Optically active poly(diphenylacetylene)s showing solvent-dependent helix inversion accompanied by modulation of helix inversion barriers.

Symmetrically substituted poly(diphenylacetylene)s bearing optically active 2-octyloxycarbonyl groups at the para-positions of the pendant phenyl rings not only show a unique solvent-dependent helix inversion to afford diastereomeric right- and left-handed helical polymers but also significant unprecedented solvent-dependent changes in the helix inversion barrier of the polymer backbone resulting in switching between static or dynamic behavior of the helical polymers at approximately room temperature depending on the solvents used.

Dynamics of Molecular Self-Assembly of Short Peptides at Liquid-Solid Interfaces - Effect of Charged Amino Acid Point Mutations.

Self-organizing solid-binding peptides on atomically flat solid surfaces offer a unique bio/nano hybrid platform, useful for understanding the basic nature of biology/solid coupling and their practical applications. The surface behavior of peptides is determined by their molecular folding, which is influenced by various factors and is challenging to study. Here, the effect of charged amino acids is studied on the self-assembly behavior of a directed evolution selected graphite-binding dodecapeptide on graphite surface. Two mutations, M6 and M8, are designed to introduce negatively and positively charged moieties, respectively, at the anchoring domain of the wild-type (WT) peptide, affecting both binding and assembly. The questions addressed here are whether mutant peptides exhibit molecular crystal formation and demonstrate molecular recognition on the solid surface based on the specific mutations. Frequency-modulated atomic force microscopy is used for observations of the surface processes dynamically in water at molecular resolution over several hours at the ambient. The results indicate that while the mutants display distinct folding and surface behavior, each homogeneously nucleates and forms 2D self-organized patterns, akin to the WT peptide. However, their growth dynamics, domain formation, and crystalline lattice structures differ significantly. The results represent a significant step toward the rational design of bio/solid interfaces, potent facilitators of a variety of future implementations.

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.

Synthesis of optically active star polymers consisting of helical poly(phenylacetylene) chains by the living polymerization of phenylacetylenes and their chiroptical properties.

Star polymers consisting of three helical poly(phenylacetylene) chains with a precisely controlled molecular weight (molar mass dispersity < 1.03) were successfully synthesized by the living polymerization of phenylacetylene derivatives with a Rh-based multicomponent catalyst system comprising trifunctional initiators, which have three phenylboronates centered on a benzene ring, the Rh complex [Rh(nbd)Cl]2, diphenylacetylene, triphenylphosphine, and a base. The analysis of chiroptical properties of the optically active star polymers obtained by the living polymerization of optically active phenylacetylene derivatives revealed that the star polymers exhibited chiral amplification properties owing to their unique topology compared with the corresponding linear polymers.

Insight into stability of dithiocarbamate-modified adsorbents: Oxidation of dithiocarbamate.

We previously reported that monoalkyl dithiocarbamate-modified cellulose (DMC) exhibited excellent adsorption performance for arsenite (AsIII), cadmium (CdII), lead (PbII), gold (AuIII), silver (AgI), platinum (PtIV), and palladium (PdII). However, its adsorption capability for AsIII decreased by 96.4% after two weeks of storage at 40 °C under an air atmosphere. This decrease in adsorption ability could occur for other metals that dithiocarbamates can extract. In this study, we investigated the adsorption performance of DMC for various metals before and after storage and proposed a possible mechanism for this decrease. We found significant decreases in the adsorption abilities of PbII (11.4%), AgI (39.5%), PtIV (65.5%), and PdII (69.6%), whereas AuIII and CdII adsorption was largely retained, with decreases of 1.1% and 4.0%, respectively. FTIR analysis of the stored DMC revealed the formation of S-S bonds and the retention of dithiocarbamate peaks, indicating the formation of dithiocarbamate dimers (thiuram disulfides). To further support thiuram disulfide formation, dialkyl thiuram disulfides were tested for the adsorption of the seven employed metals. The metal adsorption behavior of dialkyl thiuram disulfides was almost identical to that of the stored adsorbent, ensuring thiuram disulfide formation. In conclusion, the loss of adsorption capability can be mainly attributable to the formation of thiuram disulfide.

Revisiting the Synthesis of Cellulose Acrylate and Its Modification via Michael Addition Reactions.

The synthesis of cellulose acrylate from cellulose with acryloyl chloride has been problematic due to unexpected gelation of the reaction mixture, but we discovered that the use of bulky amines was crucial for the reproducibility of the synthesis of cellulose acrylate. The solubility of the obtained cellulose acrylate depended on the reaction conditions due to the possible cross-linking oxa-Michael reaction between a remaining hydroxy group and the introduced acrylate group. The synthesized cellulose acrylate worked as a useful precursor of chemically modified cellulose materials because it reacted with various functionalized nucleophiles such as secondary amines and thiols as a Michael donor. This method was applied to the synthesis of N-methyl-d-glucamine-modified cellulose that works as an adsorbent for the removal of B(OH)3 in water.

Facile Synthesis of Linear and Cyclic Poly(diphenylacetylene)s by Molybdenum and Tungsten Catalysis.

Improved methods for the synthesis of linear and cyclic poly(diphenylacetylene)s by polymerization of the corresponding diphenylacetylenes using MoCl5 - and WCl4 -based catalytic systems have been developed. MoCl5 induces migratory insertion polymerization of diphenylacetylenes in the presence of arylation reagents such as Ph4 Sn and ArSnn Bu3 to produce cis-stereoregular linear poly(diphenylacetyelene)s with high molecular weights (number-average molar mass (Mn )=30,000-3,200,000) in good yields (up to 98 %). On the other hand, WCl4 induces ring expansion polymerization of diphenylacetylenes in the presence of Ph4 Sn or reducing reagents to produce cis-stereoregular cyclic poly(diphenylacetylene)s with high molecular weights (Mn =20,000-250,000) in moderate to good yields (up to 90 %). Both catalytic systems are applicable to the polymerization of various diphenylacetylenes having polar functional groups such as esters that are not efficiently polymerized by conventional methods using WCl6 -Ph4 Sn and TaCl5 -n Bu4 Sn systems.

Helicity induction and memory of a lipophilic Brønsted acid-type poly(phenylacetylene) in non-polar solvents.

A novel lipophilic Brønsted acid-type PPA (poly-1-H) bearing a sulfonylphosphoramidic acid moiety, covered with a dynamically axially chiral biphenyl pendant, was synthesized and found to form a preferred-handed helical conformation in non-polar solvents upon complexation with non-racemic amines. This induced helicity was maintained after replacement with achiral amines ("dynamic helicity memory"). In addition, poly-1-H exhibited "static helicity memory" in which the induced helical conformation was maintained in non-polar solvents, even after acidification with a stronger acid without replacement with achiral amines.

Amplified Chirality Transfer to Aromatic Molecules through Non-specific Inclusion by Amorphous, Hyperbranched Poly(fluorenevinylene) Derivatives.

Optically active, hyperbranched, poly(fluorene-2,4,7-triylethene-1,2-diyl) [poly(fluorenevinylene)] derivatives bearing a neomenthyl group and a pentyl group at the 9-position of the fluorene backbone at various ratios acted as a chirality donor (host polymers) efficiently included naphthalene, anthracene, pyrene, 9-phenylanthracene, and 9,10-diphenyanthracene as a chirality acceptor (guest molecules) in their interior space in film as well as in solution, with the guest molecules exhibiting intense circular dichroism through chirality transfer with chirality amplification. The efficiency of the chirality transfer was much higher with higher-molar-mass polymers than lower-molar-mass ones as well as with hyperbranched polymers compared to the analogous linear ones. The hyperbranched polymers include the small molecules in their complex structure without any specific interactions at various stoichiometries. The included molecules may have ordered intermolecular arrangement that may be somewhat similar to those of liquid crystals. Naphthalene, anthracene, and pyrene included in the polymer exhibited efficient circularly polarized luminescence, where the chirality was remarkably amplified in excited states, and anthracene exhibited especially high anisotropies in the emission on the order of 10-2 .

Ultra-fast One-Handed Helix Induction and Its Static Helicity Memory in a Poly(biphenylylacetylene) with a Catalytic Amount of Chiral Ammonium Salts.

We report an ultra-fast helix induction and subsequent static helicity memory in poly(biphenylylacetylene) (PBPA-A) assisted by a catalytic amount of nonracemic ammonium salts comprised of non-coordinating tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BArF- ) as a counter anion. The remarkable acceleration of the helix-induction rate in PBPA-A accompanied by the significant amplification of the asymmetry relies on the two methoxymethoxy groups of the biphenyl pendants, which can gain access to enfold the chiral ammoniums in a crown-ether manner in specific aromatic solvents, leading to ultra-fast helicity induction, which is completed within 30 s. In aromatic solvents, helicity memory is lost rapidly, but is quite stable in long-chain hydrocarbons. The best use of specific solvents for helicity induction and static helicity memory, respectively, provides a highly sensitive chirality sensing system toward a small amount of chiral amines and amino acids when complexed with BArF- .

Effect of Oxidation on the Chiroptical Properties of Sulfur-Bridged Binaphthyl Dimers.

A series of axially chiral sulfur-bridged dimers were prepared from 1,1'-binaphthyl-2,2'-diol and subsequently oxidized to the respective sulfones. The chiroptical properties of the chiral chromophores were studied as a function of the oxidation state. Upon oxidation, an increase in quantum yields was observed for directly linked sulfur bridged binaphthyls (0.04 to 0.32), and a modest increase in dissymmetry factor was observed for diphenylsulfide-bridged binaphthyls (-8.9 × 10-4 to -1.4 × 10-3). Computational calculations were used to elucidate the changes in photophysical properties.

Full Control of the Chiral Overpass Effect in Helical Polymers: P/M Screw Sense Induction by Remote Chiral Centers After Bypassing the First Chiral Residue.

In helical polymers, helical sense induction is usually commanded by teleinduction mechanism, where the largest substituent of the chiral residue directly attached to the main chain is the one that commands the helical sense. In this work, different helical structures with different helical senses are induced in a helical polymer [poly-(phenylacetylene)] when the conformational composition of two different dihedral angles of a pendant group with more than two chiral residues is tamed. Thus, while the dihedral angle at chiral residue 1 [(R)- or (S)-alanine], attached to the backbone, produces an extended or bent conformation in the pendant resulting in two scaffolds with different stretching degree, the second dihedral angle at chiral residue 2 [(R)- or (S)-methoxyphenylacetamide] places the substituents of this chiral center in a different spatial orientation, originating opposite helical senses at the polymer that are induced through a total control of the "chiral overpass effect".

Non-uniform Self-folding of Helical Poly(fluorenevinylene) Derivatives in the Solid State Leading to Amplified Circular Dichroism and Circularly Polarized Light Emission.

An unprecedented non-uniform self-folding of artificial polymer chains composed of turn moieties and stretched segments is presented through the design of a set of optically active poly(fluorene-2,7-diylethene-1,2-diyl) (poly(fluorenevinylene)) derivatives bearing a neomenthyl group and a pentyl group attached at the 9-position of fluorene backbone at various ratios. The folded structure is formed and stabilized through inter-chain interactions in the solid state, leading to remarkably enhanced chiroptical properties (chirality amplification) in terms of circular dichroism (CD) and circularly polarized light (CPL) emission. This phenomenon is rationalized by experimental and theoretical CD and CPL spectral analyses. The polymer arrangements in the solid state were further assessed through transmission electron microscopic observations combined with enhanced sampling molecular dynamics simulations in the solid state revealing the thin film organizations.

Cross-linked dithiocarbamate-modified cellulose with enhanced thermal stability and dispersibility as a sorbent for arsenite removal.

Numerous reports have described dithiocarbamate (DTC)-modified cellulose sorbents that can selectively separate metal ions from water. We have previously synthesized a novel sorbent modified with DTC containing N-heterocycles in the backbone for the selective removal of hazardous metal ions. The sorbent was found to partially dissolve and aggregate in solution, reducing its sorption capacity. In this study, to prepare the sorbent for use as a soli-phase extraction material for the removal of arsenite (AsIII) ions, we attempted to decrease the solubility of the sorbent. The sorbent was cross-linked with epoxy or complexed with iron, and the quantities of the modifiers were varied between 3.0 and 10 mol%. As a result, the iron-complexed sorbents were still partially soluble, and cross-linkage with 6.0 mol% of epoxy made the sorbent almost insoluble and dispersed in solution. This sorbent also exhibited the highest AsIII sorption performance among the sorbents synthesized in this study. Although DTC-modified polymers are reported to lose their sorption capability after storage at 40 °C, the sorbent was found to be thermally stable. The optimum contact time and pH for AsIII removal were 20 min and 3.0, respectively. The maximum sorption capacity of the epoxy-cross-linked sorbent, calculated from the Langmuir isotherm equation, was 600 µmol g-1 (45 mg g-1) at 25 °C. Additionally, the sorbent was highly selective toward AsIII compared with previously reported sorbents and capable of removing approximately 97% of AsIII from environmental water. In conclusion, cross-linking enhances the stability of the sorbents in solutions, which facilitates the removal of AsIII from environmental water.

Enantioseparation on helical poly(diphenylacetylene)s bearing optically-active pendants: Effects of differences in higher-order structures of kinetically-trapped and thermodynamically-stable states on chiral recognition ability.

An optically-active poly(diphenylacetylene) (PDPA) bearing carboxy pendant groups with left-handed helicity memory (M-h-poly-1), synthesized using the noncovalent helicity-induction-and-memory strategy, was converted into a PDPA bearing optically-active pendant groups through an amide bonding (M-hKT-poly-2S), while maintaining the left-handed helicity memory, by reaction with (S)-1-phenylethylamine ((S)-2) using a condensing reagent at room temperature. Its chiral recognition ability was investigated as a chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC). M-hKT-poly-2S exhibited significantly different chiral recognition ability towards racemates compared to the previously reported corresponding helical PDPA bearing the same optically-active pendant groups (M-hTS-poly-2S) (prepared by the reaction of an optically-inactive PDPA bearing carboxy pendants with (S)-2, followed by thermal annealing, to induce a left-handed helical structure in the polymer main chain). Although the main chains of both M-hKT-poly-2S and M-hTS-poly-2S formed almost completely left-handed helical structures, their higher-order structures varied slightly, as confirmed by various spectroscopic methods (UV-Vis, circular dichroism (CD), IR, and vibrational CD). M-hKT-TS-poly-2S, the PDPA formed on the thermal annealing of M-hKT-poly-2S, exhibited the same higher-order structure and chiral discrimination ability as M-hTS-poly-2S. Therefore, slight differences in the higher-order structures of the kinetically-trapped metastable state (M-hKT-poly-2S) and the thermodynamically-stable state (M-hTS-poly-2S), due to differences in synthetic procedures, significantly impact their chiral recognition abilities as CSPs, even with identical primary structures and helix-sense of the polymer main chain.

Well-Controlled Living Polymerization of Phenylacetylenes in Water: Synthesis of Water-Soluble Stereoregular Telechelic Poly(phenylacetylene)s.

Well-controlled living polymerization of water-soluble phenylacetylene derivatives in water was achieved for the first time using a multicomponent catalytic system consisting of [Rh(nbd)Cl]2 , an aryl boronic acid, diphenylacetylene having carboxy groups, a tetraalkylammonium hydroxide, and a water-soluble triphenylphosphine. This catalytic system enables a direct synthesis of various water-soluble cis-stereoregular poly(phenylacetylene)s having a narrow molecular weight distribution, the molecular weight of which can be controlled by the initial feed ratio of the monomer to the catalyst. Moreover, the syntheses of water-soluble telechelic poly(phenylacetylene)s having various functional groups at both chain ends as well as a water-soluble block copolymer were achieved.

Well-Controlled Living Polymerization of N-Propargylamides and Their Derivatives by Rhodium Catalysis.

A substantially improved method for living polymerization of N-propargylamides and their derivatives has been developed. Rhodium(I) complexes bearing an aryl-substituted 1,3,5-hexatriene chain can work as excellent initiators of the polymerization of such non-conjugated terminal alkynes to give the corresponding cis-stereoregular polymers having a narrow molecular weight distribution. The typical living nature has been confirmed by investigating the effects of initial feed ratios of the monomer to the initiator on the molecular weight of the resulting polymers as well as multistage polymerization. Moreover, we demonstrated that the present method enables functionalization of both polymer chain ends and synthesis of novel block copolymers consisting of poly(N-propargylamide) and poly(phenylacetylene) blocks with a narrow molecular weight distribution.

Solvent-dependent helix inversion in optically active poly(diphenylacetylene)s and their chiral recognition abilities as chiral stationary phases for high-performance liquid chromatography.

We report the first example of solvent-dependent helix inversion in poly(diphenylacetylene) (PDPA) derivatives. Asymmetrically substituted PDPAs bearing optically active substituents linked through amide bonds formed preferred-handed helical conformations because of the optically active substituents in the pendants, whose helix-senses were inverted upon thermal annealing in polar solvents such as N,N-dimethylformamide and dimethylsulfoxide and in nonpolar solvents such as tetrachloroethane. Unlike the solvent-dependent helix inversion reported for other dynamic helical polymers, the macromolecular helicity induced in the polymer backbone of these PDPAs upon thermal annealing was stably maintained at room temperature, independent of the solvent polarity. These diastereomeric PDPAs with opposite helix-senses generated almost mirror-imaged left- and right-handed circularly polarized light in the same solvent at room temperature. Taking advantage of this unique solvent-dependent helix inversion property, the diastereomeric PDPAs with opposite helix-senses were coated on macroporous silica gel and applied to chiral stationary phases for high-performance liquid chromatography. Despite having the same optically active substituents on the pendant phenyl rings, they showed completely different chiral recognition abilities toward many racemates depending on the helix-sense of the polymer backbone, and the elution order of the enantiomers was reversed for some racemates. The combination of the helix-sense of the polymer backbone and the chirality of the pendants, which afforded a higher chiral recognition ability, differed depending on the racemates.

Speciation analysis of inorganic selenium in wastewater using a highly selective cellulose-based adsorbent via liquid electrode plasma optical emission spectrometry.

Speciation of selenium (Se) is typically carried out using a sophisticated technique such as ICP-MS after preconcentration using an adsorbent; however, the separation and preconcentration of inorganic Se has not been realized in the solutions containing high concentrations of SO42-. A dithiocarbamate-modified cellulose (DMC) was used in this study for the selective extraction and preconcentration of inorganic Se in wastewater, with a portable liquid electrode plasma-optical emission spectrometry (LEP-OES) being employed for quantification. DMC was found to selectively and quantitatively adsorb selenite (SeIV) over a wide range of pH (1.0-8.0); however, less than 3.0% of selenate (SeVI) was adsorbed in a pH range of 3.0-11. Quantitative extraction of SeIV was achieved even in the presence of 3.5 mol L-1 SO42-. The maximum sample volume from which 10 mg of DMC could quantitatively extract SeIV was found to be 500 mL. KOH (0.60 mL, 1.5 mol L-1) was found to quantitatively desorb SeIV retained on the adsorbent and yielded an enrichment factor of 833. The recovery of Se species from synthetic flue-gas desulfurization wastewater containing SeIV and SeVI at concentrations of 5.0 µmol L-1 was 96.2 ± 1.8% and 105.8 ± 1.8%, respectively.