Swelling and shrinking properties of thermo-responsive polymeric ionic liquid hydrogels with embedded linear pNIPAAM.

In this study, varying concentrations of linear pNIPAAM have been incorporated for the first time into a thermo-responsive polymeric ionic liquid (PIL) hydrogel, namely tributyl-hexyl phosphonium 3-sulfopropylacrylate (P-SPA), to produce semi-interpenetrating polymer networks. The thermal properties of the resulting hydrogels have been investigated along with their thermo-induced shrinking and reswelling capabilities. The semi-interpenetrating networks (IPN) hydrogels were found to have improved shrinking and reswelling properties compared with their PIL counterpart. At elevated temperatures (50-80 °C), it was found that the semi-IPN with the highest concentration of hydrophobic pNIPAAM exhibited the highest shrinking percentage of ~40% compared to the conventional P-SPA, (27%). This trend was also found to occur for the reswelling measurements, with semi-IPN hydrogels producing the highest reswelling percentage of ~67%, with respect to its contracted state. This was attributed to an increase in water affinity due to the presence of hydrophilic pNIPAAM. Moreover, the presence of linear pNIPAAM in the polymer matrix leads to improved shrinking and reswelling response compared to the equivalent PIL.

A portable centrifugal analyser for liver function screening.

Mortality rates of up to 50% have been reported after liver failure due to drug-induced hepatotoxicity and certain viral infections (Gao et al., 2008). These adverse conditions frequently affect HIV and tuberculosis patients on regular medication in resource-poor settings. Here, we report full integration of sample preparation with the read-out of a 5-parameter liver assay panel (LAP) on a portable, easy-to-use, fast and cost-efficient centrifugal microfluidic analysis system (CMAS). Our unique, dissolvable-film based centrifugo-pneumatic valving was employed to provide sample-to-answer fashion automation for plasma extraction (from finger-prick of blood), metering and aliquoting into separate reaction chambers for parallelized colorimetric quantification during rotation. The entire LAP completes in less than 20 min while using only a tenth the reagent volumes when compared with standard hospital laboratory tests. Accuracy of in-situ liver function screening was validated by 96 separate tests with an average coefficient of variance (CV) of 7.9% compared to benchtop and hospital lab tests. Unpaired two sample statistical t-tests were used to compare the means of CMAS and benchtop reader, on one hand; and CMAS and hospital tests on the other. The results demonstrate no statistical difference between the respective means with 94% and 92% certainty of equivalence, respectively. The portable platform thus saves significant time, labour and costs compared to established technologies, and therefore complies with typical restrictions on lab infrastructure, maintenance, operator skill and costs prevalent in many field clinics of the developing world. It has been successfully deployed to a centralised lab in Nigeria.

Temperature and pH triggered release characteristics of water/fluorescein from 1-ethyl-3-methylimidazolium ethylsulfate based ionogels.

A crosslinked poly(N-isopropylacrylamide) ionogel encapsulating an ionic liquid exhibits improved transmittance properties, enhanced water uptake/release, greater thermal actuation behaviour and distinct solvatomorphology over its hydrogel equivalent. It was also found that the rate of release of fluorescein pre-loaded into membranes was considerably enhanced for ionogels compared to equivalent hydrogels, and could be triggered through changes in pH and temperature.

An electrochromic ionic liquid: design, characterization, and performance in a solid-state platform.

This work describes the synthesis and characteristics of a novel electrochromic ionic liquid (IL) based on a phosphonium core tethered to a viologen moiety. When integrated into a solid-state electrochromic platform, the viologen modified IL behaved as both the electrolyte and the electrochromic material. Platform fabrication was achieved through in situ photo-polymerization and encapsulation of this novel IL within a hybrid sol-gel. Important parameters of the platform performance, including its coloration efficiency, switching kinetics, and optical properties were characterised using UV-vis spectroscopy and cyclic voltammetry in tandem. The electrochromic platform exhibits a coloration efficiency of 10.72 cm(2) C(-1) and a varied optical output as a function of the incident current. Despite the rather viscous nature of the material, the platform exhibited approximately 2 orders of magnitude faster switching kinetics (221 s to reach 95 % absorbance) when compared to previously reported electrochromic ILs (18,000 s).

Physicochemical study of spiropyran-terthiophene derivatives: photochemistry and thermodynamics.

The photochemistry and thermodynamics of two terthiophene (TTh) derivatives bearing benzospiropyran (BSP) moieties, 1-(3,3″-dimethylindoline-6'-nitrobenzospiropyranyl)-2-ethyl 4,4″-didecyloxy-2,2':5',2″-terthiophene-3'-acetate (BSP-2) and 1-(3,3″-dimethylindoline-6'-nitrobenzospiropyranyl)-2-ethyl 4,4″-didecyloxy-2,2':5',2″-terthiophene-3'-carboxylate (BSP-3), differing only by a single methylene spacer unit, have been studied. The kinetics of photogeneration of the equivalent merocyanine (MC) isomers (MC-2 and MC-3, respectively), the isomerisation properties of MC-2 and MC-3, and the thermodynamic parameters have been studied in acetonitrile, and compared to the parent, non-TTh-functionalised, benzospiropyran derivative, BSP-1. Despite the close structural similarity of BSP-2 and BSP-3, their physicochemical properties were found to differ significantly; examples include activation energies (E(a(MC-2)) = 75.05 kJ mol(-1), E(a(MC-3)) = 100.39 kJ mol(-1)) and entropies of activation (ΔS = 43.38 J K(-1) mol(-1), ΔS = 37.78 J K(-1) mol(-1)) for the thermal relaxation from MC to BSP, with the MC-3 value much closer to the unmodified MC-1 value (46.48 J K(-1) mol(-1)) for this latter quantity. The thermal relaxation kinetics and solvatochromic behaviour of the derivatives in a range of solvents of differing polarity (ethanol, dichloromethane, acetone, toluene and diethyl ether) are also presented. Differences in the estimated values of these thermodynamic and kinetic parameters are discussed with reference to the molecular structure of the derivatives.

Stimuli responsive ionogels for sensing applications-an overview.

This overview aims to summarize the existing potential of "Ionogels" as a platform to develop stimuli responsive materials. Ionogels are a class of materials that contain an Ionic Liquid (IL) confined within a polymer matrix. Recently defined as "a solid interconnected network spreading throughout a liquid phase", the ionogel therefore combines the properties of both its solid and liquid components. ILs are low melting salts that exist as liquids composed entirely of cations and anions at or around 100 °C. Important physical properties of these liquids such as viscosity, density, melting point and conductivity can be altered to suit a purpose by choice of the cation/anion. Here we provide an overview to highlight the literature thus far, detailing the encapsulation of IL and responsive materials within these polymeric structures. Exciting applications in the areas of optical and electrochemical sensing, solid state electrolytes and actuating materials shall be discussed.

Photochromic imidazolium based ionic liquids based on spiropyran.

We investigate the physicochemical properties of a novel imidazolium benzospiropyran derivative, SP(Im), in imidazolium based ionic liquids (ILs). SP(Im) was prepared through alkylation of an imidazole to the photoswitchable compound and this derivative was characterised in imidazolium based ILs with increasing chain length to examine the stability of its merocyanine (MC) and spiropyran (SP) forms and compared to standard spiropyran, BSP. The rate of thermal relaxation of the new derivative is found to be about ten times faster than that of BSP as reflected in rates of 13.9 x 10(-3) s(-1) and 1.0 x 10(-3) s(-1) for SP(Im) and BSP, respectively, in [C(6)mIm][NTf(2)]. Since ILs are believed to form nano-structured domains it is proposed that the covalent attachment of the imidazolium side group of SP(Im) fully integrates the photoswitchable moiety into the non-polar region through side-chain association. In contrast, unbound BSP is relatively free to migrate between both polar and non-polar regions and the MC form is more readily stabilised by the IL charge via through space interactions and spontaneous movement to charged nano-domains leading to enhancement of the MC lifetime. At higher concentrations, rheological and transport properties were investigated to determine the impact of covalent attachment of the BSP fragment to an imidazolium cation on the ionic liquid structure. Ionic conductivity was found to decrease by up to 23% for SP(Im) with effects increasing with cation side-chain length. Unlike BSP, the photoswitching of the SP(Im) did not affect conductivity or viscosity values. This may indicate that the mobility of the photoswitchable compound and the resulting disruption of such movement may be critical to the control of this physical property.

Photochromism of nitrobenzospiropyran in phosphonium based ionic liquids.

The photo-, thermo- and solvatochromic properties of 2,3-dihydro-1',3',3'-trimethyl-6-nitrospiro[1-benzopyran-2,2'-1H-indole] (BSP) and its photo-induced merocyanine isomer (MC) were investigated in phosphonium based ILs by UV-vis absorption spectroscopy. It was found that the kinetics and thermodynamics of the BSP <--> MC equilibrium were sensitive to the nature of the anion. The MC lambda(max) shifted from 560 nm to 578 nm when in solutions of [P(1,4,4,4)][tos] and [P(6,6,6,14)][dca], respectively. The BSP isomer was highly favoured at equilibrium in the ILs studied; K(e) values observed were similar to non-polar solvents such as dichloromethane. The thermal relaxation of MC in all ILs is first order, and in comparison with aprotic polar solvents possessing comparable polarity (such as acetonitrile). Thermal relaxation rates of MC were monitored over a range of temperatures; at 293 K rates varied from 5.19 to 25.03 x 10(-4) s(-1). A non-linear relationship between K(e) and k was observed; this contradicts what is expected for BSP in molecular solvents and suggests the isomers exhibit different molecular/solvation environments. The energetics of the thermal relaxation of MC in ILs were observed; activation energies ranged from 71 to 90 kJ mol(-1) and all ILs exhibit negative activation entropies ranging between -72 and -8.2 J K(-1) mol(-1). A linear relationship between activation energy and entropy was observed.

Biocompatible ionic liquids: a new approach for stabilizing proteins in liquid formulation.

Ionic liquids (ILs) have shown excellent promise as both solutes and solvents for stabilizing proteins at room temperature. Because many modern drugs are protein-based, these stabilizing characteristics have great potential to provide advances in the field of liquid formulation of therapeutic proteins. However, before these developments can be translated into clinical solutions it is essential to establish data related to the biocompatibility of these ILs. The current work investigates the cytotoxicity of several ILs that were rationally synthesized from natural biomolecules and compounds that have already been approved as excipients for drug formulations. The effect of choline dihydrogen phosphate (choline dhp), choline saccharinate, and 1-butyl 3-methyl imidazolium lactate (bmim lactate) on the metabolic activity of a mouse macrophage cell line (J774) was assessed using the reduction in resazurin as an indicator of activity and, by extension, viability. Two formulations of lysozyme (10 mg/ml and 100 mg/ml) in 80 wt % choline dhp (aq) were prepared and the proteins were evaluated for structural stability immediately following formulation and again at 1 month. Equivalent formulations in 0.1 M Na acetate aqueous buffer were evaluated as controls. A differential scanning microcalorimeter (DSC) was used to evaluate the structural stability on the basis of the unfolding temperature and the enthalpy of unfolding, and a micrococcus lysodiekticus activity test was used to evaluate functional activity. All compounds were found to be relatively benign, with toxicity increasing in the order choline dhp

Photo- and solvatochromic properties of nitrobenzospiropyran in ionic liquids containing the [NTf2]- anion.

The photo-, thermo- and solvatochromic properties of 2,3-dihydro-1',3',3'-trimethyl-6-nitrospiro-[1-benzopyran-2,2'-1H-indole] (BSP-NO(2)) were studied in ILs containing the anion [NTf(2)](-) by UV-Vis absorption spectroscopy, ab initio molecular orbital theory and density functional theory (DFT) calculations. It was found that the kinetics and thermodynamics of the BSP-NO(2) <--> MC (merocyanine) equilibrium was sensitive to the nature of the cation. It was also observed that the imidazolium cation can form a through-space orbital interaction with the MC isomer, rather than a simple electrostatic interaction, thus preventing the MC conversion back to the BSP-NO(2) isomer. The BSP-NO(2) <--> MC equilibrium thus serves as a model system for studying modes of interaction of the cations in ionic liquids.

Liquids intermediate between "molecular" and "ionic" liquids: liquid ion pairs?

Ionic liquids comprised of tetradecyltrihexyl- and tetrabutyl-phosphonium cations paired with chloride or sulfonyl amide anions exhibit properties that reflect strong ion association, including comparatively low viscosity as well as a degree of volatility, and hence exemplify an interesting intermediate state between true ionic and true molecular liquids.