bluuebunny/crossref_metadata_2025 huggingface dataset:
Revisiting N‐continuous density‐functional theory: Chemical reactivity and “Atoms” in “Molecules”
Authors: Cohen Morrel H. , Wasserman Adam
Published: July 2004

We construct an internally‐consistent density‐functional theory valid for noninteger electron numbers N by precise definition of a density functional that is continuous in N. In this theory, charge transfer between the atoms of a heteronuclear diatomic molecule, which have been separated adiabatically to infinity, is avoided because the hardness for fractional occupation of a single HOMO spin‐orbital is negative. This N‐continuous density functional makes possible a variational theory of “atoms” in “molecules” that exactly decomposes the molecular electron density into a sum of contributions from its parts. The parts are treated as though isolated. That theory, in turn, gives a deep foundation to the chemical reactivity theory provided that the hardness of entities with vanishing spin density is positive, as argued to be the case here. This transition from negative to positive hardness closely parallels the transition from the Heitler‐London to the Hund‐Mulliken picture of molecular bonding.
Electronic coupling between molybdenum and tungsten quadruple bonds in molecular squares and extended chains linked by oxalate, acetylenedicarboxylate, and perfluoroterephthalate bridges
Authors: Bursten Bruce E. , Chisholm Malcolm H. , Hadad Christopher M. , Li Jun , Wilson Paul J.
Published: July 2004

The electronic structures of dicarboxylate‐bridged complexes containing dimolybdenum and ditungsten quadruple bonds have been investigated using density function theory (gradient corrected and time‐dependent), which reveals the consequences of strong mixing of M2 δ and oxalate π orbitals within extended chains and cyclic structures. Where the bridge is oxalate, acetylene dicarboxylate, and perfluoroterephthalate (PFT), the M2 centers are in all cases strongly coupled through M2 δ to bridge π‐conjugation. In the case of the chain compounds, this is strongly mediated by torsion angles along the chain. For the squares, only when the bridge is PFT is there a dependence on the orientation of the phenyl ring.
Chiral lewis acid‐catalyzed enantioselective michael reactions in water
Authors: Kobayashi Shū , Kakumoto Kentaro , Mori Yuichiro , Manabe Kei
Published: July 2004

Asymmetric Michael reactions of ß‐ketoesters with enones were effectively catalyzed by complexes of silver salts and BINAP derivatives in water. The reactions have proved to give Michael adducts in high yields with high enantioselectivities. These reactions are the first example of Lewis acid‐catalyzed asymmetric Michael reactions in water.
Hydrogen/deuterium exchange kinetics of cytochrome C: An electrospray ionization fast flow experiment
Authors: Geller Orit , Lifshitz Chava
Published: July 2004

New experiments are described in which the gas phase hydrogen/deuterium (H/D) exchange kinetics is studied for multiply‐protonated cytochrome c ions with +10 to +17 charges. The experimental technique involves electrospray ionization (ESI) combined with a fast‐flow method. Experimental results are presented including (1) average rate constants for H/D exchange, (2) overall decay kinetics of the reactant ion, and (3) sets of profiles for consecutive deuterium exchanges as a function of the flow rate of ND3 as the deuterating agent. The maximum number of exchanged hydrogen atoms and the exchange rate are observed to increase with increasing charge. The +13 state demonstrates special reactivity with a reactant ion decay constant of 2.5 × 10−9 cc/molecule's. Further insight into the H/D exchange mechanism is anticipated upon analysis of the data with a newly developed algorithm for extracting site‐specific rate constants from profiles for H/D exchange in gas phase protonated amino acids, their clusters, and peptides. The algorithm minimizes the mutual entropy or the Kullback‐Leibler information divergence between the observed concentrations and a chosen model.
An STM investigation of the adsorption of mixtures of fatty acids and substituted acids at the solution‐graphite interface
Authors: Yablon Dalia G. , Ertas Deniz , Fang Hongbin , Flynn George W.
Published: July 2004

Scanning tunneling microscopy (STM) is used to investigate the adsorption on graphite of two‐solute mixtures from phenyloctane solvent at room temperature. The first mixture is composed of the co‐solutes hexadecanoic acid (HA) and 2‐Br‐hexadecanoic acid (2BrHA), while the second mixture is composed of co‐solutes tetracosanoic acid (TA) and octadecanoic acid (OA). While the HA/2BrHA solution exhibits a miscible co‐adsorbed surface structure, the TA/OA solution reveals a quasi‐segregated surface structure where there is a sharp transition from full surface coverage by one solute to full coverage by the second as the composition of the solution mixture is varied. A one‐dimensional Ising model is used to model the adsorption behavior of both systems, and it is shown that both the HA/2BrHA and OA/TA mixtures correspond to two different limits of this model. The HA/2BrHA mixture exhibits similar, weak interactions between adsorbed molecules, corresponding to one limit of the Ising model, which also corresponds to competitive Langmuir adsorption. Another limit of the Ising model is reached when there are significantly different interactions between the different co‐adsorbates on the surface, a situation present in the OA/TA mixture resulting in a significantly different co‐adsorption behavior.
Synthesis of polycyclic polyfunctionalized carbocycles by a cobalt(I)‐initiated tandem diels–alder reaction sequence
Authors: Hilt Gerhard , Lüers Steffen , Polborn Kurt
Published: July 2004

The cobalt(I)‐catalyzed neutral Diels–Alder reaction of acyclic 1,3‐dienes with conjugated enynes can be used to generate secondary dihydroaromatic 1,4,8‐trienes containing a 1,3‐diene substructure, in good yields under mild reaction conditions. These 1,3‐dienes can be converted, with reactive dienophiles in a tandem normal Diels–Alder reaction, into polycyclic compounds. In a similar tandem Diels–Alder sequence, the cobalt‐catalyzed neutral homo Diels–Alder reaction of 2,5‐norbornadiene can be used to generate polycyclic cycloaddition adducts. A sequential triple Diels–Alder reaction sequence can be realized when norbornadiene is reacted with the excess of the conjugated enynes under cobalt(I) catalysis. In a homo Diels–Alder, neutral Diels–Alder, normal Diels–Alder reaction sequence, the intermediately formed adducts are reacted with activated dienophiles to yield polycyclic compounds in a short sequence. The structures of several products were established by X‐ray analysis. This showed that predominantly endo‐products are formed in the tandem reaction sequences, while the exo‐product becomes predominant in the triple Diels–Alder reaction sequence.
Quantum reaction dynamics and hyperspherical harmonics
Authors: Kuppermann Aron
Published: July 2004

This paper describes how large numbers of hyperspherical harmonics for triatomic and tetratomic systems, generated analytically by a computer algebra program, can be efficiently used to solve the time‐independent reactive scattering Schrödinger equation for triatomic and tetratomic systems in the strong interaction region of configuration space.
Theoretical studies of diiron(II) complexes that model features of the dioxygen‐activating centers in non‐heme diiron enzymes
Authors: Baik Mu‐Hyun , Lee Dongwhan , Friesner Richard A. , Lippard Stephen J.
Published: July 2004

We have applied high‐level Density Functional Theory to investigate the properties of recently characterized carboxylate‐bridged diiron(II) complexes supported by 2,6‐di(p‐tolyl)benzoate (ArTolCO2‐) ligands. These compounds, prepared as synthetic models for the reduced non‐heme diiron centers in the enzymes MMO, RNR‐R2, and Δ9D, reproduce the composition of the first coordination sphere ligands as well as the core geometry. The experimentally observed flexibility of the diiron cores in the model compounds, a main design target, was confirmed computationally. Details of a possible interconversion mechanism that transforms quadruply and doubly carboxylate‐bridged isomers of [Fe2(ArTolCO2)4L2], L = pyridine or related ligand, were examined. The orientation of the pyridine ligands plays a major role and promotes an initial carboxylate shift of the bridging carboxylate ligand that is orthogonal to the pyridine ring plane. Alternative mechanisms were explored and evaluated. Structural features of the strongly coupled diiron centers could only be reproduced reliably by using the experimentally determined antiferromagnetic spin‐coupling properties of the high‐spin d6 iron(II) centers. Use of the ferromagnetic‐coupling scheme gave rise to a poor correlation of the computed structure with the experiment. The broken‐symmetry orbitals required to describe the antiferromagnetic coupling are compared to the MOs as classical symmetry‐adapted linear combinations of atomic orbitals that form the basis for the magnetic coupling scheme. The molecular orbitals responsible for the dependence of the structural results on spin coupling were identified and used to evolve an intuitive explanation for the structural differences observed.
New efficient copper fluoride‐based catalyst for enantioselective hydrosilylation of ketones in aerobic conditions
Authors: Courmarcel James , Mostefaï Naouël , Sirol Sabine , Choppin Sabine , Riant Olivier
Published: July 2004

A new copper(II) fluoride–chiral diphosphines catalytic system was developed. This one is very efficient and selective for the hydrosilylation of several substituted or unsubstituted aromatic ketones in so far as moderate to excellent enantioselectivities were obtained. An oxygen acceleration effect was observed that led us to propose a practical protocol with a low amount of catalyst.
A family of thioxanthato ruthenium and osmium aryls
Authors: Chattopadhyay Swarup , Panda Bikash Kumar , Ghosh Kaushik , Chakravorty Animesh
Published: July 2004

The title complexes of type M(RL2)(PPh3)2(CO)(S2CSEt) (2a: M = Ru; 2b: M = Os) have been synthesized in excellent yields by reacting M(RL1)(PPh3)2(CO)X (1a: M = Ru, × = Cl; 1b: M = Os, × = Br) with potassium ethyl thioxanthate and have been characterized with the help of spectral and electrochemical data. The RL2 ligand in 2 is the imine‐phenol tautomer of N‐C6H4R(p)‐4‐methylsalicylaldimine (R = Me, MeO, Cl) coordinated at the carbanionic‐C2 atom only while RL1 in 1 is the iminium‐phenolato tautomer chelated via carbanionic‐C2 and phenolato‐O atoms. The synthetic reaction is thus attended with tautomerization of the Schiff base ligand. It is also associated with a rotation of the ligand by ˜180° around the M–C bond in order to exclude steric repulsion. These features have been revealed by structure determination of 2a (R = Me). The metallated aldimine ring is found to be highly noncoplanar (dihedral angle ˜40°) with the thioxanthate chelate ring due to steric repulsion originating from the relatively large size of the sulfur atom. This phenomenon, which is absent in both the precursor 1 (R = Me) and in the carboxylate analogue Ru(MeL2)(PPh3)2(CO)(O2CMe), 7, has distinctive effects on bond parameters of 2a (R = Me). Thus the two Ru–P bonds in 2a (R = Me) differ in length by as much as 0.06 Å. The thioxanthate 2 is thermodynamically more stable than the precursor 1 as well as the carboxylate 7. Accordingly, both of these are irreversibly transformed to 2a (R = Me) upon treatment with thioxanthate.
Toward new coordination environments and molecular architectures using F8BINOL, an electron‐poor isostere of BINOL
Authors: Pandiaraju Subramanian , Lough Alan , Yudin Andrei K.
Published: July 2004

Structural study of the Ti(OiPr)4/F8BINOL interaction demonstrates that F8BINOL, an isostere of BINOL with significant electronic perturbation, leads to novel complexes with cubic Ti4O4cores and bridging, rather than commonly observed chelating, arrangements of the diolate ligands.
Density‐dependent photochemical branching ratio in supercritical CO2: Photodissociation and isomerization of diiodomethane
Authors: Grimm Christian , Kling Matthias , Schroeder Jörg , Troe Jürgen , Zerbs Jochen , Schroeder Jörg , Troe Jürgen
Published: July 2004

The photodissociation of diiodomethane following excitation at 305 nm in supercritical CO2 was investigated by femtosecond pump‐probe absorption spectroscopy at pressures between 10 and 100 MPa. As in liquid solution, transient absorption signals in the wavelength range from 350 to 450 nm generally show an instantaneous peak, followed by a fast initial decay (200–300 fs) and a subsequent rise on a 10‐ps timescale. The initial fast decay time is found to be linearly dependent on viscosity, suggesting that dissociative motion on the repulsive surface is damped by solvent friction. Both amplitude and formation rate of the rising component, which is assigned to formation of iso‐diiodomethane within the solvent cage, increase with increasing pressure. Spectral narrowing of the transient absorption band indicates vibrational cooling of hot isomer by energy transfer to CO2 in about 20–40 ps. Immediately after excitation, this band shows absorption anisotropy for about 3 ps. The anisotropy decay rate increases from 3·1011 s−1 to 2·1012 s−1 as the pressure is lowered from 80 to 10 MPa. It is tentatively assigned to rotational relaxation of “hot” CH2I radicals generated in ultrafast photodissociation of the parent molecule. The observed density dependence of formation rate and relative yield of iso‐diiodomethane are described in terms of a simple kinetic model.
Remarkable asymmetric induction from remote stereocenters in conjugate addition chemistry for the synthesis of alkyl‐branched α, ω‐diaminoazelates
Authors: Cluzeau Jérôme , Lubell William D.
Published: July 2004

Conjugate addition of aryl Grignard reagents to (2S, 5E, 8S)‐di‐tert‐butyl 4‐oxo‐2,8‐bis‐[N‐(PhF)amino]non‐5‐enedioate (6, PhF = 9‐(9‐phenyl‐fluorenyl)) in THF proceeded with complete chemoselectivity and >9:1 stereoselectivity to provide predominantly (2S,6S,8S)‐6‐aryl 4‐oxo‐2,8‐diamino‐azelates7. In the presence of magnesium dibromide, diastereoselectivity in the addition of PhMgBr to enone6was improved to 15:1 in favor of the 6S‐isomer. Although lower chemoselectivity and stereoselectivity were obtained from the analogous reaction of6with isopropyl magnesium bromide in the absence of MgBr2, both were improved significantly when the addition reaction was performed in the presence of MgBr2. In contrast, the corresponding higher‐order cyanocuprates reacted with low diastereoselectivity on6by a 1,4‐addition pathway. In an attempt to identify the source of the high selectivity in the conjugate addition chemistry with6and Grignard reagents, the syntheses of enones12and13provided model systems in which one of the two amino carboxylate moieties of6was replaced by a branched alkyl substituent. Conjugate addition reactions on12and13demonstrated that chemoselectivity with Grignard reagents in the 1,4‐addition reaction was contingent on the presence of an amino carboxylate moiety near the ketone of the enone system. Furthermore, because diastereoselectivity with Grignard reagents was significantly lower in additions to amino enones12and13relative to diamino enone6, the presence of both amino carboxylate moieties has been highlighted as an important factor for remarkable asymmetric induction in the conjugate addition of Grignard reagents.
Enantioselective tandem formation and [2,3]‐sigmatropic rearrangement of cyclic propargylic oxonium ylides catalyzed by dirhodium(II) tetrakis[N‐phthaloyl‐(S)‐tert‐leucinate]
Authors: Tsutsui Hideyuki , Matsuura Maya , Makino Kazuishi , Nakamura Seiichi , Nakajima Makoto , Kitagaki Shinji , Hashimoto Shunichi
Published: July 2004

This paper describes the first examples of catalyst‐dependent asymmetric induction in the periselective [2,3]‐sigmatropic rearrangement of propargylic oxonium ylides generated by catalytic diazo decomposition. Catalysis of α‐diazo‐ß‐keto esters 4a—g using dirhodium(II) tetrakis[N‐phthaloyl‐(S)‐tert‐leucinate] in toluene has led to the virtually exclusive formation of benzofuran‐3‐ones bearing an allenic group with up to 79% ee.
Collapse of transmissivity in a triple barrier
Authors: Lefebvre Roland , Atabek Osman , Lefebvre Roland , Martin Manuel
Published: July 2004

One generally expects that the transmissivity through a symmetric arrangement of barriers and wells should go to unity when the energy of the incident particle coincides with a resonance energy of the system. It has been noticed before that for a symmetric triple barrier, there are conditions that lead to a merging of the two lowest unit transmissivity peaks, accompanied by a collapse of the transmissivity profile. This feature has been interpreted as meaning that there is a reduction of the number of resonances under these conditions. We reanalyze this situation with the help of a model that involves the same number of bound and continuum states, but which possesses an analytic solution. Because the transition probability in this case is expressed entirely in terms of resonance parameters (positions and widths), it is possible to calculate with the expression derived from the model a profile that agrees completely with that calculated with the transfer matrix method. The resonance parameters are obtained from the poles of the transition amplitude. This shows that the merging of the peaks and the collapse of the transmissivity occurs without a reduction in the number of resonances.
Light‐induced electron spin polarization in the ground state of water‐soluble copper porphyrins
Authors: Rozenshtein Vladimir , Berg Alexander , Levanon Haim , Krueger Uwe , Stehlik Dietmar , Kandrashkin Yuri , Van Der Est Art
Published: July 2004

Light‐induced spin‐polarized transient EPR spectra are reported for several water‐soluble copper porphyrins. The spectra are assigned to the doublet ground state, with emissive spin polarization resulting from photoexcitation and subsequent electronic relaxation. In contrast to other systems for which polarization of a doublet ground state has been observed, the exchange interactions in the copper porphyrins are strong and the geometry is fixed. It is proposed that intersystem crossing from the photoexcited trip‐doublet to the trip‐quartet state can lead to net polarization of the spin system and that this polarization is maintained during electronic decay, possibly via charge‐transfer and exciplex states. The intensity of the observed spin polarization is essentially independent of the molecular orientation in the external field, but is strongly dependent on the nature of the charged peripheral groups. Possible reasons for this behavior are discussed.
Experimental and DFT calculated structure of the diruthenium(2.5) complex [(Me3TACN)Ru(μ‐Cl)3Ru(Me3TACN)](PF6)2
Authors: Kaim Wolfgang , Titze Christoph , Klein Axel , Knödler Axel , Zalis Stanislav
Published: July 2004

The diruthenium(2.5) complex [(Me3TACN)Ru(μ‐Cl)3Ru(Me3TACN)]‐(PF6)2, Me3TACN = 1,4,7‐trimethyl‐1,4,7‐triazacyclononane, has been crystallized for structural characterization. The results are reproduced by density functional theory (DFT) calculations and confirm the sensitivity of the central Ru(μ‐Cl)3Ru core to contacts between the Cl bridging atoms and the co‐ligands. The singly occupied MO is characterized as a σ* MO involving the metal dz2 orbitals and a small halide contribution by DFT calculations and EPR.
Structure and bonding of ArClF: Intermolecular potential surface
Authors: Prosmiti Rita , Villarreal Pablo , Delgado‐Barrio Gerardo
Published: July 2004

The ground‐state potential surface of the Ar‐ClF complex is determined by restricted coupled‐cluster with single and double excitations and a noniterative perturbation treatment of triple excitation (RCCSD(T)) calculations, using augmented correlation consistent basis sets supplemented with an additional set of midbond functions. Three local minima are found for the Ar‐ClF, which correspond to linear Ar‐Cl‐F and Ar‐F‐Cl configurations and a near T‐shaped structure. The well depths and the equilibrium distances are 283.62 cm−1 at 3.84 Å and 128.96 cm−1 at 4.31 Å for the linear ones and 173.13 cm−1 at 3.58 Å for the one at θ = 107.5°.

Bound‐state calculations are carried out and the linear Ar‐Cl‐F structure is found to be the most stable one, in accordance with the experiment. Dissociation energies, intermolecular distances, and vibrational frequencies are computed and compared with available experimental data.
Temperature‐dependent nonlinear effects and catalyst evolution in the asymmetric addition of diethylzinc to benzaldehyde
Authors: Balsells Jaume , Costa Anna M. , Walsh Patrick J.
Published: July 2004

Several efficient and highly enantioselective titanium‐based catalysts promote the asymmetric addition of alkyl groups to aldehydes. The catalysts involved in these reactions have been found not to exhibit nonlinear behavior. We have been able to identify a series of chiral bis(sulfonamide)‐based titanium catalysts that do show nonlinear behavior. Monitoring of the product ee's (eep's) at different conversions and different temperatures has led us to propose that nonlinear behavior is caused by an autoinduction process rather than by catalyst aggregation. Evidence to support this hypothesis includes eep's that change with the extent of conversion. We have found that when enantiopure ligand was used, the eepincreases with conversion from 72% to 80%. However, use of non‐enantiopure ligand results in eep's thatdecreasewith conversion. These results are rationalized by different rates of alkoxide exchange processes between like and unlike titanium‐alkoxide containing complexes.
New electronic and magnetic properties of monolayers of thiols on gold
Authors: Carmeli Itai , Naaman Ron , Leitus Gregory , Reich Shimon , Vager Zeev
Published: July 2004

New electronic and magnetic properties are induced by the adsorption of close‐packed monolayers of thiols on gold. In layers made from chiral molecules, unexpectedly large electronic dichroism is observed, which manifests itself as spin‐specific electron transmission. For many thiolated molecules self‐assembled on gold, a surprisingly large ferromagnetism is observed. All the observations can be rationalized by assuming orbital ferromagnetism of the organic thin layer. This is a new type of magnetism, induced by the formation of a closed packed layer of organic molecules on metal. The adsorption results in charge transfer between the substrate and the adsorbed layer, which is the origin of this magnetism.
Enantioselective addition Of diketene to aldehydes promoted by chiral schiff base—titanium alkoxide complex. Application to asymmetric synthesis of potential inhibitors of HMG coenzyme reductase
Authors: Hayashi Masahiko , Yoshimoto Kazuya , Hirata Naohito , Tanaka Kiyoshi , Oguni Nobuki , Harada Katsumasa , Matsushita Akio , Kawachi Yasuhiro , Sasaki Hiroshi
Published: July 2004

Highly enantioselective addition of diketene to aldehydes was achieved by using novel Schiff base—titanium alkoxide complexes. Up to 92% ee of 5‐hydroxy‐3‐oxoesters was obtained. This procedure provides an efficient method for the asymmetric synthesis of potential inhibitors of HMG coenzyme reductase.
Ring expansion and isomerization in methyl indene and methylene indene radicals. Quantum chemical and transition‐state theory calculations
Authors: Dubnikova Faina , Lifshitz Assa
Published: July 2004

Ring expansion and isomerization in 1‐ and 2‐methylene indene radicals and isomerizations among the three isomers of methyl indene were studied by the Becke three‐parameter hybrid method with Lee‐Yang‐Parr correlation functional approximation (B3LYP). Structure, energy, and frequency calculations were carried out with the Dunning correlation consistent polarized doubleζ, (cc‐pVDZ) basis set. In contrast to methyl cyclopentadiene, transition states for ring expansion starting from the molecule methyl indene could not be located. The potential energy surfaces for ring expansion in methylene indene radicals consist of several intermediates and transition states and involve two principal pathways. One pathway is associated with cleavage of the five‐membered ring adjacent to the methylene group and formation of a six‐membered ring. In the second pathway, the transition states of the first stage consist of a newly‐formed three‐membered ring fused to the original cyclopentadiene ring. In all cases, the reaction pathways leading to ring expansion include an intermediate that, via an additional transition state, produces an α‐ or (β‐hydronaphthalene radical. The latter, by a fast H‐atom ejection, forms naphthalene. The structure, energetics, and additional parameters on the potential energy surfaces are shown. Several transition states and intermediates are common to both ring expansion and isomerization, so that there are competing parallel pathways that determine the final distribution among the isomerization and ring expansion products. Potential energy surfaces for interisomerization among the various isomers of methyl indene were calculated, and several reaction pathways were suggested.
DIOS‐MSEED: A chip‐based method for measurement of enantiomeric excess by kinetic resolution/mass spectrometry
Authors: Shen Zhouxin , Yao Sulan , Crowell John E. , Siuzdak Gary , Finn M. G.
Published: July 2004

The determination of enantiomeric excess by kinetic resolution mass spectrometry has been implemented with the Desorption/Ionization On Silicon (DIOS) MS technique. Measurements can thereby be made much more rapidly than was previously possible, bringing this general methodology for screening asymmetric catalysts closer to true high‐throughput status.
On the collapse and restoration of condensates in n dimensions in the mean‐field approximation
Authors: Cederbaum Lorenz S. , Moiseyev Nimrod , Cederbaum Lorenz S. , Moiseyev Nimrod
Published: July 2004

The mean‐field equation of N bosons in an external potential interacting via a short‐range δ‐function potential is studied. This equation is formally equivalent to the nonlinear Schrödinger equation. Virial theorems are derived and the number of possible solutions is investigated for various dimensions n. The unboundedness from below of the underlying mean‐field operator for attractive nonlinearity and the related collapse of the wave function are studied in n dimensions. Within the symmetry preserving mean‐field approximation, an ansatz to avoid the collapse by modifying the spherically symmetric external potential is discussed and analyzed. Other suggestions to stabilize the mean‐field condensate are briefly mentioned. Illustrative numerical examples of the collapse and its restoration are given. Detailed conclusions are drawn.
Reaction of Aryl Iodides with (PCP)Pd(II)—Alkyl and Aryl Complexes: Mechanistic Aspects of Carbon—Carbon Bond Formation
Authors: Kraatz Heinz‐Bernhard , van der Boom Milko E. , Ben‐David Yehoshoa , Milstein David
Published: July 2004

The reaction of the PCP‐type complex Pd(Me){2,6‐(iPr2PCH2)2C6H3}(3) with phenyl iodide results in the formation of Pd(I){2,6‐(iPr2PCH2)2C6H3} (5), methyl iodide, toluene, and biphenyl. Formation of Pd(Ph){2,6‐(iPr2PCH2)2C6H3}(4) is observed during the reaction by 31P NMR. Reaction of 4 with aryl iodides results in the formation of 5 and Ph–Ph, Ph–Ar, and Ar–Ar, products indicative of a radical reaction. Under pseudo‐first‐order conditions, the rates of the reactions follow the order p‐OMe > p‐Me > H > p‐NO2 > m‐Cl. The reaction is likely to involve electron transfer from 4 to the aryl iodide followed by fast decomposition of a postulated radical cation [Pd(Ph){2,6‐(iPr2PCH2)2C6H3}]+. (4+.) to give a phenyl radical and [Pd{2,6‐(iPr2PCH2)2C6H3}]+ (6+). Facile decomposition of the aryl iodide radical anion generates an aryl radical and I−. Recombination of aryl radicals gives rise to mixed biaryls, and 6+ combines with I− to give 5.
Syntheses of inherently chiral monosulfinyltrithiacalix[4]arenes by the oxidation of one of the bridging sulfurs of a tetrathiacalix[4]arene fixed in the 1,3‐alternate conformation
Authors: Morohashi Naoya , Naito Ryoichiro , Iki Nobuhiko , Miyano Sotaro
Published: July 2004

A new synthetic strategy for the construction of an inherently chiral, sulfur‐bridged calix[4]arene molecular framework was presented by oxidation of one of the four epithio bonds of a tetrathiacalix[4]arene derivative of 1,3‐alternate conformation: Tetra(carboxymethyl) ether of p‐tert‐butyltetrathiacalix[4]arene of 1,3‐alternate conformation (7) was converted to the tetra(l‐menthoxycarbonylmethyl) ether (8). Oxidation of the tetra l‐menthyl ester 8 by treatment with NaBO3 (1.1 molar equiv.) afforded a pair of diastereomers of the monosulfinyl derivatives (9) in 58% yield, which were readily separable by silica‐gel column chromatography. Removal of the l‐menthyl moieties followed by methyl esterification gave enantiomerically pure samples of inherently chiral (‐)‐ and (+)‐monosulfinyltrithiacalix[4]arene derivatives ((‐)‐10 and (+)‐10) in 62 and 56% yield, respectively.
Photochemical applications of phase‐modulus interdependencies
Authors: Englman Robert , Englman Robert , Yahalom Asher
Published: July 2004

After an accolade to Joshua Jortner, we trace the influences of his chemistry background in his physics writings. On the way, we note the richness of physics in principles (or large‐scale laws) and the fact‐orientedness of chemistry.

Next we turn to a recent laser‐induced electron‐detachment experiment and utilize analytic properties of the developing wave packet in the (complex) time domain, studied by us previously, to relate the phase of the optimized laser field to its intensity. It is suggested that these results can be used to reduce the labor of pulse optimization in phase‐intensity controlled reaction dynamics. Phase‐intensity inter‐dependencies are also established in simulated results (obtained with the electron nuclear dynamics END‐algorithm) for photoexcited hydrogen molecules.
1,2‐Bond shift of the Fe(CO)3 moiety in the 1,5‐O‐heterocyclization of (1,3‐dienyl)‐tricarbonyliron diols: Application to the synthesis of novel phosphocholines
Authors: Braun Alain , Lellouche Jean‐Paul (Moshe)
Published: July 2004

A novel concept of intramolecular cationic 1,5‐O‐heterocyclization of ψ‐exo‐/ψ‐endo‐(1,3‐dienyl)tricarbonyliron diols has been demonstrated to occur under acid catalysis with a quite unusual 1,2‐migration of the complexation site. This cationic cyclization has been shown to be stereoselective when involving homochiral precursor diols. It allowed straightforward access to new racemic and optically active conformationally locked alkylphosphocholines as potential anticancer agents.
Surface tension from molecular dynamics simulation: Adsorption at the gas‐liquid interface
Authors: Mucha Martin , Hrobárik Tomáš , Jungwirth Pavel
Published: July 2004

The gas‐liquid interface of binary mixtures of argon and krypton is investigated using molecular dynamics simulations. Surface tension and local pressure profiles are extracted from the simulations and cast into individual molecular contributions. The surface excess of argon is rationalized in terms of the relative strength of van der Waals interactions.
Asymmetric synthesis of the (2S,4S,6S)‐2,4,6‐trimethylnonyl subunit of siphonarienes
Authors: Diaz David D. , Crisóstomo Fernando R. P. , Martín Víctor S.
Published: July 2004

The paper describes an asymmetric approach to the synthesis of the (2S,4S,6S)‐2,4,6‐trimethylnonyl segment of siphonarienes. The key step used is a newly developed methodology to obtain sec‐dialkyl acetylenes based on the intramolecular hydride transfer from a secondary γ‐benzyloxy group with well‐defined absolute stereochemistry, ensured by a Sharpless asymmetric epoxidation reaction, to a cation generated by Lewis acid treatment of a tertiary Co2(CO)6‐complexed propargylic alcohol.
Planar chiral ferrocenes as ligands in the vanadium‐catalyzed asymmetric epoxidation of allylic alcohols
Authors: Bolm Carsten , Kühn Toralf
Published: July 2004

Starting from either (S)‐4‐tert‐butyl‐2‐ferrocenyl‐2‐oxazoline or (S)‐S‐ferrocenyl‐S‐4‐tolyl sulfoxide, new planar chiral hydroxamic acids have been synthesized employing the directed ortho‐metalation strategy. The ferrocene‐derived hydroxamic acids are capable of serving as ligands in the vanadium‐catalyzed asymmetric epoxidation of allylic alcohols, furnishing the epoxide of 2‐methyl‐3‐phenylprop‐2‐en‐1‐ol with up to 34% ee.
Storied selves: A Critical Discourse Analysis of adult learners' literate lives
Authors: ROGERS REBECCA
Published: July 2004

ABSTRACTS

Adults bring with them a wealth of literate experiences into adult education classrooms. And yet, they and the programs they enter often do not see such experiences as significant to their learning. This is surprising because it is often in the out‐of‐school experiences where the adults demonstrate the greatest sense of agency and ability with literacy. To date, there are no systematic studies of the relationship between literate subjectivities and contexts in the adult education literature.

An interview study was conducted with 15 adult literacy students enrolled in Adult Education and Literacy (Adult Basic Education [ABE] and General Education Degree [GED]) programs in a Midwestern city, to answer the question: What is the relationship between literate identity and contexts for adults enrolled in literacy programs? The interviews were divided into three domains: past and present school experiences, home and community literacy practices, and involvement with children's education. This article analyzes the interviews using Critical Discourse Analysis and documents the linguistic markers the adults used in each domain, the shifts across domains, and the relationships between and among adults.

To foreshadow the conclusions, adults' ideas about learning and literacy shifted across the contexts. Further, their sense of self shifted with changes in the Discourses of learning and literacy. Three themes emerged from the interviews, and I describethe linguistic changes in literate self across the three domains. This research has implications for developing models of learning in adult education that take into account the learning and literacy experiences adults bring with them into their programs.
Susceptibility of SiO2, ZrO2, and HfO2dielectrics to moisture contamination
Authors: Raghu Prashant , Yim Chris , Shadman Farhang , Shero Eric
Published: July 2004

Moisture contamination of HfO2and ZrO2ultrathin dielectric films, deposited by atomic layer chemical vapor deposition (ALCVD™), is investigated and compared to that of native SiO2. Results show that HfO2and ZrO2surfaces adsorb higher amounts of moisture and bind moisture more strongly than SiO2surfaces. A multilayer model is developed to represent the dynamics of moisture interaction with these three oxides. Using this model, the fundamental kinetic parameters are determined. The adsorption rate constants are of the same order of magnitude for all three surfaces. However, the desorption rate constants for ZrO2and HfO2are almost three orders of magnitude lower than that for SiO2. Activation energies for desorption of water molecules from the first two layers are 33, 27, and 19 kJ/mol, for ZrO2, HfO2, and SiO2, respectively. Results obtained in this study suggest that the HfO2and ZrO2, as the new dielectric materials, are more prone to moisture contamination than SiO2. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1881–1888, 2004
Extended robust model predictive control
Authors: Odloak D.
Published: July 2004

The model predictive control (MPC) of stable linear systems with model uncertainty is addressed. A strategy is proposed to extend existing robust controllers that were developed for the regulator problem, to the general case in which the system equilibrium point is unknown. Nominal stability is obtained with the consideration of an infinite output horizon. The method is based on a state‐space model formulation that allows a straightforward solution to the Lyapunov equation. The method is detailed for two particular controllers of the robust MPC literature. Simulation examples illustrate the performance of the proposed approach and demonstrate that it can be implemented in real applications. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1824–1836, 2004
Pulsed dielectric barrier discharge reactor for diesel particulate matter removal
Authors: Yao S. , Okumoto M. , Madokoro K. , Yashima T. , Suzuki E.
Published: July 2004

A dielectric barrier discharge (DBD) reactor, driven by a pulsed corona surface discharge (PCSD), was developed for the removal of particulate matter (PM) in an undiluted exhaust gas of a diesel engine. The DBD reactor consisted mainly of alumina (Al2O3) plates and metal meshes covered on the surfaces of Al2O3 plates. The PCSD was carried out with a pulse power supply at atmospheric pressure and the temperature of exhaust gases. The energy efficiency for PM removal was 26.5 μg/J at maximum and 1 μg/J with 42% PM removal. The construction of the DBD reactor that promoted PM deposition on Al2O3 surfaces improved energy efficiency. The constants in PM removal model were given. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1901–1907, 2004
Energy‐based targets for multiple‐feed distillation columns
Authors: Bandyopadhyay Santanu , Mishra Mayank , Shenoy Uday V.
Published: July 2004

Invariant rectifying–stripping (IRS) curves are presented for energy analysis of distillation processes. The IRS curves are invariant to the column configuration (that is, feed location and total number of stages) and depend only on the separation problem and the operating pressure of the column. IRS curves are useful to set targets without performing multiple simulation studies. A novel method is proposed to extend the IRS curves, originally developed for simple distillation columns (with single feed and two end products), to complex multiple‐feed columns. In the proposed method, a column with n feeds is decomposed into n simple single‐feed columns. The IRS curves are generated for these simple columns and the order and location of the feeds are targeted. Then these IRS curves are added in distinct sections demarcated by the feed points to the column to obtain the composite IRS curves for the complex column. Various targets such as minimum energy requirements (that is, minimum condenser and reboiler loads), appropriate feed locations, proper order of feeds, and effect of premixing feeds can be targeted from the composite IRS curves. Thus, the composite IRS curves for complex columns retain all the advantages of the IRS curves established for the case of simple distillation columns. General guidelines are also proposed for appropriate feed preconditioning and side‐exchanger duties leading to the design of energy‐efficient complex distillation processes. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1837–1853, 2004
Instrumentation network design and upgrade for process monitoring and fault detection
Authors: Bagajewicz Miguel , Fuxman Adrian , Uribe Ariel
Published: July 2004

A mixed‐integer linear programming formulation for the design of sensor networks for simultaneous process monitoring and fault detection/resolution is presented. The objective is to find a cost‐optimal sensor set for a chemical process that provides a good estimate of the state of the system and detects as well as locate a preestablished set of faults. A continuously stirred tank reactor example is provided and extensions are discussed. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1870–1880, 2004
Brain structure variation in great apes, with attention to the mountain gorilla (Gorilla beringei beringei)
Authors: Sherwood Chet C. , Cranfield Michael R. , Mehlman Patrick T. , Lilly Alecia A. , Garbe Jo Anne L. , Whittier Christopher A. , Nutter Felicia B. , Rein Thomas R. , Bruner Harlan J. , Holloway Ralph L. , Tang Cheuk. Y. , Naidich Thomas P. , Delman Bradley N. , Steklis H. Dieter , Erwin Joseph M. , Hof Patrick R.
Published: July 2004

This report presents data regarding the brain structure of mountain gorillas (Gorilla beringei beringei) in comparison with other great apes. Magnetic resonance (MR) images of three mountain gorilla brains were obtained with a 3T scanner, and the volume of major neuroanatomical structures (neocortical gray matter, hippocampus, thalamus, striatum, and cerebellum) was measured. These data were included with our existing database that includes 23 chimpanzees, three western lowland gorillas, and six orang‐utans. We defined a multidimensional space by calculating the principal components (PCs) from the correlation matrix of brain structure fractions in the well‐represented sample of chimpanzees. We then plotted data from all of the taxa in this space to examine phyletic variation in neural organization. Most of the variance in mountain gorillas, as well as other great apes, was contained within the chimpanzee range along the first two PCs, which accounted for 61.73% of the total variance. Thus, the majority of interspecific variation in brain structure observed among these ape taxa was no greater than the within‐species variation seen in chimpanzees. The loadings on PCs indicated that the brain structure of great apes differs among taxa mostly in the relative sizes of the striatum, cerebellum, and hippocampus. These findings suggest possible functional differences among taxa in terms of neural adaptations for ecological and locomotor capacities. Importantly, these results fill a critical gap in current knowledge regarding great ape neuroanatomical diversity. Am. J. Primatol. 63:149–164, 2004. © 2004 Wiley‐Liss, Inc.
Seasonal variations in the activity budget of Japanese macaques in the coniferous forest of Yakushima: Effects of food and temperature
Authors: Hanya Goro
Published: July 2004

Seasonal variations in the activity budget of Japanese macaques in the coniferous forest of Yakushima were studied over the course of 1 year. On an annual basis, they spent 38% of the daytime feeding, 16% traveling, 14% in social interactions, and 32% engaged in resting. The effects of temperature and food‐related factors (i.e., food distribution, feeding speed, and food abundance) on the seasonal variations of activity budget were examined by stepwise multiple regression analysis. When the temperature was low, the macaques decreased traveling and feeding time, in accordance with the prediction that endothermal animals save energy under severe thermoregulatory cost. When the feeding speed of available foods was slow, they spent more time feeding. When high‐quality foods were abundant, they decreased feeding time. These macaques did not respond to fluctuations in food distribution. The present results indicate the importance of temperature, in addition to food‐related factors, as a determinant of activity budgets. Am. J. Primatol. 63:165–177, 2004. © 2004 Wiley‐Liss, Inc.
Role of magnetic resonance imaging within diagnostic criteria for multiple sclerosis
Authors: Miller D. H. , Filippi M. , Fazekas F. , Frederiksen J. L. , Matthews P. M. , Montalban X. , Polman C. H.
Published: July 2004

The diagnosis of multiple sclerosis (MS) has been improved in recent decades with the incorporation of paraclinical investigations in diagnostic workup. In the last 15 years, magnetic resonance imaging (MRI) has become an especially valuable tool for supporting MS diagnosis, and specific imaging criteria became fundamental to the guidelines for the diagnosis of MS published in 2001 by an international panel (IP). The new IP criteria include MRI evidence of dissemination in space and time, making it possible to diagnose MS after a single clinical episode. This review considers current evidence concerning the reliability of the new IP criteria for the diagnosis of relapsing‐onset MS, discusses strengths and weaknesses of the criteria, and outlines areas which may need modification or should be the focus of future research directed toward improving diagnostic accuracy. It also makes practical recommendations when using MRI and the IP criteria in MS diagnosis, especially in patients with clinically isolated syndromes or atypical presentations. The IP criteria are timely and concrete and introduce an important concept to MS diagnosis. Future modifications, based on emerging evidence, should further facilitate their implementation and improve their accuracy. Ann Neurol 2004.
Designing Web portals in intergenerational teams: Two prototype portals for elementary school students
Authors: Large Andrew , Beheshti Jamshid , Nesset Valerie , Bowler Leanne
Published: July 2004

This article describes and discusses the detailed procedures followed by two intergenerational teams comprising the researchers and a group of eight grade‐six elementary students (ages 11 to 12 years) and a group of six third‐grade elementary students (ages 8 to 9 years), respectively, in designing two prototype Web portals intended for use by elementary school students. These procedures were based on three design theories: Contextual Inquiry, Participatory Design, and Cooperative Inquiry. The article also presents and describes the two resulting Web portal prototypes and discusses the design criteria employed by the teams. Conclusions are elaborated on the basis of this research experience regarding how such a design process should be conducted in the context of an intergenerational team, and what characteristics young users expect to find in Web portals that they will use to support their informational needs in terms of elementary school projects and assignments.
Creativity and convergence in information science research: The roles of objectivity and subjectivity, constraint, and control
Authors: Ford Nigel
Published: July 2004

Objectivity, in the form of the application of external scrutiny according to standards agreed within a research community, is an essential characteristic of information science research whether pursued from positivist, interpretative, or action research perspectives. Subjectivity may represent both a legitimate focus of research (e.g., people's perceptions and attitudes) and a legitimate component of methodology (e.g., enabling researchers to enter, experience, and share the perceived worlds of their subjects). However, subjectivity that both (a) is not open to external scrutiny and (b) gives rise to contingent dependencies is problematic for research. The issue of problematic types of subjectivity is considered, and the contributions to the debate concerning possible solutions of two key thinkers—the cybernetician Gordon Pask and the methodological philosopher Brenda Dervin—are discussed. The need identified by Dervin for researchers to be able to escape (expose and test) their own assumptions is explored in terms of a dynamic interplay between relatively subjective and objective forces, each requiring the liberating and constraining energies of the other. The extent to which meta‐methodological awareness—a prerequisite for any such escape—can be fostered, for example, by the quality of research environments, is explored along with implications for those responsible for managing and funding research.
Training for Web search: Will it get you in shape?
Authors: Lucas Wendy , Topi Heikki
Published: July 2004

Given that time is money, Web searching can be a very expensive proposition. Even with the best search technology, the usefulness of search results depends on the searcher's ability to use that technology effectively. In an effort to improve this ability, our research investigates the effects of logic training, interface training, and the type of search interface on the search process. In a study with 145 participants, we found that even limited training in basic Boolean logic improved performance with a simple search interface. Surprisingly, for users of an interface that assisted them in forming syntactically correct Boolean queries, performance was negatively affected by logic training and unaffected by interface training. Use of the assisted interface itself, however, resulted in strong improvements in performance over use of the simple interface. In addition to being useful for search engine providers, these findings are important for all companies that rely heavily on search for critical aspects of their operations, in that they demonstrate simple means by which the search experience can be improved for their employees and customers.