bluuebunny/crossref_metadata_2025_split huggingface dataset:
Origin of Dissolved Organic Carbon Studied by UV‐vis Spectroscopy
Authors: Giancoli Barreto Sônia Regina , Nozaki Jorge , Barreto Wagner J. 
Published: March 2004

AbstractDissolved organic carbon (DOC) distributions in water from Lake Ipê, MS, Brazil, were investigated. The samplings were performed monthly (surface, 1 m depth, and bottom) from June 1999 to June 2000. Absorbance at 285 nm and DOC concentrations in mg dm—3, p(DOC), were highly correlated for the three depths. 77% of the surface, 85% for 1 m and bottom samples presented a variation between 20 dm3 g—1 cm—1 and 50 dm3 g—1 cm—1 of A(285 nm)/p(DOC), that characterizes the dissolved organic matter in lake water as essentially fulvic. The ratio A(254 nm)/p(DOC) was also sensitive for fulvic matter, and an A(250 nm)/A(365 nm) = 4 ratio was characteristic of strongly colored waters. The ratios A(436 nm)/p(DOC) for the three depths also showed a significant correlation. The predominance of fulvic acid is explained by environmental characteristics such as the tropical climate, temperatures above 18 °C, and the lake environment. It was demonstrated that the variation in the water carbon content due to different compartments in the lake can be monitored by UV‐vis spectroscopy ratios.
Thermodynamics of fluid‐phase equilibria for standard chemical engineering operations
Authors: Prausnitz John M. , Tavares Frederico W. 
Published: March 2004

AbstractThermodynamics provides one of the scientific cornerstones of chemical engineering. This review considers how thermodynamics is and has been used to provide phase equilibria as required for design of standard chemical engineering processes with emphasis on distillation and other conventional separation operations. While this review does not consider “modern” thermodynamics for high‐tech applications, attention is given to 50 years of progress in developing excess‐Gibbs‐energy models and engineering‐oriented equations of state; these developments indicate rising use of molecular physics and statistical mechanics whose application for chemical process design is made possible by increasingly powerful computers. As yet, results from molecular simulations have not had a major influence on thermodynamics for conventional chemical engineering; however, it is likely that molecular simulation methods will become increasingly useful, especially when supported by quantum‐mechanical calculations for describing intermolecular forces in complex systems. © 2004 American Institute of Chemical Engineers AIChE J, 50: 739–761, 2004
Decreasing self‐injurious behavior associated with awakening in a child with autism and developmental delays
Authors: DeLeon Iser G. , Fisher Wayne W. , Marhefka Jean‐Marie 
Published: March 2004

AbstractDirect observation data revealed that self‐injurious behavior (SIB) emitted by a young boy with autism occurred primarily within one hour after waking versus all other times of the day. Experimentally manipulated scheduled awakenings supported the hypothesized relation between waking and SIB. A faded‐bedtime procedure was then implemented to stabilize his sleep patterns, which reduced awakenings by 81% and post‐waking SIB by 82%. Copyright © 2004 John Wiley & Sons, Ltd.
Tris(oxalato)phosphorus Acid and Its Lithium Salt
Authors: Wietelmann Ulrich , Bonrath Werner , Netscher Thomas , Nöth Heinrich , Panitz Jan‐Christoph , Wohlfahrt‐Mehrens Margret 
Published: March 2004

AbstractThe conversion of three equivalents of anhydrous oxalic acid with phosphorus pentachloride yields tris(oxalato)phosphorus acid 1, which crystallizes from diethyl ether solutions as protonated diethyl ether complex [(Et2O)2H]+[P(C2O4)3]−. The superacidic compound can be used as catalyst for Friedel–Crafts‐type reactions. Upon neutralization with lithium hydride, the lithium salt Li[P(C2O4)3] 2 is obtained, which is highly soluble in aprotic solvents and which exhibits a wide voltage window. Thus, the lithium compound is a promising candidate as electrolyte for high performance non‐aqueous batteries.
Synthesis of (E)‐α‐Hydroxy‐β,γ‐Unsaturated Amides with High Selectivity from α,β‐Epoxyamides by Using Catalytic Samarium Diiodide or Triiodide
Authors: Concellón José M. , Bernad Pablo L. , Bardales Eva 
Published: March 2004

AbstractThe highly stereoselective synthesis of (E)‐α‐hydroxy‐β,γ‐unsaturated amides starting from α,β‐epoxyamides, by using catalytic SmI2 or SmI3, was achieved. This transformation can also be carried out by using SmI2 generated in situ from samarium powder and diiodomethane. The starting compounds 1 are easily prepared by the reaction of enolates derived from α‐chloroamides with ketones at −78 °C. A mechanism to explain this transformation has been proposed. Cyclopropanation of (E)‐α‐hydroxy‐β,γ‐unsaturated amides has been performed to demonstrate their synthetic applications.
Hydrogenation Studies Involving Halobis(phosphine)–Rhodium(i) Dimers: Use of Parahydrogen Induced Polarisation To Detect Species Present at Low Concentration
Authors: Colebrooke Simon A. , Duckett Simon B. , Lohman Joost A. B. , Eisenberg Richard 
Published: March 2004

AbstractReaction of [RhCl(PPh3)2]2 with parahydrogen revealed that the binuclear dihydride [Rh(H)2(PPh3)2(μ‐Cl)2Rh(PPh3)2] and the tetrahydride complex [Rh(H)2(PPh3)2(μ‐Cl)]2 are readily formed. While magnetisation transfer from free H2 into both the hydride resonances of the tetrahydride and [Rh(H)2Cl(PPh3)3] is observable, neither transfer into [Rh(H)2(PPh3)2(μ‐Cl)2Rh(PPh3)2] nor transfer between the two binuclear complexes is seen. Consequently [Rh(H)2(PPh3)2(μ‐Cl)]2 and [Rh(H)2(PPh3)2(μ‐Cl)2Rh(PPh3)2] are not connected on the NMR timescale by simple elimination or addition of H2. The rapid exchange of free H2 into the tetrahydride proceeds via reversible halide bridge rupture and the formation of [Rh(H)2(PPh3)2(μ‐Cl)RhCl(H)2(PPh3)2]. When these reactions are examined in CD2Cl2, the formation of the solvent complex [Rh(H)2(PPh3)2(μ‐Cl)2Rh(CD2Cl2)(PPh3)] and the deactivation products [Rh(Cl)(H)(PPh3)2(μ‐Cl)(μ‐H)Rh(Cl)(H)(PPh3)2] and [Rh(Cl)(H)(CD2Cl2)(PPh3)(μ‐Cl)(μ‐H)Rh(Cl)(H)(PPh3)2] is indicated. In the presence of an alkene and parahydrogen, signals corresponding to binuclear complexes of the type [Rh(H)2(PPh3)2(μ‐Cl)2(Rh)(PPh3)(alkene)] are detected. These complexes undergo intramolecular hydride interchange in a process that is independent of the concentration of styrene and catalyst and involves halide bridge rupture, followed by rotation about the remaining Rh–Cl bridge, and bridge re‐establishment. This process is facilitated by electron rich alkenes. Magnetisation transfer from the hydride ligands of these complexes into the alkyl group of the hydrogenation product is also observed. Hydrogenation is proposed to proceed via binuclear complex fragmentation and trapping of the resultant intermediate [RhCl(H)2(PPh3)2] by the alkene. Studies on a number of other binuclear dihydride complexes including [(H)(Cl)Rh(PMe3)2(μ‐H)(μ‐Cl)Rh(CO)(PMe3)], [(H)2Rh(PMe3)2(μ‐Cl)2Rh(CO)(PMe3)] and [HRh(PMe3)2(μ‐H)(μ‐Cl)2Rh(CO)(PMe3)] reveal that such species are able to play a similar role in hydrogenation catalysis. When the analogous iodide complexes [RhI(PPh3)2]2 and [RhI(PPh3)3] are examined, [Rh(H)2(PPh3)2(μ‐I)2Rh(PPh3)2], [Rh(H)2(PPh3)2(μ‐I)]2 and [Rh(H)2I(PPh3)3] are observed in addition to the corresponding binuclear alkene–dihydride products. The higher initial activity of these precursors is offset by the formation of the trirhodium phosphide bridged deactivation product, [{(H)(PPh3)Rh(μ‐H)(μ‐I)(μ‐PPh2)Rh(H)(PPh3)}(μ‐I)2Rh(H)2(PPh3)2]
Solvent Effects on 195Pt and 205Tl NMR Chemical Shifts of the Complexes [(NC)5PtTl(CN)n]n− (n=0–3), and [(NC)5PtTlPt(CN)5]3− Studied by Relativistic Density Functional Theory
Authors: Autschbach Jochen , Le Guennic Boris 
Published: March 2004

AbstractThe 295Pt and 205Tl NMR chemical shifts of the complexes [(NC)5PtTl(CN)n]n− n=0–3, and of the related system [(NC)5PtTlPt(CN)5]3− have been computationally investigated. It is demonstrated that based on relativistically optimized geometries, by applying an explicit first solvation shell, an additional implicit solvation model to represent the bulk solvent effects (COSMO model), and a DFT exchange‐correlation potential that was specifically designed for the treatment of response properties, that the experimentally observed metal chemical shifts can be calculated with satisfactory accuracy. The metal chemical shifts have been computed by means of a two‐component relativistic density functional approach. The effects of electronic spin–orbit coupling were included in all NMR computations. The impact of the choice of the reference, which ideally should not affect the accuracy of the computed chemical shifts, is also demonstrated. Together with recent calculations by us of the Pt and Tl spin–spin coupling constants, all measured metal NMR parameters of these complexes are now computationally determined with sufficient accuracy in order to allow a detailed analysis of the experimental results. In particular, we show that interaction of the complexes with the solvent (water) must be an integral part of such an analysis.
Indium‐Mediated Regio‐ and Diastereoselective Reduction of Norbornyl α‐Diketones
Authors: Khan Faiz Ahmed , Dash Jyotirmayee , Sudheer Ch. 
Published: March 2004

AbstractA novel, efficient, and regio‐ as well as diastereoselective conversion of non‐enolizable bicyclic α‐diketones into synthetically useful acyloins mediated by indium metal is described. The reduction is highly diastereoselective, leading exclusively to endo‐acyloins (endo‐hydroxyl groups) in excellent yields, and tolerates a variety of sensitive substituents, such as acetate, ester, and bridgehead halogens. The regioselectivity in the reductions of monosubstituted α‐diketones varied from 70:30 to 100:0 for the two possible isomeric alcohols. The methodology is extended to the synthesis of highly functionalized cyclopentane carboxaldehydes, potential building blocks in organic syntheses, by cleavage of the acyloins by treating them with Pb(OAc)4 in MeOH/PhH. Allylindium additions to carboxaldehydes 22 have been found to be highly diastereoselective.
Electronic and Vibrational Properties of Fluorenone in the Channels of Zeolite L
Authors: Devaux André , Minkowski Claudia , Calzaferri Gion 
Published: March 2004

AbstractFluorenone (C13H8O) was inserted into the channels of zeolite L by using gas‐phase adsorption. The size, structure, and stability of fluorenone are well suited for studying host–guest interactions. The Fourier transform IR, Raman, luminescence, and excitation spectra, in addition to thermal analysis data, of fluorenone in solution and fluorenone/zeolite L are reported. Normal coordinate analysis of fluorenone was performed, based on which IR and Raman bands were assigned, and an experimental force field was determined. The vibrational spectra can be used for nondestructive quantitative analysis by comparing a characteristic dye band with a zeolite band that has been chosen as the internal standard. Molecular orbital calculations were performed to gain a better understanding of the electronic structure of the system and to support the interpretation of the electronic absorption and luminescence spectra. Fluorenone shows unusual luminescence behavior in that it emits from two states. The relative intensity of these two bands depends strongly on the environment and changes unexpectedly in response to temperature. In fluorenone/zeolite L, the intensity of the 300 nm band (lifetime 9 μs) increases with decreasing temperature, while the opposite is true for the 400 nm band (lifetime 115 μs). A model of the host–guest interaction is derived from the experimental results and calculations: the dye molecule sits close to the channel walls with the carbonyl group pointing to an Al3+ site of the zeolite framework. A secondary interaction was observed between the fluorenone's aromatic ring and the zeolite's charge‐compensating cations.
Molecular Reactors and Machines: Applications, Potential, and Limitations
Authors: Easton Christopher J. , Lincoln Stephen F. , Barr Lorna , Onagi Hideki 
Published: March 2004

AbstractMolecular reactors are miniature vessels for the assembly of reactants at the molecular level, in order to change the nature of chemical transformations. It seems probable that those that will find most immediate applications are those that change product ratios or give products which would not readily form in the absence of the reactors, and thereby afford easy access to materials that are otherwise difficult to obtain. Molecular machines consist of interrelated parts with separate functions and perform some kind of work, at the molecular level. Practical examples are likely to be relatively uncomplicated and not based on individual functions of single‐molecule devices. Instead they will probably rely on extensive redundancy of the molecular components and their interactions and reactions, as well as of the machines themselves.
Biotin is endogenously expressed in select regions of the rat central nervous system
Authors: McKay Bruce E. , Molineux Michael L. , Turner Ray W. 
Published: March 2004

AbstractThe vitamin biotin is an endogenous molecule that acts as an important cofactor for several carboxylases in the citric acid cycle. Disorders of biotin metabolism produce neurological symptoms that range from ataxia to sensory loss, suggesting the presence of biotin in specific functional systems of the CNS. Although biotin has been described in some cells of nonmammalian nervous systems, the distribution of biotin in mammalian CNS is virtually unknown. We report the presence of biotin in select regions of rat CNS, as revealed with a monoclonal antibody directed against biotin and with avidin‐ and streptavidin‐conjugated labels. Detectable levels of biotin were primarily found caudal to the diencephalon, with greatest expression in the cerebellar motor system and several brainstem auditory nuclei. Biotin was found as a somatic label in cerebellar Purkinje cells, in cell bodies and proximal dendrites of cerebellar deep nuclear neurons, and in red nuclear neurons. Biotin was detected in cells of the spiral ganglion, somata and proximal dendrites of cells in the cochlear nuclei, superior olivary nuclei, medial nucleus of the trapezoid body, and nucleus of the lateral lemniscus. Biotin was further found in pontine nuclei and fiber tracts, the substantia nigra pars reticulata, lateral mammillary nucleus, and a small number of hippocampal interneurons. Biotin was detected in glial cells of major tract systems throughout the brain but was most prominent in tracts of the hindbrain. Biotin is thus expressed in select regions of rat CNS with a distribution that correlates to the known clinical sequelae associated with biotin deficiencies. J. Comp. Neurol. 473:86–96, 2004. © 2004 Wiley‐Liss, Inc.
A Novel Pentacoordinated Dioxovanadium(V) Salicylaldiminate: Solvent Specific Crystallization of Dimorphs with Contrasting Coordination Geometries, Ligand Conformations and Supramolecular Architectures
Authors: Baruah Bharat , Rath Sankar Prasad , Chakravorty Animesh 
Published: March 2004

AbstractThe reaction of the tridentate salicylaldimine of 2‐picolylamine, C6H4(OH)CHNCH2C5H4N (HL), with bis(acetylacetonato)oxovanadium(IV) at room temperature under oxygen (or with VOSO4·5H2O plus H2O2) furnished crystalline greenish‐yellow α‐VO2(L) and green β‐VO2(L) from methanol (or ethanol) and acetonitrile (or dichloromethane), respectively. The dimorphs give rise to the same solution species as revealed by spectroscopic data (UV/Vis, 1H and 51V NMR). Both forms react with 3,5‐bis(tert‐butyl)catechol (H2dbcat) furnishing the known pseudooctahedral complex VO(L)(dbcat). In the α form the V(L) fragment is planar and the VO3N2 coordination sphere is distorted trigonal bipyramidal (τ = 0.55) with the two oxo oxygen atoms and the azomethine nitrogen atom defining the trigonal plane. In β‐VO2(L) the V(L) moiety, like that in VO(L)(dbcat), is not planar but consists of two planar parts rotated away from each other along the C−N single bond. In this case the coordination sphere is distorted square pyramidal (τ = 0.20) with the three donor sites of the L ligand and an oxo oxygen atom defining the tetragonal plane. Both the α and β crystal lattices consist of dimers which associate further to form supramolecules. The noncovalent intradimer and interdimer bonding interactions are predominantly of aromatic π‐π stacking (aryl···pyridyl and pyridyl···pyridyl) and C−H···O hydrogen bonding (azomethine···oxo and aryl···phenolato) types in the α and β dimorphs, respectively. It is proposed that the low polarizability of methanol promotes π‐π stacking of planar V(L) fragments, resulting in crystallization of the α form. When the polarizability is relatively high, as in acetonitrile, the β form crystallizes. The geometrically isomeric coordination spheres of the α and β forms are sustained by the respective supramolecular architectures. The Schiff base HL′ of 2‐hydroxynapthaldehyde and 2‐picolylamine has also afforded two forms of VO2(L′) in the same manner as for VO2(L). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Ruthenium Tetraammines as a Model of Nitric Oxide Donor Compounds
Authors: Toledo José Carlos , Silva Hildo A. S. , Scarpellini Marciela , Mori Vânia , Camargo Ademir J. , Bertotti Mauro , Franco Douglas W. 
Published: March 2004

AbstractThe nitric oxide liberation fromtrans‐[Ru(NH3)4(L)(NO)]3+(where L = py, 4‐pic, isn, nic,L‐His, 4‐Clpy, imN) after one‐electron‐chemical or electrochemical reduction was investigated through spectroscopic and electrochemical techniques, reaction‐product analysis and quantum‐mechanic calculations. These complexes can be formally viewed as a RuII(NO+) species and the reduction site is located on the NO ligand. TheE° for thetrans‐[RuII(NH3)4(L)(NO+)]3+/trans‐[RuII(NH3)4(L)(NO)]2+redox process ranges from 0.072 V vs. NHE (nic) to −0.118 V vs. NHE (imN). The specific rate constants for NO dissociation fromtrans‐[RuII(NH3)4(L)(NO)]2+, evaluated through double‐step chronoamperometry, range from 0.025 s−1(nic) to 0.160 s−1(ImN) at 25 °C. The [RuIINO+/RuIINO0] redox potential and the specific rate constant (k‐NO),key steps for designing nitrosyl complexes as NO‐donor drug prototypes, proved to be controlled by a judicious choice of the ligand (L) trans to NO. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Methacrylate‐Substituted Titanium‐Yttrium Mixed‐Metal Oxo Clusters
Authors: Jupa Myhedin , Kickelbick Guido , Schubert Ulrich 
Published: March 2004

AbstractUpon reaction of titanium propoxide and yttrium 2‐methoxyethoxide with a sevenfold excess of methacrylic acid, three different mixed‐metal clusters were obtained, depending on the titanium to yttrium alkoxide ratio. Clusters of the type Ti4Y2(μ3‐O)4(μ2‐methacrylate)12(μ1‐methacrylate)2L2 (L = MeOCH2CH2OH or methacrylic acid), with two [TiO6] octahedra condensed to a zigzag chain of two [YO8] dodecahedra and two [TiO6] octahedra, were formed when the Ti/Y ratio in the precursor mixture was ⩾ 3.5. The structure of Ti4Y2O4(OMc)12(OCH2CH2OMe)2(McOH)2 obtained with a Ti/Y ratio of 2 in the precursor mixture, consists of a ring of four corner‐sharing [TiO6] octahedra to which two [YO8] dodecahedra are condensed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Strongly Nucleophilic RhI Centre in Square‐Planar Complexes with Terdentate (κ3) 2,2′:6′,2′′‐Terpyridine Ligands: Crystallographic, Electrochemical and Density Functional Theoretical Studies
Authors: de Pater Boke C. , Frühauf Hans‐Werner , Vrieze Kees , de Gelder René , Baerends Evert J. , McCormack Drew , Lutz Martin , Spek Anthony L. , Hartl František 
Published: March 2004

AbstractRhI‐terpyridine complexes have been unambiguously formed for the first time. The 2,2′:6′,2′′‐terpyridine (tpy), 4′‐chloro‐2,2′:6′,2′′‐terpyridine (4′‐Cl‐tpy) and 4′‐(tert‐butyldimethylsilyl‐ortho‐carboranyl)‐2,2′:6′,2′′‐terpyridine (carboranyl‐tpy) ligands were used for successful syntheses and characterisation of the corresponding RhI complexes with halide co‐ligands, [Rh(X)(4′‐Y‐terpyridine)] (X = Cl, Y = H, Cl, carboranyl; X = Br, Y = H). All four neutral Rh‐tpy complexes are square planar, with Rh−X bonds in the plane of the 4′‐Y‐terpyridine ligands. Full characterisation of these dark blue, highly air‐sensitive compounds was hampered by their poor solubility in various organic solvents. This is mainly due to the formation of π‐stacked aggregates, as evidenced by the crystal structure of [Rh(Cl)(tpy)]; in addition, [Rh(Cl)(carboranyl‐tpy)] merely forms discrete dimers. The (bonding) properties of the novel RhI‐terpyridine complexes have been studied with single‐crystal X‐ray diffraction, (time‐dependent) density functional theoretical (DFT) calculations, far‐infrared spectroscopy, electronic absorption spectroscopy and cyclic voltammetry. From DFT calculations, the HOMO of the studied RhI‐terpyridine complexes involves predominantly the metal centre, while the LUMO resides on the terpyridine ligand. Absorption bands of the studied complexes in the visible region (400−900 nm) can be assigned to MLCT and MLCT/XLCT transitions. The relatively low oxidation potentials of [Rh(X)(tpy)] (X = Cl, Br) point to a high electron density on the metal centre. This makes the RhI‐terpyridine complexes strongly nucleophilic and (potentially) highly reactive towards various (small) substrate molecules containing carbon−halide bonds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
A Series of Molybdenum(V) Complexes with the Oxalato Ligand Engaged in Different Binding Roles − An Unusual Staggered Conformation of the μ4‐Oxalate in [{Mo2O4(η2‐C2O4)2}2(μ4‐C2O4)]6−
Authors: Modec Barbara , Brenčič Jurij V. , Koller Jože 
Published: March 2004

AbstractSolvothermal reactions between mononuclear halooxomolybdates(V) and oxalic acid afforded smaller oligonuclear complexes with the oxalate ion engaged in different binding modes. The oxalate ion coordinates as a bidentate terminal ligand to each metal centre of the {Mo2O4}2+ unit to form the anion of (MeNC5H5)2[Mo2O4(η2‐C2O4)2py2] (1; py = pyridine; MeNC5H5+ = N‐methylpyridinium cation). (MeNC5H5)6[{Mo2O4(η2‐C2O4)2}2(μ4‐C2O4)] (2) with a tetradentate oxalate ion connecting two dinuclear subunits is a very rare example of a coordination compound with the oxalato ligand in a completely staggered conformation: the two CO2 entities of the μ4‐oxalate ion are rotated by 90° with respect to each other. Ab initio MO calculations on [{Mo2O4(η2‐C2O4)2}2(μ4‐C2O4)]6− revealed the isomer with the staggered conformation of the μ4‐oxalate ion to be of the lowest energy. The cyclic octanuclear anion of (MeNC5H5)2[Mo8O16(OMe)8(μ8‐C2O4)] (3) consists of four dinuclear subunits arranged around the central oxalate ion and additionally linked by pairs of methoxide bridges. Each oxygen atom of the oxalate ion bridges a pair of metal centres not connected by a metal−metal bond. The anionic part of [MeNC5H2(Me)3]2[HNC5H2(Me)3]2[Mo2O3(η2‐C2O4)4] (4) [MeNC5H2(Me)3+ = N‐methylcollidinium cation; HNC5H2(Me)3+ = protonated 2,4,6‐collidine] possesses an anti‐{Mo2O3}4+ structural fragment with a pair of bidentate oxalate ions coordinated to each molybdenum atom. The compounds were fully characterized by X‐ray structural analysis and infrared spectroscopy. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)