Solvent resistance of a polymer chain chemically linked onto a solid surface

Polystyrene or polystyrene–polyisoprene copolymers have been grafted onto silica by an anionic procedure. The solvent resistance of the grafts has been examined. Linear relationships between the extractable amount of polymer and the solvent extraction temperatures are observed. The extrapolation of these lines leads to temperatures that are in close agreement with the ceiling temperatures of the grafted polymers.     

The effects of solution structure on the surface conformation and orientation of a cysteine-terminated antimicrobial peptide cecropin P1

The surface structure of an antimicrobial peptide, cecropin P1, immobilized to a gold surface via a terminal cysteine residue was investigated. Using reflection-absorption infrared spectroscopy, surface plasmon resonance, and X-ray photoelectron spectroscopy, the effects of pH, solution conformation, and concentration on the immobilized peptide conformation, average orientation, and surface density were determined. Under all conditions investigated, the immobilized peptides were α-helical in a predominately flat, random orientation. The addition of the reducing agent Tris(2-carboxyethyl) phosphine hydrochloride to the buffer resulted in a twofold increase in immobilized peptide surface density.     

Solvent effect on the miscibility of polymer blends

Starting from the Flory-Huggins theory applied to a polymer/polymer/solvent solution, an expression has been derived showing the overall effect of solvent on the composition of the polymer blend in the final solid state. This expression has been experimentally verified by investigating the miscibility of two polymer blends: polystyrene/poly(α-methylstyrene) cast from tetrahydrofuran and cyclohexane, and polystyrene/poly (methyl methacrylate) obtained from tetrahydrofuran and chloroform. Besides the usual differential scanning calorimetry technique, thermogravimetric analysis might be helpful for detecting the miscibility of polymer blends.     

Complexation of transition metals with 8-hydroxyquinoline chemically immobilized on the surface of a silica gel-polyaniline composite

The complex-forming properties of a silica gel-polyaniline composite with 8-hydroxyquinoline covalently immobilized by the Mannich reaction with respect to Pb(II), Cd(II), Cu(II), Ni(II), Co(II), Al(III), Fe(III), and Mo(VI) ions were studied. The resulting adsorbent had a high sorption capacity and satisfactory kinetic characteristics, which allowed us to use it for the separation or preconcentration of transition metal ions. Data on the composition and structure of the test metal complexes with 8-hydroxyquinoline immobilized on the composite surface were obtained from an analysis of electronic diffuse reflectance spectra and corresponding adsorption isotherms.     

NaBH4-induced assembly of immobilized Au nanoparticles into chainlike structures on a chemically modified glass surface

A facile method of obtaining chainlike assemblies of gold nanoparticles (AuNPs) on a chemically modified glass surface based on NaBH(4) treatment is developed. Citrate-stabilized AuNPs (17 nm) are immobilized on a glutaraldehyde-functionalized glass surface and assembled into chainlike structures after treatment with aqueous sodium borohydride (NaBH(4)) solution. The production and morphology of the AuNP chainlike assemblies are controlled by the density of the immobilized NPs, the concentration of NaBH(4) solution, and the treatment time. The AuNP assemblies are stable in water and can undergo drying. X-ray photoelectron spectroscopic data show that the number of citrate ions on the AuNPs decreased by 43% after treatment with 5 mg/mL NaBH(4) solution. The NaBH(4)-induced partial removal of the citrate ions and the roughness of the glass surface greatly affect the binding force of AuNPs on the substrate. The immobilized AuNPs begin to move at the solid-liquid interface without desorbing when the strength of the binding force was decreased. These mobile NPs form chainlike assemblies under the driving force of van der Waals interaction and diffusion. This interface-based formation of chainlike assemblies of AuNPs may provide a simple protocol for the 1D assembly of other Au-coated colloidal nanoparticles.     

Characterization of immobilized nuclease P1

To improve the efficiency of the use of nuclease P1, enzyme immobilization technology was applied using nuclease P1. Characterization of immobilized nuclease P1 on different supports was studied. The results showed that the optimum pH and temperature of nuclease P1 immobilized via different supports were enhanced. The immobilized enzyme was obviously stable when stored for long periods and was reusable. The best results were obtained when nuclease P1 was immobilized on chitosan nanoparticles. The nanoparticles were applied to protect the activity of nuclease P1 and improved enzyme activity by 13.17% over that of free nuclease P1 at the same conditions. The Michaelis constant Km and V _max were determined for free and immobilized enzyme as well.     

Solvent size effect on the depletion layer of a polymer solution near an interface

By varying polymer concentration phi0p and Flory-Huggins parameter chi, the effect of solvent size on the depletion interaction between polymer coils and a hard wall was investigated by the real-space version of self-consistent field theory (SCFT). The depletion profiles and depletion thickness indicated that the depletion effect is strong in less good solvent with large molecular volume. Through the analysis of the respective free energies of polymer coils and solvent molecules, we found that the increment in the translation entropy of the solvent is the key to strengthening the depletion interaction. On the basis of the SCFT results, we define a solvent with volume about one to six times that of the polymer segment as a "middle-sized solvent". The density oscillations previously studied by Van der Gucht et al. and Maassen et al. were also observed in our simulation, and the addition of middle-sized solvent will magnify the amplitude of the oscillations. The solvent-size-dependent depletion interaction may be an explanation for the reduced entanglement and promoted crystallization behavior of polymer coils prepared from the solution with middle-sized solvent.     

Sliding behavior of water droplets on flat polymer surface

Flat films of methyl methacrylate-fluoroalkyl methacrylate copolymers were prepared, and their hydrophobicity was investigated. It was revealed that the F concentration directly affects the static hydrophobicity on the flat polymer surface in a systematic manner. Furthermore, the sliding behavior of a water droplet on these surfaces depends on the static hydrophobicity; the sliding motion changes from constant velocity to constant acceleration with an increase in the water contact angle.     

A polymeric chiral surface functionality immobilized on uniformly sized macroporous polymer beads

Uniformly sized functionalized macroporous polymer beads were prepared by either a classical copolymerization method or recently reported in situ surface modification method utilizing chiral methacrylamide as a functional modifier. To evaluate conformational and/or specific differences in their surface chiral functionality, we applied chromatographic evaluation techniques. The prepared modified beads were utilized as chiral stationary phase in high-performance liquid chromatography (HPLC). Those prepared by the in situ surface modification method tended to show higher chiral recognition ability than those by the classical copolymerization method, even if the equivalent amount of the chiral functional group was involved within polymer beads. Detailed chromatographic studies exhibited the in situ surface modification method could lead to polymeric methacrylamide functionality on the surface within relatively large pore size regions of the macroporous polymer beads, while the classical copolymerization method tended to form less polymeric surface functionality. The difference in the chiral surface functionality on both of macroporous polymer beads afforded drastic change in chromatographic chiral recognition ability. Complete resolution of a drug, thalidomide could be achieved on the chiral stationary phase with the polymeric chiral surface functionality, while no resolution was found on that with the monomeric one even if the same chiral methacrylamide was used as a modifier to prepare the chiral stationary phases. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2747–2757, 1997     

Solvent effect on the aggregation behavior of rod-coil diblock copolymers

The water-induced aggregation behavior of rod-coil diblock copolymers based on poly(ethylene oxide) (PEO) and poly{(+)-2,5-bis[4'-((S)-2-methylbutoxy)phenyl]styrene} (PMBPS), PEO104-b-PMBPS53, was investigated in the common solvent THF and in the selective solvent dioxane. Before adding water, PEO104-b-PMBPS53 stayed as single polymer chains no matter what conformation the PEO block took (i.e., either the random coil conformation in THF or the compact globule conformation in dioxane). The critical water content ( approximately 6 wt %) at which PEO104-b-PMBPS53 began to aggregate was also similar in both solvents, indicating that PMBPS dominated the aggregation process. However, the size, the size distribution, and the morphology of aggregates in THF/water were quite different from those in dioxane/water. Narrowly distributed spheres with Rh approximately 20 nm were observed in dioxane, whereas in THF, a bimodal distribution peaked at 3 and approximately 300 nm, was observed. The results from 2D wide-angle X-ray diffraction and polarized optical microscopy demonstrated that the PMBPS blocks packed in a parallel pattern upon aggregation in dioxane/water. The anisotropic disclike structures observed in THF/water also indicated the orientation of the PMBPS blocks upon forming aggregates in dilute solution.     

The effect of polymer network structure on diffusive transport across chemically controlled membranes

This paper focuses on the relationship between diffusive transport and membrane composition (crosslinker content and relaxed polymer volume fraction) in membranes whose permeability can be actively controlled by chemical or electrical stimuli. First, pH induced changes in permeability to uncharged fluorescent solutes were measured. Then, by correlating bath pH with membrane hydration, the transport properties of membranes of different crosslinker content and/or relaxed polymer volume fraction were compared at constant hydration. The membrane permeability was found to decrease as the amount of crosslinker added to the membrane formulation at the time of polymerization increased, while the permeability increased as the solvent content during polymerization increased. A free volume theory which was fit to the data shows good agreement, and predicts a monotonically decreasing porosity factor with increased crosslinker content.     

Solvent effect on protein binding by polymer brush grafted onto porous membranes

An epoxy-group-containing polymer chain was grafted onto the hollow-fiber form of a porous polyethylene membrane by the immersion of the electron beam-irradiated trunk polymer in glycidyl methacrylate diluted with methanol and 1-butanol. The epoxy group density ranged from 8.5 to 13.4 mol per kg of the trunk polymer. Subsequently, the epoxy groups produced were converted into sulfonic acid and diethylamino groups. The density of -SOH and -N(C2H5), groups was 0.40 and 2.2 mol per kg of the product. respectively. The polymer brush, defined as a polymer chain extending from the surface of a pore toward the interior of the pore, was evaluated from the determination of an equilibrium binding capacity of hen egg lysozyme (HEL) and bovine serum albumin (BSA). The polymer brush prepared in 1-butanol was found to be longer than that prepared in methanol from the determinations of liquid permeability and protein adsorptivity. The proteins were bound to the polymer brush prepared in 1-butanol, followed by the functionalization, at higher degrees of multilayer binding: about 30 for HEL and 6 for BSA.     

Electrochemical behavior of fullerene C60 and substituted fullerenes immobilized on an electrode surface

The effect of substituents with different donor capabilities, which are inserted into a molecule of fullerene C₆₀, on the kinetics and thermodynamics of redox conversions of fullerenes that are immobilized on an electrode, is studied for the first time. To this end, redox conversions that occur with rubbed-on films of fullerene and fulleropyrrolidines are studied using cyclic voltammetry in 0.5 M KCl/H₂O and a 0.1 M (C₄H₉)₄NBF₄/AN solution in acetonitrile. A hypothesis that the kinetics of redox conversions occurring with films of individual fullerenes is defined largely by changes in the structure of initial films in the process of their cathodic doping is used. The effect of the substituents is explained in the framework of this hypothesis by a transition from a dense crystalline structure of nonsubstituted fullerene C₆₀ to an amorphous structure of substituted fullerenes. It is demonstrated that the formal potentials corresponding to redox conversions of fullerenes in a solid cationic lipid matrix are defined by the energy of interaction of anions, which are products of reduction of fullerenes, with cations of the matrix. As a result of this interaction, the formal potentials of the process of cathodic doping shift to less negative values. It is established that the insertion of a donor substituent and increase in its donor capability amplify the energy of interaction of the fullerene anions with the lipid cations.     

Development of a hypoxanthine biosensor based on immobilized xanthine oxidase chemically modified electrode

An amperometric biosensor for hypoxanthine determination has been developed. The sensor uses a Nafion-paraquat chemically modified glassy-carbon electrode. It detects the oxygen consumed by the enzymatic reaction catalyzed by xanthine oxidase which is immobilized on the electrode surface. The sensor responds linearly to hypoxanthine over the concentration range of 1 × 10⁻⁶ M −2 × 10⁻⁴ M. The biosensor can be reused for more than 100 times without significant deterioration in performance. After 32 days storage at 3–5°C, the sensor response remains at 68% of the initial level. The high sensitivity, selectivity and stability of this biosensor demonstrates its practical applicability for a simple, rapid and economical determination of hypoxanthine in fish samples.     

Laser‐induced periodic surface structure on a polymer surface: The effect of a prerubbing treatment on the surface structure

The influence of the mechanical rubbing of a polyimide (PI) film on the laser‐induced periodic structure (LIPS) was demonstrated. The periodicity and amplitude of LIPS were greater when the rubbing direction was parallel to the laser polarization direction. The amplitude became small and the periodicity of LIPS did not show an obvious change when the rubbing direction was perpendicular to the laser polarization direction. The effect of the rubbing pretreatment on LIPS was explained on the basis of the wave‐guide effect of rubbing‐induced microgrooves on LIPS formation. The orientation of PI chains induced by mechanical rubbing was relaxed after laser irradiation, and a new orientation of PI chains was formed during the LIPS formation. When the rubbing direction was perpendicular to the laser polarization direction, the orientation of PI chains remained in the rubbing direction. The laser‐irradiated, perpendicularly rubbed PI surface could be used to verify the effects of surface morphologies and intermolecular interactions on liquid‐crystal alignment. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1273–1280, 2003     

Stability and orientation of cecropin P1 on maleimide self-assembled monolayer (SAM) surfaces and suggested functional mutations

One of the main challenges of biosensor design is to understand the protein or peptide stability on the chip in high resolution structural detail.Since conventional experimental methods are limited by the resolution for their applications on surface tethered peptides/proteins,a recently developed coarse grained simulation method is employed to explore the peptide/surface interaction in residue-level resolution.This work shows how the coarse grained model successfully describes peptide–surface interactions by evaluating thermal stability of the peptide cecropin P1 in bulk solution and on surfaces by physical adsorption and chemical tethering.The simulation also reproduces observations of peptide orientations on the self-assembled monolayer surface from earlier experimental work.Additionally,using knowledge obtained from the simulations,specific mutations are suggested and the desired structure and pose on the surface is obtained.In summary,this work sheds a light on the reasonable biosensor design that is guided by simulations.     

Photochemical cycloaddition on the pore surface of a porous coordination polymer impacts the sorption behavior

Photochemical [2+2] cycloaddition reactions in a two-dimensional interdigitated porous crystalline framework proceed in a single-crystal-to-single-crystal manner, and one-dimensional channels show structural changes that have a significant impact on the CO(2) sorption.     

The effect of feed composition on the behavior of chemically selective displacement systems

In this paper we examine whether adding a more retained protein to the feed will mitigate displacer–protein interactions in the column, thus affecting the displacement modality that occurs (chemically selective vs. traditional displacement chromatography). STD-NMR experiments were carried out to probe displacer–protein interactions for the chemically selective displacer chloroquine diphosphate and the results indicated that this displacer only had measurable interactions with the protein α-chymotrypsinogen A. For a two component feed mixture containing ribonuclease A and α-chymotrypsinogen A, the separation resulted in the displacement of ribonuclease A, with the more hydrophobic α-chymotrypsinogen A remaining on the column. On the other hand, when the experiment was repeated with cytochrome c added to the feed, all three feed proteins were displaced. Column simulations indicated that the combination of sample self-displacement occurring during the introduction of the feed, along with the dynamics of the initial displacement process at the column inlet was responsible for this behavior. These results indicate that for this class of hydrophobic-based selective displacers, in order for the protein to be selectively retained, the protein should be the most strongly retained feed component.     

Properties of 8-hydroxyquinoline immobilized on a silica surface

The ionization constants of benzeneazo-8-hydroxyquinoline grafted to a silica surface were determined by potentiometric titration. The spectrophotometric measurements showed that with increase in pH, deprotonation of the grafted 8-hydroxyquinoline nitrogen takes place. The dynamic capacity of the sorbent obtained with respect to the Cu²⁺, Co²⁺, and Ni²⁺ ions at various pH was determined. The immobilized benzeneazo-8-hydroxyquinoline is suitable for removing trace amounts of metal ions from solutions and for their chromatographic separation. It was found that the metal complexes of Cu²⁺ and Co²⁺ with grafted benzeneazo-8-hydroxyquinoline exhibit catalytic activity in the oxidation of hydrazine by molecular oxygen in aqueous solutions.Translated from Teoreticheskaya i Ékperimental'naya Khimiya, Vol. 25, No. 1, pp. 108–112, January–February, 1989.     

The effect of surface wettability on induction and growth of neurites from the PC-12 cell on a polymer surface

Surface properties of polymeric devices that are used to regenerate nervous damage are a point to be considered for axon regeneration in nerve system. In our previous studies, we prepared a wettability gradient on polyethylene (PE) surfaces using a corona discharge treatment from a knife-type electrode whose power increases gradually along the sample length. The PE surfaces were oxidized gradually with increasing power. The effect of surface wettability on the different types of cells has an important role for cell adhesion and proliferation. The purpose of this study is to investigate neurite formation on polymer surfaces with different wettability. Induction and growth of neurites from the rat pheochromocytoma (PC-12) cells attached on the polymer surfaces with different hydrophilicity were investigated using the wettability gradient PE surfaces prepared by a corona discharge treatment. Neurites were investigated for number and length of neurites in terms of surface wettability. It was observed that neurite formation of PC-12 cells was increased more onto the positions with moderate hydrophilicity of the wettability gradient surface than onto the more hydrophobic or hydrophilic positions. From those results, it could be assumed that initial adhesion of PC-12 cells was caused by more calf serum (CS) protein than nerve growth factor (NGF), whereas the neurite formation of PC-12 cells was caused by more NGF than CS protein. It follows from what has been said thus far that PC-12 cells are a differentiated neuronal phenotype with a long neurite at around the position 2.5 cm (water contact angle of about 55 deg). In conclusion, surface wettability plays an important role for neurite formation on the polymer surfaces for axon regeneration.