Tag polymerization [40 articles]

Abstract

Crescentin, the recently discovered bacterial intermediate filament protein, organizes into an extended filamentous structure that spans the length of the bacterium Caulobacter crescentus and plays a critical role in defining its curvature. The mechanism by which crescentin mediates cell curvature and whether crescentin filamentous structures are dynamic and/or polar are not fully understood. ...

Abstract

There is a need to develop improved methods for directing and maintaining the differentiation of human mesenchymal stem cells (hMSC) for regenerative medicine. Here, we present a method for embedding cells in defined protein microenvironments for the directed osteogenic differentiation of hMSC. Composite matrices of collagen I and agarose were produced by emulsification and simultaneous polymerization in the presence of hMSC to produce 30-150 mum diameter hydrogel "beads." The proliferation, morphology, osteogenic gene expression, and calcium deposition of hMSC in bead ...

Abstract

Experimental time series for a nonequilibrium reaction may in some cases contain sufficient data to determine a unique kinetic model for the reaction by a systematic mathematical analysis. As an example, a kinetic model for the self-assembly of microtubules is derived here from turbidity time series for solutions in which microtubules assemble. The model may be seen as a generalization of Oosawa's classical nucleation-polymerization model. It reproduces the experimental data with a four-stage nucleation process and a critical nucleus of 15 ...

Abstract

We present a coarse-grained model for the dynamics of living polymer solutions which explicitly includes solvent hydrodynamics. We show that lamellar and columnar structures emerge when the solution is subjected to simple shear. In the absence of shear, the model predicts a fluid-gel transition as a function of polymer concentration. At a threshold concentration, the self-intermediate scattering function indicates Zimm-like dynamics at large wave vectors and diffusive dynamics at small wave vectors. The kinetics of scission and recombination clearly demonstrates the ...

Abstract

A real-time nonlinear optimization scheme is implemented for the high temperature starved feed semi-batch solution polymerization used to produce acrylic resins for automotive coatings. The system input and state trajectories are determined on-line to minimize a cost function defined in terms of deviation from target molecular weight and composition, and batch time. The performance of the proposed strategy is examined through numerical simulation for several study cases for semibatch butyl methacrylate and styrene (BMA/STY) free radical copolymerization. Results show that polymer ...

Abstract

In vivo cell division protein FtsZ from E. coli forms rings and spirals which have only been observed by low resolution light microscopy. We show that these suprastructures are likely formed by molecular crowding which is a predominant factor in prokaryotic cells and enhances the weak lateral bonds between proto-filaments. Although FtsZ assembles into single proto-filaments in dilute aqueous buffer, with crowding agents above a critical concentration, it forms polymorphic supramolecular structures including rings and toroids (with multiple protofilaments) about 200 ...

Note (first note only)

Popp et al. polymerize FtsZ under high osmotic pressure conditions and analyze the various structures formed (rings, torroids, ...) via electron microscopy. Perhaps some parallels with structures formed by higher-order interactions of microtubules? (bundles, rings, ...)

Abstract

This chapter attempts to give an overview of the historical development and current progress of femtosecond laser micro-nanofabrication based on multiphoton absorption, and particular emphasis is placed on two-photon photopolymerization. Femtosecond laser interaction with matter differs essentially from those with longer pulses or CW lasers in its significant nonlinearity, ultrafast characteristics and the possibility of highly localization of reaction volume. These features enable three-dimensional (3D) micro-nanofabrication in solid and liquid media. In two-photon photopolymerization, when a near-infrared femtosecond laser is tightly ...

Abstract

The cyclic potential sweep (CPS) method was applied to aniline electropolymerization in several strong acids (H 2 SO 4 , HNO 3 , HCl, HBF 4 , HClO 4 and CF 3 COOH). It is mainly the type of anion that determines the morphology of polyaniline (PANI) deposits, promoting either a compact (BF − 4 , ClO 4 − and CF 3 COO − , class 1 anions) or an open structure (SO 4 2− , NO 3 − ...

Abstract

We map the phase diagram of microtubules as a function of temperature and tubulin concentration. We observe spontaneous and site-nucleated microtubule assembly. At temperatures and concentrations below the onset of spontaneous nucleation; we measure the steady-state proportion of occupied nucleation sites and the distribution of lengths of site-nucleated microtubules. Our observations reveal a transition in the length dynamics of microtubules from bounded to unbounded growth. This transition is also evident in the length dynamics of individual site-nucleated microtubules. The transition to ...

Abstract

Stress fibers are contractile cytoskeletal structures, tensile actomyosin bundles which allow sensing and production of force, provide cells with adjustable rigidity and participate in various processes such as wound healing. The stress fiber is possibly the best characterized and most accessible multiprotein cellular contractile machine. Here we develop a quantitative model of the structure and relaxation kinetics of stress fibers. The principal experimentally known features are incorporated. The fiber has a periodic sarcomeric structure similar to muscle fibers with myosin motor ...

Abstract

Highly efficient antibody immobilization is crucial for conducting high-performance immunoassays such as enzyme-linked immunosorbent assay (ELISA) in microarray and microfluidic biochips. In this study, a biotin-poly( l -lysine)-g-poly(ethylene glycol) (biotin-PLL-g-PEG) and protein A-based technique was developed to immobilize antibody on the surface of poly(methyl methacrylate) (PMMA) microchannels. First, PMMA surface was activated by oxygen plasma, followed by poly(acrylic acid) (PAA) grafting to add functional carboxyl group for subsequent binding. After the biotin-PLL-g-PEG molecules reacted with carboxyl groups through the electrostatic interactions, ...

Abstract

A detailed dynamic model of the polymerization reaction of vinyl acetate in a real-life industrial reactor is presented. With the recipe and the operating procedures observed in the factory as inputs, the model predicts with reasonable accuracy the final conversion, the average particle diameter, the solid content and the viscosity. The manual and semi-manual operations, and the decision process followed by the operator, are also modelled in order to replicate closely the process carried out in the factory. The model provides ...

Abstract

For cell-based biosensor applications, dissociated neurons have been cultured on planar microelectrode arrays (MEAs) to measure the network activity with substrate-embedded microelectrodes. There has been a need for a multi-well type platform to reduce the data collection time and increase the statistical power for data analysis. This study presents a novel method to convert a conventional MEA into a multi-well MEA with an array of micrometre-sized neuronal culture ('neuronal micro-circuit array'). An MEA was coated first with cell-adhesive layer (poly-D-lysine) which ...

Abstract

Entrapment of mammalian cells in physical membranes has been practiced since the early 1950s when it was originally introduced as a basic research tool. The method has since been developed based on the promise of its therapeutic usefulness in tissue transplantation. Encapsulation physically isolates a cell mass from an outside environment and aims to maintain normal cellular physiology within a desired permeability barrier. Numerous encapsulation techniques have been developed over the years. These techniques are generally classified as microencapsulation (involving small ...

Abstract

Macroporous microcarriers are used for the high density cultivation of mammalian cells. The large pores in the interior of these beads provide space for cell growth. However, it has been observed that the cell distribution in the interior of microcarriers is often uneven. In some cases, the pores appear to be unoccupied. Questions thus arise as to whether all pores are open to the bead surface, and whether the pores allow cell entry and proliferation. To examine the accessibility and geometrical ...

Abstract

An ultrasensitive piezoelectric method for the detection of the aflatoxin B 1 (AFB 1 ) based on the indirect competitive immunoassay and the biocatalyzed deposition amplification has been developed. In this method, the quartz crystal surface was coated with a self-assembled monolayer of 3-mercaptopropionic acid (MPA) for covalently immobilization of the BSA-AFB 1 conjugate, which could compete with the free AFB 1 for binding to the anti-AFB 1 antibody (MsIgG). After the competitive immunoreaction, the horseradish peroxidase ...

Abstract

An ultrasensitive piezoelectric immunosensor using an amplification path based on an insoluble biocatalyzed precipitation product has proposed for Schistosoma japonicum. A mercapto Schistosoma japonicum antigen was self-assembled onto the quartz crystal surface via an Au nanoparticle mediator monolayer to sense the Schistosoma japonicum antibody (SjAb). And the horseradish peroxidase labeled protein A conjugate which was bounded to the SjAb by a “sandwich” format was used as a biocatalyst for the oxidative precipitation of 4-chloro-1-naphthol by H 2 O 2 to ...

Abstract

A novel polymeric initiator coating for surface modification via atom transfer radical polymerization (ATRP) is reported. The synthetic approach involves the chemical vapor deposition of [2.2]paracyclophane-4-methyl 2-bromoisobutyrate and can be applied to a heterogeneous group of substrates including stainless steel, glass, silicon, poly(dimethylsiloxane), poly(methyl methacrylate), poly(tetrafluoroethylene), and polystyrene. Surface analysis using X-ray photoelectron spectroscopy and Fourier-transformed infrared spectroscopy confirmed the chemical structure of the reactive initiator coatings to be consistent with poly[(p-xylylene-4-methyl-2-bromoisobutyrate)-co-(p-xylylene)]. Appropriate reactivity of the bromoisobutyrate side groups was confirmed ...

Abstract

Solution-processed multilayered OLEDs are fabricated through a conceptually novel, simple, intelligent, and cost-effective strategy, namely ldquolayer-by-layer cross-linkingrdquo (LBLX). It enables the use of a wide range of conventional and low-priced wet deposition techniques (e.g., all printing techniques), and is based on ldquoPEDOT-initiated cross-linkingrdquo of oxetane-functionalized polymers, which resembles the ldquografting-fromrdquo approach. ...

Abstract

A set of Tp`TiCl3 and Tp`TiCl2(OR) complexes containing tris(pyrazolyl)borate ligands (Tp`) with diverse steric properties was evaluated for ethylene polymerization under MAO activation conditions. The highest activity was exhibited by TpMs*TiCl3 (10c, TpMs* = HB(3-mesitylpyrazolyl)2(5-mesitylpyrazolyl)), a moderately crowded catalyst. The predominant chain transfer mechanism for 10c/MAO is chain transfer to AlMe3, which results in broad molecular weight distributions at low Al/Ti ratios (Al/Ti = 2001000). ...

Abstract

Rhodium(I) tris(pyrazolyl)borate complexes TpR2Rh(cod) (R = Me, Ph, i-Pr) were found to serve as efficient catalysts for highly stereoregular polymerization of phenylacetylene derivatives (p-YC6H4C⋮CH: Y = H, Me, Cl, CN, CO2Me, COMe, NO2) to give poly(phenylacetylene) species having a head-to-tail, cis-transoidal structure. ...

Abstract

Various 3,5-substituted tris(pyrazolyl)borate nickel(II) and palladium(II) complexes have been prepared and characterised in both the solid state and solution [tris(pyrazolyl)borate = tris(3,5-dimethylpyrazolyl)borate (Tp*), tris(3- t -butyl-5-methylpyrazolyl)borate (Tp t -Bu,Me ) or tris(3-cumyl-5-methyl pyrazolyl)borate (Tp Cum,Me )]. The crystal structures of the tetrahedral complex [k 3 N , N ′, N ″-Tp t -Bu,Me NiCl] and of the trigonal–bipyramidal derivative [k 3 N , N ′, N ″-Tp Cum,Me NiCl(3-methyl-5-cumylpyrazole)] have been determined by X-ray diffraction analysis. The catalytic performance of all compounds has ...

Abstract

The ionic and nucleotide requirements for the in vitro polymerization of microtubules from purified brain tubulin have been characterized by viscometry. Protein was purified by successive cycles of a temperature dependent assembly-diassembly scheme. Maximal polymerization occurred at a concentration of 0.1 M Pipes (piperazine-N,N'-bis(2-ethanesulfonic acid)); increasing ionic strength by addition of NaCl to samples prepared in lower buffer concentrations did not result in an equivalent level of polymerization. Both Na-+ and K-+ inhibited microtubule formation at levels greater than 240 mM, ...

Note (first note only)

Andy Maloney found this classic paper which is basically the origin of the BRB80 buffer used in microtubule protocols. See Andy's summary here: http://openwetware.org/wiki/User:Andy_Maloney/Notebook/Lab_Notebook_of_Andy_Maloney/2009/05/08/Ionic_and_nucleotide_requirements_for_microtubule_polymerization_in_vitro_review The paper has been cited about 250 times. It's a very nice paper, demonstrating the need for Mg++ and GTP to polymerize MTs, and finding the optimium pH and ionic strength for polymerization. Having read Parsegian and Rau, I now see that osmotic pressure is glaringly missing from any of the

Note (first note only)

Seeing large polymerization events. In presence of XMAP215 it could be that the large XMAP215 protein is either pre-templating, or binding to the MT end and quickly templating growth of many tubulin dimers. Also interesting that it appears that the same chunks come off during subsequent MT depolymerization.

Abstract

View This Record in Scopus ...

Note (first note only)

Description of the "keyhole" optical trap used by the Dogterom group for measuring microtubule polymerization force via optical tweezers.

Abstract

10.1126/science.278.5339.856 ...

Note (first note only)

1997 Dogterom and Yurke paper measuring the polymerization force-velocity relationship for microtubule polymerization. Impressive work, though I will be skeptical of the quantitative conclusions, given how heroic and new the experiments were at the time. I just now re-read it, and noted a couple things: (1) they have very nice DIC images of MTs, and they do not use oil on their condenser. That's good to know. I've in the past reduced the NA of the condenser

Abstract

The polymerisable fluorescent monomer, 4-ethoxyl- N -allyl-1,8-naphthalimide, was synthesized from 4-bromo-1,8-naphthalic anhydride and characterized using FT-IR spectra, 1 H NMR and fluorescence spectra. A copolymer of styrene and 4-ethoxyl- N -allyl-1,8-naphthalimide was prepared by detergent-free emulsion polymerization and characterized using fluorescence spectra, SEM and fluorescence microscopy. The fluorescence spectrum of the copolymer displayed excitation at 365 nm and emission at 435 nm in acetone. SEM revealed that the copolymers were microspheres, with smooth surfaces and displayed intense blue fluorescence. ...

Abstract

Abstract  A novel one-step synthetic route, the double in situ approach, is used to produce both TiO2 nanoparticles and polymer (PET), and simultaneously forming a nanocomposite with multi-functionality. The method uses the release of water during esterification to hydrolyze titanium (IV) butoxide (Ti(OBu)4) forming nano-TiO2 in the polymerization vessel. This new approach is of general significance in the preparation of polymer nanocomposites, and will lead to a new route in the synthesis of multi-functional polymer nanocomposites. ...

Abstract

We present single-molecule, real-time sequencing data obtained from a DNA polymerase performing uninterrupted template-directed synthesis using four distinguishable fluorescently labeled deoxyribonucleoside triphosphates (dNTPs). We detected the temporal order of their enzymatic incorporation into a growing DNA strand with zero-mode waveguide nanostructure arrays, which provide optical observation volume confinement and enable parallel, simultaneous detection of thousands of single-molecule sequencing reactions. Conjugation of fluorophores to the terminal phosphate moiety of the dNTPs allows continuous observation of DNA synthesis over thousands of bases without ...

Abstract

Actin plays crucial parts in cell motility through a dynamic process driven by polymerization and depolymerization, that is, the globular (G) to fibrous (F) actin transition. Although our knowledge about the actin-based cellular functions and the molecules that regulate the G- to F-actin transition is growing, the structural aspects of the transition remain enigmatic. We created a model of F-actin using X-ray fibre diffraction intensities obtained from well oriented sols of rabbit skeletal muscle F-actin to 3.3 Å in the radial direction ...

Abstract

We have used multiphoton absorption polymerization to fabricate a series of microscale polymer cantilevers. Atomic force microscopy has been used to characterize the mechanical properties of microcantilevers with spring constants that were found to span more than four decades. From these data, we extracted a Young's modulus of E = 0.44 GPa for these microscale cantilevers. The wide stiffness range and relatively low elastic modulus of the microstructures make them attractive candidates for a range of microcantilever applications, including measurements ...

Abstract

Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging1, optical data storage2,3 and lithographic microfabrication4, 5, 6. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order lambda3 (where lambda is the laser wavelength). Any subsequent process, such as fluorescence ...

Abstract

The kinetics of the electropolymerization of 2-mercaptobenzimidazole (2-MBI) on a brass substrate in alkaline solution containing methanol was investigated using cyclic polarization, chronoamperometry and electrochemical impedance techniques. The polymeric film was prepared by successive cycles of potential of a Cu-Zn electrode between 0.2 and 2.4 V. During the second cycle, the oxidation peak of the monomer disappears indicating the formation of the insulating film. We have also shown that the monomer oxidation reaction is essentially irreversible and controlled by a diffusion process. ...

Abstract

▪ Abstract  The polymerization dynamics of microtubules are central to their biological functions. Polymerization dynamics allow microtubules to adopt spatial arrangements that can change rapidly in response to cellular needs and, in some cases, to perform mechanical work. Microtubules utilize the energy of GTP hydrolysis to fuel a unique polymerization mechanism termed dynamic instability. In this review, we first describe progress toward understanding the mechanism of dynamic instability of pure tubulin and then discuss the function and regulation of microtubule dynamic ...

Abstract

GTP-dependent microtubule polymerization dynamics are required for cell division and are accompanied by domain rearrangements in the polymerizing subunit, alpha-tubulin. Two opposing models describe the role of GTP and its relationship to conformational change in alpha-tubulin. The allosteric model posits that unpolymerized alpha-tubulin adopts a more polymerization-competent conformation upon GTP binding. The lattice model posits that conformational changes occur only upon recruitment into the growing lattice. Published data support a lattice model, but are largely indirect and so the allosteric model ...

Abstract

Myosin II motors play several important roles in a variety of cellular processes, some of which involve active assembly/disassembly of cytoskeletal substructures. Myosin II motors have been shown to function in actin bundle turnover in neuronal growth cones and in the recycling of actin filaments during cytokinesis. Close examination had shown an intimate relationship between myosin II motor adenosine triphosphatase activity and actin turnover rate. However, the direct implication of myosin II in actin turnover is still not understood. Herein, we ...

Abstract

Free radical copolymerization of styrene (S) and acrylonitrile (AN) in the ionic liquids (ILs) 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6), 1,3-dimethylimidazolium dimethylphosphate ([MMIM]Me 2PO4) and 1 -ethyl-3-methylimidazolium ethylsulfate ([EMIM]EtSO4) were investigated. 2,2'-azobisiso butyronitrile (AIBN) and dibenzoyl peroxide (BPO) were used as initiators and dimethyl formamide (DMF) and methanol as reference solvents. The influence of the viscosity on the conversion and the molecular weights was studied by variation of the reaction temperature and the IL concentration. At reaction temperatures of 80 - 85°C already after ...

Abstract

We used fluorescence microscopy to determine how polymerization of Mg-ADP-actin depends on the concentration of phosphate. From the dependence of the elongation rate on the actin concentration and direct observations of depolymerizing filaments, we measured the polymerization rate constants of ADP-actin and ADP-Pi-actin. Saturating phosphate reduces the critical concentration for polymerization of Mg-ADP-actin from 1.8 to 0.06 microM almost entirely by reducing the dissociation rate constants at both ends. Saturating phosphate increases the barbed end association rate constant of Mg-ADP-actin 15%, ...