Catalytic Enantioselective Hydrosilylation of Ketones with Rhodium-Phosphite Complexes Containing a TADDOLate and a Dihydrooxazole Unit

New types of chiral phosphorus/nitrogen ligands, capable of forming six-membered-ring metal chelates have been prepared from α,α,α′,α′-tetraaryl-1,2-dioxolane-4,5-dimethanols (TADDOLs), PCl₃, and dihydrooxazole alcohols (from amino acids) ( 7 in Scheme 1). The X-ray crystal structure of a Rh complex of one of these ligands, 8b , has been determined (Scheme 2 and Fig.). Enantioselective hydrosilylations of dialkyl and aryl alkyl ketones with Ph₂SiH₂/0.01 equiv. Rh^I⋅ 7 have been studied and found to provide secondary alcohols in enantiomer ratios of up to 97 : 3 (Scheme 3 and Table). The ligand prepared from (R,R)-TADDOL and the (R)-valine-derived (R)-α,α-dimethyl-4-isopropyl-4,5-dihydrooxazole-2-methanol gives better results than the (R,R,S)-isomer ( 7d vs. 7c in Scheme 3), and an i-Pr group on the 4,5-dihydrooxazole ring gives rise to a slightly better selectivity than a Ph group. With the (R,R,R)-ligands the hydrogen transfer occurs from the Re face of the oxo groups (Scheme 4).     

Electrosynthesis in a microemulsion using a novel cobaloxime catalyst

[Bis[μ-[(2,3-butanedione dioximato)(2-)-O:O′]]tetrafluorodiborato(2-)-N,N′,N″,N]cobalt (COBF, 1) was used as a catalyst for the conversion of trans-1,2-dibromocyclohexane (DBCH) to cyclohexene and the photoelectrochemical cyclisation of 2-(4-bromobutyl)-2-cyclohexen-1-one (BBC) to trans-1-decalone 2 in a microemulsion. Voltammetry showed clear evidence of catalytic behaviour and bulk electrolysis showed larger turnover numbers for both reactions when compared with the same system using vitamin B_12a as catalyst. For BBC, improved turnover may result from a relatively weak carbon–cobalt bond in the alkylcobalt intermediate of 1, and from better partition of 1 into the organic phase in which reactant BBC resides.     

Penimethavone A,a flavone from a gorgonian-derived fungus Penicillium chrysogenum

A novel flavone, penimethavone A (1), possessing a rare unique methyl group at ring-B, was isolated from the fungus Penicillium chrysogenum cultured from a gorgonian Carijoa sp. collected from the South China Sea. The structure was elucidated by extensive spectroscopic analysis and by comparison with related known compound. Compound 1 showed selective and moderate cytotoxicity against cervical cancer (HeLa) and rhabdomyosarcoma cell lines with IC₅₀ values of 8.41 and 8.18 μM, respectively.     

Synthesis of a Building Block for a Nucleic-Acid Analog with a Chiral,Flexible Peptide Backbone

We present here a nine-step synthesis of the thymine-containing amino ester 1 , starting from commercially available methyl N-[(tert-butoxy)carbonyl]-L -serinate. Amino ester 1 is considered as a building block for the preparation of a new nucleic-acid analog with a chiral, flexible polyamide backbone. Key steps in the synthesis are the vitamin-B₁₂-catalyzed addition of 3-bromo-N-[(tert-butoxy)carbonyl]-L -alaninate 2 to ethyl acrylate and the homologation of the corresponding N-protected α-amino acid 4 into the β-amino ester 6 by Arndt-Eistert chemistry. The latter was found to proceed with 10% inversion of configuration at the asymmetric center in 6. Resolution to enantiomerically pure material, however, was easily achieved by simple crystallization of 1 .     

Oil-Water Partitioning of a Synthetic Tetracarboxylic Acid as a Function of pH

The oil-water partitioning of a synthetic tetraacid acting as a model compound for indigenous C₈₀-C₈₂ ARN acids has been studied as a function of pH, ionic strength and type of monovalent counterion. Experimental data obtained with ultraviolet-visible and HPLC/UV analyses have been fitted to thermodynamic models based on one, two or four dissociation steps to obtain o/w partition coefficients (K _wo ) of the fully protonated acid between chloroform and aqueous solutions, and its apparent acidity constant(s), pK _a. As the study is conducted above the CMC of the tetraacid, in general high apparent acidity constants were obtained in the range from 6 to 8 resulting from micellization equilibria. K _wo values were obtained in the range from 10^?3 to 10^?4, and decreasing with increasing salinity. At 50 mM K⁺, no conclusions could be made regarding the number of distinguishable dissociation steps, while at higher ionic strength (184 mM and 452 mM K⁺) and at 184 mM Na⁺ a model with two dissociation steps provided good fits to the experimental data. The first step was found to be given by a pK _a ≈ 6.6–6.8 and the second dissociation step at pK _a values ≈ 7.8–8.3. The two-step mechanism supports previous results obtained by potentiometric titrations. No significant difference in the o/w behavior was observed when changing the counterion from potassium to sodium. The main partitioning of the tetraacid in the aqueous phase occurred above pH 8, where the fully deprotonated acid was formed.     

Miscibility of a polyarylate with a liquid crystalline copolyester

The miscibility has been investigated for binary blends of a polyarylate (PAr) with a liquid crystalline copolyester of p-hydroxybenzoate and ethylene terephthalate units in a 6/4 molar ratio (PET/PHB). The binary blends were prepared by solution precipitation. The transitions of the PET/PHB have been measured with a rheometrics dynamic spectrometer. The phases in blends have been studied with a differential scanning calorimeter, by ther-mogravimetry and with a polarizing optical microscope. The blends exhibit two glass transitions (T_gs) over the composition range 10–90 wt %. The amorphous PET phase from the PET-PHB is found to be partially miscible with PAr, which leads to a decrease of the PAr T_g. The amount of this partially miscible portion of PET has been estimated by the Couch-man equation. On heat treatment of the blends at 250 to 300°C, transesterficiation takes place, as judged by the shift of the higher of the two T_gs. © 1993 John Wiley & Sons, Inc.     

Calibration coefficient of a heat-flow DSC. Part I. Relation to the Sensitivity of a thermocouple

Relation between the calibration coefficient of a DSC sensor k(T) and the sensitivity of a thermocouple e(T) which the sensor is made from was derived from the analysis of a heat transfer inside a DSC cell. Ratio e(T)/k(T) is equal to A+BT ³. The first component depends on heat conduction and the second one on radiation. The relationship was tested for DSC-204 Netzsch using (i) data on calibration vs. enthalpies of phase transitions (reference samples) and (ii) measurements of heat capacity of corundum. Both tests show very good agreement between experimental data and predicted theoretical function. This revised version was published online in July 2006 with corrections to the Cover Date.     

Flow of polymer chains and segregation in a flow field with a hybrid simulation

Effects of a flow field (E) on segregation and flow of polymer chains are studied in two dimensions using a hybrid (discrete‐to‐continuum) simulation. The flow rate (j) of polymer chains is found to increase monotonically with E, a linear response in the low field regime followed by a slow approach to saturation in the high field regime. The effective chain permeability (ϕ_c = j/E) varies nonmonotonically on increasing the field E, with a maximum (ϕ_cm) at a characteristic value of the field (in the range 0.2 < E < 2); ϕ_cm depends on the chain length. Chain aggregates exhibit an anisotropic mass distribution due to the field with a molecular bridging at high fields. The longitudinal component of the radius of gyration (R_gx) exhibits a crossover from a random walk (RW) (R_gx ˜ L_c^1/2) at E = 0 to an elongated conformation (R_gx ˜L_c) at E ⪈ 0.2; the transverse component changes from R_gy ˜ L_c^1/2 to R_gy ˜ L_c^1/3. The width of the radial distribution function (ρ(r)) of the monomers increases while its peak varies nonmonotonically with E and is consistent with the observation of anisotropic mass distribution.     

Transitions and morphology of a thermotropic liquid-crystalline polyester with a flexible spacer

The mesomorphic transitions, crystallization from the mesophase, and the influence of the specimen preparation method on the solid-state structure of an aromatic polyester containing a triad aromatic ester mesogenic group and a decamethylene flexible spacer in the main chain were studied by DSC, SALS, WAXS, polarizing microscopy, torsional braid analysis, and depolarizing transmittance techniques. The specimens obtained from solution were semicrystalline and exhibited nematic mesophase formation above the melting point T_m, whereas the melt-cast specimens were mesomorphic as cast. A transition from the nematic phase to another mesophase, designated M_x, is proposed to occur below T_m, so this transition is monotropic. It appears that the transition to the M_x mesophase occurs before, and may even be a prerequisite for, crystallization of the melt-cast specimens. The thermal expansion coefficient of the anisotropic melt is close to that of the isotropic melt, and the T_g of the supercooled solid mesophase is close to that of the amorphous phase.     

Tripyrrindiones and a red-emitting fluorescent derivative

Abstract  

Orange-colored 7,8-dimethyl-2,3,12,13-tetramethoxy-(15H,17H)-tripyrrin-1,14-dione and its 2,3,7,8,12,13-hexaethyl analog were synthesized and converted to fluorescent derivatives by bridging a lactam nitrogen to the adjacent pyrrole nitrogen in a reaction with carbonyldiimidazole. The tripyrrindiones were also converted to the corresponding mono lactim methyl ethers by reaction with neat trimethylphosphite, and a corresponding difluoroboryl (BODIPY) derivative was made from the lactim by reaction with boron trifluoride etherate. X-ray structures of the tetramethoxytripyrrindione, the N,N′-carbonyl-bridged hexa-ethyltripyrrindione, and the lactim methyl ether of the hexa-ethyltripyrrindione were determined. The N,N′-bridged pigments exhibited very large Stokes’ shifts with fluorescence quantum yields ranging from 1.0 to 0.02.     

Elucidating the identity of Anisakis larvae from a broad range of marine fishes from the Yellow Sea,China, using a combined electrophoretic‐sequencing approach

Larval nematodes were collected from marine fishes from the Yellow Sea, China. Specimens (n=1731) of Anisakis type I from 311 fishes (representing 40 species) were each identified based on morphological characters. From the genomic DNA from individual specimens, a region of nuclear ribosomal DNA was amplified by PCR, followed by digestion with restriction endonuclease HinfI, TaqI or HhaI. Subsequently, the ITS‐1 and ITS‐2 regions of selected samples were sequenced. The results revealed three species of Anisakis, namely Anisakis pegreffii (n=1709), A. typica (n=3) and a genotype (n=19) proposed, also based on comparison with previous studies, to be a “hybrid” between A. pegreffii and A. simplex sensu stricto. Thus, A. pegreffii was the dominant species, accounting for 98.7% of the total number of specimens examined herein. This is the first report of A. typica and the “hybrid” genotype from fishes from the Yellow Sea. This study provides important basic information on Anisakis in this region and suggests that the genus Anisakis has substantial host and geographical distributions.     

Morphology of a liquid-crystalline polyester film

Morphological studies are reported for a thermotropic liquid crystalline polyester. Small angle light scattering studies were carried out as a function of temperature using H_v and V_v polarization with photographic as well as photometric techniques. No scattering was observed from a thin film cast from a dilute solution of the polymer in a highly volatile solvent. When the film was heated, scattering of light was observed above the glass transition temperature of the polyester. The scattering was found to be azimuthally dependent with V_v intensities being much higher than the corresponding H_v intensities. The size of the morphological features responsible for SALS patterns were calculated and were found not to change significantly with temperature ranging from glass transition temperature to the solid-nematic transition temperature of the polyester. The WAXS pattern of solution cast polymer was representative of an amorphous structure. Solution cast films heat treated under various conditions (all above the T_g of the polymer) contained crystalline as well as amorphous structures. The maximum apparent crystallinity for annealed samples was of the order of 30%.     

First genetic analysis of Cryptosporidium from humans from Tasmania,and identification of a new genotype from a traveller to Bali

Little is known about the molecular composition of Cryptosporidium species from humans living in the insular state of Tasmania, Australia. In the present study, we genetically characterized 82 samples of Cryptosporidium from humans following conventional coproscopic testing in a routine, diagnostic laboratory. Using a PCR‐coupled single‐strand conformation polymorphism (SSCP) technique, targeting portions of the small subunit rRNA (SSU), and 60 kDa glycoprotein (gp60) loci, we identified two species of Cryptosporidium, including C. hominis (subgenotypes IbA10G2, IdA16, IeA12G3T3, and IfA19G1) and C. parvum (IIaA16G1R1 and IIaA18G3), and a new operational taxonomic unit (OTU) that genetically closely resembled C. wrairi. This OTU was further characterized using markers in the actin, Cryptosporidium oocyst wall protein (COWP), and 70 kDa heat shock protein (hsp70) genes. This study provides the first characterization of species and genotypes of Cryptosporidium from Tasmania, and presents clear genetic evidence, using five independent genetic loci, for a new genotype or species of Cryptosporidium in a Tasmanian person with a recent history of travelling to Bali, Indonesia. It would be interesting to undertake detailed molecular‐based studies of Cryptosporidium in Indonesia and neighbouring countries, in conjunction with morphological and experimental investigations of new genotypes.     

Dielectric relaxation of a short molecule in a liquid-crystalline solvent

Abstract

Dielectric relaxation measurements of 5 mole % 4-n-hexyloxycyanobenzene (I) dissolved in 4-n-pentyloxyphenyl-trans-4-n-octylcyclohexylcarboxylate (II) were carried out from 1 kHz to 10 MHz in the nematic, smectic A and smectic B phases. The relaxation frequency of I parallel to the director is about 05 MHz in the S_Bphase and increases rapidly at the transition from S_B to S_A.     

Synthesis of a novel indolobenzodiazepine

2-[(5-Methyl-1,3,4-oxadiazol-2-yl)methyl]benzenamine ( 15 ) was prepared in four steps from o-nitrophenyl-acetic acid, and treated with triethyl orthoformate in an attempt to prepare an oxadiazolobenzodiazepine. However, the resulting product was 13-(5-methyl-1,3,4-oxadiazol-2-yl)-5H-indolo[2,1-b][1,3]benzodiazepine monohydrate ( 16 ). Indolobenzodiazepine 16 is the first reported member of a novel ring system. Interesting features of the synthesis of 16 are discussed, including the mechanism of formation from 15.     

Reactions on a 1,2-Dicarbonyl Moiety of a Fullerene Skeleton

A 1,2-dicarbonyl moiety on a cage-opened fullerene skeleton is one of suitable building blocks for the further derivatization. Herein, we discuss the chemical transformation of a 1,2-dicarbonyl compound into β-oxo-phosphorus ylide, acid anhydride, and α-methylene carbonyl derivatives. Despite possessing a sterically small methylene unit in the last one, the release of an encapsulated water molecule was significantly supressed whereas the β-oxo-phosphorus ylide bearing three bulky p-tolyl groups on the P-atom enabled the faster insertion/release dynamics, implying the flexibility of the phosphonium substituent. The replacement of the carbonyl group with phosphorus ylide and methylene units largely varied electrochemical properties of the fullerene skeleton, likely arising from the anionic charge delocalized over the entire molecule and removal of an electron-withdrawable carbonyl group, respectively.     

Stabilization of a β-Hairpin Conformation in a Cyclic Peptide Using the Templating Effect of a Heterochiral Diproline Unit

A straightforward and effective method of stabilizing a β-hairpin conformation in a cyclic protein loop mimetic is described, which exploits the templating effect of a heterochiral D -Pro-L -Pro dipeptide unit. A twelve-residue β-hairpin loop was grafted from the extracellular interferon γ receptor onto the heterochiral D -Pro-L -Pro dipeptide template to afford a fourteen-residue cyclic peptide. The residues directly attached to the D -Pro-L -Pro template are shown by NMR spectroscopy to structurally mimic corresponding residues in adjacent antiparallel β-strands in the receptor. MD Simulations with and without time-averaged distance restraints support this view and indicate that the tip of the loop is more flexible, as inferred also for the receptor protein from crystallographic data. The templating effect of the heterochiral diproline unit also promotes efficient backbone cyclization of the fourteen-residue linear peptide precursor, suggesting that a wide variety of related protein loop mimetics incorporating the D -Pro-L -Pro template might be readily accessible.     

Monte Carlo Computer Simulation of a Single Semi-Flexible Macromolecule at a Plane Surface

Summary: The properties of a single semiflexible mushroom chain at a plane surface with a long-ranged attracting potential are studied by means of lattice Monte Carlo computer simulation using the bond fluctuation model, configurational bias algorithm for chain re-growing and the Wang-Landau sampling technique. We present the diagram of states in variables temperature T vs. strength of the adsorption potential, ε_w, for a quite short semiflexible chain consisting of N = 64 monomer units. The diagram of states consists of the regions of a coil, liquid globule, solid isotropic globule, adsorbed coil and cylinder-like liquid-crystalline globule. At low values of the adsorption strength ε_w the coil–globule and the subsequent liquid–solid globule transitions are observed upon decreasing temperature below the adsorption transition point. At high values of ε_w these two transitions change into a single transition from an adsorbed coil to a cylinder-like liquid-crystalline solid globule. We conclude that for a semiflexible chain the presence of a plane attracting surface favors the formation of a globule with internal liquid-crystalline ordering of bonds.     

Neighboring effect of thiol group in acyl transfer reaction on a polymer with a lipoic acid structure

Reductive S-monoacylation of lipoamide with some carboxylic acids and tri-n-butylphosphine was carried out in acetonitrile to obtain the corresponding S-monoacylated compounds in excellent yield. This method was applied to the preparation of S-monoacylated dihydrolipoyl polymer with a neighboring thiol group. The acyl transfer from the polymer to cyclohexylamine was enhanced as much as 64 times by adding silver perchlorate.     

Dynamics of a polymer attached to a surface: Bead and spring model

The Smoluchowski formalism is used to solve the problem of a bead of frictional resistance β attached to a surface with a spring of force constant _k over which a linear shear field of strenght α flows. The power dissipation is given by βα²kT/_k. k and T have their usual meanings. The result is generalized to an n-bead polymer. It is found that the power dissipation of a Rouse model polymer attached to a surface at one end is twice that of an identical polymer flowing freely in solution. If the force constant _k arises from an entropy force, then, because of the effect of the surface on the number of polymer configurations, there is an additional factor of two. The same relationship is expected to also hold for the frequency-dependent power dissipation. It is argued that a net circulation exists in the beads above the surface and that the magnitude of the circulation is roughly comparable to that which exists in a polymer freely rotating in solution under a shear field of the same magnitude.