Direct ink writing of high-resolution cellulose structures.

3D printing is envisioned to play an important role in the production of membranes for e.g., water purification and bio-separation applications due to the prospect of creating new and cleverly designed structures. Among different 3D printing techniques, direct ink writing offers the opportunity to print a wide variety of materials with high-detail resolution. There is a range of parameters that need to be optimized in order to develop robust printing techniques at that scale. In this study, cellulose acetate (CA), which is a biocompatible material, has been used as an ink. In order to examine the printability and the possibility of printing features as small as a few µm, nozzles with different diameters and inks with varying amounts and molecular weights of CA were investigated. Findings in this study indicate that, depending on the wetting on the underlaying structure, the nozzle's internal and external diameter affects the detail resolution of the printed structure. Different inks result in different widths of printed strands and generally a higher amount and higher molecular weights of CA results in higher detail resolution. However, too high amount of CA and molecular weight will increase the clogging risk in the nozzle. In this study, the internal size of the nozzle was 3 µm, and by selecting a  suitable ink, it was possible to print strands down to 1 µm size and 6 µm inter-strand distance in the air, bridging supports with limited sagging. Furthermore, wall structures consisting of 300 layers, corresponding to about 300 µm in total height, were successfully printed.

A glimpse of the inner workings of the templated site.

This is the first direct experimental probe, using EXAFS, of the active site within molecularly imprinted polymers and paves the way to a more detailed understanding of the inner workings of molecular imprinting.

The use of FTIR and NMR spectroscopies to study prepolymerisation interactions in nitrogen heterocycles.

A detailed investigation into the functional groups responsible for the formation of a noncovalent complex between 2-aminopyridine (template) and methacrylic acid (functional monomer) has been carried out using FTIR spectroscopy and confirmed by (1)H NMR spectroscopic data. The approach adopted to confirm the mechanism of interaction was the analysis of the template plus the structurally similar 2-methylaminopyridine and 2-dimethylaminopyridine. A 1:1 stoichiometry of complexation was determined by Job plot analysis following titration, with FTIR results complementing those of the (1)H NMR study. The strength of interaction between 2-aminopyridine and the functional monomer measured through band shifts by FTIR spectroscopy was compared with such interactions for the isomers 3- and 4-aminopyridine. This comparison identified a clear correlation between template pK(a), degree of interaction and subsequent nonspecific binding in the nonimprinted polymer. Using FTIR spectroscopy it was also possible to observe the effect of temperature on the prepolymerisation solution. IR spectra showed that lower temperatures led to more stabilized interactions of the hydrogen-bonded complex. The potential advantages of FTIR spectroscopy compared with (1)H NMR spectroscopy in studying prepolymerisation solutions have been identified.

A class II aldolase mimic.

[structures: see text] A class II aldolase-mimicking synthetic polymer was prepared by the molecular imprinting of a complex of cobalt (II) ion and either (1S,3S,4S)-3-benzoyl-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one (4a) or (1R,3R,4R)-3-benzoyl-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one (4b) in a 4-vinylpyridine-styrene-divinylbenzene copolymer. Evidence for the formation of interactions between the functional monomer and the template was obtained from NMR and VIS titration studies. The polymers imprinted with the template demonstrated enantioselective recognition of the corresponding template structure, and induced a 55-fold enhancement of the rate of reaction of camphor (1) with benzaldehyde (2), relative to the solution reactions, and were also compared to reactions with a series of reference polymers. Substrate chirality was observed to influence reaction rate, and the reaction could be competitively inhibited by dibenzoylmethane (6). Collectively, the results presented provide the first example of the use of enantioselective molecularly imprinted polymers for the catalysis of carbon-carbon bond formation.