bluuebunny/crossref_metadata_2025_split huggingface dataset:
Formation of Bridging Nitride Versus Terminal Oxovanadium Promoted by a Vanadium(II) Macrocyclic Complex
Authors: Jubb Jayne , Scoles Ludmila , Jenkins Hilary , Gambarotta Sandro 
Published: September 2007

AbstractThe reaction of [VCl2(tmeda)2] with the tetralithium salt of octaethylporphyrinogen (oepg)[Li(thf)]4 initially yielded a monomeric VII complex [(oepg)‐VLi4Cl2(thf)4] (1). Treatment of this species with tetramethylethylenediamine afforded a mixture from which [(oepg)‐V(thf)2][Li(tmeda)2].0.5 toluene (2 a) (or 2 b when ethyl is replaced by nPr) and the unprecedented nitrido‐bridged dimeric species [{oepg)V}2(μ‐N)(μ‐Li) 4]‐[Li(tmeda)2] (3) were isolated and characterized. The bridging nitrogen atom probably originated from the cleavage of dinitrogen, since the same reaction carried out under exclusion of N2 gave [(oepg)VO]‐[Li(tmeda)]2 (4), where the oxo atom probably originated from deoxygenation of THF. The connectivity of 1, 2 b, 3, and 4 was demonstrated by X‐ray analysis.
Structure and Conductivity of an Electrocrystallized Ruthenium [1,8]Binaphthyridine Complex
Authors: Pérez‐Cordero Eduardo , Brady Nancy , Echegoyen Luis , Thummel Randolph , Hung Chi‐Ying , Bott Simon G. 
Published: September 2007

AbstractFor the first time, the crystal structure of a RuII binaphthyridine complex and that of its corresponding oneelectron reduced product are reported. Reductive electrocrystallization of [Ru‐(binap‐2)3](PF6)2 (1, where binap‐2 = 3,3′‐dimethylene ‐2,2′ ‐ bi [1, 8] naphthyridine) from an acetonitrile solution resulted in the formation of dark blue crystals of the one‐electron reduction product, [Ru‐(binap‐2)3](PF6) (2) having one fewer PF−6 per formula unit. X‐ray analysis reveals that the reduced complex retains the three‐ligand d6 coordination around the central RuII. Based on electrostatic considerations and the positions of the PF−6 anions in the lattice, the added electron appears to be delocalized over two nearly equivalent binap‐2 ligands in 2, in marked contrast to monoreduced and electrocrystallized [Na ⊂ (trisbipyridyl cryptand)]0, in which the electron is localized on only one of the bipyridyl subunits. However, based on the available data, alternative interpretations are possible. The crystal packing diagram of 2 shows several intermolecular π–π interactions, with 12 of these being shorter than 3.5 Å. In contrast, there are no intermolecular distances shorter than 3.5 Å in the crystals of 1. Two‐probe electrical conductivity measurements under anaerobic conditions indicate that the crystals of 2 behave as semiconductors with a band gap of 0.53 eV, while those of the unreduced compound are insulating. This represents the first molecular semiconducting material with the potential for bidimensional behavior of its kind.
Enantioselective Synthesis of Highly Functionalized 4‐Piperidones by the Asymmetric Imino‐Diels–Alder Reaction of Chiral 2‐Amino‐1,3‐Butadienes
Authors: Barluenga José , Aznar Fernando , Ribas Cristina , Valdés Carlos , Fernández Monica , Cabal María‐Paz , Trujillo Jesús 
Published: September 2007

AbstractChiral 2‐amino‐1,3‐butadienes 1 derived from commercially available (S)‐2‐methoxymethylpyrrolidine react with aromatic N‐trimethylsilylaldimines and N‐phenylaldimines in the presence of ZnCl2 to give, after the reaction workup, 4‐piperidones 4 and 6, respectively, with moderate to very high enantiomeric excesses. In addition, the absolute configurations of derivatives of 4 a and 4 g were determined by circular dichroism and NMR spectroscopy on the Mosher ester, respectively.
Total Synthesis of Swinholide A, Preswinholide A, and Hemiswinholide A
Authors: Nicolaou K. C. , Patron A. P. , Ajito K. , Richter P. K. , Khatuya H. , Bertinato P. , Miller R. A. , Tomaszewski M. J. 
Published: September 2007

AbstractThe total synthesis of synthesis of swinholide A (1) has been accomplished via key intermediate aldehyde 12 (Fig. 3), whose construction started from L‐rhamnose (18), epoxide 21, and phenylsulfone orthoester 22, and proceeded through an Enders asymmetric alkylation (16 + 17 → 15), a Ghosez cyclization (21 + 22 → 20), and a Corey‐Sharpless coupling reaction (13 + 14 → 12). Elaboration of compound 12 along slightly different pathways culminated in the synthesis of carboxylic acid 10 and hydroxy compound 11, whose union by an esterification reaction, followed by ring closure of the subsequently derived hydroxy acid under Yamaguchi conditions, led to swinholide A (1) upon deprotection. The chemistry developed also allowed the total synthesis of preswinholide A methyl ester (7), preswinholide A (8), and hemiswinholide A (78).
Oxypyriporphyrin, the First Fully Aromatic Porphyrinoid Macrocycle with a Pyridine Subunit
Authors: Lash Timothy D. , Chaney Sun T. 
Published: September 2007

AbstractThe synthesis of the first example of an aromatic pyridine‐containing porphyrinoid 10 has been accomplished in excellent yields by the acid‐catalyzed “3 + 1” condensation of 3‐hydroxy‐pyridinedicarboxaldehyde (8) with tri‐pyrrane 9. The key intermediate 8 was obtained by the selenium dioxide oxidation of the known biscarbinol 7. The aromaticity of “oxypyriporphyrin” 10 has been confirmed by MS, NMR, IR, and UV/Vis spectroscopy. This system afforded a monocation in 0.2% TFA‐chloroform, and a dication was observed in 2% TFA‐chloroform; these species also retained macrocyclic aromaticity. Oxypyriporphyrin readily formed the corresponding metal chelates 14a‐c by reaction with zinc, copper(II), or nickel(II) acetate, and this observation suggests that there are extensive possibilities for the use of 10 in coordination chemistry. Oxypyriporphyrin and the related semiquinone system oxybenziporphyrin represent the first two members of a new class of aromatic porphyrinoids.
Oxidative Addition of Aryl Halides to Transient Anionic à‐Aryl–Palladium(0) Intermediates—Application to Palladium‐Catalyzed Reductive Coupling of Aryl Halides
Authors: Amatore Christian , Carré Emmanuelle , Jutand Anny , Tanaka Hideo , Ren Qinghua , Torii Sigeru 
Published: September 2007

AbstractThe rates and mechanism of the reactions of a series of aryl‐ligated, anionic palladium(0) complexes Ar‐Pd0‐(PPh3)‐2 with para‐substituted iodobenzenes were investigated by means of transient electrochemistry. The reaction was found to be first order in each reactant and to proceed similarly to oxidative addition of aryl halides to the halide‐ligated species X‐Pd0(PPh3)‐2, although much faster and less sensitive to electronic factors. Owing to the short lifetime (t1/2 ≈︁ 1 – 5 ms) of the product of this reaction, it could not be characterized in detail. However, based on kinetic results, this transient species is thought to be an anionic pentacoordinated bisarylpalladium(II) complex, which undergoes rapid loss of halide ligand to yield, most probably, a bisarylpalladium(II) neutral species. Based on the study of this reaction and on previously reported results, we propose a mechanism for the palladium‐catalyzed homocoupling of aryl halides consisting of a catalytic cycle initiated by oxidative addition of an aryl halide to a zerovalent tris‐ligated palladium center. Two‐electron reduction of the pentacoordinated arylpalladium(II) anionic species thus formed gives a tris‐ligated anionic arylpalladium(0) center, which undergoes oxidative addition with a second aryl halide molecule to eventually lead to a bisaryl‐palladium(II) neutral species. Reductive elimination of a bisaryl molecule from this center closes the catalytic cycle by regenerating the initial zerovalent palladium complex. The application of this sequence to the catalytic heterocoupling of aryl halides is discussed, and it is concluded, on the basis of Hammett correlations, that statistical yields should be observed, in agreement with the results obtained for preparative reactions in DMF.
Structural Motifs of the Dimeric Lewis Glycolipids as Determined by NMR Spectroscopy and Molecular Dynamics Simulations
Authors: Geyer Armin , Hummel Gerd , Eisele Thomas , Reinhardt Stefan , Schmidt Richard R. 
Published: September 2007

AbstractSeveral monomeric and dimeric Lewis glycolipids have been investigated by NMR spectroscopy, and structural aspects were modelled by computer. From the pseudo‐C2‐symmetric tetrasaccharide unit that forms the recognition domain of the Lewis Y and Lewis b antigens, a totally C2‐symmetric tetrasaccharide was designed that contains the structural element common to all Lewis antigens. Finally, a model for the presentation of dimeric Lewis antigens at membrane surfaces was derived. The overall shapes of the dimeric Lewis oligosaccharides are defined by the connectivity of the sugar residues within rigid tri‐ and tetrasaccharide building blocks.
Protonation and Alkylation of the Thiolato Donors in [Fe(CO)(“NHS4”)]: Effects on the Structural, Electronic, and Redox Properties of Metal–Sulfur Complexes
Authors: Sellmann Dieter , Becker Thomas , Knoch Falk 
Published: September 2007

AbstractThe effects of protonation and alkylation at the sulfur donors in metal‐sulfur complexes have been investigated by taking the specific example of [Fe(CO)(“NHS4”)] (1). The 18 valence electron (VE) complex 1 consists of a low‐spin FeII center and the dithioether thiolato amine ligand “NHS4”2‐‐ ( = 2,2′‐bis(2‐mercaptophenylthio)diethylamine(2‐)). Complex 1 can be reversibly protonated at the two thiolato donors; this results in an increase in ν(CO) of 35 cm‐1 after the first protonation and 45 cm‐1 after the second. Alkylation of 1 with one or two equivalents of the oxonium salts R3OBF4 (R = Me, Et) yields [Fe(CO)(“NHS4”‐R)]BF4 (R = Me: 4, Et: 5), [Fe(CO)(“NHS4” ‐R2)](BF4)2 (R = Me: 6, Et: 7), and the methyl ethyl derivative [Fe(CO)(“NHS4” ‐Me‐Et)](BF4)2 (8). An increase in ν(CO) of 31–32 cm‐1 is observed for each successive alkylation. Due to the C1 symmetry of 1, complexes 4, 5, and 8 are formed as 1 : 1 mixtures of two diastereomers, whereas 6 and 7 are present as only one stereoisomer. Acidic hydrolysis of 4, 6, and 7 liberates the corresponding ligands [“NHS4” ‐Rn](BF4)n (9–11; n = 1,2), which were isolated as the ammonium tetrafluoroborate salts. The molecular structure of 8a has been elucidated by X‐ray structure analysis. This shows that the Fe–N and Fe–S bonds in the [FeNS4] core do not change after alkylation of the thiolato donors despite the Δν(CO) of ca. 60 cm‐1 between 1 and 8, which indicates a distinct decrease in electron density at the Fe center. This decrease can be rationalized by increased π‐acceptor character of the sulfur donors upon protonation or alkylation. The change in electron density at the [Fe(“NS4”)] core is further corroborated by cyclic voltammetry. For each successive protonation or alkylation of 1, the redox couple potentials shift by 600–800 mV. As a consequence, the diethyl derivative, for example, gives rise to reduced species (19 or 20 VE) which are not observed for 1. The implications of these results for the reduction of N2 within the coordination sphere of the FeMo cofactor of nitrogenases are discussed.
An Unexpected Structural Principle for Crystalline MgBr2·OEt2: Chains of Trigonal Bipyramids
Authors: Ecker Achim , Üffing Christoph , Schnöckel Hansgeorg 
Published: September 2007

AbstractMgBr2·OEt2 (1), which is commercially available and has been examined by different methods in the past, was obtained in crystalline form as a by‐product of the reaction of amine‐stabilised AlCl solution with mesitylene magnesium bromide. The following unexpected structure was obtained by X‐ray techniques: five‐coordinate magnesium centres form trigonal bipyramids, which are connected by two common bromine atoms into chains. Structural details and especially the relationship with solid MgBr2, MgBr2·(OEt2)2 and MgI2·(OEt2)2 (2) are discussed in order to illuminate the unusual bonding in 1.
Multi‐Mode Switching Based on Dihydroazulene/vinylheptafulvene Photochromism: Synergism of Photochromism and Redox Switching in Heteroaryl‐Functionalized Systems
Authors: Spreitzer Hubert , Daub Jörg 
Published: September 2007

AbstractThe syntheses of the dihydroazulenes (DHAs) DHA‐a‐DHA‐f containing covalently linked heteroaromatic subunits derived from dibenzodioxin, thianthrene, phenoxathiine, N‐methylphenothiazine, N‐methylphenoxazine, and N,N′‐dimethylphenazine groups are described, and their spectroscopic and analytical data are reported. The dihydroazulene/vinylheptafulvene (DHA/VHF) photochromism (photochemical forward and thermal back reaction) depends with high sensitivity on the electronic properties of the functional groups. Whereas the dimethylphenazine derivative DHA‐f is photochemically inactive towards rearrangement, all other DHAs (DHA‐a‐DHA‐e) were found to isomerize to the corresponding vinylheptafulvene forms under irradiation. Cyclic voltammetry revealed that the DHA and the VHP forms have significantly different oxidation and reduction waves. The products of the‐oxidative one‐electron transfer are characterized by UV/Vis/NIR spectroelectrochemistry. Those DHAs having weaker donor substituents (DHA‐a‐DHA‐c) undergo oxidative dimerization whereas DHAs with stronger donating heterocyclic subunits (DHA‐d‐DHA‐f) form stable radical cations.
Molecular Structure, Vibrational Spectrum and Ionization Energy of m‐Dimethoxybenzene
Authors: Huang Jian‐Han , Huang Ke‐Long , Liu Su‐Qin , Luo Qiong 
Published: September 2007

AbstractThe optimized molecular geometries of the three rotamers of m‐dimethoxybenzene in the ground S0 and electronically excited S1 states were predicted by ab initio and density functional theory (DFT) calculations. Their vibrational spectra in the S1 state were studied by one color resonant two photon ionization (1C‐R2PI) method, and their ionization energies were measured by two color resonant two photon ionization (2C‐R2PI) experiment. The optimized molecular geometries showed that the total energy of conformer a was the lowest in the S0 state. Most of the active vibrations assigned from the 1C‐R2PI spectrum were found to be of the in‐plane ring modes. The ioniza‐ tion energies (IE) of conformers a, b and c were determined to be 63521, 64487 and 63755 cm−1, respectively.
Iridium Oxide Film‐Enhanced Impedance Immunosensor for Rapid Detection of Carcinoembyronic Antigen
Authors: Ding Yan‐Jun , Wang Hua , Jiang Jian‐Hui , Shen Guo‐Li , Yu Ru‐Qin 
Published: September 2007

AbstractA simple, rapid and sensitive impedance immunosensor based on iridium oxide (IrOx) thin film for the detection of carcinoembyronic antigen (CEA) in human sera has been proposed. Gold electrode was electrochemically modified with IrOx thin film and simultaneously functionalized with protein A (PA) to bind anti‐CEA antibodies in an orientated way. It has been found that the antibody loading amount was dependent on the PA concentration and the deposition time of IrOx matrix. Under the optimized experimental conditions, the electron transfer resistances obtained were linearly related to the CEA concentration ranging from 36.2 to 460.0 ng/mL, with a detection limit of 28.0 ng/mL. Analytical results of clinical samples from cancer patients show that the proposed immunoassay is reasonably comparable with the chemiluminescence immunoassay (CLIA), indicating the feasibility of using the proposed method for CEA immunoassay in clinical laboratory.
Two Novel Antibacterial Flavonoids from Myrsine Africana L.
Authors: Kang Lu , Zhou Jian‐Xia , Shen Zheng‐Wu 
Published: September 2007

AbstractTwo novel flavonoids, myrsininone A (1), an isoflavone and myrsininone B (2), a flavanone, with very strong antibacterial activities, were isolated from the stems of Myrsine africana L. Their structures were elucidated by extensive spectroscopic analyses. The antibacterial activities were determined by modified Resazuric MIC methods.
Environmentally Benign Oxidation of Some Organic Sulfides with 34% Hydrogen Peroxide Catalyzed by Simple Heteropolyoxometalates
Authors: Tayebee Reza , Alizadeh Mohammad Hassan 
Published: September 2007

AbstractAn environmentally benign oxygenation protocol was developed for selective oxidation of some types of aromatic and aliphatic sulfides in good to excellent yields utilizing 34% hydrogen peroxide catalyzed by simple heteropolyoxometalates in normal drinking water at room temperature. The catalysts could be recovered and reused for at least seven reaction cycles under the described reaction conditions without considerable loss of reactivity. This procedure introduced a new insight into the use of simple heteropolyanions as recoverable catalysts for the oxidation of organic sulfides by an environmentally acceptable protocol.
Synthesis and Electrospray Ionization Mass Spectra of N‐(1,3, 2‐Dioxaphosphorinan‐2‐ylmethyl)thiophosphoramidates
Authors: Miao Zhi‐Wei , Fu Cui‐Rong , Wang Bin , Cui Zhan‐Wei , Zhang Jian‐Feng , Chen Ru‐Yu 
Published: September 2007

AbstractN‐(1,3,2‐Dioxaphosphorinan‐2‐ylmethyl)thiophosphoramidates were synthesized and determined by NMR spectra and positive ion electrospray ionization mass spectrometry (ESI‐MS) in conjunction with tandem mass spectrometry (MS/MS). The fragmentation pathways were investigated. The results show that these characteristic ions in ESI mass spectra are useful in the structural determination of N‐(1,3,2‐dioxaphosphorinan‐2‐ylmethyl)thiophosphoramidates.
Synthesis and Microbial Studies of New Pyridine Derivatives‐III
Authors: Patel N. B. , Agravat S. N. 
Published: September 2007

Abstract2‐Amino substituted benzothiazole 4a–4l and p‐acetamidobenzenesulfonyl chloride 2 were used to prepare 2‐(p‐aminophenylsulfonamido) substituted benzothiazole 6a–6l using mixture of pyridine and acetic anhydride which formed an electrophilic complex (N‐acetyl pyridinium) to facilitate condensation to give desired product by removal of HCl. 2‐{p‐[(3‐Carboxypyrid‐2‐yl)amino]phenylsulfonamido}benzothiazoles 8a–8l were synthesized from 2‐chloropyridine‐3‐carboxylic acid 7 and 6a–6l in 2‐ethoxy ethanol using Cu‐powder and K2CO3. Acid chlorides 9a–9l were condensed with 2‐hydroxyethyl piperazine 10 and 2,3‐dichloropiperazine 11 for amide derivatives 2‐(p‐((3‐(4‐(2‐hydroxyethyl)piperazin‐1‐ylcarbonyl)pyrid‐2‐yl)amino)phenylsulfonamido)benzothiazoles 12a–12l and 2‐{p‐[3‐(2,3‐dichloropiperazin‐1‐ylcarbonyl)pyrid‐2‐ylamino]phenylsulfonamido}benzothiazoles 13a–13l respectively. The structures of the new compounds have been established on the basis of their chemical analysis and spectral data (IR, 1H NMR and mass). All the compounds have been screened for their antibacterial and antifungal activities.
Theoretical Investigation on the Absorption and Emission Properties of the Three Isomers of Bis(thiocyanato)(2,2′‐bipyridyl)platinum(II)
Authors: Hu Xiao‐Ying , Liu Xiao‐Juan , Feng Ji‐Kang 
Published: September 2007

AbstractThis paper presents a Density Functional or Time Dependent Density Functional (DFT/TDDFT) study of the molecular and electronic structures, optical absorption and emission spectra of three linkage isomers:bis(isothiocyanato‐S)(2,2′‐bipyridyl) platinum(II) ([Pt(SCN)2(bpy)]), (isothiocyanato‐S)(thiocyanato‐N)‐(2,2′‐bipy‐ ridyl) platinum(II) ([Pt(SCN)(NCS)(bpy)]), and bis(thiocyanato‐N)(2,2′)‐bipyridyl)platinum(II) ([Pt(NCS)2(bpy)]), in which different coordination ligands based on the N‐ and S‐coordination of the thiocyanato ligands control the luminescent color. The electronic structures were studied using the B3LYP functional. Optimized geometries were compared to the experimentally observed structures. TDDFT calculation was carried out to investigate the excited singlet and triplet states. Calculations have been performed both in vacuo and in solvents, using a polarized continuum model (PCM) to account for solute‐solvent interactions. Inclusion of the solvent led to a significant energy change, and as a consequence, the computed spectrum calculated in the presence of the solvent was in good agreement with the experimental determinations. The first two absorptions were found to originate from mixed platinum‐SCN (or NSC) to bipyridyl‐π* transitions rather than pure metal‐to‐ligand‐charge‐transfer (MLCT) transitions, whereas the higher‐energy bands arose from intraligand π→π* transitions. The stretching frequencies of C≡N have been calculated both in the ground and excited states, which are relative to the charge transition during the excitation. In addition, different sizes of basis sets were also discussed in this paper.
Effect of Concentration of Structurally‐Different Carboxylic Acids on Growth and Aggregation of Calcium Oxalate in Gel Systems
Authors: Deng Sui‐Ping , Ouyang Jian‐Ming 
Published: September 2007

AbstractThe effect of concentration of structurally‐different carboxylic acids such as ethylene diamine tetraacetic acid (H4edta), citric acid (H3cit), tartaric acid (H2tart), and acetic acid (HOAc) on growth and aggregation of calcium oxalate (CaOxa) in gel systems was comparatively investigated. H2tart and H3cit could change the morphology of calcium oxalate monohydrate (COM) and induce the formation of calcium oxalate dihydrate (COD). H4edta could induce the formation of COD at a lower concentration of 0.33 mmol/L and have the strongest ability to inhibit aggregation of COM. HOAc inhibited COM aggregation only at a higher concentration than 500 mmol/L. With increasing the number of carboxylic groups in an acid or increasing the concentration of carboxylic acid, the capacity of this acid to induce COD formation and to inhibit growth and aggregation of COM crystals increased. That is, this capacity followed the order:H4edta>H3cit>H2tart>>HOAc. The result in this work suggested that the presence of H3cit and H2tart in urine played a role in the natural defense against stone formation.
Hormone replacement therapy and lung cancer risk in Chinese
Authors: Chen Kuan‐Yu , Hsiao Chin‐Fu , Chang Gee‐Chen , Tsai Yin‐Huang , Su Wu‐Chou , Perng Reury‐Perng , Huang Ming‐Shyan , Hsiung Chao A. , Chen Chien‐Jen , Yang Pan‐Chyr ,   the GEFLAC Study Group
Published: September 2007

AbstractBACKGROUND.The association between hormone replacement therapy (HRT) and a reduced lung cancer risk has been reported in previous studies. There is a high female to male ratio in Chinese lung cancer patients, and female patients have different clinicopathological characteristics compared with Western patient populations. The authors investigated whether HRT may reduce lung cancer risk in Taiwan.METHODS.The authors used a case‐control study design to investigate 826 women with lung cancer and 531 healthy controls. Personal interviews based on a structured questionnaire were performed to collect information on HRT use of at least 3 months, age, ethnicity, active and passive smoking, exposure to air pollution, cooking or incense fumes, body mass index (BMI), menopause, and family history of cancers.RESULTS.HRT use was associated with reduced lung cancer risk with a multivariate, adjusted odds ratio of 0.70 (95% CI, 0.53–0.94; P = .019). HRT use was associated with reduced odds ratio of lung cancer in all subset analyses stratified by histology, active and passive cigarette smoking, BMI, history of incense burning, cooking, and motorcycle riding, as well as family history of certain cancers.CONCLUSIONS.This study confirmed that HRT is associated with a reduced lung cancer risk. The results appeared to be applicable to Chinese female population groups. Cancer 2007. © 2007 American Cancer Society.