bluuebunny/crossref_metadata_2025 huggingface dataset:
TGFβ inhibition of yolk-sac-like differentiation of human embryonic stem-cell-derived embryoid bodies illustrates differences between early mouse and human development
Authors: Poon Ellen , Clermont Frederic , Firpo Meri T. , Akhurst Rosemary J.
Published: February 2006

Transforming growth factor β (TGFβ) plays an important role in development and maintenance of murine yolk sac vascular development. Targeted deletions of Tgfb1 and other components of this signaling pathway, such as Acvrl1, Tgfbr1 and Tgfbr2, result in abnormal vascular development especially of the yolk sac, leading to embryonic lethality. There are significant differences between murine and primate development that limit interpretation of studies from mouse models. Thus, to examine the role of TGFβ in early human vascular development we used the model of differentiating human embryonic stem cell-derived embryoid bodies to recapitulate early stages of embryonic development. TGFβ was applied for different time frames after initiation of embryoid body cultures to assess its effect on differentiation. TGFβ inhibited the expression of endodermal, endothelial and hematopoietic markers, which contrasts with findings in the mouse in which TGFβ reduced the level of endodermal markers but increased endothelial marker expression. The inhibition observed was not due to changes in proliferation or apoptosis. This marked contrast between the two species may reflect the different origins of the yolk sac hemangiogenic lineages in mouse and human. TGFβ effects on the hypoblast, from which these cell lineages are derived in human, would decrease subsequent differentiation of hematopoietic, endothelial and endodermal cells. By contrast, TGFβ action on murine hypoblast, while affecting endoderm would not affect the hemangiogenic lineages that are epiblast-derived in the mouse. This study highlights important differences between early human and mouse embryonic development and suggests a role of TGFβ in human hypoblast differentiation.
Par-1 kinase establishes cell polarity and functions in Notch signaling in theDrosophilaembryo
Authors: Bayraktar Jennifer , Zygmunt Deborah , Carthew Richard W.
Published: February 2006

The Drosophila protein kinase Par-1 is expressed throughout Drosophila development, but its function has not been extensively characterized because of oocyte lethality of null mutants. In this report, we have characterized the function of Par-1 in embryonic and post-embryonic epithelia. Par-1 protein is dynamically localized during embryonic cell polarization, transiently restricted to the lateral membrane domain, followed by apicolateral localization. We depleted maternal and zygotic par-1 by RNAi and revealed a requirement for Par-1 in establishing cell polarity. Par-1 restricts the coalescing adherens junction to an apicolateral position and prevents its widespread formation along the lateral domain. Par-1 also promotes the localization of lateral membrane proteins such as Delta. These activities are important for the further development of cell polarity during gastrulation. By contrast, Par-1 is not essential to maintain epithelial polarity once it has been established. However, it still has a maintenance role since overexpression causes severe polarity disruption. Additionally, we find a novel role for Par-1 in Notch signal transduction during embryonic neurogenesis and retina determination. Epistasis analysis indicates that Par-1 functions upstream of Notch and is critical for proper localization of the Notch ligand Delta.
The role of MAP65-1 in microtubule bundling duringZinniatracheary element formation
Authors: Mao Guojie , Buschmann Henrik , Doonan John H. , Lloyd Clive W.
Published: February 2006

The MAP65 family of microtubule-associated proteins performs various functions at different stages of the cell cycle and differentiation. In this study, we have investigated the synchronous transdifferentiation of Zinnia mesophyll cells into tracheary elements in vitro. This allowed us to examine the role of the microtubule-associated protein MAP65 during the characteristic bunching of cortical microtubules that underlie the developing ribs of secondarily thickened cell wall. Immunofluorescence confirmed the microtubule bundles to be decorated with anti-MAP65 antibodies. Three Zinnia MAP65 genes were examined; the expression of ZeMAP65-1 was found to match that of the differentiation marker TED2 and both were found to be upregulated upon addition of inductive hormones. We cloned the full-length sequence of ZeMAP65-1 and found it to be most similar to other MAP65 isoforms known to bundle microtubules in other plant species. However, not all MAP65 proteins crosslink cortical microtubules and so, to confirm its potential bundling capacity, ZeMAP65-1 was transiently overexpressed in Arabidopsis suspension cells. This resulted in the super-bundling of microtubules in patterns resembling those in differentiating xylem cells. These findings establish that the MAP65-1 group of proteins is responsible for the bundling of cortical microtubules during secondary cell wall formation of xylogenesis as well as during the expansion of primary cell walls.
A Divide-and-Conquer Algorithm Use to Study Some Benzenoid Hydrocarbons. A Graphtheoretic and Computational Approach
Authors: Patra Swarna M , Mishra Rama K
Published: February 2006

A computer program based on a divide-and-conquer algorithm was used to numerically split a univariate polynomial into factors depicting the various parts of Eπ (π: electronic energy) and K (total Kekulé structure count) of the benzenoid graphs. A multivariate regression equation is suggested, taking n, m, and Ki as the independent variables and Eπ (total) as the dependent variable; n, m, and Ki are the number of vertices, edges, and the fraction of the total K, respectively. A satisfactory correlation coefficient (R2 > 0.99) was obtained.
ESR Studies on Irreversible Reactions of Poly(methyl methacrylate) Radicals and on Structures of Stable Polymer Radicals in the Frozen State
Authors: Sugiyama Yoshio
Published: February 2006

Irreversible reactions of poly(methyl methacrylate) radicals generated from the polymerization of methyl methacrylate (MMA) and structures of the produced stable polymer radicals in the frozen state have been investigated by Electron Spin Resonance (ESR). The stable polymer radicals were produced through disproportionation and addition reactions of poly(MMA) radicals. The structure of stable polymer radicals was also determined by the simulation of the ESR spectrum.
Extractive Separation of Selenium and Tellurium Using 2,3,5-Triphenyltetrazolium Chloride
Authors: Ramesh A , Subramanian M S
Published: February 2006

A simple and selective solvent-extraction method has been devised for the separation of SeIV and TeIV, not only from each other, but also from the other accompanying elements. 2,3,5-Triphenyltetrazolium chloride has been used as an extractant for the quantitative extraction of TeIV and SeIV from bromide and thiocyanate medium, respectively. The formed ion-pair complex of TeIV and SeIV can be quantitatively extracted into a dichloromethane and 1 : 1 cyclohexanol–toluene solvent mixture, respectively. The optimum conditions have been evaluated based on a critical study of the acid concentration, extractant concentration, period of equilibration, effect of dilution and effect of the solvent. Water was used for the stripping of tellurium, while a fresh solution of sodium hypobromite was used for selenium. This separation procedure in conjunction with the developed methods was applied to an analysis of the selenium and tellurium content of copper concentrate, incineration ash and In–Sb alloy samples.
Aggregation Effects on Electrochemical and Spectroelectrochemical Properties of [2,3,9,10,16,17,23,24-Octa(3,3-dimethyl-1-butynyl)phthalocyaninato]cobalt(II) Complex
Authors: Isago Hiroaki , Leznoff Clifford C , Ryan Matthew F , Metcalfe Robert A , Davids Rifka , Lever A B P
Published: February 2006

The title complex, [Co(odmbpc)], which is a single isomer and is highly soluble in common organic solvents, has been prepared and investigated electrochemically and spectroelectrochemically in dichloromethane solutions. The cyclic voltammograms of this complex at a concentration of ca. 6 × 10−5 mol dm−3 exhibited two reversible reduction waves at E1/2 = −0.67 V (vs. ferrocenium+/ ferrocene) and −1.74 V, which were attributed to cobalt-centered and triple-bond-centered (in a peripheral substituent) reductions, respectively, and three quasi-reversible oxidation waves at 0.26, 0.46, and 0.74 V, the former two and the latter one of which were attributed to phthalocyanine-chromophore-centered and cobalt-centered oxidations, respectively. Some of these assignments were supported by the electronic absorption spectra of the electro-generated species. The first reduction wave was not observed at 6 × 10−4 mol dm−3 until the applied potential was swept to the second reduction wave. Nevertheless, under the same conditions, the controlled-potential electrolyses in an optically transparent thin-layer electrode at potentials around the first reduction wave gave rise to drastic spectral changes without any preliminary electrolysis at potentials around the second reduction wave. Such strange phenomena are discussed in terms of molecular aggregation of the complexes in solutions. The peripheral alkynyl group has been found to be slightly electron-donating.
Preparation and Properties of S-Bridged CoIIIAgI3CoIII Pentanuclear Complexes Having a Triple Helical Chirality. Crystal Structure of [Ag3{Co(aet)3}2](BF4)3 (aet = 2-Aminoethanethiolate)
Authors: Konno Takumi , Tokuda Keiji , Suzuki Tomoya , Okamoto Ken-ichi
Published: February 2006

Novel S-bridged CoIIIAgI3CoIII pentanuclear complexes, [Ag3{Co(aet)3}2]3+ (1) and [Ag3{Co(l-cys-N,S)3}2]3− (2), were prepared by reacting fac(S)-[Co(aet)3] (aet = 2-aminoethanethiolate) or ΔLll-fac(S)-[Co(l-cys-N,S)3]3− (l-cys = l-cysteinate) with Ag+ in a ratio of 2 : 3. The crystal structure of 1(BF4)3 was determined by X-ray crystallography. 1(BF4)3·H2O, chemical formula C12H38B3N6OF12S6Co2Ag3, crystallizes in the orthorhombic space group Pnma with a = 16.397(2), b = 13.239(2), c = 15.803(4) Å, V = 3430.5(9) Å3, Z = 4, and R = 0.066. In 1 the two thiolato S atoms from two octahedral fac(S)-[Co(aet)3] units coordinate to each of three Ag atoms, such that the three S–Ag–S linkages form a triple helical structure. 1 gave only racemic isomer, ΔΔ and ΛΛ, which were optically resolved by cation-exchange column chromatography, while the ΔLllΔLll isomer was selectively formed for 2 with a retention of the absolute configuration of the starting ΔLll-fac(S)-[Co(l-cys-N,S)3]3−. 1 was converted to the S-bridged tricobalt(III) complex [Co{Co(aet)3}2]3+ by a reaction with I− in the presence of Co2+, accompanied by an intermolecular exchange and racemization of the Δ/Λ-fac(S)-[Co(aet)3] units. The electronic absorption and CD spectral properties of 1 and 2 are also reported.
Chromatographic Resolution of a Diastereomeric Mixture of Tris(trans-1,2-diaminocyclohexane)cobalt(III) by Bis(μ-tartrato)diantimonate(III) Anion and Association Modes Found in Their Diastereomeric Salts
Authors: Mizuta Tsutomu , Sasaki Ken-ichi , Yamane Hiromi , Miyoshi Katsuhiko , Yoneda Hayami
Published: February 2006

The chromatographic resolution of a diastereomeric mixture of Λ-ob3-, Δ-ob3-, Λ-lel3-, and Δ-lel3-[Co(chxn)3]3+ (chxn = trans-1,2-diaminocyclohexane) was carried out on an ion-exchange column using bis(μ-tartrato)diantimonate(III), [Sb2(d-tart)2]2− as a resolving reagent. The resulting elution order of Λ-ob3 > Λ-lel3 > Δ-lel3 > Δ-ob3 was interpreted on the basis of an association model in which lone-pairs on three oxygen atoms of [Sb2(d-tart)2]2− form triple hydrogen bonds with three N–H groups directed along the C3-axis of [Co(chxn)3]3+. Since the three N–H groups of the Λ-ob3 isomer have a right-handed helicity, they form the strongest linear hydrogen bonds with the three lone-pairs of [Sb2(d-tart)2]2−, which are also spirally oriented in the same sense, whereas those of the two lel3 isomers having practically no such helicity form weaker hydrogen bonds, and those of the Δ-ob3 isomer having the opposite helicity have the hydrogen bonds much damaged. To obtain structural evidence for the above association model, crystal structures of diastereomeric salts, Λ-ob3-[Co(chxn)3]X[Sb2(d-tart)2]·nH2O, X− = Cl− (1) and ClO4− (2) have been determined by single-crystal analyses. The crystal data are as follows: 1 is orthorhombic, with a space group P212121, Z = 4, a = 10.823(2), b = 17.901(7), c = 21.477(6) Å, V = 4161(2) Å3, and R = 0.057; 2 is monoclinic with a space group P21, Z = 4, a = 13.338(2), b = 17.119(3), c = 18.060(3) Å, β = 98.31(1)°, V = 4080(1) Å3, and R = 0.049. In both crystals, [Sb2(d-tart)2]2− approaches Λ-ob3-[Co(chxn)3]3+ along the C3-axis of the complex to form multiple hydrogen bonds, as expected, and one of the contact modes found in 2 is close to our proposed association model.
Characteristic Behavior of an Electron-Transfer Reaction across a Tributyl Phosphate Droplet/Water Interface: Micrometer Droplet-Size Effect
Authors: Chikama Katsumi , Nakatani Kiyoharu , Kitamura Noboru
Published: February 2006

An electron-transfer (ET) reaction between decamethylferrocene in a single tributyl phosphate (TBP) droplet and hexacyanoferrate(III) in the surrounding water phase was investigated by laser trapping, microspectroscopic, and electrochemical techniques. The interfacial ET rate constant (kobs) was inversely proportional to the droplet radius (r) at > 5 μm, but deviated from a linear relationship between kobs and r−1 at r < 5 μm. The characteristic droplet-size effect was independent of the Galvani potential between the TBP and water phases. The results are discussed in terms of the physical properties of the micrometer-sized TBP droplet/water interface.
Molecular Structure of Hg-Bridged Tetramethyl[2]ferrocenophane Salt ([{C5H4(CH3)2}2Fe–Hg–Fe{C5H4(CH3)2}2]2+ (BF4−)2) and Related Salts
Authors: Watanabe Masanobu , Nagasawa Akira , Sato Masaru , Motoyama Izumi , Takayama Toshio
Published: February 2006

The crystal form of the salt [{C5H4(CH3)2}2Fe–Hg–Fe{C5H4(CH3)2}2Hg(BF4)2, 1], prepared by a reaction of tetramethyl[2]ferrocenophane and Hg(CN)2 in ethanol containing HBF4, is triclinic, space group , a = 9.315(3), b = 12.823(4), c = 14.108(5) Å, α = 106.055(2), β = 100.253(2), γ = 94.460(2)°, Z = 2 and the final R = 0.059 and Rw = 0.072. Two ferrocene moieties are coordinated to the Hg atom from the opposite side, and the previously proposed Fe–Hg–Fe bridged structure has been verified. The structural feature of the cation is found in the conformation of the ferrocene moiety around the Fe–Hg–Fe bond. In order to reduce the steric hindrance between the Hg and ferrocene moieties, each moiety rotates largely with respect to the other (the torsion angle of the Cpcnt–Fe(1)···Fe(2)–Cpcnt is 75(1)° and Cpcnt is defined as the centroid of the Cp-ring). The mean Fe–Hg distance is 2.598(8) Å and the Fe–Hg–Fe bond angle is 176.4(1)°. The two C5H4 rings are greatly tilted, the mean tilting angle between them being 33.72°. Analogous Hg(II) salts of ruthenocene (2) and osmocene (3) were prepared by a similar method. Crystal 2 is monoclinic, space group P21/a, a = 9.633(1), b = 18.864(3), c = 13.388(1) Å, β = 94.161(9)°, Z = 4 and the final R = 0.058 and Rw = 0.072. The mean Ru–Hg distance is 2.661(2) Å and the Ru–Hg–Ru bond angle is 174.4(1)°; the mean tilting angle between the C5H4-planes is 27.39°. The structure of the cation is very similar to that of 1 (the torsion angle of the Cpcnt–Ru(1)···Ru(2)–Cpcnt is 70(1)°).

The crystal form of 3 is triclinic, space group , a = 9.823(1), b = 11.194(1), c = 12.241(1) Å, α = 113.822(8), β = 95.828(8), γ = 90.104(8)°, Z = 2 and the final R = 0.030 and Rw = 0.032. The mean Os–Hg distance is 2.69(2) Å and the Os–Hg–Os angle is 170.1(3)°. The most interesting structural difference of 3 compared with 1, 2 is found to be the conformation of the osmocene moieties around the Os–Hg–Os bond. The two moieties are coordinated to Hg in parallel, and the torsion angle of Cpcnt–Os(1)···Os(2)–Cpcnt is negligible (2(1)°) so as to reduce the steric hindrance between the cations and the PF6− anions.
High Activities of Hydrogen Peroxide Decomposition Catalyzed by Dinuclear Schiff Base Mn(III)–Cu(II) Complexes Accompanying Metal Substitution in N,N-Dimethylformamide and the Crystal Structure of a Substituted Schiff Base Cu(II) Complex
Authors: Uehara Minori , Urade Mika , Ueda Atsuko , Sakagami Narumi , Abe Yuriko
Published: February 2006

The effects of divalent metal ions (M2+ = Mn2+, Co2+, Ni2+, Cu2+, and Zn2+ ions) on the catalase-like activities of mononuclear Schiff base Mn(III) complexes, such as [Mn(salen)Cl] (H2salen: N,N′ -ethylenebis(salicylideneamine)), [Mn(saltn)Cl] (H2saltn: N,N′-propane-1,3-diylbis(salicylideneamine)), [Mn(saltnOH)Cl] (H2saltnOH: N,N′-(2-hydroxypropane-1,3-diyl)bis(salicylideneamine)), and [Mn(saltnOCOPh)Cl] (H2saltnOCOPh: N,N′-(2-benzoyloxypropane-1,3-diyl)bis(salicylideneamine)), in N,N-dimethylformamide (DMF) have been reported. Except for the Cu2+ ion, H2O2 decomposition was depressed in the presence of M2+ = Mn2+, Co2+, Ni2+, and Zn2+ ions because [Mn(salen)]+reacted with M2+ to give dinuclear Mn(III)–M(II) and trinuclear Mn(III)2–M(II) complexes inactive toward H2O2 in DMF. For the Cu2+ ion, the dinuclear complexes with the salen and saltnOCOPh ligands showed high activities, although the trinuclear complexes were inactive toward H2O2. The ESR spectra suggested that the intramolecular electron transfer from Cu(II) to Mn(III) on the dinuclear Mn(III)–Cu(II) complex partly occurs to produce a dinuclear Mn(II)–Cu(III) complex active toward H2O2. During H2O2 decomposition including the radical reaction path, [Cu(salR)] (R = en, tnOCOPh) and Mn2+ were produced accompanying metal substitution by Cu2+ on the dinuclear complex. To clarify the substituted product, the preparation and an X-ray crystal structure analysis of [Cu(saltnOCOPh)] were carried out. Three independent [Cu(saltnOCOPh)] complexes (CuA, CuB, and CuC) were present along with an intermolecular π–π stacking interaction between benzene rings on the salicylidenediamine moiety and benzene ring on the benzoyloxy group in the crystal. The geometries around the coppers in both CuA and CuC are more distorted toward tetrahedral from square plane than that in CuB. No stacking interaction between benzene rings on [Cu(saltnOCOPh)] occurs in DMF solution.
Studies on the Retrogradation and Structural Properties of Waxy Corn Starch
Authors: Ogawa Kazuo , Yamazaki Isao , Yoshimura Toshiaki , Ono Shin , Rengakuji Seichi , Nakamura Yuuko , Shimasaki Choichiro
Published: February 2006

The protective effect of guanidine hydrochloride (Gu-HCl) on the retrogradation of waxy corn starch (WCS) gel was studied using differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR), and solid-state 1H nuclear magnetic resonance (NMR). The areas of the endothermic peaks on DSC curves attributed to re-gelatinization of WCS gels became small and shifted to lower temperature with increasing Gu-HCl contents; finally, the endothermic peak for WCS gel containing 40% Gu-HCl disappeared, indicating that the WCS gel remained in the gelatinized state.

The solid-state 1H NMR and FT-IR spectra for retrograded WCS gels showed significant changes compared with those for gelatinized WCS gels. In the process of retrogradation, these spectral changes should imply the formation of intra- and intermolecular hydrogen bonds of WCS and the increase of free water molecules. However, the 1H NMR and FT-IR spectra for a WCS gel containing 40% Gu-HCl did not show such changes along with the progress of retrogradation. From these results, we found that the retrogradation of starch can be protected by the addition of hydrogen bond-breaking materials, such as Gu-HCl.
Thermally Irreversible Photochromic Systems. Reversible Photocyclization of 2-(1-Benzothiophen-3-yl)-3-(2 or 3-thienyl)maleimide Derivatives
Authors: Uchida Kingo , Kido Yuichi , Yamaguchi Tadatsugu , Irie Masahiro
Published: February 2006

Non-symmetric diarylethenes that have a 1-benzothiophene ring on one end and a 2-thienyl or 3-thienyl group on the other end of the double bond of maleimide were synthesized in order to study the effects of the substitution position of the thiophene ring on the absorption bands and the reactivities. The open-and closed-ring forms of N-cyanomethyl-2-(2,4-dimethyl-5-phenyl-3-thienyl)-3-(2-methoxy-1-benzothiophen-3-yl)maleimide showed absorption bands at 420 and 563 nm in hexane, respectively. When 3-thienyl was changed to 2-thienyl, the absorption bands of N-cyanomethyl-2-(3,4-dimethyl-5-phenyl-2-thienyl)-3-(2-methoxy-1-benzothiophen-3-yl)maleimide shifted to 448 nm (the open-ring form) and 487 nm (the closed-ring form), respectively. The cyclization and ring-opening quantum yields were also dependent on the substitution position. The cyclization yield decreased from 0.30 to 0.03 by changing the position from 3- to 2-thienyl, while the ring-opening yield increased from 0.03 to 0.13. No absorption spectral change by photoirradiation was observed for N-cyanomethyl-2,3-bis(3,4-dimethyl-5-phenyl-2-thienyl)maleimide, which has two 2-thienyl groups.
The Role of Water-Solvation in the Optical Resolution of Dl-Leucine with (S)-(−)-1-Phenylethanesulfonic Acid. Characterization and X-Ray Crystal Structures of Their Diastereomeric Salts
Authors: Yoshioka Ryuzo , Okamura Kimio , Yamada Shin-ichi , Aoe Ken-ichi , Da-te Tadamasa
Published: February 2006

In the optical resolution by diasteromeric salt formation of Dl-leucine with (S)-(−)-1-phenylethanesulfonic acid (PES), the less-soluble l-Leu·(−)-PES salt preferentially crystallized from acetonitrile–methanol and, in contrast, the same resolution from acetonitrile–water afforded the monohydrated d-salt [d-Leu·(−)-PES·H2O]. The role of the water of crystallization formed during this resolution system has been explored through a comparison of the crystalline characteristics of d-, monohydrated d-, and l-Leu·(−)-PES by thermoanalysis (DSC) and spectroscopy. The DSC indicated that d-Leu·(−)-PES had a polymorphic form with the water of crystallization; that is, d-Leu·(−)-PES·H2O was thoroughly dehydrated at 60—90 °C and simultaneously converted into the d-Leu·(−)-PES form. However, l-Leu·(−)-PES does not have the water of crystallization even in 75% relative humidity. Detailed comparisons among the X-ray crystal structures of three salts have revealed that in all of the salts the conformations of the PES anion and the Leu cation, respectively, were approximately the same, and their crystal structures comprised specific interaction modes having characteristic hydrogen-bond networks. In particular, in d-Leu·(−)-PES·H2O the PES and Leu ions are cross-linked to each other through water molecules. These observations suggested that the water of crystallization, together with the formation of a stable crystal-packing mode by cross-linking the PES and Leu ions, presumably plays an important role in the selective crystallization in the resolution.
Molecular Design of Highly Selective and Sensitive “Sugar Tweezers” from Boronic Acid-Appended μ-Oxo-bis[porphinatoiron(III)]s
Authors: Takeuchi Masayuki , Imada Tomoyuki , Shinkai Seiji
Published: February 2006

5,10,15,20-Tetrakis[3- and 4-(dihydroxyboryl)phenyl]porphinatoiron(III)s (1a and 1b, respectively) were synthesized and the saccharide-binding ability of their μ-oxo dimers was investigated. The saccharide-binding process with boronic acids can be conveniently monitored by CD spectroscopy. The μ-oxo dimer of 1b with 4-(hydroxyboryl) groups can bind glucose and galactose among monosaccharides with extremely high selectivity and sensitivity (association constants 104—105 dm3 mol−1), whereas that of 1a with 3-(hydroxyboryl) groups shows only a weak affinity with these monosaccharides. A similar trend was also observed for disaccharides. The origin of the CD activity in 2b can be ascribed to the formation of 1 : 1 μ-oxo dimer/saccharide complexes, in which two porphyrin rings are chirally bridged by one saccharide molecule. The CD sign is well-correlated with the absolute configuration of these saccharides. Thus, the present paper demonstrates that the μ-oxo dimer of 1b, which is formed in a self-assembled manner in aqueous alkaline solution, acts as an excellent pair of artificial “sugar tweezers”.
Synthesis and Physical Properties of Pyrido[1′,2′ : 1,2]imidazo[4,5-b]quinoxalines
Authors: Tomoda Haruhiko , Saito Shojiro , Araki Koji , Shiraishi Shinsaku
Published: February 2006

A series of 2-, 3-, or 4-substituted pyrido[1′,2′ : 1,2]imidazo[4,5-b]quinoxalines (PIQs) were synthesized in moderate-to-good yields by the reactions of 2-amino-3-chloroquinoxalines (ACQs) with substituted pyridines, and the structures were established. The reactions of ACQs with 3-phenoxycarbonyl and 3-benzoylpyridines gave the corresponding 2-substituted PIQs, while those with 3-methyl, 3-ethyl, 3-benzyl, 3-phenyl, 3-ethoxycarbonyl, and 3-acetylpyridines gave the corresponding 4-substituted PIQs. PIQ derivatives having substituents at the 2,4,8, and/or 9-positions were also studied. The spectroscopic and electrochemical properties of a series of PIQs derivatives were studied. PIQ showed a strong green fluorescence at 481.5 and 505 nm (Φ = 0.40) in ethanol. The introduction of substituents at the 3 position of PIQ altered the color of the fluorescence from blue to green without deteriorating the high quantum yield of PIQ. All of the derivatives showed strong (blue to orange) fluorescence in both solution and the solid state.
Hydrogen-Transfer Polymerization of Vinyl Monomers Derived from p-Tolylsulfonyl Isocyanate and Acrylamide Derivatives
Authors: Iwamura Takeru , Tomita Ikuyoshi , Suzuki Masato , Endo Takeshi
Published: February 2006

The hydrogen-transfer polymerization of N-acryloyl-N′-p-tolylsulfonylurea (1) prepared by the reaction of p-tolylsulfonyl isocyanate with acrylamide, was carried out at 80 °C for 24 h in N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile (MeCN), and toluene containing N-phenyl-2-naphthylamine (1 mol%) as a radical inhibitor using t-BuOK or 1,3-diazabicyclo[5.4.0]undec-7-ene (DBU) (3 mol%) as an initiator. Polymers obtained by t-BuOK in polar solvents were composed of the hydrogen-transfer polymerization unit selectively, while those afforded by t-BuOK in less polar solvents or by DBU were composed of both the hydrogen-transfer and the vinyl polymerization units. Although N-acryloyl-N-methyl-N′-p-tolylsulfonylurea (2) prepared by the reaction of p-tolylsulfonyl isocyanate with N-methylacrylamide, gave low molecular-weight compounds (6—8) via the generation of the sulfonyl isocyanate, N-acryloyl-N′-methyl-N′-p-tolylsulfonylurea (3) underwent the selective hydrogen-transfer polymerization.
Hydrocarbon Anions with High Stability. Part 2. Structure and Stability of Cyclopentadienide Ions with Condensed Aromatic Rings
Authors: Kinoshita Tomomi , Fujita Masaya , Kaneko Hideyuki , Takeuchi Ken’ichi , Yoshizawa Kazunari , Yamabe Tokio
Published: February 2006

The ionization-potential and oxidation-potential values have been examined as stability parameters in the gas and solution phase, respectively, for cyclopentadienide ions with from one to four condensed aromatic rings. They indicate that, without solvation effects, the condensed aromatic rings intrinsically stabilize the cyclopentadienide ion in solution as well as in the gas phase, and that an apparent destabilization effect by the aromatic rings in solution is most probably ascribed to a decrease in the stabilizing solvation effects due to charge delocalization on the carbanions. Theoretical investigations from governing orbital interactions using the frontier orbital theory demonstrate that the essential stability of the cyclopentadienide ions is dependent on the structure, itself.
N- and C-Terminal Effect of Amphiphilic α-Helical Peptides on the Interaction with Model- and Bio-Membranes
Authors: Kitamura Akiko , Kiyota Taira , Lee Sannamu , Sugihara Gohsuke
Published: February 2006

We previously designed and synthesized five N- and C-termini-free amphiphilic α-helical model peptides (Hel series) with a systematically varied hydrophobic–hydrophilic balance (HHB) that showed hemolytic activity, but no antimicrobial activity. However, an N-acetylated and C-amidated model peptide, peptide 3 [S. E. Blondelle and R. A. Houghten, Biochemistry, 31, 12688 (1992)], similar to a Hel series peptide, Hel 9-9, whose hydrophobic and hydrophilic amino acid residues and areas are equal in the α-helical structure, have exhibited both hemolytic and antimicrobial activities. Thus, to investigate the N- and C-terminal effect of the Hel series peptides on their antimicrobial activity, we designed and synthesized three peptides (Cap-Hel series), both termini-blocked by N-acetyl and C-amide groups. Their interaction mode with membranes was examined through reverse-phase high-performance liquid chromatography and circular dichroism spectroscopy as well as measurements of the hemolytic activity, antimicrobial activity, and membrane-clearing ability. No essential difference was found in either the terminal-free or -protected peptides, indicating that acetylation of the N-terminal and amidation of C-terminal did not affect their intrinsic antimicrobial activity in spite of a considerable change in the binding properties to lipids and hemolytic activities.
Distal Effect of Amide and Amino Groups on the Oxygen Activation Ability and Rate of the Redox Reaction of Simplified Analogs of Bleomycin
Authors: Arai Takayuki , Shinozuka Kazuo , Sawai Hiroaki
Published: February 2006

New simple bleomycin (BLM) model compounds, which bear a carbamide (1), bulky t-butyl (2), simple alkyl (3), or amino group (4) around the sixth coordination site, have been synthesized in order to study the effect of the distal substituents on the redox reaction and oxygen activation ability of the iron complexes. The carbamide group in 1 lowers the pK values of the all-amino donors of the ligand, which enhances complex formation. The oxygen activation ability of the Fe(II) complexes of 1, 2, 3, and 4, is 74, 69, 43, and 41%, respectively, of that of BLM. The rate of reduction of the Fe(III) complexes of the model compounds and BLM with a reducing agent is more than ten-times lower than that of the oxygenation and activation of the corresponding Fe(II) complexes, indicating the low turnover of the iron complexes of the model compounds and BLM in the reversible redox reaction.
Synthesis of 9-Deoxy-15-hydroxycotylenol and Its Germination-Stimulating Activity on Lettuce Seeds
Authors: Kato Nobuo , Li Feng , Mori Akira , Takeshita Hitoshi
Published: February 2006

Cotylenins and fusicoccins, fungal diterpenoid glycosides, are know to have identical, yet unique, plant growth-regulating activities. These compounds widen the stomatal pore, stimulate cell enlargement, break seed dormancy, and stimulate rhizogenesis. Because of these plant-hormone like activities, fusicoccin, a representative of this family, has been widely utilized in plant physiology. During the course of our study on the structure-activity relationships of this class of compounds, 9-deoxy-15-hydroxycotylenol and its 15-methoxymethyl ether were synthesized in order to clarify the role of the 9α-hydroxy group of cotylenol, a common aglycon of cotylenins. Since these cotylenol analogs retained germination-stimulating activity on lettuce seeds, it has been clarified that the 9α-hydroxy group of cotylenol is not essential for its biological activities. This finding is informative in designing useful tools for targeting the 14-3-3 protein, which has recently been identified as the binding protein of fusicoccin.
Ring-Opening and Ring-Expansion Study of 3,4-Di(1-adamantyl)-1,2-dithiete
Authors: Nakayama Juzo , Masui Nobuo , Sugihara Yoshiaki , Ishii Akihiko
Published: February 2006

Reduction of 3,4-di(1-adamantyl)-1,2-dithiete (2) with LiEt3BH, followed by treatment with MeI, gave (E)-1,2-di(1-adamantyl)-1,2-bis(methylthio)ethene (7-E) in 87% yield. Configuration of the double bond part of 7-E was determined by X-ray diffraction analysis. Treatment of 2 with MeLi and then with MeI also gave the same alkene 7-E in 90% yield, whereas treatment of 2 with MeLi followed by acidification afforded thermally labile (E)-1,2-di(1-adamantyl)-2-methylthioethenethiol in a good yield. Reduction of 2 with LiEt3BH followed by treatment with CS2, SOCl2, and PhBCl2 gave 4,5-di(1-adamantyl)-1,3-dithiole-2-thione, 4,5-di(1-adamantyl)-1,2,3-trithiole 2-oxide, and 4,5-di(1-adamantyl)-2-phenyl-1,3,2-dithiaborole, respectively, in moderate yields. The CuCl(I)-catalyzed decomposition of Ph2CN2 in the presence of 2 afforded 4,5-di(1-adamantyl)-2,2-diphenyl-1,3-dithiole quantitatively, whereas that of tosyl azide produced 1,2-di(1-adamantyl)-2-(p-tolylsulfonyl)iminoethane-1-thione in 10% yield.
Synthesis of Dibenzo[d,g][1,3,6]trithiocins
Authors: Maruta Teruo , Sugihara Yoshiaki , Tanaka Sanae , Ishii Akihiko , Nakayama Juzo
Published: February 2006

6-Acetoxy-, 6-methoxy-, 6-azido-, and 6-(methylthio)dibenzo[d,g][1,3,6]trithiocins (13, 14, 17, and 18, respectively) were synthesized by reactions of 9aH-9,10-dithia-4b-thioniaindeno[1,2-a]indene chloride (4) with appropriate nucleophiles in good yields. The trithiocin 13 was also prepared by the Pummerer reaction of dibenzo[d,g][1,3,6]trithiocin 5-oxide (12) in 97% yield. In many reactions of 4 with nucleophiles, the trimeric partial hydrolysis product, bis{o-[(dibenzo[d,g][1,3,6]trithiocin-6-yl)thio]phenyl} sulfide (15), was formed either as the major or a minor product. Structure of 15 was determined by X-ray diffraction analysis. Meanwhile, heating 4 in boiling methanol or ethanol gave the hydrolysis product, bis(o-mercaptophenyl) sulfide (16), in good yields. Condensation of 16 with benzaldehyde and pivalaldehyde gave 6-phenyl- and 6-t-butyldibenzo[d,g][1,3,6]trithiocins in good yields.
CH/π Interaction in the Crystal Structure of Organic Compounds. A Database Study
Authors: Umezawa Yoji , Tsuboyama Sei , Honda Kazumasa , Uzawa Jun , Nishio Motohiro
Published: February 2006

The CH/π interaction is a weak molecular force occurring between CH groups and π-groups. A study was carried out by use of the Cambridge Structural Database in order to obtain insights into the nature of the CH/π interaction and to examine its role in the crystal packing. The proportion of organic molecules bearing at least one CH/π interaction in their crystal structures has been found considerable. The CH hydrogen atoms tend to point toward the center of the aromatic ring. A number of short CH/π distances have been shown in the crystal structures of organic compounds. Moreover, the mean CH/π distance decreases as the acidity of the CH group increases. These results suggest that the CH/π interaction is not simply due to the dispersion force but involves other types of interactions, which are orientation-dependent and effective at wider ranges. It was suggested that the CH/π interaction constitutes one of the important factors in controlling the crystal packing of molecules.
Metal-Templated Macrolactamization of Triamino and Tetramino Esters. Facile Synthesis of Macrocyclic Spermidine and Spermine Alkaloids, (S)-(+)-Dihydroperiphylline, (±)-Buchnerine, (±)-Verbacine, (±)-Verbaskine, and (±)-Verbascenine
Authors: Kuroki Yoshichika , Ishihara Kazuaki , Hanaki Naoyuki , Ohara Suguru , Yamamoto Hisashi
Published: February 2006

The total synthesis of spermidine and spermine alkaloids, (S)-(+)-dihydroperiphylline (1), (±)-buchnerine (2), (±)-verbacine (3), (±)-verbaskine (4), and (±)-verbascenine (5), is described. The construction of macrocyclic lactams has been efficiently accomplished by the metal-templated cyclization of triamino esters and tetraamino esters. It was also found that the antimony(III) ethoxide is useful as an intermolecular amidation catalyst.
Synthesis of 2,5-Dihydro-1,2,4-oxadiazoles through Formal [3 + 2] Cycloaddition of Oxazoles with Nitrosobenzene Derivatives
Authors: Suga Hiroyuki , Shi Xiaolan , Ibata Toshikazu
Published: February 2006

The reactions of substituted oxazoles with nitrosobenzene gave 2-phenyl-2,5-dihydro-1,2,4-oxadiazoles regioselectively through formal [3 + 2] cycloadditions proceeding via a ringopening of oxazoles by an attack of nitrosobenzene. The reactions with 1-chloro- and 1-methyl-4-nitrosobenzenes also produced the corresponding 2,5-dihydro-1,2,4-oxadiazoles regioselectivity.
An Efficient Aerobic Oxidation of Isobutane to t-Butyl Alcohol by N-Hydroxyphthalimide Combined with Co(II) Species
Authors: Sakaguchi Satoshi , Kato Susumu , Iwahama Takahiro , Ishii Yasutaka
Published: February 2006

Highly selective aerobic oxidation of isobutane to t-butyl alcohol was successfully achieved by the use of a radical catalyst, N-hydroxyphthalimide (NHPI) in the presence of Co(II) salt under relatively mild conditions. The oxidation of isobutane by NHPI combined with Co(acac)2 under a pressure of air (10 atm) in benzonitrile at 100 °C gave t-butyl alcohol in high yield (84%) along with acetone (13%). The reaction is thought to proceed via hydrogen abstraction from isobutane by the phthalimidooxyl radical (PINO), which seems to be a key active species. The formation of acetone can be explained by a partial β-scission of the t-butoxy radical, generated from the redox decomposition of t-butyl hydroperoxide by cobalt ion. Alkyl-substituted butanes and pentanes were difficult to be oxidized selectively under these conditions because of easy degradation to smaller fragments of the resulting alkoxyl radical intermediates.
Relationship between the Yields of Products from Ethanol over Titanium Dioxide and the Quantity of Light
Authors: Iseda Kozo , Towata Atsuya , Watanabe Eiji , Fukaya Mitsuharu , Taoda Hiroshi
Published: February 2006

Acetaldehyde, acetaldehyde diethyl acetal (acetal), ethylene, hydrogen, methane, and carbon dioxide were produced from neat ethanol over TiO2 powder without metal in an Ar atmosphere under light irradiation. The yields of these products decreased in the above order. The following observation was obtained by using a filter which cut light at wavelengths below 390 nm. The yield of carbon dioxide was slightly decreased. The yield of acetaldehyde was greatly decreased at the initial irradiation, while it was slightly decreased with continuing of irradiation. The yield of acetal somewhat decreased, and that of ethylene, methane, and hydrogen roughly decreased to 1/2, 1/5, and 1/10, respectively.
Chemical Consequences of Arylnitrenes in the Crystalline Environment
Authors: Sasaki Akito , Mahé Loïc , Izuoka Akira , Sugawara Tadashi
Published: February 2006

UV photolysis of powdered crystals of several aryl azides at cryogenic temperatures afforded azo compounds predominantly. In the cases of p-(N-methylacetamido)phenyl azide and 2-azidobiphenyl, a CH insertion product or a carbazole was formed, competing with azo formation. These products can be considered to be formed through topotactic processes when the crystal structures are taken into account. The arylnitrenes generated in the azide crystals were monitored by ESR spectroscopy; they turned out to have extremely long half life-times, compared with those in the gas phase or in solution. Such high kinetic stabilities are ascribed to the inert environment around the generated nitrenes. The decay process of arylnitrenes in the initial stage obeyed a pseudo-first order kinetics; activation parameters were evaluated by Arrhenius plots. The activation enthalpies and entropies indicate that the diffusional processes of arylnitrenes may be the vital factors determining the kinetic stability and the product distribution in the crystalline environment.
Excited State Dynamics of Microcrystalline Acridine by Femtosecond Diffuse Reflectance Spectroscopy
Authors: Asahi Tsuyoshi , Furube Akihiro , Masuhara Hiroshi
Published: February 2006

The electronic structure of the excited states and triplet formation dynamics in the acridine microcrystal have been studied by femtosecond diffuse reflectance absorption spectroscopy and picosecond fluorescence spectroscopy. It was confirmed that an excimer was formed in the microcrystal within a few picoseconds after excitation. The time constant of triplet formation from the lowest excited singlet (S1) state was obtained to be about 900 ps at room temperature, which is about ten times slower than that in an aprotic solvent. Also, triplet formation was not observed up to 6 ns at 77 K. Slow intersystem crossing in the crystal was explained in terms of a selective stabilization of the 1ππ* electronic configuration due to excimer formation. An important role of intermolecular interactions on the intersystem crossing process of the crystal is discussed.
Molecular Recognition of Naphthalenedicarboxylic Acid Regioisomers by Cyclodextrins
Authors: Tan Wei Hua , Niino Noriaki , Ishikura Takahiro , Maruta Aya , Yamamoto Tatsuyuki , Matsui Yoshihisa
Published: February 2006

Complexation of cyclodextrins (CD’s) with some regioisomers of naphthalenedicarboxylic acid (NDC) was examined in 0.1 mol dm−3 NaHCO3 at 25 °C by means of 1H NMR spectroscopy, together with the measurement of induced circular dichroism spectra of NDC’s with the addition of CD’s. The 1H NMR spectra of 2,6- and 2,7-NDC’s showed characteristic AB-type patterns, which changed continuously with increasing CD concentration in accord with the Pople theory. The binding constants (Ka) for β-CD complexes with NDC’s increased in the order of: 1,4-NDC ≈ 1,5-NDC < 1,3-NDC < 1,6-NDC < 2,3-NDC < 2,7-NDC ≤ 2,6-NDC, indicating that β-CD is able to recognize the molecular structures of NDC’s. On the other hand, interactions of α- and γ-CD’s with NDC’s were very weak and nonspecific to NDC’s. The molecular structures of β-CD complexes with some NDC’s were estimated based on the ROESY spectra of the systems. Column chromatography of NDC’s using a β-CD-(2-chloromethyloxirane) polymer column showed that the retention volumes for NDC’s increased in the order of: 1,4-NDC < 1,6-NDC < 2,3-NDC < 2,7-NDC < 2,6-NDC, which agreed with the order the Ka values.
Molecular Mechanics Calculation of Titanium(IV) Schiff-Base Complexes
Authors: Rajan Ramalingam , Subramanian Venkatesan , Nair Balachandran Unni , Ramasami Thirumalachari
Published: February 2006

The force field for Ti(IV) Schiff-base complexes having the general formula Ti(Schiff-base) Cl2 (where Schiff-base = −OC6H4–CH=N–(CH2)n–N=CH–C6H4O− and n = 2, 3, 4, 5, and 6) has been generated. Using the generated force-field minimum energy conformers have been predicted for the corresponding Ti(IV) complexes. It has been shown that when n = 2 and 3, the compound prefers a trans-configuration. In the case where n = 4, 5 and 6, the total energy difference between the cis- and trans-conformers are not large enough for one to make any definite predictions about the preferred conformation. However the total energy of the trans-conformer is also lower than that of the cis-conformer in these cases.
Deswelling Kinetics of Macroporous Poly(N-isopropylacrylamide) Gel in Salt Solution
Authors: Kato Norihiro , Takahashi Fujio
Published: February 2006

The deswelling kinetics of a macroporous poly(N-isopropylacrylamide) gel in a NaCl solution was investigated. NaCl was used as the probe in order to trace out any hydration from the hydrated polymer chains. In the case of macroporous gel immersed in a NaCl solution, the minimum of the initial deswelling rate (v = 0.06 s−1) appeared at around 0.2—0.3 M (1 M = 1 mol dm−3) when the equilibrated gels (at 22 °C) were heated to 40 °C. The maxima of the apparent activation energy (Ea = 110 kJ mol−1) and the change in the activation entropy (ΔS313 = 80 J K−1 mol−1) were at 0.2—0.3 M NaCl. These results indicate that deswelling of the gel in a NaCl solution advanced on the condition of the following two factors. One is an electrostatic repulsion between Cl− ions below 0.2—0.3 M. Another is a salting-out effect due to NaCl above 0.2—0.3 M. The deswelling kinetics and the lower critical solution temperatures of the gels in other alkalimetal halide solutions were also measured in order to clarify the effect of the species of the cations and the anions on the interaction between the water and polymer chains.
Neutron Diffraction Studies on the Hydrogen-Bonded Structure in Concentrated Aqueous Hydrochloric Acid Solutions
Authors: Kameda Yasuo , Usuki Takeshi , Uemura Osamu
Published: February 2006

The neutron diffraction measurement with the H/D isotopic substitution technique has been carried out on the aqueous 21 mol% hydrochloric acid solutions, in order to investigate the short-range structure in the concentrated aqueous acid solution, in comparison with the structural information available on liquid pure water. Observed partial structure factors : aHH(Q), aXH(Q), and aXX(Q) (X: O, Cl), determined by the least-squares fitting analysis, have exhibited that the nearest-neighbor intermolecular hydrogen-bond distances, r(H···H) and r(O···H), between oxonium ion and water molecule in the 21 mol% hydrochloric acid solution were 2.02 ± 0.05 and 1.69 ± 0.02 Å, respectively; such values are much smaller than those in liquid pure water. Consequently, a strong intermolecular hydrogen bond between oxonium ion and its nearest-neighbor water molecules is concluded to be present in the concentrated aqueous hydrochloric acid solution.
Novel One-Dimensional Organic Conductor Based on Selenium-Containing Bis-Fused Tetrathiafulvalene Derivative, (TSM-TTP)(I3)5/3
Authors: Mori Takehiko , Kawamoto Tadashi , Misaki Yohji , Tanaka Kazuyoshi
Published: February 2006

A novel selenium-containing bis-fused tetrathiafulvalene donor, TSM-TTP (2,5-bis[4,5-bis(methylseleno)-1,3-dithiol-2-ylidene]-1,3,4,6-tetrathiapentalene) forms a 3 : 5 triiodide salt, (TSM-TTP)(I3)5/3. This salt has uniform one-dimensional columns of the donors, and is isostructural to the corresponding complex of the sulfur analog. This compound shows a high electrical conductivity, 200 S cm−1 at room temperature, and undergoes a metal-insulator transition around 20 K. Another insulating (σrt = 0.03 S cm−1) phase with trimerized columns is also obtained.
Synthesis and Structure of Palladium(II) Complexes with N(21),N(22)-Bridged Porphyrin Ligands
Authors: Takao Yuko , Takeda Tokuji , Miyashita Keiko , Setsune Jun-ichiro
Published: February 2006

Palladium complexes of N(21),N(22)-(etheno)-bridged porphyrins were synthesized by the reaction of palladium(II) chloride and N(21),N(22)-(etheno)-tetraphenylporphyrins or N(21),N(22)-(etheno)-octaethyl-5,22-dihydroporphyrins. The metallation proceeded via an initially produced monoprotonated porphyrin with a palladate anion. Dinuclear complexes including two PdCl2 units were preferentially produced and were converted into mononuclear complexes by a treatment with a saturated aqueous NaCl solution. Single-crystal X-ray diffraction shows the di-μ-chlorodipalladium(II) structure of the dinuclear complex, N(21),N(22)-(EtC=CEt)(TPP)(PdCl2)2·CH2Cl2·H2O (TPP = 5,10,15,20-tetraphenylporphyrin dianion). Pd(1) is coordinated by two adjacent imine nitrogens of the porphyrin as the terminal ligands and placed out of the porphyrin 4N mean plane by 1.32 Å. The distal Pd(2) is placed at a distance of 3.78 Å from the porphyrin 4N mean plane and comes close to the porphyrin ring with a dihedral angle of 139.8° between the two square planes of the Pd coordination. The NMR spectrum in solution indicated the influence of the distal Pd(2) on the porphyrin ring. The etheno bridge keeps the geometry of the 4N core of the porphyrin relatively undeformed in comparison with the previously reported methano bridge, which accounts for the enhanced stability of Pd(II) complexes.