bluuebunny/crossref_metadata_2025_split huggingface dataset:
Threading Intercalators as a New DNA Structural Probe
Authors: Takenaka Shigeori , Takagi Makoto 
Published: December 2003

Abstract
Nogalamycin is a threading intercalator and when it binds with double stranded DNA, one of the two sugar substituents goes between adjacent base pairs of DNA to form a stable complex in which the two substituents of nogalamycin are projecting out in each groove of DNA. Since the molecular volume of the substituents of nogalamycin is larger than that of the space created through the motion of DNA strands constituting the double helix, a cleavage of hydrogen bonds in the base pairs of DNA duplex is necessary to form such a complex. The structure of double-stranded DNA is dynamic, and the base pair cleavage (base pair opening) and re-formation (closing) occur frequently at ambient temperature. A wider variety of threading intercalators is obtainable synthetically, and they include several families such as 1,5-disubstituted anthraquinones, 9,10-disubstituted anthracenes, and naphthalene bis(dicarboximide) derivatives. Kinetic study of the complex formation and dissociation of naphthalene bis(dicarboximide) carrying substituents of different size have made one recognize the dynamic character of duplex DNA in intercalation reaction. A cyclic bis-intercalator was also able to form a threading complex of a catenane-like structure. A thorough study of the binding behavior of natural and synthetic threading intercalators with DNA revealed that a proper design of substituents on threading intercalators can produce ligands which specifically bind either to single- or double-stranded DNA. These ligands, synthetic ones in particular, will hopefully serve not only as new DNA structural probes but also as chemotherapeutic agents.
Energy Transfer, Electron Transfer, and Addition Reactions of Triplet State of 1,3-Dihydroimidazole-2-thiones Investigated by Laser Flash Photolysis
Authors: Alam Maksudul M , Ito Osamu 
Published: December 2003

Abstract
The transient absorption bands observed at ca. 400 and 550 nm for 1,3-dihydro-2H-imidazole-2-thione (IT), 1,3-dihydro-1-methyl-2H-imidazole-2-thione (MIT), and 1,3-dihydro-2H-benzimidazole-2-thione (BIT) have been assigned to their triplet states (3IT* ’s) by the quenching and sensitizing experiments using laser flash photolysis technique. Short intrinsic triplet lifetimes and relatively high triplet energies have been evaluated as characteristics of 3IT* ’s. For electron acceptors, photoinduced electron-transfer reaction occurs via 3IT* ’s in the diffusion controlled limit. The nucleophilic character of 3IT* ’s was confirmed by changing the substituents of alkenes on the addition reactions. MO calculations indicate that the lowest electronic configurations of both 3IT* and 3MIT* have 3(n,π*) character, while 3BIT* has 3(π,π*) character. The addition reactivity of 3BIT* is slightly higher than those of 3IT* and 3MIT*, which is opposite to the general tendency.
Photochemistry of Bifunctional Chain Molecules Containing Benzophenone and Anilino Chromophores. Magnetic Field and Magnetic Isotope Effects on Lifetimes of Triplet Biradicals
Authors: Nakagaki Ryoichi , Yamaoka Masaharu , Mutai Kiyoshi 
Published: December 2003

Abstract
The decay time of biradicals containing a benzophenone ketyl and an anilino-alkyl radical has been examined by nano-second laser photolysis in the presence of external magnetic fields up to 1 T. When sites with high spin densities are labeled with heavy carbon, noticeable magnetic isotope effects are observed on the decay kinetics for biradicals. Small kinetic effects are observed for deuterated species. The obtained results can be interpreted in terms of spin-lattice relaxation due to anisotropic hyperfine and dipole–dipole interactions. Procedures for preparing labeled species are also described.
Rate-Determining Step of Deswelling for Conventional and Macroporous Poly(N-isopropylacrylamide) Gels
Authors: Kato Norihiro , Takahashi Fujio 
Published: December 2003

Abstract
The kinetic parameters of deswelling for conventional and macroporous poly(N-isopropylacrylamide) gels were determined in order to point out the rate-determining step on the deswelling process in a NaCl or KCl solution. The apparent activation energy for the deswelling of the conventional gel in water (130 kJ mol−1) was larger than that of the macroporous gel in water (25 kJ mol−1). The split process of the skin layer, which was formed on the surface of the gel by heating from outside of gel, was considered concerning the rate-determining step in the case of the conventional gel. The activation entropy changes at 313 K (ΔS313’s) of the macroporous gel were determined to be −65 J K−1 mol−1 in 0.1 M NaCl (1 M = 1 mol dm−3), of which the cation exhibits a structure-forming property, and 180 J K−1 mol−1 in 0.1 M KCl, of which the cation exhibits a structure-breaking property. The sign of ΔS313 for the macroporous gel was negative at higher than 0.3 M NaCl or KCl. In order to point out the rate-determining step, the process of the salting-out effect, that of bond formation between the polymer chains, and that of forming water clusters in the presence of the cation inside of the gel are discussed.
Pressure Effect on Phase Transitions in Hexamethylbenzene Crystals
Authors: Takeshita Hideyoshi , Suzuki Yoshio , Nibu Yoshinori , Shimada Hiroko , Shimada Ryoichi 
Published: December 2003

Abstract
The pressure effect on the phase transitions in hexamethylbenzene and hexa(methyl-d3)benzene crystals was studied compared with the temperature effect on the phase transitions. The transition from phase II to phase III of hexa(methyl-d3)benzene crystal takes place under lower pressure than that for hexamethylbenzene crystal. The change in the spectral structure due to the intermolecular vibrations caused by an increase in the pressure indicates that the marked interaction between the intermolecular rotational vibration and the intramolecular methyl torsional vibration of hexa(methyl-d3)benzene crystal takes place under lower pressure than that for hexamethylbenzene crystal. These facts suggest that the intramolecular methyl torsional vibration plays an important role for the II-to-III phase transition in hexamethylbenzene crystals.
A Statistical Model of the Extraction-Process Parameters of Uranium–N-Phenylbenzohydroxylamine–Trioctylphosphine Oxide Complex in Chloroform Solution
Authors: Sarkar Jaya , Bag Saswati Prasad , Basumallick Amitava 
Published: December 2003

Abstract
The solvent extraction of uranium has been carried out with chloroform solutions of N-phenylbenzohydroxamic acid (BPHA) and Trioctylphosphine oxide (TOPO). The experiments were statistically planned to quantitatively assess the effect of the concentration of BPHA, the concentration of TOPO and the aqueous-phase pH of the solution on the percentage extraction of uranium. In addition, the interactional influence of the above-mentioned variables was also studied. A regression equation has been developed which successfully predicts the percentage extraction of uranium with the values of the variables lying between the selected range of experiments.
Structures and Electronic Spectra of Aquadiiminebis(succinimidato)copper(II) Complexes with Square Pyramidal [CuN4O] Chromophores (Diimine = 1,10-Phenanthroline and 2,2′-Bipyridine)
Authors: Akitsu Takashiro , Komorita Seiko , Kushi Yoshihiko 
Published: December 2003

Abstract
Copper(II) complexes [Cu(succim)2(phen)H2O]·H2O (1) (succim = succinimidate, phen = 1,10-phenanthroline) and [Cu(succim)2(bpy)H2O] (2) (bpy = 2,2′-bipyridine) were prepared and the crystal structures were determined by X-ray crystallography. The coordination geometries are found to be five-coordinated square-based pyramidal [CuN4O] for each complex. Crystal data for complex 1 are monoclinic with space group P21/n; a = 9.602(4), b = 12.003(4), c = 17.618(4) Å; β = 100.38(3)°; V = 1997(1) Å3; Z = 4. Crystal data for complex 2 are monoclinic with space group P21/n; a = 9.616(2), b = 11.616(3), c = 15.871(2) Å; β = 90.61(2)°; V = 1772.8(6) Å3; Z = 4. The axial Cu–O(water) bond distances of the present complexes (2.548(5) Å for 1 and 2.673(4) Å for 2) are appreciable longer than those of other square pyramidal trans-[CuN4O] complexes. The diffuse reflectance spectra showing a broad peak at about 17000 cm−1 were analyzed by means of Gaussian curve fitting and angular overlap model (AOM) calculations with respect to dxy, dyz, and dzx orbitals distributing in the [CuN4] basal plane. According to the analyses, transferability of AOM parameters is valid for succim. The ligand field of bpy can be described by the same parameters as py (py = pyridine). However, it is necessary to set a larger π-bonding AOM parameter for phen than that of py to reproduce the experimental results. The reason for this is out-of-plane lone pairs and π-conjugation of phen. The assignment of the one-electron orbital sequences is presumed to be dx2−y2 &gt; dz2 &gt; dxy &gt; dyz &gt; dzx based on the AOM calculations for each complex.
A New Halogen-Exchange Reaction between Sn–F and Li–X: Selective 1,2- and 1,4-Reductions of α,β-Unsaturated Ketones and Effects of Halogen Substituents on the Regioselectivity of Organotin Hydrides
Authors: Moriuchi-Kawakami Takayo , Matsuda Haruo , Shibata Ikuya , Miyatake Masato , Suwa Toshihiro , Baba Akio 
Published: December 2003

Abstract
We have found that halogen-exchange occurs effectively between Sn–F and Li–X (X = I, Br, Cl) in tin hydride reagents. This fact induced a complete change in the regiochemistry in the reductions of α,β-unsaturated ketones 1 with Bu2SnH2–Bu2SnF2 (Reagent A): the use of Reagent A in combination with HMPA performed 1,2-reductions, while the addition of LiI to Reagent A achieved 1,4-reductions. It was demonstrated that the regioselectivity of organotin hydrides greatly depends on the properties of the halogen substituents attached to tin atoms.
Model Studies Related to Synthesis and 1,4-Dipolar Cycloaddition Reactions of Mesoionic Heterocycles
Authors: Issac Yvette Abd El-Sayed 
Published: December 2003

Abstract
The reaction of 2-(substituted amino)pyridine with reactive malonic acid derivatives provided an extremely facile synthesis of the mesoionic compound 4-oxo-4H-pyrido[1,2-a]pyrimidin-1-ium-2-olates. N,N′-Disubstituted amidine reacted with diethyl malonate to afford 4-quinolone in a one-pot cyclization and rearrangement (type A/I) of 4-oxopyridiniumolate 6. The latter compound was isolated via a reaction of acyclic amidine with AME’s. A cycloaddition reaction of the mesoionic pyrimidine 6 with maleic anhydride or N-phenylmaleimide yielded [2+4] cycloadducts. Triphenyl pyrrolopyridinetrione 12 was achieved via a ring transformation of the cycloadduct 4-benzyl-3,5-dioxo-1,2,6-triphenyl-2,6-diazabicyclo[2.2.2]octane-7,8-dicarboxylic anhydride 11d. In contrast, the cycloadduct 4-ethyl derivative 11c and substituted 3,5-dioxo-1,2,6-triphenyl-2,6-diazabicyclo[2.2.2]octane-7,8-dicarboxylic N-phenylimides did not give 12 under the same reaction conditions. The mechanistic pathway for the formation of 12 was studied. Dimethyl acetylenedicarboxylate reacted with 6b,c to furnish 2-oxo-1,2-dihydropyridine-4,5-dicarboxylates.
Synthesis and Solution Conformations of Cyclo(Pro–Leu–Gly)2 and Cyclo(Pro–Leu–Gly)4
Authors: Wang Jun , Osada Satoshi , Kodama Hiroaki , Kato Tetsuo , Kondo Michio 
Published: December 2003

Abstract
Two cyclic peptides containing the C-terminal tripeptide sequence of oxytocin, cyclo(Pro–Leu–Gly)2 and cyclo(Pro–Leu–Gly)4, have been synthesized from the corresponding linear hexapeptide active ester under high dilution conditions. Cyclo(Pro–Leu–Gly)4 serves as an example of the synthesis of cyclic peptides from linear peptides containing an even number of amino acid residues through dimerization. These two compounds are characterized by TLC, HPLC, amino acid analysis, NMR, and mass spectra. Cyclo(Pro–Leu–Gly)2 has also been synthesized from the linear tripeptide precursor independently, and its properties have been shown to be identical to that from linear hexapeptide. Circular dichroism indicated that cyclo(Pro–Leu–Gly)2 contains β-turns as expected; in contrast, cyclo(Pro–Leu–Gly)4 exhibited a random structure pattern. The NMR spectra demonstrated that cyclo(Pro–Leu–Gly)2 is fixed in only one conformer in DMSO, while in a CDCl3 solution, several conformations with a rapid interconversion are present. Unlike the cyclohexapeptide, cyclo(Pro–Leu–Gly)4 showed more complicated NMR spectra in the two solvents; two or more conformers are considered to be present.
Osmotic Stability of Muramyl Dipeptide-Bearing Liposomes and Molecular Miscibility in Their Membranes
Authors: Kim Suhk-mann , Kiyonaga Hiroshi , Yamaguchi Hideto , Morozumi Hiroto , Fujiwara Toshimichi , Ando Shuichi , Tsuge Hideya , Akutsu Hideo 
Published: December 2003

Abstract
Muramyl dipeptide is the minimal and essential structural unit for the immunopotentiating activities of bacterial cell walls. The muramyl dipeptide derivative N-acetyl-6-O-(2-tetradecylhexadecanol)muramyl-l-alanyl-d-isoglutamine (B30-MDP) and its amide derivative (B30-MDPA) are good basic materials for use in artificial liposome vaccines (virosomes). The osmotic stability of muramyl dipeptide-bearing liposomes composed of various binary mixtures was examined to find conditions favoring stable liposome formation. The osmotic properties of B30-MDP-bearing and B30-MDPA-bearing liposomes were significantly different from each other. Nevertheless, a good correlation between osmotic stability and virosome formation was found for both types of liposomes. Furthermore, the dynamic structures and the intermolecular interactions of phospholipids in muramyl dipeptide-bearing liposomes were investigated by solid-state 2H and 31P NMR. The results suggested that molecular miscibility in the liposomes is not an essential factor for osmotic stability. Negative charges on the liposome surface and flexible hydrophilic moieties were found to be the most important factors in keeping isolated liposomes osmotically stable.
Generation and Reactivity of 2-Substituted Adamantenes
Authors: Okazaki Takao , Tokunaga Kazuhiko , Kitagawa Toshikazu , Takeuchi Ken’ichi 
Published: December 2003

Abstract
The title bridgehead olefins, generated by the dehalogenation of 1,2-dihalo-2-R-adamantanes (R = Me, Et, Ph, p-CF3C6H4) with excess t-BuLi, yielded 2-t-butyl-2-R-adamantanes (15), 1-t-butyl-2-R-adamantanes (16), and dimeric products. The ratios of the yields (%) of 16 to 15 were 20 : 3 (R = Me), 32 :&lt; 1 (R = Et), 4 : 60 (R = Ph), and 5 : 57 (R = p-CF3C6H4). 2-Alkyladamantenes predominantly yielded the products t-butylated at C(1), whereas 2-aryladamantenes gave the products t-butylated at C(2). The total yields of the dimers decreased with the bulkiness of substituents at position C(2). The dimerization of 2-methyladamantene gave a head-to-head dimer, 1-(2-methyl-1-adamantyl)-2-methyleneadamantane, as well as a head-to-tail dimer, 1-(2-methyl-2-adamantyl)-2-methyleneadamantane. The [4+2] cycloaddition between two molecules of 2-phenyladamantene, in which the phenyl group participates as a part of the diene, yielded a dimer of the head-to-tail type.
These results suggest that: i) a substituent at position C(2) can kinetically stabilize 2-R-adamantene and suppress the dimerization, ii) 2-alkyladamantenes might have a biradical nature, and iii) the regioselective [4+2] cycloaddition and t-BuLi addition of 2-phenyladamantene in THF can be explained by assuming a certain contribution of zwitterionic nature in the double bond that may be dependent on the media and nucleophiles.
Syntheses, Structures, and Redox Properties of 1,4-Bis(dimesitylphosphino)-2,3,5,6-tetrafluorobenzene and the Corresponding Bis(phosphoryl) and Bis(phosphonio) Derivatives
Authors: Sasaki Shigeru , Tanabe Yoshihiro , Yoshifuji Masaaki 
Published: December 2003

Abstract
Sterically hindered 1,4-bis(dimesitylphosphino)-2,3,5,6-tetrafluorobenzene (1) was synthesized by the aromatic nucleophilic substitution of lithium dimesitylphosphide with hexafluorobenzene. Two phosphorus atoms of 1 were oxidized and methylated to give the corresponding bis(phosphoryl)benzene 2 and bis(phosphonio)benzene 32+·2TfO− (TfO− = trifluoromethanesulfonyl), respectively. On the other hand, reaction of 1 with butyllithium and phenyllithium gave more crowded 2,5-dibutyl-1,4-bis(dimesitylphosphino)-3,6-difluorobenzene (4) and 1,4-bis(dimesitylphosphino)-2,5-difluoro-3,6-diphenylbenzene (5), respectively. Structures of 1, 2, 32+·2TfO−, 4, and 5 were confirmed by conventional spectroscopic methods; particularly 19F NMR spectroscopy reflected their crowded structures. Molecular structures of 1, 2, and 32+·2TfO−, were further investigated by X-ray crystallography, where unusually large bond angles around phosphorus atoms were observed. Electrochemical measurements were carried out to investigate redox properties of 1, 32+·2TfO−, 4, and 5. Although the cyclic voltammogram of diphosphine 1 showed irreversible oxidation waves above 0.8 V, in spite of substitution at all the ortho positions to the phosphorus atoms in 1, displacement of the two fluorine atoms of 1 by the butyl or the phenyl groups lowered the oxidation potential and improved the stability of the corresponding radical cations. Particularly, 5 clearly showed two-step oxidation waves. On the other hand, bis(phosphonium salt) 32+·2TfO− showed two steps of quasi-reversible redox waves, which suggested reduction to the cation radical and the neutral species, although their stability was limited.
Substituent Effects on the Solvolysis Rates and Gas Phase Stabilities of 1,2,2-Trimethyl-1-phenylpropyl and 1,2,2-Trimethyl-1-(2-methylphenyl)propyl Systems
Authors: Nakata Kazuhide , Fujio Mizue , Mishima Masaaki , Nomura Hideyuki , Tsuno Yuho , Nishimoto Kichisuke 
Published: December 2003

Abstract
Substituent effects on the solvolysis rates of 1,2,2-trimethyl-1-phenylpropyl chlorides in 80% (v/v) aq acetone at 45 °C and 1,2,2-trimethyl-1-(2-methylphenyl)propyl p-nitrobenzoates in 50% (v/v) aq ethanol at 75 °C were correlated with the Yukawa–Tsuno equation to give ρ = −4.28 and r = 0.91, and ρ = −2.78 and r = 0.70, respectively. The reduction in r values from r = 1.00 for full conjugation is ascribed to deviation from coplanarity of the carbocationic center and the benzylic π-system in the transition state. Substituent effects on the gas phase stabilities of 1,2,2-trimethyl-1-phenylpropyl cations and 1,2,2-trimethyl-1-(2-methylphenyl)propyl cations were correlated to give ρ = −9.1 and r = 0.89, and ρ = −6.6 and r = 0.70, respectively. The identical r values were obtained for the transition states and for the intermediates. The experimentally obtained torsion angles for twisting estimated from the relationship r/rmax = cos2 θ are in good agreement with theoretically calculated dihedral angles of the corresponding Becke3LYP/6-31G* optimized carbenium ions. This identity provides convincing evidence for occurrence of steric inhibition of resonance through loss of coplanarity and provides strong support for our characterization of the r value as a resonance demand parameter.
Phosphorescence of Benzophenone in Sol–Gel Silica
Authors: Matsui Kazunori , Nozawa Kazuhiro , Yoshida Tsutomu 
Published: December 2003

Abstract
The phosphorescence spectra of benzophenone (BP) were studied in tetramethoxysilane (TMOS) sol–gel systems at 77 K. The phosphorescence spectra ascribed to solvent-free benzophenone (f-BP), aggregated benzophenone (a-BP), and a benzophenone–water complex (w-BP) were observed in these systems. The results showed that the spectra varied with the BP concentration and sol–gel conditions, such as the water/TMOS ratios, catalyst, and the various sol–gel reaction stages. The w-BP phosphorescence lifetimes showed a single-exponential decay of 8 ms in sol systems and a double-exponential decay of 8—12 ms and 31 ms in xerogel systems. The longer lifetime component corresponds to a w-BP complex hydrogen bonded with silanol groups. These changes are discussed in terms of the sol–gel structure and surface adsorption effects.
Asymmetric Catalysis of New Generation Chiral Metallosalen Complexes
Authors: Ito Yoshio N , Katsuki Tsutomu 
Published: December 2003

Abstract
Chiral metallosalen complexes have been recognized as one of the most promising catalysts for various asymmetric reactions. The studies on asymmetric epoxidation catalyzed by chiral (salen)manganese complexes will be reviewed at first. The enantioselectivities have reached to the level as high as 90—99% ee for the epoxidation of conjugated cis-di- and trisubstituted olefins by developing the second generation of chiral salen ligands. Although it has been proven by Freichtinger and Plattner that epoxidation proceeds through an oxo species, the mechanism of asymmetric induction is still surrounded by controversy. However, our recent studies have clarified that the conformation of the salen ligand in oxo(salen)manganese(V) species plays a very important role in determining the direction of the olefin’s access to the oxo species. This study led to the new finding that an achiral (salen)metal complex can be used as a chiral catalyst by regulating the conformation of achiral ligand. The appropriately modified (salen)manganese(III) complexes can also be applicable for asymmetric oxidation of enol ether derivatives, kinetic resolution of racemic allenes, enantioselective benzylic C–H oxidation, asymmetric desymmetrization of meso-heterocycles, and asymmetric oxidation of alkyl aryl sulfides. In the asymmetric aziridination of styrene derivatives by using PhI=NTs as a terminal oxidant, high enantioselectivity of up to 94% has been achieved by the further modification of the chiral (salen)manganese(III) complex. The chiral (salen)cobalt(III) complex is a good catalyst for asymmetric cyclopropanation of styrene derivatives and asymmetric S-ylide formation from allyl aryl sulfides, in which the resulting S-ylides undergo [2,3]-Wittig rearrangement in situ to produce chiral 2-(phenylthio)pentanoate derivatives.
Pd L3-Edge XANES Spectra of Supported Pd Particles Induced by the Adsorption and the Absorption of Hydrogen
Authors: Kubota Takeshi , Kitajima Yoshinori , Asakura Kiyotaka , Iwasawa Yasuhiro 
Published: December 2003

Abstract
We measured Pd L3-edge X-ray absorption near-edge structure (XANES) spectra for small Pd particles dispersed on inorganic oxide supports (SiO2 and Al2O3) and the spectra changes induced by the adsorption and the absorption of hydrogen. When the XANES spectra were measured under the atmosphere of H2, a new peak appeared at about 8 eV above the inflection point of the absorption edge. The peak position was invariant but its intensity decreased with the decrease of Pd particle size. This peak is caused by hydrogen absorption in the Pd particles. Hydrogen at the subsurface region little affected the Pd L3-edge XANES spectra. A new peak also appeared for the Pd sample accompanied with hydrogen adsorbed on the surface. The peak energy relative to the edge was independent of the Pd particle size and the peak intensity increased with the amount of adsorbed hydrogen. The XANES spectra can quantify the adsorbed and absorbed hydrogen atoms. We presented a model of Pd particles composed of surface, subsurface and bulk atoms.