bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on the β-Turn of Peptides. VIII. β-Turn Preferences of N-Acetyltetrapeptide Methylamides Related to the β-Turn Part of Gramicidin S
Authors: Sato Kazuki , Higashijima Tsutomu , Sugawara Rika , Nagai Ukon 
Published: July 2006

Abstract
N-Acetyl-l-Leu–X–l-Pro–l-Val methylamides (IIa: X=d-Ala, IIb: X=Gly, IIc: X=l-Ala) were synthesized and subjected to CD and 1H NMR measurements to study the β-turn preferences of these peptides. Temperature dependences of l-Val4–NH proton chemical shifts in CD3OH solution were in the order of IIa&lt;IIb&lt;IIc, suggesting that the populations of the β-turn conformer with 4→1 hydrogen bonding were in the order of IIa&gt;IIb&gt;IIc. This order of β-turn preferences coincides with the order of the magnitudes of the Cotton effects in the CD spectra of the chromophoric derivatives, N-(2,4-dinitrophenyl)tetrapeptide p-nitroanilides, having the same sequences. This agreement supports the validity of the chiroptical method to study turn tendency of tetrapeptide sequences using chromophoric derivatives reported previously.
Studies on the Mechanism of Zeolite X Crystallization. I. Effects of Silica Sources of Starting Materials on the Crystallization of Zeolite X
Authors: Hino Ryozi , Matuura Ryohei , Toki Kenzi 
Published: July 2006

Abstract
The crystallization mechanism for zeolite was investigated. Tetraethyl orthosilicate and silica sol were used as silica sources. Many kinds of solid phases were obtained at various reaction times. These solid phases were characterized by analyses for chemical compositions, X-ray diffraction, adsorption of nitrogen gas and water vapor, and IR spectroscopy. The results obtained suggest that the solid phase derived from tetraethyl orthosilicate at an early stage of reaction is composed of slightly ordered skeletons. In addition, during aging of gel at room temperature, the structure of the solid phase of gel undergoes a rearrangement to form a crystalline structure. On the other hand, the gel phase obtained from silica sol is predominantly made up by the coagulation of disordered aluminosilicate polymers or silicic polymers. These gel phases act as a precursor, and a part of the gel dissolved into the liquid phase and the dissolved species are converted into crystals in the liquid phase. Thus, the silica sources influence the structure of gel and crystals. In general, the crystallization mechanism is strongly influenced by the starting materials, especially by the silica sources.
Penetration of Lysine–Leucine Copolymers into Lecithin Monolayers from Underlying Aqueous Solutions
Authors: Nakagaki Masayuki , Okamura Emiko , Kubota Shigeo 
Published: July 2006

Abstract
The penetration of water soluble polymers into lecithin monolayers was investigated for the random copolymers of l-lysine and l-leucine at various compositions in order to discuss the effect of hydrophobicity and charge density of the copolymers on their interaction with lipid monolayers. Compared to the penetration of the amino acids(l-lysine and l-leucine), the copolymer penetrated at very low concentration whereas the monomer (amino acid) did not. The amount of copolymer penetration increased significantly when the leucine fraction of a copolymer, XLeu, was larger than 0.3, while little penetration occurred when XLeu was smaller than 0.25. From these facts, it has been concluded that the penetration of lysine–leucine copolymers was not only attributed to the hydrophobicity or the charge density of copolymer molecules, but also to specific surface effects such as (1) the enhanced penetration of macromolecules by the preceded penetration of polymer segments of the same molecule, or (2) the formation of a compact α-helical structure as the result of the restricted motion of the segment near the lipid surface.
A Chromatographic Study of the Acidic Hydrolysis of cyclo-Hexa- and cyclo-Octaphosphate
Authors: Kura Genichiro 
Published: July 2006

Abstract
The hydrolysis rate of inorganic cyclo-hexa- and cyclo-octaphosphate in 0.1 mol dm−3 HCl was determined by means of anion-exchange chromatography. The phosphorus content in the column effluent was determined automatically by the use of the MoV–MoVI reagent. The hydrolysis reactions were first-order. The rate constant decreases from cyclo- tri- to cyclo-hexaphosphate with the increased ring, however, that of cyclo-octaphosphate increases again. This increase is thought to be due to the stronger proton affinity of cyclo-octaphosphate. The Arrhenius activation energies for cyclo-hexa- and cyclo-octaphosphate hydrolysis were 91.5 and 96.9 kJ mol−1 respectively.
Studies of the Selective O-Alkylation and Dealkylation of Flavonoids. VI. Demethylation of 8-Hydroxy-5,7-dimethoxyflavones with Anhydrous Aluminum Chloride or Bromide in Acetonitrile
Authors: Horie Tokunaru , Kourai Hiroki , Fujita Nobuhisa 
Published: July 2006

Abstract
The demethylation of seven 8-hydroxy-5,7-dimethoxyflavones with anhydrous aluminum chloride or bromide in acetonitrile was studied and the following results were obtained. (1) Anhydrous aluminum chloride in acetonitrile selectively split the 5-methoxyl group without cleavage of the 7-methoxyl group, and seven 5,8-dihydroxy-7-methoxy-flavones were quantitatively synthesized by the demethylation. (2) In the demethylation with anhydrous aluminum bromide, the 5- and 7-methoxyl groups on 4′,5,7-trimethoxy- and 3′,4′,5,7-tetramethoxy-8-hydroxyflavone were selectively split to give the corresponding 5,7,8-trihydroxyflavones in good yield. However, the demethylation was not accessible to the synthesis of 5,7,8-trihydroxy-3′,4′,5′-trimethoxyflavone, 4′,5,7,8-tetrahydroxy-3′-methoxy-, and 3′,5,7,8-tetrahydroxy-4′-methoxyflavone, because of the cleavage of the methoxyl groups on the B ring. The synthesized flavones were employed for the identification of the two natural flavones, which were proposed to be 4′,5,8-trihydroxy-7-methoxyflavone and 4′,5,8-trihydroxy-3′,7-dimethoxyflavone. The former, salvitin, was revised to 4′,5,7-trihydroxy-6-methoxyflavone and the latter seemed to be 4′,5,7-trihydroxy-3′,8-dimethoxyflavone.
Studies of Peptide Antibiotics. XLV. Syntheses of Gramicidin S-like Analogs with Macro-ring Structures
Authors: Ando Setsuko , Takiguchi Hideo , Izumiya Nobuo 
Published: July 2006

Abstract
Three cyclic tetradecapeptides related to gramicidin S (GS): cyclo(–Leu–Orn–Leu–Orn–Leu–d-Phe–Pro-)2, cyclo(–Leu–Orn–Leu–Orn–Leu–d-Phe–Sar–)2, and cyclo(–Leu–Orn–Leu–Orn–Leu–d-Phe–Gly–)2, were synthesized to investigate the contributions of the ring size of cyclic peptides and of the number of the basic amino acid residues to the antibacterial activity. The protected cyclic tetradecapeptides were synthesized through a cyclization reaction of the linear tetradecapeptide azide in pyridine. Hydrogenolysis of the protected cyclic peptides afforded crystalline tetrahydrochlorides of the analogs. The homogeneity of the analogs was ascertained by TLC, paper electrophoresis, and elemental analysis. In the experiment of circular dichroism, the two analogs with 7,7′-Pro or 7,7′-Sar gave spectra similar in shape to that of GS, while the analog with 7,7′-Sar gave a slightly different spectrum from that of GS. The antibacterial assays showed that the analog with 7,7′-Pro exhibited considerable activities against the microorganisms tested, particularly against Gram-negative bacterias such as Escherichia coli and Shigella sonnei. On the other hand, the analogs with 7,7′-Sar or 7,7′-Gly exhibited weaker activities than that of GS.
Mechanisms of Singlet and Triplet Sensitized Decomposition of Bis(2-phenylbenzoyl) Peroxide
Authors: Kitamura Akihide , Tanikawa Hiroharu , Oohashi Kunio , Sakuragi Hirochika , Tokumaru Katsumi 
Published: July 2006

Abstract
Bis(2-phenylbenzoyl) peroxide (2-PhBPO) was found to decompose on singlet and triplet sensitized irradiations in benzene and carbon tetrachloride. The quantum yields were determined to be 0.48 and 0.43 on direct excitation and chrysene sensitization in benzene, respectively, and 0.62 and 0.60 on benzophenone and 3′-methoxyacetophenone sensitizations in carbon tetrachloride, respectively. The reaction mechanisms are discussed from the standpoint of the modes of bond cleavage.
Effects of Lysine and Arginine Derivatives on the Base Stacking Association of 2′-Deoxyguanosine 5′-Monophosphate
Authors: Hirota Kazumi , Igarashi Mitsuru , Inoue Yoshio , Chûjô Riichirô 
Published: July 2006

Abstract
The effects of basic amino acid residues on the base stacking of nucleotides have been studied to clarify the nature of interaction between histones and DNA′s. For this purpose, lysine and arginine derivatives were used as models for basic amino acid residues in histone. The base stacking association of 2′-deoxyguanosine 5′-monophosphate(5′-dGMP) in aqueous solution has been studied by the measurement of the concentration dependence of 1H NMR chemical shifts of 5′-dGMP both in the absence and in the presence of the basic amino acid derivatives at different pH’s. We clarified that the lysine favors the base stacking association of 5′-dGMP through the interaction with the phosphate group(s), while an excess of the arginine destabilizes the stacking aggregates through the interaction with the base moiety. We also clarified that the ionization of the phosphate group destabilizes the stacking association of 5′-dGMP both in the absence and in the presence of the basic amino acids.
Studies on Salt Hydrates for Latent Heat Storage. IV. Crystallization in the Binary System CH3CO2Na–H2O
Authors: Wada Takahiro , Kimura Fumiko , Matsuo Yoshihiro 
Published: July 2006

Abstract
In the binary system CH3CO2Na–H2O, crystallization temperature on slow cooling from a melt, glass transition temperature and crystallization temperature on slow heating from a quenched vitrified solid were measured by varying the CH3CO2Na concentration. The crystallization behaviour in the binary system CH3CO2Na–H2O is characterized as follows; (1) crystallization region of ice extends into the CH3CO2Na-rich side from the eutectic composition, (2) a hard crystallization region exists in the composition between CH3CO2Na 35wt% and 40wt%, (3) the crystallization temperature range of CH3CO2Na·3H2O is from −50 °C to −30 °C and very narrow.
Laser Flash Photolysis of Benzene. VI. Photolysis in Aqueous Solution
Authors: Shimo Nobuo , Nakashima Nobuaki , Yoshihara Keitaro 
Published: July 2006

Abstract
Three transient absorption spectra in aqueous solution were observed by irradiation of benzene with an excimer laser (KrF, 248 nm or ArF, 193 nm). A short-lived absorption with a peak at 275 nm is assigned to the Sn←S1 absorption. A long-lived absorption, which appears as a clear shoulder at 230 nm, stays longer than 500 ns and is not shortened by oxygen. This species is tentatively assigned to benzvalene, and the quantum yield is determined to be ca. 0.1. Solvated electron with a peak at 720 nm was formed via multiphoton processes at a power level of 60 mJ/cm2 of an ArF laser. The Tn←T1 absorption was lower than our detection limit (ΦT&lt;0.1).
Electronic Spectra and Crystal Structure of Organic Radical Salt: Dimethyldibenzotetrathiafulvalenium Tetrafluoroborate
Authors: Tanaka Chizuko , Tanaka Jiro , Dietz Karlheinz , Katayama Chuji , Tanaka Masashi 
Published: July 2006

Abstract
The single crystal of dimethyldibenzotetrathiafulvalenium tetrafluoroborate (1 : 1) has been prepared by electrocrystallization. The crystal structure has been determined by X-ray crystal analysis. The salt crystallizes in Ibam with a=14.637(3), b=17.625(6), c=13.614(3) Å. The radical cations align along the c axis at nearly equal spacing forming eclipsed dimers and the dimeric units are stacked with a staggered mode. The electronic spectra of the radical cation and the dimer have been measured in solution and the assignment has been presented with an aid of the MO calculation by Pariser-Parr-Pople method. A charge transfer (CT) band observed in the dimer has been correlated with the charge resonance of unpaired electron between the HOMOs of the radical cations. Polarized reflection spectra of single crystal have been measured with three different crystal planes and the assignment of both the CT and molecular type bands have been confirmed with polarization measurement. The energy and the intensity of the CT band indicate that the unpaired electron is localized on each radical, but the CT configuration is involved significantly. The crystal is an insulator as is expected from the electronic structure; the large U, which is evidenced by the energy of the CT band, and the staggered packing hinders electronic conduction. It implies that a monovalent radical salt is difficult to be metallic unless a mixed valence state is involved.
The Synthesis and Decomposition of Calcium Bis(hydrogenphosphoramidate)
Authors: Watanabe Makoto , Inagaki Toshihiko , Sato Shoji 
Published: July 2006

Abstract
Calcium bis(hydrogenphosphoramidate)–water (2/3) was made by adding an aqueous calcium chloride solution to an aqueous potassium hydrogenphosphoramidate solution. The product decomposed slowly to diammonium calcium diphosphate monohydrate in air at room temperature. When the product was heated above 600 °C, the decomposition product was β-type calcium metaphosphate. According to the result of the isothermal decomposition of the product at 150 °C in air, no formation of P–NH–P linkages by the elimination of NH3 from P–NH2 linkages was observed, and it was concluded that the phosphoramidate thermally decomposed to form only polyphosphates in air.
The Autoxidation of 2,3-Dihydroxy-2-propenal (Triose Reductone). The Effects of the pH on the Rate Constants
Authors: Abe Yasuo , Horii Hideo , Taniguchi Setsuo , Kamai Kazuo , Takagi Masanosuke 
Published: July 2006

Abstract
The autoxidation of 2,3-dihydroxy-2-propenal (triose reductone) was investigated between pH 2.83 and 13.91 in the presence of disodium dihydrogen ethylenediaminetetraacetate (EDTA 2NA). The reaction obeyed the first-order rate law with respect to the triose reductone and the zeroth-order rate law with respect to oxygen when the oxygen concentration was higher than 0.246 mM (1 mM=10−3 mol dm−3) at 30 °C. The pH dependence of the reaction rates showed that the reaction rates are governed by the acid-base equilibrium of triose reductone. The rate constants for neutral and singly- and doubly-charged anions of triose reductone at 30 °C were (3.6±0.1)×10−6, (7±1)×10−5, and (1.8±0.1)×10−2 s−1 respectively. The hydrogen peroxide produced as a result of the triose reductone oxidation was also found to oxidize triose reductone.
Highly Stereoselective Isomerization of Monosubstituted 1-Alkenes to (E)-2-Alkenes by Catalysis of (C5Me5)2TiCl2/NaC10H8
Authors: Akita Munetaka , Yasuda Hajime , Nagasuna Kinya , Nakamura Akira 
Published: July 2006

Abstract
The catalyst systems which consist of MCl2(C5R5)2(M=Ti, Zr; R=H, CH3)/NaC10H8, i-C3H7MgBr, n-C4H9Li or LiAlH4 in 1 : 2 ratio were highly effective for the stereoselective isomerization of monosubstituted 1-alkenes to (E)-2-alkenes. Unconjugated dienes were converted to (E)- or (E,E)-dienes. The catalysis of (C5Me5)TiCl2/NaC10H8 was extremely high and resulted in the complete isomerization of 1-alkenes in &gt;99% stereoselectivity within a short period. The use of the bulky C5Me5 ligand is essential to find out the excellent stereoselectivity. Systems, (C5H5)2TiCl2/NaC10H8 and (C5H5)2TiCl2/i-C3H7MgBr showed less selectivity and the catalysis of the corresponding zirconium systems was very poor irrespective of the reducing agents and substrates.
Proton-driven Ion Transport and Metal-assisted Amino Acid Transport with an Anion-capped Azacrown Ether
Authors: Shinkai Seiji , Kinda Hidefumi , Araragi Yoshikazu , Manabe Osamu 
Published: July 2006

Abstract
We have found that 1,10-diaza-4,7,13,16-tetraoxa-18-crown-6 with a carboxylate cap and a hydrophobic dodecanoyl group (1) acts as a new class of ion carrier for membrane transport. The rate of K+ transport across a chloroform liquid membrane was significantly affected by pH of the OUT aqueous phase: The rate decreased with increasing or decreasing pH, providing a maximum at around pH 5. The main species of 1 in the neutral pH region should be zwitterionic 1±, so that one may rationalize the pH-rate profile in terms of (i) “enforced ion release” due to protonation of the ring nitrogen and (ii) high lipophilic nature of zwitterionic 1±. The efficiency of 1 was further demonstrated by active K+ transport from the basic IN aqueous phase to the neutral OUT aqueous phase. Also, 1 was capable of carrying amino acids in the presence of alkaline earth metal cations. These results suggest that, being different from conventional anion-capped crown ethers, the aza crown ethers carrying the N-substituted carboxylate cap exhibit a new class of ionophore functions.
Facile Synthesis of Cyclic Dipeptides and Detection of Racemization
Authors: Ueda Toshihisa , Saito Morinobu , Kato Tetsuo , Izumiya Nobuo 
Published: July 2006

Abstract
Several cyclic dipeptides were synthesized by refluxing methanolic solution of dipeptide methyl esters in high yield and purity. Cyclic dipeptides prepared by the Fischer method, the Nitecki method, and the present methanol-reflux method were compared with respect to yield and optical purity. The methanol-reflux method usually gave good results. High-performance liquid chromatography was effectively applied to detect racemization.
The Mechanism of the Reaction of (Aryloxy)trimethylstannane with Methanesulfonyl Chloride. Solvent and Substituent Effects on the Rate of the Reaction
Authors: Kozuka Seizi , Yamaguchi Shigeru , Tagaki Waichiro 
Published: July 2006

Abstract
A kinetic study has been conducted on the reactions of (aryloxy)trimethylstannanes with methanesulfonyl chloride giving chlorotrimethylstannane and aryl methanesulfonates. The reaction was found to obey a second order kinetic equation. The solvent effect on the rate of the reaction appeared obscure although a small rate enhancement was observed in a polar solvent. Substituent effect of the aryloxyl group was found to be dependent on the solvent used while a clear isokinetic relationship was observed. A charge separated four-center transition state has been suggested for the reaction.
Effect of the Polydispersity of Molecular Length on the Decay Process of Transient Electric Birefringence of Rodlike Macromolecules in Dilute Solution
Authors: Yamaoka Kiwamu , Fukudome Kiyohiro 
Published: July 2006

Abstract
The effect of polydispersity on transient electric birefringence (EB) was examined for a dilute solution which contains like macromolecules of varying lengths. The molecules were assumed to be rigid rods of cylindrical symmetry, so that the molecular weight is linearly proportional to length. Polydispersity was expressed by the ratio of the weight-average to the number-average lengths lw/ln. A logarithmic-normal type continuous length distribution was generally used. Calculations were performed for the birefringence-average relaxation time 〈τ〉EB and initial slope 〈S〉EB as a function of the electric field strength E, which is applied prior to the start of the decay process, with the electric parameter (βw)2/2γw, which is related to the weight-average permanent dipole moment (the βw-term) and polarizability anisotropy (the γw-term). Both 〈τ〉EB and 〈S〉EB are very sensitive to E, lw/ln, and (βw)2/2γw. A convenient method was devised for determining the polydispersity parameters (lw/ln and lw) from the weight-averages of relaxation time and initial slope, which are free from the mechanism of field orientation. Examples are given for a polydisperse, rigid rodlike sonicated DNA sample in aqueous solution.
Esterification of Aromatic Carboxylic Acids with Alcohols Using 2-Chloro-3,5-dinitropyridine as a Condensing Agent
Authors: Takimoto Seiji , Abe Naomi , Kodera Yasushi , Ohta Hiroshi 
Published: July 2006

Abstract
The reaction of 2-chloro-3,5-dinitropyridine (CDNP) with carboxylic acids and alcohols was examined, and it was found that CDNP was a useful condensing agent. Various esters were prepared in good yields.
Cyanation of 1-Halocycloalkenes Catalyzed by Tetracyanocobaltate(I). Convenient Synthesis of 1-Cyanocycloalkenes
Authors: Funabiki Takuzo , Kishi Hirohito , Sato Yoshihiro , Yoshida Satohiro 
Published: July 2006

Abstract
1-Cyanocycloalkenes (1-cyanocyclopentene, -hexene, -heptene, and -octene) were readily synthesized by catalytic cyanation of the corresponding 1-halocycloalkenes with tetracyanocobaltate(I). Reactivities of methyl-substituted 1-chlorocyclohexenes were lower than that of 1-chlorocyclohexene, and 1-chloro-2-methylcyclohexene scarecely reacted. Hydrogenation and isomerization of 1-cyanocycloalkenes were observed only with 1-cyanocycloheptene and 1-cyano-6-methylcyclohexene, respectively.
Studies of Aromatic Sesquiterpenes. IV. The Synthesis of γ-Calacorene, Calamenene, and 4-Methoxyisocadaiene
Authors: Adachi Kazuo , Mori Masahito 
Published: July 2006

Abstract
The Grignard reaction of 3,4-dihydro-4,7-dimethyl-1(2H)-naphthalenone with isopropylmagnesium bromide gave a 3 : 1 mixture of normal reaction product and α-isopropylidene ketone, from which, the title sesquiterpenes and 1,2-bis(3-isopropyl-4-methoxy-6-methyl-1-naphthyl)ethane were synthesized.
Infrared and Visible Absorption Spectra of Doped (CH)x, (CD)x, and Copolymers [(C2H2)1−y(C2D2)y]x
Authors: Fujimoto Hitoshi , Tanaka Masashi , Tanaka Jiro 
Published: July 2006

Abstract
Infrared and visible absorption spectra of (CH)x, (CD)x, and the copolymers [(C2H2)1−y(C2D2)y]x doped with Br2 or I2 were measured for various values of y between 0 and 1. By the doping, the π→π* band located in the 19000 cm−1 region disappeared while several new bands were observed at 800–900-, 1000–1400-, and 5000-cm−1 regions. The absorption band shapes and the locations of the 5000- and 19000-cm−1 bands did not depend appreciably upon the value of y. The charged soliton induced vibrational bands were found at 870-and 1370-cm−1 in (CH)x and 1230-, 1100-, and 780-cm−1 in (CD)x. In addition, another new bands were found around 570–660 cm−1 region by decreasing the temperature of the doped film to 160 K. These new bands were not shifted by the isotopic substitution. A plausible mechanism for the appearance of this band is suggested as an oscillation of trapped charged soliton around the negatively charged dopant. For the heavily doped (CH)x film, the gapless transition was observed and the optical conductivity was estimated by the Drude formula and was compared with the value obtained by a direct conductivity measurement.
Sodium Isotopic Exchange Rate between Disodium Zirconium(IV) Bis(orthophosphate) Trihydrate and Aqueous Solutions
Authors: Inoue Yasushi , Yamada Yoshimune 
Published: July 2006

Abstract
The sodium isotopic exchange rate between the large crystals of disodium zirconium(IV) bis(orthophosphate) trihydrate and aqueous solutions was determined radiochemically. The exchange proceeded quickly up to 5% of the total, followed by a slow process. The first step was attributed to the instantaneous attainment of the equilibrium between the imperfect surface layers of the crystals and the solution, and the second step was found to be controlled by the diffusion of sodium ions along the direction perpendicular to the layers consisting of zirconium atoms. The diffusion constant, D, was calculated with the equation obtained by Fick’s diffusion law under the conditions of slab geometry and infinite solution volume. From the dependence of D on temperature, the activation energy for the diffusion was evaluated to be 101 kJ mol−1.
Electrocatalytic Reduction Using Raney Nickel
Authors: Chiba Toshiro , Okimoto Mitsuhiro , Nagai Hiroshi , Takata Yoshiyuki 
Published: July 2006

Abstract
The Raney nickel catalyst was employed as a catalytic electrode in the electrohydrogenation of various unsaturated compounds, including ketones, aromatic aldehydes, Schiff’s bases, oximes, nitriles, aromatic nitro compounds, olefins, and acetylenes. The hydrogen generated electrochemically was adsorbed and activated at the surface of the catalyst; it effectively hydrogenated these compounds, affording products which are very similar to those obtained in a normal catalytic hydrogenation with Raney nickel.