Highly branched thermoresponsive polysaccharide derivative in water. Partly substituted highly branched cyclic dextrin ethylcarbamate.

A thermoresponsive highly branched polysaccharide derivative was revealed from commercially available highly branched cyclic dextrin (HBCD), originally synthesized from amylopectin. Eight samples of partially substituted ethyl carbamate derivatives of HBCD (HEC) were prepared with a degree of substitution DS ranging from 0.27 to 1.46. Three samples with DS = 0.88, 1.05, and 1.22 showed LCST type phase separation in water. The intrinsic viscosity and form factor in water were typical of the hyperbranched structure. The intermolecular interactions between HEC and iodine or 1-anilinonaphthalene-8-sulfonic acid (ANS) were appreciably different from those of the linear analog (AEC), suggesting that the locally bent helical conformation of highly branched HEC chains has a different interaction with small molecules. The phase diagram of HEC-water systems was accidentally similar to that of the linear chain with the same molar mass and DS, although the one phase region of the branched polymer chain-poor solvent system is usually wider than that of the corresponding linear chain. This is likely due to the lower hydration nature of the polymer segment of HEC chains than that of the corresponding linear chain.

Solution characterization of a hyperbranched polysaccharide carbamate derivative and specific phase separation behavior due to chain branching.

A hyperbranched polymer consisting of rigid helical part chains was prepared as highly branched cyclic dextrin tris(phenylcarbamate) (HTPC) with the weight-average molar masses of 880 and 590 kg mol-1. Small-angle X-ray scattering (SAXS) measurement and viscometry were performed on the samples in good and poor solvents to determine the dimensional and hydrodynamic properties in solution. The HTPC molecule has a much more compact conformation than the linear chain with the same molar mass as expected for the hyperbranched architecture. While the corresponding linear polymer is soluble in methyl acetate (MEA) over a wide temperature range, HTPC is only soluble in the solvent at low temperatures. A typical LCST-type phase diagram was observed for the HTPC-MEA system, indicating that the interactions between the polymer segment of HTPC and the MEA molecules are substantially different from those of the linear chains. This is most likely due to the bending helical chains near the branching point of HTPC having different interactions with solvent molecules.

Molecular structure and chiral recognition ability of highly branched cyclic dextrin carbamate derivative.

A hyperbranched polymer, highly branched cyclic dextrin tris(3,5-dimethylphenylcarbamate) (HDMPC), consisting of rigid rodlike subchains was synthesized to investigate dimensional and hydrodynamic properties of HDMPC in methyl acetate and 4-methyl-2-pentanone at 25 °C. Both gyration radii and intrinsic viscosities of the HDMPC sample in the two solvents were much smaller than those for the linear amylose tris(3,5-dimethylphenylcarbamate) (ADMPC) chain with the corresponding molar mass. The chiral column made of the HDMPC sample has chiral separation ability for 8 racemates with a mobile phase of hexane/2-propanol while 6 of them were also separated by our previously investigated linear ADMPC column. These results indicate that HDMPC retains the functionality of the rigid linear ADMPC chain with much smaller chain dimensions and lower solution viscosity than those for the linear chain with the same molar mass.

Kinetics of denaturation and renaturation processes of double-stranded helical polysaccharide, xanthan in aqueous sodium chloride.

Circular dichroism (CD) and small-angle X-ray scattering (SAXS) measurements were made for three xanthan samples, a double helical polysaccharide, in 5 or 10 mM aqueous NaCl after rapid temperature change to investigate the kinetics of the conformational change between the ordered and disordered states. After the rapid heating, the CD signal mainly reflecting the carbonyl groups on the side chains quickly changed (<150 s) while the scattering intensity from SAXS around q (magnitude of the scattering vector) = 1 nm-1 changed more gradually, reflecting the main-chain conformation. The difference between CD and SAXS implies us the intermediate conformation which can be regarded as a loose double helix. The SAXS profile in the rapid cooling process showed that the loose double helical structure was constructed within 150 s, but the CD signal slowly changed with around 2 days to recover the native tight double helix.

Complex Formation of Silica Nanoparticles with Collagen: Effects of the Conformation of Collagen.

Negatively charged Ludox silica nanoparticles (SiNPs) form a complex with atelocollagen (AC) in acidic buffers (pH = 4 or 3). AC is a low-immunogenic derivative of collagen obtained by the removal of N- and C-terminal telopeptide components. Mixed solutions of negatively charged SiNPs and AC were turbid, while positively charged SiNPs (Ludox CL) did not form a complex with AC in pH 4 buffer, indicating that electrostatic attraction is the dominant force to form the complex. Small-angle X-ray scattering (SAXS) and circular dichroism (CD) measurements were made for AC and Ludox LS (or CL) solutions in acetate buffer (pH 4.0) and citrate buffer (pH 3.0). The CD data showed that the stability of the triple helical structure of AC in the buffers is not affected by the complexation. The resulting complex consisting of triple helical AC and SiNPs did not influence the SAXS profile except for the lowest q region investigated. On the contrary, different scattering profiles were observed for the single chain AC and SiNP mixture indicating densely packed SiNPs in the complex. This scattering behavior was fairly explained in terms of the sticky hard sphere model (SHSM). This AC conformation-dependent complexation may be because of the hydrogen bonding interaction between the single chain AC and SiNPs. The temperature-induced change of the complex formation can be applied for thermoresponsive hybrid materials.

Self-Assembly of Amphiphilic Amylose Derivatives in Aqueous Media.

Six amylose derivative (C12CMA) samples with hydrophobic dodecyl ether groups and hydrophilic sodium carboxymethyl groups were synthesized from an enzymatically synthesized amylose for which the weight-average molar mass is 50 kg mol-1 to realize amylose-based amphiphilic polymer micelles. The degree of substitution of hydrophobic (DSC12) and hydrophilic (DSCM) groups ranges between 0.076 and 0.39 and between 0.35 and 1.83, respectively. Static and dynamic light scattering, small-angle X-ray scattering (SAXS), and fluorescence measurements with pyrene as a probe were carried out for the samples in 150 mM aqueous NaCl to characterize the higher-order structure in solution. The fluorescence from pyrene showed that all six samples have hydrophobic environment, while the hydrophobicity tends to increase with rising DSC12. All six samples have high scattering intensity owing to the relatively large concentrated droplets ranging in the hydrodynamic radius from 50 to 110 nm, whereas the weight fraction of such large particles is substantially small except for the highest DSC12 sample. Most polymer chains for relatively low DSC12 of 0.076 were molecularly dispersed with a very small amount of large droplets. The dispersed chain has a slightly smaller helix pitch per residue and a more rigid main chain than those for amylose in dimethyl sulfoxide, suggesting that the amylosic main chain of C12CMA has a helical structure with dodecyl groups at least locally. On the other hand, an anisotropic shaped micelle-like structure is only found for relatively high DSC12 (0.23 and 0.39) samples, which was detected by the SAXS profile at a high scattering vector range. The micelle structure for high DSC12 samples is consistent with the high chain stiffness.

Does local chain conformation affect the chiral recognition ability of an amylose derivative? Comparison between linear and cyclic amylose tris(3,5-dimethylphenylcarbamate).

Coated-type chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC) were prepared from three cyclic amylose tris(3,5-dimethylphenylcarbamate) (cADMPC) samples, of which weight-average molar mass (Mw) ranges from 19 to 91 kg mol-1, and from three linear ADMPC samples ranging in Mw from 25 to 90 kg mol-1. CSPs made of cADMPC showed appreciably different chiral separation ability comparing with those for ADMPC with a mixed eluent of n-hexane and 2-propanol. Local conformation plays an important role for the chiral separation taking into account that the local helical structure of cADMPC in dilute solution is extended comparing with ADMPC. Immobilized-type CSPs were also prepared from enzymatically synthesized linear and cyclic amylose samples with 3-(triethoxysilyl)propylcarbamate linkers (ADMPCi and cADMPCi) of which Mw's are in the range from 18 to 130 kg mol-1. When we choose quite high linker contents, CSPs of cADMPCi were fairly close to those of ADMPCi. This suggests that local conformations of ADMPCi and cADMPCi are similar in the stationary phase since they are crosslinked to the other polymer chains with multiple points on the polymer chain.

Colloidal Dispersion of a Perfluorosulfonated Ionomer in Water⁻Methanol Mixtures.

We have investigated the dispersion state of a perfluorosulfonated ionomer (PFSI; Nafion®) in aqueous dispersion and the effect of methanol (MeOH) added to the aqueous dispersion by small-angle X-ray scattering (SAXS) as well as static and dynamic light scattering (SLS and DLS, respectively). Although both electrostatic and hydrophobic interactions of PFSI are expected to be strong in the dispersions, SAXS profiles obtained were satisfactorily fitted by the spherical particle model of a bimodal molar mass distribution. The rod-like aggregate model proposed in previous papers was denied at least for the present PFSI dispersion. Although the SAXS profiles exhibited a weak peak and the auto-correlation functions of DLS showed a log-time decay by the "repulsive cage effect" due to the long-ranged electrostatic interaction among PFSI particles, the concentration dependence of SLS results was probably normal because the cancellation of the electrostatic and hydrophobic interactions. The addition of MeOH into the aqueous dispersion of PFSI weakened both the hydrophobic and electcrostatic interactions of PFSI, and it is rather difficult to classify whether MeOH is a good or poor solvent (dispersant) for PFSI.

Structural Analysis of Hydrophobe-Uptake Micelle of an Amphiphilic Alternating Copolymer in Aqueous Solution.

We investigated the structure of the hydrophobe-uptake micelle of an alternating amphiphilic copolymer in aqueous solutions, by combining light scattering and small-angle X-ray scattering (SAXS). When the copolymer micelle includes the hydrophobe (1-dodecanol), the unicore flower micelle transforms into the multicore flower necklace, and the flower necklace is slightly stiffer than the hydrophobe-free flower necklace of the same copolymer. Moreover, the hydrophobe is included not in the hydrophobic core region but in the intermingled region of the hydrophobic group and the loop chain of the unit flower micelle. Therefore, the structure of the hydrophobe-uptake micelle of the amphiphilic alternating copolymer is quite different from that of hydrophobe-uptake spherical micelles of low molar mass surfactants and of amphiphilic block copolymers, where the hydrophobe is included in the hydrophobic region of the micelles.

Conformational change from rigid rod to star: a triple-helical peptide with a linker domain at the C-terminal end.

Small-angle X-ray scattering and circular dichroism measurements were made for a triple-helical peptide of which one end was linked by the thermally stable trimerization domain of type XIX collagen. The radius of gyration decreased steeply around the transition temperature while the scattering intensity at zero angle did not significantly change, indicating no molar mass change through the conformational transition. Thus, the data were analyzed in terms of the rigid cylinder model for the data at low temperatures and the wormlike star model at high temperatures. It was confirmed that the peptide molecules behave as a rod-like cylinder at low temperature and a semi flexible three-arm star-like chain at high temperature of which the single-coil peptide chain is appreciably extended by the high segment density nearby the linking domain.

Local conformation and intermolecular interaction of rigid ring polymers are not always the same as the linear analogue: cyclic amylose tris(phenylcarbamate) in Θ solvents.

Small-angle X-ray scattering and static and dynamic light scattering measurements were made for cyclic amylose tris(phenylcarbamate) (cATPC) of which weight-average molar mass M(w) ranges from 1.3 × 10(4) to 1.5 × 10(5) to determine their z-average mean square radius of gyration z, particle scattering function P(q), hydrodynamic radius R(H), and second virial coefficient A2 in methyl acetate (MEA), ethyl acetate (EA), and 4-methyl-2-pentanone (MIBK). The obtained z, P(q), and R(H) data were analyzed in terms of the wormlike ring to estimate the helix pitch per residue h and the Kuhn segment length λ(-1) (the stiffness parameter, twice the persistence length). Both h and λ(-1) for cATPC in MEA, EA, and MIBK are smaller than those for linear amylose tris(phenylcarbamate) (ATPC) in the corresponding solvent and the discrepancy becomes more significant with increasing the molar volume of the solvent. This indicates that not every rigid ring has the same local helical structure and chain stiffness as that for the linear polymer in the M(w) range investigated while infinitely long ring chains should have the same local conformation. This conformational difference also affects A2. In actuality, negative A2 was observed for cATPC in MIBK at the Θ temperature of linear ATPC whereas intermolecular topological interaction of ring polymers increases A2.

Side-chain-dependent helical conformation of amylose alkylcarbamates: amylose tris(ethylcarbamate) and amylose tris(n-hexylcarbamate).

Eight amylose tris(ethylcarbamate) (ATEC) samples ranging in the weight-average molar mass M(w) from 1.0 × 10(4) to 1.1 × 10(6) g mol(-1) and five amylose tris(n-hexylcarbamate) (ATHC) samples of which M(w) varies from 4.9 × 10(4) to 2.2 × 10(6) g mol(-1) have been prepared from enzymatically synthesized amylose samples having narrow dispersity indices and no branching. Small-angle angle X-ray scattering (SAXS), light scattering, viscometry, and infrared (IR) absorption measurements were carried out for their dilute solutions, that is, ATEC in tetrahydrofuran (THF), 2-methoxyethanol (2ME), methanol (MeOH), and ATHC in THF and 1-propanol (1PrOH) to determine M(w), particle scattering functions, intrinsic viscosities, and IR spectra. SAXS and viscosity measurements were also made on ATEC in d- and l-ethyl lactates. The data were analyzed in terms of the wormlike cylinder model to estimate the helix pitch (or contour length) per residue h and the Kuhn segment length λ(-1) (stiffness parameter, twice the persistence length). Both ATEC and ATHC have large λ(-1) in THF, that is, 33 and 75 nm, respectively, and smaller λ(-1) were obtained in alcohols, indicating that they have rigid helical conformation stabilized by intramolecular hydrogen bonds in THF. On the contrary, the helical structure estimated from the h value significantly depends on the alkyl side groups in a complex fashion, that is, h = 0.36 nm for ATEC, h = 0.29 nm for ATHC, and h = 0.26 nm for amylose tris(n-butylcarbamate) (ATBC). This is likely related to the bulkiness of side groups packed inside the amylosic helices. The solvent dependence of h, λ(-1), and the fraction f(hyd) of intramolecular hydrogen bonds for ATEC can be explained by a current model as is the case with ATBC [ Terao , K. ; Macromolecules 2010 , 43 , 1061 ], in which each contour point along the chain takes loose helical and rigid helical sequences independently.

Solvent-dependent conformation of a regioselective amylose carbamate: amylose-2-acetyl-3,6-bis(phenylcarbamate).

Six amylose-2-acetyl-3,6-bis(phenylcarbamate) (AAPC) samples ranging in weight-average molar mass M(w) from 1.8 × 10(4) g mol(-1) to 1.1 × 10(6) g mol(-1) have been prepared from enzymatically synthesized amylose samples. Static light scattering, small-angle X-ray scattering, sedimentation equilibrium, and viscosity measurements were made for the samples in 1,4-dioxane (DIOX), 2-ethoxyethanol (2EE), and 2-butanone (MEK) all at 25°C to determine particle scattering functions, z-average radii of gyration, intrinsic viscosities, as well as M(w). The data were analyzed in terms of the wormlike cylinder model mainly to yield the helix pitch per residue h and the Kuhn segment length λ(-1), which corresponds to twice of the persistence length. The latter parameters (λ(-1)) in 2EE (11 nm) and MEK (12 nm) are quite smaller than those for amylose tris(phenylcarbamate) (ATPC) in the same solvent (16 nm in 2EE and 18 nm in MEK) whereas those for AAPC (21 nm) and ATPC (22 nm) in DIOX are essentially the same as each other. This indicates that the chain stiffness of AAPC is more strongly influenced by the solvents since the number of intramolecular H-bonds of AAPC is more changeable than that for ATPC.

Rigid Cyclic Polymer in Solution: Cycloamylose Tris(phenylcarbamate) in 1,4-Dioxane and 2-Ethoxyethanol.

Six cyclic amylose tris(phenylcarbamate) (ATPC) samples have been prepared from enzymatically synthesized cyclic amylose ranging in the number of repeat units N from 24 to 290. Synchrotron-radiation small-angle X-ray scattering measurements were made for the samples in 1,4-dioxane (DIOX) and 2-ethoxyethanol (2EE) to determine the z-average radius of gyration ⟨S2⟩z and the particle scattering function P(q). Molar mass dependencies of ⟨S2⟩z in the two solvents were successfully explained by the current theories for the wormlike ring with the same parameters for linear ATPC in the corresponding solvent, that is, the helix pitch h (or contour length) per residue and the Kuhn segment length λ-1 (stiffness parameter, twice the persistence length). The latter parameter λ-1 is 22 and 16 nm in DIOX and 2EE, respectively. Except for the low-q region, P(q) was also explained by the rigid ring having the same contour length Nh as that for linear ATPC. Further, their local conformation estimated from circular dichroism spectra is essentially unaltered from that for linear ATPC at least when N ≥ 24.

Solvent-dependent conformation of amylose tris(phenylcarbamate) as deduced from scattering and viscosity data.

The z-average mean-square radius of gyration S(2)(z), the particle scattering function P(k), the second virial coefficient, and the intrinsic viscosity [eta] have been determined for amylose tris(phenylcarbamate) (ATPC) in methyl acetate (MEA) at 25 degrees C, in ethyl acetate (EA) at 33 degrees C, and in 4-methyl-2-pentanone (MIBK) at 25 degrees C by light and small-angle X-ray scattering and viscometry as functions of the weight-average molecular weight in a range from 2 x 10(4) to 3 x 10(6). The first two solvents attain the theta state, whereas the last one is a good solvent for the amylose derivative. Analysis of the S(2)(z), P(k), and [eta] data based on the wormlike chain yields h (the contour length or helix pitch per repeating unit) = 0.37 +/- 0.02 and lambda(-1) (the Kuhn segment length) = 15 +/- 2 nm in MEA, h = 0.39 +/- 0.02 and lambda(-1) = 17 +/- 2 nm in EA, and h = 0.42 +/- 0.02 nm and lambda(-1) = 24 +/- 2 nm in MIBK. These h values, comparable with the helix pitches (0.37-0.40 nm) per residue of amylose triesters in the crystalline state, are somewhat larger than the previously determined h of 0.33 +/- 0.02 nm for ATPC in 1,4-dioxane and 2-ethoxyethanol, in which intramolecular hydrogen bonds are formed between the C==O and NH groups of the neighbor repeating units. The slightly extended helices of ATPC in the ketone and ester solvents are most likely due to the replacement of those hydrogen bonds by intermolecular hydrogen bonds between the NH groups of the polymer and the carbonyl groups of the solvent.

Circular dichroism of optically active poly(dialkylsilane) aggregates in microcapsules.

Poly[n-hexyl-(S)-3-methylpentylsilane] aggregates confined in microcapsules to keep the aggregation number and ranging in average polymer mass m(p) in a microcapsule from 2 x 10(-)(16) to 2 x 10(-)(14) g were studied by circular dichroism measurements in ethanol (a nonsolvent) and tetrahydrofuran (an associative solvent at low temperature) at various temperatures. The weight-average molecular weight M(w) and the polydispersity index (the ratio of M(w) to the number-average molecular weight) of the polysilane sample were 6.6 x 10(4) and 1.07, respectively, and the average number of polymer molecules in each capsule was estimated to be 1.9 x 10(3) for m(p) = 2 x 10(-)(16) g and 1.7 x 10(5) for m(p) = 2 x 10(-)(14) g. The size of each aggregate did not affect the optical activity because the circular dichroism thus obtained was proportional to m(p) under the same conditions in the investigated m(p) range; on the other hand, the peak height of the circular dichroism in tetrahydrofuran had a significant hysteresis between 0 and 25 degrees C. Moreover, the circular dichroism appreciably reflected the prepared method, that is, the temperature and solvent; in other words, the aggregates memorized the initial conditions in their stacking structures.

Preparation and characterization of core-shell nanoparticles hardened by gamma-ray.

Core-shell nanoparticles have been prepared by irradiation of gamma-ray on block copolymer micelles consisting of hydrophilic polyacrylic acid and hydrophobic polyisoprene with each 40 monomer units. The structure was determined by means of dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and atomic force microscopy (AFM). The size distribution of the core-shell nanoparticles determined by DLS and AFM was very narrow. The average diameter of the particles decreased from 48 nm for the original micelles to 26 nm by the irradiation of 30 kGy. The core size determined by SAXS combined with DLS was roughly constant of 10 nm, irrespective of irradiation dose, whereas the shell thickness of the micelles was twice as large as the core size, and decreased with increasing irradiation dose.

Single-particle light scattering study of polyethyleneglycol-grafted poly(ureaurethane) microcapsule in ethanol.

Microcapsules having polyethyleneglycol-grafted poly(ureaurethane) (PUU) membrane and di-2ethylhexyl phthalate core have been prepared, and the structure when they were suspended in dispersing ethanol have been studied by means of single-particle light scattering method. The PUU membrane was synthesized from monomers with aromatic functional groups (microcapsule MC110) and hexamethylene functional groups (microcapsule MC160). Because the outer and inner solvent passed through the membrane easily, the outside and inside of the membrane were the same at the equilibrium state. The thickness of the wall membrane was significantly smaller than that calculated from the overall weight ratio of the wall-forming material and the core solvents. It was attributed to low affinity of PUU membranes and ethanol.