Lewis base catalyzed ring opening of aziridines with silylated nucleophiles

The ring opening of N-tosylaziridines with trimethylsilylated nucleophiles, catalyzed by N,N,N',N'-tetramethylethylenediamine, led to the production of beta-functionalized sulfonamides in good to excellent yields with high regioselectivity. [reaction: see text]     

Cu-loaded dealuminated Y zeolites active in selective catalytic reduction of nitric oxide with ammonia

The selective catalytic reduction of NO with ammonia in the presence of oxygen has been carried out on Cu-loaded dealuminated Y zeolite catalysts. Copper was introduced by the usual ion-exchange procedure with an aqueous solution of cupric acetate. On deeply dealuminated USY zeolites, Cu²⁺ was supported in the amount larger than 2Cu/Al=2, resulting in the formation of CuO fine particles in addition to the isolated and dimer Cu²⁺ species. The specific catalytic activity per surface copper on the CuO particles was very high compared with these Cu²⁺ species. NO adsorption measurement revealed the higher dispersion of CuO on the deeply dealuminated USY than on SiO₂, which made Cu/USY a better catalyst for the reduction of NO. The reaction intermediates were investigated through the IR spectra of adsorbed species.     

Role of jasmonate in the rice (Oryza sativa L.) self-defense mechanism using proteome analysis

Exogenously applied jasmonic acid (JA) was used to study changes in protein patterns in rice (Oryza sativa L.) seedling tissues, to classify these changes, and to assign a role for these changes, in order to define the role of JA in the rice self-defense mechanism. High resolution two-dimensional polyacrylamide gel electrophoretic analysis revealed induction of new proteins in both leaf and stem tissues after JA treatment, with the major protein spots further analyzed through N-terminal and internal amino acid sequencing, purification, antibody production, and immunoblot analysis. JA treatment results in necrosis in these tissues, which is accompanied by drastic reductions in ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) subunits, and was confirmed using immunoblotting. Induction of novel proteins was found particularly in the stem tissues, including a new basic 28 kDa Bowman-Birk proteinase inhibitor protein (BBPIN; jasmonate-induced stem protein, JISP 6), and acidic 17 kDa pathogenesis-related class 1 protein (PR-1, JISP 9). This induction of proteins was blocked by a protein synthesis inhibitor cycloheximide (CHX) indicating de novo protein synthesis. Kinetin (KIN), a cytokinin and free radical scavenger reversed RuBisCO decreases, but not induction of proteins. Immunoblot analysis using antibodies generated against these purified proteins revealed a tissue-specific expression pattern and time-dependent induction after JA treatment. Our results indicate that jasmonate affects defense-related gene expression in rice seedlings, as evidenced by de novo synthesis of novel proteins with potential roles in plant defense.     

Convergent synthesis of the ABCDE-ring fragment of the Caribbean ciguatoxin C-CTX-1

Ciguatoxin C-CTX-1 was isolated as a principal causative toxin of ciguatera seafood poisoning in the Caribbean Sea, and is structurally classified as a ladder-shaped polycyclic ether. In this Letter, we report the convergent synthesis of the pentacyclic left half of C-CTX-1, based on a newly developed acyl radical strategy.     

Development of selective,visible light-excitable,fluorescent magnesium ion probes with a novel fluorescence switching mechanism

Novel fluorescent Mg2+ probes, 2'-carboxyfluorescein (2'-CF) and its derivatives, that are excitable by visible light, were designed, synthesized and characterized. After complexation with Mg2+, the absorption and emission maxima of these fluorescent probes were red-shifted and the fluorescence intensity was increased 11-fold at neutral pH. The apparent dissociation constant (Kd) of the Mg2+-2'-CF complex was 15.8 mM at neutral pH. The Kd of the Ca2+-2'-CF complex was about 10 times larger than that of the Mg2+ complex and the other derivatives showed similar characteristics. In contrast, all the commercially available fluorescent Mg2+ probes have a higher affinity for Ca2+ than Mg2+. 2'-CF fluoresced in alkaline solution (pH > 8) and the pK, value was 8.8. The pKa value of the Mg2+-2'-CF complex was 6.8, and the fluorescence intensity was increased in the neutral conditions. Thus, the addition of Mg2+ resulted in a lowering of the pKa, and also an increase of the fluorescence intensity.     

Synthesis of protoheme IX derivatives with a covalently linked proximal base and their human serum albumin hybrids as artificial hemoprotein

The simple one-pot reaction of protoporphyrin IX and omega-(N-imidazolyl)alkylamine or O-methyl-L-histidyl-glycine with benzotriazol-1-yl-oxytris(dimethylamino)phosphonium hexafluorophosphate at room temperature produced a series of protoporphyrin IX species with a covalently linked proximal base at the propionate side-chain. The central iron was inserted by the general FeCl2 method, converting the free-base porphyrins to the corresponding protoheme IX derivatives. Mesoporphyrin IX and diacetyldeuteroporphyrin IX analogues were also prepared by the same procedure. The Fe(II) complexes formed dioxygen (O2) adducts in dimethylformamide at 25 degrees C. Some of them were incorporated into the hydrophobic domain of recombinant human serum albumin (rHSA), providing albumin-heme hybrids (rHSA-heme), which can bind and release O2 in aqueous media (pH 7.3, 25 degrees C). The oxidation process of converting the dioxygenated heme in rHSA to the inactive Fe(III) state obeyed first-order kinetics, indicating that the mu-oxo dimer formation was prevented by the immobilization of heme in the albumin scaffold. The rHSA-heme, in which the histidylglycil tail coordinates to the Fe(II) center, showed the most stable O2 adduct complexes.     

Generation and cycloaddition of polymer-supported azomethine ylide via a 1,2-silatropic shift of alpha-silylimines: traceless synthesis of pyrrolidine derivatives

The 1,3-dipolar cycloaddition of polymer-supported azomethine ylides to dipolarophiles gave pyrrolidine derivatives in good yields. The azomethine ylides were generated from resin-bound alpha-silylimines via a 1,2-silatropic shift. The features of this method are not only a traceless synthesis but also a unique solid-phase route to pyrrolidines with extensive diversity. [reaction: see text]     

Synthesis of Oligo(thienylfuran)s with Thiophene Rings at Both Ends and Their Structural,Electronic, and Field‐Effect Properties

Oligo(thienylfuran)s with thiophene rings at both ends ( SOSOSOS , DE‐SOSOS , DH‐SOSOS , DE‐SOSOSOS , and DH‐SOSOSOS ; S and O denote thiophene and furan rings, respectively, DE and DH denote diethyl‐ and dihexyl‐substituted, respectively) were newly synthesized by repetitive Stille coupling reactions. The UV/Vis maximum absorptions of the oligomers, SO , SOSO , SOSOS , SOSOSO , and SOSOSOS , exhibited a clear bathochromic shift with increasing number of heterocycles. The value of the oxidation peak potential (E_pa¹) determined by cyclic voltammetry decreased with an increase in the number of heterocycles by 0.06–0.08 V per heterocycle. The crystal‐packing structures of DE‐SOSOS and DH‐SOSOS determined by X‐ray crystallography have a herringbone motif and are denser than the reported structures of pentacene and α‐sexithiophene. The morphologies of thin films prepared by vacuum deposition and spin coating were investigated by atomic force microscopy and X‐ray diffraction. Among these films, those of DE‐SOSOS and DH‐SOSOS exhibited highly ordered arrangements. The devices based on vacuum‐deposited and spin‐coated films of DE‐SOSOS and DH‐SOSOS displayed the highest FET mobilities of 10^?2–10^?3 cm² V^?1 s^?1 among the oligomers reported in this study.     

pH‐Triggered Self‐Assembly of Cellulose Oligomers with Gelatin into a Double‐Network Hydrogel

Multicomponent systems for self‐assembled molecular gels provide huge opportunities to generate collective or new functions that are not inherent in individual single‐component gels. However, gelation tends to require careful and complicated procedures, because, among a myriad of kinetically trapped structures related to the degree of mixing of multiple components over a wide range of scales, from molecular level to macroscopic scale, a limited number of structures that exhibit the desired function need to be constructed. This study presents a simple method for the construction of double‐network (DN) hydrogels with improved stiffness composed of crystalline cellulose oligomers and gelatin. The pH‐triggered self‐assembly of cellulose oligomers leads to the formation of robust networks composed of crystalline nanofibers in the presence of dissolved gelatin, followed by cooling to allow for the formation of soft gelatin networks. The resultant DN hydrogels exhibit improved stiffness; the improvement in gel stiffness with double networking is comparable to that of previously reported DN hydrogels produced via a time‐consuming enzymatic reaction.