A facile synthesis of novel pyrazolo[5′,1′:3, 4]-[1, 2, 4]triazino[6, 5-f][1, 3, 4]thiadiazepines

The reaction of the 3-substituted 4-aminopyrazolo[5, 1-c][1, 2, 4]triazines 1a-d with thiosemicarbazide hydrochloride in acetic acid gave new pyrazolo[5′,1′:3, 4][1, 2, 4]triazino[6, 5-f][1, 3, 4]thiadiazepines 3, 4 and 6 , which were converted into the 5-oxo derivatives 5 and 7 by hydrolysis in hydrochloric acid/acetic acid.     

Surface-initiated living radical polymerization from silica particles functionalized with poly(ethylene glycol)-carrying initiator

A novel yet versatile approach is described for surface-initiated living radical polymerization (SI-LRP) from silica particles (SiPs). Monodisperse SiPs were surface-modified with a newly designed surface-fixable initiator (BPEGE) having three components: a triethoxysilane moiety, a poly(ethylene glycol) (PEG) unit, and an initiation site for atom transfer radical polymerization (ATRP) in the form of a 2-bromoisobutyryl group. The surface-initiated ATRP of methyl methacrylate (MMA) mediated by a copper complex was carried out with the BPEGE-fixed SiPs. The polymerization proceeded in a living manner, producing SiPs coated with well-defined poly(MMA) of a target molecular weight with a graft density as high as 0.5 chains/nm². Thanks to the amphiphilic property of PEG, the system was successfully applied for SI-ATRP of PEG methacrylate and sodium p-styrenesulfonate in aqueous media in which the BPEGE-fixed SiPs were highly dispersed without causing any aggregations. The formation of colloidal crystals with the polymer brush-afforded SiPs demonstrated the high uniformity and perfect dispersibility of the hybrid particles.     

A theoretical analysis of rheodielectric response of type‐A polymer chains

For type‐A polymer chains having type‐A dipoles parallel along the chain backbone (such as cis‐polyisoprene), a theoretical analysis was conducted for the rheodielectric response to relate this response to the chain dynamics. The rheodielectric response in the shear gradient direction (y direction) under steady shear was analyzed on the basis of a Langevin equation. It turned out that the relaxation time is exactly the same for the rheodielectric relaxation function and the end‐to‐end vector autocorrelation function defined in the shear gradient direction and that the relaxation mode distribution also coincides for these functions at least up to second order of the shear rate (corresponding to the lowest order of nonlinearities of these functions). Consequently, the Green‐Kubo theorem holds satisfactorily, and the rheodielectric intensity is proportional to the squared chain size in y direction, 〈R〉, averaged over the time‐independent conformational distribution function under steady shear. The situation is more complicated under large amplitude oscillatory strain (LAOS) because the conformational distribution function f_LAOS is synchronized with LAOS to oscillate at the LAOS frequency, Ω. The rheodielectric response under LAOS was found to detect this oscillation of f_LAOS being coupled with the oscillation of the electric field, E(t) = E₀sin ωt, and thus, split into a series of components oscillating at frequencies ω and ω ± βΩ (β = 1, 2, …). Consequently, the rheodielectric intensity under LAOS, evaluated from the component oscillating at ω, is no longer proportional to 〈R〉. However, the relative mode distribution and relaxation time of this component can be directly related to those of the end‐to‐end vector correlation averaged over a nonoscillatory part of f_LAOS. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1039–1057, 2009     

Development of a new fluorescence decay measurement system using two-dimensional single-photon counting

A new fluorescence decay measurement system has been developed. The system consists of a spectrograph and a new two-dimensional photon counter. The combination enables measurements to be made of the fluorescence decay as a function of time and wavelength simultaneously. The time resolution is better than 5 ps with deconvolution processing, and the wavelength resolution is approximately 0.15 nm with 1200 grooves mm⁻¹ gratings. The dynamic range is 10⁵. The instrument response function (IRF) of the system is nearly gaussian, and has no tail or “after pulses” which are commonly observed using a photomultiplier in a time-correlated photon counting (TCPC) system. Therefore fast fluorescence decay of several tens of picoseconds can be measured accurately. In addition, the two-dimensional single-photon counting can be performed without wavelength scanning, so that the wavelength-dependent fluorescence decay can be easily and direcly observed with a fast throughput and a high signal-to-noise ratio. The principle of two-dimensional photon counting is discussed together with characteristics including linearity and statistical behavior.     

Thermal hysteresis and thickness dependence of the molecular orientation of poly(di-n-hexylsilane) in the film state

Molecular orientation of poly(di-n-hexylsilane) adsorbed on poly(vinyl alcohol) film has been studied by making use of the stretching technique. Dichroic ratio, Rd, strongly depended on the thickness of poly(di-n-hexylsilane) thin film and the highest value ca. 19 was observed at the film thickness of 110 +/- 30 nm. The thermal hysteresis of the molecular orientation was observed in the heating-cooling cycles. By studying the fluorescence spectrum it was confirmed that a portion of the poly(di-n-hexylsilane) molecules were in transoid conformation even at 320 K, although most of poly(di-n-hexylsilane) molecules were in disordered conformation (conformation D). This poly(di-n-hexylsilane) in transoid conformation is formed in the stretching process and may play a role of crystallization nucleus to induce the whole orientation of the poly(di-n-hexylsilane) in the film state.     

The Synthesis and Dynamic Structures of Multinuclear Complexes of Large Porphyrinoids Expanded by Phenylene and Thienylene Spacers

1,3‐Bis(2‐pyrryl)benzene was used to prepare dibenziamethyrin, in which two pyrrole units of [24]amethyrin(1.0.0.1.0.0) are replaced by benzene. 1,4‐Bis(2‐pyrryl)benzene, 2,5‐bis(2‐pyrryl)thiophene, and 4,4′‐bis(2‐pyrryl)biphenyl were also used in place of 2,2′‐bipyrrole to give expanded analogues of [24]rosarin(1.0.1.0.1.0) and [32]octaphyrin(1.0.1.0.1.0.1.0). These large porphyrinoids can incorporate multiple metal units of Rh(CO)₂ and Pd(π‐allyl) with considerable deviation of the metal atoms from the dipyrrin planes, evidenced by X‐ray crystallography. The coordinated Rh(CO)₂ group shuttled between both sides of the macrocycle; the rate was dependent on the spacer, ring size, and number of metal atoms. Variable temperature ¹H NMR spectroscopy showed that the tris‐rhodium complexes of the expanded rosarins with 1,4‐phenylene or 2,5‐thienylene spacers adopt a C_3v‐symmetric form and a C_s‐symmetric form as a result of the Rh(CO)₂ groups hopping through the macrocycle cavity. The C_3v‐symmetric form has a greater dipole moment and, therefore, is favored in solvents of greater polarity. The Rh(CO)₂ groups in the tris‐rhodium complex of the expanded rosarin with 4,4′‐biphenylene spacers hop so fast that an averaged spectral pattern (D_3h) was seen in the ¹H NMR spectrum, even at ?60 °C. Expanded octaphyrins with 1,4‐phenylene and 2,5‐thienylene spacers bind four Rh(CO)₂ groups outside the macrocycle cavity to form a D_2d‐symmetric saddle‐shaped structure that did not show any dynamic behavior on the NMR timescale, even at 80 °C. This tetranuclear complex is one of the largest porphyrinoid metal complexes characterized by X‐ray crystallography to date.     

Studies on nepalese crude drugs. XXVIII. Chemical constituents of Bhote Khair, the underground parts of Eskemukerjea megacarpum HARA

From the underground parts of Eskemukerjea megacarpum HARA, two new stilbenes (14, 15) were isolated, together with a known coumarin, 5,7-dihydroxycoumarin (1), a tyramine derivative, trans-feruloyltyramine (2), two pyrogallol derivatives, gallic acid (3) and beta-glucogallin (4), four flavonoids, trifolin (5), hyperin (6), myricetin 3-O-beta-D-galactopyranoside (7), and myricitrin (8), five stilbenes, resveratorol (9), astringenin (10), piceid (11) astringin (12), and resveratorol 3-O-beta-D-(6-O-galloyl)glucopyranoside (13), a flavan-3-ol, (-)-epigallocatechin 3-O-gallate (16), two proanthocyanidins, catechin-(4alpha-->8)-epigallocatechin 3-O-gallate (17) and epicatechin 3-O-gallate-(4beta-->8)-epigallocatechin 3-O-gallate (18), and an anthocyanin, idaein (19). Compounds 14 and 15 were identified as (E)-3,5,3',4'-tetrahydroxystilbene 3-O-beta-D-(6-O-galloyl)glucopyranoside and (E)-3,5,4'-trihydroxystilbene 3-O-beta-D-(6-O-galloyl)glucopyranoside, respectively, based on spectral and chemical data.     

Improved 2-nitrobenzenesulfenyl method: optimization of the protocol and improved enrichment for labeled peptides

We have developed the NBS (2-nitrobenzenesulfenyl) method, a quantitative proteome analysis method utilizing stable isotope labeling followed by mass spectrometry. The potential of this method was reported previously, and the procedure has now been further optimized. Here, we describe a procedure utilizing urea or guanidine hydrochloride as a protein denaturant, in conjunction with an improved chromatographic enrichment method for the NBS-labeled peptides using a phenyl resin column. By using this new protocol, both sample loss throughout the protocol and the elution of unwanted unlabeled peptides can be minimized, improving the efficiency of the analysis significantly.     

Quenching mechanism of Rose Bengal triplet state involved in photosensitization of oxygen in ethylene glycol

The quenching rate constants of the excited triplet state of Rose Bengal (RB) by oxygen (k(obs)) were measured in ethylene glycol (EG) at different temperatures using nanosecond laser flash photolysis. Although a plot of the quenching rate constant k(obs) for RB triplet state vs oxygen concentration is linear at 20 degrees C, the oxygen dependence of k(obs) does not exhibit linearity but upward curvature at high temperatures from 130 to 140 degrees C. The upward curvature at high temperatures is not well-described by a kinetic scheme first postulated by Gijzeman et al., which is characterized by exciplex formation and a unimolecular dissociation of the exciplex to products, but instead by a more comprehensive mechanism involving a bimolecular dissociation in addition to a unimolecular one. The measurements of the oxygen dependence of k(obs) for RB triplet state at different temperatures yielded a reaction enthalpy for the exciplex formation of 150 kJ mol(-1). Due to the large exothermic reaction enthalpy, equilibrium was obtained for the exciplex at 20 degrees C even at low oxygen concentration and the bimolecular quenching by oxygen became the major dissociation process. The equilibrium attainment and bimolecular dissociation provide a linear oxygen dependence of k(obs) to all outward appearances. Therefore, linearity does not always mean that exciplex dissociation proceeds solely through a unimolecular mechanism.     

Molecular-shape imprinting and immobilization of biomolecules on a polymer containing azo dye

We demonstrate a novel technique for molecular imprinting and immobilization on a surface of a polymer containing azo dyes (azopolymer). The azopolymer was found to be capable of immobilizing micrometer- and nanometer-scale macromolecules (e.g., lambda-DNA, immunoglobulin G (IgG), bacterial protease, and 1-mum polystyrene particles) through photoirradiation with blue-wavelength light. Fluorescence and atomic force microscopy studies revealed that the azopolymer surface deformed along with the shape of the macromolecules, holding them in place after photoirradiation. The desorption of the immobilized macromolecules from the azopolymer surface in an aqueous medium was observed to be very slow, on the time scale of 10 min to weeks, depending on the photoirradiation time. Immunological and enzymatic studies showed that IgG and bacterial protease immobilized on the azopolymer surface retained their original functionality. These results suggest that the azopolymer physically, not chemically, binds the macromolecules because of the increase in contact area between the macromolecules and the azopolymer surface after photoirradiation.