Polymacromonomers with polyolefin branches synthesized by free-radical homopolymerization of polyolefin macromonomer with a methacryloyl end group

Polymacromonomers with polyolefin branches were successfully synthesized by free-radical homopolymerization of polyolefin macromonomer with a methacryloyl end group. Propylene-ethylene random copolymer (PER) with a vinylidene end group was prepared by polymerization using a metallocene catalyst. Then, the unsaturated end group was converted to a hydroxy end group via hydroalumination and oxidation. The PER with the hydroxy end group was easily reacted with methacryloyl chloride to produce methacryloyl-terminated PER (PER macromonomer; PERM). The free-radical polymerization of thus-obtained PERM was done using 2,2′-azobis(isobutyronitorile) (AIBN) as a free-radical initiator. From NMR analyses, the obtained polymers were identified as poly(PERM). Based on gel permeation chromatography (GPC), the estimated degree of polymerization (D_p) of these polymers were about 30. Thus, new class of polymacromonomers with polyolefin branches was synthesized.     

AtTrxh3, a Thioredoxin,Is Identified as an Abscisic AcidBinding Protein in Arabidopsis thaliana

Abscisic acid (ABA, 1) is a plant hormone that regulates various plant physiological processes such as seed developing and stress responses. The ABA signaling system has been elucidated; binding of ABA with PYL proteins triggers ABA signaling. We have previously reported a new method to isolate a protein targeted with a bioactive small molecule using a biotin linker with alkyne and amino groups, a protein cross-linker, and a bioactive small molecule with an azido group (azido probe). This method was used to identify the unknown ABA binding protein of Arabidopsis thaliana. As a result, AtTrxh3, a thioredoxin, was isolated as an ABA binding protein. Our developed method can be applied to the identification of binding proteins of bioactive compounds.     

Synthesis and properties of calixarene analogs incorporating a thiophene unit in the macrocyclic ring

Calixarene analogs containing a thiophene unit in the macrocyclic ring were prepared by a stepwise method. The macrocycles adopt a cone‐like form as the preferred conformation in solution. The induced chemical shift change, nOe experiment, and ¹H relaxation time (T₁) measurement supported the fact that the macrocycle forms a complex with the N‐methylpyridinium salt. In contrast, O‐tetramethylated macrocycles and linear phenol‐formaldehyde tetramer, could not efficiently include the N‐methylpyridinium salt.     

Diffraction efficiency of relief-type gratings in amorphous chalcogenide films

In As-Se-(S)-Ge amorphous films, the chemical etching rate between the heat treated and the light irradiated states differs as well as the optical properties do. A relief-type grating made by the etching has a high diffraction efficiency (∽15%). The diffraction efficiency of the relief-type grating is analyzed by a Fourier expansion method under some assumptions and good agreement is obtained between the calculated and the experimental values.     

Precursor structure and hydrolysis-gelation process of Al(O-sec-Bu)3 modified with ethylacetoacetate

The precursor structure and hydrolysis-gelation process of aluminum-sec-butoxide, Al(O-sec-Bu)₃, modified with ethylacetoacetate (EAcAc) were investigated using IR, UV and high magnetic field (11.7 T) ²⁷Al NMR spectra. ²⁷Al NMR showed that the reaction of EAcAc with Al(O-sec-Bu)₃ led to the formation of six-coordinated structural units and most of the precursors were assumed to be present as linear trimer containing a four- and two six-coordinated Al atoms. It was found that EAcAc formed the strong chelating bonds with Al(O-sec-Bu)₃, which were hardly hydrolyzed by the attack of water molecules in the gelation process.     

Living polymerization of ethylene catalyzed by titanium complexes having fluorine-containing phenoxy-imine chelate ligands

Seven titanium complexes bearing fluorine-containing phenoxy-imine chelate ligands, TiCl(2)[eta(2)-1-[C(H)=NR]-2-O-3-(t)Bu-C(6)H(3)](2) [R = 2,3,4,5,6-pentafluorophenyl (1), R = 2,4,6-trifluorophenyl (2), R = 2,6-difluorophenyl (3), R = 2-fluorophenyl (4), R = 3,4,5-trifluorophenyl (5), R = 3,5-difluorophenyl (6), R = 4-fluorophenyl (7)], were synthesized from the lithium salt of the requisite ligand and TiCl(4) in good yields (22%-76%). X-ray analysis revealed that the complexes 1 and 3 adopt a distorted octahedral structure in which the two phenoxy oxygens are situated in the trans-position while the two imine nitrogens and the two chlorine atoms are located cis to one another, the same spatial disposition as that for the corresponding nonfluorinated complex. Although the Ti-O, Ti-N, and Ti-Cl bond distances for complexes 1 and 3 are very similar to those for the nonfluorinated complex, the bond angles between the ligands (e.g., O-Ti-O, N-Ti-N, and Cl-Ti-Cl) and the Ti-N-C-C torsion angles involving the phenyl on the imine nitrogen are different from those for the nonfluorinated complex, as a result of the introduction of fluorine atoms. Complex 1/methylalumoxane (MAO) catalyst system promoted living ethylene polymerization to produce high molecular weight polyethylenes (M(n) > 400 000) with extremely narrow polydispersities (M(w)/M(n) < 1.20). Very high activities (TOF > 20 000 min(-1) atm(-1)) were observed that are comparable to those of Cp(2)ZrCl(2)/MAO at high polymerization temperatures (25, 50 degrees C). Complexes 2-4, which have a fluorine atom adjacent to the imine nitrogen, behaved as living ethylene polymerization catalysts at 50 degrees C, whereas complexes 5-7, possessing no fluorine adjacent to the imine nitrogen, produced polyethylenes having M(w)/M(n) values of ca. 2 with beta-hydrogen transfer as the main termination pathway. These results together with DFT calculations suggested that the presence of a fluorine atom adjacent to the imine nitrogen is a requirement for the high-temperature living polymerization, and the fluorine of the active species for ethylene polymerization interacts with a beta-hydrogen of a polymer chain, resulting in the prevention of beta-hydrogen transfer. This catalyst system was used for the synthesis of a number of unique block copolymers such as polyethylene-b-poly(ethylene-co-propylene) diblock copolymer and polyethylene-b-poly(ethylene-co-propylene)-b-syndiotactic polypropylene triblock copolymer from ethylene and propylene.     

Intramolecular reaction of a phenonium ion. Novel lactonization of 4-aryl-5-tosyloxypentanoates and 4-aryl-5-tosyloxyhexanoates concomitant with a phenyl rearrangement

The novel lactonizations of methyl 4-aryl-5-tosyloxypentanoate 1 and 4-aryl-5-tosyloxyhexanoate 3 concomitant with a phenyl rearrangement are reported. The lactonizations were promoted by silica gel or heating in various solvents. By examining the effects of substituents of the aromatic ring on the reactivity, it was found that the reaction proceeded via a phenonium ion. This finding was supported by the stereochemical results for the lactonization of optical active 1. Silica gel-promoted lactonization of 1 gave only gamma-lactone 2, whereas that of 3 afforded gamma-lactone 4 and delta-lactone 5. These lactonizations proved to be kinetically controlled. On the other hand, when 3c was heated in CH(3)NO(2) at 70 degrees C, the highly selective formation of 4c was observed. Further detailed experiments confirmed that the thermal lactonization in CH(3)NO(2) was thermodynamically controlled.     

Asymmetrical A-Frame Triplatinum Clusters Bridged by Small Organic Molecules and Bis((diphenylphosphino)methyl)phenylphosphine

Reactions of the linear triplatinum complex [Pt(3)(&mgr;-dpmp)(2)(XylNC)(2)](2+) (3) with small organic molecules led to formation of asymmetrical A-frame triplatinum complexes with an additional bridge across one of the metal-metal bonds, where dpmp is bis((diphenylphosphino)methyl)phenylphosphine. Reaction of complex 3 with electron deficient alkynes (R(1)C&tbd1;CR(2): R(1) = R(2) = CO(2)Me; R(1) = H, R(2) = CO(2)Me; R(1) = R(2) = CO(2)Et) afforded a new series of triplatinum clusters formulated as [Pt(3)(&mgr;-dpmp)(2)(&mgr;-R(1)CCR(2))(XylNC)(2)](PF(6))(2) (5a, R(1) = R(2) = CO(2)Me; 5b, R(1) = H, R(2) = CO(2)Me; 5c, R(1) = R(2) = CO(2)Et) in good yields. The complex cation of 5b was characterized by X-ray crystallography to have an asymmetrical A-frame structure comprising three Pt atoms bridged by two dpmp ligands, in which an acetylene molecule was inserted into one of the Pt-Pt bonds (triclinic, P&onemacr;, a = 19.507(3) ?, b = 20.327(4) ?, c = 14.499(4) ?, alpha = 107.69(2) degrees, beta = 102.08(2) degrees, gamma = 71.30(1) degrees, V = 5148 ?(3), Z = 2, R = 0.070, and R(w) = 0.084). The Pt-Pt bond length is 2.718(1) ? and the Pt.Pt nonbonded distance is 3.582(1) ?. Treatment of 3 with an excess of HBF(4).Et(2)O gave the asymmetrical cluster [Pt(3)(&mgr;-dpmp)(2)(&mgr;-H)(XylNC)(2)](BF(4))(3).CH(2)Cl(2) (6.CH(2)Cl(2)), in 61% yield, and a similar reaction with p-NO(2)C(6)H(4)NC led to the formation of [Pt(3)(&mgr;-dpmp)(2)(&mgr;-R(3)NC)(XylNC)(2)](PF(6))(2).CH(2)Cl(2) (7.CH(2)Cl(2)) in 94% yield (R(3) = p-NO(2)C(6)H(4)). Complexes 6 and 7 are assumed to have a single atom-bridged, asymmetrical A-frame structures. Reaction of the complex syn-[Pt(2)(&mgr;-dpmp)(2)(XylNC)(2)](2+) (1) with [MCl(2)(cod)] (M = Pt, Pd) gave the dimer-monomer combined trinuclear cluster [Pt(2)MCl(2)(&mgr;-dpmp)(2)(XylNC)(2)](PF(6))(2) (8a, M = Pt, 89%; 8b, M = Pd, 55%). The structure of 8a was determined by X-ray crystallography to be comprised of a metal-metal-bonded diplatinum core and a monomeric platinum center bridged by two dpmp ligands with a face-to-face arrangement (triclinic, P&onemacr;, a = 18.082(7) ?, b = 19.765(6) ?, c = 15.662(4) ?, alpha = 98.51(2) degrees, beta = 94.24(3) degrees, gamma = 109.82(2) degrees, V = 5161 ?(3), Z = 2, R = 0.069, and R(w) = 0.080). The Pt-Pt bond length is 2.681(2) ? and the Pt.Pt nonbonded distance is 3.219(2) ?. The heteronuclear complex 8b was transformed to an A-frame trinuclear cluster, [Pt(2)PdCl(&mgr;-Cl)(&mgr;-dpmp)(2)(XylNC)](PF(6))(2) (9), which was characterized by X-ray crystallography (monoclinic, C2/c, a = 33.750(9) ?, b = 28.289(9) ?, c = 23.845(8) ?, beta = 118.19(4) degrees, V = 20066 ?(3), Z = 8, R = 0.082, and R(w) = 0.077). The diplatinum unit (Pt-Pt = 2.606(2) ?) is connected to the mononuclear Pd center by a chloride bridge (Pt.Pd = 3.103(3) ?, Pt-Cl-Pd = 79.6(3) degrees ).