Molecular Weight Of PEI Research Articles

A Novel Approach for the Synthesis of Responsive Core-Shell Nanogels with a Poly(N-Isopropylacrylamide) Core and a Controlled Polyamine Shell.

Microgel particles can play a key role, e.g., in drug delivery systems, tissue engineering, advanced (bio)sensors or (bio)catalysis. Amine-functionalized microgels are particularly interesting in many applications since they can provide pH responsiveness, chemical functionalities for, e.g., bioconjugation, unique binding characteristics for pollutants and interactions with cell surfaces. Since the incorporation of amine functionalities in controlled amounts with predefined architectures is still a challenge, here, we present a novel method for the synthesis of responsive core-shell nanogels (dh < 100 nm) with a poly(N-isopropylacrylamide) (pNIPAm) core and a polyamine shell. To achieve this goal, a surface-functionalized pNIPAm nanogel was first prepared in a semi-batch precipitation polymerization reaction. Surface functionalization was achieved by adding acrylic acid to the reaction mixture in the final stage of the precipitation polymerization. Under these conditions, the carboxyl functionalities were confined to the outer shell of the nanogel particles, preserving the core's temperature-responsive behavior and providing reactive functionalities on the nanogel surface. The polyamine shell was prepared by the chemical coupling of polyethyleneimine to the nanogel's carboxyl functionalities using a water-soluble carbodiimide (EDC) to facilitate the coupling reaction. The efficiency of the coupling was assessed by varying the EDC concentration and reaction temperature. The molecular weight of PEI was also varied in a wide range (Mw = 0.6 to 750 kDa), and we found that it had a profound effect on how many polyamine repeat units could be immobilized in the nanogel shell. The swelling and the electrophoretic mobility of the prepared core-shell nanogels were also studied as a function of pH and temperature, demonstrating the successful formation of the polyamine shell on the nanogel core and its effect on the nanogel characteristics. This study provides a general framework for the controlled synthesis of core-shell nanogels with tunable surface properties, which can be applied in many potential applications.

Nanozyme controlled photothermal heat generation on nanoceria decorated MoS2 nanoflowers for enhanced cytotoxicity in cancer chemo-photothermal therapy

In recent years, the fabrication of nanomaterials with built-in ability to mimick biological enzymes (nanozymes) is gaining popularity for biomedical applications, especially for cancer photothermal therapy, based on non-toxic and photo-thermal heat generating 2D materials. The use of 2D inter-layered MoS2 nanoflowers (NFs) is especially interesting as it results in nanozymes that are photostable and biocompatible for normal cells under physiological conditions. In this work, we have synthesized MoS2 nanoflowers (NFs) decorated with CeO2 nanoparticles (NPs) using two linker molecules of cysteine and polyethylenimine connected through carbodiimide chemistry. The electron microscopy investigations revealed the formation of flower shaped MoS2 of 400 ± 100 nm in size decorated with spherical shaped CeO2 NPs of 15±5 nm in size. The fabricated nanozymes were investigated by UV–visible (UV–vis), FTIR spectroscopy, Raman spectroscopy and dynamic light scattering. The NFs decorated with long-chain PEI molecules demonstrated higher photo-thermal heat generation when compared to nanozymes decorated with low molecular weight PEI. Notably, the photo-thermal heat generation, biocompatibility, anti-cancer activity of nanozymes are significantly influenced by molecular weight of PEI, concentration of nanozymes, time duration of near-infrared (NIR) light exposure, power density of NIR light and folic acid (FA) conjugation. The nanozymes conjugated with FA on their surface exhibited excellent anti-cancer activity against human colon cancer cells under NIR light exposure at 808 nm and 0.5 W/cm2. Hence, the nanozymes demonstrated here have huge potential as nanophoto-thermal agents in cancer photothermal therapy.

Effect of molecular weight on the shape of polyethyleneimine capped CuO nanoparticles

Polymers assist in getting the nanoparticles with the desired shape, size and dispersion of nanoparticles. Herein, polyethyleneimine-copper oxide (PEI-CuO) nanoparticles were developed via a precipitation technique by varying the molecular weight of cationic PEI. The effect of PEI molecular weight on the shape of CuO was confirmed with electron microscopes. The crystalline structure of formed nanoparticles were confirmed with X-ray diffraction studies. This is the first report on the synthesis of CuO with different morphology using PEI as a capping agent.

Dual-functional amino-quinone coatings on cotton fabrics assembled with different molecular weight polyethyleneimine and dopamine

The bonding of textiles and surface coatings was often assisted by the use of chemical cross-linking agents. Inspired by mussel chemistry, we propose that the strategy of co-assembly of quinone compound (dopamine, DA) and amino compound (polyethyleneimine, PEI) to form amino-quinone network (AQN) coating can effectively solve the problem. In this work, the molecular weight of PEI was used to regulate the surface coating morphology and its properties on cotton fabrics.The results showed that the roughness (Ra) of AQN coatings formed on the surface of glass slides by DA and low, medium or high molecular weight PEI were 3.94, 24.1 or 71.4 nm, respectively. In addition, the antibacterial rates of AQN-coated cotton fabric against E. coli and S. aureus were above 98 %, and the ultraviolet protection factor (UPF) value was above 50. After several washes, the antibacterial and UPF values only decreased by about 1 %, which indicates that AQN coating gives cotton fabric good antibacterial and UV protection properties, as well as strong bonds with cotton fabric.This provides insight into the wide application of AQN coating technology in the field of textile modification.

Preparation of Copolymer of Dihydroxy Monomer and Acrylamide and Its Solution Properties with Polyphenylboronic Acid Compounds

: The construction of composite flooding system based on dynamic covalent bonds is one of the effective methods to improve the salt and temperature resistance of polymer flooding agents. The polymers used in most composite systems are xanthan gum and guar gum. In this paper, a novel multi-hydroxyl polymer was synthesized, and a new composite system was constructed based on the dynamic boronic ester bonds. Firstly, the multi-hydroxyl polymer P(AM-DPMOH2) was prepared by aqueous solution copolymerization of acrylamide (AM) and a dihydroxy monomer 2,3-dihydroxy-N-(3-methacrylamidopropyl)-N,N-dimethylpropan-1-aminium (DPMOH2), which was obtained by quaternization reaction between 3-chloro-1,2-propanediol and N-(3-dimethylaminopropyl). Then, the composite system was prepared by the P(AM-DPMOH2) solution and polyboronic acid compound (BPEI). The effects of DPMOH2 content in P(AM-DPMOH2), molecular weight of P(AM-DPMOH2), molecular weight of BPEI, phenylboronic acid groups content in BPEI and pH on the formation of thickening composite system were investigated. The results showed that when the content of DPMOH2 in P(AM-DPMOH2) exceeded 40 wt%, viscosity average molecular weight of P(AM-DPMOH2) was higher than 5.0×105 g/mol, the molecular weight of PEI in BPEI was larger than 3000 g/mol, the content of phenylboronic acid groups in BPEI was more than 39.3 %, and pH was in the range of 8–9, the thickening composite system can be formed by P(AM-DPMOH2) and BPEI. In addition, both the temperature and salt resistance of the composite system formed by 3000 mg/L P(AM-DPMOH2) and 2000 mg/L BPEI was much better than that of 3000 mg/L P(AM-DPMOH2). The results of this paper provide a new finding of how to construct a composite flooding system with dynamic covalent bonds.

Grafting of Poly(ethylene imine) to Silica Nanoparticles for Odor Removal from Recycled Materials.

One of the major obstacles to the reuse of recycled plastic materials is the emanation of after-process odors from recycled polymers and composites. Typically, recycled polymers are blended with an off-odor adsorbent additive in the recycling chain to eliminate these smells. This article describes an innovative ultrasonically assisted method of grafting poly(ethylene imine) (PEI) to silica nanoparticles (SiO2) initiated by benzoyl peroxide (BP) which acts as an odor remover. To prepare the PEI/Si, the branched PEI was grafted onto the silica surface without a coupling agent. This made the grafting process straightforward, easy and low in cost. Fourier Transform Infrared (FTIR) analysis confirmed the successful grafting of PEI to silica. The thermogravimetric analysis (TGA) indicated the formation of two different fractions: a polymeric fraction covalently attached to the nanoparticle surface and a non-grafted PEI fraction that was removed during extraction. Up to 30% of the grafted-PEI fractions were produced at the lowest BP concentration with the highest PEI molecular weight at silica-to-PEI weight ratios of (1:1) to (3:1). The sensory assessment showed a substantial reduction in overall odor intensity for 30% of the recycled plastic-containing materials and a ~75% reduction in volatile organic compounds (VOCs) for 100% of the recycled plastics. These results strongly suggest that this innovative PEI/Si nanocomposite can be successfully commercialized for odor removal. To the authors’ best knowledge, this is the first reported work describing a one-pot reaction for grafting PEI to different nanoparticle surfaces.

A Facile Co-Deposition Approach to Construct Functionalized Graphene Quantum Dots Self-Cleaning Nanofiltration Membranes

In this study, a novel photocatalytic self-cleaning nanofiltration (NF) membrane was fabricated by constructing aspartic acid-functionalized graphene quantum dots (AGQDs) into the polydopamine/polyethyleneimine (PDA/PEI) selective layer via the co-deposition method. The chemical composition, microstructure, and hydrophilicity of the prepared membranes were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), attenuated total reflection (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and water contact angle (WCA). Meanwhile, the effects of PEI molecular weight and AGQDs concentration on NF membrane structures and separation performance were systematically investigated. The photocatalytic self-cleaning performance of the PDA/PEI/AGQDs membrane was evaluated in terms of flux recovery rate. For constructing high-performance NF membranes, it is found that the optimal molecular weight of PEI is 10,000 Da, and the optimal concentration of AGQDs is 2000 ppm. The introduction of hydrophilic AGQDs formed a more hydrophilic and dense selective layer during the co-deposition process. Compared with the PDA/PEI membrane, the engineered PDA/PEI/AGQDs NF membrane has enhanced water flux (55.5 LMH·bar−1) and higher rejection (99.7 ± 0.3% for MB). In addition, the PDA/PEI/AGQDs membrane exhibits better photocatalytic self-cleaning performance over the PDA/PEI membrane (83% vs. 69%). Therefore, this study provides a facile approach to construct a self-cleaning NF membrane.

A diaminoethane motif bearing low molecular weight polymer as a new nucleic acid delivery agent

Among polymer-based gene delivery systems, poly(ethylene imine) (PEI) stands out as an effective polycation. However, the toxic effects of PEI especially at higher molecular weights limit its usage. Although the effects of PEI's architecture and molecular weight on gene delivery is controversial in literature, low molecular weight PEI appears to be efficient at transfection while having lower toxicity. Herein, as an alternative to low molecular weight, linear PEI, a methacrylate polymer bearing diamimoethane motifs, poly(2-((2-aminoethyl)amino)ethyl methacrylate) (P(AEAEMA)), was evaluated in vitro as a new nucleic acid delivery agent. P(AEAEMA) (8 kDa) showed low toxicity on Skov-3-luc and NIH/3T3 cell lines at polymer concentrations where PEI (8 kDa) was highly toxic. P(AEAEMA) could efficiently form complexes with siRNA at an N/P ratio of 2 as shown by gel electrophoresis. The diameter of P(AEAEMA)-siRNA complexes was found to be significantly lower than PEI-siRNA complexes almost at all tested N/P ratios. P(AEAEMA) could improve the stability of siRNA in serum containing media by protecting the siRNA against serum nucleases. siRNA and pDNA transfection efficiency of P(AEAEMA) on luciferase expressing Skov-3-luc cell line and HEK 293T cell line, respectively was found to be comparable to well-known nucleic acid carrier, PEI. The transfection efficiency of both P(AEAEMA) and PEI was found to be cell-type-dependent. None of the polymers were able to transfect MDA-MB-231 cells with siRNA or pDNA.

Polyethylenimine quantity and molecular weight influence its adjuvanting properties in liposomal peptide vaccines

We recently reported that polyethylenimine (PEI; molecular weight of 600 Da) acted as a vaccine adjuvant for liposomal group A Streptococcus (GAS) vaccines, eliciting immune responses in vivo with IgG antibodies giving opsonic activity against five Australian GAS clinical isolates. However, to date, no investigation comparing the structure–activity relationship between the molecular weight of PEI and its adjuvanting activity in vaccine development has been performed. We hypothesized that the molecular weight and quantity of PEI in a liposomal vaccine will impact its adjuvanting properties. In this study, we successfully formulated liposomes containing different molecular weights of PEI (600, 1800, 10k and 25k Da) and equivalents of PEI (0.5, 1 and 2) of branched PEI. Outbred mice were administrated the vaccine formulations intranasally, and the mice that received a high ratio of PEI 600 reported a stronger immune response than the mice that received a lower ratio of PEI 600. Interestingly, mice that received the same quantity of PEI 600, PEI 10k and PEI 25k showed similar immune responses in vivo and in vitro. This comparative study highlights the ratio of PEI present in the liposome vaccines impacts adjuvanting activity, however, PEI molecular weight did not significantly enhance its adjuvanting properties. We also report that the stability of PEI liposomes is critical for vaccines to elicit the desired immune response.

Development of a safe and efficient gene delivery system based on a biodegradable tannic acid backbone

Finding a safe and efficient gene delivery vector is a major international challenge facing the development of gene therapy. Tannic acid (TA) is a natural cross-linker owing to its hydroxyl and carboxyl groups that can interact with biopolymers for different biomaterial design. In this work, three polyethyleneimine-modified TA polymers were prepared, and the polymers were characterized by FTIR, UV–vis, elemental analysis and 1H NMR. The potential of PTAs as gene vector was studied in vitro, including DNA loading capacity, DNA protection ability and biocompatibility. In addition, the particle size, zeta potential, DNA encapsulation efficiency, cell uptake and transfection efficiency of the PTA-pDNA polyplexes were also studied. The results showed that PTA2k and PTA30k could completely condense DNA at N/P of 2, and PTA600 could only completely condense DNA at N/P of 50. The PTA/pDNA polyplexes could protect DNA from degrading by DNA enzymes and could be efficiently uptaked by cells. Biocompatibility assay showed that PTA had no significant cytotoxicity and effect on cell proliferation compared to PEI. At low N/P ratios of 1–4, PTA showed higher transfection efficiency than PEI, and the transfection efficiency increased with the increase of PEI molecular weight in PTA. At N/P of 3, PTA30k showed the highest transfection efficiency of 23.8%, while PEI30k showed only 6.7%. These results indicate that PTA is a promising candidate vector for safe and efficient gene delivery.

Binding Characterization of Aptamer-Drug Layered Microformulations and In Vitro Release Assessment

Efficient delivery of adequate active ingredients to targeted malignant cells is critical, attributing to recurrent biophysical and biochemical challenges associated with conventional pharmaceutical delivery systems. These challenges include drug leakage, low targeting capability, high systemic cytotoxicity, and poor pharmacokinetics and pharmacodynamics. Targeted delivery system is a promising development to deliver sufficient amounts of drug molecules to target cells in a controlled release pattern mode. Aptameric ligands possess unique affinity targeting capabilities which can be exploited in the design of high pay-load drug formulations to navigate active molecules to the malignant sites. This study focuses on the development of a copolymeric and multifunctional drug-loaded aptamer-conjugated poly(lactide-co-glycolic acid)–polyethylenimine (PLGA-PEI) (DPAP) delivery system, via a layer-by-layer synthesis method, using a water-in-oil-in-water double emulsion approach. The binding characteristics, targeting capability, biophysical properties, encapsulation efficiency, and drug release profile of the DPAP system were investigated under varying conditions of ionic strength, polymer composition and molecular weight (MW), and degree of PEGylation of the synthetic core. Experimental results showed increased drug release rate with increasing buffer ionic strength. DPAP particulate system obtained the highest drug release of 50% at day 9 at 1 M NaCl ionic strength. DPAP formulation, using PLGA 65:35 and PEI MW of ∼800 Da, demonstrated an encapsulation efficiency of 78.93%, and a loading capacity of 0.1605 mg bovine serum albumin per mg PLGA. DPAP (PLGA 65:35, PEI MW∼25 kDa) formulation showed a high release rate with a biphasic release profile. Experimental data depicted a lower targeting power and reduced drug release rate for the PEGylated DPAP formulations. The outcomes from the present study lay the foundation to optimize the performance of DPAP system as an effective synthetic drug carrier for targeted delivery.

Improvement of lipase activity by synergistic immobilization on polyurethane and its application for large-scale synthesizing vitamin A palmitate

We have developed an improved and effective method to immobilize lipase on hydrophobic polyurethane foam (PUF) with different modifications. PUF was treated with hydrochloric acid to increase the active sites and then the active carboxyl groups and amino groups were exposed. Enzyme activity of lipase immobilized on PUF-HCL (8000 U/g) was 50% higher than that of lipase immobilized on PUF (5300 U/g). There is an increase in the activity of the immobilized lipase on AA/PEI-modified support (115,000 U/g), a 2.17-fold increase compared to lipase immobilized on the native support was observed. The activity of immobilized lipases was dependent on the PEI molecular weight, with best results from enzyme immobilized on PUF-HCL-AA/PEI (MW 70,000 Da, 12,800 U/g)), which was 2.41 times higher compared to that of the same enzyme immobilized on PUF. These results suggest that the activity of immobilized lipase is influenced by the support surface properties, and a moderate support surface micro-environment is crucial for improving enzyme activity. Finally, the immobilized lipase was used for the production of vitamin A palmitate. The immobilized lipase can be reused for up to 18 times with a conversion rate above 90% for 12 h in a 3 L bioreactor.Research highlightsAn efficient immobilization protocol on polyurethane foam was developedPolyethyleneimine and acetic acid were used to regulate the micro-environment concurrentlyThe activity of lipase immobilized on PUF-HCL-AA/PEI was improved by 2.41 timesImmobilized lipase exhibited excellent operational stability for vitamin A palmitate synthesis

Polyethyleneimine cross-linked graphene oxide for removing hazardous hexavalent chromium: Adsorption performance and mechanism

It is essential and important to understand the adsorption mechanism and identify the removal efficiency when applying an adsorption technique to remove toxic heavy metals from wastewater. A facile and cost-effective route to preparing polyethyleneimine cross-linked graphene oxide (GO-PEI) is developed and reported herein. With significantly enhanced adsorption capacity, the obtained GO-PEI materials found promising prospects as an effective adsorbent toward Cr(VI) in comparison with untreated GO and rGO. Their structure and morphology were characterized with XRD, FT-IR, XPS, SEM and TEM techniques, and detailed mechanism for the adsorption behavior was systematically investigated in terms of the optimal molar ratio, pH effect, kinetics, isotherm models, and interference. Experiments suggested that PEI molecular weight at 70 k combined with GO and the ratio of 1:2 were conducive to the optimal adsorption efficiency. The prepared GO-2PEI exhibited a high capacity of 436.20 mg g−1 for adsorption toward Cr(VI) anions, which guaranteed eligible discharge at the final Cr(VI) concentration. According to XPS, Cr(VI) were reduced partially to Cr(III), and these trivalent ions would be chelated on GO-2PEI surface for simultaneous immobilization during Cr(VI) adsorption. The kinetic process of Cr(VI) adsorption fitted better with the pseudo-second-order model and was subject to multi-step influence. Adsorption mechanisms consisted of electrostatic interaction, reduction, and chelation. This work not only provides a simple and environmental-friendly synthetic route to GO-PEI, but also offers valuable clues for wastewater treatment.

Regenerable biocatalytic nanofiltration membrane for aquatic micropollutants removal

A trade-off between operation stability and activity regeneration limits the application of biocatalytic membrane, and when it is applied for micropollutants removal from drinking water under flow-through mode, a high removal efficiency is required. To address these issues, a regenerable nanofiltration (NF) biocatalytic membrane was fabricated by immobilizing laccase on polydopamine/ polyethyleneimine (PDA/PEI)-coated NF membrane via physical adsorption. The effect of base membrane properties, dopamine coating time, PEI molecular weight, loading pH on the biocatalytic membrane performance was investigated in terms of permeability, enzyme loading and activity. It was proved that electrostatic and hydrophobic interactions between laccase and PEI molecules were the main immobilization mechanisms, and 750000Da PEI molecule was selected to immobilize laccase at pH 5. The bisphenol A (BPA) removal by such biocatalytic membrane under flow-through mode was improved mainly due to its enhanced rejection ability (pore narrowing and surface hydrophilicity enhancement by the PDA/PEI layer). To further increase the BPA removal, the synthetic and natural mediators were introduced to improve the laccase-induced BPA oxidation by accelerating electron transfer, and the BPA removal kept higher than 97% during 7 reuse cycles without detectable loss of mediators. Moreover, traces of BPA in water was enriched on the surface of the biocatalytic membrane by pressure-driven filtration, thus improving BPA biodegradation by the laccase-mediator system. The biocatalytic membrane could be fast regenerated by chemical cleaning and reloading, and during the storage or operation, the leaked enzymes were also able to be recaptured. This work not only proposed a novel concept of regenerable biocatalytic NF membrane, but also offered a sustainable solution to quickly remove micropollutants in drinking water.

Effects of polyethyleneimine molecular weight and proportion on the membrane hydrophilization by codepositing with dopamine

ABSTRACTMussel‐inspired chemistry has attracted widespread interest in the surface modification of polymer membranes. We have previously demonstrated a dopamine (DA) assisted codeposition process of polyethyleneimine onto polypropylene microfiltration membranes (PPMMs) for surface hydrophilization. In this work, we further investigate the effects of PEI molecular weight and DA/PEI mass ratio on the codeposition process and membrane performance. The results indicate that only low‐molecular‐weight PEI bring a distinct promotion in both surface wettability and water permeation flux for PPMMs. On the other hand, either excess DA or PEI is detrimental to the surface hydrophilicity of the studied membranes. The optimized PEI molecular weight is 600 Da and the corresponding mass ratio is 1:1 for the surface hydrophilization of PPMMs. These results are beneficial to understand those codeposition processes of dopamine with other polymers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43792.

Phase behaviour of the ternary system: monoolein-water-branched polyethylenimine.

Addition of a branched polymer, polyethyleneimine, significantly alters the organization of a glycerol monooleate (GMO) lipid-water system. We present detailed data over a wide range of compositions (water content from 10 to 40%, relative to GMO and PEI fractions from 0 to 4%) and temperatures (25-80 °C). The PEI molecular weight effects are examined using polymers over a range from 0.8 to 25 kDa. Addition of PEI induces the formation of higher curvature reverse phases. In particular, PEI induces the formation of the Fd3m phase: a discontinuous phase comprising reverse micelles of two different sizes stacked in a cubic AB2 crystal. The formation of the Fd3m phase at room temperature, upon addition of polar, water soluble PEI is unusual, since such phases typically are formed only upon addition of apolar oils. The largest stability window for the Fd3m phase is observed for PEI with a molecular weight = 2 kDa. We discuss how PEI influences the formation and stability of high curvature phases.

One-pot synthesis of water-soluble superparamagnetic iron oxide nanoparticles and their MRI contrast effects in the mouse brains.

Water-soluble superparamagnetic iron oxide nanoparticles (SPIONs) were synthesized by the thermal decomposition of iron (III) acetylacetonate (Fe(acac)3) in the mixture of poly(ethylene glycol) (PEG) and poly(ethylene imine) (PEI). The average sizes of the SPIONs are in the range of 6-12nm, which could be tuned by adjusting the synthesis temperature and molecular weight of PEI. Benefiting from the coating of hydrophilic PEG and PEI, the resulted SPIONs showed excellent colloidal stability in deionized water and other physiological buffers. The XRD patterns indicate that the obtained SPIONs are magnetite. The PEG/PEI-SPIONs exhibited high r2/r1 ratio. In vivo magnetic resonance imaging (MRI) of the mouse brains after intravenous injection of the SPIONs showed their good contrast effect. Considering the facile fabrication process and excellent imaging performance of the water soluble PEG-SPIONs and PEG/PEI-SPIONs, it is believed that the SPIONs will find great potential in advanced MRI.

Controlled etching of internal and external structures of SiO2 nanoparticles using hydrogen bond of polyelectrolytes.

We have demonstrated a novel strategy for the synthesis of mesoporous silica nanoparticles (MSNPs) using a surfactant-free method under ambient conditions. By the simple addition of an amine-based polymer (polyethylenimine; PEI) with a high molecular weight to a silica nanoparticle (SNP) solution, two types of MSNPs, including rambutan-like MSNPs (R-MSNPs) and hollow MSNPs (H-MSNPs), were produced. The structural changes of the MSNPs were systematically studied using various reaction conditions (reaction time, molar ratio and molecular weight of PEI, etc.) and were observed using electron microscopic techniques. The formation mechanisms of both MSNPs were carefully investigated using XPS, Raman, and IR spectroscopies. Because the synthesized MSNPs are highly porous materials that contain internal organic/inorganic networks, we investigated the removal/adsorption properties of these MSNPs with respect to pollutants toward possible future use in environmental remediation applications. The H-MSNPs exhibited better environmental remediation capabilities relative to the R-MSNPs because PEI is present between the cobweb-like internal structures of the H-MSNPs, thereby providing a significant number of reaction sites for the adsorption of pollutants. The approach presented here can also be used as a direct method for the preparation of intraconnected networks within the substructures.

Homeostatic Competition between Phasic and Tonic Inhibition

The GABAA receptors are the major inhibitory receptors in the brain and are localized at both synaptic and extrasynaptic membranes. Synaptic GABAA receptors mediate phasic inhibition, whereas extrasynaptic GABAA receptors mediate tonic inhibition. Both phasic and tonic inhibitions regulate neuronal activity, but whether they regulate each other is not very clear. Here, we investigated the functional interaction between synaptic and extrasynaptic GABAA receptors through various molecular manipulations. Overexpression of extrasynaptic α6β3δ-GABAA receptors in mouse hippocampal pyramidal neurons significantly increased tonic currents. Surprisingly, the increase of tonic inhibition was accompanied by a dramatic reduction of the phasic inhibition, suggesting a possible homeostatic regulation of the total inhibition. Overexpressing the α6 subunit alone induced an up-regulation of δ subunit expression and suppressed phasic inhibition similar to overexpressing the α6β3δ subunits. Interestingly, blocking all GABAA receptors after overexpressing α6β3δ receptors could not restore the synaptic GABAergic transmission, suggesting that receptor activation is not required for the homeostatic interplay. Furthermore, insertion of a gephyrin-binding-site (GBS) into the α6 and δ subunits recruited α6(GBS)β3δ(GBS) receptors to postsynaptic sites but failed to rescue synaptic GABAergic transmission. Thus, it is not the positional effect of extrasynaptic α6β3δ receptors that causes the down-regulation of phasic inhibition. Overexpressing α5β3γ2 subunits similarly reduced synaptic GABAergic transmission. We propose a working model that both synaptic and extrasynaptic GABAA receptors may compete for limited receptor slots on the plasma membrane to maintain a homeostatic range of the total inhibition.

Effects of physico-chemical properties between poly(ethyleneimine) and silica abrasive on copper chemical mechanical planarization

We investigated the effect of poly (ethyleneimine) (PEI)-modified silica abrasive on the removal rate and the degree of dishing during Cu chemical mechanical planarization (CMP). The PEI-modified silica abrasive was prepared by mutually attractive electrostatic forces between PEI and silica abrasive. The physico-chemical behaviors between PEI and the silica abrasive were evaluated by total organic carbon (TOC), force-separation measurements using atomic force microscopy (AFM) with molecular weight of PEI, which was found to adsorb on silica at pH 7.0 following a Langmuir isotherm. The maximum adsorbed amounts of low and high molecular weight PEI were 0.195mg/m2 and 0.228mg/m2, respectively. AFM results showed the repulsive force of the adsorbed PEI layers on the silica surface and the adsorption thickness of PEI on silica vary with the molecular weight of PEI. A twofold change was observed in the AFM analysis. First, the increased areal density of adsorbed PEI caused a higher zeta-potential and longer reaching repulsive force. Second, the adsorption thickness was also significantly enlarged. High molecular weight showed increased adsorption thickness under similar conditions compared to low molecular weight of PEI. These changes of silica abrasive such as electrostatic forces and steric interaction vary with molecular weight of PEI reduced the dishing of Cu pattern film from 50 to 20nm.