Enzymatic transformation of bacterial polyhydroxyalkanoates into repolymerizable oligomers directed towards chemical recycling

The enzymatic transformation into an oligomer was carried out with the objective of developing the chemical recycling of bacterial polyesters. Poly(R-3-hydroxyalkanoate)s (PHAs), such as poly[(R-3-hydroxybutyrate)-co-12%(R-3-hydroxyhexanoate)] and poly[(R-3-hydroxybutyrate)-co-12%(R-3-hydroxyvalerate)], were degraded by granulated Candida antarctica lipase B immobilized on hydrophilic silica (lipase GCA) in a diluted organic solvent at 70 degrees C. The degradation products were cyclic oligomers having a molecular weight of a few hundreds. The obtained cyclic oligomer was readily repolymerized by the same lipase (lipase GCA) to produce the corresponding polyester in a concentrated solution. The cyclic oligomer was copolymerized with epsilon-caprolactone using lipase to produce the corresponding terpolymers having an Mw of 21,000. This is the first example of the enzymatic chemical recycling of bacterial PHAs using lipase. Poly(R-3-hydroxybutyrate) [P(3HB)] was also degraded into the linear-type R-3HB monomer to trimer by P(3HB)-depolymerase (PHBDP) in phosphate buffer at 37 degrees C. The degradation using PHBDP required a longer reaction time compared with the lipase-catalyzed degradation in organic solvent. The monomer composition of the oligomer depended on the origin of the PHBDP. The R-3HB monomer was predominately produced by PHBDP from Pseudomonas stutzeri, while the R-3HB dimer was produced by PHBDP from Alcaligenes faecalis T1. Repolymerization of these oligomers by lipase in concentrated organic solvent produced a relatively low-molecular-weight P(3HB) (e.g., Mw=2,000). Degradation of P(3HB) by lipase in organic solvent into repolymerizable cyclic oligomer and degradation of P(3HB) by PHBDP in buffer into hydroxy acid type R-3HB dimer.     

Changes in electronic structure upon lithium insertion into the A-site deficient perovskite type oxides (Li,La)TiO3

Investigation on variation of the electronic structure accompanying the electrochemical lithium insertion into the perovskite type oxide, (Li,La)TiO3, has been carried out by X-ray absorption spectroscopy (XAS). During the electrochemical lithium insertion, titanium ion reduced its oxidation state from Ti4+ to Ti3+, while La3+ does not contribute to the reduction reaction resulting from Ti K-edge and La L3-edge XAS, respectively. Furthermore, O K-edge XAS showed marked spectral changes with electrochemical lithium insertion, indicating the electronic structure around oxide ion affected by lithium insertion reaction. From the XAS measurement, we have concluded the variation observed in O K-edge XAS was related to the strong interaction with inserted Li ion. To confirm this, first-principles band calculations were performed for the perovskite structure before and after electrochemical lithium insertion. The calculated results showed that the electron originated from inserted Li transferred to neighboring oxide ion locally as well as to Ti ion. This may be due to local neutralization effect of Li to reduce the electrostatic interaction in the crystal.     

Effect of titanium dioxide on photostability of solid-state mequitazine

TiO(2) has been widely used in pharmaceutical products, and it also has been used as a photocatalyst. In this study, the influence of photocatalytic activity on the stability of solid-state mequitazine, an H(1)-blocker, was investigated. The photo-degradation of mequitazine with TiO(2) occurred under irradiation with both light sources. The degree of degradation of mequitazine with anatase was higher than that of rutile. The degradation was significantly enhanced with increasing relative humidity. The relationship between the apparent degradation rate constant and water vapor pressure could be clearly described by a simple power law. The major photo-degradation products of mequitazine, resulting from photocatalytic activity of TiO(2), were mequitazine-S-oxide and mequitazine-sulphone. A remarkable degradation of mequitadine occurred with addition of TiO(2), and its photocatalytic activity was controlled by water vapor pressure. The photo-degradation of mequitazine with TiO(2) is a different process from mequitazine without TiO(2), because mequitazine-S-oxide and mequitazine-sulphone are not formed with normal photo-degradation of mequitazine.     

Highly selective iodide-sensing silicone ladder polymer membranes containing a porphyrin and a quaternary ammonium salt.

It has been demonstrated that a glass-like silicone ladder-type polymer permits one to homogeneously incorporate high amounts of ionophores into the covalently-bonded double chain structure. Furthermore, by making use of this feature, we have successfully fabricated an iodide ion-sensitive field-effect transistor based on two kinds of ionophores and silicone ladder polymer matrix. As ionophores, 5,10,15,20-tetraphenyl-21H,23H-porphyrin and dimethyloctadecyl-3-trimethoxylsilylpropylammonium chloride were homogeneously incorporated into the matrix. The ion-sensitive field-effect transistor showed a linear potential response ranging in the I- concentration between 1.0 x 10(-5) and 1.0 x 10(-1) M. The selectivity coefficients for I- towards interferences of ClO4- and NO3- were estimated to be Kpot(I-,ClO4-) approximately 6.2 x 10(-4) and Kpot(I-,No3-) approximately 4.9 x 10(-4). The matrix has proved to be so stable that the selectivity coefficients have not been altered over six months.     

An efficient solid‐state polycondensation method for synthesizing stereocomplexed poly(lactic acid)s with high molecular weight

Simultaneous solid‐state polycondensation (SSP) of the powdery prepolymers of poly(L ‐lactic acid) (PLLA) and poly(D ‐lactic acid) (PDLA) can produce entire stereocomplexed poly(lactic acid)s (sc‐PLA) with high molecular weight and can be an alternative synthetic route to sc‐PLA. Ordinary melt polycondensations of L ‐ and D ‐lactic acids gave the PLLA and PDLA prepolymers having medium molecular weight which were pulverized for blending in 1:1 ratio. The resultant powder blends were then subjected to SSP at 130–160 °C for 30 h under a reduced pressure of 0.5 Torr. Some of the products thus obtained attained a molecular weight (M_w) as high as 200 kDa, consisting of stereoblock copolymer of PLLA and PDLA. A small amount of the stereocomplex should be formed in the boundaries of the partially melted PLLA and PDLA where the hetero‐chain connection is induced to generate the blocky components. The resultant SSP products showed predominant stereocomplexation after their melt‐processing in the presence of the stereoblock components in spite of containing a small amount of racemic sequences in the homo‐chiral PLLA and PDLA chains. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3714–3722, 2008     

Vicker's Hardness of glass

An equation has been derived for the direct calculation of Vicker's hardness number of glasses from their chemical compositions. The method is based on a consideration of deformation during indentation, which was related to Young's modulus and the average single bond strength of a glass.Excellent agreement is obtained between calculated and measured values of Vicker's hardness number for a variety of glasses.     

Carbon sources of natural cyanamide in Vicia villosa subsp. varia

The 13C labels of [13C]carbon dioxide and D-[13C?]glucose were incorporated into cyanamide (NH?CN) when they were administered to Vicia villosa subsp. varia shoots. In contrast, the administration of sodium [2,3-13C?]pyruvate did not affect the relative area of the [M + 1]+ ion of cyanamide in the gas chromatography-mass spectrometry analysis. [2,3-13C?]pyruvate was incorporated into organic acids that are part of the citric acid cycle, such as succinate and fumarate, confirming that the shoots absorbed and metabolised it. These observations demonstrated that the carbon atom of cyanamide is derived from any of the carbohydrates that are present upstream of pyruvate in the metabolic pathway.     

One-pot hydrothermal synthesis of an assembly of magnetite nanoneedles on a scaffold of cyclic-diphenylalanine nanorods

The assembly of metal oxide nanoparticles (NPs) on a biomolecular template by a one-pot hydrothermal synthesis method is achieved for the first time. Magnetite (Fe₃O₄) nanoneedles (length: ~100 nm; width: ~10 nm) were assembled on cyclic-diphenylalanine (cFF) nanorods (length: 2–10 μm; width: 200 nm). The Fe₃O₄ nanoneedles and cFF nanorods were simultaneously synthesized from FeSO₄ and l-phenylalanine by hydrothermal synthesis (220 °C and 22 MPa), respectively. The samples were analyzed by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (IR), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID) magnetometry. Experimental results indicate that Fe₃O₄ nanoneedles were assembled on cFF nanorods during the hydrothermal reaction. The composite contained 3.3 wt% Fe₃O₄ nanoneedles without any loss of the original magnetic properties of Fe₃O₄.     

Methods of Asymmetric Synthesis—Enantioselective Catalytic Hydrogenation

It is proposed that asymmetric syntheses be divided into enantioselective and diastereoselective syntheses. The enantioselective hydrogenations discussed in the present progress report were catalyzed by Raney nickel that had previously been treated with solutions of optically active compounds. Relationships exist between the enantioselectivity of the catalyst and the structure of the chiral compound used to modify it.     

A characteristic ribbon-like supramolecular structure and intermolecular D–A interactions in the crystals of triptycenequinones, triptycene-TCNQs and their clathrates as studied by X-ray investigations

A common ribbon-like structure was found in the crystals of triptycenequinones (TPQs), triptycene-TCNQs (TP-TCNQs) and their clathrates. The characteristic structure can be regarded as a supramolecular unit the formation of which is aided by weak intermolecular D–A interactions. This view is supported by the host–guest D–A interactions appeared in the crystals of the clathrates of 5,8-dimethyl-TPQ and 5,8-dimethoxy-TP-TCNQ. Intermolecular C–HO hydrogen bonds seem to be present in TPQ derivatives.