bluuebunny/crossref_metadata_2025 huggingface dataset:
Potentiometric Determination of Some Aliphatic Aldehydes Using the Silver/Sulfide Ion-Selective Electrode
Authors: M. Zaki M Tarek , Fawzy M H
Published: July 2006

A simple, selective and reproducible method for the potentiometric determination of some aliphatic aldehydes is described. The method is based on oxidation of the aldehydes with silver oxide packed in a column. The formed silver salts of the fatty acids are eluted with water and the silver ion concentration is determined with a silver/sulfide ion-selective electrode using either a calibration graph or a standard addition technique. The effects of experimental variables and the interference of other organic functional groups are investigated. Samples containing up to 5.0 mg aldehyde are analyzed with an average recovery of 98.5% and 98.4% using the proposed techniques, respectively.
Interactions of Excited Lithium Atom with Molecular Hydrogen. III. Orthogonality Constrained MCSCF+NCI Calculations of Potential Energy Surfaces and Electronic Wave Functions in the Potential Crossing Region
Authors: Toyama Masayuki , Uchide Takayuki , Yasuda Toshimasa , Kasai Tokuo , Matsumoto Shiro
Published: July 2006

A method of calculating the excited state MCSCF electronic wave function by constraining it to be orthogonal to the predetermined ground state wave function was applied to calculate wave functions of the Li–H2 system near the center of a conical intersection of the lowest two potential energy surfaces. Combined with an additional nonorthogonal configuration interaction process, it has proved to be an efficient method to get systems of wave functions that are continuous throughout whole geometries. Qualitative characters of wave functions near the center of potential crossing previously inferred have been reconfirmed.
Mechanism of Stabilization of ZnO Photoanodes in High pH Solutions
Authors: Kikuchi Eiji , Itoh Kiminori , Katoh Tamihiko , Fujishima Akira
Published: July 2006

Stabilization of ZnO photoanodes was investigated using ZnO thin film electrodes under controlled potential in various pH solutions; the effects of light intensity and agitation were also studied. The photocorrosion of ZnO photoanodes was suppressed at sufficiently cathodic potentials and/or at low light intensity. Agitation of solution also suppressed photocorrosion. On the basis of the experimental results, the mechanism of the stabilization in high pH solutions is discussed and a model is proposed.
Temperature Dependence and Decay Kinetics of the High-Energy Band in DPH Fluorescence
Authors: Yamashita Shoji , Szabo Aurthur G , Cavatorta P
Published: July 2006

The temperature dependence and associated decay kinetics of the high energy band centered at 380 nm in the fluorescence spectrum of 1,6-diphenyl-1,3,5-hexatriene in a nonpolar solvent were investigated. Below 150 K the emission intensity at 380 nm relative to that of a sharp band near 400 nm was very small. Above this temperature the intensity at 380 nm increased with increasing temperature. The fluorescence decay analysis of this band showed two components with decay times of 62 ps and 13.4 ns. The 62 ps component was assigned to the prompt fluorescence of the S2 (1Bu*) state and 13.4 ns component to a delayed type fluorescence from the same state after establishment of a thermal equilibrium with lower S1 (1Ag*) state.
The Addition of the Cyanide Ion to the N-Methyl-3-carbamoylpyridinium Ion in Reversed Micelles
Authors: Goto Ayako , Kishimoto Hiroshi
Published: July 2006

The addition reaction of the cyanide ion to the N-methyl-3-carbamoylpyridinium ion was carried out in reversed micelle systems, and the functions of the electric charge of surfactants and of the entrapped water in the micelle were studied by measuring the rate and equilibrium constants. Reversed micelles formed by hexadecyltrimethylammonium bromide (HTAB), a cationic surfactant, not only enhanced the reaction, but also stabilized the product, 4-cyano-1,4-dihydro-N-methylnicotinamide (P), which is thermodynamically unstable in aqueous media. This was in contrast to sodium 1,2-bis(2-ethylhexyloxycarbonyl)ethanesulfonate (AOT), an anionic surfactant, reversed micelles. In both reversed micelle systems the reaction could be controlled by varying the water content, although neither is favorable for the reaction at a higher water content. From the distribution measurements and spectroscopic studies, it can be suggested that the reaction occurred preferably in the micellar phase, especially in the water pool. Three kinds of effects were proposed for interpreting the enhancement as compared to the reaction in aqueous systems. The first was the local concentration of reaction species in the water pools, and the second was the lower micropolarity of water pools. The third concerned the electric nature of the surfactant and reactant ions.
Limitation of Absorbance Measurement by Using Photoacoustic Method
Authors: Terazima Masahide , Azumi Tohru
Published: July 2006

The solute dependence of the photoacoustic (PA) signal intensity has been examined. The results show that the PA signal intensity depends not only on the released energy, but also on the nature of the solute. This means that the absorbance of an unknown sample cannot be precisely measured by comparing the PA signal intensity with that of a standard solution containing a different solute.
Solvent Extraction of Uni- and Bivalent Metal Picrates with 16-Crown-5 into Benzene
Authors: Takeda Yasuyuki , Kimura Tokutaro , Kudo Yoshihiro , Matsuda Hiroaki , Inoue Yoshihisa , Hakushi Tadao
Published: July 2006

Distribution constant (KD,L) of 16-crown-5 (16C5) and overall extraction equilibrium constants (Kex) of uni- and bivalent metal picrates with 16C5 were determined between benzene and water at 25 °C. The Kex values were analyzed by four fundamental equilibria, extraction constant of picric acid, KD,L formation constant in water and ion-pair extraction constant (Kex,ip) with a picrate ion of the 16C5–metal ion complex. The Kex value of 16C5 for the uni- and bivalent metal ions decreases in the order Ag+>Na+>Tl+>K+>Rb+>Cs+>Li+ and Pb2+>Ba2+≥Sr2+>Ca2+, respectively. Size-fit relationship holds for extraction-selectivity of 16C5 toward alkali metal ions, but it does not hold for that toward alkaline earth metal ions. Factors influencing extractability and extraction-selectivity of 16C5 for metal ions were discussed from the viewpoint of molecular grounds. Kex,ip value of 16C5 varies with a cation of the same charge held in the cavity. Kex,ip values of 16C5–metal picrate complexes were compared with those of 15-crown-5–metal picrate complexes. Various effects on ion-pair extractability of a 16C5–metal ion complex with a picrate anion were explained.
A Structural Study of a Series of Bis(2,3-alkanedione dioximato)nickel(II) Complexes in the Crystal and the Liquid States by X-Ray Absorption Spectroscopy
Authors: Yamashita Seiichi , Yanase Yoshio , Yamaguchi Toshio , Wakita Hisanobu
Published: July 2006

The structures of a series of bis(2,3-alkanedione dioximato)nickel(II) complexes, [Ni(R,R′-dioxH)2], with dioxH=C(=NOH)–C(=NO), R and R′=H(A), R=CH3 and R′=H(B), CH3(C), C2H5(D), n-C3H7(E), n-C4H9(F), n-C5H11(G), n-C6H13(H), or n-C10H21(I), were investigated in crystals, pyridine solution, and melt (160 °C) by means of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES), magnetic susceptibility, and UV/visible spectra. The magnetic susceptibility of complexes C, F, and H in crystals revealed a diamagnetic character. The electronic spectra of crystalline samples E, F, and H changed with the alkyl substituents of the glyoximato ligands, while the corresponding spectra in a pyridine solution were very similar to each other, independent of the glyoximato ligands. The EXAFS data showed that the average Ni–N distance within nickel(II) glyoximato complexes is 1.85–1.88 Å, practically independent of the alkyl substituents of the glyoximato ligands. The XANES spectra were found to correlate with the molecular packing structures of nickel(II) glyoximato complexes in crystals, pyridine solutions, and melt.
A New Synthesis of 3-Hydroxy-2,5-dialkyl-1,4-benzoquinone from 3-Halo-3,6-dialkyl-1,2-cyclohexanedione Using Iodine–Copper(II) Acetate
Authors: Horiuchi C Akira , Suzuki Yasuto
Published: July 2006

The reaction of 3-iodo-3,6-dialkyl-1,2-cyclohexanedione (2) with iodine–copper(II) acetate in acetic acid–water (5:1) at 80 °C gave the respective 3-hydroxy-2,5-dialkyl-1,4-benzoquinone in 38–80% yields. On the other hand, the reaction of 2 with copper(II) acetate in acetic acid–water (10:1) under refluxing afforded the respective 3,3′-dihydroxy 2,2′,5,5′-tetraalkyl-4,4′-diphenoquinone (5) in 41–85% yields. In the case of 3-bromo-3,6-dialkyl derivative (3) with copper(II) acetate, the diphenoquinone derivatives and 3-hydroxy-2,5-dialkyl-1,4-benzoquinone were obtained.
Synthetic Photochemistry. LI. Structure Elucidation of the Pyrolysates Formed by “Retro-Benzilic Acid Rearrangement” of the Proto-Photocycloadducts of Methyl 2,4-Dioxopentanoate-Olefins
Authors: Hatsui Toshihide , Nojima Chitoshi , Takeshita Hitoshi
Published: July 2006

Pyrolysates obtained from the proto-photoadducts of methyl 2,4-dioxopentanoate with olefins were shown to be 3-acetyl-1,2-cyclopentanedione derivatives. One-pot formation of polyfunctionalized cyclopentane derivatives via a photocycloaddition has no precedence. Intentional preparation of the ring system was also achieved by a diethyl azodicarboxylate–triphenylphosphine treatment of the proto-adducts.
Syntheses and Some Reactions of Trimethylsilylated Dinitrogen Complexes of Tungsten and Molybdenum
Authors: Komori Keiko , Sugiura Seiya , Mizobe Yasushi , Yamada Masaki , Hidai Masanobu
Published: July 2006

A series of new trimethylsilyldiazenido complexes [MX(NNSiMe3)(L)4] (M=Mo: X=I; M=W: X=CF3SO3; L=PMe2Ph or 1/2 dpe; dpe=Ph2PCH2CH2PPh2) and trimethylsilylhydrazido(2−) complexes [MX2(NNHSiMe3)(PMe2Ph)3] (M=Mo: X=I or Br; M=W: X=CF3SO3) and [MX(NNHSiMe3)(dpe)2]X (M=Mo: X=I; M=W: X=CF3SO3) were prepared by treatment of dinitrogen complexes cis-[M(N2)2(PMe2Ph)4] or trans-[M(N2)2(dpe)2] with Me3SiX in benzene. The trimethylsilyl groups on the terminal nitrogen atoms were easily replaced by hydrogen by the reaction with MeOH or H2O, affording, for example, diazenido and hydrazido(2−) complexes such as [WI(NNH)(dpe)2] and [WI2(NNH2)(PMe2Ph)3] from [WI(NNSiMe3)(dpe)2] and mer-[WI2(NNHSiMe3)(PMe2Ph)3], respectively. When reduced with excess Na in THF under N2, complexes trans-[MI(NNSiMe3)(PMe2Ph)4] (M=Mo or W) and mer-[WI2(NNHSiMe3)(PMe2Ph)3] gave (Me3Si)2NH and NH3 in substantial yields, accompanied by the regeneration of the parent dinitrogen complexes. Additional amount of NH3 was obtained by the hydrolysis of the evaporated reaction mixture residue.
Effect of α-Cyclodextrin on the Electrochemistry of (Ferrocenylmethyl)dodecyldimethylammonium Bromide at a Glassy Carbon Electrode
Authors: Opallo Marcin , Kobayashi Nagao , Osa Tetsuo , Yamada Hiroshi , Onodera Shinji
Published: July 2006

The influence of α-cyclodextrin (α-CD) on the electrochemistry of (ferrocenylmethyl)dodecyldimethylammonium bromide (I) was studied with a glassy carbon (GC) electrode. α-CD increases the apparent diffusion coefficient of I. This unusual effect is explained in terms of disruptive effect of α-CD on I’s aggregates. α-CD also influences, to some extent, I’s adsorption onto GC electrode when adsorbed from its micromolar aqueous solution.
Dielectric Properties of Dehydrated Ca1Na10-A and Na12-A Zeolites
Authors: Ohgushi Tatsuo , Nonaka Kenji , Yoshida Hiroyuki , Takaishi Tetsuo
Published: July 2006

Dielectric properties of completely dehydrated Ca1Na10-A and Na12-A zeolites were studied. The properties of Ca1Na10-A bore close parallels to those of Na11-ZK4 having almost the same cation distribution as Ca1Na10-A. The properties of Na12-A were markedly different from those of Ca1Na10-A and the unusual behavior of the zeolite were attributed to a larger mobility of Na+ ion on the 4-ring site.
Absence of the Enhanced Methanation Activity of Ni/TiO2 in the SMSI State as Examined with Pulse Surface Reaction Rate Analysis
Authors: Mori Toshiaki , Suzuki Kenzi , Saito Masahiro , Hattori Tadashi , Murakami Yuichi
Published: July 2006

From rate measurements with pulse surface reaction rate analysis, it was found that the methanation activity of Ni/TiO2 was the same both in the SMSI and in the normal states.
Evaluation of Oxidation of Vegetable Oils by Pyrolytic Sulfurization Gas Chromatography
Authors: Kawai Itsuro , Hara Tadashi
Published: July 2006

Oxygen determination by pyrolytic sulfurization gas chromatography was applied to observe the degree of oxidation of vegetable oils. Oxidation deterioration of vegetable oil and the effect of antioxidants were evaluated.
Preparation and Characterization of Triethylenetetramine Cobalt(III) Complexes with 1,2-Ethanedithiolate or 1,2-Ethanedisulfinate
Authors: Konno Takumi , Umehara Hideki , Okamoto Ken-ichi , Hidaka Jinsai
Published: July 2006

Triethylenetetramine (trien) cobalt(III) complexes with 1,2-ethanedithiolate (edt) or 1,2-ethanedisulfinate (edsi) were prepared and characterized by absorption, CD, and 13C NMR spectra. Each of the two complexes gave three possible geometrical isomers (cis-α, cis-β-RR,SS, and cis-β-RS,SR) which were separated and optically resolved by fractional crystallization and/or column chromatography.
Preparation of Bicyclic Crown Ethers Containing Amide Groups: Coordination of the Oxygen Atoms of the Amide Groups
Authors: Kumagai Takeshi , Akabori Sadatoshi
Published: July 2006

9,12,23,26,31,36-Hexaoxa-1,6,15,20-tetraaza-3,4: 17,18-dibenzotricyclo[18.8.5.56,15]octatriaconta-3,17-diene-2, 5,16,19-tetraone (7a) was obtained by the reaction of phthaloyl dichloride with 1,4,10-trioxa-7,13-diazacyclopentadecane in 38% yield, and related compounds were prepared by a similar method. Compound 7a showed high extraction abilities toward alkali, alkaline earth, and other metal cations (Ag+, Tl+, and Pb2+), especially lithium and sodium cations.
Asymmetric Alkylation of β-Keto Esters with Alkylsulfonium Salts Containing a Sugar Group
Authors: Umemura Kazuyuki , Matsuyama Haruo , Kobayashi Michio , Kamigata Nobumasa
Published: July 2006

The asymmetric alkylation of 2-methoxycarbonyl-1-indanone (2) and ethyl 2-methylacetoacetate (5) with an alkylsulfonium salt containing a sugar group were investigated. (S)-Ethyl 2-allyl-2-methylacetoacetate (6b) was obtained with up to 25% optical purity on alkylation of the enolate ion of 5 using the allyl(p-tolyl)sulfonio d-glucoside derivative (1h).
Reaction of Methyl 2,3,5,6,11,11b-Hexahydro-3-oxo-1H-indolizino[8,7-b]indole-5-carboxylate and Its Derivatives with N-Bromosuccinimide
Authors: Irikawa Hajime , Mutoh Susumu , Uehara Masahiro , Okumura Yasuaki
Published: July 2006

Methyl 2,3,5,6,11,11b-Hexahydro-3-oxo-1H-indolizino[8,7-b]indole-5-carboxylate was converted into the tetrahydro, dihydro, and dehydro esters using N-bromosuccinimide. On treatment with acetic acid, the 6a-bromo indolenine derivative bearing a substituent on C-11b gave a mixture of 8- and 9-bromo compounds by migration of the bromine to the benzene ring, while the corresponding 6a-chloro derivative afforded the oxindole.
A Synthetic Route to (±)-Humulone
Authors: Obara Heitaro , Onodera Jun-ichi , Machida Yoshihisa , Yada Shuji
Published: July 2006

The synthesis of (±)-humulone was achieved by the prenylation of 2,3,4,6-tetrahydroxyisovalerophenone with 1-bromo-3-methyl-2-butene.
An Improved Synthetic Method of (S)-2-Alkoxypropanals from Ethyl (S)-Lactate
Authors: Kobayashi Yuko , Takase Mitsuru , Ito Yoshio , Terashima Shiro
Published: July 2006

The title synthetic method which undergoes without racemization, was explored employing sequential amidolysis with a secondary amine, alkylation with an alkyl halide under basic conditions, and reduction with sodium bis(methoxyethoxy)aluminium hydride.
A Novel Use of the Ionic Hydrosilation in the Synthesis of Carbapenem Key Intermediate
Authors: Kobayashi Yuko , Ito Yoshio , Terashima Shiro
Published: July 2006

The ionic hydrosilation of the 3-acetyl-2-azetidinone derivative in the presence of boron trifluoride etherate was found to effect highly stereoselective reduction of the acetyl group (at most, 17:1), giving rise to the desired 3-[(R)-1-hydroxyethyl]-2-azetidinone derivative as a major product. Simultaneous reductive removal of the bis(p-methoxyphenyl)methyl group was also observed depending upon the reaction conditions.
A Facile Preparation of 7-(Substituted amino)-6H-pyrrolo[3,4-d]pyrimidine Derivatives
Authors: Noguchi Michihiko , Kiriki Yasutoshi , Kajigaeshi Shoji
Published: July 2006

6-Phenyl-7-(substituted amino)-6H-pyrrolo[3,4-d]pyrimidine-2,4(1H,3H)-diones 3 were obtained by the reaction of 5-formyl-1,3-dimethyl-6-[(substituted amino)methyl]-2,4(1H,3H)-pyrimidinediones (1) with aniline (2a).
A Facile Halogenative Cyclization of 4-(2-Benzothiazolyldithio)azetidinones (Kamiya’s Disulfide) into 2β-(Halomethyl)penams in a Two Layer System
Authors: Tanaka Hideo , Tanaka Motoaki , Yamada Sho-zo , Nakai Akira , Ohbayashi Hisashi , Terada Tadafumi , Torii Sigeru
Published: July 2006

Chlorinative cyclization of 4-(2-benzothiazolyldithio)azetidinones into 2β-(chloromethyl)penams has been successfully performed by treatment with aqueous sodium nitrite in a two-layer solution comprising aqueous hydrochloric acid and dichloromethane layers. Similarly, the corresponding 2β-(bromomethyl)penams can be obtained by use of aqueous hydrobromic acid in place of aqueous hydrochloric acid.
Efficient Reduction of 2-Haloacetophenone Derivatives to the Corresponding Halohydrins by 9,10-Dihydro-10-methylacridine in the Presence of Titanium Tetrachloride, Comparison with the Reduction in the Presence of Perchloric Acid
Authors: Mochizuki Seiji , Fukuzumi Shunichi , Tanaka Toshio
Published: July 2006

2-Haloacetophenone derivatives are reduced by an acid-stable NADH model compound, 9,10-dihydro-10-methylacridine, in the presence of HClO4 in acetonitrile at 335 K to yield 10-methylacridinium ion and the parent acetophenone derivatives as well as halohydrins, while the reduction of 2-haloacetophenone derivatives in the presence of TiCl4 in dichloromethane undergoes much more readily even at 298 K to yield the corresponding halohydrins selectively.
Conductimetric Studies of Ionic Association of Tetraalkylammonium Halides and Tetraphenylborate in N,N-Dimethylformamide–Methyl Ethyl Ketone Mixtures at 25 °C
Authors: Islam Nurul , Zaidi S B A , Ansari Aijaz Ahmad
Published: July 2006

The molar conductivities of Et4NBr, n-Pr4NBr, n-Bu4NBr, and n-Bu4NBPh4 have been measured in N,N-dimethylformamide–methyl ethyl ketone (DMF–MEK) mixtures (34.5≥D≥20.10) over the maximum concentration range (2×D3×10−7 mol dm−3) along with the densities and viscosities of the solvent mixtures at 25 °C. The conductance data have been analyzed by using the Fuoss-1978 (F78) conductance equation and the results compared with those obtained from the Justice (J) and the Fuoss-Onsager-Skinner (FOS) equations. The molar conductivities at infinite dilution (Λ0), the thermodynamic association constant (KA) and the distance or the ion-size parameter (R or a°) are evaluated from these data. A better fit of the parameters was provided by the F78 equation which yielded KA and R values. The Λ0 and the KA values are found to increase with decrease in the dielectric constant of the medium and in a given solvent mixture they follow the order Et4NBr>n-Pr4NBr>n-Bu4NBr>n-Bu4NBPh4.
The Complexation Equilibria of Mercury(II) Ions with Macromonocyclic 16-Membered Dioxopentamine, 18-Membered Dioxohexamine, and Their Related Compounds
Authors: Kodama Mutsuo , Kimura Eiichi
Published: July 2006

We have investigated the equilibria of complexation reactions of mercury(II) ions with 16-membered macrocyclic dioxopentamine (dioxo[16]aneN5), 18-membered macrocyclic dioxohexamine (dioxo[18]aneN6), and their related compounds by employing a polarographic method and pH-metric titration. Dioxo[16]aneN5, dioxo[18]aneN6, and other dioxo ligands except dioxotetramines were found to form solely 1 : 1 ratio mercury(II) complexes designated as HgH–1L+ with displacement of one amide proton, while the macrocyclic 16-membered monooxopentamine(monooxo[16]aneN5) forms HgL2+ in addition to HgH–1L+. The substitution of amine nitrogen of dioxo[16]aneN5 by the sulfur donor unexpectedly gave no increase in the stability of mercury(II) complex of dioxo ligand, HgH–1L+.
Syntheses and Structures of Indolo[6,7-g]indoles, a New Heteroaromatic System
Authors: Nagawa Yoshinobu , Goto Midori , Honda Koichi , Nakanishi Hiroshi
Published: July 2006

Photolysis of 1,1′-(1,8-naphthylene)-bis(1H-1,2,3-triazole)s (1) in methanol has given new heteroaromatic system compounds, indolo[6,7-g]indoles (2). The spectral properties of these compounds were studied in comparison with those of the corresponding benz[g]indoles (4) obtained from the similar photolysis of 1-(1-naphthyl)-1H-1,2,3-triazoles (3). The 1H NMR and IR spectra of 2 and 4 suggest the existence of a strong intramolecular hydrogen bonding in 2. The X-ray crystallographic analysis of tetraethyl 1H, 10H-indolo[6,7-g]indole-2,3,8,9-tetracarboxy late, 2a, indicates that the molecule has almost twofold rotational symmetry, and the framework is distorted due to the steric overcrowding.
Lipid-Protein Interaction in Mixed Monolayers from Phospholipids and Proteins
Authors: Mita Tomoyoshi
Published: July 2006

The thermotropic behavior of different proteins with phospholipids in monolayers was investigated by measuring the surface pressure and the surface viscosity. When phospholipids, such as dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC), were mixed with the hydrophobic proteins, such as hemoglobin and β-casein, below their phase transition temperatures (Tc), a considerable expansion of monolayers was observed. On the other hand, when phospholipids were mixed with the hydrophilic proteins, such as bovine serum albumin (BSA) and lysozyme below Tc, no expansion was observed. When DMPC was mixed with different proteins at Tc or above, all mixtures formed slightly deviated monolayers from ideal mixing, independent of a variety of proteins. This type of behavior suggests that the hydrophobic proteins perturb the structure of boundary lipids near the protein molecule below Tc, while the hydrophobic proteins do not perturb the phospholipid structure below Tc because of their low hydrophobicities. At Tc or above the membrane properties are independent of a variety of proteins, because all lipid hydrocarbon chains cause a disordering, even without proteins. In addition, when DPPC was mixed with a hydrophobic protein, such as hemoglobin, the fluidity of monolayer increased significantly.
High-Pressure Aminolysis of Lactones to Hydroxy Amides
Authors: Matsumoto Kiyoshi , Hashimoto Shiro , Uchida Takane , Okamoto Tadashi , Otani Shinichi
Published: July 2006

The preparation of hydroxy amides from a wide variety of lactones and amines has been achieved at 9 kbar and 30 or 65 °C. The yields of hydroxy amides were moderate to excellent. Some limitations were encountered in the reaction of 6-hexanolide; for example, diethylamine gave only a 15% yield of the corresponding amide at 8 kbar and 60 °C. 4-Pentanolide did react with extremely unreactive amines such as 4-nitroaniline and diphenylamine, and the product was a mixture of the hydroxy amide and 3-aminobutyric acid.
The Ullmann Condensation Reaction of Haloanthraquinone Derivatives with Amines in Aprotic Solvents. VI. The Combination of Cu(I) and Hydroxo or Alkoxo Cu(II) as Effective Catalyst System
Authors: Arai Sadao , Hashimoto Yoshio , Yamagishi Takamichi , Hida Mitsuhiko
Published: July 2006

The reaction rate of the Ullmann condensation reaction of haloanthraquinone with ethylenediamine (EN) by copper(I) halide catalyst decreased along with the formation of inactive Cu(II) species [Cu(EN)2X2] by one-electron transfer from Cu(I) to haloanthraquinone. However, the combination of Cu(I) and Cu(II) salts, having an OH, OCH3, or OCOR group, enhanced the reaction rate in the following order: CuCl<CuCl–CuCl(OCH3)<CuCl–Cu(OCH3)2<CuCl–Cu(OH)2. In condensation using Cu(OR)2 or CuCl(OCH3) alone, the Cu(II) species was reduced to Cu(I) to form an active catalyst system [Cu(I)+Cu(II)]. On the other hand, CuBr2 or CuCl2 was not reduced and was ineffective for the reaction. These were confirmed by ESR measurements and the presence of a dehalogenation product. Mixed valence species bridged by the alkoxo or hydroxo group was proposed as an active species.
Crystal Structure and Photochemical Behavior of 2,2,4,6-Tetraphenyldihydro-1,3,5-triazine and Its Inclusion Compounds
Authors: Mori Yukie , Ohashi Yuji , Maeda Koko
Published: July 2006

Crystal structures of 2,2,4,6-tetraphenyldihydro-1,3,5-triazine (1), which shows photocoloration, and its photostable propylamine solvate (2) have been determined. The molecular structure of the dihydrotriazine in 1 and 2 showed that it exists in 2,3-dihydro form in the crystals, but the bond distance of N(3)–C(4) was shorter than a normal C–N single bond, indicating that lone-pair electrons on N(3) interact with the π system of C(4)=N(5)–C(6)=N(1). Comparison of crystal structures of 1, 2, and other inclusion compounds previously determined revealed that the difference in the photochemical behavior of the crystals is attributable to different hydrogen bonding schemes. Photolysis of 1 in the solid state, which was carried out in connection with the structural investigation of the photocolored species, gave 2,4,6-triphenyl-1,3,5-triazine as a main product.
Reactions of Alkenes with Iodine(III) Tris(trifluoroacetate)
Authors: Futami Yasuo , Nishino Hiroshi , Kurosawa Kazu
Published: July 2006

The reactions of 1-arylethene, 1,1-diarylethenes, and 1,1-diarylpropenes with iodine(III) tris(trifluoroacetate) gave 1,2-diaryl-1-alkanones, 1-aryl-2-(4-iodophenyl)-1-alkanones, benzoins, benzils, and iodoethenes. A similar reaction of 1,1,4,4-tetraaryl-1,3-butadiene yielded 1,2,4,4-tetraaryl-3-buten-1-one. The reactions of 1,1,5,5-tetraaryl-1,4-pentadienes and 1,1,6,6-tetraaryl-1,5-hexadienes also gave dicarbonyl compounds. The reaction involves aryl migration. The mechanisms and the utility of the reaction for organic synthesis are discussed.
Studies of the Acidity and Ionic Conductivity of Silica-Supported Heteropoly Compounds. I. The Dehydration of t-Butyl Alcohol over Heteropoly Compound Catalysts
Authors: Ohtsuka Reiji , Morioka Yoshio , Kobayashi Jun-ichi
Published: July 2006

The dehydration of t-butyl alcohol (TBA) using various heteropoly compound (HPC) catalysts has been studied. Taking the adsorption of water on the surface of the catalyst into consideration, it is presumed that the dehydration of liquid TBA is governed by a Langmuir–Hinshelwood-like mechanism. Also, the change in the catalytic activity with the amount of HPC supported on the silica suggests that TBA is dehydrated through a pseudo-liquid mechanism in which a few layers of the HPC supported take part in the catalytic reaction. The layer thickness, regarded as a pseudo-liquid phase, depends markedly on the kind of HPC supported. For the dehydration of gaseous TBA, on the contrary, the reaction is found to be of the zero-order; it proceeds through in outer-surface mechanism in which only the outer layer of HPC is effective.
Selective Preparation of 2,3-Epoxypropanamide and Its Facile Conversion to 2,3-Dihydroxypropanamide with Acidic Resins
Authors: Sugiyama Shigeru , \ {O}higashi Shinji , Sawa Ryûichi , Hayashi Hiromu
Published: July 2006

In the equimolar reaction of acrylonitrile with hydrogen peroxide to 2,3-epoxypropanamide (glycidamide), the selectivity and the yield of the epoxide were improved by adding aq. NaOH solution continuously at a constant rate. The conventional literature procedure, by controlled pH from 7.0 to 7.5, resulted in an unfavorable decomposition of hydrogen peroxide. 2,3-Epoxypropanamide could be easily converted to 2,3-dihydroxypropanamide (glyceramide) by a catalytic amount of commercially available acidic resins.
Acidity Enhanced Pillared Clay Catalysts. Modification of Exchangeable Sites on Fluor-tetrasilicic Mica by the Fixed Interlayer Cations
Authors: Sakurai Hiroaki , Urabe Kazuo , Izumi Yusuke
Published: July 2006

By the use of fluor-tetrasilicic mica (TSM) as a starting material, La3+-modified pillared TSM was prepared by calcining La3+-exchanged TSM followed by Al-pillaring. Nonmodified pillared TSM managed only a 0.1% conversion for toluene alkylation with methanol, but the alkylation activity was greatly enhanced by the modification to give more than a 7% conversion, the activity level of which was roughly comparable to that of the conventional pillared montmorillonite. The effect of modification greatly depended on the calcination temperature at the pretreatment of La3+-exchanged TSM prior to a pillaring operation; the optimum calcination temperature was between 300 and 400 °C. Other multivalent cations with large ionic radii, such as Ce3+, Ca2+, and Sr2+, were also useful as modifiers. On the basis of the results of measurements involving X-ray diffraction, cation-exchange capacity and IR spectra of the adsorbed pyridine, it was concluded that a part of the thermally dehydrated La3+ ions lost their exchangeability to be fixed on the cation exchange sites of layers, remained between layers even after Al-pillaring, and took charge of the genesis of acidic sites.
The Sensitive and Selective Determination of Palladium(II) Based on Ternary-Complex Formation with Phloxine and Thiamine
Authors: Fujita Yoshikazu , Mori Itsuo , Toyoda Minako , Nakahashi Yoshihiro , Kato Keiji , Nakamura Masaki
Published: July 2006

A sensitive and selective spectrophotometric determination of palladium(II) based on ternary-complex formation with Phloxine and thiamine was established. The apparent molar absorptivity of the proposed method, which does not require an extraction procedure, was 1.02×105 dm3 mol−1 cm−1 at 565 nm. Only gold(III) in an equimolar ratio of palladium(II) among the metal ion examined interfered. The method was applied to a determination of palladium in palladium carbon and palladium asbestos; the results were in good agreement with those obtained by potassium iodide method, the Michler’s thioketone method and ICP-AES. The sensitivity could be further enhanced by about 20 times over that of spectrophotometry and/or fluorimetry by combining it with a membrane filter preconcentration technique. It was suggested that the collection of an aggregate on a membrane filter depends on the molecular size through observing by an scanning electron microscope.
Solvent and Reversed Phase Extraction Chromatographic Separation of Molybdenum and Tungsten with Quaternary Ammonium Salt Reagent, Aliquat 336
Authors: Das Nitya Ranjan , Chattopadhyay Putul
Published: July 2006

A quaternary ammonium salt reagent, Aliquat 336 has effectively been used for radioanalytical separations of molybdenum and tungsten through the techniques of solvent extraction and reversed phase extraction chromatography (RPEC). Studies on solvent extraction revealed that quantitative separations of the elements in a mixture can be achieved by extracting tungsten with ca. 10−4 mol dm−3 solution of Aliquat 336 in cyclohexane from an aqueous solution of 1 mol dm−3 H3PO4. The efficiency of separation of the elements which form varieties of metal salts of poly- and heteropolyanion species in aqueous solution is very much dependent on the types of acids as well as on the reagent concentration. In RPEC system, both the elements were found to be quantitatively extracted by an Aliquat 336 impregnated column of Kieselguhr from an alkaline solution containing a hydroxy compound like tartaric acid. The extracted species were subsequently separated by eluting molybdenum and tungsten respectively with HCl solutions of 0.05 mol dm−3 and 0.1 mol dm−3 concentrations. The purity of the separated species at various stages of their separations was verified by means of gamma-ray spectrometry.
Prototropic Equilibria in Few β-Hydroxy-Substituted 1-Naphthylamines in the Ground and Excited Singlet States
Authors: S. Sarpal Ranjit , K. Dogra Sneh
Published: July 2006

The longest wavelength transition in the absorption spectra of β-hydroxy-substituted 1-naphthylamines is long axis polarised, whereas the fluorescence occurs from the more polar, short axis polarized state. This is based on the spectral characteristics in different solvents. Five different prototropic species are formed in the ground state and six species are obtained in the S1 state. The ground state precursor for the formation of zwitterion is the monocation. pKa values for the different prototropic reactions have been calculated in the ground and excited singlet states.
Prebiotic Evolution of Oxidoreductases: [Fe(III)(CN)5(L)]n− Complexes as Models
Authors: Kamaluddin  , Mala Nath , Sushama W Deopujari
Published: July 2006

The transition state, where primary ligands like CN− partially replaced by biomolecules, has been assumed to be interesting from point of view of chemical evolution of oxidoreductase enzymes. Complexes of type [Fe(III)(CN)5(L)]n− (where n=2, 3 and L=glycine, imidazole, triglycine, and histidine) are proposed as models for peroxidases and catalases. Detailed kinetic investigations of decomposition of hydrogen peroxide catalyzed by [Fe(III)(CN)5(L)]n− complexes at 40 °C over a wide pH range 6.0–11.0 are discussed. The decomposition reaction is highly pH dependent. In alkaline media, initially L− is substituted by −OH in [Fe(III)(CN)5(L)]; subsequently HOO− binds to −OH through weak intramolecular hydrogen bonding, formation of peroxo complexes has been proposed to be an active intermediate responsible for accelerating the reaction. Decomposition of hydrogen peroxide catalyzed by [Fe(III)(CN)5(L)]n− complexes conforms to Michaelis Menten type of kinetics.
Correlation of 13C Shifts with Substituent Parameters in 3,4-Diphenyl-1,2,5-oxadiazole 2-Oxides Substituted at the Para-Positions of Either or Both Phenyl Rings
Authors: Balasubrahmanyam S N , Rajendran N , Singh D K
Published: July 2006

C-1′, C-1″, C-3, and C-4 13C shifts in 3,4-di(4′-or/and 4″-X)phenyl-1,2,5-oxadiazole 2-oxides (3,4-diarylfurazan 2-oxides; three series: X=NMe2, OMe, Me, Cl, H, and NO2) were correlated vs. seven different divided substituent parameter sets. Results have implied that i) the C-3–C-4 bond does not transmit mesomeric effects efficiently; ii) no effects can be specifically attributed to the possibility that the C-3 aryl maintains a higher dihedral angle with respect to the furoxan ring than the C-4 aryl; iii) there appears to be a directionality to the propagation of localized π-polarization due to lesser ability of C=N(O)→O to convey effects compared with C=N(O); and, iv) the furazan N-oxide ring, being generally an electron acceptor, transmits substituent effects nonlinearly.
Aromatic Acetonylation by Using Aryltins with Acetonylium Equivalents under the Palladium Catalysis
Authors: Kosugi Masanori , Miyajima Yoshio , Nakanishi Hideyuki , Sano Hiroshi , Migita Toshihiko
Published: July 2006

Palladium-catalyzed reactions of heteroaromatic tins with 2-ethoxyallyl diethyl phosphate and of nitrophenyltins with 2-methoxymethoxyallyl chloride were found to give the coupling products, which can be hydrolyzed to the corresponding acetonylated aromatics in good yields.
A Convenient Synthesis of Trifluoromethylated Pyrroles and Porphyrins
Authors: Ono Noboru , Kawamura Hisayuki , Maruyama Kazuhiro
Published: July 2006

4-Alkyl-3-trifluoromethyl-2-pyrrolecarboxylic acid esters (2) were conveniently prepared by the reaction of trifluoromethylated β-nitro acetates (1) with ethyl isocyanoacetate. The pyrroles were converted into the corresponding porphyrins via tetramerization of 2-(hydroxymethyl)pyrroles.
Stereoisomerism and Crystal Structure of (1R,2S,5R)-(+)-4-(Benzoyloxymethylene)-2,6,6-trimethylbicyclo[3.1.1]heptan-3-one{(1R,2S,5R)-(+)-4-(Benzoyloxymethylene)-3-pinanone}
Authors: Azani Nasser , Labruyere Francis , Metge Claude , Bertrand Charles , Sotiropoulos Jean , Jaud Joël
Published: July 2006

Conjugated esters from (+)-isopinocamphone, with a terpenic skeleton which is easily epimerizable may theoretically exist as four diastereomers (2R,4E; 2R,4Z; 2S,4E; 2S,4Z). X-Ray analysis shows that the reaction leads to a single isomer, namely an isopinocamphone derivative (2S,4E).
α-Iodination of Ketones and Enol Acetates with Poly[styrene-co-(4-vinylpyridinium dichloroiodate(1–))]
Authors: \u{S}ket Boris , Zupet Pavel , Zupan Marko , Dolenc Darko
Published: July 2006

Crosslinked poly[styrene-co(4-vinylpyridinium dichloroiodate(1–))] can be used as a very efficient polymeric reagent for α-iodination of ketones, diketones, and corresponding enol acetates.
The β-Sheet Structure-Disrupting Potential of Electron-Donor and -Acceptor Solvents and Role of Mixed Solvents in Solvation of Peptides
Authors: Narita Mitsuaki , Honda Shinya , Obana Satoshi
Published: July 2006

The β-sheet structure-disrupting potential of hydrogen-donor and -acceptor solvents was in the good relationship with their electron-acceptor and -donor numbers (AN and DN), respectively. As AN and DN of solvents are larger, their β-sheet structure-disrupting potential becomes higher. Based on the results of the β-sheet structure disruption in the three component solvent system, it can also be clarified that combinations of homogeneous solvents are suitable for peptide and protein synthesis, but those of heterogeneous ones are not effective. The results of this study are of quite significance for the search for effective solvents in peptide and protein synthesis.
Interfacial Adsorption of Iron(II)–4,7-Diphenyl-1,10-phenanthroline Complex in Ion-Association Extraction Systems
Authors: Watarai Hitoshi , Shibuya Yoko
Published: July 2006

The interfacial adsorptivity of an iron(II)–4,7-diphenyl-1,10-phenanthroline (DPP) complex in chloroform/aqueous salt solution systems was investigated by means of a high-speed stirring method and interfacial tension measurements. The interfacial spectra observed in the stirred system suggested that the adsorbed species at the interface is the tris-DPP complex. A minor effect of the anion concentration on the adsorptivity suggested that the tris-complex adsorbed as an ion-pair in a 0.1 M anion concentration. The interfacial adsorption of the ion-pair under stirring was analyzed by the Langmuir isotherm. The adsorptivity increased, depending on the counter ions, in the order ClO4−<CCl3COO−\simeqBr−<Cl−<SO42−, i.e. the order of increasing hydration energies of these anions.
Temperature Dependence of Conductivities and Ion-Association Constants of Potassium Sulfate in Water
Authors: Yokoyama Haruhiko , Ohta Tomoko
Published: July 2006

From the temperature dependence of the ion-association constants between K+ and SO42− at 0 to 50 °C, the contact ion-pair formation and short-range interactions are discussed while considering the hydration of the anion. The limiting molar conductivities of SO42− are expressed as a cubic equation of the temperature.
Chromatographic Separation of Rare Earth Pairs by a Chelating Resin Having Bis(carboxymethyl)amino Groups
Authors: Kanesato Masatoshi , Yokoyama Toshiro , M. Suzuki Toshishige
Published: July 2006

Adsorption properties of rare earth elements toward a cross-linked polystyrene resin having bis(carboxymethyl)amino groups (CMA) have been studied. The selectivity sequence of the resin for a series of rare earth metals was in good accordance with that of the corresponding stability constants of diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA) complexes. The chromatographic separation of La(III)/Pr(III), Nd(III)/Sm(III), and Y(III)/Gd(III) has been carried out by use of the present resin. The chromatographic conditions were empirically evaluated in terms of resolution (Rs), with varying column length, pH of the eluent, the flow rate and the column temperature.
Binding of Modified Guanine Nucleotides to Ribonuclease T1 as Studied by Absorption Spectroscopy. 8-Aminoguanosine 2′-Phosphate, 8-Methylaminoguanosine 2′-Phosphate, and 8-Dimethylaminoguanosine 2′-Phosphate
Authors: Yoshida Hiroshi , Sugiyama Masazumi , Shibagaki Yoshio
Published: July 2006

The title nucleotides have been synthesized and their binding to ribonuclease T1 studied by means of absorption spectroscopy. Measurements were made at pH 5.5 and 4.1, where a major portion of the base moiety of the nucleotides was in a neutral form and a cationic form protonated at N7, respectively. At both pH’s, difference absorption spectra were induced upon binding of the nucleotides to the enzyme. A comparison of the difference spectra with that for guanosine 2′-phosphate has led to the conclusion that perturbation in the bound nucleotide is the principal cause for the difference spectra. The difference spectra at pH 5.5 and 4.1 were similar, suggesting that the protonation at N7 of the nucleotides can be ruled out as the cause for the difference spectra. The dissociation constants at pH 5.5 and 4.1 of the enzyme–8-aminoguanosine 2′-phosphate complex were of the same magnitude, indicating that both the neutral and the protonated forms bind tightly to the enzyme. However, the cationic form of 8-methylamino- or 8-dimethylaminoguanosine 2′-phosphate has been shown to interact with the enzyme much more loosely than the neutral form.
Synthesis and Spectroscopic Investigation of Directly Conjugated Polyyne Porphyrins
Authors: Maruyama Kazuhiro , Kawabata Shigeki
Published: July 2006

A series of conjugated polyyne porphyrin, in which porphyrin macrocycle is directly connected with one end of diarylpolyyne through aromatic ring, has been prepared and their spectroscopic behaviors were investigated. Diarylpolyynes consisting of aryl group and conjugated triple bond system have rigid and linear structure, and the two chromophores are held at a fixed geometry and a determined distance. The UV-vis absorption spectra of these compounds showed strong conjugative interaction, showing broadening of their spectra and slightly red shifted porphyrin Soret bands with increasing the number of acetylenic bond. From their fluorescence excitation spectra energy transfer efficiencies from polyyne moiety to porphyrin moiety were estimated. The energy transfer efficiencies were almost unity regardless of their substituted position, geometry, and orientation.
Synthesis of 1,5-Bifunctionalized Optically Active 3-Pentanol as a Reversible Chiral Building Block. Asymmetric Reduction of 4-(1,3-Dithian-2-yl)-3-oxobutanoates with Fermenting Bakers’ Yeast
Authors: Chikashita Hidenori , Ohkawa Kazuhiko , Itoh Kazuyoshi
Published: July 2006

Bakers’ yeast reduction of a homologous series of 4-(1,3-dithian-2-yl)-3-oxobutanoates to the corresponding chiral 4-(1,3-dithian-2-yl)-3-hydroxybutanoates was investigated. A shift in enantiomeric excess, stereochemistry, and chemical yield of the reduction product was observed as the size of the ester alkoxyl group was changed. The kind of bakers’ yeast (raw or dry) and reaction conditions also affected the optical purity and chemical yield of the product. These studies showed that the reduction of methyl 4-(1,3-dithian-2-yl)-3-oxobutanoate with the raw yeast in the absence of additives was most efficient, giving methyl (S)-4-(1,3-dithian-2-yl)-3-hydroxybutanoate with 77% ee in 37% yield.
A Practical Optical Resolution of (Arylsulfinyl)acetones and Its Application to the Synthesis of 2-(Arylsulfinyl)cycloalkanones
Authors: Ogura Katsuyuki , Ishida Michio , Tomori Hiroshi , Fujita Makoto
Published: July 2006

Racemic (arylsulfinyl)acetones (1) were efficiently resolved by formation of their oxazolidine derivatives with (R)- or (S)-2-amino-2-phenylethanol followed by chromatography on Florisil–MgO and the subsequent hydrolysis to give (S)- or (R)-1, respectively. Further, derivation of 1 to optically active 2-(p-tolylsulfinyl)cyclohexanone and 2-(p-tolylsulfinyl)-4-cycloheptenone is described.
2-Methoxyethyl Group for Protection of Reducing Hydroxyl Group of Aldose
Authors: Koto Shinkiti , Morishima Naohiko , Takenaka Kazuhiro , Kanemitsu Kumi , Shimoura Noriko , Kase Miyuki , Kojiro Shizuko , Nakamura Teiko , Kawase Tomoko , Zen Shonosuke
Published: July 2006

A variety of benzylated 1-OH derivatives, having an acetyl or an allyl group, of d-glucose, d-galactose, d-mannose, d-xylose, l-arabinose, l-fucose, and l-rhamnose, were synthesized from the corresponding protected 2-methoxyethyl glycosides through a brief treatment with TiCl4 in dichloromethane and a subsequent hydrolysis of the intermediary 1-Cl derivatives on a silica-gel column.
The β-Sheet Structure-Stabilizing Potential of Twenty Kinds of Amino Acid Residues in Protected Peptides
Authors: Narita Mitsuaki , Kojima Yoshihisa
Published: July 2006

A host–guest approach was devised to investigate the β-sheet structure-stabilizing potential of the 20 common amino acid residues in protected peptides where functional groups in side chains were protected by suitable groups commonly used in peptide synthesis. The potential was evaluated using solvent-titration curves for the disruption of the β-sheet structure of cross-linked polystyrene resin-bound host–guest hexa- and octapeptides in CH2Cl2 by HFIP. The β-sheet structure of host–guest hexapeptides, Boc–Val–Ile–X2–Val–Ile-NHCH2–resins, in which X stands for guest amino acid residues, was disrupted in CH2Cl2 by adding increasing amounts of HFIP; the disrupted behaviors were strongly dependent on the nature of guest amino acid residues. A scale for the β-sheet structure-stabilizing potential of the 20 kinds of amino acid residues in CH2Cl2 could be derived at 0.25 M of HFIP concentration as follows: Ile, Val>>Asn>His(Tos) or His, Gln, Cys(Bzl), Tyr(Bzl)>Phe, Gly, Lys(Z), Arg(Tos), Leu>Thr(Bzl), Ala, Met(O), Glu(OBzl), Trp(CHO)>>Ser(Bzl), Asp(OBzl)>>Pro. To confirm the scale, their β-sheet structure-stabilizing potential was further examined using host–guest octapeptides, Boc–X2–Val–Ile–X2–Val–Ile–NHCH2–resins. The disrupted behaviors of the octapeptides having Gly, Ala, and Thr(Bzl) residues as guests were remarkably different from those of the corresponding hexapeptides; the β-sheet structure-stabilizing potential of the Gly, Ala, and Thr(Bzl) residues became significantly high with an increase in their ratios to host residues. The potential of the Gly, Ala, and Thr(Bzl) residues appears to reflect the ratios of guest amino acid residues to hosts, the repeated sequence, and/or neighbor interactions in the sequence. The significance of the present study in the design of synthetic routes for peptides and proteins is briefly discussed.
Peptide Segment Separation by Tertiary Peptide Bonds. Synthesis and Conformational Analysis of Cross-Linked Polystyrene Resin-Bound Human Proinsulin C-Peptide Fragments
Authors: Narita Mitsuaki , Umeyama Hiroshi , Yoshida Toshihiko
Published: July 2006

In order to clarify the role of tertiary peptide bonds in the conformational development of protected peptides in organic solvents, cross-linked polystyrene resin-bound human proinsulin C-peptide fragments were prepared by a fragment condensation method. For the purpose of clarifying the role of tertiary peptide bonds, it is indispensable to force coupling reactions to completion; the addition of HFIP in coupling reactions in CH2Cl2 was significantly effective for their completion when they did not proceed smoothly. The conformational behavior of resin-bound human proinsulin C-peptide fragments in CH2Cl2 was successively investigated using IR absorption spectroscopy. Two Pro residues forming tertiary peptide bonds played the role of stopping the development of helix and β-sheet structures in peptides, and the structure of N- and C-terminiand side-chain-protected human proinsulin C-peptide could be regarded as being assembled with peptide segment structures separated by the two Pro residues. When a peptide segment had a high helix-forming potential, a Pro residue in an N-terminal part of the peptide segment promoted its helix formation. β-Sheet structures formed by peptide segments in CH2Cl2 were easily disrupted by a strong electron-acceptor solvent of HFIP, suggesting that the β-sheet structure disruption of resin-bound peptides is important in achieving efficient coupling reactions.