Ritu Kataky

Emulsion-templated porous materials (PolyHIPEs) for selective ion and molecular recognition and transport: applications in electrochemical sensing

Functionalised emulsion-templated polymers (PolyHIPEs) are reported as new materials for electroanalytical applications. PolyHIPEs, which are prepared from high internal phase emulsions (HIPEs), were tailored by optimisation of polymerisation conditions to yield well-defined, tubular, porous membranes. The PolyHIPE membrane backbone was activated by incorporating ionophores, graphite particles, electron mediators and enzymes. The results show that a valinomycin ionophore impregnated, plasticised membrane shows a Nernstian response to K+ ions with improved detection limits and selectivity coefficients compared to traditional PVC membranes. The graphite/mediator/enzyme loaded membranes exhibit quasi-reversible redox behaviour with semi-infinite linear diffusion at fast scan rates tending to radial diffusion at slow scan rates. Additionally, composite, asymmetric membrane structures with a porous PolyHIPE membrane and a PVC membrane exclude proteins such as BSA (bovine serum albumin) and α1 acid glycoprotein (AAG). These preliminary results demonstrate that plasticised membranes with functionalised skeletons and with controllable porosity such as PolyHIPE membranes are very promising for the fabrication of sensors with integrated separation.

Synthesis of a kinetically stable yttrium-90 labelled macrocycle–antibody conjugate

Lysine is a precursor for the synthesis of an aminobutyl C-functionalised tetra-azacyclododecane tetra-acid which has been linked to B72.3 antibody and may be labelled with 90Y to form a kinetically stable complex of potential use in radioimmunotherapy.

Potentiometric, enantioselective sensors for alkyl and aryl ammonium ions of pharmaceutical significance, based on lipophilic cyclodextrins

Lipophilic alpha, beta and gamma cyclodextrins (CDs) have been systematically analysed in order to establish their selective binding to onium ions. They have been identified as excellent ionophores for a range of ions of vital importance in clinical, pharmaceutical and forensic analysis. From the results obtained we found the following. A peroctylated cyclodextrin provides a size-selective cavity for the binding and detection of onium ions. Potentiometric alpha, beta and gamma cyclodextrin-based electrodes selectively sense NH4+, NMe4+ and NEt4+ ions respectively. These experiments were performed in order to enable us to understand the nature of analyte recognition by the lipophilic cyclodextrins. Peroctylated alpha CD is a suitable ionophore for dopamine hydrochloride, -log[C] = 5.4, -log K = 2.0 (in serum level of Na+, K+, Ca2+) whereas peroctylated and 2,6 didodecyl beta CD sense acetylcholine chloride, -log[C] = 5.0, -log K = 4.2 (in serum level of Na+, K+, Ca2+) and creatinine hydrochloride, -log K = 2.7 (in serum level of Na+, K+, Ca2+), respectively. The 2,6 didodecyl beta CD responds to more bulky aryl ammonium ions such as the anaesthetics procaine, prilocaine and lignocaine hydrochlorides, -log K = 4.2 (in serum level of Na+, K+, Ca2+). Partially octylated alpha CD has been identified as an enantioselective sensor for ephedrine hydrochloride, -log K = 4.5 (in serum level of Na+, K+, Ca2+), -log Kpot+/- = 2.6, and related compounds such as amphetamine hydrochloride. The 2,6 didodecyl beta CD is enantioselective for propranalol hydrochloride, -log K = 4.2 (in serum level of Na+, K+, Ca2+), -log Kpot+/- = 2.7. Complexation has also been studied by electrospray mass spectrometry (ESMS).

Comparative performance of 14-crown-4 derivatives as lithium-selective electrodes

A series of neutral ionophore-based lithium-selective liquid-membrane electrodes have been prepared and the electrode performance compared with similar electrodes based on the lithium ionophores ETH 1810-ortho-nitrophenyl octyl ether (oNPOE) and ETH 2137-bis(1-butylpentyl) adipate (BBPA). By using a diamide substituted 14-crown-4 macrocycle, selectivities for Li+ in the presence of Na+ of log kpotLi,Na = -3.25 and -2.92 were obtained for diisobutylamide-oNPOE and di-n-butylamide-oNPOE derivatives. The di-n-butylamide-oNPOE based electrode functioned satisfactorily in serum, exhibiting a fast response time (10-15 s), an acceptable lifetime of 50 d and minimal protein interference.

Potential of enzyme mimics in biomimetic sensors: a modified-cyclodextrin as a dehydrogenase enzyme mimic.

This paper reports the application of a dehydrogenase enzyme mimic as a biomimetic sensor. The model compound investigated was a beta-cyclodextrin (beta-CD) derivative with a nicotinamide group attached to the secondary face of a beta-CD (Fig. 1g). It was envisaged that the nicotinamide group would act as the electron transfer agent and that the cyclodextrin would provide a suitable hydrophobic cavity for the reaction to take place in. Ethanol, propranalol, dopamine and acetone were used as substrates in backgrounds of hydrophilic and hydrophobic anions. Electrochemical and fluorescence techniques were used to study the catalytic effects in solution. It was found that the size of the analyte and the hydrophobicity of the anion affected the catalytic activity of the dehydrogenase mimic. Catalytic effects were most enhanced with ethanol and dopamine in presence of larger and more strongly solvated anions, SO4(2-) and H2PO4- which are excluded from the cavity. The molecule was also immobilised in a sol-gel matrix and investigated as a sol-gel electrochemical biomimetic sensor. Concentration dependence with increasing aliquots of ethanol was observed. These results indicated that a re-usable biomimetic sensor is indeed feasible.

Synthesis of 1,10-dithia-4,7,13,16-tetra-azacyclo-octadecane, 1-aza-4,7-dithiacyclononane, and N,N′-1,2-bis(1-aza-4,7-dithia-cyclononyl)ethane. Structural and solution studies of their silver complexes

The synthesis of the ligands 1-aza-4,7-dithiacyclononane, N,N′-1,2-bis(1-aza-4,7-dithiacyclo-nonyl)ethane, and 1,10-dithia-4,7,13,16-tetra-azacyclo-octadecane and their silver(I) complexes are reported. Stability constants in water and methanol have been determined using pH-metric methods, and enthalpies of complexation measured calorimetrically in methanol. The N-alkyl derivatives show enhanced enthalpies of complexation, but exhibit unfavourable entropies of complexation. Crystal structures of the [18]-N4S2 and bis[9]-NS2 silver complexes reveal distorted octahedral co-ordination geometry, although in aqueous solution the bis[9]-NS2 silver complex does not adopt the sandwich structure revealed in the crystallographic analysis.

Platinum(II) complexes of N^C^N-coordinating 1,3-bis(2-pyridyl)benzene ligands: thiolate coligands lead to strong red luminescence from charge-transfer states.

A new family of platinum(II) complexes of the form PtL(n)SR have been prepared, where L(n) represents a cyclometalating, N^C^N-bound tridentate ligand and SR is a monodentate thiolate ligand. The complexes fall into two groups, those of PtL(1)SR where HL(1) = 1,3-bis(2-pyridyl)benzene, and those of PtL(2)SR, where HL(2) = methyl 3,5-bis(2-pyridyl)benzoate. Each group consists of five complexes, where R = CH3, C6H5, p-C6H4-CH3, p-C6H4-OMe, p-C6H4-NO2. These compounds, which are bright red, orange, or yellow solids, are formed readily upon treatment of PtL(n)Cl with the corresponding potassium thiolate KSR in solution at room temperature. The replacement of the chloride by the thiolate ligand is accompanied by profound changes in the photophysical properties. A broad, structureless, low-energy band appears in the absorption spectra, not present in the spectra of PtL(n)Cl. In the photoluminescence spectra, the characteristic, highly structured phosphorescence bands of PtL(n)Cl in the green region are replaced by a broad, structureless emission band in the red region. These new bands are assigned to a πS/dPt → π*N^C^N charge-transfer transition from the thiolate/platinum to the N^C^N ligand. This assignment is supported by electrochemical data and TD-DFT calculations and by the observation that the decreasing energies of the bands correlate with the electron-donating ability of the substituent, as do the increasing nonradiative decay rate constants, in line with the energy-gap law. However, the pair of nitro-substituted complexes do not fit the trends. Their properties, including much longer luminescence lifetimes, indicate that the lowest-energy excited state is localized predominantly on the arenethiolate ligand for these two complexes. Red-emitting thiolate adducts may be relevant to the use of PtL(n)Cl complexes in bioimaging, as revealed by the different distributions of emission intensity within live fibroplast cells doped with the parent complex, according to the region of the spectrum examined.

Sol–gel-immobilised terbium complexes for luminescent sensing of dissolved oxygen by analysis of emission decayElectronic supplementary information (ESI) available: examples of the analysis of the emission decay data for calibration purposes and examples of data sets and their treatment at different delay times. See http://www.rsc.org/suppdata/nj/b1/b110743g/

Cationic terbium complexes bearing an N-methylphenanthridinium chromophore have been incorporated in sol–gel thin films and their response characteristics analysed with respect to variations in dissolved oxygen concentration. Analysis of the emission lifetime decay curves (547 nm) has allowed a linear calibration model to be defined over an oxygen concentration range from zero to 0.5 mM (H2O, 295 K).

Modular assembly of a preorganised, ditopic receptor for dicarboxylates

Two types of calix[4]arene derived hosts for anions with, respectively, 1,3-alternate and cone conformations have been prepared; the 1,3-alternate system binds dicarboxylate anions in a ditopic manner while the cone compounds are deprotonated by carboxylates.

DEPENDENCE OF THE RELAXIVITY AND LUMINESCENCE OF GADOLINIUM AND EUROPIUM AMINO-ACID COMPLEXES ON HYDROGENCARBONATE AND PH

Reversible binding of hydrogencarbonate to a chiral di-aqua lanthanide complex occurs in the pH range 6.5–8.5, limiting the measured relaxivity in the gadolinium complex and enhancing the metal-based emission in the europium analogue.