Raman and Wide-Angle X-Ray Diffraction Studies on Molecular Structure,Crystallinity, and Morphology of Uncompatibilized and Compatibilized Blends of High Molecular Weight Polyethylene/Nylon 12

Molecular structure, crystallinity and morphology of uncompatibilized and compatibilized blends of high molecular weight polyethylene (HMWPE) and Nylon 12 were investigated by using Fourier-transform (FT) Raman spectroscopy, wide-angle x-ray diffraction (WAXD), and scanning electron microscopy (SEM). One of the important purposes of the present study is to compare the present results for HMWPE/Nylon 12 with the previously obtained results for high-density polyethylene (HDPE/Nylon 12). Uncompatibilized and compatibilized blends of HMWPE/Nylon 12 with a Nylon 12 content ranging from 10 to 90 wt% at increments of 10 wt% were prepared. The compatibilized polymer blends were prepared by adding a small amount of maleic anhydride (MAH), and SEM images show that the addition of the small amount of MAH (0.5 wt%) yields a marked improvement of dispersion of HMWPE and Nylon 12. To evaluate the crystallinity of HMWPE from Raman spectra, the relative intensities of bands at 1418 and 1129 cm⁻¹ to the intensity of a band at 1000 cm⁻¹ (I₁₄₁₈/I₁₀₀₀ and I₁₁₂₉/I₁₀₀₀) were estimated for all the uncompatibilized and compatibilized blends of HMWPE/Nylon 12. From the comparison of the relative intensities (I₁₄₁₈/I₁₀₀₀ and I₁₁₂₉/I₁₀₀₀) between the uncompatibilized and compatibilized blends of HMWPE/Nylon 12 it was found that when the Nylon 12 content reaches 40 wt% the crystallinity of HMWPE in the compatibilized blends becomes higher than that of HMWPE in the uncompatibilized blends. The uncompatibilized and compatibilized blends of HMWPE/Nylon 12 (50/50) show quite different x-ray diffraction patterns; the compatibilized blend shows a significantly larger orientational effect in the x-ray pattern of HMWPE. It seems that the increase of interaction of MAH-HMWPE with the Nylon 12 matrix leads to the additional crystallinity.     

Voltammetric behavior of 1,2-dihydroxyanthraquinones attached to glassy carbon electrodes and their surface complexation with copper

The adsorption behavior of 1,2-dihydroxyanthraquinones on electrochemically treated GC electrodes has been analyzed on the basis of the Frumkin adsorption isotherm allowing for long-range interactions between adsorbed species. Their slow-scan voltammetric response corresponded with a voltammetric theory for reversible surface reactions accompanied by intermolecular interactions. The negative interaction parameter obtained indicated a repulsive interaction between the surface-confined species, which bound Cu²⁺ firmly at weakly acidic pHs. Although 1,2-dihydroxyanthraquinones behave normally as a bidentate ligand, the surface-immobilized species formed only a 1:1 complex with Cu(II), probably because of motional restraints imposed on them. The 1,2-dihydroxy groups of the ligand chelated a partially hydrolyzed copper(II) species, their oxidation thus being depressed. Surface-bound copper underwent a two-electron redox reaction repetitively without being released from the surface.     

Determination of nanocellulose fibril length by shear viscosity measurement

The lengths of ten types of cellulose nanofibrils were evaluated by shear viscosity measurement of their dilute dispersions. Aqueous dispersions of surface-carboxylated cellulose nanofibrils with a uniform width of ~3 nm were prepared from wood cellulose by 2,2,6,6-tetramethylpiperidine-1-oxyl-mediated oxidation and successive mechanical treatment. Cellulose nanofibril samples with different average lengths were prepared by controlling the conditions of the oxidation or mechanical treatment. The viscosity-average lengths, L _visc, of the nanofibrils were calculated by applying the shear viscosities of the dilute dispersions to an equation for the dilute region flow behavior of rod-like polymer molecules. The obtained L _visc values ranged from 1,100 to 2,500 nm and showed a linear relationship to the length-weighted average length, L _w, measured by microscopic observation; the relation was described as L _visc = 1.764 × L _w + 764. The influences of the electric double-layer of the nanofibrils and surface-carboxylate content on the value of L _visc were also investigated.     

SEC-MALS analysis of cellouronic acid prepared from regenerated cellulose by TEMPO-mediated oxidation

The 4-amino-2,2,6,6-tetramethylpiperidine-1-oxy radical (4-amino-TEMPO)-mediated oxidation was applied to regenerated cellulose, and the obtained cellouronic acid was analyzed by size-exclusion chromatography attached with a multi-angle laser light scattering detector (SEC-MALS). Although the cellouronic acid filtered with the usual 0.1 μm membrane gave a bimodal SEC-elution pattern, the high-molecular-mass fraction was removed by micro filtration of the cellouronic acid solution with a 0.02 μm membrane. It is likely, therefore, that some colloidal particles formed from regenerated cellulose by the TEMPO-mediated oxidation are present as incompletely oxidized residues in the cellouronic acid sample and behave as the high-molecular-mass fraction in the SEC elution pattern. Then, the SEC-MALS analysis was applied to the 0.02 μm membrane-filtered cellouronic acid, and the accurate DPw value of 36 was obtained for cellouronic acid. This DPw value was far lower than that of carboxymethyl cellulose, hydroxypropyl cellulose or alginic acid, resulting from significant depolymerization of cellulose chains during the TEMPO-mediated oxidation. Because the value of DPw 36 for cellouronic acid is close to the leveling-off DP (about 40) of regenerated celluloses obtained by the dilute and heterogeneous acid hydrolysis, the DPw value of cellouronic acid must reflect the solid-state structure of the original regenerated cellulose used in the TEMPO-mediated oxidation.     

Thermal and liquid crystalline properties of cellulose β-ketoesters prepared by homogeneous reaction with ketene dimers

Cellulose β-ketoesters having long alkyl or alkenyl chains were prepared by homogeneous reactions with alkyl or alkenyl ketene dimmers (OKD or AKD), and were characterized by X-ray diffractometory, differential scanning calorimetry, optical microscopy with cross polarizers and others. The Cellulose/OKD and AKD β-ketoesters with degrees of substitution (DS) of more than 1.5 were gummy solid at room temperature and had birefringence due to liquid crystalline structures in wide temperature range. The liquid crystalline/isotropic phase transition points were 150–175 °C, depending on the DS and substituents introduced into cellulose hydroxyls. X-ray diffraction patterns indicated that cellulose backbones had disordered structures at room temperature, while alkyl chains in the substituents formed ordered or crystalline domains in the cellulose β-ketoesters. Films of the cellulose/AKD β-ketoesters prepared by casting their chloroform solutions on glass plates had highly hydrophobic nature, and contact angles of water droplet on the films were more than 90°. The water-contact angles on the films decreased to some extent just after heating of the films at 105 °C, whereas they were gradually recovered to the initial values by conditioning at ambient temperature.     

Nanofibrillation of alkyl ketene dimer (AKD)-treated cellulose in tetrahydrofuran

A hardwood bleached kraft pulp (HBKP) was reacted with alkyl ketene dimer (AKD) under solvent-free and heterogeneous conditions, and a fibrous chloroform-insoluble fraction with a degree of substitution of AKD β-ketoester groups of 0.75 was obtained at a weight ratio of 95 % of the total reaction product. When this AKD-treated and CHCl₃-insoluble HBKP was mechanically disintegrated in tetrahydrofuran, the suspension turned to a viscous and translucent gel. When an unfibrillated fraction was removed by filtration using a glass filter with 40 μm pore size, the weight recovery ratio of the filter-passed fraction was approximately 30 %. Scanning and transmission electron microphotographs of the glass filter-passed fraction showed that this fraction consisted of cellulose nanofibrils more than several micrometers in length, the surfaces of which probably had AKD β-ketoesters in high densities.     

Effects of pressure and solvents on the infrared absorption intensities of C-I stretching modes of methyl and ethyl iodides in solutions

We have investigated effects of pressure and solvents on infrared intensities of methyl and ethyl iodides in solutions using a hydrostatic high-pressure cell with synthetic diamond windows. We focused on the absolute intensity of the C-I stretching mode, which was measured in carbon disulfide solvent up to 300MPa and at 293K, and in n-hexane solvent at 298K. For comparison, we investigated the effect of solvents on the absorption intensity. Effects of pressure and solvents on the infrared intensity were analyzed using two electrostatic models, which assume the shape of solute cavity as sphere or spheroid. The latter model is approximately in agreement with both effects on the intensity, particularly, for the pressure effect. This paper demonstrated that the electrostatic model taking the shape of the cavity into account is useful to explain the medium effect on the infrared intensity and also suggests that more improved models could provide information of the solvation structure from the medium effect on the infrared intensity.     

Selective covalent targeting of SARS-CoV-2 main protease by enantiopure chlorofluoroacetamide

The coronavirus disease 2019 (COVID-19) pandemic has necessitated the development of antiviral agents against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The main protease (M^pro) is a promising target for COVID-19 treatment. Here, we report an irreversible SARS-CoV-2 M^pro inhibitor possessing chlorofluoroacetamide (CFA) as a warhead for the covalent modification of M^pro. Ugi multicomponent reaction using chlorofluoroacetic acid enabled the rapid synthesis of dipeptidic CFA derivatives that identified 18 as a potent inhibitor of SARS-CoV-2 M^pro. Among the four stereoisomers, (R,R)-18 exhibited a markedly higher inhibitory activity against M^pro than the other isomers. Reaction kinetics and computational docking studies suggest that the R configuration of the CFA warhead is crucial for the rapid covalent inhibition of M^pro. Our findings highlight the prominent influence of the CFA chirality on the covalent modification of proteinous cysteines and provide the basis for improving the potency and selectivity of CFA-based covalent inhibitors.

Chlorofluoroacetamide (CFA) was used as the warhead for covalent targeting of SARS-CoV-2 M^pro. The chirality at CFA showed marked influence on inhibitory activity, suggesting stereospecific activation of CFA for cysteine modification in the protein.     

Asymptotic expansions for the distributions of latent roots ofS h S e −1 and of certain test statistics in MANOVA

S _e andS _n are independent central and noncentral Wishart matrices having Wishart distributionsW _p (n _e , Σ) andW _p (n _h , Σ; Ω) respectively. Asymptotic expansions are given for the distributions of latent roots ofS _h S _e ⁻¹ and of certain test statistics in MANOVA under the assumption thatn=n _e +n _h becomes large with a fixed ration _e ∶n _h =e∶h(e+h=1,e>0,h>0) andΩ=O(n).