bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparative Ab initio and Hybrid DFT Studies Relevant to an Experimental Investigation of Neutral and Cationic [Si, P, H2] Isomers
Authors: Hrušák Jan , Schröder Detlef , Schwarz Helmut , Iwata Suehiro 
Published: June 2006

Abstract
The neutral and the lowest cationic (singlet and triplet) potential-energy surfaces of [Si, P, H2] have been explored by means of ab initio MO calculations at the G2 level of theory as well as the hybrid DFT (B3LYP/6-311G**) method. Contrary to the neutral and triplet surfaces, where the H2SiP+/0 isomers represent the global minima, for the singlet cation a doubly bridged P(H)2Si+ structure has been identified as the most stable isomer, with the non-bridged H2SiP+ species being significantly less stable (ΔE = 31.7 kcal mol−1 at G2). As far as the comparison of the two quantum-chemical methods (i.e. G2 and B3LYP) is concerned, the calculated relative energies ΔE are quite close to each other, with deviations smaller than 4 kcal mol−1. However, while the non-bridged SiPH2+ (1A′) represents a minimum at the G2 level, it could not be located using the hybrid DFT method. The computationally predicted singlet and triplet [Si, P, H2]+ potential-energy surfaces provide insight into the course of the ion/molecule reactions of Si+• with phosphine and P+ with silane, respectively, which were examined experimentally. Thus, the reaction of the doublet species Si+• with phosphine allows access to the non-classical, bridged P(H)2Si+ structure, while in the reaction of the P+ triplet cation with silane, no evidence for Si–P bond formation is obtained.
Preparation, Characterization, and Solid State Thermal Studies of Nickel(II) Squarate Complexes of 1,2-Ethanediamine and Its Derivatives
Authors: Das Debasis , Ghosh Ashutosh , Ray Chaudhuri Nirmalendu 
Published: June 2006

Abstract
[NiL3]C4O4 [L = 1,2-ethanediamine (en) and 1,2-N,N′-dimethylethanediamine (N,N′-dmen)], [NiL3]C4O4·nH2O [for L = 1,2-N-methylethanediamine (meen) and 2-methyl-1,2-propanediamine (ibn); n = 1, and for L = 1,2-propanediamine (pn); n = 2], and [NiL2C4O4]·2H2O [L = 1,2-N-ethylethanediamine (eten), 1,2-N-propylethanediamine (pren), 1,2-N,N-dimethylethanediamine (N,N-dmen) and 1,2-N,N′-diethylethanediamine (N,N′-deten)] have been synthesized by the addition of the respective diamines to finely powdered nickel(II)squarate dihydrate, NiC4O4·2H2O. All of the tris-species, except for [Ni(N,N′-dmen)3]C4O4 were also prepared by adding diamines to NiC4O4·2H2O dissolved in aqueous ammonia (25%). When the latter method was followed, the bis-species [NiL2C4O4] [L = eten, pren, 1,2-N-isopropylethanediamine (ipren), N,N-dmen, N,N′-dmen, and N,N′-deten] were also obtained. [NiL2C4O4] (L = en, meen, N,N′-dmen, pn, and ibn) were also prepared from their corresponding tris(diamine) species upon heating in the solid state. [Ni(ibn)3]C4O4·nH2O after dehydration underwent an irreversible endothermic (145—160 °C; ΔH = 6.5 kJ mol−1) phase transition without showing any visual color change. [Ni(ipren)2C4O4] exhibited a reversible phase transition (78—107 °C; ΔH = 1.4 kJ mol−1 for heating and 105—72°C; ΔH = −1.3 kJ mol−1 for cooling). The phase transitions are considered to have been due to conformational changes of the diamine chelate rings. All of the tris as well as bis(diamine) complexes possess an octahedral geometry, except for [Ni(ibn)2]C4O4, which is square-planar. The bis-species [NiL2C4O4] (L = eten, pren, N,N-dmen, and N,N′-deten) exists in two isomeric forms.
Sensing of Poly(styrenesulfonate)s by Polymeric Membrane Electrodes Based on Liquid Anion-Exchangers
Authors: Ohki Akira , Tsurugasaki Masato , Kondo Yasunori , Naka Kensuke , Maeda Shigeru 
Published: June 2006

Abstract
The potentiometric responses of ion-selective electrodes (ISEs) based on various liquid anion-exchangers for poly(styrenesulfonate)s (PSSs) were examined. The liquid anion-exchangers included lipophilic monoammonium, monophosphonium, diphosphonium, and triphosphonium salts. The molecular weights of PSSs, which had narrow molecular-weight distributions (Mw/Mn &lt; 1.2), were varied from 1.8 × 103 (PSS-1.8K) to 3.5 × 104 (PSS-35K). For PSS-1.8K, ISEs based on diphosphonium salts, polymethylenebis(trioctylphosphonium) dibromides 1—3, exhibited good responses, the response slope and linear response range being −20 to −21 mV/decade and 5.0 × 10−5—5.0 × 10−3equiv dm−3, respectively. As the molecular weight of PSS was increased, the linear response range became smaller, while the response slope was almost constant. Finally, PSS-35K gave almost no response. On the other hand, a wide molecular-weight distribution PSS (Mw/Mn = 3.6) provided a good response, although it had a high average molecular weight (Mw = 1.6 × 104). The selectivity coefficients for PSS over various anions of ISEs, based on diphosphonium and monophosphonium salts, were assessed.
Complex Formation between Tributyl Phosphate and Nitric Acid and the Hydration of the Complexes in Dodecane
Authors: Naganawa Hirochika , Tachimori Shoichi 
Published: June 2006

Abstract
Complex-formation of nitric acid with tributyl phosphate (TBP) and the hydration of the complexes in dodecane were examined from the acid and water distribution data between the aqueous and organic phases at 298 K. The equilibrium constants were determined by analyzing the acid and water distribution data as functions of the TBP concentration in the organic phase, the aqueous acid activity, and the water activity. Three complexes (TBP·HNO3, (TBP)2·HNO3, and (TBP)3·HNO3) were found in the organic phase when the aqueous nitric acid concentration was not higher than 3 mol dm−3. The hydration numbers for these complexes were also obtained. The TBP·HNO3 was chiefly anhydrous, but partially a monohydrate. In contrast, the (TBP)2·HNO3 was only a monohydrate and (TBP)3·HNO3 was only a tetrahydrate. The TBP–HNO3–H2O stoichiometry, by taking account of these complexes in addition to the TBP hydrates and free nitric acid in the organic phase, applied very well, up to 2 mol dm−3 (54.6 vol%) TBP in dodecane without any activity correction.
Structures of Bis(5,5-diphenylhydantoinato)copper(II) Complexes with Primary Amines Involving Square Pyramidal CuN4O Chromophores
Authors: Akitsu Takashiro , Komorita Seiko , Kushi Yoshihiko , Li Chunmin , Kanehisa Nobuko , Kai Yasushi 
Published: June 2006

Abstract
Copper(II) complexes [CuL2(i-PrNH2)2·H2O] (1a), [CuL2(i-PrNH2)2] (1b), [CuL2(EtNH2)2·H2O] (2a), [CuL2(EtNH2)2]·CHCl3 (2b), [CuL2(EtNH2)2·H2O]·2CHCl3 (2c), and [CuL2(EtNH2)2·MeOH] (2d) (L = 5,5-diphenylhydantoinate) have been prepared. The crystal structures of 1a, 2c, and 2d were determined by X-ray analysis. Each CuN4O chromophore is a five-coordinated square-based pyramidal geometry. The axial Cu–O distances are Cu(1)–O(1)(water) = 2.362(10) Å, Cu(1)–O(1)(water) = 2.436(9) Å and Cu(1)–O(1)(MeOH) = 2.33(1) Å, for complexes 1a, 2c, and 2d, respectively. Intramolecular hydrogen bonds are formed between the carbonyl oxygens and amino hydrogens (C=O···H–N) as well as the axial ligand (C=O···H–O). The latter hydrogen bonds stabilize the axial ligand for coordination. Moreover, double intermolecular hydrogen bonds link the 5,5-diphenylhydantoinate ligands (C=O···H–N) belonging to be adjacent complex molecules in all three complexes. The electronic spectra of the complexes in the solid state and in chloroform solutions were determined at room temperature, and a considerable change in ligand field bands was observed. The five-coordinated complexes in the chloroform solutions release their axial water ligand and the CuN4O chromophore converts into a distorted tetrahedral CuN4 chromophore.
Electrocatalytic Hydrogenation of Organic Compounds on a Poly[N-(5-hydroxypentyl)pyrrole] Film-Coated Electrode Incorporating Palladium Microparticles
Authors: Takano Nobuhiro , Nakade Akihito , Takeno Noboru 
Published: June 2006

Abstract
A poly[N-(5-hydroxypentyl)pyrrole] film-coated carbon-fiber electrode incorporating palladium metal microparticles was prepared and the catalytic ability in the electrochemical hydrogenation of organic compounds was investigated. This electrode exhibited a high catalytic ability and a strong physical stability with respect to hydrogen evolution. By using this electrode, the electrocatalytic hydrogenation for organic compounds in an organic solvent–buffer solution led to an efficient formation of hydrogenated products, such as saturated compounds, amino compounds, and hydroxy compounds, in high yields and current efficiencies. Furthermore, a catalytic polymer film electrode was successfully applied to the hydrogenative deprotection of a benzyl group and the dehalogenation of bromobenzene in electroreduction media.
Conformation of Gramicidin in Monolayers, Organic Solvents and Phospholipid Bilayers
Authors: Ogoshi Satori , Mita Tomoyoshi 
Published: June 2006

Abstract
The properties of gramicidin and its action on membranes were investigated by the use of monolayers, organic solvents and phospholipid vesicles in relation to cation-binding. The behavior of a gramicidin monolayer was strongly dependent on the organic solvent in which it was dissolved, showing the dependence of the solvent history. A gramicidin monolayer prepared from an ethanol solution caused a large conformational change upon the binding of K+, whereas that prepared from a 2,2,2-trifluoroethanol (TFE) solution showed no conformational change upon the binding of K+. In two organic solvents, gramicidin showed a different calorimetric behavior, due to a difference in conformation. Gramicidin in ethanol markedly decreased the phase-transition temperature and transition enthalpy (ΔH) upon the binding of K+, whereas gramicidin in TFE did not change in calorimetric behavior upon the binding of K+. Incorporating gramicidin into lipid bilayers led to a broadening of the transition and a decrease in the ΔH of the lipid, showing that about 20 lipid molecules per gramicidin molecule were immobilized. By binding K+ to the gramicidin channel, the perturbing effect of gramicidin for the lipid bilayers was depressed, implying aggregation among the peptide channels.
A Novel Method for Constructing β-d-Mannosidic, 2-Acetamido-2-deoxy-β-d-mannosidic, and 2-Deoxy-d-arabino-hexopyranosidic Units from the Bis(triflate) Derivative of β-d-Galactoside
Authors: Sato Ken-ichi , Yoshitomo Akira , Takai Yoshimitsu 
Published: June 2006

Abstract
An efficient construction of the β-d-mannosidic, 2-Acetamido-2-deoxy-β-d-mannosidic, 2-deoxy-2-fluoro-β-d-mannosidic, and 2-deoxy-β-d-arabino-hexopyranosidic units from the same intermediate, 2-4-bis(O-trifluoromethylsulfonyl) derivative of β-d-galactoside, was achieved in good yields in a stepwise inversion at C-4 and C-2 by using cesium acetate, n-Bu4NN3, n-Bu4NF, and n-Bu4NBH4. A convenient and practical protection of β-d-mannoside to the straightforward synthesis of antennary oligosaccharides was also achieved by using cesium trifluoroacetate.
Practical Synthesis of Optically Pure Bifunctionalized Heterohelicenes
Authors: Osuga Hideji , Suzuki Hitomi , Tanaka Kazuhiko 
Published: June 2006

Abstract
Optically active 2-(hydroxymethyl)- and 2-(ethylthiocarbonyl)[1]benzothieno[5′,4′ : 2,3][1]benzothieno [4′,5 : 4,5]thieno[3,2-f]quinolines containing π-excessive thiophene and π-deficient pyridine units were prepared by the use of exo-3-amino-2-hydroxybornane as a chiral auxiliary. This procedure consists of separation of the helical diastereomers prepared by photocyclization of 1,2-diarylethylenes and removal of the chiral auxiliary by a thiolate ion. Large scale preparation of the helicenes can be accomplished by a modified procedure of the photocyclization reaction. Optical purities of both enantiomers of 2-(hydroxymethyl)- and 2-(ethylthiocarbonyl)[1]benzothieno[5′,4′ : 2,3][1]benzothieno[4′,5′ : 4,5]thieno[3,2-f]quinolines were &gt;99.5%. Their absolute configurations were determined by comparison of CD spectra.
Comparison of the Reactivities of Neutral and Cationic Organopalladium Complexes toward CO, Isocyanides, and Olefins
Authors: Kayaki Yoshihito , Shimizu Isao , Yamamoto Akio 
Published: June 2006

Abstract
Cationic solvent-coordinated organopalladium complexes [PdR(solvent)(L)2]+A− 2 (R = organic group, L = tertiary phosphine, A = counter anion such as BF4, PF6, and triflate) have been prepared by removal of the halide ligand X in neutral complexes, [PdR(X)(L)2] 1 with an equimolar amount of silver salt. The cationic complexes 2 show much greater rates of CO insertion than the parent neutral complexes 1. Comparison of the reactivities of 2 and of the other cationic complexes [PdMe(Y)(L)2]+ (Y = strongly coordinating ligand such as tertiary phosphine, pyridine, and isocyanide) toward CO insertion indicates that availability of the site for incoming CO is a dominant factor in determining their reactivities. In contrast, insertion of isocyanides into Pd–C bond is not hindered by occupation of the vacant site in the organopalladium complexes. Successive hetero-insertions of isocyanide and CO into Me–Pd bond, i.e., CO insertion into the 1-iminoalkyl–Pd bond and isocyanide insertion into the acetyl–Pd, were realized. Olefins were found not to undergo the insertion into Pd–Me bond in phosphine-coordinated complexes, whereas insertion of methyl acrylate into the Me–Pd bond in a cationic complex having bipyridine ligand was observed.
Electron-Transfer Reactions in Organic Chemistry
Authors: Formosinho Sebastião J , Arnaut Luís G 
Published: June 2006

Abstract
The Intersecting-State Model (ISM) is used to calculated the absolute rate constants of self-exchange electron-transfer reactions (ET) of organic species. The systems studied include aromatic hydrocarbons, quinones, nitrobenzene, aromatic nitriles, tetracyanoethylene, aromatic amines, and alkylhydrazines. All of the calculated rates are within one order of magnitude of the experimental ones, and the correlation coefficient between the two sets is 0.96. An electron-tunneling model has been developed to calculate distance-dependent nonadiabatic factors of intramolecular ET. This model can be used with ISM to calculate intramolecular ET rates. The system biphenylyl-spacer-naphthyl in tetrahydrofuran, whose distance-dependent intramolecular rates were measured by Closs and Miller, was used to test our calculations, because its ET rates can be calculated without adjustable parameters. Our absolute rate calculations are in an order-of-magnitude agreement with the experimental ones.
Density and Volumetric Behavior of 1,2-Dimethoxyethane + Water Binary Mixtures from −10 to 80 °C
Authors: Marchetti Andrea , Tassi Lorenzo , Ulrici Alessandro 
Published: June 2006

Abstract
The densities (ρ) and excess molar volumes (VE) for 1,2-dimethoxyethane + water binary mixtures were determined, when possible, at 19 different temperatures ranging from −10 up to +80 °C. The experimental measurements were used to test some empirical relations giving the dependence of the density on the temperature and binary composition: ρ = ρ(t), ρ = ρ(X1), and ρ = ρ(t,X1). Furthermore, the results of VE calculations are discussed in terms of the influence of interactions between the components, of the order and degree of packing in the mixtures, and of the free-volume differences.
Synthesis and Catalytic Properties of Vanadium Nitrides
Authors: Choi Jeong-Gil , Jung Moon-Ki , Choi Saemin , Park Tae-Keun , Kuk Il Hiun , Yoo Jae Hyung , Park Hyun Soo , Lee Han-Soo , Ahn Do-Hee , Chung Hongsuk 
Published: June 2006

Abstract
Vanadium nitride catalysts were synthesized by the temperature-programmed reduction of vanadium oxide (V2O5) with pure NH3. The resulting materials contained VN or VN with a negligible amount of vanadium sesquioxide (V2O3) in the bulk after the nitrization of V oxides, indicating that the structural properties of these materials were strong functions of the heating rate and space velocity employed. The V nitrides proved to be active NH3 decomposition catalysts. Since the activity varied with changes in the surface area and particle size, ammonia decomposition over the V nitrides appeared to be structure-sensitive. While detailed relationships between the catalytic activity and surface composition could not be ascertained, there was a direct correlation between the activity, and the surface area and grain-boundary length. The most active catalyst, VN-c, which contained the δ-phase, had the greatest grain-boundary length. The catalytic properties of V nitrides were comparable or superior to those of a Ni/SiO2·Al2O3 catalyst. These results suggested that the characteristics of the active sites in the vanadium nitrides were similar to those in the Group 8—10 metal-based catalysts.
Ordering the Isomeric Molecules through the Graph Spectrum: Generation of Two Topological Indices Depicting the Branch and Linear Characters (A Computational Method)
Authors: Patra Swarna M , Mishra Rama K 
Published: June 2006

Abstract
Octane isomeric molecules have been ordered by using the graph spectrum of the vertex adjacency matrix and a Fortran-77 program. The program not only orders the isomeric molecules into various subgroups, but also generates topological descriptors, which primarily depict the branching and linear characters of the molecule. These descriptors are correlated with different physical properties, like standard entropy (), standard entropy of formation (), heat of vaporization (Hv), octane number (MON), and A coefficient of Antoine equation. Good correlations of the descriptors with the above properties have been obtained.
Boyfriends, Girlfriends and Teenagers' Risk of Sexual Involvement
Authors: Marín Barbara VanOss , Kirby Douglas B. , Hudes Esther S. , Coyle Karin K. , Gómez Cynthia A. 
Published: June 2006

CONTEXT: Having a boyfriend or girlfriend, especially an older one, is associated with increased sexual risk in early adolescence. The mechanisms underlying this association are unclear.METHODS: Middle school students in Northern California were surveyed annually from 1997 to 2000. For a sample of 1,214 males and 1,308 females who were sexually inexperienced in seventh grade, logistic and linear regression were used to explore associations between relationship status in seventh grade and sexual activity in ninth grade, controlling for sixth‐grade and eighth‐grade characteristics.RESULTS: Males who had had a girlfriend their age by seventh grade were more likely than those who had had no relationship to report sexual activity in ninth grade (odds ratio, 2.1). Similarly, for females, the odds of being sexually active in ninth grade were elevated among those who had had a boyfriend their age (2.9); however, they also were higher among those who had had an older boyfriend than among those who had had one their age (2.1). With sixth‐grade risk factors controlled, relationship status in seventh grade remained significant only for females; the association was explained by early menarche and by participation in situations that could lead to sex and riskier peer norms in eighth grade. For males, eighth‐grade situations that could lead to sex, Hispanic ethnicity and sixth‐grade peer norms explained ninth‐grade sexual behavior.CONCLUSIONS: To reduce the risk of adolescent sexual activity, parents and communities should encourage youth in middle school, especially females who experience early menarche, to delay serious romantic relationships.
Greater Expectations: Adolescents' Positive Motivations for Sex
Authors: Ott Mary A. , Millstein Susan G. , Ofner Susan , Halpern‐Felsher Bonnie L. 
Published: June 2006

CONTEXT: Effective STD and pregnancy prevention efforts should benefit from knowledge of what motivates adolescents to have sex. Positive motivations, and how they differ by gender and sexual experience, are poorly understood.METHODS: A sample of 637 ninth graders were asked about their relationship goals, expectations of the degree to which sex would satisfy these goals and sexual experience. Three scales measured adolescents' goals for intimacy, sexual pleasure and social status within a romantic relationship. Another three scales measured expectations that sex would lead to these goals. Data were examined in analyses of variance and mixed models.RESULTS: Participants valued intimacy the most, then social status and, finally, sexual pleasure. These relationship goals differed significantly by gender and sexual experience. Females valued intimacy significantly more and sexual pleasure less than males. Sexually experienced adolescents valued both intimacy and pleasure more than sexually inexperienced adolescents. Among females, but not males, sexually experienced adolescents valued the goal of social status less than those with no sexual experience did. Adolescents expected that sex would most likely lead to sexual pleasure, then intimacy and, finally, social status. Females and sexually inexperienced adolescents reported lower expectations that sex would meet goals than did males and sexually experienced participants.CONCLUSIONS: Adolescents view intimacy, sexual pleasure and social status as important goals in a relationship. Many have strong positive expectations that sex would satisfy these goals. Prevention programs and providers should address the risks of sex in the context of expected benefits.
Early Adolescents' Cognitive Susceptibility To Initiating Sexual Intercourse
Authors: L'Engle Kelly Ladin , Jackson Christine , Brown Jane D. 
Published: June 2006

CONTEXT: Better methods for investigating sexual risk before the initiation of sexual intercourse are needed to support programming for younger adolescents, especially for abstinent adolescents who are susceptible to initiating intercourse.METHODS: A sample of 854 adolescents in seventh or eighth grade who had never had sexual intercourse completed sexuality surveys in 2002 and 2004. A five‐item index that assessed beliefs and expectations about the onset of intercourse was created to indicate adolescents' cognitive susceptibility to initiating intercourse. Logistic regression analysis was used to assess associations between levels of susceptibility and initiation of intercourse by follow‐up. The construct and predictive validity of the index were examined using a variety of tests.RESULTS: Thirty‐eight percent of respondents were classified as being nonsusceptible to initiating intercourse, 34% as having low susceptibility and 28% as being highly susceptible. Adolescents who were susceptible were more physically mature, had greater sexual feelings and competency, perceived that more peers were sexually active and had fewer positive connections with parents, school and religion than nonsusceptible respondents. Males, blacks and older adolescents were more susceptible than females, whites and younger adolescents, respectively. Compared with nonsusceptible respondents, those with low and high susceptibility had higher odds of initiating intercourse two years later (odds ratios, 2.5 and 8.1, respectively).CONCLUSIONS: The cognitive susceptibility index provides a valid method for assessing sexual risk before the onset of intercourse. Assessing susceptibility among early adolescents could support efforts to delay the onset of intercourse through targeted research and health programming.