High-Intensity Circular Dichroism of Head-To-Tail Regioregular Poly(1,4-Phenylene)s in the Aggregated State.

Circular dichroism (CD) studies on poly(1,4-phenylene)s bearing a chiral side chain in the aggregated conditions were carried out. Little CD was observed in a solution form, while addition of a poor solvent into the polyphenylene solution induced aggregation and a strong CD was observed, accordingly. Applying the controlled degree of polymerization (DP) of poly(1,4-phenylene) in the use of bidentate diphosphine Chiraphos as a ligand for the nickel catalyst, the relationship of DP with CD strength was studied to reveal to show the highest CD at the DP=84 (gabs=ca. 2×10-2). It was also found that the related aggregation was observed in good solvent 1,2-dichloroethane upon standing the solution at 4 °C for 3-23 days to observe gabs=ca. 10-1. Studies on the substituent effect of poly(1,4-phenylene) suggested that CD behaviors were dependent on the type of non-chiral substituent on the aromatic ring as well as the side-chain chirality.

Temperature-Dependent Left- and Right-Twisted Conformational Changes in 1:1 Host-Guest Systems: Theoretical Modeling and Chiroptical Simulations.

An efficient strategy for high-performance chiral materials is to design and synthesize host molecules with left- and right- (M- and P-) twisted conformations and to control their twisted conformations. For this, a quantitative analysis is required to describe the chiroptical inversion, chiral transfer, and chiral recognition in the host-guest systems, which is generally performed using circular dichroism (CD) and/or proton nuclear magnetic resonance (1H-NMR) spectroscopies. However, the mass-balance model that considers the M- and P-twisted conformations has not yet been established. In this study, we derived the novel equations based on the mass-balance model for the 1:1 host-guest systems. Then, we further applied them to analyze the 1:1 host-guest systems for the achiral calixarene-based capsule molecule, achiral dimeric zinc porphyrin tweezer molecule, and chiral pillar[5]arene with the chiral and/or achiral guest molecules by using the data obtained from the CD titration, variable temperature CD (VT-CD), and 1H-NMR experiments. The thermodynamic parameters (ΔH and ΔS), equilibrium constants (K), and molar CD (Δε) in the 1:1 host-guest systems could be successfully determined by the theoretical analyses using the derived equations.

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.

One-Handed Helical Polyacetylenes Bearing Axially-Chiral 2-Arylpyridyl-N-Oxide Units for Efficient Chromatographic Enantioseparation of Chiral Aromatic and Aliphatic Alcohols.

A series of poly(biarylylacetylene)s (PBAs) bearing axially-chiral (S)-and (R)-pyridyl-N-oxide residues with a methoxy, propoxy, or acetyloxy substituent at the 3-position of the biaryl units was synthesized. All the PBAs formed a preferred-handed helix, while the helical sense preference was varied depending on the substituents despite the same twist-sense of the biaryl units. Among them, the propoxy-bound helical PBA showed an exceptionally high chiral recognition ability as a chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC) and efficiently resolved not only various chiral aromatic alcohols, but also a variety of chiral aliphatic alcohols; the latter still remains difficult to resolve by commercially-available CSPs in HPLC. Such practically-useful both handed helical PBA-based CSPs can be produced from the racemic PBA composed of fully racemic monomer units through deracemization of the biaryl units with a chiral alcohol.

Supramolecular Helical Assemblies of Dirhodium(II) Paddlewheels with 1,4-Diazabicyclo[2.2.2]octane: A Remarkable Substituent Effect on the Helical Sense Preference and Amplification of the Helical Handedness Excess of Metallo-Supramolecular Helical Polymers.

We report unique coordination-driven supramolecular helical assemblies of a series of dirhodium(II) tetracarboxylate paddlewheels bearing chiral phenyl- or methyl-substituted amide-bound m-terphenyl residues with triethylene glycol monomethyl ether (TEG) or n-dodecyl tails through a 1:1 complexation with 1,4-diazabicyclo[2.2.2]octane (DABCO). The chiral dirhodium complexes with DABCO in CHCl3/n-hexane (1:1) form one-handed helical coordination polymers with a controlled propeller chirality at the m-terphenyl groups, which are stabilized by intermolecular hydrogen-bonding networks between the adjacent amide groups at the periphery mainly via a cooperative nucleation-elongation mechanism as supported by circular dichroism (CD), vibrational CD, and variable-temperature (VT) absorption and CD analyses. The VT visible-absorption titrations revealed the temperature-dependent changes in the degree of polymerization. The columnar supramolecular helical structures were elucidated by X-ray diffraction and atomic force microscopy. The helix sense of the homopolymer carrying the bulky phenyl and n-dodecyl substituents is opposite those of other chiral homopolymers despite having the same absolute configuration at the pendants. A remarkably strong "sergeants and soldiers" (S&S) effect was observed in most of the chiral/achiral copolymers, while the copolymers of the bulky chiral phenyl-substituted dirhodium complexes with n-dodecyl chains displayed an "abnormal" S&S effect accompanied by an inversion of the helix sense, which could be switched to a "normal" S&S effect by changing the solvent composition. A nonracemic dirhodium complex of 20% enantiomeric excess bearing the less bulky chiral methyl substituents with n-dodecyl chains assembled with DABCO to form an almost one-handed helix (the "majority rule" (MR) effect), whereas the three other nonracemic copolymers showed a weak MR effect.

Emergence of Highly Enantioselective Catalytic Activity in a Helical Polymer Mediated by Deracemization of Racemic Pendants.

Any polymers composed of racemic repeating units are obviously optically inactive and hence chiral functions, such as asymmetric catalysis, will not be expected at all. Contrary to such a preconceived notion, we report an unprecedented helical polymer-based highly enantioselective organocatalyst prepared by polymerization of a racemic monomer with no catalytic activity. Both the right- and left-handed helical poly(biarylylacetylene)s (PBAs) composed of dynamically racemic 2-arylpyridyl-N-oxide monomer units with N-oxide moieties located in the vicinity of the helical polymer backbone can be produced by noncovalent interaction with a chiral alcohol through deracemization of the biaryl pendants. The macromolecular helicity and the axial chirality induced in the PBAs are retained ("memorized") after complete removal of the chiral alcohol. Accordingly, the helical PBAs with dual static memory of the helicity and axial chirality show remarkable enantioselectivity (86% ee) for the asymmetric allylation of benzaldehyde. The enantioselectivity is slightly lower than that (96% ee) of the homochiral PBAs prepared from the corresponding enantiopure (R)- and (S)-monomers, but is comparable to that (88% ee) of the helical PBA composed of nonracemic monomers of ca. 60% ee.

Kinetic Study of Chiral Intermolecular Interactions by Moment Analysis Based on Affinity Capillary Electrophoresis.

Capillary electrophoresis is a method for analyzing intermolecular interactions that does not require immobilization of molecules to a solid surface or introduction of a luminescent moiety. Recently, an advanced method, moment analysis based on affinity capillary electrophoresis (MA-ACE), was developed. This method can determine not only the equilibrium constant but also the rate constants of an intermolecular interaction. Through MA-ACE, it became possible to theoretically predict an increase in the variance of an observed peak caused by intermolecular interaction. In this study, we confirm the prediction and determine the kinetic constants by using MA-ACE to analyze an intermolecular interaction between cyclodextrin and phenoxypropionic acid. A numerical calculation is performed to confirm that the derived rate constants by MA-ACE are appropriate.

Ambidextrous Chirality Transfer Capability from Cellulose Tris(phenylcarbamate) to Nonhelical Chainlike Luminophores: Achiral Solvent-Driven Helix-Helix Transition of Oligo- and Polyfluorenes Revealed by Sign Inversion of Circularly Polarized Luminescence and Circular Dichroism Spectra.

We investigated whether helicity and/or chirality of cellulose tris(phenylcarbamate) (CTPC) can transfer to noncharged, nonhelical oligo- and polyfluorenes when CTPC was employed as a solution processable homochiral platform of a D-glucose-skeletal polymer. Noticeably, CTPC revealed the solvent-driven, ambidextrous intermolecular helicity/chirality transfer capability to these fluorenes. The chiroptical inversion characteristics of circularly polarized luminescence (CPL) and the corresponding CD spectra were realized by solely choosing a proper achiral solvent and/or achiral cosolvent. When the solution of PF6 and CTPC in tetrahydrofuran (THF) was cast on a quartz substrate, the dissymmetry ratio of CPL (gCPL) from the polymer film showed gCPL = +2.1 × 10-3 at 429 nm. Conversely, when dichloromethane (DCM) was used as the solvent, the CPL sign was inverted to gCPL = -2.4 × 10-3 at 429 nm. The dissymmetry ratio of Cotton CD band (gCD) from the THF solution was gCD = +3.2 × 10-3 at 392 nm; conversely, from the DCM, the CD sign inverted to gCD = -0.8 × 10-3 at 371 nm. The sign and magnitude of the gCD values were interpreted to a London dispersion term (δd) of Hansen solubility parameter (δ) of the casting solvents rather than a dipole-dipole interaction term (δp) and a hydrogen bonding interaction term (δh) of the δ values and dielectric constant (ε). Analysis of solvent-driven changes in FTIR spectra, wide-angle X-ray diffraction profiles, and differential scanning calorimetry diagrams indicated that solvent driven on-off switching of multiple hydrogen bonds due to three urethane groups of CTPC play the key for the inversion. Intermolecular CH/π and π-π interactions among phenyl rings and alkyl groups were assumed to be crucial for helicity/chirality transfer capability based on molecular mechanics and molecular dynamics simulations of PF6-CTPC hybrids. These chiroptical inversion characteristics arose from solvent-driven order-disorder transition characteristics of the CTPC helix rather than a helix-helix transition of CTPC itself.

Evaluation of Migration Time and Variance for Accurate Kinetic Studies Based on Affinity Capillary Electrophoresis.

Affinity capillary electrophoresis (ACE) has been widely applied to evaluate binding constants of various systems. Recently, moment equations were derived based on the moment analysis (MA) theory for describing the influence of reaction kinetics and longitudinal diffusion on the elution peak profiles measured by ACE (MA-ACE). The equations enable one to obtain not only the binding constants but also the reaction rate constants from the migration time and variance of elution peaks. However, it is necessary to consider other factors (e.g., sample injection, detector window, Joule heating, and ramp time of the voltage increase) to improve the accuracy of MA-ACE. The variance of these effects was quantified under typical experimental conditions. Such quantification clarified the process to obtain the rate constants. The best experimental conditions to achieve high accuracy were discussed.

Enhancing circularly polarised luminescence by extending the π-conjugation of axially chiral compounds.

Circularly polarised luminescence (CPL) and photoluminescence (PL) properties of π-conjugated (R)- and (S)-2,2'-diphenyl-4-biphenanthrol (VAPOL) exhibited an efficient CPL (∼1.3 × 10(-3)) with a quantum yield (ΦF) of 0.20 at 376 nm. By comparison, (R)- and (S)-3,3-diphenyl-2,2-bi-1-naphthol (VANOL) exhibited no CPL or PL.

Chiroptical inversion in helical Si-Si bond polymer aggregates.

To elucidate the factors involved in the chiroptical properties of polymer aggregates composed of helical building blocks, a series of rigid rod helical poly[alkyl-(S)-2-methylbutylsilane]s (achiral alkyl side chains = ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl) have been investigated. It was found that the chiroptical sign in the circular dichroism (CD) spectra of the polysilane aggregates depends on the achiral side chain length and cosolvent fraction. Concerning the achiral side chains, the n-propyl group was of a critical length for solvent-dependent chiroptical inversion on aggregation. This unique side chain length-dependent chiroptical inversion was theoretically predictable by using the novel approach of combining the cholesteric hard-core model and exciton chirality method. The latter was also investigated theoretically by Gaussian 03 (TD-DFT, B3LYP, 6-31G(d) basis set) calculations applied to two spatially arranged helical Si-Si bonded decamer models.

Optically active conjugated polymer from solvent chirality transfer polymerization in monoterpenes.

Disubstituted acetylene monomers [1,2-diphenylacetylenes (DPAs: DPA-pC1, DPA-mC1, DPA-pC8); 1-phenyl-2-hexylacetylene (PHA-pC1)] are tested for asymmetric polymerization in chiral monoterpenes used as solvents and compared with the corresponding monosubstituted acetylene monomer [1-phenylacetylene (PA-pC1)]. DPA-pC1 containing a trimethylsilyl group in the para-position of the phenyl ring produces an optically active polymer with a large Cotton effect, despite the absence of a stereogenic center. The polymer sample obtained by polymerization in 87% ee (-)-α-pinene shows the strongest CD signal (gCD value at 385 nm: ∼3.2 × 10⁻³). The Cotton bands of the polymers obtained in (-)- and (+)-α-pinenes show the opposite sign in the CD signals. Theoretical calculations show that only the cis-cisoid model adopts a helical conformation. A time-correlated single photon counting experiment shows that the emission of the chiral polymer originates from a virtually single excited species with a 98% component fraction. This polymer solution does not show any significant decrease in gCD value over a wide temperature range of 20 to 80 °C. No noticeable decrease in the gCD value is detected when the polymer solution is kept at relatively low temperatures for a prolonged period (35 d). In contrast, the other polymers show no CD signal.

Rapidly progressive and fatal neurocutaneous melanosis presenting as recurrent headache.

Neurocutaneous melanosis is an extremely rare disease characterized by large or multiple congenital melanocytic nevi and benign or malignant proliferation of melanocytes in the central nervous system. Neurological manifestations usually develop during the first three years of life and the prognosis of patients with NCM who manifest neurological symptoms is very poor. Here we describe a 9-year-old girl who manifested neurological symptoms caused by communicating hydrocephalus and died of proliferation of melanocytes in the central nervous system 11 months after the initial symptoms. Serum and cerebrospinal fluid 5-S-CD levels could be a useful marker of disease progression, even in patients with NCM without apparent malignant findings at initial biopsy.

Liquid-phase photo-induced covalent modification (PICM) of single-layer graphene by short-chain fatty acids.

We report an efficient photo-induced covalent modification (PICM) of graphene by short-chain fatty acids (SCFAs) with an alkyl chain at the liquid-solid interface for spatially resolved chemical functionalization of graphene. Light irradiation on monolayer graphene under an aqueous solution of the SCFAs with an alkyl chain efficiently introduces sp3-hybridized defects, where the reaction rates of PICM are significantly higher than those in pure water. Raman and IR spectroscopy revealed that a high density of methyl, methoxy, and acetate groups is covalently attached to the graphene surface while it was partially oxidized by other oxygen-containing functional groups, such as OH and COOH. A greater downshift of the G-band in Raman spectra was observed upon the PICM with longer alkyl chains, suggesting that the charge doping effect can be controlled by the alkyl chain length of the SCFAs. The systematic research and exploration of covalent modification in SCFAs provide new insight and a potentially facile method for bandgap engineering of graphene.

A light-mediated covalently patterned graphene substrate for graphene-enhanced Raman scattering (GERS).

We report covalently patterned graphene with acetic acid as a new potential candidate for graphene-enhanced Raman scattering (GERS). Rhodamine 6G molecules in direct contact with the covalently modified region show an enormous enhancement (∼25 times) compared to the pristine region at 532 nm excitation. The GERS enhancement with respect to the layer thickness of the probed molecule, excitation wavelength, and covalently attached groups is discussed.

Understanding nonlinear composition dependency of enantioselectivity in chiral separation using mixed micelle.

HYPOTHESIS: Mixtures of chiral and achiral building blocks of supramolecules exhibit interesting cooperative phenomena, indicated by the nonlinear composition dependence of the chiral properties. However, the nonlinear composition dependence of the enantioselectivity of mixed micelles is not well understood. It was hypothesized that in-depth understanding can be achieved by carefully investigating the composition dependence of the properties. EXPERIMENTS: In this work, the nonlinear composition dependence of the enantioselectivity was found for the mixed micelle of achiral and chiralN-acyl amino acids by micellar electrokinetic chromatography (MEKC). Capillary electrophoresis, circular dichroism (CD) spectroscopy, surface tension measurement, and fluorescence spectroscopy were used to investigate the mechanisms. FINDINGS: Four mechanisms that could be causing the nonlinearity were investigated: (i) synergistic and antagonistic interactions of the surfactants; (ii) the chiral transfer from chiral to achiral surfactant; (iii) differences in the retention factor; and (iv) cooperative chiral recognition of the chiral and achiral surfactant. The investigation of the composition dependency of critical micelle concentration (CMC) and molar circular dichroism revealed that the effect of (i) and (ii) was negligibly small. The newly derived equations for (iii) and (iv) revealed that (iii) and (iv) have a major or medium effect on the nonlinear enantioselectivity.

Irregular and suppressed elastic deformation by a structural twist in cellulose nanofibre models.

The elastic responsiveness of single cellulose nanofibres is important for advanced analysis of biological tissues and their use in sophisticated functional materials. However, the mechanical responsiveness derived from the twisted structure of cellulose nanofibres (CNFs) has remained unexplored. In this study, finite element simulations were applied to characterize the deformation response derived from the torsional structure by performing tensile and bending tests of an unconventionally very long and twisted rod model, having the known dimensional parameters and properties of CNFs. The antagonistic action of two types of structural elements (a contour twist and a curvilinear coordinate) was found to result in an irregular deformation response but with only small fluctuations. The contour twist generated rotational displacements under tensile load, but the curvilinear coordinate suppressed rotational displacement. Under bending stress, the contour twist minimized irregular bending deformation because of the orthotropic properties and made the bending stress transferability a highly linear response.

One-Step Simultaneous Synthesis of Circularly Polarized Luminescent Multiple Helicenes Using a Chrysene Framework.

A series of multiple helicenes was simultaneously synthesized in one step by intramolecular cyclization of a single chrysene derivative containing two 2-[(4-alkoxyphenyl)ethynyl]phenyl units accompanied by rearrangements of the aryl pendants. The electrophile-induced double cyclization with or without aryl migrations proceeded efficiently under acidic conditions to afford annulative π-extension of the chrysene units and produced quadruple (QH-2), triple (TH-2), and double (DH-2) helicenes containing [4]- and/or [5]helicene frameworks with dynamic and/or static helicene chirality in one step. Three multiple helicenes' structures were determined by X-ray crystallography and/or density functional theory calculations. The multiple TH-2 and DH-2 helicenes were separated into enantiomers because of the stable one and two [5]helicene moieties, respectively, and showed intense circular dichroism and circularly polarized luminescence. Although QH-2, which comprises four [4]helicene subunits, was not resolved into enantiomers, the TH-2 enantiomers were further separated into a pair of diastereomers at low temperature resulting from their substituted [4]helicene chirality.

Moment Analysis of Mass Transfer Kinetics in Micellar Electrokinetic Chromatography Systems.

Moment equations were developed for quantitatively studying the separation characteristics of micellar electrokinetic chromatography (MEKC). They explain how the first absolute and second central moments of elution peaks are correlated with some fundamental parameters of the partition equilibrium and mass transfer kinetics in MEKC systems. In order to discuss the influence of the mass transfer kinetics on peak broadening, the moment equations were used to analyze the separation behavior in MEKC systems. Separation conditions were chosen on the basis of practical MEKC experiments previously conducted. It was quantitatively clarified that both the solute permeation at the interfacial boundary of surfactant micelles and axial diffusion of solute molecules in a capillary had a predominant contribution to the spreading of the elution peaks in MEKC systems. This is a preliminary study for the analytical determination of rate constants concerning solute permeation at the interface of surfactant micelles from elution peak profiles measured by MEKC. In addition, it was also indicated that the experimental conditions of MEKC systems could be controlled so that the interfacial solute permeation would have a predominant role for the band broadening. For example, the contribution of the interfacial permeation was about 33 times larger than that of the axial diffusion of solute molecules under the MEKC conditions in a previous study. This means that the rate constants could appropriately be determined for the interfacial solute permeation.

Characteristics of the Japanese Diet Described in Epidemiologic Publications: A Qualitative Systematic Review.

CONTEXT: International interest in the Japanese diet has grown in recent years. OBJECTIVE: The aim of this systematic review was to evaluate and organize the Japanese diet and dietary characteristics from an epidemiological perspective, mainly focusing on the nutritional and dietary elements. DATA SOURCES: PubMed, Web of Science, Japan Medical Abstracts Society, JDream III, and CiNii databases were searched. STUDY SELECTION: The eligibility criteria included research with an epidemiological study design that was either cross-sectional, cohort, or case-control-based that defined the dietary patterns of the Japanese diet using dietary pattern analysis. A total of 39 research articles that described the Japanese diet were included. DATA EXTRACTION: The data that were extracted included the following: implementing country, location, study design, participant characteristics, key outcomes, methods used in the analysis of dietary patterns, and descriptions of the Japanese diet. DATA SYNTHESIS: As a result of the systematic review analyzing the descriptions of the Japanese diet from 39 selected articles, we were able to aggregate the descriptions into 16 categories from 33 factors. After performing a content analysis using a further aggregation of categories, we found that the top three applicable categories were soybeans/soybean-derived products, seafood, and vegetables; these were followed by rice and miso soup. CONCLUSION: The Japanese dietary content was found to be diverse based on an examination of epidemiological studies; however, we were able to aggregate the content into 16 categories. The Japanese diet is considered to be a dietary pattern that contains a combination of factors: the dietary staple, side dishes, and soup.