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Structural Isomers (structural + isomer)
Selected AbstractsDramatic Effects of the Substituents on the Solid-State Fluorescence Properties of Structural Isomers of Novel Benzofuro[2,3-c]oxazolocarbazole-Type Fluorophores.CHEMINFORM, Issue 2 2007Yousuke Ooyama Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Synthesis of Azinoazole Structural Isomers by Photocyclization.CHEMINFORM, Issue 49 2006A. N. Frolov Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Comparison of the hydrolytic stability of S -(N,N -diethylaminoethyl) isobutyl methylphosphonothiolate with VX in dilute solutionJOURNAL OF APPLIED TOXICOLOGY, Issue S1 2001M. D. Crenshaw Abstract The stability of S -(N,N -diethylaminoethyl) isobutyl methylphosphonothiolate,a V-type nerve agent developed by the former Soviet Union,in the environment is an important parameter in threat assessment analysis and for the determination of use, production, testing and storage of this chemical warfare agent. S -(N,N -Diethylaminoethyl) isobutyl methylphosphonothiolate is a structural isomer of the nerve agent VX developed by the USA and the UK and will be referred to as VXA (VX analog) in this presentation. Because VXA and VX differ structurally, even though they do have the same molecular formula, it is expected that their physical and chemical properties would be different. This preliminary investigation was undertaken to determine the relative hydrolysis rate of VXA compared with VX. The hydrolysis of each compound at approximately 1 mg ml,1 in unbuffered water at pH 7 was determined side-by-side. The half-lives for VXA and VX were determined to be 12.4 days and 4.78 days, respectively. Agent VXA hydrolyzed 2.6 times more slowly than VX, and each agent followed second-order hydrolysis kinetics. These results imply that VXA is more persistent in the environment and therefore poses a greater threat. These results also imply that VXA is more likely to be detected, if present, during an inspection in support of the Chemical Weapons Convention. Copyright © 2001 John Wiley & Sons, Ltd. [source] Lanthanide(III) Complexes of DOTA,Glycoconjugates: A Potential New Class of Lectin-Mediated Medical Imaging AgentsCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2004João P. André Dr. Abstract The synthesis and characterization of a new class of DOTA (1,4,7,10-tetrakis(carboxymethyl)-1,4,7,10-tetraazacyclododecane) monoamide-linked glycoconjugates (glucose, lactose and galactose) of different valencies (mono, di and tetra) and their SmIII, EuIII and GdIII complexes are reported. The 1H NMR spectrum of EuIII,DOTALac2 shows the predominance of a single structural isomer of square antiprismatic geometry of the DOTA chelating moiety and fast rotation about the amide bond connected to the targeting glycodendrimer. The in vitro relaxivity of the GdIII,glycoconjugates was studied by 1H nuclear magnetic relaxation dispersion (NMRD), yielding parameters close to those reported for other DOTA monoamides. The known recognition of sugars by lectins makes these glycoconjugates good candidates for medical imaging agents (MRI and gamma scintigraphy). [source] Differentiation of structural isomers in a target drug database by LC/Q-TOFMS using fragmentation predictionDRUG TESTING AND ANALYSIS, Issue 6 2010Elli Tyrkkö Abstract Isomers cannot be differentiated from each other solely based on accurate mass measurement of the compound. A liquid chromatography/quadrupole time-of-flight mass spectrometry (LC/Q-TOFMS) method was used to systematically fragment a large group of different isomers. Two software programs were used to characterize in silico mass fragmentation of compounds in order to identify characteristic fragments. The software programs employed were ACD/MS Fragmenter (ACD Labs Toronto, Canada), which uses general fragmentation rules to generate fragments based on the structure of a compound, and SmartFormula3D (Bruker Daltonics), which assigns fragments from a mass spectra and calculates the molecular formulae for the ions using accurate mass data. From an in-house toxicology database of 874 drug substances, 48 isomer groups comprising 111 compounds, for which a reference standard was available, were found. The product ion spectra were processed with the two software programs and 1,3 fragments were identified for each compound. In 82% of the cases, the fragment could be identified with both software programs. Only 10 isomer pairs could not be differentiated from each other based on their fragments. These compounds were either diastereomers or position isomers undergoing identical fragmentation. Accurate mass data could be utilized with both software programs for structural elucidation of the fragments. Mean mass accuracy and isotopic pattern match values (SigmaFit; Bruker Daltonics Bremen, Germany) were 0.9 mDa and 24.6 mSigma, respectively. The study introduces a practical approach for preliminary compound identification in a large target database by LC/Q-TOFMS without necessarily possessing reference standards. Copyright © 2010 John Wiley & Sons, Ltd. [source] Using measured octanol-air partition coefficients to explain environmental partitioning of organochlorine pesticidesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2002Mahiba Shoeib Abstract Octanol-air partition coefficients (Koa) were measured directly for 19 organochlorine (OC) pesticides over the temperature range of 5 to 35°C. Values of log Koa at 25°C ranged over three orders of magnitude, from 7.4 for hexachlorobenzene to 10.1 for 1,1-dichloro-2,2-bis (p-chlorophenyl) ethane. Measured values were compared to values calculated as KowRT/H (where R is the ideal gas constant [8.314 J mol,1 K,1], T is absolute temperature, and H is Henry's law constant) were, in general, larger. Discrepancies of up to three orders of magnitude were observed, highlighting the need for direct measurements of Koa. Plots of Koa versus inverse absolute temperature exhibited a log-linear correlation. Enthalpies of phase transition between octanol and air (,Hoa) were determined from the temperature slopes and were in the range of 56 to 105 kJ mol,1 K,1. Activity coefficients in octanol (,o) were determined from Koa and reported supercooled liquid vapor pressures (p), and these were in the range of 0.3 to 12, indicating near-ideal solution behavior. Differences in Koa values for structural isomers of hexachlorocyclohexane were also explored. A Koa -based model was described for predicting the partitioning of OC pesticides to aerosols and used to calculate particulate fractions at 25 and ,10°C. The model also agreed well with experimental results for several OC pesticides that were equilibrated with urban aerosols in the laboratory. A log-log regression of the particle-gas partition coefficient versus Koa had a slope near unity, indicating that octanol is a good surrogate for the aerosol organic matter. [source] Syntheses and Crystal Structures of Copper and Silver Complexes with New Imine Ligands , Air-Stable, Photoluminescent CuIN4 ChromophoresEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2003Goutam Kumar Patra Abstract A series of new imine ligands [1 (C12H12N2S2), 2 (C12H12N2S2), 3 (C24H18N4S2), and 5 (C30H27N7)] have been synthesized (1 and 2 are structural isomers). CuI and AgI complexes of the nonconjugated dithiophene-diimine ligands 1, 2 and the tripodal imine-amine ligand 5 have also been prepared and thoroughly characterized by spectroscopic techniques as well as by X-ray diffraction. In cyclic voltammetry at a glassy carbon milli electrode in anhydrous dichloromethane under dry N2, the corresponding CuI complexes [6 (2C12H12N2S2·CuClO4), 7 (2C12H12N2S2·CuClO4), and 12 (C30H27N7·CuClO4)] show quasi-reversible CuII/I couples with high redox potentials (1.001 V for 6, 0.958 V for 7, and 0.692 V for 12, vs. Ag/AgCl). This indicates that the ,-acid ligands 1, 2, and 5 preferentially stabilize copper(I) over copper(II). The CuIN4 chromophores in the complexes 6, 7, and 12 display photoluminescence in dichloromethane at room temperature. The related silver complexes of the same three ligands 10 (2C12H12N2S2·AgClO4), 11 (2C12H12N2S2·AgClO4), and 13 [C30H27N7·Ag(CH3CN)ClO4] reveal similar structural features but lack specific photophysical properties. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Rational Design of Chelating Phosphine Functionalized Os(II) Emitters and Fabrication of Orange Polymer Light-Emitting Diodes Using Solution Process,ADVANCED FUNCTIONAL MATERIALS, Issue 2 2008M. Cheng Abstract A new series of charge neutral Os(II) pyridyl azolate complexes with either bis(diphenylphosphino)methane (dppm) or cis -1,2-bis(diphenylphosphino)ethene (dppee) chelates were synthesized, and their structural, electrochemical, photophysical properties and thermodynamic relationship were established. For the dppm derivatives 3a and 4a, the pyridyl azolate chromophores adopt an eclipse orientation with both azolate segments aligned trans to each other, and with the pyridyl groups resided the sites that are opposite to the phosphorus atoms. In sharp contrast, the reactions with dppee ligand gave rise to the formation of two structural isomers for all three kind of azole chromophores, with both azolate or neutral heterocycles (i.e., pyridyl or isoquinolinyl fragments) located at the mutual trans -disposition around the Os metal (denoted as series of a and b complexes). These chelating phosphines Os(II) complexes show remarkably high thermal stability, among which and several exhibit nearly unitary phosphorescence yield in deaerated solution at RT. A polymer light-emitting device (PLED) prepared using 0.4 mol % of 5a as dopant in a blend of poly(vinylcarbazole) (PVK) and 30 wt % of 2- tert -butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) exhibits yellow emission with brightness of 7208 cd m,2, an external quantum efficiency of 10.4 % and luminous efficiency of 36.1 cd A,1 at current density of 20 mA cm,2. Upon changing to 1.6 mol % of 6a, the result showed even better brightness of 9212 cd m,2, external quantum efficiency of 12.5 % and luminous efficiency of 46.1 cd A,1 at 20 mA cm,2, while the max. external quantum efficiency of both devices reaches as high as 11.7 % and 13.3 %, respectively. The high PL quantum efficiency, non-ionic nature, and short radiative lifetime are believed to be the determining factors for this unprecedented achievement. [source] Structure Investigation of Bridgehead Aziridine: Synthesis, Theoretical, and Crystallographic Study of 2,4,6-Triphenyl-1,3-diazabicyclo[3.1.0]hex-3-eneHELVETICA CHIMICA ACTA, Issue 2 2006Giuseppe Bruno Abstract A one-pot three-component procedure to efficiently create the 1,3-diazabicyclo[3.1.0]hex-3-ene system is reported. The molecular structure of 2,4,6-triphenyl-1,3-diazabicyclo[3.1.0]hex-3-ene (3) was studied by X-ray diffraction and compared to ab initio and density-functional-theory (DFT) calculations restricted to the core moiety. Geometry optimizations for structural isomers and tautomeric forms of this aziridine fragment, taken as simplified models, were carried out at high calculation levels. Moreover, the same methods were utilized to evaluate the proton affinity of two crucial aziridine tautomers. [source] Time-dependent density functional calculations of the Q-like bands of phenylene-linked free-base and zinc porphyrin dimersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2001Yoichi Yamaguchi Abstract Time-dependent density functional theory (TDDFT) calculations have been performed on the excitation energies and oscillator strengths of the Q-like bands of three structural isomers of phenylene-linked free-base (FBP) and zinc (ZnP) porphyrin dimers. The TDDFT calculated results on the low-lying excited states of the reference monomers, FBP and ZnP, are in excellent agreement with previously calculated and experimental results. It is found that the 1,3- and 1,4-phenylene-linked dimers have monomerlike Q bands that are slightly red-shifted compared to the monomers and new Q, bands comprised of the cross-linked excitations from the FBP (ZnP) ring to the ZnP (FBP) ring at considerably lower energies than the monomer Q bands. For the 1,2-phenylene-linked dimer, the direct ,,, interaction between porphyrin rings caused by the van der Waals repulsion between them provides strong mixing of the Q, bands with the Q bands, which causes its minimum excitation energy to be red-shifted by 0.05 eV compared to the other isomers. The oscillator strengths of the Q, bands are also unexpectedly found to be as strong as those of the Q bands in the dimers. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 84: 338,347, 2001 [source] Bank Security Dye Packs: Synthesis, Isolation, and Characterization of Chlorinated Products of Bleached 1-(methylamino)anthraquinoneJOURNAL OF FORENSIC SCIENCES, Issue 6 2006James M. Egan Ph.D. ABSTRACT: Banknote evidence is often submitted after a suspect has attempted to disguise or remove red dye stain that has been released because of an anti-theft device that activates after banknotes have been unlawfully removed from bank premises. Three chlorinated compounds have been synthesized as forensic chemical standards to indicate bank security dye bleaching as a suspect's intentional method for masking a robbery involving dye pack release on banknotes. A novel, facile synthetic method to provide three chlorinated derivatives of 1-(methylamino)anthraquinone (MAAQ) is presented. The synthetic route involved Ultra CloroxÔ bleach as the chlorine source, iron chloride as the catalyst, and MAAQ as the starting material and resulted in a three-component product mixture. Two mono-chlorinated isomers (2-chloro-1-(methylamino)anthraquinone and 4-chloro-1-(methylamino)anthraquinone) and one di-chlorinated compound (2,4-dichloro-1-(methylamino)anthraquinone) of the MAAQ parent molecule were detected by gas chromatography mass spectrometry (GC-MS), and subsequently isolated by liquid chromatography (LC) with postcolumn fraction collection. Although GC-MS is sensitive enough to detect all of the chlorinated products, it is not definitive enough to identify the structural isomers. Liquid-state nuclear magnetic resonance (NMR) spectroscopy was utilized to elucidate structurally the ortho- and para-mono-chlorinated isomers once enough material was properly isolated. A reaction mechanism involving iron is proposed to explain the presence of chlorinated MAAQ species on stolen banknotes after attempted bleaching. [source] Regioselective synthesis of pyrimido[5,4-c][2,1]benzothiazines by reactions of ,-chloroaldehydes with n-c-n binucleophilesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 1 2010Kirill Popov The method of pyrimidine ring fusion at the [c] side of benzothiazines based on the reaction of their chloroaldehyde derivatives with amidines is described. Formation of the structural isomers of reaction products was investigated, and regioselectivity of heterocyclization reactions was shown. A number of novel pyrimidobenzothiazines were synthesized. J. Heterocyclic Chem., 2010. [source] Synthetic approaches to 3H -naphtho[2,1- b]pyrans and 2,3-dihydro-1H -naphtho[2,1- b]pyransJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 6 2009Amitabh Jha Naphtho[2,1- b]pyran nuclei are prevalent in natural products with significant biological and medicinal properties. 3,3-Disubstituted 3H -naphtho[2,1 -b]pyrans are photochromic and find use in electronic display systems, ophthalmic lenses, optical switches, and temporary or permanent memories. Of the various possible structural isomers of naphthopyran framework, this review is an account of reported synthetic procedures to produce 3H -naphtho[2,1-b]pyrans and their dihydro analogs, 2,3-dihydro-1H -naphtho[2,1 -b]pyrans. The advantages and disadvantages of each procedure in terms of yields, complexity, formation of side-products, use of uncommon/expensive reagents, etc., are also described. J. Heterocyclic Chem., (2009). [source] Profiling of polar metabolites in biological extracts using diamond hydride-based aqueous normal phase chromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 13 2009Damien L. Callahan Abstract Highly polar metabolites, such as sugars and most amino acids are not retained by conventional RP LC columns. Without sufficient retention low concentration compounds are not detected due ion suppression and structural isomers are not resolved. In contrast, hydrophilic interaction chromatography (HILIC) and aqueous normal phase chromatography (ANP) retain compounds based on their hydrophilicity and therefore provides a means of separating highly polar compounds. Here, an ANP method based on the diamond hydride stationary phase is presented for profiling biological small molecules by LC. A rapid separation system based upon a fast gradient that delivers reproducible chromatography is presented. Approximately 1000 compounds were reproducibly detected in human urine samples and clear differences between these samples were identified. This chromatography was also applied to xylem fluid from soyabean (Glycine max) plants to which 400 compounds were detected. This method greatly increases the metabolite coverage over RP-only metabolite profiling in biological samples. We show that both forms of chromatography are necessary for untargeted comprehensive metabolite profiling and that the diamond hydride stationary phase provides a good option for polar metabolite analysis. [source] Highly sensitive and accurate profiling of carotenoids by supercritical fluid chromatography coupled with mass spectrometryJOURNAL OF SEPARATION SCIENCE, JSS, Issue 9 2009Atsuki Matsubara Abstract We attempted to establish a high-speed and high-resolution profiling method for a carotenoid mixture as a highly selective and highly sensitive detection method; the analysis was carried out by supercritical fluid chromatography (SFC) coupled with mass spectrometry (MS). When an octadecyl-bonded silica (ODS) particle-packed column was used for separation, seven carotenoids including structural isomers were successfully separated within 15 min. This result indicated not only improved separation but also improved throughput compared to the separation and throughput in RP-HPLC. The use of a monolithic ODS column resulted in additional improvement in both the resolution and the throughput; the analysis time was reduced to 4 min by increasing the flow rate. Furthermore, carotenoids in biological samples containing the complex matrices were separated effectively by using several monolithic columns whose back pressure was very low. The mass spectrometer allowed us to perform a more sensitive analysis than UV detection; the detection limit of each carotenoid was 50 pg or below. This is the first report of carotenoid analysis carried out by SFC-MS. The profiling method developed in this study will be a powerful tool for carrying out accurate profiling of biological samples. [source] Synthesis and Structure,Efficiency Relations of 1,3,5-Benzenetrisamides as Nucleating Agents and Clarifiers for Isotactic Poly(propylene),MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 2 2010Frank Abraham Abstract This paper presents the synthesis and properties of 1,3,5-benzenetrisamides with a particular focus on structure-efficiency relationships of nucleation and optical property enhancement of isotactic poly(propylene) (i -PP). A family of twenty 1,3,5-benzenetrisamide derivatives was synthesized, in which the direction of the amide linkage between the core and the peripheral substituents, as well as their length (C-3 to C-6) and flexibility were systematically varied. Dissolution- and recrystallization temperatures of the additives in the polymer melt, the crystallization temperature of i -PP, and the optical properties clarity and haze were determined in the additive concentration range from 200 to 2,500,ppm. Within the reported series of compounds, few exhibited very good nucleating and clarification abilities, only one with outstanding characteristics, whereas other, very closely related derivatives were found to be incapable to nucleate or clarify i -PP, although, intriguingly, most are structural isomers. We conclude that it is the particular chemical structure of the additive that determines its crystallization/self-assembly process, and, therewith, the structure of the heterogeneous nuclei, and at a higher hierarchical level the morphology of the poly(propylene) solid state and its final properties; and, hence, that a predictive understanding is still elusive. [source] Predicting the low energy landscape of nanoscale silica using interatomic potentialsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2006S. T. BromleyArticle first published online: 18 APR 200 Abstract The energies of 52 of the lowest lying structural isomers of the (SiO2)12 nanocluster are accurately calculated via energy minimisations employing density functional theory (DFT) and also with two silica interatomic potentials (IPs). Of the tested IPs, one was specifically parameterised with respect to small silica nanoclusters, and the other was biased to accurately recover bulk silica properties, although having been applied numerous times to silica nanosystems. The predicted energetic ordering of the nanocluster isomers resulting from the IP optimisations are compared with respect to their deviance from benchmark nanocluster energies from DFT calculations. Although both IPs predict the DFT ground state isomer to be a very low energy cluster and thus are of use in global optimisation studies, large fluctuations in the IP energies of other low lying isomers (relative to the respective DFT energies) shed doubt on their wider applicability to nanoscale silica systems. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ring conformations and intermolecular interactions in two fused dibenzoazocinesACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2010Andrés F. Yepes 5-Acetyl-2-chloro-8,11-dimethyl-5,6,11,12-tetrahydrodibenzo[b,f]azocine, C19H20ClNO, (I), crystallizes as a single fully ordered isomer, but 14-acetyl-8,11-dimethyl-7,8,13,14-tetrahydrobenzo[f]naphtho[1,2- b]azocine,14-acetyl-8,9-dimethyl-7,8,13,14-tetrahydrobenzo[f]naphtho[1,2- b]azocine (74/26), C23H23NO, (II), exhibits threefold whole-molecule disorder involving both configurational and structural isomers. In (I) and in the predominant form of (II), the azocine rings adopt very similar conformations, forming boat-shaped rings having approximate twofold rotational symmetry. There are no direction-specific intermolecular interactions in the crystal structure of (I), but the molecules of (II) are weakly linked into chains by an aromatic ,,, stacking interaction. The compounds were made under green conditions using an acid-catalysed cyclization process having very high atom utilization. [source] The Study of Molecular Modeling for Heavy Oil Thermal CrackingCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2007L. Yan Abstract The tighter specifications for refining products have gradually led refineries to focus on the molecular modeling of petroleum processing. In this work, a systematic methodology is presented for the molecular modeling of heavy oil thermal cracking (HOTC). This research which is based on a microscopic understanding provides a basis to achieve better design, management, optimization, and control of HOTC. The molecular information of HOTC product streams is represented in the form of a MTHS (molecular type homologous series) matrix. From consideration of the complexity of structural isomers in heavy petroleum fractions, the heavy molecules in a homologous series are grouped to reduce the dimension of the MTHS matrix. Transformation correlations are developed to capture the molecular properties of each homologous series in the MTHS matrix and to interrelate the molecular composition and bulk properties of the product streams. The HOTC process model was built on the basis of the molecular representation provided by the MTHS matrix and the transformation correlations. Two case studies are illustrated for validation of the proposed model and methodology. [source] Online coupling of enantioselective capillary gas chromatography with proton nuclear magnetic resonance spectroscopyCHIRALITY, Issue 9 2010Maximilian Kühnle Abstract The hyphenation of enantioselective capillary gas chromatography and mass spectrometry is not always sufficient to distinguish between structural isomers, thus requiring peak identification by NMR spectroscopy. Here the first online coupling of enantioselective capillary gas chromatography with proton nuclear resonance spectroscopy is described for the unfunctionalized chiral alkane 2,4-dimethylhexane resolved on octakis(6- O -methyl-2,3-di- O -pentyl)-,-cyclodextrin at 60°C. NMR allows constitutional and configurational isomers (diastereomers and enantiomers) to be distinguished. Enantiomers display identical spectra at different retention times, which enable an indirect identification of these unfunctionalized alkanes. The presented method is still at an early development stage, and will require instrumental optimization in the future. Chirality 2010. © 2010 Wiley-Liss, Inc. [source] | ||||||||||||||||||||||||||||