Stationary phases for chromatography prepared by ring opening metathesis polymerization

Molecularly Imprinted Porous Monolithic Materials from Melamine-Formaldehyde for Selective Trapping of Phosphopeptides

Thirty-five melamine-formaldehyde (MF) monolithic materials with bimodal pore distributions were synthesized in fused silica capillaries by catalyst-free polycondensation, starting with an aqueous MF precondensate, using acetonitrile as the macroporogen and a variety of aliphatic polyethers and triblock copolymeric surfactants as porogens and mesoporogens, respectively. By varying the prepolymer composition and the type and molecular weight of the polymeric porogen components, a library of porous monolithic materials was produced, covering a range of meso- and macroporous properties. A multivariate evaluation revealed that the amount of surfactant was the strongest contributor to specific surface area and pore volume and to the inversely related mesopore size, whereas the macropore dimensions were controlled mainly by the amount of aliphatic polyether porogen. One of these capillary monoliths, chosen based on the combination of meso- and macropores providing optimal percolative flow and accessible surface area, was synthesized in the presence of N-Fmoc and O-Et protected phosphoserine and phosphotyrosine to prepare molecularly imprinted monoliths with surface layers selective for phosphopeptides. These imprinted monoliths were characterized alongside nonimprinted monoliths by a variety of techniques and finally evaluated by liquid chromatography-mass spectrometry in the capillary format to assess their abilities to trap and release phosphorylated amino acids and peptides from partly aqueous media. Selective enrichment of phosphorylated targets was demonstrated, suggesting that these materials could be useful as trapping media in affinity-based phosphoproteomics.

Monolithic space-filling porous materials from engineering plastics by thermally induced phase separation

Six different uncompounded engineering and commodity polymers were evaluated for their ability to produce space-filling monolithic entities by thermally induced phase separation (TIPS) from 22 different solvents. Attempts were first made to dissolve the polymers at elevated temperatures, selected below the boiling point of each solvent. Then the solutions of polymers that were homogeneous dissolved underwent a controlled temperature decrease to induce a phase separation as the upper critical solution temperature was passed. Twelve of the solvents gave monolithic entities by this procedure, materials that were characterized with regard to their specific surface area and pore size distribution. These measured parameters were then correlated with their macroporous morphology, assessed by scanning electron microscopy. Monolithic materials with widely different mesoporous properties were obtained with specific surface areas ranging from 169 m(2)/g to structures with essentially nonporous skeletons and distinct mesopore size distribution modes from 6 to 15 nm. The materials furthermore had a wide variation in their macroporous morphologies-among the same polymer processed in different solvents and between different polymers dissolved in the same solvent. TIPS processing therefore appears to be a viable route to prepare space-filling meso- and macroporous support materials for a wide variety of purposes in separation science and heterogeneous chemistry.

A new combined nuclear magnetic resonance and Raman spectroscopic probe applied to in situ investigations of catalysts and catalytic processes

Both Raman and nuclear magnetic resonance (NMR) spectroscopies are valuable analytical techniques capable of providing mechanistic information and thereby providing insights into chemical processes, including catalytic reactions. Since both techniques are chemically sensitive, they yield not only structural information but also quantitative analysis. In this work, for the first time, the combination of the two techniques in a single experimental apparatus is reported. This entailed the design of a new experimental probe capable of recording simultaneous measurements on the same sample and/or system of interest. The individual datasets acquired by each spectroscopic method are compared to their unmodified, stand-alone equivalents on a single sample as a means to benchmark this novel piece of equipment. The application towards monitoring reaction progress is demonstrated through the evolution of the homogeneous catalysed metathesis of 1‑hexene, with both experimental techniques able to detect reactant consumption and product evolution. This is extended by inclusion of magic angle spinning (MAS) NMR capabilities with a custom made MAS 7 mm rotor capable of spinning speeds up to 1600 Hz, quantified by analysis of the spinning sidebands of a sample of KBr. The value of this is demonstrated through an application involving heterogeneous catalysis, namely the metathesis of 2-pentene and ethene. This provides the added benefit of being able to monitor both the reaction progress (by NMR spectroscopy) and also the structure of the catalyst (by Raman spectroscopy) on the very same sample, facilitating the development of structure-performance relationships.

Preparation of Monolithic Capillary Chromatographic Columns Using Supercritical Fluid as a Porogen Solvent

Monolithic polymeric beds were synthesized in fused silica capillaries using either trimethylolpropane trimethacrylate (TRIM) or a mixture of butyl methacrylate (BMA) with ethylene glycol dimethacrylate (EDMA) as monomers. Carbon dioxide at temperature and pressure conditions above its critical values was used as a porogen solvent. The purpose of using the supercritical carbon dioxide was to have the possibility of changing the solvation power (and thus the porosity of the resulting monolith) of the porogen by pressure and temperature changes instead of changing the porogen composition. The experiments were performed using a special setup consisting of a stainless steel high-pressure reactor to which the fused silica capillary was connected. The synthesized monoliths underwent liquid chromatographic evaluation. The polyTRIM capillary monoliths were characterized by different permeability, which depended on the pressure of the synthesis. BMA/EDMA columns were applied for separation of alkylbenzenes and a model mixture of proteins.

Ring-opening metathesis polymerization-derived large-volume monolithic supports for reversed-phase and anion-exchange chromatography of biomolecules

Preparative-scale monolithic columns up to 433.5 mL in volume were prepared via transition metal-catalyzed ring-opening metathesis polymerization (ROMP) from norborn-2-ene (NBE) and trimethylolpropane-tris(5-norbornene-2-carboxylate) (CL) using the 1(st)-generation Grubbs initiator RuCl(2)(PCy(3))(2)(CHPh) (Cy = cyclohexyl) (1) in the presence of a macro- and microporogen, i.e. of 2-propanol and toluene. To prepare large-volume monoliths, bulk polymerizations were completed within borosilicate or PEEK column formats with diameters in the range of 3 to 49 mm. The pore structure of the large-volume monoliths was investigated by electron microscopy and inverse-size exclusion chromatography (ISEC), respectively. Monolithic columns with inner diameters (I.D.s) in the range of 10-49 mm were tested for the separation of a mixture of five proteins, i.e., insulin, cytochrome C, lysozyme, conalbumin, and β-lactoglobulin. Preparative separation of these proteins was achieved within less than 12 min in a 433.5 mL monolithic column by applying gradient elution in the RP-HPLC mode. Furthermore, weak and strong anion exchangers were prepared via post-synthesis grafting of bicyclo[2.2.1]hept-5-en-2-yl-methyl-N,N-dimethylammonium hydrochloride (4) and bicyclo[2.2.1]hept-5-en-2-ylmethyl-N,N,N-trimethylammonium iodide (5), respectively. The weak and strong anion exchangers were used for the preparative-scale separation of 5'-phosphorylated oligodeoxythymidylic acid fragments of d[pT](12-18) at pH values ranging from 5 to 9.