersion in base, the recombination lifetime significantly improved from around 8 µs to over 30 µs, due to a negative monolayer surface charge. As the charge is further from the silicon surface, both the recombination lifetime and surface photovoltage (SPV) decrease. This in turn indicates a reduction in the surface electron concentration. Once the surface charge is neutralized, both the recombination lifetime and SPV return to their starting value.

Age-related macular degeneration (AMD) is the most common cause of blindness in the developed world. There is currently no treatment for the cellular loss, which is characteristic of AMD. Transplantation of retinal pigment epithelium (RPE) cells represents a potential therapy. Because of AMD-related pathology in the native support, Bruch's membrane, transplanted RPE cells require a scaffold to reside on. We present here the development of an electrospun fibrous scaffold derived from methyl methacrylate and poly(ethylene glycol) (PEG) methacrylate for novel application as an RPE scaffold. Scaffolds were chemically modified to improve cell adhesion by functionalization not previously reported for this type of copolymer system. A human RPE cell line was used to investigate cell-scaffold interactions for up to two weeks in vitro. Scanning electron microscopy was used to characterize the fibrous scaffolds and confirm cell attachment. By day 15, cell area was significantly (p < 0.001) enhanced on scaffolds with chemical modification of the PEG chain terminus. In addition, significantly, less-apoptotic cell death was demonstrable on these modified surfaces.

Oxygen sensing is required for the understanding of many chemical processes across a diverse set of fields including medicine, environmental science and chemical synthesis. Oxygen sensing can be achieved through the use of electronic sensors. However, there are limitations associated with electronic sensors including susceptibility to electromagnetic interference and presenting a spark risk in flammable environments. Optical fiber and integrated optical chemical sensors overcome these limitations of electrical based sensing methods.

X-ray structural studies of cis-1,4-dihydro-4-tritylbiphenyl (2a) and its 4'-bromo derivative 2b reveal that, in contrast with earlier predictions based on solution NMR data, both adopt a similar congested conformation in which the cyclohera-1,4-diene ring is almost planar, forcing the isolated aromatic ring into the π-cloud of one of the benzene rings of the trityl substituent and leading to considerable stretching of the C 1 -C 11 bond and a close intramolecular edge-to-face aromatic interaction. Variable-temperature 1 H NMR experiments suggest that this interaction becomes increasingly important at low temperatures

A photoactive material has been synthesised in which azobenzene units are attached to a methyl methacrylate/2-hydroxyethyl methacrylate co-polymer and shows repeated photoresponsive switching upon irradiation at 365 nm and 254 nm with long term thermal stability. In combination with a direct UV-written silica-on-silicon Bragg grating, this has been used to fabricate a prototype optical device which undergoes reversible refractive index changes at telecom wavelengths. The 63 GHz tuning response demonstrated by this device has potential applicability for reconfigurable dispersion compensation for use in optical networks.

Low-frequency a.c. dielectric spectroscopy has been used to probe contact effects on, and the dielectric behaviour of, a series of structurally related organic dyes (hydroxypyridone trimethine oxonol salts) as compressed powders. The technique reveals contributions from dipolar relaxation, small-particle migration, and electronic conductivity depending on the nature of the counter cation. In general, whilst changing contacts to the samples modified the relaxation rate, neither the spectral form nor the magnitude of the a.c. response were affected.

Poly(amidoamine) (PAMAM) dendrimers are promising multipotent gene delivery vectors, providing favorable DNA condensation properties also in combination with the possibility of conjugation of different targeting ligands to their surface. They have been used for transfection both in vitro and in vivo, but their application is currently somewhat limited due to inherent cytotoxicity. In this work we investigate how two types of surface modification, acetylation and PEGylation, affect the DNA binding characteristics, the cytotoxicity and the in vitro transfection efficiency of generation 4 and 5 PAMAM dendrimers. Particularly, we address how the morphology of DNA-dendrimer complexes, formed under low salt conditions, changes upon dilution in cell growth medium, an event that inevitably occurs before the complexes reach the cell surface in any transfection experiment. We find that acetylation and PEGylation essentially eliminates the inherent dendrimer cytotoxicity. However, the transfection efficiency of the modified dendrimers is lower than that of the corresponding unmodified dendrimers, which can be rationally understood by our observations that DNA is less condensed when complexed with these modified dendrimers. Although small DNA-dendrimer particles are formed, the availability for ethidium intercalation and nuclease degradation is significantly higher in the modified DNA-dendrimer complexes than in unmodified ones. Dilution in cell growth medium has a drastic effect on these electrostatically assembled complexes, resulting in increase in size and DNA availability. Our results strongly add to the notion that it is of importance to perform a biophysical characterization under conditions as close to the transfection situation as possible, to enable conclusions regarding structure-activity relations of gene delivery vectors.