Cationic gel crystals of lightly cross-linked poly(2-vinylpyridine) spheres (170∼180 nm in diameter) in the deionized aqueous suspension

Colloidal crystallization of deionized suspensions of the cationic gel spheres of lightly cross-linked poly(2-vinylpyridine), AIBA-P2VP (170～180 nm in diameter) has been studied from the microscopic observation, morphology, phase diagram, and elastic property. Critical concentrations of melting that coexisted with ion-exchange resins were low compared with those without resins and decreased as the degree of cross-linking decreased. The density of a gel sphere in suspension state (ρ), i.e., weight percent of the gel spheres divided by the corresponding volume percent, was between 0.5 and 0.8, and decreased as the degree of cross-linking of the spheres decreased. The ρ values also decreased with decreasing size of gel spheres, which supports the small P2VP gel spheres being softer than the large ones. The closest intersphere distances of the crystals were much longer than the hydrodynamic diameters of the gel spheres especially at low sphere concentrations. Fluctuation parameters evaluated from the rigidities of the crystals of AIBA-P2VP (0.05～0.09) were similar to those of gel crystals of cationic gel spheres of lightly cross-linked poly(2-vinylpyridine) spheres coated with poly(ethylene glycol), 400 nm in diameter, and thermo-sensitive gel spheres of pNIPAm, poly(N-isopropylacrylamide), but larger than those of typical colloidal hard spheres. The stable crystal phase formed beyond the adsorbed monolayer of cationic gel spheres on the surface of the substrate. These experimental findings support important role of the extended electrical double layers around the cationic gel spheres in addition to the excluded volume effect of the sphere themselves on the crystallization.     

Drying dissipative structures of the deionized aqueous suspensions of colloidal silica spheres ranging from 29 nm to 1 μm in diameter

Macroscopic and microscopic dissipative structural patterns formed in the course of drying a series of the colloidal silica spheres ranging from 29 nm to 1 m in diameter have been observed in the aqueous deionized suspension on a cover glass. The broad ring patterns of the hill accumulated with the silica spheres are formed around the outside edges in the macroscopic scale for all spheres examined. The spoke-like cracks are also observed in the macroscopic scale and their number decreases sharply as sphere size increases. The pattern area and the time for the dryness have been discussed as a function of sphere size and concentration. The convection flow of water accompanied with that of the silica spheres and interactions among the silica spheres and substrate are important for the macroscopic pattern formation. The microscopic fractal structures of the wave-like patterns and branched strings are formed. Their fractal dimensions are determined. Microscopic patterns form in the narrow range of sphere sizes and concentrations and are determined mainly by the electrostatic and polar interactions between the spheres and/or between the sphere and substrate in the course of solidification.     

Drying dissipative structure of similar sized aggregates (1.5 μm in diameter) of nano-sized diamond particles (4 nm in diameter)

Macroscopic and microscopic drying patterns were observed on a cover glass, a watch glass, and a Petri glass dish during the course of dryness of aqueous suspensions of similar sized aggregates of diamonds (CD1), which formed from the deionization of the pre-particles of diamond 4 nm in diameter. Two kinds of macroscopic patterns, i.e., outer and inner broad rings, and spoke lines were formed. Cooperative drying processes of the convection, sedimentation, and solidification were clarified. Microscopic drying patterns showing the formation of very large dendritic aggregates from the CD1 particles were observed only when the excess amount of sodium chloride higher than 2 mM coexisted in the initial suspensions before dryness and further initial CD1 concentration is lower than 0.17 wt%.     

How does the nature of the steric stabilizer affect the pickering emulsifier performance of lightly cross-linked, acid-swellable poly(2-vinylpyridine) latexes?

A near-monodisperse styrene-functionalized poly[2-(dimethylamino)ethyl methacrylate] (PDMA) macromonomer was evaluated as a reactive steric stabilizer for the preparation of poly(2-vinylpyridine (P2VP) latexes via emulsion polymerization. The solution pH was shown to be a critical parameter for successful syntheses: stable latexes with minimal coagulum were only obtained at (or above) neutral pH. The presence of the grafted PDMA stabilizer in a near-monodisperse P2VP latex of 280 nm diameter was indicated by FT-IR spectroscopy and quantified at 6.0 wt % using 1H NMR spectroscopy. XPS studies confirmed that this stabilizer was located at the latex surface, as expected. Combined DLS and electrophoretic data indicated that these PDMA-P2VP particles exist in three states depending on the solution pH: swollen cationic microgels were obtained below pH 4.1, nonsolvated latex particles with a cationic stabilizer layer were obtained at intermediate pH, and flocculated latex particles with neutral PDMA stabilizer chains were obtained at around pH 8.5. Finally, this PDMA-P2VP latex was shown to be a superior Pickering emulsifier for stabilizing water-in-1-undecanol emulsions than either a poly(ethylene glycol)-stabilized P2VP latex or a charge-stabilized P2VP latex. This serves to illustrate the important role played by the steric stabilizer in determining particle wettability.     

Distorted colloidal crystal of similar-sized aggregates (1.5 μm in diameter) of nano-sized diamond particles (4 nm in diameter)

Distorted colloidal crystal suspension of similar-sized aggregates of diamonds (1.5 μm in diameter) was obtained by the deionization of aqueous suspension of the pre-particles of diamond, 4 nm in diameter. The stability, characteristics, and the rigidity of the crystal-like suspensions were studied. The main cause for the formation of the similar-sized aggregates is deduced to be the cooperation between the van de Waals inter-particle attraction and the repulsion induced by the vigorous thermal motion of the pre-particles. The rigidity was evaluated from the microscopic observation in the sedimentation equilibrium. Fluctuation parameters of the distorted colloidal crystals estimated from the rigidities were between 0.03 and 0.06, which are quite similar to those of typical colloidal crystals and solids of hard spheres.     

Convectional, sedimentation, and drying dissipative patterns of colloidal silica (183 nm in diameter) suspensions in a glass dish and a watch glass

Convectional, sedimentation, and drying dissipative structural patterns formed during the course of drying aqueous colloidal crystals of silica spheres (183 nm in diameter) have been studied in a glass dish and a watch glass. Spoke-like convectional patterns were observed in a watch glass. The broad ring sedimentation patterns formed especially in a glass dish within 30–40 min in suspension state by the convectional flow of water and colloidal spheres. The macroscopic broad ring drying patterns formed both in a glass dish and a watch glass. The ratio of the broad ring size in a glass dish against the initial size of suspension, i.e., inner diameter of the glass dish, d _f/d _i, in this work, were compared with previous work of other silica spheres having sizes of 305 and 560 nm and 1.2 μm in diameter. The d _f/d _i values in a glass dish increased as sphere concentration increased, but were rather insensitive to colloidal size. The d _f/d _i values on a watch glass also increased as sphere concentration increased, and further increased as sphere size decreased. Segregation effect by sphere size in a watch glass takes place by the balancing between the upward convectional flow of spheres in the lower layers of the liquid and the downward sedimentation of spheres. Colorful microscopic drying patterns formed both in a glass dish and a watch glass.     

Elucidation of the structure of poly(γ-benzyl-l-glutamate) nanofibers and gel networks in a helicogenic solvent

The synthesis, characterization, self-assembly, and gel formation of poly(γ-benzyl-l-glutamate) (PBLG) in a molecular weight range from ca. 7,000–100,000 g/mol and with narrow molecular weight distribution are described. The PBLG is synthesized by the nickel-mediated ring-opening polymerization and is characterized by size-exclusion chromatography coupled with multiple-angle laser light scattering, NMR, and Fourier transform infrared spectroscopy. The self-assembly and thermoreversible gel formation in the helicogenic solvent toluene is investigated by transmission electron microscopy, atomic force microscopy, small-angle X-ray scattering, and synchrotron powder X-ray diffraction. At concentrations significantly below the minimum gelation concentration, spherical aggregates are observed. At higher concentrations, gels are formed, which show a 3D network structure composed of nanofibers. The proposed self-assembly mechanism is based on a distorted hexagonal packing of PBLG helices parallel to the axis of the nanofiber. The gel network forms due to branching and rejoining of bundles of PBLG nanofibers. The network exhibits uniform domains with a length of 200?±?42 nm composed of densely packed PBLG helices.      

Interaction of poly(vinylpyrrolidone) with cationic and nonionic surfactants in aqueous solution studied by <Superscript>1</Superscript>H NMR

Aqueous solutions of surfactant at various concentrations with 0.2% poly(vinylpyrrolidone) (PVP) were studied by ¹H NMR methods, including relaxation time and self-diffusion coefficient measurements and two-dimensional nuclear Overhauser enhancement spectroscopy. Two surfactants were concerned: cationic cetyltrimethylammonium bromide (CTAB) and nonionic Triton X-100 (TX-100). In the presence of 0.2% PVP, the variation of the T ₂ values of CTAB protons is similar to that in the absence of PVP. Relaxation times of PVP protons are not significantly affected by the increasing concentration of CTAB. This indicates that no interaction between PVP and CTAB could be detected. However, in the presence of 0.2% PVP, TX-100 micelles are formed at a concentration lower than its normal critical micellization concentration. According to the results of relaxation time measurement of water protons, the presence of 0.2% PVP also induces the contraction of the hydrophilic layer of the TX-100 micelle. This indicates some interaction between PVP and TX-100, but the mechanism of this interaction needs further investigation.     

Quantitative analysis of hydrogen bonding in electrospun fibers of poly(4-vinyl pyridine)/(4,4′-biphenol) complexes by ATR using liquid blends as models

To understand the characteristics of electrospun fibers of poly(4-vinyl pyridine) (P4VP) that are potentially crosslinked by hydrogen-bonding when blended with small molecules like 4,4′-biphenol (BiOH), it is necessary to determine the proportion of hydrogen-bonded pyridine rings (f_b) and to contrast it with F_OH, the mole percent of OH groups available for interacting with the pyridine rings. While this can be done by Fourier transform infrared spectroscopy (FTIR), two practical difficulties must be overcome. First, the correct intensities of the overlapped bands of free and hydrogen-bonded pyridine must be obtained, which is possible using the second derivative spectra. Second, the band absorption coefficient ratio (a) of the pair of bands must be known. In the P4VP/BiOH system, only the pair of free and hydrogen-bonded pyridine ring bands at 993 and 1007 cm⁻¹ can be used for quantitative analysis. We determined, by analysis of liquid blends of BiOH as well as phenol with a model compound, 4-ethylpyridine (EtPy), using the attenuated total reflection mode (ATR), that a = 0.40. This led to values of f_b = F_OH, indicative of full complexation of the OH groups to pyridine, in the EtPy/BiOH liquid blends up to the BiOH solubility limit in EtPy (F_OH = 60%) and in the EtPy/phenol blends up to F_OH = 100%. In the electrospun P4VP/BiOH fibers prepared from solutions with F_OH up to about 120%, f_b averages 0.76F_OH, and full complexation of the pyridine groups is achieved only at about F_OH = 160%. In both P4VP/BiOH and EtPy/BiOH, the complexation occurs between one pyridine ring and one hydroxyl group. This work thus shows a new method to quantify the relative number of hydrogen-bonded pyridine rings in P4VP; it is expected to be applicable to other polymer-small molecule and polymer-polymer blends having suitable liquid models.     

Effect of block lengths on the association behavior of poly(l-lactic acid)/poly(ethylene glycol) (PLA–PEG–PLA) micelles in aqueous solution

A series of poly(l-lactic acid)/poly(ethylene glycol) triblock copolymers with a PLA–PEG–PLA architecture were synthesized by a ring-opening polymerization (ROP) process. The copolymers were characterized by ¹H NMR and GPC. The total number average molecular weights were in the range of 4,700–50,000, whereas the degrees of polymerization of the PLA and PEG blocks varied from 15 to 359 and from 68 to 136, respectively. The self-association of these copolymers in aqueous environment was studied by emission fluorescence spectroscopy of anilinonaphthalene probe and the critical association concentration (CAC) of the copolymers was measured. It was found that the micellization process of these copolymers was mainly determined by the length of the hydrophobic LA block, while the length of the hydrophilic PEG block had little effect. Furthermore, the low CAC values of the copolymers suggest that the copolymers form stable supramolecular structures in aqueous solutions.     

Swelling-shrinking behavior of chemically cross-linked polypeptide gels from poly(α-L-lysine), poly(α-DL-lysine), poly(ɛ-L-lysine) and thermally prepared poly(lysine): effects of pH, temperature and additives in the solution

We synthesized the glutaraldehyde cross-linked hydrogels using four kinds of poly(lysine)s (PLs) and measured the equilibrium swelling ratio (Q) as a function of pH. Also measured was the temperature change of Q at a fixed pH (11.6) in the absence and presence of additives (LiBr, methanol and urea) that affect the secondary structure of PLs. The swelling data were examined using a force balance approach in which the repulsive and attractive interactions among the cross-linked PL chains were considered based on the conformational properties of PLs in aqueous solutions. It was found that the formation of the helical segments in the cross-linked chain has little effect in the gel collapse, but their association acts as the attractive interaction causing the gel to shrink. The formation of the beta-sheet structure within the network also acts as the attractive interaction. These attractive interactions are mainly due to the hydrogen bonding, but hydrophobic interactions between the lysine side chains should be considered. In addition, in the swelling behavior of all the PL gels the polyampholyte nature appears due to electrostatic interactions of the basic groups with the C-terminal carboxyl group.     

Effects of acrylic acid incorporation on the pressure–temperature behavior and the calorimetric properties of poly(N-isopropylacrylamide) in aqueous solutions

 We studied the effects of pH on the pressure–temperature dependence of coil–collapse transition for aqueous solutions of copolymers of N-isopropylacrylamide and acrylic acid (Ac). At low pressures, the transition temperature (T _tr) increased with pressure, but T _tr decrease with increasing pressure at pressures higher than 50–100 MPa. By increasing the pH, the transition contour shifted to a higher temperature. When the Ac content was increased, the effects of pH became more evident. From a calorimetric study at atmospheric pressure, ΔH _tr was found to become smaller by increasing the portion of the ionized residues in the copolymer. The ratio to the van't Hoff enthalpy changes became larger with an increase in pH, which indicated that the production of charge decreased the cooperative domain size. Received: 19 July 1999 /Accepted in revised form: 7 September 1999     

Alternate sign reversal in the ζ potential and synchronous expansion and contraction in the absorbed multi-layers of poly(4-vinyl-N-n-butylpyridinium bromide) cations and poly(styrene sulfonate) anions on colloidal silica spheres

Alternative multiple absorbed layers of up to ten macrocations [poly(4-vinyl-N-n-butylpyridinium bromide)] and macroanions [sodium poly(styrene sulfonate)] are formed on colloidal silica spheres above the critical concentration of macroions, m*. The m* value is the minimum number of macroions required to reverse the sign of the ζ potential of the spheres in the first absorption step. Alternative sign reversal in the ζ potential and expansive–contractive thickness changes are observed by the repeated and alternate addition of macrocations first and macroanions next. During multiple absorption, the pH and conductivity values decrease and increase continuously as the number of absorbed layers increases. When the macroanions are added first, sign reversal in the ζ potential and reversible expansion and contraction do not occur. Breaking of the alternate multiple-type absorption occurs when equivalency in the number of dissociative groups of macrocations and macroanions is broken. Synchronous conformational changes of macrocations and macroanions in the multiple- absorbed layers, where balancing of the conformational rigidities with the multiple electrostatic attraction and repulsion between macrocations and anions occurs, are supported strongly. Received: 12 January 1999 Accepted in revised form: 25 March 1999     

Synergic extraction of lanthanide(III) ions with 2-thenoyltrifluoroacetone in the presence of 2,2′-bipyridine or pyridine

The synergic extraction of various tervalent lanthanides (Ln), La, Ce, Nd, Sm, Gd, Tb, Yb and Lu, with 2-thenoyltrifluoroacetone (Htta) in the presence of a bidentate heterocyclic amine, 2,2′-bipyridine (bipy), in benzene was investigated. The synergic enhancement was attributed to the formation of the adducts, Ln(tta)₃(bipy). The synergic extraction of La(III), Sm(III) and Lu(III) with Htta and a unidentate amine, pyridine (py), was also studied and the formation of the adducts, Ln(tta)₃py and Ln(tta)₃(py)₂, was observed. The adduct formation constants, β_s,1 and β_s,2, were determined. The β_s,2 values for py decrease with increasing atomic number of Ln(III), but β_s,1 values for bipy increase with increasing atomic number of Ln(III). The synergic extraction constants and the separation factors in the bipy system were also determined.     

The features of absorption of aqueous–organic mixtures by polyurethane–poly(2-hydroxyethyl methacrylate) matrix by the data of NMR spectroscopy

The features of hydration of the interpenetrating polymer network consisting of 83% polyurethane and 17% poly(2-hydroxyethyl methacrylate) as well as the initial polymers are studied by the method of lowtemperature NMR spectroscopy. It is shown that the two-component polymer matrix is capable of absorption of significant amounts of water in the form of clusters, with the size strongly depending on the presence of organic compounds, such as chloroform and trifluoroacetic acid. Thus, the changes in the medium composition allow one to control the state of water absorbed by the polymer in a wide range. The found effect may be used to create materials with the controlled delivery of biologically active substances whose retention by the matrix is determined to a great extent by the energy of binding of water by the polymer.     

Characterization of the Cysteine Content in Proteins Utilizing Cysteine Selenylation with 266 nm Ultraviolet Photodissociation (UVPD)

Characterization of the cysteine content of proteins is a key aspect of proteomics. By defining both the total number of cysteines and their bound/unbound state, the number of candidate proteins considered in database searches is significantly constrained. Herein we present a methodology that utilizes 266 nm UVPD to count the number of free and bound cysteines in intact proteins. In order to attain this goal, proteins were derivatized with N-(phenylseleno)phthalimide (NPSP) to install a selectively cleavable Se–S bond upon 266 UVPD. The number of Se–S bonds cleaved upon UVPD, a process that releases SePh moieties, corresponds to the number of cysteine residues per protein.

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The influence of molecular interaction on polymerization—11: A study of the influence of the solvent on the tacticities of poly(2-naphthyl methacrylated) and poly(cumylphenyl methacrylate) obtained in various solvents

Polymerizations of 2-naphthyl methacrylate and 4(1-methylphenethyl)phenyl methacrylate (cumylphenyl methacrylate) have been carried out in solvents with different dielectric constants and donor numbers (DN). By means of ¹H-NMR and fluorescence spectroscopy, the tacticities of the polymers were studied. It was found that the structures of the polymers depend on the dielectric constant of the solvent and not on its donor number. In solvents with high dielectric constant, the contents of isotactic triads are higher than for solvents with low dielectric constants.     

Effect of bovine serum albumin on the micellization of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers in aqueous solutions by fluorescence spectroscopy

Effect of bovine serum albumin (BSA) on the temperature-dependent association behavior of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers was investigated using pyrene fluorescence spectroscopy. The critical micellization temperature (CMT) of pluronics in aqueous solution was increased by the addition of BSA. A closed association model was used to obtain the standard free energies (△G0), enthalpies (△H 0), and entropies (△S 0) of micellization. The standard enthalpy and entropy of micellization for pluronic polymers in water were decreased with an increase of the BSA content. The more PPO component in the pluronic polymer, the higher the changed values of micellization enthalpy and entropy. The hydrophobic part of the pluronics, PPO, was responsible for the interaction between pluronics and BSA. Hydrophobic interaction between PPO and BSA was correlated to the alternation of the PPO-PPO interaction by the addition of BSA, which would shift the CMT toward higher temperature and alter the thermodynamic parameters of micellization for pluronics in aqueous solutions.