Control of One-Handed Helicity in Polyacetylenes: Impact of an Extremely Small Amount of Chiral Substituents.

Controlling the one-handed helicity in synthetic polymers is crucial for developing helical polymer-based advanced chiral materials. We now report that an extremely small amount of chiral biphenylylacetylene (BPA) monomers (ca. 0.3-0.5 mol %) allows complete control of the one-handed helicity throughout the polymer chains mostly composed of achiral BPAs. Chiral substituents introduced at the 2-position of the biphenyl units of BPA positioned in the vicinity of the polymer backbones contribute to a significant amplification of the helical bias, as interpreted by theoretical modeling and simulation. The helical structures, such as the helical pitch and absolute helical handedness (right- or left-handed helix) of the one-handed helical copolymers, were unambiguously determined by high-resolution atomic force microscopy combined with X-ray diffraction. The exceptionally strong helix-biasing power of the chiral BPA provides a highly durable and practically useful chiral material for the separation of enantiomers in chromatography by copolymerization of an achiral functional BPA with a small amount of the chiral BPA (0.5 mol %) due to the robust helical scaffold of the one-handed helical copolymer.

Biosynthesis of hydrazine from ammonium and hydroxylamine using an anaerobic ammonium oxidizing bacterium.

OBJECTIVES: To synthesize hydrazine (N2H4) from ammonium and hydroxylamine (NH2OH) using an anaerobic ammonium oxidation (anammox) bacterium, Candidatus Kuenenia stuttgartiensis. RESULTS: K. stuttgartiensis cells were anoxically cultivated with the addition of ammonium (2 mM) and NH2OH (1-100 mM) at pH 6-10.5, and 4-65 °C to examine the favorable cultivation conditions for N2H4 production. The influence of NH2OH concentration was more prominent than that of pH and temperature, and NH2OH concentration higher than 1 mM deteriorated N2H4 yields significantly. The following conditions were found to be favorable for N2H4 production using K. stuttgartiensis cells: pH 9, 38 °C, and < 1 mM NH2OH. In a continuous-feed system operated at these conditions, K. stuttgartiensis cells produced N2H4 with a maximum concentration of 0.65 mM, which is the highest N2H4 concentration previously reported in biological processes. CONCLUSIONS: Optimal cultivation conditions for K. stuttgartiensis for N2H4 production were successfully determined, and the present study is the first to document potential biological N2H4 production using anammox bacteria.

Synthesis of one-dimensional metal-containing insulated molecular wire with versatile properties directed toward molecular electronics materials.

We report, herein, the design, synthesis, and properties of new materials directed toward molecular electronics. A transition metal-containing insulated molecular wire was synthesized through the coordination polymerization of a Ru(II) porphyrin with an insulated bridging ligand of well-defined structure. The wire displayed not only high linearity and rigidity, but also high intramolecular charge mobility. Owing to the unique properties of the coordination bond, the interconversion between the monomer and polymer states was realized under a carbon monoxide atmosphere or UV irradiation. The results demonstrated a high potential of the metal-containing insulated molecular wire for applications in molecular electronics.

Retention of fetuin-A in renal tubular lumen protects the kidney from nephrocalcinosis in rats.

The serum glycoprotein fetuin-A is an important inhibitor of extraosseous calcification. The importance of fetuin-A has been confirmed in fetuin-A null mice, which develop widespread extraosseous calcification including the kidney. However, the mechanism how fetuin-A protects kidneys from nephrocalcinosis remains uncertain. Here, we demonstrate that intratubular fetuin-A plays a role in the prevention of nephrocalcinosis in the proximal tubules. Although normal rat kidney did not express mRNA for fetuin-A, we found punctate immunohistochemical staining of fetuin-A mainly in the S1 segment of the proximal tubules. The staining pattern suggested that fetuin-A passed through the slit diaphragm, traveled in the proximal tubular lumen, and was introduced into proximal tubular cells by megalin-mediated endocytosis. To test this hypothesis, we inhibited the function of megalin by intravenous injection of histidine-tagged soluble receptor-associated protein (His-sRAP), a megalin inhibitor. His-sRAP injection diminished fetuin-A staining in the proximal tubules and led to urinary excretion of fetuin-A. We further analyzed the role of fetuin-A in nephrocalcinosis. Continuous injection of parathyroid hormone (PTH) 1-34 induced nephrocalcinosis mainly in the proximal tubules in rats. His-sRAP retained fetuin-A in renal tubular lumen and thereby protected the kidneys of PTH-treated rats from calcification. Our findings suggest that tubular luminal fetuin-A works as a natural inhibitor against calcification in the proximal tubules under PTH-loaded condition.

Asymmetrically tilted alignment of rigid-rod helical polysilanes on a rubbed polyimide surface.

The homogeneous alignments of helical rod-like polysilanes on a rubbed polyimide alignment layer were investigated by polarized optical microscopy (POM) and atomic force microscopy (AFM) analyses. The POM and AFM observations determined that polysilanes with a series of aliphatic side chains helically arranged around the main chains were tilted to the right and left by 33° from the rubbing direction when the handedness of the side-chain helical array is left and right, respectively. It is interesting to note that the side-chain arrays run perpendicular to the rubbing direction on the polyimide surface, which is different from intuitive "knob and hole" packing of the extended polyimide chain and the helical grooves between the side-chain arrays surrounding the polysilane backbone. More surprisingly, both right- and left-tilting smectic domains were simultaneously observed with an equal probability for an achiral polysilane, which apparently has the interconverting right- and left-handed helical segments separated by helical reversals. This might be the first observation of the chiral segregation of dynamic helical polymers.

Latticelike smectic liquid crystal phase in a rigid-rod helical polyisocyanide with mesogenic pendants.

We report a unique macromolecule consisting of a rodlike helical polyisocyanide backbone with a narrow molecular weight distribution and rigid mesogenic chiral pendants linked via a flexible spacer that exhibits lyotropic nematic and latticelike new smectic (lat-Sm) liquid crystal phases at different concentrations. The unprecedented lat-Sm phase is associated with the smectic ordering of both the stiff polymer backbone and the rigid-rod side groups. A detailed investigation of the films using X-ray scattering and atomic force microscopy revealed a novel tilted smectic layer structure of the polymer backbone aligned perpendicular to the smectic layer of the mesogenic pendants, which arrange in an antiparallel overlapping interdigitated manner.

Visualization of polymer chain conformations in amorphous polyisocyanide Langmuir-Blodgett films by atomic force microscopy.

Polymer Langmuir monolayers are an ideal model for two-dimensional (2D) polymer chains, but our understanding of them is still limited. Using atomic force microscopy, we have for the first time successfully visualized the polymer chain packings in amorphous polyisocyanide monolayers deposited on mica. The long polymer chains, which were partially forced to form hairpin-like conformations, were sophisticatedly packed in the 2D film without any chain stacking. The trend of the persistent lengths of the polymers in the 2D films fairly corresponded to those of 3D chains in solution. The molecular-level information provided by direct observations such as these will improve our understanding of polymers in 2D space.

Unusual swelling of HPC in toluene forming a microspherical domain structure that causes Christiansen scattering coloration.

The unusual swelling behavior of hydroxypropyl cellulose (HPC) by toluene is described. At temperatures as high as 100 degrees C, toluene molecules can enter the HPC film up to the weight fraction of 55%; however, they are segregated from the HPC matrix and form microspherical domains. The size of the spherical domain is approximately 4.5 microm in diameter on average. Such an unusual swelling behavior is due to the amphiphilic nature of the HPC; HPC polymers rearrange to contact their hydrophobic group with toluene and confine the toluene molecules in spherical domains. Because of the similarity in refractive indices of the toluene microspherical phase and the HPC continuum phase, the swollen film shows a beautiful scattering color that is called the Christiansen filter effect.

Enantiomer-selective and helix-sense-selective living block copolymerization of isocyanide enantiomers initiated by single-handed helical poly(phenyl isocyanide)s.

Rigid-rodlike right (P)- and left (M)-handed helical polyisocyanides (P-poly-L-1 and M-poly-L-1) prepared by the living polymerization of an enantiomerically pure phenyl isocyanide bearing an L-alanine pendant with a long n-decyl chain (L-1) with the mu-ethynediyl Pt-Pd catalyst were found to block copolymerize L-1 and D-1 in a highly enantiomer-selective manner while maintaining narrow molecular weight distributions. The M-poly-L-1 preferentially copolymerized L-1 over the antipode D-1 by a factor of 6.4-7.7, whereas the D-1 was preferentially copolymerized with P-poly-L-1 composed of the same L-1 units, but possessing the opposite helicity by a factor of 4.0. Circular dichroism and high-resolution atomic force microscopy revealed that the enantiomer-selective block copolymerizations proceed in an extremely high helix-sense-selective fashion, and the preformed helical handedness determines the overall helical sense of the polyisocyanides irrespective of the configuration of the monomer units of the initiators during the block copolymerizations. The block copolymers are rigid-rod helical polymers with a narrow molecular weight distribution and exhibit a lyotropic smectic liquid crystalline phase.

Synthesis of organic-soluble conjugated polyrotaxanes by polymerization of linked rotaxanes.

Extensive research on the use of cyclodextrin for insulating pi-conjugated polymer chains has been carried out. However, the resulting polyrotaxanes do not exhibit high and constant covering ratios and are generally insoluble in organic solvents. Here we demonstrate a new method of synthesizing permethylated cyclodextrin-based polyrotaxanes involving the polymerization of linked rotaxane monomers. The insulated molecular wires obtained by this method are highly soluble in organic solvents and have a high covering ratio, rigidity, and photoluminescence efficiency. A cholesteric liquid-crystal phase was observed for these highly rigid polyrotaxanes, in which threading of a pi-conjugated polymer chain through chiral macrocycles occurs.

Mechanism of helix induction in poly(4-carboxyphenyl isocyanide) with chiral amines and memory of the macromolecular helicity and its helical structures.

An optically inactive poly(4-carboxyphenyl isocyanide) (poly-1-H) changed its structure into the prevailing, one-handed helical structure upon complexation with optically active amines in dimethylsulfoxide (DMSO) and water, and the complexes show a characteristic induced circular dichroism in the polymer backbone region. Moreover, the macromolecular helicity induced in water and aqueous organic solutions containing more than 50 vol % water could be "memorized" even after complete removal of the chiral amines (h-poly-1b-H), while that induced in DMSO and DMSO-water mixtures containing less than 30 vol % water could not maintain the optical activity after removal of the chiral amines (poly-1a-H). We now report fully detailed studies of the helix induction mechanism with chiral amines and the memory of the macromolecular helicity in water and a DMSO-water mixture by various spectroscopic measurements, theoretical calculations, and persistence length measurements together with X-ray diffraction (XRD) measurements. From the spectroscopic results, such as circular dichroism (CD), absorption, IR, vibrational CD, and NMR of poly-1a-H, h-poly-1b-H, and original poly-1-H, we concluded that the specific configurational isomerization around the C horizontal lineN double bonds occurs during the helicity induction process in each solvent. In order to obtain the structural information, XRD measurements were done on the uniaxially oriented films of the corresponding methyl esters (poly-1-Me, poly-1a-Me, and h-poly-1b-Me) prepared from their liquid crystalline polymer solutions. On the basis of the XRD analyses, the most plausible helical structure of poly-1a-Me was proposed to be a 9-unit/5-turn helix with two monomer units as a repeating unit, and that of h-poly-1b-Me was proposed to be a 10-unit/3-turn helix consisting of one repeating monomer unit. The density functional theory calculations of poly(phenyl isocyanide), a model polymer of h-poly-1b-Me, afforded a 7-unit/2-turn helix as the most possible helical structure, which is in good agreement with the XRD results. Furthermore, the persistence length measurements revealed that these structural changes accompany a significant change in the main-chain stiffness. The mechanism of helix induction in poly-1-H and the memory of the macromolecular helicity are discussed on the basis of these results.

Double-stranded helical polymers consisting of complementary homopolymers.

Two complementary homopolymers of chiral amidines and achiral carboxylic acids with m-terphenyl-based backbones were synthesized by the copolymerization of a p-diiodobenzene derivative with the diethynyl monomers bearing a chiral amidine group and a carboxyl group using the Sonogashira reaction, respectively. Upon mixing in THF, the homopolymer strands assembled into a preferred-handed double helix through interstrand amidinium-carboxylate salt bridges, as evidenced by its absorption, circular dichroism, and IR spectra. In contrast, when mixed in less polar solvents, such as chloroform, the complementary strands kinetically formed an interpolymer complex with an imperfect double helical structure containing a randomly hybridized cross-linked structure, probably because of strong salt bridge formations. This primary complex was rearranged into the fully double helical structure by treatment with a strong acid followed by neutralization with an amine. High-resolution atomic force microscopy revealed the double-stranded helical structure and enabled the determination of the helical sense.

Two- and three-dimensional smectic ordering of single-handed helical polymers.

Rodlike polymers with precisely defined architectures are ideal building blocks for self-assembled structures leading to novel nanometer-scale devices. We found that the living polymerization of a single isocyanide enantiomer bearing an l-alanine pendant with a long n-decyl chain simultaneously produced diastereomeric right- and left-handed helices with different molecular weights and narrow molecular weight distributions. Each single-handed, rodlike helical polymer with a controlled length and handedness isolated by a facile solvent fractionation method with acetone self-assembled to form well-defined two- and three-dimensional smectic ordering on the nanometer scale on a substrate and in a liquid crystalline state as evidenced by direct atomic force microscopic observations and X-ray diffraction measurements, respectively.

Liquid crystal formation of RecA-DNA filamentous complexes.

Spontaneous optical birefringence of RecA-bound linear and closed circular single-stranded DNA filaments, as well as RecA self-assembled polymer, was observed in aqueous buffer solutions, which demonstrates the formation of lyotropic liquid crystalline phases.

The Christiansen effect of brightly colored colloidal dispersion with an amphiphilic polymer.

A novel coloration phenomenon in a colloidal dispersion with an amphiphilic polymer was found. The dispersion consists of tetrahydrofuran (THF), an aqueous solution of sodium thiosulfate (Na(2)S(2)O(3).5H(2)O), and hydroxypropylcellulose (HPC). The dispersion was emulsified by HPC as an amphiphilic polymer, so that the aqueous phase was confined in droplets in the THF matrix. It typically appeared bluish violet at room temperature and turned into blue with increasing temperature. In this system, the refractive indices of the inside and outside of the droplet coincided at a certain wavelength at which the light passes through without scattering, which is called the Christiansen effect. The color observed was successfully simulated by Mie's scattering theory in combination with the Christiansen effect.