Ian R. Dunkin

Investigations of solvent–solute interactions in room temperature ionic liquids using solvatochromic dyes

Different measures of polarity and nucleophilicity of a range of ionic liquids have been investigated using two solvatochromic dyes; the polarity appears to be largely cation controlled, while the donor strength is entirely anion dependent.

The effects of anion and cation substitution on the ultrafast solvent dynamics of ionic liquids: A time-resolved optical Kerr-effect spectroscopic study

Ultrafast solvent dynamics of room-temperature ionic liquids have been investigated by optical heterodyne-detected Raman-induced Kerr-effect spectroscopy (OHD-RIKES) by studying the effects of cation and anion substitution on the low frequency librational modes. The spectra of two series of imidazolium salts are presented. The first series is based on the 1-butyl-3-methylimidazolium salts [bmim]+ containing the anions trifluoromethanesulfate [TfO]−, bis(trifluoromethanesulfonyl)imide [Tf2N]−, and hexafluorophosphate [PF6]−. The second series is based on [Tf2N]− salts containing the three cations 1-butyl-2,3-dimethylimidazolium [bmmim]+, 1-methyl-3-octylimidazolium [omim]+, and [bmim]+. It is found in all five samples that the signal is due to libration of the imidazolium ring at three frequencies around 30, 65, and 100 cm−1 corresponding to three local configurations of the anion with respect to the cation.

Production of Super Selective Polysulfone Hollow Fiber Membranes for Gas Separation

Polysulfone gas separation hollow fiber membranes were manufactured using a dry/wet spinning process with forced convection in the dry gap. Hollow fibers were produced using two different bore coagulants: one pure water and one with reduced water activity. An optimized multi-component dope was used which proved to be a shear-thinning power-law fluid. For each bore system, membranes were spun at low and high dope extrusion rates (DERs) corresponding to shear rates of around 4000 s−1 and 10 000 s−1, respectively, at the outer spinneret wall. Plane polarized infrared spectroscopy was used to probe the membrane active layer. Pressure-normalized fluxes and selectivities were evaluated using pure carbon dioxide and methane. For the spinning conditions used here, the combination of reduced water activity in the bore and high DER produced highly selective membranes. Some selectivities reached about three times the recognized intrinsic value for the polymer.

Direct measurement of rheologically induced molecular orientation in gas separation hollow fibre membranes and effects on selectivity

Asymmetric polysulfone hollow fibre membranes for gas separation were spun using a dry/wet spinning process. An optimised four component dope solution was used: 22% (w/w) polysulfone, 31.8% (w/w) N,N-dimethylacetamide, 31.8% (w/ w) tetrahydrofuran and 14.4% (w/w) ethanol. Fibres were spun at low- and high-dope extrusion rates and hence at different levels of shear. Molecular orientation in the active layer of the membranes was measured by plane-polarised infrared spectroscopy. Gas permeation properties (permeability and selectivity) were evaluated using pure carbon dioxide and methane. The spectroscopy indicated that increased molecular orientation occurs in the high-shear membranes. The selectivities of these membranes were heightened and even surpassed the recognised intrinsic selectivity of the membrane polymer. The results suggest that increased shear during spinning increases molecular orientation and, in turn, enhances selectivity.

Bimolecular rate constants for diffusion in ionic liquidsElectronic supplementary information (ESI) available: Fig. S1: isokinetic plot obtained for the energy transfer reaction of 3BP* and N in five ionic liquids, toluene and acetonitrile. See http://www.rsc.org/suppdata/cc/b2/b202944h/

The temperature dependence of the bimolecular rate constants for a diffusion controlled reaction involving neutral reactants have been directly determined in five commonly used ionic liquids over the temperature range 5-70 degrees C.

Molecular orientation and the performance of synthetic polymeric membranes for gas separation

Asymmetric polysulfone and polyacrylonitrile flat sheet membranes have been produced by a simple dry-wet casting technique. Both membrane types were cast at low and high shear rate. Molecular orientation in the membranes was determined using polarized reflection i.r. spectroscopy. Gas permeation properties were examined using carbon dioxide and methane as test gases. I.r. dichroism was detected in all samples, the extent being greater in the high shear membranes for both polysulfone and polyacrylonitrile. The effects, however, were more intense in the polyacrylonitrile samples. Gas permeation tests showed that for both polymer types, the high shear membranes exhibited greater selectivity (CO2/CH4). Selectivities were greater and permeabilities lower for the polysulfone samples. The results show (i) that polarized reflection i.r. spectroscopy can be used to determine—at least qualitatively—the degree of molecular orientation in sheared polymers, (ii) that molecular orientation is enhanced by shear during casting, and (iii) that this has a favourable effect on membrane selectivity. In the examples chosen molecular orientation was more pronounced in the polyacrylonitrile membranes, but with these the potential for high selectivity was thwarted by the poor intrinsic permeability of the polymer which causes flow through pores or imperfections to dominate.

Optical spectroscopic methods for probing the conformational stability of immobilised enzymes

We report the development of biophysical techniques based on circular dichroism (CD), diffuse reflectance infrared Fourier transform (DRIFT) and tryptophan (Trp) fluorescence to investigate in situ the structure of enzymes immobilised on solid particles. Their applicability is demonstrated using subtilisin Carlsberg (SC) immobilised on silica gel and Candida antartica lipase B immobilised on Lewatit VP.OC 1600 (Novozyme 435). SC shows nearly identical secondary structure in solution and in the immobilised state as evident from far UV CD spectra and amide I vibration bands. Increased near UV CD intensity and reduced Trp fluorescence suggest a more rigid tertiary structure on the silica surface. After immobilised SC is inactivated, these techniques reveal: a) almost complete loss of near UV CD signal, suggesting loss of tertiary structure; b) a shift in the amide I vibrational band from 1658 cm(-1) to 1632 cm(-1), indicating a shift from alpha-helical structure to beta-sheet; c) a substantial blue shift and reduced dichroism in the far UV CD, supporting a shift to beta-sheet structure; d) strong increase in Trp fluorescence intensity, which reflects reduced intramolecular quenching with loss of tertiary structure; and e) major change in fluorescence lifetime distribution, confirming a substantial change in Trp environment. DRIFT measurements suggest that pressing KBr discs may perturb protein structure. With the enzyme on organic polymer it was possible to obtain near UV CD spectra free of interference by the carrier material. However, far UV CD, DRIFT and fluorescence measurements showed strong signals from the organic support. In conclusion, the spectroscopic methods described here provide structural information hitherto inaccessible, with their applicability limited by interference from, rather than the particulate nature of, the support material.

Molecular imprinting of flat polycondensed aromatic molecules in macroporous polymers

Abstract 2,6-Diaminoanthroquinone (DAAQ) has been used as a non-covalently bound template in order to generate shape-selective cavities in crosslinked porous polymers based on ethylene glycol dimethacrylate (EGDMA) and divinylbenzene (DVB). Dimethylsulphoxide was used as a solvent and porogen. When acrylic and methacrylic acid were employed to form a complementary binding site within the cavity, there was no evidence for selective resorption of DAAQ and hence no evidence for shape-selective cavity formation. However, when a monomer containing sulphonic acid groups was used in place of the polymerizable carboxylic acids, stronger interaction with DAAQ was achieved and shape-selective cavities within polymers were formed as indicated by the selective resorption of DAAQ by such polymers relative to analogous non-templated polymers. Similarly selective sorption of non-functional anthracene, with a similar framework to DAAQ, was also demonstrated, confirming the shape-selective nature of the cavities.

Orbital symmetry conservation and frontier orbital control in the reactions of organic radical cations

Abstract Electrocyclic ring-openings, cycloreversions, cycloadditions, and sigmatropic rearrangements of organic radical cations are discussed in terms of a simple qualitative theory, based on orbital symmetry conservation or frontier orbital interactions. Special emphasis is placed on the photo-chemical reactions of the radical cations, numerous examples of which have recently been discovered experimentally. The theoretical models are in good general accord with the apparent facility with which radical cation rearrangements and fragmentations have been observed to take place, and provide some detailed predictions, especially with respect to stereochemistry, for further experimental testing.

Ionic liquids: polar, but weakly coordinating solvents for the first biphasic oligomerisation of ethene to higher α-olefins with cationic Ni complexes

Ethylene oligomerisation in ionic liquids gives predominately alk-1-ene products with better reactivity and selectivity than in conventional solvents; turnover frequencies are correlated with polarity data obtained using solvatochromic dyes.