bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diffusion‐Weighted MRI and Response to Anti‐Cancer Therapies
Authors: Galons Jean Philippe , Morse David L. , Jennings Dominique R. , Gillies Robert J. 
Published: April 2004

AbstractIn oncology practice, longitudinal studies are routinely conducted to monitor the size and enhancement of tumors in cancer patients undergoing therapy. Imaging protocols typically use gadolinium‐enhanced T1‐weighted images or T2‐weighted images from which tumor size is inferred and tumor response estimated. The past few years have also seen the emergence of diffusion‐weighted magnetic resonance imaging (DWMRI) as a potential alternative to monitor therapeutic response (Kauppinen, R.A., NMR Biomed. 2002, 15, 6). The attractiveness of DWMRI resides in its ability to detect local microstructural changes associated with treatment long before their effects are translated into effective size changes. Damage to cell membrane integrity, changes in viscosity, and/or relative size of intra‐ vs. extracellular compartments all translate into changes in the apparent diffusion coefficient of tumor water measured by DWMRI. This dependence makes DWMRI a particularly sensitive method to detect response to a wide variety of chemotherapeutic agents. This review will focus on the emerging role of DWMRI to monitor the response of tumors to anti‐cancer chemotherapies.
Generalized Diffusion Tensor Imaging (GDTI): A Method for Characterizing and Imaging Diffusion Anisotropy Caused by Non‐Gaussian Diffusion
Authors: Liu Chunlei , Bammer Roland , Moseley Michael E. 
Published: April 2004

AbstractFor non‐Gaussian distributed random displacement, which is common in restricted diffusion, a second‐order diffusion tensor is incapable of fully characterizing the diffusion process. The insufficiency of a second‐order tensor is evident in the limited capability of diffusion tensor imaging (DTI) in resolving multiple fiber orientations within one voxel of human white matter. A generalized diffusion tensor imaging (GDTI) method was recently proposed to solve this problem by generalizing Fick's law to a higher‐order partial differential equation (PDE). The relationship between the higher‐order tensor coefficients of the PDE and the higher‐order cumulants of the random displacement can be derived. The statistical property of the diffusion process was fully characterized via the higher‐order tensor coefficients by reconstructing the probability density function (PDF) of the molecular random displacement. Those higher‐order tensor coefficients can be measured using conventional diffusion‐weighted imaging or spectroscopy techniques. Simulations demonstrated that this method was capable of quantitatively characterizing non‐Gaussian diffusion and accurately resolving multiple fiber orientations. It can be shown that this method is consistent with the q‐space approach. The second‐order approximation of GDTI was shown to be DTI.
A Density Functional Study of Ethylene Insertion into the M‐methyl (M = Ti, Zr) Bond for Different Catalysts, with a QM/MM Model for the Counterion, B(C6F5)3CH3−
Authors: Vanka Kumar , Xu Zhitao , Ziegler Tom 
Published: April 2004

AbstractSingle site homogeneous catalysts have been studied extensively in recent years as alternatives to traditional heterogeneous catalysts. The current theoretical study uses density functional theory to study the insertion process of the ethylene monomer into the titanium‐carbon chain for contact ion‐pair systems of the type [L1L2TiCH3‐μ‐CH3‐B(C6F5)3], where L1, L2, are Cp, NPH3, and other ligands. Different modes of approach cis and trans to the μ‐CH3 bridge were considered. The counterion, B(C6F5)3CH3−, was modeled by QM/MM methods. The value of ΔHtot—the total barrier to insertion—was found to be positive (in the range of 4–15 kcal/mol). The ability of the ancillary ligands, L1 and L2, to stabilize the ion‐pair was found to be an important factor in determining the value of δHtot. On replacing the titanium metal center with zirconium, the ΔHtot values were found to be lowered (in the range of 2–9 kcal/mol), indicating that they would be better catalysts than their titanium analogues. The size of the ligands L1 and L2 was increased by replacing hydrogens in the ligands with tertiary butyl groups. The value of ΔHtot was found to increase (in the range of 10–28 kcal/mol) in contrast to the simple systems, for both the cis and trans cases of approach, with the cis mode of approach giving lower values of ΔHtot. Solvent effects were incorporated with cyclohexane (ε = 2.023) as the solvent, and were found to have a minor influence, ±(0.5–1.5) kcal/mol) on the insertion barrier for all the cases studied.
Binding of cadmium, copper, and zinc to humic substances originating from municipal solid waste compost
Authors: Kaschl Arno , Römheld Volker , Chen Yona 
Published: April 2004

AbstractThe application of municipal solid waste (MSW) compost increases both the trace metal loading and the organic matter in the soil. To characterize the quality and metal‐binding capacity of the compost OM, we extracted humic acid (HA) and fulvic acid (FA) from mature MSW compost and analyzed them for elemental composition, acid‐titratable functional groups, total metal content, and structural components (by 13C NMR). HA constituted 67% of all extracted humic substances and differed significantly from HAs of cultivated lands: The compost HA exhibited smaller molecular size, a higher N content, and lower aromaticity due to large amounts of saturated aliphatic components. Metal complexation studies of the extracted HA and FA were performed by equilibrium dialysis titration. The complexing capacity (CC) was highest for Cu: CCHA = 3357 and CCFA = 5221 μmol Cu g−1 of dissolved organic carbon (DOC) at pH 5. Zn and Cd were bound (at pH 7) in smaller concentrations: CCHA(Zn) = 2167, CCFA(Zn) = 2809, CCHA(Cd) = 2386, and CCFA(Cd) = 2468 μmol metal g−1 of DOC. Stability constants for binding on the strongest sites (pKint) were determined as pKintHA = 6.6 and pKintFA = 7.3 for Cu at pH 5; and pKintHA = 8.0 and pKintFA = 6.4 for Cd at pH 7. Since these measured parameters fall within the ranges of values obtained for soil humic substances, we conclude that in soils with little organic matter, compost addition will significantly increase the amount of highly reactive organic complexing agents for trace metals in the soil.
Formation and reactions of cluster ions from aromatic carboxylic acids together with amino acids
Authors: Meffert Anja , Grotemeyer Jürgen 
Published: April 2004

AbstractThe cluster formation of several aromatic carboxylic acids, ferulic acid, vanillic acid, sinapinic acid, and 3,4‐dihydroxybenzoic acid was investigated by means of laser desorption into a supersonic beam followed by multiphoton ionization‐time‐of‐flight mass spectrometry. The formation of not only homogeneous clusters, but also of heterogeneous clusters with some small amino acids was studied. The different neutral clusters formed in the supersonic expansion were ionized by a multiphoton process employing either nano‐ or femtosecond laser pulses.Strong differences in the detection of cluster ions due to the laser pulse length employed for multiphoton ionization were observed. Only femtosecond activation led to mass spectra with intense signals of the cluster ions. In addition, in the case of femtosecond ionization, protonated amino acids were detected in the mass spectra. As direct ionization of the free amino acids is not possible under the chosen ionization conditions because they lack an adequate chromophore, these protonated amino acids are assumed to be formed via an intracluster proton transfer in the heterogeneous dimer and subsequent decay of the ionized cluster (dissociative proton transfer). Such well‐known processes for heterogeneous clusters consisting of a substituted aromatic molecule and small polar solvent molecules may be involved in the matrixassisted laser desorption ionization (MALDI) process.
Thermal effects in the ultrafast photoinduced electron transfer from a molecular donor anchored to a semiconductor acceptor
Authors: Stier William , Prezhdo Oleg V. 
Published: April 2004

AbstractA nonadiabatic molecular dynamics (MD) simulation of the photoinduced electron transfer (ET) from a molecular electron donor to the TiO2 semiconductor acceptor is carried out in a microcanonical ensemble with an average temperature of 350 K. The electronic structure of the dye–semiconductor system and the adiabatic dynamics are simulated by ab initio MD, while the nonadiabatic (NA) effects are incorporated by a quantum‐classical mean‐field approach. The ET dynamics are driven by thermal fluctuations that dominate ionic motions at the simulated temperature. The ground and excited state ion dynamics are similar; therefore, the change in the quantum force due to the electronic photoexcitation can be neglected, and the analysis is greatly simplified. The simulated ET occurs on a 5‐fs timescale, in agreement with recent ultrafast experimental data. Vibrational motions of the chromophore ring carbons induce an oscillation of the photoexcited state energy, resulting in a bimodal distribution of the initial conditions for ET. At low energies the photoexcited state is localized primarily on the chromophore, while at high energies the photoexcited state is substantially delocalized into the TiO2 surface. Thermally driven adiabatic transfer is the dominant ET mechanism. Compared to the earlier simulation at 50 K, the rate of NA transfer at 350 K remains almost unchanged, whereas the rate of adiabatic ET increases substantially.
Printed organic transistors and molded plastic lasers
Authors: Rogers John A. , Tate Jennifer , Li Wenjie , Bao Zhenan , Dodabalapur Ananth 
Published: April 2004

AbstractWe describe the use of microcontact printing and elastomeric molding for fabricating two types of devices that incorporate thin films of active organic materials: thin film transistors and plastic lasers. The simplicity of these techniques and the good performance of devices formed with them suggest their potential utility for emerging applications of organic materials in electronic and optical systems.
Mass‐independent isotope effects and their use in understanding natural processes
Authors: Thiemens Mark H. 
Published: April 2004

AbstractIn 1983, Thiemens and Heidenreich (Science 219, 1073) reported the discovery of a mass‐independent isotope process in oxygen. Subsequently, mass‐independent isotopic compositions were observed in meteorites, atmospheric O2, CO2, O3, H2O2, CO, N2O, and aerosol sulfate and nitrate. In addition, solid samples from the Namibian Desert, Antarctic dry valleys, Miocene volcanic ash, and Death Valley varnishes all possess mass‐independent isotopic compositions that have permitted new scientific insights to be obtained. Sulfur mass‐independent isotopic anomalies in Precambrian samples have provided a completely new mechanism to track atmospheric O2 levels and the evolution of life from ∼3.9 to 2.2 × 109 years ago. Measurements of mass‐independent isotopic compositions in Martian meteoritic sulfates and carbonates have also provided new information on Martian atmosphere‐regolith interactions and history.In sum, the use of mass‐independent isotopic compositions has advanced a wide range of geo‐ and cosmo‐chemical frontiers. In addition, these newly discovered effects have provided a new means to probe the chemical physics of molecular transition state theory.
Surface Model for Gas‐Phase Polymerizations of Ethylene and Propylene Using Supported Metallocene/Methylalumoxane Catalysts
Authors: Kaminsky Walter , Lemstra Piet J. , Loos Joachim , Müller Fabian , Niemantsverdriet J.W. (Hans) , Thüne Peter C. , Weingarten Ulrich 
Published: April 2004

AbstractIn order to obtain more detailed information about supported metallocene/methylaluminoxane catalysts, two catalysts are supported onto a flat silicon wafer by spincoating impregnation. These model catalysts are characterized by SEM and EDX showing a film of metallocene catalyst dispersed inside the methylaluminoxane matrix, as well as regions of a localized increased concentration of the catalyst. Applying these model catalysts in a gas‐phase polymerization reactor results in rather homogeneous films of polyethylene and polypropylene, respectively. In addition, crater‐like and spherical polymer structures can be observed, probably formed by inhomogeneous catalyst distribution.
Syndiospecific Living Catalysts for Propylene Polymerization: Effect of Fluorination on Activity, Stereoselectivity, and Termination
Authors: Mason Andrew F. , Tian Jun , Hustad Philip D. , Lobkovsky Emil B. , Coates Geoffrey W. 
Published: April 2004

AbstractThe polymerization of propylene using a variety of fluorinated bis(phenoxyimine)titanium complexes is reported. The synthesis of ten complexes containing varying fluorinated N‐aryl substituents is described. X‐ray structural and solution NMR data indicate that these complexes are C2‐symmetric in the solid state, although in some cases C1‐symmetric isomers are observed in solution. When activated with methylalumoxane, all complexes formed syndiotactic polypropylene. Catalysts with ortho‐fluorine substituents formed polymers with very narrow molecular weight distributions, indicative of a living polymerization. Catalysts with fluorine in at least the ortho and para positions exhibited the highest syndio‐specificities. Catalysts with meta‐ or para‐fluorine‐containing substituents were more active for propylene polymerization than the corresponding non‐fluorinated catalyst.
Asymmetric Aldol Reactions Using Boron Enolates
Authors: Cowden Cameron J. , Paterson Ian 
Published: April 2004

Abstract
The directed aldol reaction allows the construction of new carbon–carbon bonds in a regio‐, diastereo‐, and enantioselective manner. The kinetically controlled, boron‐mediated aldol reaction is particularly powerful for the efficient synthesis of β‐hydroxy carbonyl compounds. Compared to other metal enolates, the boron–oxygen bond in boron enolates is relatively short which, on addition to aldehydes, leads to tight cyclic transition states and highly stereoselective carbon–carbon bond formation. Moreover, variation of the steric demands of the ligands on boron allows discrimination between competing transition states. Chiral auxiliaries attached to the boron enolate are frequently employed to control the relative and absolute stereochemistry of the aldol products. Asymmetric reactions using chiral ligands on boron are also possible and these produce useful enantiomerically enriched adducts. The utility of boron‐mediated aldol reactions has been demonstrated in numerous total syntheses of complex polyoxygenated natural products, and several of these are highlighted in the Application to Synthesis section of this chapter.

Several reviews of the directed aldol reaction are available, including the
Organic Reactions
chapter by Mukaiyama in 1981.
9
The material covered in this review concerns only the asymmetric formation of β‐hydroxy carbonyl compounds using boron enolates and surveys the literature from 1981 until the end of 1995.
Epoxide Migration (Payne Rearrangement) and Related Reactions
Authors: Hanson Robert M. 
Published: April 2004

AbstractUnder a variety of basic conditions, 2,3‐epoxy alcohols rearrange with inversion at C‐2. The reaction, originally referred to in the literature as the β‐oxanol rearrangement, is now exclusively referred to as epoxide migration or Payne rearrangement.Epoxide migration is reversible, often leading to a mixture of epoxy alcohol isomers. Furthermore, in the presence of hydroxide or other nucleophiles,in situopening of the equilibrating species may be observed. When such opening is desired, epoxide migration becomes a powerful method for the introduction of functionality into a substrate containing a 2,3‐epoxy alcohol moiety. However, when opening is not desired, epoxide migration can become a significant problem.The epoxide migration process lends itself to other synthetically useful manipulations. For example, the anionic equilibrating species may also be trapped with electrophiles such as alkyl and silyl halides, alkyl sulfonates, and epoxides. Electrophilic trapping may be inter‐ or intramolecular, and has been used as a means of delivering functionality to either C‐2 or C‐3 selectively.The intent of this chapter is to provide a comprehensive review of epoxide migration, including factors influencing the equilibrium position, conditions leading toin situepoxide opening, and examples of electrophilic trapping. The reaction is discussed in relation to its utility as a synthetic method as well as its prevention as an unwanted side reaction.Related rearrangements in which either the epoxide or hydroxy oxygen has been replaced with nitrogen or sulfur have also been studied. These reactions, referred to in the literature as aza‐Payne and thia‐Payne rearrangements, respectively, are comprehensively included in this chapter as well. For the purposes of this discussion, the term “forward” aza‐Payne rearrangement refers to the direction of reaction leading from oxirane to aziridine. Similarly, “forward” thia‐Payne rearrangement refers to the direction of reaction leading from oxirane to thiirane. In the case of aza‐Payne rearrangements, both forward and reverse reactions have been effected, and in this chapter the term “reverse” aza‐Payne rearrangement refers to reactions leading from aziridine to oxirane.Epoxides have long been considered important in the chemistry of carbohydrates, and epoxide migration in the context of carbohydrate chemistry has been discussed in several reviews. In addition, particularly since discovery of the catalytic asymmetric epoxidation of allylic alcohols and the rise in importance of enantiomerically enriched acyclic epoxy alcohols, epoxide migration within situopening in acyclic systems has been much studied. The tabular survey summarizes the literature of epoxide migration and related reactions, including equilibration, in situ opening and trapping, aza‐Payne rearrangements, and thia‐Payne rearrangements, from 1931 to 1999. Reports referring to reactions involving addition at C‐1 or C‐3 without inversion of stereochemistry at C‐2 as “Payne rearrangements” are not covered in this review.
Dioxirane Epoxidation of Alkenes
Authors: Adam Waldemar , Saha‐Möller Chantu R. , Zhao Cong‐Gui 
Published: April 2004

Abstract

An ideal oxidant should be highly reactive, selective, and environmentally benign. It should transform a broad range of substrates with diverse functional groups, preferably under catalytic conditions, and be readily generated from commercially available and economical starting materials. Of course, such an ideal oxidant has not yet been invented; however, the dioxiranes, which have risen to prominence during the past few decades, appear to fulfill these requirements in many respects. These three membered ring cyclic peroxides are very efficient in oxygen transfer, yet very mild toward the substrate and product. They exhibit chemo‐, regio‐, diastereo‐, and enantioselectivities, act catalytically, and can be readily prepared from a suitable ketone (for example, acetone) and potassium monoperoxysulfate (2KHSO
5
· K
2
SO
4
· Caroate
®
, Oxone
®
, or Curox
®
), which are low‐cost commercial bulk chemicals. Throughout the text KHSO
5
is used to specify this oxygen source, rather than refer to one of the commercial trade names.

Isolated dioxiranes (as solutions in the parent ketones) perform oxidation under strictly neutral conditions so that many elusive oxyfunctionalized products have been successfully prepared in this way for the first time. Epoxidations, heteroatom oxidations, and X‐H insertions constitute the most investigated oxidations by dioxiranes. An overview of these transformations is displayed in a rosette scheme. These preparatively useful oxidations have been extensively reviewed during the last decade in view of their importance in synthetic chemistry.

This chapter deals mainly with the epoxidation of carbon‐carbon double bonds [π bonds in simple alkenes and with these electron donors (ED), electron acceptors (EA), and with both ED and EA] with either isolated or
in situ
generated dioxiranes. In view of the vast amount of material on alkene oxidation, the epoxidation of the double bonds in cumulenes (allenes, acetylenes) and arenes is covered in a separate chapter, together with the oxidation of heteroatom functionalities (nonbonding electron pairs), X‐H insertions (σ bonds) and transition‐metal complexes.
Self‐tuning control for polynomial systems using a receding horizon observer and control strategy
Authors: Mareels Iven 
Published: April 2004

AbstractA receding horizon observer and control scheme is introduced for non‐linear systems described by polynomial maps. This control scheme has a natural interpretation as a two‐stage adaptive or self‐tuning control algorithm. The non‐linear feedback that results is defined only on the basis of past input and output measurements. The computational complexity aspects of this approach to adaptive or self‐tuning control are briefly discussed. A linear system and a Hénon map example are used to illustrate the ideas. Copyright © 2004 John Wiley & Sons, Ltd.
Thermal and morphological studies on γ‐Fe2O3 polystyrene composites and the affect of additives
Authors: Govindaraj B. , Sastry N. V. , Venkataraman A. 
Published: April 2004

Abstractγ‐Fe2O3polystyrene (PS) composite films were prepared by a gel‐casting technique to obtain monodisperse composite films. To understand the effect of additives on the prepared composite films, additives such as rice husk ash and thiourea were made to disperse into the PS matrix. The as‐prepared γ‐Fe2O3 PS composite films, along with their additives, were subjected to characterization and study by X‐ray diffraction, scanning electron microscopy, thermal, IR, and dielectric measurement techniques. These studies showed monodisperse and chemically homogenous composite films with an increase in thermal behavior. An interesting self‐assembly of rod‐like nanoparticles of γ‐Fe2O3 particles into the polymer matrix, which formed spherical packets, was observed for the γ‐Fe2O3PS composite film. The electrical behavior of these films was interesting, as some showed conduction whereas others showed an increase in dielectric behavior. This nature was explained by the dielectric measurements. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 778–788, 2004
Wear properties and mechanisms of nylon and carbon‐fiber‐reinforced nylon in dry and wet conditions
Authors: Wang Junxiang , Gu Mingyuan 
Published: April 2004

AbstractA microinjection machine was used to prepare specimens of nylon 1010 and carbon fiber (CF)‐reinforced nylon 1010 composites. The friction and wear properties were investigated with a ring–block wear tester in wet and dry conditions. The wear rate of nylon 1010 increased, but the friction coefficient decreased in water in comparison to that in dry sliding. The wear resistance of CF–nylon increased remarkably by two orders of magnitude due to the reinforcement of the CF. The minimum wear rate was obtained with a 20 vol % content of CF filled in nylon in wet lubrication. The wear rate of CF–nylon in dry sliding friction was as much as approximately eight times, and the friction coefficient decreased to approximately half its value compared with that in water under a load of 200 N. The morphologies and the wear mechanisms of worn surfaces were also examined with Fourier transform infrared spectroscopy and scanning electron microscopy. The results show that the hydrolization of amide groups and the resulting decrease in hydrogen bonds between the molecules of nylon 1010 were important factors that led to a high wear rate of nylon in water. We concluded that the fiber, protruding out of the rubbing surface and carrying the main load between the contacting surfaces, held up the swelling properties and improved the mechanical strength of nylon, which would account for the evident reduction of wear in the nylon composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 789–795, 2004