Isospecific polymerizations of alkyl methacrylates with a bis(alkyl)Yb complex and formation of stereocomplexes with syndiotactic poly(alkyl methacrylate)s

Yb[C(SiMe₃)₃]₂ initiates the living polymerization of methyl methacrylate (MMA) at −78°C to give the polymer with M_n of 51.0×10⁴ (M_w/M_n=1.1) and high isotacticity (97%) in a quantitative yield. Mixing of the acetone solution of resulting polymer (M_n=16.3×10⁴) with the acetone solution of syndiotactic poly(MMA) (M_n=15.7×10⁴) prepared by the (C₅Me₅)₂SmMe(THF) initiator produces desired stereocomplex in high yield bearing very high T_m whose tensile modulus is higher than the respective isotactic and syndiotactic poly(MMA)s. Yb[C(SiMe₃)₃]₂ also generated isotactic (98%) poly[2-(dimethylamino)ethyl methacrylate] (DMEMA), and (C₅Me₅)₂SmMe(THF) affords the syndiotactic (97%) polymer in high yields. The combination of isotactic poly(MMA)-block-poly(DMEMA) (97/3) and syndiotactic poly(MMA)-block-poly(DMEMA) (97/3) provides the amphiphathic stereocomplex. In sharp contrast to the catalysis of Yb[C(SiMe₃)₃]₂ in toluene, the addition of THF or HMPA resulted in the formation of syndio-rich poly(MMA).     

Organization of polyhydroxyalkanoate synthase for in vitro polymerization as revealed by atomic force microscopy

Individual polyhydroxyalkanoate synthase molecules from Ralstonia eutropha (PhaCRe) were directly visualized on highly oriented pyrolytic graphite (HOPG) by atomic force microscopy (AFM). PhaCRe molecule was observed as a spherical particle of 2.9 +/- 0.4 nm in height and 28 +/- 4 nm in width. In vitro polymerization reaction on HOPG was carried out for 5 min by reacting the PhaCRe molecules with (R)-3-hydroxybutyryl-CoA monomers. The reaction product was then observed after the removal of water solution. Several PhaCRe molecules associated with each other to form an assembly, which was attached to a fibrillar structure of ca. 0.2-0.3 nm in height. The fibrillar structure that elongated from the PhaCRe assembly was interpreted as the poly[(R)-3-hydroxybutyrate] polymer chain. High resolution AFM suggested that the PhaCRe assembly was composed of 3-4 subunits of PhaCRe molecules. This was further supported by SDS-PAGE analysis of the cross-linked PhaCRe enzyme. These results suggest that more than two subunits of PhaCRe are necessary for the in vitro polymerization of PHB molecular chains.     

Isolation, Purification and Characterization of Large-Ring Cyclodextrins (CD36∼ ∼CD39)

Large-ring cyclodextrins (LR-CDs) composed of more than 9 d-glucose units are not well studied. In this study, LR-CDs composed of 36, 37, 38 and 39 d-glucose units (CD₃₆∼ ∼CD₃₉) were isolated and purified from a LR-CD mixture, and their physicochemical properties including aqueous solubility, surface tension, specific rotation and acid-catalyzed hydrolysis rate were elucidated. The aqueous solubilities of CD₃₆∼ ∼CD₃₉ were greater than those of α-, β-, γ-CD, CD₉, CD₁₀, CD₁₄ and CD₂₆. CD₃₆∼ ∼CD₃₉ did not show any surface activity. The acid-catalyzed hydrolysis of CD₃₆∼ ∼CD₃₉ was a little faster than that of other LR-CDs (CD₉∼ ∼CD₃₅). There was no marked difference in specific rotation or the acid-catalyzed hydrolysis rate among CD₃₆∼ ∼CD₃₉. Furthermore, we compared these findings with the physicochemical properties of α-, β-, γ-CD and other LR-CDs (CD₉∼ ∼CD₃₅).     

Nonlinear magnetooptical effects caused by piezoelectric ferromagnetism in F3m-type Prussian blue analogues

The second harmonic generation (SHG) and magnetization-induced SHG (MSHG) of AMA[MB(CN)6]-type (F3m) Prussian blue analogues (i.e., CsCo[Cr(CN)6].0.5H2O and RbMn[Fe(CN)6]) were observed. A large interaction between the nonlinear optical response and magnetic spins was observed in CsCo[Cr(CN)6].0.5H2O. These observations of SHG and MSHG imply that AMA[MB(CN)6]-type Prussian blue analogues are piezoelectric above the Curie temperature (TC) and piezoelectric ferromagnet below TC.     

Asymmetric synthesis of axially chiral biaryls: inversion of planar chirality vs axial isomerization and functionalization at the side chain of biaryl chromium complexes

Axially chiral syn-biaryl chromium complexes having a coordinating heteroatom substituent at the benzylic position gave anti-biaryl chromium complexes 5 with inversion of the planar chirality by heating in a nonaromatic solvent, while syn-biaryl chromium complexes with an o-methyl or formyl substituent afforded axially isomerized anti-biaryl chromium complexes under heating in an aromatic solvent. syn-biaryl and both enantiomeric anti-biaryl chromium complexes with the o-formyl group were stereoselectively prepared from an identical planar chiral arene chromium complex as chiral source. The formyl group of the axially chiral chromium complexes was functionalized by radical cyclization and beta-lactam formation, and hetero-Diels-Alder reaction.     

Asymmetric total syntheses of (+)-cheimonophyllon e and (+)-cheimonophyllal

The highly enantiocontrolled total syntheses of natural (+)-cheimonophyllon E (5) and (+)-cheimonophyllal (6), biologically intriguing oxygenated bisabolane-type sesquiterpenoids, have been completed. The present synthetic strategy featured the use of an asymmetric aldol-type reaction for preparing in the first synthetic step an optically active 6-C-substituted 3-methyl-2-cyclohexenone derivative. Thus, a Mukaiyama aldol reaction of 1-methyl-3-silyloxy-1,3-cyclohexadiene 31 with alpha,beta-unsaturated aldehyde 11 in the presence of a chiral (acyloxy)borane (CAB)-type Yamamoto catalyst 33 proceeded with high levels of both diastereo- and enantioselectivities. The predominant aldol adduct, syn-9, was transformed into gamma,delta-epoxy allylic alcohol 8 by a nine-step sequence, including the substrate-controlled 1,2-reduction of enone, syn-12, also the epoxidation of allylic alcohol 15. Epoxy-alcohol 8 underwent 5-exo-cyclization in a high regioselective manner under acidic conditions to produce a bicyclic key intermediate (+)-7, which was eventually efficiently converted to (+)-cheimonophyllon E (5) or (+)-cheimonophyllal (6).     

Interaction between poly[(R)-3-hydroxybutyrate] depolymerase and biodegradable polyesters evaluated by atomic force microscopy

Adsorption of PHB depolymerase from Ralstonia pickettii T1 to biodegradable polyesters such as poly[(R)-3-hydroxybutyrate] (PHB) and poly(l-lactic acid) (PLLA) was investigated by atomic force microscopy (AFM). The substrate-binding domain (SBD) with histidines within the N-terminus was prepared and immobilized on the AFM tip surface via a self-assembled monolayer with a nitrilotriacetic acid group. Using the functionalized AFM tips, the force-distance measurements for polyesters were carried out at room temperature in a buffer solution. In the case of AFM tips with immobilized SBD and their interaction with polyesters, multiple pull-off events were frequently recognized in the retraction curves. The single rupture force was estimated at approximately 100 pN for both PLLA and PHB. The multiple pull-off events were recognized even in the presence of a surfactant, which will prevent nonspecific interactions, but reduced when using polyethylene instead of polyesters as a substrate. The present results provide that the PHB depolymerase adsorbs specifically to the surfaces of polyesters and that the single unbinding event evaluated here is mainly associated with the interaction between one molecule of SBD and the polymer surface.     

Study on simultaneous speciation of arsenic and antimony by HPLC-ICP-MS

A method was developed for the simultaneous speciation of arsenic and antimony with HPLC-ICP-MS using C30 reversed phase column. Eight kinds of arsenic compounds (As(III), As(V), monomethylarsonic acid (MMAA), dimethylarsinic acid (DMAA), arsenobetaine (AB), arsenocholine (AsC), trimethylarsine oxide (TMAO) and tetramethylarsonium (TeMA)), Sb(III) and Sb(V) were simultaneously separated by the special mobile phase containing ammonium tartrate. Especially for the species of organic As, a C30 column was better than a C18 column in the effect of separation. Limits of detection (LOD) for these elements were 0.2 ng ml⁻¹ for the species of each As, and 0.5 ng ml⁻¹ for the species of each Sb, when a 10 μl of sample was injected, respectively. The proposed method was applied to a hot spring water and a fish sample.     

Coordination polymer glass from a protic ionic liquid: proton conductivity and mechanical properties as an electrolyte

High proton conducting electrolytes with mechanical moldability are a key material for energy devices. We propose an approach for creating a coordination polymer (CP) glass from a protic ionic liquid for a solid-state anhydrous proton conductor. A protic ionic liquid (dema)(H₂PO₄), with components which also act as bridging ligands, was applied to construct a CP glass (dema)_0.35[Zn(H₂PO₄)_2.35(H₃PO₄)_0.65]. The structural analysis revealed that large Zn–H₂PO₄⁻/H₃PO₄ coordination networks formed in the CP glass. The network formation results in enhancement of the properties of proton conductivity and viscoelasticity. High anhydrous proton conductivity (σ = 13.3 mS cm⁻¹ at 120 °C) and a high transport number of the proton (0.94) were achieved by the coordination networks. A fuel cell with this CP glass membrane exhibits a high open-circuit voltage and power density (0.15 W cm⁻²) under dry conditions at 120 °C due to the conducting properties and mechanical properties of the CP glass.

A proton-conducting coordination polymer glass derived from a protic ionic liquid works as a moldable solid electrolyte and the anhydrous fuel cell showed I–V performance of 0.15 W cm⁻² at 120 °C.     

Speciation of chromium in Australian fly ash

The concentrations of chromium (III) and (VI) in fly ash from nine Australian coal fired power stations were determined. Cr(VI) was completely leached by extraction with 0.01 M NaOH solution and the concentration was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). This was confirmed by determining Cr(III) and Cr(VI) in the extracts of fly ash that had been spiked with chromium salts. These analytical measurements were done using a combination of ion-exchange chromatography and ICP-AES. The elutant was 0.05 M HNO₃ containing 0.5%-CH₃OH. When the column was operated at a flow rate of 1.2 ml min⁻¹ and samples were injected by use of a sample loop with a volume of 100 μl, Cr(III) and Cr(VI) in sample solution was exclusively separated within approximately 10 min. The detection limits (3σ) were 5 ng for Cr(III) (0.050 mg l⁻¹) and 9 ng for Cr(VI) (0.090 mg l⁻¹), respectively. A relative standard deviation of 1.9% (n = 6) was obtained for the determination by IC-ICP-AES of 0.25 mg l⁻¹ Cr(III) and Cr(VI).