Preparation and Properties of C60-Polysiloxane Hybrids

C₆₀-polysiloxane hybrids were prepared by the reaction of triethoxysilylated C₆₀ (TES-C₆₀) with methylpolysiloxane (MPS) or , -dihydroxypolydimethylsiloxane (STPDS). TES-C₆₀ was synthesized by hydrosilylation using triethoxysilane and C₆₀ in the presence of chloroplatinic acid. TES-C₆₀ was mixed with MPS and heated to provide a bulk body of C₆₀ containing polysiloxane hybrid in a Si/C₆₀ molar ratio of 1000:500. The formation of this hybrid is based on the hydrolytic polycondensation of TES-C₆₀ and MPS to fix C₆₀ into the silica matrix by a chemical bond. TES-C₆₀ and STPDS also provide an isolatable thin film of C₆₀ containing polysiloxane hybrid by an ethanol-forming condensation reaction. Because no gelation was observed when only STPDS was aged, it is thought that TES-C₆₀ serves as a cross-linking point in gel formation.     

Syntheses and properties of sila-functional oligosiloxanes: Synthesis, structure, and spectra of linear and cyclic isocyanato(methyl)oligosiloxanes

Synthesis, structure, and spectra of novel linear and cyclic isocyanato(methyl)oligosiloxanes with the silicon number up to eight were investigated. The linear and cyclic oligosiloxanes were synthesized selectively in good or appreciable yields by vapor phase and liquid phase hydrolysis, respectively. They were isolated as liquids by distillation under reduced pressure except for cyclic tetrasiloxane and pentasiloxane which were provided as solids. The cyclic trisiloxane was obtained as amixture of isomers as confirmed by nuclear magnetic resonance (NMR) spectra. The X-ray analysis of cyclic tetra- and pentasiloxane obtainedrevealed that they have cis-trans-cis andpropeller-like structure, respectively. The infrared (IR) spectra of cyclic siloxanes showed a sharp peak due to ν_Si?O?Si and a remarkable shift fromthe tri- to the tetrasiloxane while peak broadening and almost no shift were observed for the higher homologues. On the other hand, the sharp peak for linear disiloxanes became broad and split into two peaks for the higher homologues, while the peak at low wavenumber shifted even lower as the siloxane linkages increased, yet no corresponding shift is observed for thepeak at higher wavenumber. In the ²⁹Si NMR spectra of linearoligosiloxanes, the signals appeared separately at low and high fields in narrow regions, which are ascribed to the terminal silicon atom and the silicon associatedwith the silylmethyl groups, respectively. These regions hardly changed, regardless of the length of siloxane linkage. Similar trends were observed in the ¹H and ¹³C NMR spectra.     

Thiocarbonyl induced heterocumulenic Pauson-Khand type reaction: expedient synthetic method for thieno[2,3-b]indol-2-ones

The first examples of C[double bond, length as m-dash]S induced Pauson-Khand type reactions are described; 2-alkynylphenyl isothiocyanates were converted to 3-substituted-2H-thieno[2,3-b]indol-2-ones in the presence of a stoichiometric amount of Mo(CO)(6) or Co(2)(CO)(8), or a catalytic amount of Rh catalyst under an atmospheric pressure of carbon monoxide.     

Rhodium-catalyzed intramolecular alkyne-carbodiimide Pauson-Khand-type reaction

[structure: see text]. An efficient, Rh-catalyzed intramolecular Pauson-Khand-type carbonylation of alkyne-carbodiimides leading to 4,5-dihydro-1H-pyrrolo[2,3-b]pyrrolin-2-ones and 1H-pyrrolo[2,3-b]indol-2-ones is described.     

A method for Lyapunov spectrum estimation using cloned dynamics and its application to the discontinuously-excited FitzHugh–Nagumo model

This work presents a new method to calculate the Lyapunov spectrum of dynamical systems based on the time evolution of initially small disturbed copies (“clones”) of the motion equations. In this approach, it is not necessary to construct the tangent space associated with the time evolution of linearized versions of motion equations, being the Lyapunov exponents directly estimated in terms of the rate of convergence or divergence of these disturbed clones with respect to the fiducial trajectory, there being periodic correction via the Gram–Schmidt Reorthonormalization procedure. The proposed method offers the possibility of partial estimation of the Lyapunov spectrum and can also be applied to nonsmooth dynamics, since the linearization procedure is no longer required. The idea is tested for representative continuous- and discrete-time dynamical systems and validated by means of comparison with the classical method to perform this calculation. To illustrate its applicability in the nonsmooth context, the largest Lyapunov exponent of the FitzHugh–Nagumo neuronal model under discontinuous periodic excitation is calculated taking the amplitude of stimulation as control parameter. This analysis reveals some complex behaviours for this simple neuronal model, which motivates relevant discussions about the possible role of chaos in the cognitive process.     

Synthesis and evaluation of simplified functionalized bongkrekic acid analogs

Bongkrekic acid (BKA) is a strong inhibitor of adenine nucleotide translocase (ANT), inducing inhibition of adenosine triphosphate synthesis. We designed and synthesized simplified benzene-ring-containing BKA analogs. The key reaction is the one-pot double Sonogashira reaction, which forms the main skeleton. The analogs were efficiently synthesized in 8–10 longest linear sequence steps. This synthetic method can be applied for the preparation of other analogs having different combinations of carbon chain lengths. Furthermore, the allyloxy group on the benzene ring can be easily replaced by other functional groups. Our preliminary biological evaluation based on mitochondrial inhibitory effects revealed the high potency of the analogs bearing the same carbon chain length as that of BKA. In particular, the prefunctionalized analogs are potential ANT inhibitors.     

Photo-induced polarity alteration and photodegradation behavior of O-acryloyl acetophenone oxime and phenyl vinyl ketone copolymers

Photochemical reactions of copolymers of O-acryloyl acetophenone oxime (AAPO) and phenyl vinyl ketone (PVK) in the solid phase were investigated. The decrease of molecular weight of these copolymers in the photolysis was limited compared to that of PVK homopolymer. Results of IR and elemental analyses showed that pendant acyloxyimino (AOI) groups were phototransformed into the pendant amino groups. This behavior suggests that PVK units in this copolymer worked as a sensitizer for the photolysis of AOI groups. The energy transfer from PVK units to AOI groups was confirmed to proceed via an excited triplet state by the quenching study of phosphorescence of a PVK homopolymer by a model compound, O-cyclohexanecarbonyl acetophenone oxime. Dissolution alteration of AAPO copolymers before and after irradiation was also investigated. © 1996 John Wiley & Sons, Inc.     

Two-step total synthesis of an anti-MRSA and myosin-inhibiting marine natural product pentabromopseudilin via Suzuki-Miyaura coupling of a MIDA boronate ester

A marine natural product isolated from Pseudoalteromonas sp., pentabromopseudilin, with promising anti-MRSA and myosin ATPase inhibition activities was synthesized in two steps using recently developed MIDA boronate Suzuki-Miyaura coupling technology. Additionally, bromination was shown to be necessary for the antimicrobial activity of pentabromopseudilin.     

Stereochemical assignments of rubiaquinones A–C,naphthoquinone derivatives from Rubia yunnanensis

Three new naphthoquinone derivatives, rubiaquinones A–C (1–3), were isolated from the roots of Rubia yunnanensis. Rubiaquinone A (1) was a racemic naphthoquinone dimer consisting of a 1,4-dihydroxynaphthalene and a 4-hydroxy-1,2-naphthoquinone moieties with a 2-oxo-propyl group. Rubiaquinones B (2) and C (3) were structurally unique trimeric naphthoquinones with a racemic nature possessing one chiral axis and one chiral carbon in common. The planar structures of 1–3 were assigned by detailed spectroscopic analyses, and enantiomers of 1–3 were obtained by optical resolutions. The absolute configurations of (+)-1 and (?)-1 were elucidated by interpretation of the ECD spectra with the aid of TDDFT ECD calculation, while those of enantiomers obtained from 2 and 3 were assigned by analyses of the composite ECD spectra generated by summing appropriate ECD spectra of enantiomers. Rubiaquinone A (1) exhibited antimicrobial activity against Bacillus subtilis.