bluuebunny/crossref_metadata_2025_split huggingface dataset:
1H and 13C NMR Detection of the Carbocations or Zwitterions from Rhodamine B Base, a Fluoran-Based Black Color Former, Trityl Benzoate, and Methoxy-Substituted Trityl Chlorides in the Presence of Alkali Metal or Alkaline Earth Metal Perchlorates in Acetonitrile Solution
Authors: Hojo Masashi , Ueda Tadaharu , Yamasaki Masanori , Inoue Akihiko , Tokita Sumio , Yanagita Mitsuhiro 
Published: September 2002

Abstract
The cleavage of C–O bonds in two fluoran-based dyes by the addition of alkali metal (M+ = Li+, Na+) and alkaline earth metal (M2+ = Mg2+, Ba2+) perchlorates in acetonitrile solution was examined by means of UV-visible absorption and 1H and 13C NMR spectroscopy at room temperature. Although the 1H NMR signals of the xanthene part of Rhodamine B base (3′,6′-bis(diethylamino)fluoran) were shifted toward lower fields, those of the isobenzofuran (or the benzoate) part were not shifted much upon the addition of M+ and M2+. The appearance of 13C signals at 163.6 and 162.4 ppm (vs TMS) in the presence of Li+ and Ba2+, respectively, confirmed the formation of the zwitterions from Rhodamine B base. The assignments of the 1H and 13C signals were performed by the HMBC method. The colored zwitterion of a practical black color former, 2′-anilino-6′-dibutylamino-3′-methylspiro[3H-isobenzofuran-1, 9′-(9H)xanthene]-3-one, was produced by the addition of M+ and M2+. The 13C NMR signals at 162.2 and 159.8 ppm in the presence of 2.0 mol dm-3 Mg(ClO4)2 and Ba(ClO4)2, respectively, gave conclusive evidence of the formation of the sp2-hybrid carbon center for the black color former. The interaction between the metal ions and the zwitterions from the fluoran-based dyes decreased as Mg2+ &gt; Ba2+ &gt; Li+ &gt; Na+. The 1 : 1 complex formation constants with the metal ions for both dyes were evaluated based on the UV-visible absorption data. The smaller formation constants of the black color former, compared with those of Rhodamine B base, indicate some more difficulty in the cleavage of the γ-lactone ring, which is probably based on the asymmetric structure of the compound, i.e, only a single dibutylamono-group at the 3′- and 6′-positions. The evidence for the formation of both the trityl cation and the benzoate ion was obtained by the 1H NMR signals from trityl benzoate in the presence of Mg(ClO4)2 in CD3CN containing a small amount of CF3SO3D. The C–Cl bond cleavage of 4-methoxy, 4,4′-dimethoxy, and 4,4′,4′′-trimethoxytrityl chlorides, through the chemical interaction between Ba2+ and Cl- in acetonitrile soluition, was justified by our 13C NMR results.
Effects of an Axial Ligand on the Reduction Potential, Proton Dissociation, and Fluorescence Quantum Yield of Hydroxo(porphyrinato)antimony(V) Complexes
Authors: Shiragami Tsutomu , Andou Yoshito , Hamasuna Yuichiro , Yamaguchi Futoshi , Shima Kensuke , Yasuda Masahide 
Published: September 2002

Abstract
The substituent effects on the reduction potentials (E1/2red), the proton dissociation constants of a hydroxo ligand (Ka), and the fluorescence quantum yields (Φ) in aryloxo(hydroxo)tetraarylporphyrinatoantimony(V) complexes were investigated. The E1/2red and Ka values were affected by substituents in the axial aryloxo ligand but, little affected by substituents in the porphyrin ring. Since E1/2red of tetraarylporphyrinatoantimony(V) complexes were higher than those of other metal-porphyrin complexes, it was suggested that the metal orbital greatly contributed to the LUMO level of the complex which can be related to the E1/2red and Ka values. Therefore, the substituent effects of the axial aryloxo ligand on the E1/2red and Ka values were attributed to the electron density of the antimony ion, which affected the LUMO level of the complexes. Moreover, the Φ of the porphyrin moiety depended on both the oxidation potential of the axial aryloxo ligands and the polarity of the solvent used. The fluorescences of the porphyrin moiety were quenched by the axial aryloxo ligands at rate constants of 108 – 1011 s-1.
Novel Synthesis of the Main Central 2,3,6-Trisubstituted Pyridine Skeleton [Fragment A-B-C] of a Macrobicyclic Antibiotic, Cyclothiazomycin
Authors: Shin Chung-gi , Okabe Akihiro , Ito Akinori , Ito Akio , Yonezawa Yasuchika 
Published: September 2002

Abstract
The useful synthesis of the main central 2,3,6-trisubstituted pyridine skeleton [the protected Fragment A-B-C] of a macrobicyclic antibiotic, cyclothiazomycin, was first accomplished. First, the 2-[2-(2-substituted thiazol-4-yl)]-4,5-dihydrothiazole-4-carboxylate [Fragment A derivative], attached to the 6-substituent of the main pyridine skeleton, was synthesized by two consecutive thiazolations of the protected Ser thioamide derivative with 3-bromopyruvate, and then thiazolination of the C-terminal Ser residue of the sequence. Secondly, an efficient synthesis of the central 2-(2-{2-[(1R)-1-aminoethyl]pyridin-6-yl}thiazol-4-yl)-4,5-dihydrothiazole-4-carboxylate [Fragment B derivative] was also achieved by thiazolation of the formyl group of the 2-(1-aminoethyl)-6-formylpyridine derivative, and then thiazolination. Thirdly, a convenient synthesis of the protected dehydrotetrapeptide [Fragment C derivative], which is bound to the 2-substituent of the pyridine skeleton, was attained by the usual stepwise elongation of the appropriate α-amino acids and β-elimination of a Thr residue of the sequence. Finally, the facile fragment condensation of the three Fragments thus obtained gave the protected Fragment A-B-C derivative via Fragment A-B. Furthermore, the configurational structures of the three Fragments (A, B, and C) were also investigated.
Fluorination of Sulfides Using IF5–Et3N–3HF
Authors: Ayuba Shinichi , Yoneda Norihiko , Fukuhara Tsuyoshi , Hara Shoji 
Published: September 2002

Abstract
Mono- and difluorinations of sulfides were achieved using a novel fluorinating reagent, IF5–Et3N–3HF. The reagent is applicable for substrates having various electron-withdrawing groups, such as an ester, amide, ketone, nitrile, sulfone, or trifluoromethyl. Because more than one fluorine atom on IF5 is used, a large excess amount of the reagent is not necessary, even for the difluorination reaction.
The Interaction of DNA and Water-Soluble Polymeric Schiff-Base Nickel Complexes
Authors: Xiao Yao-Nan , Zhang Chun-Xia 
Published: September 2002

Abstract
The modes and activities of the interaction of DNA and water-soluble polymeric Schiff-base nickel complexes, prepared by polymeric analogous reaction, have been discussed according to the absorption spectra, circular dichroism spectra, and fluorescent probe results. The polymeric matrix effect and increasing solubility in water can increase the interaction of these water-soluble polymeric metal complexes with DNA.
Properties of SiO2–MxOy Composites Doped with the Europium(III) Di(1,10-phenanthroline) Complex
Authors: Li Huihui , Ueda Daisuke , Inoue Satoshi , Machida Ken-ichi , Adachi Gin-ya 
Published: September 2002

Abstract
The europium(III) 1,10-phenanthroline complex ([Eu(phen)2]Cl3) was doped into the SiO2–MxOy xerogel matrices derived from tetraethyl orthosilicate (TEOS) and metal alkoxides (M(OR)n, M = Zr, Ta) by the sol-gel method. The resultant composites were characterized by X-ray diffraction, luminescence, UV-visible, and FT-IR spectroscopic measurements. In addition, phonon sideband (PSB) and luminescence quantum efficiency measurements have been conducted on some of the (SiO2–ZrO2) : Eu(phen)23+ composites. The luminescence emission intensity of the (SiO2–MxOy) : Eu(phen)23+ composites was found to be dependent on the matrix composition, i.e. the emission intensity maximized at the matrix composition of Si : M = 9 : 1. This observation was interpreted from various factors, such as the –OH groups in the matrices, the UV-absorbance and coupling with the lattice-vibration of the host matrices, and the non-radiative energy transfer between the neighboring Eu3+ ions, that affect the luminescence intensities of the resultant composites.
Weak Nonbonded S···X (X = O, N, and S) Interactions in Proteins. Statistical and Theoretical Studies.
Authors: Iwaoka Michio , Takemoto Shinya , Okada Mai , Tomoda Shuji 
Published: September 2002

Abstract
Sulfur-containing functional groups of cystine (an SSC group) and methionine (a CSC group) are usually considered as hydrophobic moieties or weak hydrogen-bond acceptors in folded protein structures. However, database analysis as well as theoretical calculations carried out in this study have provided strong evidence for the presence of specific nonbonded interactions between the divalent sulfur atoms (S) and nearby polar non-hydrogen atoms (X). Close S···X (X = O, N, S, C, etc.) atomic contacts were statistically analyzed in 604 high-resolution heterogeneous X-ray structures selected from a protein databank (PDB_SELECT). The S···O interactions found for both SSC and CSC groups showed a specific character as a π(C=O) → σ*(S) orbital interaction based on the directional preferences. The interactions were most frequently observed in α-helices. Ab initio calculations applying the second order Møller–Plesset perturbation theory (MP2) suggested the primary importance of electron correlations. The total stabilization energies were calculated to be ∼3.2 and ∼2.5 kcal/mol for SSC and CSC groups, respectively, including the contribution from a coexisting CH···O hydrogen bond. On the other hand, the S···N interactions observed for a CSC group exhibited structural characters as a π(N) → σ*(S) orbital interaction and an NH···S hydrogen bond, and the S···S interactions for an SSC group showed a structural character as an n(S) → σ*(S) orbital interaction. The S···C(π) interactions should be rather weak and long-range.
UV-Irradiated DNA Matrix Selectively Accumulates Heavy Metal Ions
Authors: Yamada Masanori , Kato Kozue , Nomizu Motoyoshi , Haruki Masahiro , Ohkawa Kousaku , Yamamoto Hiroyuki , Nishi Norio 
Published: September 2002

Abstract
We recently demonstrated the preparation of a water-insoluble DNA matrix by UV irradiation. The UV-irradiated DNA matrix selectively accumulated DNA-intercalating compounds and some endocrine disruptors. We evaluated the accumulation of metal ions in the UV-irradiated DNA matrix using a UV-irradiated DNA-film and DNA-immobilized glass beads. When DNA-immobilized glass beads were incubated with an aqueous solution of Hg2+, Cd2+, Pb2+, Zn2+, Cu2+, or Fe3+, the heavy metal ions were accumulated in the DNA-beads. The maximum amounts of the accumulated Hg2+, Cd2+, and Cu2+ in the DNA-beads were approximately 0.21, 0.13, and 0.22 mmol per gram of immobilized-DNA, respectively. The amounts of the accumulated Pb2+, Zn2+, and Fe3+ were lower than that of Hg2+, Cd2+, and Cu2+. Further, Fourier transform infrared (IR) studies using a UV-irradiated DNA-film with heavy metals suggested that the heavy metal ions interacted with not only the nucleic acid bases but also the phosphate groups. In contrast, the DNA-immobilized glass beads could not accumulate Ca2+ and Mg2+. These results suggested that the UV-irradiated DNA could selectively accumulate metal ions. The UV-irradiated DNA matrix has potential utility as a functional material to remove harmful heavy metal ions from contaminated water.
Electric Field Effects on Photochemical Dynamics in Solid Films
Authors: Ohta Nobuhiro 
Published: September 2002

Abstract
Electric field effects on photochemical dynamics have been examined with particular regard to photoinduced electron transfer (PIET) and excimer formation, based on the measurements of the field effects on emission spectra and emission decays. In various pairs of electron donor and acceptor and in their linked compounds, the following processes are shown to be significantly influenced by an electric field in a polymer film: the initial step of PIET, back-electron transfer which produces an fluorescent state, charge recombination, and dissociation of radical–ion pairs generated by PIET. With an oriented molecular system where vectorial interlayer PIET occurs, PIET is shown to be controlled by an electric field; the rate is depressed or enhanced by an electric field, depending on the field direction relative to the direction of the electron transfer. Electric field effects on excimer formation processes suggest that not only the level shift but also the change in orbital overlap between different chromophores play an significant role in electric field effects on photochemical dynamics.
Inorganic Chemistry Based on Tp Ligands —From Dioxygen Complexes to Organometallic Systems—
Authors: Akita Munetaka , Hikichi Shiro 
Published: September 2002

Abstract
Our recent research on transition metal complexes containing hydrotris(pyrazolyl)borato ligands (TpR), which ranges from bioinorganic chemistry of dioxygen complexes to organometallic systems, is reviewed. The TpR ligand turns out to be versatile in a wide variety of inorganic studies, because the coordination properties (both steric and electronic) can be finely tuned in a systematic manner by choosing appropriate substituents on the pyrazolyl rings to serve the purpose of the study (e.g. stabilization, activation, functionalization). For first row transition metal complexes, TpR serves as a tetrahedral enforcer to form a coordinatively unsaturated tetrahedral species, which is interconverted with five- and six-coordinate structures via coordination/dissociation of donor(s). In addition to the traditional view of TpR as a ligand system isoelectronic with cyclopentadienyls (η5-C5R5), the TpR ligand is now recognized as a unique ancillary ligand suitable for bioinorganic studies, because the tripodal ligand can mimic the coordination environment created by three imidazolyl groups from histidine residues, which is frequently found in the active sites of metalloenzymes. Through extension of the metal in TpRM-O2 adducts to those not related to biological systems we have unveiled the following new aspects of the chemistry of transition metal dioxygen complexes: (1) formation of higher valent bis(μ-oxo) species, TpRM(μ-O)2MTpR (M = Co, Ni), via O–O cleavage of TpRM(μ-η2 : η2-O2)MTpR intermediates and their relevance to the active intermediate of methane monooxygenase, (2) formation and full characterization of a variety of peroxo, hydroperoxo (Pd, Rh) and alkylperoxo species (Mn, Co, Ni, Pd), (3) structural evidence for conversion of molecular oxygen into hydroperoxide via protonation of the η2-peroxo intermediate (Rh), and (4) formation of an active species which undergoes oxidative C–C cleavage reaction (Ru). The property of the TpR ligand as a tetrahedral enforcer is best demonstrated in organometallic systems. The hydrocarbyl complexes, TpRM-R′ (M= Fe, Co), are stable with respect to thermal decomposition processes involving β-hydrogen elimination despite their highly coordinatively unsaturated electronic structure [Fe(14e), Co(15e)], when they are kept under inert atmosphere. The stability has been ascribed to a high spin configuration caused by the tetrahedral geometry. All frontier orbitals are occupied by unpaired electrons or electron pairs and no vacant frontier orbital is left for interaction with the electron pairs of a donor. Dinuclear xenophilic complexes, TpRM–M′Ln, with a polar metal–metal bond which bridges a Werner complex type hard open-shell metal center and a coordinatively saturated metal carbonyl fragment are also synthesized and fully characterized.
Single-Crystalline Photochromism of Diarylethene Mixtures
Authors: Yamada Taro , Kobatake Seiya , Irie Masahiro 
Published: September 2002

Abstract
Crystal structures of 1,2-bis(2,4-dimethyl-3-thienyl)perfluorocyclopentene 1a, 1,2-bis(2,4,5-trimethyl-3-thieny)per-fluorocyclopentene 2a and their mixture were determined by X-ray crystal structure analysis and their photochromic reactivities were compared. In the crystal of 1a, 17 mol% of molecules adopted a photoactive anti-parallel conformation and underwent photochromism. The crystal of 2a was not photochromic, because the dithienylethenes are packed in a photochemically inactive anti-parallel conformation. In the co-crystal of 1a and 2a, 2a adopted a photoactive anti-parallel conformation and the ratio of molecules in a photoactive conformation increased to 27 mol%. In the co-crystal, the spectrum of the closed-ring form isomers, 1b and 2b, generated by UV irradiation was broader and blue-shifted by ca. 10 nm in comparison with that of the 1a homocrystal.
Strategies and Development of Molecular Probes for Nitrogen Monoxide Monitoring
Authors: Katayama Yoshiki , Soh Nobuaki , Maeda Mizuo 
Published: September 2002

Abstract
Current methods for monitoring nitrogen monoxide (NO) and new strategies for designing NO probes are reviewed. The production of endogenous NO must be monitored if we are to understand the physiological and pathological roles of NO. Many methods have been reported for this purpose, including colorimetry, fluorometry, electrochemical methods, and electron paramagnetic resonance (EPR). Among these methods, one of the most promising for practical use is EPR using (dithiocarbamato)iron(II) complex as a spin trap. In the structure–sensitivity relationship, it was found that an electron-donating group on the dithiocarbamato ligand is favorable for enhancing the sensitivity of NO detection due to the stabilization of the Fe(II) complex form. A new concept, “radical-exchange”, is also introduced to solve the issue of low sensitivity in EPR methods. This concept has been used to develop two types of NO probe: spin trap and fluorescent probes. These reagents detect NO to a detection limit of 10 nM–sub-µM. This strategy, using radical exchange in conjunction with EPR, is potentially useful for the design of sensitive probes that can detect NO directly.
A Bimetallic Magnetic System Exhibiting Reversible Ferromagnetism/Metamagnetism Modulation
Authors: Usuki Naoki , Ohba Masaaki , Okawa Hisashi 
Published: September 2002

Abstract
A cyanide-bridged bimetallic compound, [Ni(1,1-dmen)2]2[Fe(CN)6](BPDS)0.5·4H2O (1) (1,1-dmen = 1,1-dimethylethylenediamine, BPDS2− = biphenyl-4,4′-disulfonate), has been prepared. It has a pseudo 2-D network structure based on a Fe4Ni4 square unit with two Fe–CN–Ni–NC–Fe and two Fe–CN···H2O–Ni–NC–Fe linkages and shows a metamagnetic ordering with TC = 3.3 K. The dehydration of 1 at 150 °C has afforded [Ni(1,1-dmen)2]2[Fe(CN)6](BPDS)0.5 (1a). It has a definite 2-D network structure based on a Fe4Ni4 square unit with four Fe–CN–Ni–NC–Fe linkages and shows essentially a ferromagnetic ordering with TC = 10.7 K under weak applied field (&gt; 250 G). 1a is hygroscopic and adsorbed atmospheric moisture to afford [Ni(1,1-dmen)2]2[Fe(CN)6](BPDS)0.5·2H2O (1b), which has a pseudo 2-D network structure similar to that of 1 and shows a metamagnetic ordering with TC = 4.0 K. 1a and 1b can be interconverted by dehydration at 150 °C and hydration in open air at room temperature, producing a unique molecular magnetic system exhibiting a reversible ferromagnetism/metamagnetism modulation.
Laser (248 nm) Flash Photolysis and Pulse Radiolysis of CF2Br2 in Aqueous Solution: Atmospheric Implications
Authors: Saini Rameshwar D , Dhanya Suresh , Das Tomi Nath 
Published: September 2002

Abstract
Henry’s law constant (Kh) of CF2Br2 was measured to be 0.058 M atm−1 at room temperature. The steady state as well as laser (248 nm) flash photolysis of CF2Br2 was carried out in aqueous solution. The formation of Br2•− radicals involving two primary photodissociation channels was observed in the flash photolysis. One channel produced CF2Br• and Br• radicals, and the other led to the formation of Br− and H+. The spectrum and reactions of CF2Br• were studied in aqueous solution by pulse radiolysis. The CF2Br• radical was found to absorb in the 230–270 nm region with a molar absorbance (ε) of 710 M−1 cm−1 at λmax = 245 nm. The rate constants of some of the reactions were measured at 299 K as follows: k (eaq− + CF2Br2) = 1.20 ± 0.13 × 1010, 2k (CF2Br• + CF2Br•) = 1.4 ± 0.4 × 109, k(CF2Br• + O2) = 1.9 ± 0.5 × 109 M−1 s−1. The CF2BrO2• radical absorbed in the 245–360 nm region with ε = 593 M−1 cm−1 at λmax = 265 nm. An apparatus used to measure Kh, and a closed-loop flow system used to carry out the flash photolysis/pulse radiolysis of sparingly soluble gases, like CF2Br2, are reported.
Monolayer Formation of Cytochrome b562 on Gold Surfaces and Its Reconstitution Reaction, Studied by Surface Plasmon Resonance Spectroscopy
Authors: Kobayashi Kazutoshi , Shimizu Masafumi , Nagamune Teruyuki , Sasabe Hiroyuki , Fang Yu , Knoll Wolfgang 
Published: September 2002

Abstract
Association and dissociation reactions of cytochrome b562 on solid surfaces were investigated by means of surface plasmon resonance spectroscopy. Propionates of side chains in the heme molecule were modified with sulfur moiety as an anchor part to be adsorbed on the gold substrate. This modified heme was firstly reconstituted with apo-protein in solution. This reconstituted holo-protein was then adsorbed on either bare gold substrate or pre-modified gold substrate. Native cytochrome b562 was also adsorbed to the same substrates for the control experiment. The reconstituted cytochrome b562 was successfully adsorbed on the pre-treated gold substrate without denaturation in structure, probably with homogeneous anisotropic orientation. Guanidine hydrochloride in the buffer of pH 5.0 was applied to remove the apo-protein from the surface, with the thiolated heme derivative remaining on the surfaces. Apo-protein was again introduced to the same surface for the reconstitution of holo-cyt.b562. The success of the association and dissociation reactions between apo-protein and tethered heme molecules on the surfaces was confirmed by the optical thickness changes.
A Theoretical Study of the Substituent Effects on the P–X (X = H, F, Cl) Bond Dissociation Energies in para- and meta-Substituted Aromatic Phosphines
Authors: Cheng Yu-Hui , Fang Ying , Zhao Xin , Liu Lei , Guo Qing-Xiang 
Published: September 2002

Abstract
The P–X (X = H, F, and Cl) bond dissociation energies (BDEs) for a number of para- and meta-substituted aromatic phosphines were calculated using R(O)MP2/6-311++g(d, 2p)//(U)B3LYP/6-31g(d) method. The results showed the importance of the radical effect as well as the ground effect on the BDEs. For X = H case, because the substituent affected the neutral phosphine to the same extent as it affected the radical, substituent effects on the P–H BDE were small (ρ+ = 0.28 kJ/mol). In comparison, for X = F or Cl case, because the substituent affected the neutral phosphine much more strongly than it affected the radical, substituent effects on the P–F (ρ+ = −3.25 kJ/mol) or P–Cl (ρ+ = −1.31 kJ/mol) BDEs were significant. Therefore, the substituent effects on BDEs of the Z–X bonds in compounds of the general formula 4-YC6H4Z–X varied when X changed, which meant that a recent proposal (J. Am. Chem. Soc., 123, 5518 (2001)) was unfortunately not supported.
The Relation between the Eigenvalue Sum and the Topological Index Z Revisited
Authors: Gutman Ivan , Vidovic Dusica , Hosoya Haruo 
Published: September 2002

Abstract
The topological index Z (put forward by one of the present authors, Bull. Chem. Soc. Jpn., 44, 2332 (1971)) has proved to be a structure-descriptor suitable for modeling physico-chemical properties of both saturated and conjugated unsaturated organic compounds. A linear relation between log Z and the Hückel molecular orbital total π-electron energy Eπ was established a long time ago (Theor. Chim. Acta 38, 37 (1975)), but was restricted to π-electron species without non-bonding molecular orbitals (n0 = 0, where n0 is the number of zero eigenvalues of the molecular graph). Recently a novel structure-descriptor ES was put forward, the “eigenvalue sum” equal to Eπ/2, but applicable to saturated hydrocarbons. In this case n0 need not be zero. We demonstrate that, for each group of alkane isomers with a fixed value of n0, there is a linear relation between ES and log Z.