Yukiteru Katsumoto

Relationship between the Broad OH Stretching Band of Methanol and Hydrogen-Bonding Patterns in the Liquid Phase

The OH stretching (nu(OH)) band of methanol observed in condensed phase has been analyzed in terms of hydrogen-bonding patterns. Quantum chemical calculations for methanol clusters have revealed that broadening of the nu(OH) envelope is reasonably reproduced by considering nearest and next-nearest neighbor interactions through hydrogen bonding. Because the hydrogen bond formed between donor (D) and acceptor (A) is cooperatively strengthened or weakened by a newly formed hydrogen bond at D or A, we have proposed the following notation for hydrogen-bonding patterns of monohydric alcohols: a(D)DAd(A)a(A), where a is the number of protons accepted by D (a(D)) or A (a(A)), and d(A) is the number of protons donated by A. The indicator of the hydrogen-bond strength, which is given by M(OH) = a(D) + d(A) - a(A), is correlated well with the nu(OH) wavenumber of the methanol molecule D participating in the a(D)DAd(A)a(A) pattern. The correlation between M(OH) and the hydrogen-bonding energy of the a(D)DAd(A)a(A) pattern has also been deduced from the calculation results for the clusters. The nu(OH) bands of methanol measured in the CCl4 solution and pure liquid have been successfully analyzed by the method proposed here.

Molecular understanding of the UCST-type phase separation behavior of a stereocontrolled poly(N-isopropylacrylamide) in bis(2-methoxyethyl) ether.

The upper critical solution temperature (UCST)-type phase separation of an isotactic-rich poly( N-isopropylacrylamide) (PNiPA) in bis(2-methoxyethyl) ether (diglyme) has been investigated by turbidity measurement and infrared (IR) spectroscopy. The IR spectra of stereocontrolled PNiPAs in various solvents have clearly indicated that the amide I bands do not directly reflect the tacticity of the polymer. The relative intensity of the amide I bands changes depending upon the molecular environment around the amide groups of PNiPA, which is influenced by the tacticity. During the UCST-type phase separation of the isotactic-rich PNiPA in diglyme, the amide I band at around 1625 cm (-1) changes. To link the IR spectral change with the molecular information, quantum chemical calculations have been carried out for NiPA n-mers ( n = 1-4) with an isotactic stereosequence. The result has suggested that the amide I band at around 1625 cm (-1) arises from a helical structure formed by the isotactic stereosequences in the PNiPA main chain with the aid of intramolecular CO...H-N hydrogen bonding. The experimental IR spectra have revealed that the helical structures are unfolded as the temperature rises. The folding and unfolding of the isotactic sequences in the main chain may induce the thermal change in the solubility of the isotactic rich PNiPA in diglyme, resulting in the UCST-type phase separation of the solution.

Near-Infrared Spectroscopic Study of Interaction Between Methyl Group and Water in Water–Methanol Mixtures

Near-infrared spectra were measured for water–methanol mixtures with a methanol content of 0–100 wt % at 25 °C. The second derivative of the NIR spectra clearly reveals that the first overtones of the CH3 asymmetric stretching modes of methanol near 5950 and 5900 cm−1 show a downward shift by about 30 cm−1 with the increase in the concentration of methanol. This is unambiguous evidence for the direct interaction of the CH3 group of methanol with the OH group of water. Similar downward shifts were also observed for water–ethanol and water–1-propanol mixtures, although the shifts are much smaller for the water–ethanol and water–1-propanol mixtures. Based upon the results of NIR spectra, we propose a model for the interaction between the C–H bond of the CH3 group of methanol and water. This intermolecular interaction is analogous to the intramolecular “(O) CH … O” interaction in compounds having both a CH3 group binding to an oxygen atom and an OH group. This paper demonstrates novel potential of NIR spectroscopy in investigating interactions containing a C–H bond.

Practical Algorithm for Reducing Convex Spike Noises on a Spectrum

Quantitative data analysis and high-sensitivity measurements by use of Raman and infrared spectroscopy often suffer from noisy spikes such as those due to cosmic rays and water vapor. Since these spikes are unidirectional and isolated, the conventional smoothing techniques do a poor job of removing them. However, a small modification can improve these smoothing techniques significantly. In this paper, we present a simple denoising technique for a single-scan spectrum that is corrupted by convex spikes. In general, the noisy spikes arising from cosmic rays or water vapor have a much narrower bandwidth compared with target “informative” bands in Raman and infrared spectra. This means that these noisy spikes can be separated from the target bands by means of the difference in the bandwidths. The proposed method employs the moving window averaging procedure to distinguish and separate the convex spike. The proposed algorithm allows us to take away the convex spikes from measured spectra without preparing multiply recorded spectra and (much) biasing the measured spectrum.

Thermoreversible gelation of isotactic-rich poly(N-isopropylacrylamide) in water

We report the experimentally determined phase diagram for an aqueous solution of isotactic-rich poly(N-isopropylacrylamide) (PNiPAM) composed of the sol-gel transition curve and the cloud-point curve. The meso diad content of isotactic-rich PNiPAM is 64%, and it is soluble in water at low temperatures, but undergoes a sol-to-gel transition with increasing temperature in the investigated concentration range of 1.8 wt. %-6.0 wt. %. With a further increase in temperature, the system becomes turbid. The gel formation and clouding behavior are thermally reversible. This is the first observation of thermoreversible gelation under the cloud-point temperature for an aqueous solution of PNiPAM. On the basis of the determined phase diagram, we carried out light scattering experiments to characterize the sol-gel transition behavior as a function of temperature.

Molecular Approach To Understand the Tacticity Effects on the Hydrophilicity of Poly(N-isopropylacrylamide): Solubility of Dimer Model Compounds in Water

Although it has been suggested that the tacticity affects the hydrophilicity of poly(N-isopropylacrylamide) (PNiPA), little is known about the physical background of this phenomenon. In this study, we investigated the solubility of the dimer model compounds (DNiPA). The partition coefficient of DNiPA in the two phases of a water/chloroform mixture has indicated that DNiPA with the racemo configuration (r-DNiPA) is more soluble in water than DNiPA with the meso configuration (m-DNiPA). The difference of the hydration free energy between m- and r-DNiPA is estimated to be 1.2 kJ mol(-1). The molecular mechanics (MM) calculations with the GB/SA model have revealed that r-DNiPA in water is more stable by ca. 1 kJ mol(-1) than m-DNiPA, which is in excellent agreement with the experimental result. The MM calculations have also indicated that the intramolecular interaction of m-DNiPA is stronger than that of r-DNiPA, while r-DNiPA is advantageous in terms of the hydration free energy and conformational entropy.

Rubber elasticity for incomplete polymer networks

We investigated the relationship between the elastic modulus, G and the reaction probability, p for polymer networks. First, we pointed out that the elastic modulus is expressed by G = {(fp∕2 - 1) + O((p - 1)(2))} Nk(B)T∕V (percolated network law), which does not depend on the local topology of the network structure or the existence of the loops. Here, N is the number of lattice point, V is the system volume, f is the functionality of the cross-link, k(B) is the Boltzmann constant, and T is the absolute temperature. We also conducted simulations for polymer networks with triangular and diamond lattices, and mechanical testing experiments on tetra-poly(ethylene glycol) (PEG) gel with systematically tuning the reaction probability. Here, the tetra-PEG gel was confirmed to be a potential candidate for ideal polymer networks consisting of unimodal strands free from defects and entanglements. From the results of simulations and experiments, it was revealed, for the first time, that the elastic modulus obeys this law in the wide range of p (p(c) ≪ p ≤ 1), where p(c) is the reaction probability at gelation threshold.

Multivariate analysis of DSC–XRD simultaneous measurement data: a study of multistage crystalline structure changes in a linear poly(ethylene imine) thin film

AbstractA multivariate analytical technique has been applied to the analysis of simultaneous measurement data from differential scanning calorimetry (DSC) and X-ray diffraction (XRD) in order to study thermal changes in crystalline structure of a linear poly(ethylene imine) (LPEI) film. A large number of XRD patterns generated from the simultaneous measurements were subjected to an augmented alternative least-squares (ALS) regression analysis, and the XRD patterns were readily decomposed into chemically independent XRD patterns and their thermal profiles were also obtained at the same time. The decomposed XRD patterns and the profiles were useful in discussing the minute peaks in the DSC. The analytical results revealed the following changes of polymorphisms in detail: An LPEI film prepared by casting an aqueous solution was composed of sesquihydrate and hemihydrate crystals. The sesquihydrate one was lost at an early stage of heating, and the film changed into an amorphous state. Once the sesquihydrate was lost by heating, it was not recovered even when it was cooled back to room temperature. When the sample was heated again, structural changes were found between the hemihydrate and the amorphous components. In this manner, the simultaneous DSC–XRD measurements combined with ALS analysis proved to be powerful for obtaining a better understanding of the thermally induced changes of the crystalline structure in a polymer film. FigureDSC–XRD combined with ALS analysis provides a powerful method for elucidating thermally induced changes of crystalline structure in a polymer film

Synchronicity and Linearity in Generalized Two-Dimensional Correlation Spectroscopy: Concepts Relevant to the Analysis of Nonperiodic, Monotonically Increasing or Decreasing Spectroscopic Signals

The theory and terminology for two-dimensional (2D) infrared correlation spectroscopy were originally developed for the analysis of dynamic IR signals induced by periodic perturbations. The generalized 2D spectroscopy method defines synchronous and asynchronous relationships mathematically rigorously, both for periodic and nonperiodic perturbations. However, the concept of synchronicity may not be intuitively easy to understand when applying the generalized 2D spectroscopy method to the analysis of nonperiodic perturbations. We propose an alternative and novel measure and concept especially useful for nonperiodic perturbations. Our main proposal, when interpreting 2D maps, is to focus on linearity instead of synchronicity. We also propose a simple plot to reveal, verify, and identify linear and nonlinear relationships in the variable space. In addition, we are proposing the alternative use of four terms: (1) linearity as an alternative measure and concept to synchronicity; (2) covariance maps, peaks, etc. as an alternative term to synchronous maps, spectrum, peaks, etc.; (3) disvariance maps, peaks, etc., as an alternative term to asynchronous maps, spectrum, peaks, etc.; and (4) disrelation coefficient as an alternative term to normalized asynchronicity. In an example using FT-IR data from a three-component evaporation experiment, most peaks in the covariance or the traditional synchronous 2D map represented linear relationships, but also peaks representing nonlinear relationships between the involved spectroscopic bands were found. All larger peaks in the disvariance or the traditional asynchronous 2D map represented nonlinear relationships between the involved spectroscopic variables. Our proposed plot visually revealed the type and the degree of non-linearity.

Supramolecular Porphyrin Copolymer Assembled through Host–Guest Interactions and Metal–Ligand Coordination

Bisporphyrin cleft molecule 1 Zn possessing a guest moiety assembled to form supramolecular polymers through host-guest interactions. Bispyridine cross-linkers created interchain connections among the supramolecular polymers to form networked polymers in solution. Solution viscometry confirmed that the cross-linked supramolecular polymers were highly entangled. Frequency-dependent linear viscoelastic spectroscopy revealed that the supramolecular polymers generated well-entangled solutions with associating and networking polymers, whereas the solid-like aggregates moved individually without breaking and reforming structures below the transition temperature of 9.6 °C. Morphological transition of the supramolecular polymers was evidenced by AFM images; the non-cross-linked polymer resulted in wide-spread thin networks, while the cross-linked networks produced thicker worm-like nanostructures. The supramolecular networks gelled in 1,1,2,2-tetrachloroethane, and an elastic free-standing film was fabricated with a Youngs modulus of 1 GPa.