Lipid bilayer curvature and pore formation induced by charged linear polymers and dendrimers: the effect of molecular shape

We performed molecular dynamics (MD) simulations of multiple copies of poly- l-lysine (PLL) and charged polyamidoamine (PAMAM) dendrimers in dimyristoylphosphatidylcholine (DMPC) bilayers with explicit water using the coarse-grained model developed by Marrink et al. ( J. Chem. Theory Comput. 2008, 4, 819 ). Membrane disruption is enhanced at higher concentrations and charge densities of both spheroidally shaped dendrimers and linear PLL polymers, in qualitatively agreement with experimental studies by Hong et al. (Bioconjugate Chem. 2006, 17, 728 ). However, larger molecular size enhances membrane disruption and pore formation only for dendrimers and not for the linear PLL. Despite more intimate electrostatic interactions of linear molecules than are possible for spheroidal dendrimers, only the dendrimers were found to perforate membranes, apparently because they cannot spread onto a single leaflet, and so must penetrate the bilayer to get favorable electrostatic interactions with head groups on the opposite leaflet. These results indicate that a relatively rigid spheroidal shape is more efficient than a flexible linear shape in increasing membrane permeability. These results compare favorably with experimental findings.     

Chromatography of functional polymers: A new approach to the characterization of reactive polymers obtained by chemical modification

High-performance liquid chromatography (HPLC) has been used to complement size-exclusion (gel permeation) chromatography (SEC) for the characterization of functional polymers. Whereas SEC is unable to detect compositional changes, HPLC in an appropriate interacting medium can provide detailed information on compositional changes occurring during chemical modification of a polymer. The method has been demonstrated using a normal-phase column consisting of porous monodisperse 10 μm poly(2,3-dihydroxypropyl methacrylate-co-ethylene dimethacrylate) beads that have a homogeneous coverage of aliphatic hydroxyl groups for the analysis of brominated poly(isobutylene-co-4-methylstyrene). Differences of well below 1 mol % of bromomethylstyrene units are easily detected and quantified. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1173–1180, 1997     

Double-helical ultrastructure of polycationic dendronized polymers determined by single-particle Cryo-TEM

The ultrastructure of cationic dendronized polymers (denpols) of third and fourth generations (PG3 and PG4) in water was determined by using single-particle cryo-transmission electron microscopy (cryo-TEM). At concentrations in the region of 50 mg L(-1), networks of double-stranded fibers were revealed that exhibit well-defined diameters of 5.9 nm+/-0.4 nm for PG3 and 7.4 nm+/-0.4 nm for PG4. The structure varies with progression along the fibers, and includes a double helix with a pitch of 7.0+/-0.4 nm for PG3 and 9.0+/-0.4 nm for PG4. The formation of the double strands is attributed to the hydrophobic effect and limited crowding in the dendron shell of the third and fourth generation denpols investigated. From solutions of lower concentrations (around 10 mg L(-1)), isolated molecular fibers were adsorbed onto high-energy surfaces and examined by performing scanning force microscopy (SFM) on mica, and after staining, TEM on glow-discharged carbon films. In both cases, characteristic undulations of single strands were observed, which are attributed largely to the adsorption process.     

Synthesis and characterization of polymers based on the cyanate functional group

The chemistry and growth of polymer structures based on the cyanate linkage has been studied. The monofunctional model compound 2-(4-cyanatophenyl)-2-phenylpropane was used to study the reaction products. The synthesis was performed with four different transition metal catalysts and also without a catalyst. The quenched products were analyzed using Size Exclusion Chromatography(SEC) and ¹³C NMR. It was found that the reaction is relatively clean, with trimerization being the major product. A few side products were also detected, which included dimers and higher oligomeric species. Crosslinked polymers were synthesized without catalyst based on the bifunctional monomer 2, 2-bis(4-cyanatophenyl)propane. The structure was analyzed using ¹³C NMR. The conversion and number-average degree of polymerization based on ¹³C NMR is reported. Conversion at the gel point was found to be higher than 60%. On this basis it was concluded that polymerization based on cyanate linkages at the conditions studied is diffusion controlled and therefore not described by Flory's mean-field theory.     

Enhancing the photoluminescence intensity of conjugated polycationic polymers by using quantum dots as antiaggregation reagents

The aggregation in conjugated polyelectrolytes (CPs) can be effectively reduced by the formation of CP/nanoparticle assemblies. The photophysical properties of various nanoassemblies were studied by means of UV-visible and fluorescence spectroscopy in solution and as thin films. The dissociation of the polymer chains is caused by favorable electrostatic interactions between the cationic substituents of the CPs and the anionic charges present on the surface of the nanoparticles. Such an efficient displacement of pi-stacking by competitive positive interactions constitutes the first example of positive aggregation modulation.     

Vinyl ethers with a functional group: Living cationic polymerization and synthesis of monodisperse polymers

The living cationic polymerization of vinyl ethers (VEs) having a (polar) functional pendant has been achieved by the hydrogen iodide/iodine (HI/I₂) initiating system to give polymers with a very narrow molecular weight distribution (MWD) (M_w/M_n ≤ 1.2). The functional pendants include benzyl, saturated or unsaturated ester, (poly) oxyethylene, and substituted phenoxyl groups. Although these polar groups often disturb cationic vinyl polymerization by inducing chain transfer and termination, the HI/I₂ initiator cleanly polymerized the “functionalized” VEs without side reactions, mostly in nonpolar media at low temperatures below −15 °C. The HI/I₂-initiated living polymerization also provided facile methods to synthesize new functional polymers, including water-soluble polymers, macromolecular amphiphiles, and macromers, all having a narrow MWD. The simplest example is the living polymerization of VEs carrying an oxyethylene chain [-(CH₂CH₂O)_n-R] as pendant, which directly yields water-soluble polymers. The debenzylation of poly(benzyl VE) prepared with HI/I₂ led to poly(vinyl alcohol). Polymers of the saturated ester-containing monomers (2-acetoxyethyl and 2-benzoyloxyethyl VEs) were readily hydrolyzed into poly (2-hydroxyethyl VE), soluble in water and swellable in methanol. This lead was extended to the synthesis of a new amphiphile, poly(cetyl VE-b-2-hydroxyethyl VE), from a block copolymer of cetyl and 2-acetoxyethyl VEs prepared by their sequential living polymerization initiated with HI/I₂. An adduct between HI and 2-vinyloxyethyl methacrylate [CH₃-CH(I)-OCH₂CH₂OCOC(CH₃) =CH₂] was found to initiate living polymerizations of VEs in the presence of iodine; the products were methacrylate-type macromers carrying a poly(VE) side chain with a narrow chain-length distribution.     

Fluorescent detection of chemical warfare agents: functional group specific ratiometric chemosensors

Indicators providing highly sensitive and functional group specific fluorescent response to diisopropyl fluorophosphate (DFP, a nerve gas (G-agent) simulant) are reported. Nonemissive indicator 2 reacts with DFP to give a cyclized compound 2+A- that shows a high emission due to its highly planar and rigid structure. Very weak emission was observed by the addition of HCl. Another indicator based on pyridyl naphthalene exhibits a large shift in its emission spectrum after reaction with DFP, which provides for quantitative ratiometric detection.     

Manipulating supramolecular self-assembly via tailoring pendant group size of linear vinyl polymers

In a series of poly[di(alkyl) vinylterephthalates] (PDAVTs) synthesized via radical polymerization, fine-tuning the size and shape of the side groups manipulated the supramolecular self-assembly and led to control over the formations between amorphous and 2D ordered hexagonal phases. To introduce the 2D long-range ordered structure, the size of the ester side groups at the 2- and 5-positions of the phenyl rings laterally attached to the backbones had to be in the range of propyl/isopropyl to hexyl. The relatively extended backbones observed in these polymers were attributed to steric effects from the side groups. When the n-alkyl groups were larger than hexyl, the ability to form the liquid crystalline phase gradually decreased. A completely disordered phase could be observed by substituting dodecyl groups as side groups.     

脂双层膜表面结构与稳定性的原子力显微镜研究

用原子力显微镜研究了1,2－二油酸甘油－3－磷酸－1甘油（DOPG）脂双层膜 的表面结构与稳定性。实验结果表明,原子力显微镜的探针与脂双层膜的相互作用 导致脂双层膜表面产生一个永久的损伤。静电相互作用对脂双层膜结构和稳定性的 影响表明,在NaCl溶液中制成的脂质体,随着NaCl浓度的增加,它们的双层膜更稳 定。在低的NaCl浓度则经常被损伤,在1 mol/L NaCl溶液中制备的指双层变得更稳 定。在KCl溶液中结果恰好相反。在高的KCl浓度中经常被损伤,随着KCl浓度的降 低,它们的双层膜更稳定。葡萄糖和蔗糖对脂双层膜结构有稳定作用。     

Density functional study of the roles of chemical composition of di-transition-metal-substituted gamma-Keggin polyoxometalate anions

The roles of chemical composition (X, M and M(FW)) of di-transition-metal-substituted gamma-Keggin polytungstates and polymolybdates, [(X(n)(+)O(4))M(2)(OH)(2)(M(FW))(10)O(32)]((8-n)-), on the geometry, electronic structure, and magnetic properties of these species have been investigated at the density functional level. It was shown that the change of the heteroatom X via Al(III)-Si(IV)-P(V)-S(VI) slightly stabilizes the broken-symmetry (BS) state over the high-spin (HS) state, increases the antiferromagnetic coupling constant, J, of these species, and lowers the energies of their highest-occupied molecular orbitals (HOMOs) and lowest-unoccupied molecular orbitals (LUMOs). The change of the redox-active center M from Mn to Fe slightly increases the M-(XO(4)) interaction, J-coupling constant, and energy gap between the HS and BS states. Meanwhile, the LUMOs are stabilized, indicating the stronger oxidant character of [(X(n)(+)O(4))M(2)(OH)(2)W(10)O(32)]((8-n)-) for M = Fe than Mn. It was shown that the change of addenda atom M(FW) from W to Mo makes (a) the geometry of Keggin "cage" slightly smaller, (b) the interaction of redox-active centers (Fe) with the central XO(4)-unit slightly stronger, and (c) the J-coupling constant, as well as the energy gap DeltaE(BS-HS), slightly larger.     

One-dimensional protein-based nanoparticles induce lipid bilayer disruption: carbon nanotube conjugates and amyloid fibrils

Along with recent progress of nanotechnology, concern has risen about biological impacts of nanoparticles deriving from their interaction with cell membranes. Nanoparticles tend to adsorb proteins in vivo. Therefore, the physical properties of the conjugates to cell membranes must be investigated to elucidate and assess their properties. We examined whether one-dimensional protein-based nanoparticles induce liposome leakage in physiological saline. Carbon nanotube conjugates with adsorbed lysozyme interacted with the liposome through electrostatic interaction, leading to liposome leakage. Surprisingly, amyloid fibrils of lysozyme resembled the conjugate in terms of their effects on liposome leakage. Results described herein provide new insight into the interaction between nanoparticles and cell membranes in terms of their shape, mechanical properties, and noncovalent interactions.     

New class of biodegradable polymers formed from reactions of an inorganic functional group

Although numerous small molecules have been synthesized with sulfenamide bonds (R(2)N-SR), this is the first report of the synthesis of polysulfenamides. These polymers are readily synthesized at room temperature using secondary diamines and dithiosuccinimides. The dithiosuccinimides were readily synthesized in one step by the reaction of dithiols such as HS(CH(2))(6)SH with N-chlorosuccinimide. The resulting dithiosuccinimides were either recrystallized or readily purified by chromatography on silica gel and required no special handling. The conversions of polymerization ranged from 95 to 98%, and the molecular weights of the polymer reached as high as 6,300 g mol(-1). The sulfenamide bond was very stable in organic solvents, and no degradation was observed under atmospheric conditions in C(6)D(6) for 30 days. In contrast, the sulfenamide bond readily decomposed in less than 12 h in D(2)O. Polysulfenamides were fabricated into micron-sized particles loaded with dye and endocytosed into JAWSII immature dendritic and HEK293 cells. Polysulfenamides represent a new class of polymers that are readily synthesized, stable in aprotic solvents, and readily degrade in water.     

Kinetic study of cell disruption by ionic polymers with varied charge density

The effect of charge density and hydrophobicity of the polymeric cations on cell disruption is studied thermodynamically and kinetically by using the budding yeast protoplast. It is found that cationic polymers drastically disrupt the cells above a certain concentration while nonionic and anionic ones do not. Reduced charge density of copolymers of cationic and nonionic monomers resulted in decreased cell disruption. However, it is further experimentally proved that the disruption of the cells occurs only when the polycation has a certain hydrophobicity. The stronger the hydrophobicity of the cationic polymer, the more cooperatively the cells are disrupted. Received: 29 May 2000 Accepted: 1 September 2000     

Lipid bilayer discs and banded tubules: photoinduced lipid sorting in ternary mixtures

The self-assembly of biological amphiphiles has proved a fascinating topic in recent years, the hollow cylindrical lipid tubule morphology being of particular interest due to its potential applications in "soft" microtechnologies. Lateral coexistence of liquid-ordered (lo) and liquid-disordered (ld) phases, which may resemble raft formation in cell membranes, was investigated in lipid tubules, prepared from 1,2-dioleoyl-sn-glycero-3-phosphocholine, egg-sphingomyelin, and cholesterol. Fluorescence microscopy shows that the appearance of micrometer-scale lo domains in the lipid tubule is not an intrinsic phase behavior of the system but a consequence of photoinduced lipid peroxidation. Most interestingly, new photoinduced bilayer structures: lipid discs, essentially stable flattened liposomes, were observed for the first time in a model membrane system. This investigation not only aids in our understanding of lipid sorting phenomena in cell membranes but also demonstrates how control of this process may provide a route to the generation of new, functional structures.     

Lipid bilayer membrane technologies: A review on single-molecule studies of DNA sequencing by using membrane nanopores

Nanopores based on α-hemolysin and MspA represent attractive sensing platforms due to easy production and operation with relatively low background noise. Such characteristics make them highly favorable for sequencing nucleic acids. Artificial lipid bilayer membranes, also referred to as black lipid membranes, in conjunction with membrane nanopores, can be applied to both the detection and highly efficient sequencing of DNA on a single-molecule level. However, the inherently weak physical properties of the membrane have impeded progress in these areas. Current issues impeding the ultimate recognition of the artificial lipid bilayer as a viable platform for detection and sequencing of DNA include membrane stability, lifespan, and automation. This review (with 105 references) highlights attempts to improve the attributes of the artificial lipid bilayer membrane starting with an overview on the present state and limitations. The first main section covers lipid bilayer membranes (BLM) in general. The following section reviews the various kinds of lipid bilayer membrane platforms with subsections on polymer membranes, solid-supported membranes, hydrogel-encapsulated membranes, shippable and storable membrane platforms, and droplet interface bilayers. A further section covers engineered biological nanopore sensor applications using BLMs with subsections offering a comparative view of different DNA sequencing methods, a detailed look at DNA Sequencing by synthesis using alpha-hemolysin nanopores, sequencing by synthesis using the MspA nanopore and quadromer map, and on limitations of sequencing based on synthesis technology. We present an outlook at the end that discusses current research trends on single-molecule sequencing to highlight the significance of this technology and its potential in the medical and environmental fields.

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Graphical abstract Sequencing by Synthesis, a novel method of sequencing DNA, uses the αHL biological nanopore and the artificial lipid bilayer membrane platform. Polymer tags attached to nucleotides bind to the polymerase-primer–template complex and are characterized by the nanopore upon release.

     

Separation of plant hormones from biofertilizer by capillary electrophoresis using a capillary coated dynamically with polycationic polymers.

A new, simple and rapid capillary electrophoresis (CE) method, using hexadimethrine bromide (HDB) as electroosmotic flow (EOF) modifier, was developed for the identification and quantitative determination of four plant hormones, including gibberellin A3 (GA3), indole-3-acetic acid (IAA), alpha-naphthaleneacetic acid (NAA) and 4-chlorophenoxyacetic acid (4-CA). The optimum separation was achieved with 20 mM borate buffer at pH 10.00 containing 0.005% (w/v) of HDB. The applied voltage was -25 kV and the capillary temperature was kept constant at 25 degrees C. Salicylic acid was used as internal standard for quantification. The calibration dependencies exhibited good linearity within the ratios of the concentrations of standard samples and internal standard and the ratios of the peak areas of samples and internal standard. The correlation coefficients were from 0.9952 to 0.9997. The relative standard deviations of migration times and peak areas were < 1.93 and 6.84%, respectively. The effects of buffer pH, the concentration of HDB and the voltage on the resolution were studied systematically. By this method, the contents of plant hormone in biofertilizer were successfully determined within 7 min, with satisfactory repeatability and recovery.     

Approaches to ultimate functional polymers: quantum functional and molecular engineering materials

Both quantum functional material (Ψ‐engineering material) and molecular engineering materials are of interest as ultimate functional materials. The former creates a novel property which is specific to the structure, and the latter gives he functional material of the smallest size. In this paper, some aspects to construct those materials with polymer having big varieties and flexible applications are described: 1. Conjugating polymer superlattice (conjugating polymer multilayers which is able to change wave length of emission light). 2. Porphyrin arrays connected with molecular wires (a proto‐type photo‐information housing‐in and reading out polymeric material). 3. Oligonucleotide shackled with porphyrin (an artificial restrictive photoactive enzyme).     

Grafting onto carbon black by the reaction of reactive carbon black having masked isocyanate or acyl azide group with functional polymers

Although isocyanate group (NCO) introduced onto carbon black surface was inactivated rapidly upon storage, it could be stabilized by masking the NCO group with active hydrogen compounds such as acetylacetone, diethyl malonate, and sodium hydrogensulfite. Upon heating these carbon blacks having masked NCO group at 150°C, the NCO group was regenerated on carbon black by the decomposition of the masked NCO group. On the other hand, acyl azide (CON₃) group introduced onto carbon black was stable at below 20°C, but readily decomposed to NCO group by heating. By means of the reaction of NCO group on carbon black with functional polymers having hydroxyl, amino, and carboxyl group, these polymers were effectively grafted onto carbon black surface. When carbon black having CON₃ group was used as reactive carbon black, the grafting ratio of diol-type polyethylene glycol (M_n = 8.2 × 10³), polyethyleneimine (M_n = 2.0 × 10⁴), polyvinyl alcohol (M_n = 2.2 × 10⁴), and bifunctional carboxyl-terminated polystyrene (M_n = 1.1 × 10⁵) was determined to be 29.7, 81.7, 32.2, and 50.4%, respectively. The number of grafted polymer chain decreases with an increase in molecular weight of the polymers, because the shielding effect of NCO group by grafted polymer chain is enhanced with an increase in molecular weight of the polymer.