Preparation of polymeric monoliths by copolymerization of acrylate monomers with amine functionalities for anion-exchange capillary liquid chromatography of proteins

Two novel polymeric monoliths for anion-exchange capillary liquid chromatography of proteins were prepared in a single step by a simple photoinitiated copolymerization of 2-(diethylamino)ethyl methacrylate and polyethylene glycol diacrylate (PEGDA), or copolymerization of 2-(acryloyloxy)ethyl trimethylammonium chloride and PEGDA, in the presence of selected porogens. The resulting monoliths contained functionalities of diethylaminoethyl (DEAE) as a weak anion-exchanger and quaternary amine as a strong anion-exchanger, respectively. An alternative weak anion-exchange monolith with DEAE functionalities was also synthesized by chemical modification after photoinitiated copolymerization of glycidyl methacrylate (GMA) and PEGDA. Important physical and chromatographic properties of the synthesized monoliths were characterized. The dynamic binding capacities of the three monoliths (24 mg/mL, 56 mg/mL and 32 mg/mL of column volume, respectively) were comparable or superior to values that have been reported for various other monoliths. Chromatographic performance was also similar to that provided by a modified poly(GMA-ethylene glycol dimethacrylate) monolith. Separation of standard proteins was achieved under gradient elution conditions using these monolithic columns. Peak capacities of 34, 58 and 36 proteins were obtained with analysis times of 20–30 min. This work represents a successful attempt to prepare functionalized monoliths via direct copolymerization of monomers with desired functionalities. Compared to earlier publications, additional surface modifications were avoided and the PEGDA crosslinker helped to improve the biocompatibility of the monolithic backbone.     

Soft‐Chemical Exfoliation Route to Layered Cobalt Oxide Monolayers and Its Application for Film Deposition and Nanoparticle Synthesis

A colloidal suspension of exfoliated, layered cobalt oxide nanosheets has been synthesized through the intercalation of quaternary tetramethylammonium ions into protonated lithium cobalt oxide. According to atomic force microscopy, exfoliated nanosheets of layered cobalt oxide show a plateau‐like height profile with nanometer‐level height, underscoring the formation of unilamellar 2D nanosheets. The exfoliation of layered cobalt oxide was cross‐confirmed by X‐ray diffraction, UV/Vis spectroscopy, and transmission electron microscopy. The maintenance of the hexagonal in‐plane structure of the cobalt oxide lattice after the exfoliation process was evidenced by selected‐area electron diffraction and Co K‐edge X‐ray absorption near‐edge structure analysis. The zeta‐potential measurements clearly demonstrated the negative surface charge of cobalt oxide nanosheets. Adopting the nanosheets of layered cobalt oxide as a precursor, we were able to prepare the monodisperse CoO nanocrystals with a particle size of ≈10 nm as well as the heterolayered film composed of cobalt oxide monolayer and polycation.     

Easy deposition of Ag onto polystyrene beads for developing surface-enhanced-Raman-scattering-based molecular sensors

We describe a very simple electroless plating method that can be used to prepare Ag-coated polystyrene beads. Robust Ag nanostructures are reproducibly fabricated by soaking polystyrene beads in ethanolic solutions of AgNO(3) and butylamine. When the molar ratio of butylamine to AgNO(3) is far below 1.0, distinct nanosized Ag particles are formed on the polystyrene beads, but by increasing the amount of butylamine, network-like Ag nanostructures are formed that possess very broad UV/vis absorption characteristics extending from the near-UV to near-infrared regions. In conformity with the UV/vis absorption characteristics, the Ag-deposited polystyrene beads were highly efficient surface-enhanced Raman scattering (SERS) substrates, with an enhancement factor estimated using 4-aminobenzenethiol (4-ABT) as a model adsorbate to be larger than 1.1x10(6). On the basis of the nature of the SERS peaks of 4-ABT, those Ag-deposited polystyrene beads were confirmed, after attaching biotin groups over 4-ABT, to selectively recognize streptavidin molecules down to concentrations of 10(-11) g mL(-1) (i.e., approximately 0.2 pM). Since a number of different molecules can be used as SERS-marker molecules (such as 4-ABT), multiple bioassays are readily accomplished via SERS after attaching appropriate host or guest molecules onto them.     

Preparation and evaluation of hydrophilic C18 monolithic sorbents for enhanced polar compound retention in liquid chromatography and solid phase extraction

Hydrophilic C18 monolithic polymer sorbents were synthesized for use in solid phase extraction (SPE) and in capillary liquid chromatography (LC). The approach involved incorporating both hydrophobic and hydrophilic monomers into a monolithic material, by copolymerization of stearyl methacrylate (SMA), poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) and ethylene dimethacrylate (EDMA) in the presence of selected porogens, to produce translucent mesoporous monolithic materials in bulk (SPE) or white macroporous monoliths inside fused silica capillary columns (capillary LC). A capillary column containing one of the hydrophilic C18 monoliths (i.e. poly(SMA-co-PEGMEMA-co-EDMA) with 15% (w/w) PEGMEMA) demonstrated nearly 35% reduction in retention of polycyclic aromatic compounds and greater than 40% increase in retention of phenols compared to a hydrophobic C18 monolithic column. In addition, the hydrophilic monolith demonstrated significantly improved resolution of phenols. Similar monolithic materials prepared in bulk were ground and sieved to obtain 45-65 μm particles with desired rigidity for SPE. To achieve optimum extraction performance for phenols, several parameters, including sample pH and volume, and eluent type and volume, were investigated. Under optimized experimental conditions, the method demonstrated good sensitivity (1.6 ng/mL LOD) and linearity (R(2)>0.97 for 10-200 ng/mL). Again, incorporation of 15% (w/w) PEGMEMA in the monolith increased the extraction efficiency of phenols in water from approximately 20% to 67-92% compared to a hydrophobic C18 monolithic material. Increased wettability of the sorbent by the aqueous sample matrix and the presence of hydrogen-bonding interactions are responsible for the improved retention of polar compounds.     

Control of Enzymatic Degradation of Microbial Polyesters by Plasma Modification

The rate of enzymatic degradation of surface‐modified microbial polyesters, poly[(R)‐3‐hydroxybutyrate] and poly[(R)‐3‐hydroxybutyrate‐co‐3‐hydroxyvalerate], was studied. The plasma treatments were carried out in a CF₃H or O₂ environment. It was found that the CF₃H plasma‐treated polyesters exhibited significant retardation of enzymatic erosion because of the surface fluorocarbon groups induced by CF₃H plasma. These surface fluorocarbon groups act as retardants on enzymatic degradation due to increased hydrophobicity and of the inactivity of enzymes. However, the increased surface hydrophilicity of polyesters induced by O₂ plasma results in no significant acceleration of the enzymatic erosion, which may be due to the thin modified layer.

Weight loss profiles of P(3HB) film exposed to CF₃H plasma as a function of plasma exposure time.     

Pretreatment of wastepaper and pulp mill sludge by aqueous ammonia and hydrogen peroxide

Pretreatment of two different softwood-based lignocellulosic wastes (newsprint and Kraft pulp mill sludge) was investigated. Pretreatment was done by aqueous ammonia and hydrogen peroxide (H₂O₂), two delignifying reagents that are environmentally benign. Three different treatment schemes were employed: aqueous ammonia alone (ammonia recycled percolation [ARP]), mixed stream of aqueous ammonia and H₂O₂ and successive treatment with H₂O₂ and aqueous ammonia. In all cases there was a substantial degree of delignification ranging from 30 to 50%. About half of the hemicellulose sugars were dissolved into the process effluent. Retention of cellulose after pretreatment varied from 85 to 100% for newspaper feedstock and from 77 to 85% for the pulp mill sludge. After treatment with aqueous ammonia alone (ARP), the digestibility of newspaper and the pulp mill sludge was improved only by 5% (from 40 to 45% for the former and from 68 to 73% for the latter), despite a substantial degree of delignification occurring after the ARP process. The lign in content thus did not correlate with the digestibility for these substrates. Simultaneous treatment with H₂O₂ and aqueous ammonia did not bring about any significant improvement in the digestibility over that of the ARP. A succcessive treatment by H₂O₂ and ARP showed the most promise because it improved the digestibility of the newspaper from 41 to 75%, a level comparable to that of α-cellulose.     

Aggregation‐Induced Electrochemiluminescence of Carboranyl Carbazoles in Aqueous Media

The aggregation‐induced electrochemiluminescence (AIECL) of carboranyl carbazoles in aqueous media was investigated for the first time. Quantum yields, morphologies, and particle sizes were observed to determine the electrochemiluminescence (ECL) performance of these aggregated organic dots (ODs). All compounds exhibit much higher ECL stability and intensity than the carborane‐free compound, demonstrating the essential role of the carboranyl motif. Moreover, the results of cyclic voltammetry (CV) suggest that oxidation/reduction reactions take place at the carboranyl motif. The excited states of ODs were proposed to be generated by the mechanism of surface state transitions. More importantly, these compounds show a reductive–oxidative mechanism in contrast to other organic materials that show oxidative–reductive mechanisms. Our experiments and data have established the relation between AIE organic structures and ECL properties that has a strong potential for biological and diagnostic applications.     

Effect of aromatic substitution on the cure reaction and network properties of anhydride cured triphenyl ether tetraglycidyl epoxy resins

A systemic study of the impact of aromatic substitution on the reaction rate and network properties of the isomers of a tetraglycidylaniline triphenyl ether epoxy resin cured with anhydride hardeners is presented here. The epoxy resins synthesized in this work were based upon N,N,N,N‐tetraglycidyl bis(aminophenoxy)benzene (TGAPB), where the glycidyl aniline and ether groups change from being all meta (133 TGAPB), to meta and para (134 TGAPB), and finally to an all para substituted epoxy resin (144 TGAPB). Increasing para substitution increased reaction rate, promoted the onset of vitrification and increased epoxide conversion. Thermal properties such as glass transition temperatures (T_g) and coefficients of thermal expansion (CTE) both increased consistently with increasing para substitution, although thermal stability as measured via thermogravimetric analysis decreased. Mechanical properties also varied systematically with flexural strength and ductility increasing with increased para substitution, while the modulus decreased. Indeed, the ductility almost doubled, as measured by the work of fracture and displacement at failure highlighting the importance of substitution on properties.