Preparation of macroporous,monodisperse, functionalized styrene–divinylbenzene copolymer beads: Effect of the nature of the monomers and total porogen volume on the porous properties

The staged templated suspension polymerization method was used for the preparation of 5 μm beads from mixtures of styrene and several substituted styrene monomers, including 4-methylstyrene, 4-aminostyrene, 3-aminostyrene, 4-acetoxystyrene, and 4-tert-butoxycarbonyl oxystyrene, with divinylbenzene in the presence of various amounts of linear polystyrene and dibutyl phthalate as porogens. The nature of the monomer as well as the total percentage of porogenic compounds in the polymerization mixture have a large effect on the porous properties and surface morphology of the monodisperse beads. Beads with large pores can only be obtained once the percentage of porogen in the mixture exceeds a threshold value that varies with the type of monomers involved in the polymerization. The level of incompatibility of the functional polymer chains formed during the crosslinking polymerization with the linear polystyrene porogen that is present in the polymerization mixture is another variable that also affects both the porous properties and the morphology of the beads. Because better compatibility is achieved, this effect is less pronounced if unfunctionalized styrene is used as a monomer. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 597–607, 1998     

Polar polymeric stationary phases for normal-phase HPLC based on monodisperse macroporous poly(2,3-dihydroxypropyl methacrylate-co-ethylene dimethacrylate) beads

The effect of variables such as shape template size, porogen composition and percentage, content of cross-linking monomer, and polymerization temperature on the properties of uniformly sized 3-microm porous poly(glycidyl methacrylate-co-ethylene dimethacrylate) beads prepared by the staged templated suspension polymerization technique has been studied. The porous properties of the beads including surface morphology, pore size distribution, and specific surface area have been optimized to obtain highly efficient stationary phases for normal-phase HPLC. A column packed with diol stationary phase obtained by hydrolysis of poly(glycidyl methacrylate-co-ethylene dimethacrylate) beads affords an efficiency of 67,000 plates/m for toluene using THF as the mobile phase. The retention properties and selectivity of the diol beads are easily modulated by changes in the composition of the mobile phase. The performance of these beads is demonstrated with the separations of a variety of polar compounds including positional isomers, aniline derivatives, and basic tricyclic antidepressant drugs.     

Dual-function microanalytical device by in situ photolithographic grafting of porous polymer monolith: integrating solid-phase extraction and enzymatic digestion for peptide mass mapping

Microfluidic devices with a dual function containing both a solid-phase extractor and an enzymatic microreactor have been prepared, and their operation has been demonstrated. The devices were fabricated from a 25-mm-long porous poly(butyl methacrylate-co-ethylene dimethacrylate) monolith prepared within a 50-microm-i.d. capillary. This capillary with a pulled 9-12-microm needle tip was used as a nanoelectrospray emitter coupling the device to a mass spectrometer. Photografting with irradiation through a mask was then used to selectively functionalize a 20-mm-long portion of the monolith, introducing reactive poly(2-vinyl-4,4-dimethylazlactone) chains to enable the subsequent attachment of trypsin, thereby creating an enzymatic microreactor with high proteolytic activity. The other 5 mm of unmodified hydrophobic monolith served as micro solid-phase extractor (microSPE). The dual-function devices were used in two different flow directions; concentration of myoglobin that was absorbed from its dilute solution, followed by elution and digestion or digestion, followed by concentration. Operations in both directions afforded equal sequence coverage. Different volumes of myoglobin solution ranging from 2 to 20 microL were loaded on the device. Very high sequence coverages of almost 80% were achieved for the highest loading. Despite the very short length of the extractor unit, the device operated in the digest-solid-phase extraction direction also enabled the separation of peaks that mostly contained undigested protein and peptides.     

Preparative soft and reactive landing of multiply charged protein ions on a plasma-treated metal surface

Soft landing on a plasma-treated metal surface of multiply protonated protein ions from the gas phase results in a substantial retention of protein function, as demonstrated for trypsin and streptavidin. The majority of trypsin ions soft-landed at hyperthermal kinetic energies are undamaged and retain 72-98% of enzymatic activity after being washed into solution. A small fraction of trypsin ions that were landed at nominal kinetic energies of 130-200 eV remain tethered to the surface and show approximately 50% enzymatic activity. The streptavidin tetramer is found to dissociate to monomer units upon multiple charging in electrospray. The majority of soft-landed monomers can be washed into solution where they show affinity to biotin. The layer of streptavidin monomer that is immobilized on the surface can be detected if fluorescence-tagged and retains the ability to reversibly bind biotin. A mechanism is proposed to explain nondestructive protein ion discharge on the surface that considers proton migration from the soft-landed cations to the metal oxide layer and metal ion reduction by electron transfer from the bulk metal.     

Contribution to quantification of highly inhomogeneous microstructures

In highly inhomogeneous microstructures with a wide range of grain sizes, the problem arises of defining an effective average grain size. An original method for the estimation of effective average grain size and a parameter describing the homogeneity of microstructure are presented. The coefficients of homogeneity for equiaxed and columnar microstructures are calculated. The effective average grain size is calculated as a weighted sum of the average grain sizes of homogeneous grain groups.     

Adsorption von phenolen aus den wäßrigen lösungen an nichtionogenen adsorberharzen

The adsorption and desorption of phenol and p-nitrophenol from aqueous solution on macroporous non-ionic adsorption resins and on active carbon, respectively, has been studied. The reversibility of adsorption on the resins has been observed, in opposition to the nonreversible process found on the active carbon. The adsorption isotherme data measured have been used to the surface area estimation; the method of inflection point and BET-equation have been compared. The practical identity of both methods above has been demonstrated, in the case of straight isotherme curves the BET-equation proved to be useful.     

Absolute quantification of specific proteins in complex mixtures using visible isotope-coded affinity tags

The identification of proteins in complex mixtures is most useful when quantitative information is also obtained. We describe a new type of protein tagging reagent called the visible isotope-coded affinity tag (VICAT) which allows the absolute amount of a target protein or proteins to be quantified in a complex biological sample such as a eukaryotic cell lysate. VICAT reagents tag thiol groups of cysteines or thioacetylated amino groups and introduce into the tryptic peptide a biotin affinity handle, a visible moiety for tracking the chromatographic location of the target peptide by a method other than mass spectrometry, a photocleavable linker for removing a portion of the tag, and an isotope tag for distinguishing sample and internal standard peptides. We demonstrate the use of VICAT reagents together with isoelectric focusing of peptides on an immobilized gel strip followed by combined micro-liquid chromatography/electrospray ionization mass spectrometry operating in selected reaction monitoring mode to determine the absolute abundance of a specific protein, human group V phospholipase A(2), in eukaryotic cell lysates. It is found that human lung macrophages contain 66 fmol of this protein per 100 microg of cell protein. Western blot analysis of human group V phospholipase A(2) in macrophages gave inconclusive data. VICAT reagents should be useful for numerous applications including the analysis of candidate disease markers in complex mixtures such as serum.     

Shielded stationary phases based on porous polymer monoliths for the capillary electrochromatography of highly basic biomolecules

A novel stationary phase for capillary electrochromatography has been prepared via photoinitiated grafting of two layers of polymer chains onto the pore surface of a porous polymer monolith. To achieve the desired retention, the original monolith with optimized porous properties was grafted with an "interior" layer consisting of the ionizable monomer, 2-acrylamido-2-methyl-1-propanesulfonic acid, followed by a "covering" layer of hydrophobic polymer chains. This technique affords monolithic CEC columns that facilitate electroosmotic flow (EOF) while preventing ionized analytes from interacting with the charged surface functionalities. Grafting of the second layer does not adversely affect the EOF. Grafting times of 30 and 60 s for AMPS and butyl acrylate, respectively, enabled the preparation of a monolith with full shielding of the analytes from the ionizable functionalities and excellent chromatographic performance. This approach allows for the first time the independent optimization of both electroosmotic flow and retention properties in CEC columns. The efficient isocratic separations of mixtures of peptides, including some that are highly basic and would be affected by unshielded charges, were routinely achieved in 40-90 s using a simple MS compatible mobile phase consisting of 20 mmol/L ammonium acetate in a 1:1 water-acetonitrile mixture.     

The effect of native Al2O3 skin disruption on properties of fine Al powder compacts

In the presented study we characterize how various powder metallurgical routes (extrusion, forging, and HIP/sintering) affect the fracture of native Al₂O₃ layer present on the surface of ultra-fine atomized Al powders. It is shown that the different distribution, morphology and interconnectivity of in situ introduced Al₂O₃ dispersoids strongly affect the thermal stability and mechanical and thermal properties of subsequent powder compacts.