Electrochemistry and Spectroelectrochemistry of Luminescent Europium Complexes

Fast, cost effective, and robust means of detecting and quantifying lanthanides are needed to support more efficient tracking within the nuclear, medicinal, and industrial fields. Furthermore, methods for isolating lanthanide signal from spectroscopic interferents are also needed. Applying spectroelectrochemistry to the detection of these species can meet those needs. However, application of this technique is limited by the low molar absorptivities and quantum yields of the lanthanides. These limitations can be circumvented by complexing the lanthanides with sensitizing ligands that enhance fluorescence, thereby dropping the limits of detection. Complexation will also cause changes in the electrochemical behavior of the lanthanides. To demonstrate this concept, studies were completed using europium as a model lanthanide in complexes with four different sensitizing ligands, which included 2,2′‐bipyridine and related derivatives. Results indicate that all four studied complexes demonstrate quasi‐reversible redox couples and improvements in limits of detection where electrochemical and spectroscopic characteristics showed some dependence on attached ligand. All four complexes studied display the necessary characteristics for spectroelectrochemical analysis, which was successfully and reproducibly applied to all Eu complexes.     

Validating Eaton's Hypothesis: Cubane as a Benzene Bioisostere

Pharmaceutical and agrochemical discovery programs are under considerable pressure to meet increasing global demand and thus require constant innovation. Classical hydrocarbon scaffolds have long assisted in bringing new molecules to the market place, but an obvious omission is that of the Platonic solid cubane. Eaton, however, suggested that this molecule has the potential to act as a benzene bioisostere. Herein, we report the validation of Eaton's hypothesis with cubane derivatives of five molecules that are used clinically or as agrochemicals. Two cubane analogues showed increased bioactivity compared to their benzene counterparts whereas two further analogues displayed equal bioactivity, and the fifth one demonstrated only partial efficacy. Ramifications from this study are best realized by reflecting on the number of bioactive molecules that contain a benzene ring. Substitution with the cubane scaffold where possible could revitalize these systems, and thus expedite much needed lead candidate identification.     

Towards a bio-based industry: benign catalytic esterifications of succinic acid in the presence of water

The biorefinery of the future will need to integrate bioconversion and appropriate low environmental impact chemical technologies (Green Chemistry) so as to produce a wide range of products from biomass in an economically effective and environmentally acceptable manner. The challenge for chemists is to develop chemistry that works with fermentation-derived dilute, aqueous mixtures of oxygenated chemicals (platform molecules) rather than the petroleum-derived non-aqueous, non-oxygenated feedstocks we have been working with for 50+ years and to avoid energy intensive and wasteful concentration and purification steps. Here we show that a new family of tuneable mesoporous carbonaceous catalysts derived from starch can be used to accomplish efficient chemistry in aqueous solution. Our new aqueous catalytic chemistry relies on the ability to adjust the surface properties including the hydrophobicity-hydrophilicity balance of mesoporous Starbons by carbonisation at different temperatures (250-750 degrees C). Simple treatment of these materials with sulfuric acid then provides a series of porous solid acids that can function under a range of conditions including dilute aqueous solution. The reactions of succinic acid (platform molecule) in aqueous alcohol demonstrate the outstanding activities of these new catalysts.     

Controlled MegaDalton assembly with locally stiff but globally flexible polyphenylene dendrimers

The divergent polyphenylene dendrimer synthesis of the largest chemically monodisperse molecules to date, up to 28 nm at 271.6 kDa for the sixth generation, is presented. Monodispersity, conformational flexibility, and an assembly behavior reminiscent of multimeric proteins for the locally stiff, macroporous dendrimers were evaluated with a combination of molecular and polymer characterization tools, namely size exclusion chromatography, atomic force microscopy, ultrahigh-mass MALDI-TOF mass spectrometry, and dynamic light scattering. Remarkably, the high-precision MegaDalton assembly of shape-adaptable dendrimers occurs in the absence of electrostatic or hydrogen-bonding interactions and is the product of Lilliputian solvophobic interactions, mediated by the dendrimer arm size, shape, and stiffness. This covalent/noncovalent approach offers a general molecular shaping motif that is completely different than what has been previously accessible with conventional self-assembly.     

Gas chromatography-mass spectrometry analysis of regioisomeric ring substituted methoxy methyl phenylacetones

The methoxy methyl phenylacetones share an isobaric relationship (equivalent mass but different elemental composition) to the controlled precursor substance 3,4-methylenedioxyphenylacetone. The 10 methoxy methyl phenylacetones as well as the methylenedioxyphenylacetones show essentially equivalent mass spectra with major fragment ions at m/z 135 and 43. Those methoxy methyl phenylacetones with the methoxy group substituted ortho to the benzylic cation in the m/z 135 ion show a further fragmentation to lose formaldehyde (CH2O) and yield a significant ion at m/z 105. The loss of formaldehyde from the ortho methoxy benzyl cation was confirmed using commercially available regioisomeric 2-, 3-, and 4-methoxyphenylacetones. The 10 regioisomeric methoxy methyl phenylacetones were prepared from the appropriately substituted benzaldehydes. Complete gas chromatographic resolution of all ten regioisomeric ketones was obtained on a stationary phase containing modified beta-cyclodextrin. Using the cyclodextrin containing phase, the ortho methoxy-substituted ketones (K1-K4) eluted before the meta-methoxy-substituted ketones (K5-K8) and the para-methoxy-substituted ketones (K9-K10) showed the greatest affinity for the stationary liquid phase and eluted last. Complete separation of the 10 ketones was not obtained on Rtx-1 and Rtx-200 columns.     

Controllable porous polymer particles generated by electrospraying

In this paper, an electrospraying technique was applied to prepare polycaprolactone (PCL) polymer particles with a different microstructure. The PCL particles can be controlled to have a porous microstructure by tailoring the evaporation of solvents during the electrospraying process. The effect of various concentrations on the morphology and microstructure of PCL particles was investigated. The experiment has demonstrated the versatile capability of the electrohydrodynamic atomization process for preparing polymer PCL porous particles and fibers. The thermally induced and evaporation-induced phase separations are proposed as the main mechanisms for the porous microstructure formation. The results demonstrate that the electrospraying method is a simple, innovative and cost-effective method for preparing polymer particles with controllable microstructures.