Monolithic Network Research Articles

Hybrid silica monolith for microextraction by packed sorbent to determine drugs from plasma samples by liquid chromatography–tandem mass spectrometry

The present study (1) reports on the synthesis of two hybrid silica monoliths functionalized with aminopropyl or cyanopropyl groups by the sol–gel process; (2) evaluates these monoliths as selective stationary phase for microextraction by packed sorbent (MEPS) to determine drugs in plasma samples via liquid chromatography–tandem mass spectrometry (LC–MS/MS) in the multiple reactions monitoring (MRM) mode; and (3) discusses important factors related to the optimization of MEPS efficiency as well as the carryover effect. The prepared hybrid silica monoliths consisted of a uniform, porous, and continuous silica monolithic network. The structure of the aminopropyl hybrid silica monolith was more compact than the structure of the cyanopropyl hybrid silica monolith. The Fourier-transform infrared spectroscopy (FTIR) spectra of the hybrid silica monoliths displayed readily identifiable peaks, characteristic of the cyanopropyl and aminopropyl groups. Compared with the aminopropyl hybrid silica phase, the cyanopropyl hybrid silica phase exhibited higher binding capacity for most of the target drugs. The developed method afforded adequate linearity at concentrations ranging from the lower limit of quantification (0.05–1.00ngmL−1) to the upper limit of quantification (40–10,500ngmL−1); the coefficients of determination (r2) were higher than 0.9955. The precision of the method presented coefficients of variation (CV) lower than 14%; the relative standard error (RSE) of the accuracy ranged from −12% to 14%. The developed method allowed for simultaneous analysis of five antipsychotics (olanzapine, quetiapine, clozapine, haloperidol, and chlorpromazine) in combination with seven antidepressants (mirtazapine, paroxetine, citalopram, sertraline, imipramine, clomipramine, fluoxetine), two anticonvulsants (carbamazepine and lamotrigine), and two anxiolytics (diazepam and clonazepam) in plasma samples from schizophrenic patients, which should be valuable for therapeutic drug monitoring purposes.

Preparation of polyhedral oligomeric silsesquioxane based hybrid monoliths by thiol-ene click chemistry for capillary liquid chromatography.

A facile organic-silica hybrid monolith was prepared by a thiol-ene click reaction of polyhedral oligomeric silsesquioxane methacryl substituted (POSS-MA) with 1,4-bis(mercaptoacetoxy) butane (BMAB) using toluene and dodecanol as a porogenic system. The effects of the ratio of POSS-MA-BMAB and porogenic solvents and click reaction temperature on the morphology, permeability and column performance of the resulting POSS-BMAB hybrid monoliths were studied in detail. A uniform monolithic network with a high porosity was obtained. The POSS-BMAB hybrid monolith exhibited good permeability and high thermal and mechanical stability. A series of test compounds, including alkylbenzenes, polycyclic aromatic hydrocarbon, phenols and, anilines were used to evaluate the retention behaviors of the POSS-BMAB hybrid monolith in capillary liquid chromatography. The prepared POSS-BMAB hybrid monolith exhibited typical reversed-phase chromatographic behavior toward neutral solutes. The minimum plate height of this hybrid monolith was determined as 12.6 and 13.7 μm for thiourea and benzene, respectively. These results demonstrate that thiol-ene click chemistry can provide a facile and robust approach for the preparation of a POSS-based hybrid monolith.

High efficiency polyethylene glycol diacrylate monoliths for reversed-phase capillary liquid chromatography of small molecules

Highly cross-linked monolithic networks (i.e., polyethylene glycol diacrylate, PEGDA) synthesized from monomers containing varying ethylene oxide chain lengths were fabricated inside fused silica capillary columns for use in liquid chromatography (LC) of small molecules. Tergitol was used as a surfactant porogen in combination with other typical organic liquid porogens. Column performance was correlated with quantitative descriptors of the physical/chemical properties of the monomers and porogens using a statistical model. Solubility and viscosity values of the components were identified as important predictors of monolith morphology and efficiency. The chromatographic retention mechanism was determined to be principally reversed-phase (RP) with additional hydrogen bonding between the polar groups of the analytes and the ethylene oxide groups embedded in the monolith structure. The fabricated monolithic columns were evaluated under RPLC conditions using phenols, hydroxy benzoic acids, and alkyl parabens as test compounds. Isocratic elution of hydroxy benzoic acids at a linear velocity of 0.04cm/s using a PEGDA-700 monolith gave chromatographic peaks with little tailing (i.e., tailing factor<1.28). The chromatographic efficiency measured for a non-retained compound (uracil) using this column was 186,000plates/m when corrected for injector dead volume. High resolution gradient separations of selected pharmaceutical compounds and phenylurea herbicides were achieved in less than 18min. Optimized monoliths synthesized from all four crosslinking monomers exhibited high permeability and demonstrated little swelling or shrinking in different polarity solvents. Column preparation was highly reproducible, with relative standard deviation (RSD) values less than 2.1%, based on retention times of the phenol standards (3 different columns).

One-pot preparation of glutathione–silica hybrid monolith for mixed-mode capillary liquid chromatography based on “thiol-ene” click chemistry

A novel glutathione (GSH)–silica hybrid monolithic column synthesized via a combination of thiol-ene click reaction and one-pot process was described, where thiol-end GSH organic monomer and 2,2-azobisisobutyronitrile (AIBN) were mixed with hydrolyzed tetramethyloxysilane (TMOS) and γ-methacryloxypropyltrimethoxysilane (γ-MAPS) and then introduced into a fused-silica capillary for simultaneous polycondensation and “thiol-ene” click reaction to form the GSH–silica hybrid monolith. The effects of the molar ratio of TMOS/γ-MAPS, the amount of GSH, and the volume of porogen on the morphology, permeability and pore properties of the prepared GSH–silica hybrid monoliths were studied in detail. A uniform monolithic network with high porosity was obtained. A series of test compounds including alkylbenzenes, amides, and anilines were used to evaluate the retention behaviors of the GSH–silica hybrid monolithic column. The results demonstrated that the prepared GSH–silica hybrid monolith exhibited multiple interactions including hydrophobicity, hydrophilicity, as well as cation exchange interaction. The run-to-run, column-to-column and batch-to-batch reproducibilities of the GSH–silica hybrid monolith for phenols’ retention were satisfactory with the relative standard deviations (RSDs) less than 1.3% (n=5), 2.6% (n=3) and 3.2% (n=3), respectively, indicating the effectiveness and practicability of the proposed method. In addition, the GSH–silica hybrid monolith was applied to the separation of nucleotides, peptides and protein tryptic digests, respectively. The successful applications suggested the potential of the GSH–silica hybrid monolith in complex sample analysis.

Enhanced Cycle Performance in a Binder Free Lithium Sulfur Battery Using Few-Layer Graphene Foam Scaffold

A lithium-sulfur (Li-S) battery has a high theoretical specific capacity (1675 mAh g-1 of elemental sulfur) and a high nominal energy density (2500 Wh kg-1 of cell weight), which offers the prospect of a significant energy density improvement compared to the mainstream lithium-ion batteries (150 Wh kg-1). However, the development of Li-S battery technology has been plagued by problems arising from the highly insulating nature of sulfur (5×10-30 S cm-1 at 25 °C), the high solubility of lithium polysulfides in the electrolyte and volumetric expansion of sulfur during lithiation. Here, we demonstrate the design and preparation of few-layer graphene (FLG) foam scaffold for sulfur loading to fabricate cathode structures for lithium-sulfur batteries. In this work, a free-standing FLG monolithic network foam was formed as a negative of a Ni metallic foam template by CVD followed by etching away of Ni. Then, a three-dimensional (3-D) cathode system for lithium sulfur (Li-S) batteries has been synthesised by loading sulfur on to this interconnected network of few-layered graphene (FLG) via a sulfur solution infiltration method. This cathode system did not require any additional binding agents, conductive additives or a separate metallic current collector thus decreasing the weight of the cathode by typically ~20-30 wt%. A Li-S battery with the sulfur/FLG foam cathode shows good electrochemical stability and high rate discharge capacity retention for up to 400 discharge/charge cycles at a high current density of 3200 mA g-1, which due to the FLG foam offers excellent electrical conductivity, an appropriate pore structure for containing the electro-active sulfur and facilitates rapid electron/ion transport. Even after 400 cycles the capacity decay is only ~0.064% per cycle relative to the early (e.g. the 5th cycle) discharge capacity, while yielding an average columbic efficiency of ~96.2%. To further understand the sulfur loading ability of FLG foam, the composites with high content (up to 72 wt %) were also investigated. The composite with high content of sulfur still presented good initial discharge capacity and good cycle stability after 200 cycles. Our results indicate the potential suitability of graphene foam for efficient and high-performance batteries.

Monitoring the morphology development of polymer-monolithic stationary phases by thermal analysis

Thermal analysis and SEM were employed to gain insights in the different stages of morphology development and the thermal properties of polymer-monolithic stationary phases. The studied system was a thermally initiated free-radical copolymerization reaction at 70°C of styrene and divinylbenzene in the presence of tetrahydrofuran and 1-decanol. The key events in the early stages of morphology development are initiation, chain growth, branching, and cyclization, leading to microgel particles. Interparticle reactions through pendant vinyl groups lead to the formation of microgel clusters. The rapid increase in molecular weight and cross-link density of the microgel clusters causes a reaction-induced phase separation, and the formation of a macroscopic network of interconnected globules was observed (macrogelation) at around 45 min. After 3 h or 65% conversion, a space-filling macroporous monolithic network was observed. Afterwards, mainly growth of existing globules takes place, reducing the macropore size. The porogen ratio affects the timing of the reaction-induced phase separation, strongly influencing the morphology of the polymer material. The use of a mixture of divinylbenzene isomers yielded a monolithic material that is less cross-linked at the surface compared to the central part of the polymer backbone due to copolymerization-composition drift. The less cross-linked outer layer starts devitrifying at 100°C.

The Autonomic Brain: An Activation Likelihood Estimation Meta-Analysis for Central Processing of Autonomic Function

The autonomic nervous system (ANS) is of paramount importance for daily life. Its regulatory action on respiratory, cardiovascular, digestive, endocrine, and many other systems is controlled by a number of structures in the CNS. While the majority of these nuclei and cortices have been identified in animal models, neuroimaging studies have recently begun to shed light on central autonomic processing in humans. In this study, we used activation likelihood estimation to conduct a meta-analysis of human neuroimaging experiments evaluating central autonomic processing to localize (1) cortical and subcortical areas involved in autonomic processing, (2) potential subsystems for the sympathetic and parasympathetic divisions of the ANS, and (3) potential subsystems for specific ANS responses to different stimuli/tasks. Across all tasks, we identified a set of consistently activated brain regions, comprising left amygdala, right anterior and left posterior insula and midcingulate cortices that form the core of the central autonomic network. While sympathetic-associated regions predominate in executive- and salience-processing networks, parasympathetic regions predominate in the default mode network. Hence, central processing of autonomic function does not simply involve a monolithic network of brain regions, instead showing elements of task and division specificity.

The development of a capillary microreactor for transesterification reactions using lipase immobilized onto a silica monolith

The use of lipase immobilized on a silica monolith as a microreactor for performing lipid transformations is reported. The microreactor consists of a monolithic network formed within a 320 μm internal diameter fused silica capillary that provides a very large surface area for enzyme immobilization. Candida antarctica lipase was covalently bound onto the silica monolith using glutaraldehyde as the cross linking reagent. Successful immobilization was demonstrated by FTIR measurements on monolith fragments. The effectiveness of flow-through microreactors was tested for the ethanolysis of triolein (TO) at room temperature. TO was quantitatively transformed into ethyl oleate when using flow rates of < 1 μL/min. Non-aqueous reversed phased-high performance liquid chromatography (NARP-HPLC) with an evaporative light scattering detector (ELSD) and gas chromatography/mass spectrometry with electron impact ionization (GC/MS-EI) were both used for characterization and quantification of the products. The microreactors were used to perform lipid transformations directly online with atmospheric pressure photoionization (APPI) ionization mass spectrometry. They were also shown to be reusable without loss of activity for ~15 runs when operated at room temperature and flow rates of < 1 μL/min.

Organic sol–gel synthesis of microporous molecular networks containing spirobifluorene and tetraphenylmethane nodes

AbstractThe microporous molecular networks based on rigid tetrafunctional units are synthesized via organic sol–gel polymerization of 2,2′,7,7′‐tetraamino‐9,9′‐spirobifluorene (TASBF) and/or tetrakis(4‐aminophenyl)methane (TAPM) with a diisocyanate, hexamethylene diisocyanate (HDI), or p‐phenylene diisocyanate. This study is performed as an extension of our previous report on the first organic sol–gel method, which enabled the synthesis of microporous molecular networks via a two‐stage mechanism involving the formation of colloidal dispersions of the nanoparticulate molecular networks and their subsequent growth to monolithic networks on solvent evaporation. The sol–gel‐synthesized molecular networks obtained by incorporating TASBF as a network former show improved porosity, processability, and thermal stability than the TAPM‐based system. The improved porosity of TASBF‐based networks is attributed to higher rigidity of the spirobifluorene compared with the tetraphenylmethane units. We also demonstrate the synthesis of mixed organic molecular networks by sol–gel copolymerization of the two network formers, TASBF and TAPM, and a diisocyanate monomer. The sol–gel transformation of TASBF/TAPM/HDI occurred at longer reaction times with increasing the amount of TASBF in the TASBF/TAPM/HDI mixture. The results indicate that the organic sol–gel method can be further optimized by adjusting various synthesis parameters to create new functional organic molecular network materials. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Resilience in optical ring-resonant switches

Phase-modulated ring resonant switches are receiving increasing attention for monolithic Silicon photonic networks. Resilience to fabrication variations and operational tolerances are however required to create networks with sufficient connectivity and bandwidth. In this work we use the combination of vectorial optical-mode propagation and transfer matrix calculation to map fabrication-level feature size variation to the optical switch performance metrics for extinction ratio, bandwidth and power penalty. Fabrication tolerances may be relaxed considerably through the combination of moderate size directional couplers of up to 30 µm, moderate 400 GHz free spectral range resonator design and the use of fifth order resonance. High speed 10 Gb/s, wavelength-multiplex-compliant, optical signal routing is predicted with on-state power penalties of 0.2 dB - 0.7 dB and off-state signal extinctions of - 62 dB.

Convenient enantioseparation by monolithic imprinted capillary clamped in a chip with electrochemical detection

A microchip integrated with a monolithic imprinted capillary has been manufactured for performing the chip-based capillary electrochromatographic enantioseparation. The microporous monolith anchored on the inner wall of the microchannel was prepared by in situ chemical copolymerization, and characterized with scanning electron microscopy, IR spectroscopy, and solid-state UV-vis spectroscopy. The monolithic network with high porosity gave a large surface area, good permeability, low mass-transfer resistance, and thus high separation efficiency. A portable microchip was conveniently constructed by integrating an imprinted capillary with 5-cm length as the separation channel and a carbon fiber microdisk working electrode for amperometric detection. Using L-tyrosine (L-Tyr) as the template molecule, Tyr enantiomers could be baseline separated within 55 s under the optimized preparation and separation conditions. The linear ranges for online amperometric detection of both Tyr enantiomers were from 20 to 2400 μM. The microporous monolithic chip strategy exhibited excellent separation efficiency and promising analytical application in enantioseparation. It opens an avenue for high-throughput screening of chiral compounds.

Poly(ethylene glycol) cryogels as potential cell scaffolds: effect of polymerization conditions on cryogel microstructure and properties

We report the synthesis and characterization of interconnected macroporous network structures of poly(ethylene glycol) (PEG) using cryogelation techniques. Novel monolithic networks containing a gradient of pore size in a layered fashion were created from a single precursor by manipulating their polymerization kinetics. Maintaining conditions that promote the rate of gelation compared to that of the nucleation of ice crystals leads to formation of either conventional hydrogel-like network structures or continuous heterogeneous networks containing layers of hydrogel-like and cryogel-like microstructures. In contrast, conditions promoting a faster rate of the nucleation of ice crystals compared to rate of gelation result in cryogels with a nearly homogeneous interconnected macroporous network. The rates of polymerization and nucleation of ice crystals were altered using a number of different parameters such as concentration of initiator, freezing temperature, and degree of supercooling. Compared to conventional hydrogels, the cryogels exhibit higher stress and strain at break; their mechanical and equilibrium swelling properties show a strong correlation with the network microstructure. Cell viability studies suggest no detrimental effect of these scaffolds on cell attachment and their distribution. Furthermore, a time dependent increase in chondrocyte proliferation was observed in cryogels over a long period of culture.

Synthesis and Characterization of Novel Poly(Vinyl Ester Resin-co-Ethylene Dimethacrylate) Monolithic Network Columns

In this report we introduce a new monolithic column for HPLC. The monolithic column was prepared using vinyl ester resin-co-ethylene dimethacrylate as the monomer. Using the free radical polymerization method a polymer network was formed, which was different from the traditional globular particles. The main factors affecting the porous structure of vinyl ester (VE) resin-based monolithic columns were investigated. By varying the porogen solvent, its content and the amount of initiator, different porous structures could be obtained. In order to evaluate the mechanical stability of the column material, the pressure drop across the column was measured at different flow-rates. Finally, using phenol, resorcinol and catechol as the test compounds, the normal-phase character of the poly(vinyl ester resin-co-ethylene dimethacrylate) monolith was evident.

Volume Image Analysis of Ceramic Sponges

AbstractThe three‐dimensional structure of monolithic networks such as ceramic sponges and their geometrical dimensions are part of the fundamentals necessary for investigation in most possible applications in chemical engineering. A volume imaging method must be applied to determine this structure and to measure features such as the specific surface area and the pore diameter. Magnetic Resonance Imaging was chosen for such measurements in this study. The analysis of volume images is performed with various methods based on different principles, which are compared with each other as well as with data generated by conventional techniques and from literature models.

Ground, sieved, and C18 modified monolithic silica particles for packing material of microcolumn high-performance liquid chromatography

We here report a new type of stationary phase for microcolumns. C18 modified silica monolith particles were prepared by grinding and sieving the silica monolith followed by C18 modification and end-capping, and were used as packing material. Ground silica monolith particles were not spherical but irregular with some residual monolithic network structure. The separation efficiency of the stationary phase made of sieved monolith particles (5–10 μm) was better than that of the stationary phase made of unsieved particles. The microcolumn packed with the sieved C18 ground monolith particles (5–10 μm) showed quite good separation efficiency (height equivalent to theoretical plate, HETP, as low as 15 μm) and it was even superior to the microcolumn packed with a commercial spherical 5 μm C18 stationary phase. The column pressure drop of C18 monolith particles was about two-third of that of the commercial spherical C18 phase. The preparation method of C18 stationary phase with ground and sieved silica monolith particles presumably suggests advantages of simplicity and convenience in modification and washing procedures compared to bulk silica monolith. It also showed both improved separation efficiency and low back pressure.

A Spatial Analysis of Loop Closing Among Recycling, Remanufacturing, and Waste Treatment Firms in Texas

SummaryIndustrial ecology has emerged as a key strategy for improving environmental conditions. A central element of industrial ecology is the concept of closing the loop in material use (cycling) by directing used material and products (wastes) back to production processes. This article examines the issue of geographic scale and loop closing for heterogeneous wastes through an analysis of the location and materials flows of a set of recycling, remanufacturing, recycling manufacturing, and waste treatment (RRWT) firms in Texas. The results suggest that there is no preferable scale at which loop closing should be organized. RRWT firms are ubiquitous and operate successfully throughout the settlement hierarchy. The cycling boundaries of RRWT firms are dependent primarily upon how and where their products are redirected to production processes rather than the firm's location in the settlement hierarchy. In other words, loop closing is dominated by the spatial economic logic of the transactions of the firm involved. These results suggest that we cannot assign loop closing to any particular spatial scale a priori nor can we conceive of closing the loop via RRWT firms in terms of monolithic networks bounded in space or place with internal material flows.

Ku-band antenna array feed distribution network with ferroelectric phase shifters on silicon

This paper presents the design, fabrication, and experimental results of a 1 : 4 monolithic power distribution network for Ku-band array antenna applications. The network integrated on a high-resistivity silicon (HRS) substrate surface stabilized by polysilicon consists of three Wilkinson power dividers, four dc blocking filters, and four coplanar waveguide (CPW)-to-microstrip (MS) transitions. Each output ports are fed with a barium-strontium-titanate phase shifter. It is found that the introduction of the polysilicon layer between the oxide and HRS reduces RF losses significantly, which will enable the monolithic integration of high-power controller modules onto silicon because of the existence of the oxide layer, preventing any degradation of RF performances. The individual components show insertion losses ranging from 0.4 to 2.6 dB at 15 GHz, and the interconnecting CPW lines result in a loss of 0.064 dB/mm. This network was successfully integrated with MS patch antennas monolithically, showing good performance of 32-dB return loss at 14.85 GHz, and 10/spl deg/ beam-steering capability.

Feature decomposition architectures for neural networks: algorithms, error bounds, and applications.

In recent years, systems consisting of multiple modular neural networks have attracted substantial interest in the neural networks community because of various advantages they offer over a single large monolithic network. In this paper, we propose two basic feature decomposition models (namely, parallel model and tandem model) in which each of the neural network modules processes a disjoint subset of the input features. A novel feature decomposition algorithm is introduced to partition the input space into disjoint subsets solely based on the available training data. Under certain assumptions, the approximation error due to decomposition can be proved to be bounded by any desired small value over a compact set. Finally, the performance of feature decomposition networks is compared with that of a monolithic network in real world bench mark pattern recognition and modeling problems.

Monolithic RC All-Pass Networks with Constant-Phase-Difference Outputs

All-pass network techniques have made it possible to realize very small monolithic lumped active phase shifters with decade bandwidths, high yield, and relative phase stability, even when the device parameters vary +-20 percent. We have successfully demonstrated fully monolithic first-order networks (at 250 MHz) and second-order networks (at 4 GHz).

Why the design nod goes to resistors made as thin-film monolithic networks : Donald B. Bruck and Allen L. Pollens. Electronics p. 99 (3 August 1978)

Why the design nod goes to resistors made as thin-film monolithic networks : Donald B. Bruck and Allen L. Pollens. Electronics p. 99 (3 August 1978)