Surface Of Mt Research Articles

Synthesis of silicate clay minerals-based novel Mt/YF3:Eu3+ nanocomposites for regulated luminescent intensity-quantum yield-fluorescence lifetime

Rare earth luminescent materials have broad application prospects in the fields of white light LED lighting, flat panel display, biological imaging and so on. Here, we developed a novel silicate clay minerals-based montmorillonite nanosheet(Mt)/YF3:Eu3+ nanocomposites with strong luminescence performance. Mt carrier plays a three role: (1) reducing the size and improving dispersion of YF3: Eu3+ nanoparticles by surface effect; (2) narrowing down the band gap and increasing Urbach tail energy by interface effect; (3) reducing the shielding of the hole-electron Coulomb interactions while improving the exciton binding energy of YF3:Eu3+, thus improving the radiative recombination by dielectric effect. Therefore, orthogonal phase YF3: Eu3+ nanoparticles (diameter 20∼140 nm) binding to the surface of Mt via chemical bond interactions. The combination of Mt and YF3:Eu3+ not only enhanced luminescent intensity (about 2 times) but also improved the quantum yield (0.14% to 0.4%) and fluorescence lifetime (0.338 ns to 0.405 ns) of YF3:Eu3+ nanoparticles at 595 nm. In addition, the combination of Mt and YF3:Eu3+ give luminescent properties to Mt thereby improving the utilization rate of Mt and YF3: Eu3+ nanoparticles. It was found that the research supplies an insight on the development of new type luminescent materials, and hopefully it could promote them application in many fields.

New insights into physicochemical aspects involved in the formation of chitosan@alginate biobased polyelectrolyte complexes on natural montmorillonite clay surface

The use of alginate@chitosan-based polyelectrolyte complexes (PEC) in encapsulation process is common due to the electrostatic interactions between the two oppositely charged biopolymers. However, the incorporation of montmorillonite (Mt) particles in the complex formation for improving the encapsulation efficiency as well as the physicochemical properties of PEC remains a challenge due to the competitive polymer–polymer and polymer-nanoparticle interactions. This study aimed to investigate the binding mechanism of alginate and chitosan through layer-by-layer approach in the presence of montmorillonite nanoparticles as a function of pH and the addition order of the components. Various techniques were employed to examine the formation of the alginate@chitosan PEC on the surface of Mt, such as zeta potential, conductivity and turbidity measurements. The characterization of the different PEC systems was performed using Fourier Transformed Infrared spectroscopy (FTIR), X-Ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). The results indicate that the formation of the complex is pH-dependent. The highest intercalation of the complex was observed when chitosan was added first at a lower pH, while the intercalation was reduced at neutral pH. Additionally, the thermal stability of PEC was enhanced in the presence of montmorillonite, and was dependent on both pH and the order of addition of the biopolymers. This study provides a new understanding of the complex formation mechanism between alginate and chitosan in the presence of montmorillonite nanoparticles, showing that the combination of biopolymer-based PEC with clay particles can potentially provide a low-cost, more stable and effective nanocomposite for encapsulation and delivery of active agents.

Association with cationized gelatin nanospheres enhances cell internalization of mitochondria efficiency

The objective of this study is to confirm the methodological feasibility of cationized gelatin nanospheres (cGNS) to enhance the internalization efficiency of mitochondria (Mt) isolated to cells for their increasing functions. The cGNS were simply associated on the surface of Mt by the electrostatic interaction. Different sizes of cGNS were used to allow Mt to associate on the Mt surface (Mt-cGNS). As a control, cationized gelatin (cG) was used to modify the Mt surface (Mt-cG). The Mt-cG and Mt-cGNS prepared were cultured with H9c2 cells to examine their internalization. The internalization efficiency significantly increased by utilizing cGNS. However, there was no significant difference in the internalization efficiency among cGNS with different sizes. After incubation of Mt, Mt-cG, and Mt-cGNS, the superoxide amount and ATP generation were evaluated. Significantly lower superoxide amount and higher ATP amount were observed for the Mt-cGNS group compared with those of non-modified Mt group. It is conceivable that cGNS enhance the cellular internalization of Mt, leading to an improve mitochondrial functions in the recipient cells. In conclusion, cGNS are promising to improve the efficacy in mitochondria internalization.

Synthesis of Nano Pigments Using Clay Minerals and Organic Dyes and Their Application as Colorants in Polymer Matrix.

A new generation of clay-based nano pigments has been introduced, providing the advantage of both inorganic pigments and organic dyes. These nano pigments have been synthesized through a stepwise procedure where, initially, an organic dye is adsorbed onto the surface of the adsorbent, and then dye adsorbed adsorbent is used as pigment for further applications. The objective of the current paper was to examine the interaction of non-biodegradable toxic dyes, Crystal Violet (CV) and Indigo Carmine (IC), with clay minerals (montmorillonite (Mt), vermiculite (Vt), and clay bentonite (Bent)) and their organically modified forms (OMt, OBent, and OVt) and to develop a novel methodology for the synthesis of the value-added products and clay-based nano pigments without creating second generation waste materials. In our observation, the uptake of CV was more intense onto pristine Mt, Bent, and Vt, and the uptake of IC was more onto OMt, OBent, and OVt. CV was found to be in the interlayer region of Mt and Bent, as supported by XRD data. Zeta potential values confirmed the presence of CV on their surface. In contrast, in the case of Vt and organically modified forms, the dye was found on the surface, confirmed by XRD and zeta potential values. In the case of indigo carmine, the dye was found only on the surface of pristine Mt, Bent, Vt, and organo Mt, Bent, Vt. During the interaction of CV and IC with clay and organoclays, intense violet and blue-colored solid residues were obtained (also known as clay-based nano pigments). The nano pigments were used as colorants in a poly (methyl-methacrylate) (PMMA) polymer matrix to form transparent polymer films.

Development and characteristics of layered EGCG/Montmorillonite hybrid: An oral controlled-release formulation of EGCG

An oral controlled-release formulation of epigallocatechin-3-gallate (EGCG) was developed by intercalating EGCG into the interlayer space of Food and Drug Administration-approved mucoadhesive montmorillonite (Mt) nanolayers, and characterized by ultraviolet–visible, X-ray diffraction, Fourier transform infrared, and thermogravimetry. The EGCG intercalation was only possible at acidic pH, and occurred through electrostatic and hydrogen bonding interactions allowing restacking of exfoliated Mt nanolayers with EGCG molecules. It was inferred that EGCG molecules were adsorbed flat on the interlayer surface of Mt in a monolayer and formed two-sided hydrogen bonds with the Mt faces, leading to a ∼2-fold increase in the EGCG decomposition temperature. A maximum EGCG loading of ∼40 wt% was achieved at pH 3, reaction time 1 h, and EGCG:Mt ratio 40:10 mg/mL. The EGCG/Mt hybrid showed a sustained release of EGCG in simulated gastric and intestinal fluids in a pH-dependent manner. Deprotonation of EGCG was responsible for further EGCG release at pH 7.4 compared to pH 1.2. The release profiles were fitted to the parabolic diffusion and Bhaskar models, implying that the release was controlled by a diffusion process. These results suggest that Mt with a high loading capacity can be used as the controlled-release nanocarrier of EGCG in oral administration.

Adsorption of cadmium on clay-organic associations in different pH solutions: The effect of amphoteric organic matter

Clay minerals are important soil components and usually coexist with organic matter, forming mineral-organic associations (MOAs), which control the speciation, mobility, and bioavailability of heavy metals. However, the adsorption mechanism of cadmium (Cd) by MOAs is still unclear, especially for the associations of amphotericorganic matter and clay minerals. In this study, 12-aminododecanoic acid (ALA) and montmorillonite (Mt) were chosen to prepare MOAs via intercalation (Mt-ALA composite) and physical mixing (Mt-ALA mixture). Batch experiments were conducted to investigate the adsorption mechanism of Cd(II) by MOAs under different pH values and initial Cd(II) concentrations. The results showed that the Cd(II) adsorption capacities followed as Mt > Mt-ALA mixture > Mt-ALA composite under acidic conditions, Mt-ALA mixture > Mt > Mt-ALA composite under neutral conditions, and Mt-ALA mixture > Mt-ALA composite > Mt under alkaline conditions, suggesting the adsorption behaviors of Cd(II) by MOAs were primarily constrained by the speciation of ALA and solution pH. Under acidic conditions, cationic HALA+ could intercalate into the interlayer of Mt and occupy the adsorption sites, reducing the adsorption capacity of Cd(II). As pH increased to neutral, HALA+ decreased and changed to a zwitterionic state, which caused ALA to release out from the interlayer of Mt-ALA composite or not easily enter into Mt-ALA mixture and promoted Cd(II) adsorption. Under alkaline conditions, the increase of anion ALA- would cause ALA to be mainly adsorbed on the surface of Mt and chelate with Cd(II), enhancing the adsorption of Cd(II). Further analysis by Fourier transform infrared and X-ray photoelectron spectroscopy indicated that the carboxyl and amino groups of ALA both participated in the adsorption of Cd(II). These findings could extend the knowledge on the mobility and fate of Cd in clay-based soils and be used as a basis for understanding the biogeochemical behavior of Cd in the environment.

In situ growth of Fe3O4 on montmorillonite surface and its removal of anionic pollutants.

An environmentally functional material for the efficient removal of anionic pollutants in water was prepared for our study. Montmorillonite (M) was modified by hydrochloric acid (HCl) and cetyltrimethylammonium bromide (CTAB). Fe3O4 was grown in situ to prepare modified Fe3O4/montmorillonite (AC Fe3O4–Mt) composites. The number of hydroxyl sites on the surface of Mt and the surface tension were increased by HCl and CTAB modification, respectively, which enabled higher Fe3O4 surface growth, promoting the multi-directional crystallisation of Fe3O4 and improving reactivity. The XRD results show that Fe3O4 grows on the surface of Mt and has good crystallinity and high purity, meaning that AC Fe3O4–Mt is more reactive than Fe3O4. When AC Fe3O4–Mt is used to remove anionic pollutants in water, the removal effect under the synergistic action of adsorption-redox is significantly improved, and the maximum removable quantities of Cr(vi) and 2-4-dichlorophenol can reach 41.57 mg g−1 and 239.33 mg g−1, respectively. AC Fe3O4–Mt is a high efficiency and environmentally functional material with green environmental protection, which can be used in the field of sewage treatment.

Exploration of adsorption mechanism of 2-phosphonobutane-1,2,4-tricarboxylic acid onto kaolinite and montmorillonite via batch experiment and theoretical studies

Two clay minerals, kaolinite (Kaol) and montmorillonite (Mt) with different crystal structures were chosen to investigate the comparative adsorption of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) through batch control experiments and theoretical studies. The systematical isotherm and kinetic studies agreed with Langmuir model and pseudo-second-order model, confirming a monolayer and chemisorption interaction process, respectively. The maximum removal capacities of Kaol and Mt for PBTC were 72.297 mg/g and 121.163 mg/g at pH=3.0 and T=298 K, respectively. Furthermore, the adsorption mechanisms were investigated by molecular dynamic (MD) simulations and density functional theory (DFT). The Interface force field (IFF) was firstly introduced into Materials Studio package to explore the microscopic mechanism of clay mineral interface. The dynamics behaviors verified that the oxygen (O) atom of carboxyl group has stronger affinity at the external surface of Mt, which consistent with the experimental data well. For DFT calculations, quantitative analysis around molecular van der Waals (vdW) surface was adopted to predict reactive sites for the electrophilic reaction. Independent Gradient Model (IGM) and Hirshfeld surface analyses in Multiwfn indicated that the high adsorption effect mainly attributes to hydrogen bond action. These findings improve our ability to explore the related properties occurring at the interface of different clay minerals.

Surface Functionalization of Montmorillonite with Chitosan and the Role of Surface Properties on Its Adsorptive Performance: A Comparative Study on Mycotoxins Adsorption.

Understanding surface and interfacial information, which has a close relationship to the structures and properties of materials, helps guide the design of materials for specific applications. This study focuses on the surface functionalization of montmorillonite (Mt) with chitosan (CTS) and exploring the role of surface properties on its adsorptive performance. Two prototypical products, namely, 180-Htc@Mt and 250-Htc@Mt, were fabricated via the hydrothermal method at 180 and 250 °C, respectively. Field emission scanning electron microscopy revealed that hydrothermal carbon (Htc) derived from CTS anchored on the surface of Mt uniformly with a spherical morphology. The introduction of Htc endowed the surface of Mt with abundant hydroxy, amine, and amide groups; organic carbon; developed porosity; and hydrophobic interfacial property. Hydrothermal temperature has huge impacts on the surface system, and smaller particles (average size of 27 vs 53 nm) with deeper carbonization, higher content of carbonaceous and nitrogenous functional groups, more developed porosity (66.149 vs 39.434 m2/g of specific surface area, 0.115 vs 0.090 cm3/g of pore volume), and slightly decreased hydrophobicity can be readily achieved at a higher temperature. The incoming surface protonated amine and amide functional groups show an ion-dipolar interaction to polar aflatoxin B1 (AFB1), and the increased organic carbon content as well as interfacial hydrophobicity generate a hydrophobic interaction to weak polar zearalenone (ZER). Consequently, the surface functionalization affords Mt enhanced adsorption capacity for AFB1, approximately two times compared with Mt, and superior adsorption ability for ZER (10 mg/g). The present work provides sufficient evidence of "surface directs application" of Mt, which encourages researchers to focus on studies of the surface science of clay minerals.

Co-intercalation of organic cations/amide molecules into montmorillonite with tunable hydrophobicity and swellability

Organo-montmorillonite (OMt) has been widely used in paints, drilling fluids, clay/polymer nanocomposites, adsorbents and biosensors, however the full potential of OMt is yet to be discovered. The co-introduction of cationic and nonionic species into Mt has great potential to expand modification strategies and applications of Mt However, details regarding the intercalation mechanism of dual organic species remain unclear and the aspects of hydrophobicity and swellability of OMt are unknown. In this work, the co-introduction into OMt of octadecyltrimethylammonium (ODTMA+) cations and a nonionic specie erucamide (EA), and ODTMA+ with an oleamide (OA). was investigated. The resultant OMt samples were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. Hydrophobicity and swellability of the OMt were examined. The results showed that neither EA nor OA could be effectively introduced into the interlayer spaces of Mt, although adsorption of EA and OA onto the external surface of Mt did occur. In the presence of ODTMA+, however, both EA and OA were successfully co-intercalated into the interlayer spaces of Mt, and the basal spacing (d001) of ODTMA+, EA and OA co-intercalated OMt increased to as much as 4.2 nm. Such dual modification appeared to be effective at tailoring hydrophobicity. The swellability of ODTMA+, EA and OA co-intercalated OMt in xylene increased with the increase in the amount of EA and OA loaded. When Mt was modified using 1.0 CEC ODTMA+ with 0.5–1.75 CEC EA, 0.2 g OMt in 10 mL xylene swelled to take 10 ml volume, equating to a swell index of 100%. Here, a two-stage intercalation is proposed: cationic exchange of ODTMA+ to form a paraffin-type monolayer, followed by hydrophobic entropy-driven adsorption of nonionic EA and OA by intertwining organic chains into the interlayer spaces of the OMt The findings show the promise of co-intercalation to introduce many other cations and nonionic organic species into the interlayer spaces of Mt, and thus greatly expands the types of OMt for new applications.

Ethylene glycol monoethyl ether (EGME) adsorption by organic matter (OM)-clay complexes: Dependence on the OM Type

The ethylene glycol monoethyl ether (EGME) adsorption method has been used as an available technique for measuring the total specific surface area (TSSA) of soils and clay-rich rocks. However, the existence of organic matters (OM) has recently been proposed to affect the accurate measurement of the TSSA. To explore the effects of OM on the TSSA evaluation of clay-rich samples, EGME adsorption experiments were performed on OM and the OM-clay minerals (OM-clay) complexes that widely exist in soil and clay-rich rocks. Two types of OM, 12-aminolauric acid (ALA) and lauric acid (LA) were used, and montmorillonite (Mt) was selected as the representative clay mineral. OM-clay complexes with OM in interlayer space or OM-clay mixture with OM on the external surface of an expanding clay mineral were prepared to investigate the influence of occurrence sites of OM on the EGME adsorption. The combined methods of X-ray diffraction (XRD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) were used to study the structural characteristics of the OM-clay complexes before and after EGME adsorption for revealing the EGME adsorption mechanisms. The results showed both the occurrence sites and the functional groups of OM significantly influence the EGME adsorption behaviour and TSSA for OM-clay complexes. As ALA intercalated into interlayer space of Mt, it can occupy parts of adsorption sites of EGME leading to a lower TSSA than that of Mt. While as LA located on the external surface of Mt, it affects access to the interlayer surface by the EGME and occupies parts of EGME adsorption sites of the external surface of Mt, resulting in lower adsorption capability and the slight smaller TSSA than Mt. In addition, EGME reacted strongly with LA producing excess TSSA, which brings about a great difference between LA-Mt and ALA-Mt on EGME adsorption behaviour. These fundamental results demonstrated that OM could strongly affect the EGME adsorption on the OM-Mt complexes and further influence detection of TSSA. The occurrence sites and the functional groups of OM in OM-clay complex must be considered when the EGME adsorption method is used for TSSA evaluation of such clay-rich rocks and soil samples.

Antimicrobial activity of organoclays based on quaternary alkylammonium and alkylphosphonium surfactants and montmorillonite

Abstract Organoclays are mostly materials composed of clay minerals modified with organic surfactants, predominantly of an alkylammonium type. Such hybrid materials often exhibit properties which are superior to those of their components. The main objective of this study was to characterize the antimicrobial activity and physico-chemical properties of tetrabutylammonium (TBA), dodecyltrimethylammonium (DDA), and tetrabutylphosphonium (TBP) cations, and the effectiveness of the organoclays composed of montmorillonite SWy-2 (Mt) and those cations. Their activity was tested on the Gram-positive bacteria Staphylococcus aureus and the Gram-negative bacteria Escherichia coli. Prior to the determination of their antimicrobial activity, organoclays were characterized using X-ray diffraction and infrared spectroscopy. The results confirmed the irreversible adsorption of organic cations onto the surface of Mt and the stability of the complexes in the medium used for biological experiments. The cytotoxicity of the organic cations on a HeLa cell line determined by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) reduction assay proved to be dependent mainly on the type of surfactant. While DDA with long alkyl chains fully inhibited surviving HeLa cells at concentrations of 1 and 0.5 mmol L−1, lower concentrations (0.1 and 0.05 mmol L−1) were not toxic. On the other hand, TBA and TBP also exhibited a very low toxicity at the higher concentrations. DDA alone exhibited the highest antimicrobial properties. It inhibited surviving S. aureus and E. coli at a concentration of 1 mmol L−1, estimated by the determination of colony forming units (CFU). Both TBA and TPB were only effective at a concentration of 10 mmol L−1. All organoclays were prepared with a ratio of organic cation/Mt of 10−3 mol g−1 at a concentration ≤ 1 mmol L−1. The antimicrobial effect of Mt alone was negligible and did not interfere with the effect of the organic cations. At this concentration, the most effective organoclay was based on DDA, which reduced the survival of both S. aureus and E. coli by over 93%. The organoclays based on TBA and TBP exhibited much lower antimicrobial effectiveness. The effectiveness of organic cations bound to the surface of Mt particles at a concentration of 0.1 mmol L−1 was similar with S. aureus and lower with E. coli compared to that of the respective surfactant solutions. The results of this work provided new knowledge on the biological activities of the selected quaternary ammonium and phosphonium cations, which are often used in organoclays. The antimicrobial activity of the organoclays should be considered when they are applied as carriers of bioactive substances or in other applications dealing with biological systems.

Pyrolysis behaviors of organic matter (OM) with the same alkyl main chain but different functional groups in the presence of clay minerals

Abstract Organic matter (OM)-clay mineral complexes, especially OM-clay interlayer complexes, exist widely in soil, sediment, and source rock. These associations can influence the pyrolytic behaviors of OM. In addition, the nature of OM may also affect pyrolysis due to the variety and complexity of the structure and chemical composition of natural organics. In this study, to investigate the influences of the nature of OM as well as the interface association between OM and clay minerals on the pyrolysis of OM, interlayer clay-OM complexes and clay-OM mixtures were prepared and thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR) was adapted to monitor the pyrolytic temperatures and products of these complexes. A series of OM with the same alkyl main chain but different functional groups, i.e., Lauric acid (LA), Dodecylamine (DA), 12-Aminolauric acid (ALA) and Dodecyl trimethyl ammonium bromide (DTAB), was used, and montmorillonite (Mt) was selected as the representative clay mineral. The results showed that Mt decreased the decomposition temperature of the carboxyl groups that contained OM (LA and ALA), promoted the generation of CO2 via the catalysis of the Lewis acid sites of Mt, and delayed the decomposition of DA and DTAB. The interlayer Bronsted acid sites allowed the nitrogen-containing organics to undergo Hoffmann elimination. The pyrolytic behaviors of OM within the interlayers of Mt were more strongly affected than those on the external surface of Mt The pyrolytic performance of OM was closely related to the association ways between OM and clay minerals, the nature of clay minerals, and the nature of OM. The interlayer space was shown to be particularly important for the preservation and catalysis of organics.

Spectral induced polarization of Na-montmorillonite dispersions

Montmorillonite (Mt) clays have a high specific surface area and surface charge, which confer them remarkable adsorption properties. Nevertheless, their electrochemical and aggregation behavior are not completely elucidated because of the complexity of their microstructural and interfacial properties. In this work, the conductive and dispersive properties of Na-Mt suspensions of weight fractions 0.5–5.2% were investigated for the first time using the spectral induced polarization method. A four-electrode system was used to reduce errors introduced by electrode polarization and contact resistances. Complex conductivity spectra in the low-frequency range of 0.1Hz to 45kHz were successfully described using a triple layer model of the basal surface of Mt and a complex conductivity model that considers conduction of the diffuse layer and polarization of the Stern layer. Aggregate size distributions were inferred from inverted relaxation time distributions. We found that the negative and permanent surface charge of the basal plane of Na-Mt controls its quadrature (imaginary) conductivity, which is not very sensitive to pH and salinity (NaCl) in the 100Hz to 45kHz frequency range. For lower frequencies, the sudden increase of the quadrature conductivity at the highest salinities was explained by considering coagulation of Na-Mt particles.

Insight into thiabendazole interaction with montmorillonite and organically modified montmorillonites

The interactions of the fungicide, thiabendazole (TBZ) on montmorillonite (Mt) and organoclays synthesized from phosphatidylcholine (DSPC) and octadecyltrimethylammonium bromide (ODTMA) was investigated for water remediation. The affinity of TBZ on the surface of Mt and organoclays was evaluated by powder X-ray diffraction, X-ray photoelectron spectroscopy and the experimental results were also reinforced by molecular modelling in order to explore the surfaces arrangements. TBZ was protonated upon interaction with negative charged Mt and therefore this strong electrostatic interactions prevented it's desorption in water. Repulsive electrostatic interactions between the cationic surfactant ODTMA and the cationic form of TBZ on the outer surface of the ODTMA modified Mt resulted in high desorption values. In the DSPC modified Mt, TBZ was anchored within the surfactant chains and a small amount of interlayer water was released from the interlayer space.

Polyethyleneimine as shale inhibitor in drilling fluid

In this paper, the inhibition property of polyethyleneimine (PEI) in drilling fluid was studied. The inhibition property was evaluated by linear swell test and roll recovery. The addition of PEI70000 resulted in the lowest swelling height, compared with the others inhibitor. Especially PEI was environmental and friendly. The inhibition mechanism was investigated by Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Scanning electron microscopy, Zeta potential and Surface area analyzer. The negative charge in the surface of montmorillonite (Mt) was neutralized by the positive charge of PEI. PEI was adsorbed in the surface of Mt and intercalated into the interlayer of Mt, which reduced the hydration repulsion of diffuse electric double layer and leaded to inhibit the hydration of clay. Hydrogen bonding between amino groups in PEI and hydroxyl in the surface of Mt can be formed in the process. The coordination of electrostatic interaction and hydrogen bonding presented water molecules from the interlayer space of Mt, which resulted from the adsorption and intercalation of PEI in the surface and interlayer space of Mt. There was an amount of nitrogen in the backbone and side of PEI, leading to more positive ion than chitosan quaternary ammonium salt (HTCC). The more positive ion resulted in the stronger force between inhibitor and clay due to the protonation of nitrogen in water. The molecular weight of PEI has great influence on inhibition property. The larger molecular weight of PEI performed the better inhibition property except for PEI1800. Indicating the molecular weight of PEI was not the sole factor to control the inhibition property. What was more, the larger molecular weight of PEI leaded to the worse water-solubility.

Microwave assisted green synthesis and characterization of silver/montmorillonite heterostructures with improved antimicrobial properties

Silver (Ag)/montmorillonite (Mt) heterostructures were effectively synthesized utilising microwave (MW) irradiation technique in the absence of any reducing agent. Compared to conventional thermal reduction processes, this approach is simple, faster and environmentally friendly. The MW process yielded Mt surfaces with uniform distribution of Ag nanoparticles with an average size of 8–10nm. The presence of reducing agents was found to inhibit the formation of Ag nanoparticles in MW synthesis. The method was also successfully used for the preparation of Ag/organically modified Mt. However, the transmission electron microscopy analysis showed that, on the surface of Mt which is organically modified, the Ag nanoparticles have a tendency to aggregate forming bigger Ag clusters. The nanostructures prepared by the MW assisted method showed substantially higher levels of antimicrobial properties against Gram-positive bacteria, i.e., S. aureus and B. cereus as well as Gram-negative bacteria namely E. coli, P. aeruginosa and S. enterica.

The Ndc80 Loop Region Facilitates Formation of Kinetochore Attachment to the Dynamic Microtubule Plus End

SummaryProper chromosome segregation in mitosis relies on correct kinetochore-microtubule (KT-MT) interactions. The KT initially interacts with the lateral surface of a single MT (lateral attachment) extending from a spindle pole and is subsequently anchored at the plus end of the MT (end-on attachment) [1]. The conversion from lateral to end-on attachment is crucial because end-on attachment is more robust [2–4] and thought to be necessary to sustain KT-MT attachment when tension is applied across sister KTs upon their biorientation [1]. The mechanism for this conversion is still elusive. The Ndc80 complex is an essential component of the KT-MT interface [1, 5], and here we studied a role of the Ndc80 loop region, a distinct motif looping out from the coiled-coil shaft of the complex [6], in Saccharomyces cerevisiae. With deletions or mutations of the loop region, the lateral KT-MT attachment occurred normally; however, subsequent conversion to end-on attachment was defective, leading to failure in sister KT biorientation. The Ndc80 loop region was required for Ndc80-Dam1 interaction and KT loading of the Dam1 complex, which in turn supported KT tethering to the dynamic MT plus end [3, 7]. The Ndc80 loop region, therefore, has an important role in the conversion from lateral to end-on attachment, a crucial maturation step of KT-MT interaction.

Using Electron Tomography to Determine How Kinetochores Bind and Alter the Conformations of Microtubule Plus Ends

Chromosome alignment during mitosis and meiosis is mediated through the interaction between kinetochores and spindle microtubules (Mts). Kinetochores are fibrous mat-like structures, located at the primary constriction of chromosomes, that bind spindle Mts, generate poleward chromosome motion, and delay progression through mitosis until chromosome alignment is complete. Mts are polar polymers that function as tracks for the movement of a variety of cellular organelles and vesicles. Chromosome alignment requires a unique form of Mt-based motion because kinetochores capture and bind the plus ends of a bundle of Mts, rather than moving along the lateral surface of a single Mt . As a result, the direction of chromosome motion must be coordinated with the growth and shrinkage of Mts. Furthermore, the kinetochore maintains continuous attachment to growing and shrinking Mts and simultaneously permits the addition and dissociation of tubulin subunits within its confines

Organization of Disparity-Selective Neurons in Macaque Area MT

Neurons selective for binocular disparity are found in a number of visual cortical areas in primates, but there is little evidence that any of these areas are specialized for disparity processing. We have examined the organization of disparity-selective neurons in the middle temporal visual area (MT), an area shown previously to contain an abundance of disparity-sensitive neurons. We recorded extracellularly from MT neurons at regularly spaced intervals along electrode penetrations that passed through MT either normal to the cortical surface or at a shallow oblique angle. Comparison of multiunit and single-unit recordings shows that neurons are clustered in MT according to their disparity selectivity. Across the surface of MT, disparity-selective neurons are found in discrete patches that are separated by regions of MT that exhibit poor disparity tuning. Within disparity-selective patches of MT, we typically observe a smooth progression of preferred disparities (e.g. , near to far) as our electrode travels parallel to the cortical surface. In electrode penetrations normal to the cortical surface, on the other hand, MT neurons generally have similar disparity tuning, with little variation from one recording site to the next. Thus disparity-tuned neurons are organized into cortical columns by preferred disparity, and preferred disparity is mapped systematically within larger, disparity-tuned patches of MT. Combined with other recent findings, the data suggest that MT plays an important role in stereoscopic depth perception in addition to its well known role in motion perception.