bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasonically induced birefringence in polymer solutions
Authors: Nomura H. , Matsuoka Tatsuro , Koda Shinobu
Published: October 2007

For ultrasonically induced birefringence in polymer solutions, both the linear sinusoidal birefringence and the nonlinear stationary birefringence were observed. The sign and value of the stationary ultrasonically induced birefringence depended on the molecular structure of segment and its anisotropy in polarizability. Furthermore, no molecular weight dependence could be observed above the molecular weight 104. The theory based on the viscoelastic ones using the Rouse-Zimm model could not explain our experimental results as a whole. These results strongly suggest that the stationary ultrasonically induced birefringence should be caused by the local segmental motion of polymer chain in solution. For all polymer solutions investigated here, the stationary birefringence per ultrasonic intensity decreased with increasing frequency. This frequency dependence is not consistent with the present treatment for the ultrasonically induced birefringence.
External double reference method to study concentration and temperature dependences of chemical shifts determined on a unified scale
Authors: Mizuno K. , Tamiya Y. , Mekata Mamoru
Published: October 2007

We present the principle of an external reference method of NMR, named the external double reference method, to study concentration and temperature dependences of chemical shifts. By the method, we refer chemical shifts of various samples at different temperatures to the peak of a reference substance at a fixed referring temperature. Thus, we can determine the chemical shifts in a variety of sample conditions on a unified scale. Results of the application of the method to 1H- and 1
3C-chemical shifts of water and methanol are presented. We also report new data of volume magnetic susceptibilities for several deuterated solvents useful for the calibration in the method.
Dynamics and metastable surface structure of double atomic layer of water molecules and ions at the interface between KBr(c) and water
Authors: Ichikawa K. , Sato S. , Shimomura N.
Published: October 2007

The metastable surface structure and dynamics of water molecules, cations, and anions at the interface between KBr(001) and water have been demonstrated from the images in situ observed in atomic resolution using atomic force microscopy. The vertical motion of potassium ions, which means their own transfer from the equilibrium sites to the upper height right on the underlying bromide ions, has been observed at the interface. They are used to be located in some steady state stabilized by their interaction with water molecules in the double atomic layer at the interface. The observed water molecules bridge two bromide ions by hydrogen bond; the water molecules are sandwiched by the potassium ions and vice versa.
Dynamics and structure of an amphiphilic triblock copolymer of styrene and 5-(N,N-diethylamino) isoprene in selective solvents
Authors: Riegel I. C. , de Bittencourt F. M. , Terrau O. , Eisenberg A. , Petzhold C. L. , Samios D.
Published: October 2007

Solution properties of a highly asymmetric aminofunctionalized triblock copolymer of 5-(N,N-diethylamino)isoprene and styrene were investigated in dilute regime. Toluene, THF, 1,4-dioxane, or DMF were used to prepare the solutions. It was found that the solvent selectivity for one or both block affects the copolymer solution behavior as reflected by the calculated parameters through light-scattering techniques: weight-averaged, molecular-weight, radius of gyration, translational diffusion coefficient, and hydrodynamic radius. According to what was determined, the quality of the polymer-solvent interactions decreases in the order: toluene, THF, 1,4-dioxane, and DMF. After quaternization with dimethyl sulfate, the triblock copolymer consisted of a polystyrene (PS) block with short poly[5-(N,N,N-diethylmethylammonium)isoprene][methyl sulfate] block at both chain ends, shows a better solvation in polar solvents. Transmission electron microscopy (TEM) was used to characterize the crew-cut aggregates prepared from the quaternized copolymer.
Supercritical water: Local order and molecular dynamics
Authors: Tassaing T. , Danten Y. , Besnard M.
Published: October 2007

This paper is a study of the structure and dynamics of near-critical and supercritical water for thermodynamic states above the critical temperature in a wide range of density by infrared absorption and quasi-elastic neutron scattering. The evolution of the shape of the infrared profiles associated with the internal vibrational modes of water has been investigated. In supercritical water, at T = 380 °C and low pressure (density), in the range 25-50 bar (0.01-0.05 g·cm-3), only monomers are detected. A progressive increase of the pressure (density) from 50 to 250 bar (from 0.05 to 0.4 g·cm-3) leads to the appearance of dimers and trimers. In order to obtain information on the dynamics, we have performed incoherent quasi-elastic neutron-scattering experiments on light water for several thermodynamic states (200 < T < 400 °C and 184 < P < 400 bar) corresponding to densities ranging from 0.2 to 0.9 g·cm-3. The results have been analyzed using a jump diffusion model and the two parameters of this model, namely, τ0, the residence time and D, the translational diffusion coefficient, have been determined as a function of the density.
Local density inhomogeneities detected by Raman scattering in supercritical hexafluorobenzene
Authors: Cabaço M. I. , Besnard M. , Tassaing T. , Danten Y.
Published: October 2007

The influence of the local density inhomogeneities in supercritical hexafluorobenzene C6F6 has been assessed using Raman spectroscopy.

The polarized and depolarized profiles associated with the "breathing" mode of the molecule has been analyzed for the fluid in a wide density range, namely under isothermal conditions.

The evolution upon the density of the band center position of the isotropic profile along the near-critical isotherm showed an anomalous behavior, characterized by a plateau in the density range (0.6 < ρ* = ρ/ρC < 1.3), which is not observed along the isotherm T* ~ 1.11. It has been interpreted as due to the existence of local-density inhomogeneities and the density enhancement factor has been evaluated.

The rotational dynamics of the main symmetry axis of the molecule is governed by a diffusional process. The rotational correlation time τ2R exhibits an anomalous behavior (plateau regime) for both isotherms.

These findings put in evidence the existence of local density inhomogeneities in a pure fluid and show that Raman spectroscopy is well adapted to investigate these phenomena.
Critical Raman line shape behavior of fluid nitrogen
Authors: Musso M. , Matthai F. , Keutel D. , Oehme K.-L.
Published: October 2007

Isotropic Raman line shapes of simple molecular fluids exhibit critical line broadening near their respective liquid-gas critical points. In order to observe this phenomenon, it is essential that the band position of a given vibrational mode is density-dependent, and that vibrational depopulation processes negligibly contribute to line broadening. Special attention was given to the fact that the isotropic (i.e., nonrotationally broadened) line shape of liquid N2 is affected by resonant intermolecular vibrational interactions between identical oscillators. By means of the well-chosen isotopic mixture (14N2).975 - (14N15N).025, the temperature and density dependences of shift, width, and asymmetry of the resonantly coupled 14N2 and, depending on the S/N ratio available, of the resonantly uncoupled 14N15N were determined, with up to milli-Kelvin resolution, in the coexisting liquid and gas phases and along the critical isochore, using a highest-resolution double monochromator and modern charge-coupled device detection techniques. Clear evidence was found that vibrational resonance couplings are present in all dense phases studied.
Raman noncoincidence effect: A spectroscopic manifestation of the intermolecular vibrational coupling in dipolar molecular liquids
Authors: Giorgini M. G.
Published: October 2007

This lecture addresses the analysis of the noncoincidence effect (NCE), a spectroscopic manifestation of the intermolecular coupling in molecular liquids. The vibrational bandshapes of molecular groups like C=O (strongly active in the IR spectrum) in dipolar liquids exhibit this phenomenon at a rather large extent. It will be shown that the vibrational exciton approach, developed under the assumption of the transition dipole coupling (TDC) mechanism, predicts how the orientational structure of the molecular liquid determines the magnitude and sign of the NCE. Specifically, it predicts that in simple molecular liquids, solely structured by dipolar forces, the NCE is large and positive, whereas when liquid structures are dominated by non-dipolar forces (as those present in H-bonded liquids), this scenario dramatically changes and IR-active modes may give rise to negative NCEs.

This lecture is intended to offer a general overview of NCEs observed in dipolar (simple and structured) liquids in different thermodynamic conditions and of the theoretical and simulation results that assisted in their interpretation.
Spectroscopy of interparticle interactions in ionic and molecular liquids: Novel approaches
Authors: Kirillov S. A.
Published: October 2007

The paper deals with several novel approaches to the studies of interactions and dynamics in liquids. A new, flexible time-correlation function is introduced. It has an analytical counterpart in the frequency domain and enables one to fit even badly overlapped vibrational line profiles obtaining dynamical information at the same time. As examples, quantitative description of the interaction potential in molten salts containing halide complexes of zinc and manganese is presented, the dynamic criterion of complex entities in a melt is introduced, and the spectroscopic features of molten alkali and alkaline earth halides are explained in terms of short-lived collision complexes. Finally, the model treatment of "anomalous" noncoincidence effects in liquids is discussed, and the contribution of repulsion and attraction forces resulting in frequency non-coincidences is separated.
Peripheral substituent and solvent effects on the aggregation and photochemical properties of copper(II)phthalocyanine and copper(II)phthalocyanine-3,4',4'',4'''-tetrasulfonic anion
Authors: Szymczyk I. , Abramczyk H.
Published: October 2007

The role played by the peripheral substituent and the solvent on the aggregation and photochemical properties of copper(II) phthalocyanine and copper(II)phthalocyanine-3,4',4'',4'''-tetrasulfonic anion [Cu(tsPc)-4] in aqueous solution has been studied by resonance Raman spectroscopy (RRS). The vibrational mode ν4 (1530 cm-1) and the symmetric and antisymmetric stretching modes of water have been used as a probe of interactions and aggregation in resonance Raman measurements. It has been shown that the Cu(tsPc)-4 molecules have a tremendous influence on water properties in solutions. In contrast, the influence of water on the Cu(tsPc)-4 properties appears to be weak.
Derivation of a molecular mechanics force field for cholesterol
Authors: Cournia Zoe , Vaiana A. C. , Ullmann G. M. , Smith J. C.
Published: October 2007

As a necessary step toward realistic cholesterol:biomembrane simulations, we have derived CHARMM molecular mechanics force-field parameters for cholesterol. For the parametrization we use an automated method that involves fitting the molecular mechanics potential to both vibrational frequencies and eigenvector projections derived from quantum chemical calculations. Results for another polycyclic molecule, rhodamine 6G, are also given. The usefulness of the method is thus demonstrated by the use of reference data from two molecules at different levels of theory. The frequency-matching plots for both cholesterol and rhodamine 6G show overall agreement between the CHARMM and quantum chemical normal modes, with frequency matching for both molecules within the error range found in previous benchmark studies.
Structure of the porphyrazine monolayer at the air-water interface: Computer simulation
Authors: Borodin A. , Kiselev M.
Published: October 2007

Molecular dynamics simulations of porphyrazine monolayers at the air-water interface have been carried out. All possible molecular orientations found by analysis of the π-A isotherms are reproduced by computer simulations. The existence of "guest-water" molecules has been observed in the simulation; this confirms the assumptions of experimentalists concerning this phenomenon.
Translational and rotational dynamics in supercritical methanol from molecular dynamics simulation
Authors: Chalaris Michalis , Samios J.
Published: October 2007

The purpose of this paper is to review our latest molecular dynamics (MD) simulation studies on the temperature and density dependence of the translational and reorientational motion in supercritical (SC) methanol. In the present treatment, Jorgensen's [W. L. Jorgensen. J. Phys. Chem. A
102, 8641 (1998)] transferable potential model, tested in a recent MD study of hydrogen bonds in this fluid [M. Chalaris and J. Samios, J. Phys. Chem. B
103, 1161 (1999)], was employed to simulate the dynamics of the system. The simulations were performed in the canonical (NVT) ensemble along the isotherms 523, 623, and 723 K and densities corresponding to the pressures from 10 to 30 MPa. Several dynamical properties of the fluid have been obtained and analyzed in terms of appropriate time-correlation functions (CFs). With respect to the translational dynamics, the self-diffusion coefficients obtained have been used to test the applicability of the well-known Chapman-Enskog kinetic theory. We have found that the theoretical predictions for the self-diffusion coefficients are only in qualitative agreement with the MD results over the whole temperature and density range studied. Finally, the inspection of the reorientational CFs and their corresponding correlation times lead to the conclusion that the reorientational motion of the SC methanol molecules in the sample is anisotropic.
Origin of the enhanced structural and reorientational relaxation rates in the presence of relatively weak dc electric fields
Authors: Vegiri A.
Published: October 2007

The origin of the dramatic increase of the reorientational and structural relaxation rates of single water molecules in clusters of size N = 16, 32, and 64 at T = 200 K, under the influence of an external, relatively weak electric field (~0.5 107 V/cm) is examined through molecular dynamics simulations. The observed effect is attributed not to any profound structural changes, but to the increase of the size of the molecular cage. The response of water to an electric field in this range shows many similarities with the dynamics of water under low pressure. By referring to simulations and experiments from the literature, we show that in both cases the observed effects are dictated by a common mechanism.
Transport properties of diatomic ions in moderately dense gases in an electrostatic field
Authors: Koutselos A. D. , Samios J.
Published: October 2007

The motion of diatomic ions in moderately dense fluids under the action of an electrostatic field is studied through a nonequilibrium molecular dynamics simulation method. The method simulates the motion of the ions and the fluid molecules that constitute their immediate environment. Thus, effectively, the dissipation of the excess energy of the ions is reproduced leading to steady drift motion. Results revealed the effect of the fluid density on mobility, ion-effective temperatures and diffusion coefficients parallel and perpendicular to the field at various field strengths for a model diatomic ion in Ar. Extension of the method to dense fluids and to polyatomic ions and neutral molecules is discussed.
Calculation of the free energy of solvation from molecular dynamics simulations
Authors: Gonçalves P. F. B. , Stassen H.
Published: October 2007

Molecular dynamics simulation has been employed in the computation of the free energy of solvation for a large number of solute molecules with different chemical functionalities in the solvents water, acetonitril, dimethyl sulfoxide, tetrahydrofuran, and carbon disulfide. The free solvation energy has been separated into three contributions: the work necessary to create a cavity around the solute in the solvent, the electrostatic contribution, and the free energy containing the short-range interactions between solute and solvent molecules. The cavitational contribution was computed from the Claverie-Pierotti model applied to excluded volumes obtained from nearest-neighbor solute-solvent configurations treating the solvent molecules as spherical. The electrostatic term was calculated from a dielectric continuum approach with explicitly incorporating the solvent's partial charges. The short-range contribution to the free solvation energy was obtained from the force field employed in the simulations. For solutions with available experimental data for the free energy of solvation, we found a satisfactory agreement of the computed free solvation energies and the experimental data set.
Vibration-rotation spectra of hydrogen halides in rare-gas liquids: Q-branch absorption
Authors: Medina A. , Roco J. M. M. , Hernández A. C. , Velasco S.
Published: October 2007

Near-infrared spectra of HCl highly diluted in liquid Ar show intense absorption in the P-R interbranch region, so-called Q-branch absorption. In spite of its relevance for the shape of the bands, its physical origin has been elusive to date. We employ molecular dynamics simulations to study the influence of some physical effects that could contribute to Q-branch absorption. We check that multipole-induced dipole induction mechanisms are not quantitatively relevant in this spectral region. We show that the particular characteristics of accurate HCl-Ar anisotropic potentials and the peculiar hindered rotational motion they provoke on the diatomic probe are essential to understand Q-branch absorption.
Pressure dependence of the liquid structure and the Raman noncoincidence effect of liquid methanol revisited
Authors: Torii H.
Published: October 2007

Pressure dependence of the liquid structure and the Raman noncoincidence effect of liquid methanol is examined with the combination of molecular dynamics (MD) simulations and the intermolecular resonant vibrational interactions determined by the transition dipole coupling (TDC) mechanism (MD/TDC method). It is shown that the observed decrease of the Raman noncoincidence νNCE of the CO stretching band with increasing density reported in the literature is quantitatively reproduced by the present calculation. As the density increases, the hydrogen bonds get slightly shorter, but molecules belonging to different hydrogen-bond chains get closer to each other to a greater extent. This anisotropic change in the liquid structure is the reason for the behavior of νNCE. It is also shown that the concentration dependence of νNCE in the methanol/CCl4 binary mixtures reported in a previous study, and the pressure dependence of νNCE in methanol may be described in a consistent way as a function of the number density of methanol in the liquid systems.
Molecular structure, reorientational dynamics, and intermolecular interactions in the neat ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate
Authors: Antony J. H. , Mertens D. , Breitenstein Tobias , Dölle Andreas , Wasserscheid P. , Carper W. R.
Published: October 2007

Results on the molecular and liquid structure and the reorientational dynamics are reported for the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]). In quantum-chemical calculations for [BMIM][PF6] in the gas phase, hydrogen bonding between the proton at carbon 2 in the aromatic ring and the fluorine atoms of the hexafluorophosphate anion was found. From the analysis of 13C relaxation data, the reorientational motions were evaluated, and the Vogel-Fulcher-Tammann and Arrhenius activation energies for the overall and internal reorientational motions, respectively, of the different 13C-1H vectors are given as well as correlation times at 300 K. By performing molecular dynamics (MD) simulations, pair distribution functions between moieties in the cation and the phosphorous atom in the anion were determined. The pair distribution function for the proton at carbon 2 exhibits a particular sharp and strong maximum indicating a strong interaction with the anion. The quantum-chemical calculations, the motional parameters, and the results from the MD simulations support the existence of hydrogen bonding and the formation of ion pairs in the ionic liquid.
Photodegradation and photosensitization in pharmaceutical products: Assessing drug phototoxicity
Authors: Cosa Gonzalo
Published: October 2007

Toxic reactants are a common result of the interaction of sunlight with pharmaceutical agents transported in the blood system or applied topically. Over the past decade there has been a considerable amount of research toward understanding both the unimolecular deactivation pathway of photoexcited pharmaceutical products and their photosensitizing capability in the presence of biological substrates. This work summarizes recent developments in the study of the photodegradation mechanism of ketoprofen, fenofibric acid, and tiaprofenic acid. An analysis of excited-state electronic energy levels, the type of intermediates formed following excitation, and transient intermediate lifetimes is presented. The analysis involves both parent drugs and their major photoproducts. Phototoxicity, usually the result of adverse photochemical reactions following direct photoexcitation of the drugs, is shown to be strongly related to the photoexcitation of photoproducts when high radiation dose conditions prevail. The photoproducts are the species directly involved in photosensitizing reactions.
Recent developments in the coordination chemistry of stable free radicals
Authors: Lemaire M. T.
Published: October 2007

Several advances in the coordination chemistry of stable free-radical species over the past six years are documented in this review article. Specifically, a number of recent reports focused on the coordination chemistry of chelating nitroxide ligands are highlighted, with an emphasis on enhanced magnetic or optical properties in these complexes. Furthermore, very intriguing recent magnetic and optical studies with one-dimensional nitroxide chain complexes (new "Glauber" chains and chiral magnets) are also discussed. The verdazyls are another family of stable radicals whose coordination chemistry was literally unexplored prior to 1997. A summary of recent reports discussing metal-verdazyl coordination complexes is also presented, followed by an eye to the future of stable radical design and the coordination chemistry of these interesting molecules.
Simulations on many scales: The synapse as an example
Authors: Tai K.
Published: October 2007

Computer simulation methods spanning several temporal and spatial scales are reviewed, focusing on their applications on the neuromuscular synapse. Quantum mechanics treats the enzymatic catalysis of neurotransmitters on the picometer scale. Molecular dynamics reveals conformational changes of the enzyme acetylcholinesterase for nanoseconds. Brownian dynamics follow the substrate molecule in its diffusion on the microsecond level. Methods such as finite elements describe the diffusion of neurotransmitters as a changing concentration continuum in the synapse. Promising directions for future research include integration of methods on several scales, and applying these methods to the acetylcholine receptor.
Understanding the reaction that powers this world: Biomimetic studies of respiratory O2 reduction by cytochrome oxidase
Authors: Boulatov Roman
Published: October 2007

Cytochrome c oxidase (CcO) is an enzyme that catalyzes efficient, selective, and fast reduction of molecular oxygen to water as a means of respiratory energy generation. The biomimetic approach provides a valuable alternative to traditional biochemical methods to unravel the structural and electronic properties of the CcO's catalytic (heme/CuB) site that endow the enzyme with its unique reactivity. However, the contribution of biomimetic studies of CcO to our understanding of CcO's biochemistry has been complicated by the lack of convincing evidence that the reactivity of the biomimetic analogs is relevant to that of CcO. Recently reported porphyrin-based compounds are the first analogs that reproduce key aspects of the reactivity of CcO toward O2. Extensive data collected with these biomimetic analogs demonstrate that the bimetallic nature of the CcO's catalytic site may be an adaptation to reduction of O2 under turnover-limiting electron flux; a monometallic heme-only site appears sufficient for rapid O2 reduction under physiologically relevant conditions of pH and electrochemical potential, provided that electron flow to the heme is not kinetically limited. These biomimetic data suggest that in CcO the distal Cu ion (CuB) may serve as an electron-preloading site to allow the enzyme to accumulate a sufficient number of external reducing equivalents before it even binds O2. This mechanism minimizes the population of enzymatic species containing partially reduced oxygen species.
Copper(II) proteins are amenable for NMR investigations
Authors: Bertini Ivano , Pierattelli R.
Published: October 2007

The possibility of investigating copper proteins by nuclear magnetic resonance is here treated. It is shown that the solution structure and dynamic information can be obtained on Type I Cu(II) proteins, which have a relatively short electron relaxation time (τ
S = 10-10 s). The experimental approach, in this case, is routine, although tailored for fast-relaxing nuclei.

In the case of Type II Cu(II) proteins, when the electron relaxation times are larger (τ
S = 10-8 - 10-9 s) and proton linewidths are broadened beyond detectable limits, heteronuclear 13C spectra with direct detection can be used and the solution structure can again be obtained.

In this review, it is shown that Cu(II) proteins are now amenable for NMR investigation, the size being the only limit as in diamagnetic proteins.
Probing fundamental mechanisms of nitric oxide reactions with metal centers
Authors: Ford P. C.
Published: October 2007

Studies in this laboratory have been concerned with mapping the chemical properties and mechanisms of NO interactions with hemes and other metal centers. These are models relevant to the mammalian biology of nitric oxide, an important bioregulatory molecule. Presented here will be an overview of flash photolysis kinetics investigations of ferri- and ferro-heme nitrosyl formation in model complexes and several heme proteins. Also described will be ongoing studies of reductive nitrosylation mechanisms involving the reactions of NO with water-soluble Fe(III) porphyrins and ferri-heme proteins and of several Cu(II) model complexes.
Cooperation of metals with electroactive ligands of biochemical relevance: Beyond metalloporphyrins
Authors: Kaim Wolfgang , Schwederski B.
Published: October 2007

In addition to the widely studied biometal complexes of tetrapyrrole ligands such as hemes (Fe), cobalamins (Co), and factor F430 (Ni), there are other, more recently established systems in which transition metals and redox-active cofactors such as pterins, flavins, quinones, or phenoxyl radicals cooperate in electron transfer and substrate activation. The cases of the molybdenum or tungsten containing oxotransferases involving pyranopterin as essential ligand and the copper-dependent quinoproteins such as amine oxidases will be discussed. The structural and functional description of these systems will be complemented by results from model studies.
Synthesis of texaphyrin conjugates
Authors: Magda D. J. , Wang Z. , Gerasimchuk Nikolay , Wei W.-H. , Anzenbacher P. , Sessler J. L.
Published: October 2007

This paper summarizes recent synthetic efforts devoted to the generation of new, second-generation texaphyrin-type drugs, specifically species that involve known or potential anticancer agents covalently attached to a tumor-localizing texaphyrin core. Particular emphasis will be placed on the strategies needed to prepare such systems, as well as on the choice of active group being subject to attachment.
Adenosine 5'-triphosphate (ATP4-): Aspects of the coordination chemistry of a multitalented biological substrate
Authors: Sigel H.
Published: October 2007

Firstly, the self-stacking properties of ATP4- and the effects of metal ions and protons on these properties are described. Some examples involving macrochelate formation between phosphate-coordinated metal ions (M2+) and N7 of the adenine residue in MATP2- are discussed, and this is followed by considerations on mixed ligand complexes consisting of ATP4-, M2+, and amino acid anions with side chains that allow either aromatic-ring stacking or hydrophobic interactions with the adenine moiety; this gives rise to selectivity. Next, the properties of diphosphorylated 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA2-; Adefovir), i.e., of PMEApp4-, are compared with those of (2'-deoxy)ATP4- with regard to their metal ion-binding qualities, and in this way it can be explained why PMEApp2- is initially an excellent substrate for nucleic acid polymerases. Of course, after incorporation of the PMEA residue into the growing nucleic acid chain, this is terminated and this is how PMEA exerts its antiviral properties [its bis(pivaloyloxymethyl)ester, Adefovir dipivoxil, was recently approved for use in hepatitis B therapy]. Finally, the change in free energy connected with (macro)chelate formation or intramolecular stacking interactions and the effect of a reduced dielectric constant of the solvent on the stability of complexes and their structures in solution is considered.
Rheological and mechanical properties of poly(α-methylstyrene-co-acrylonitrile)/ poly[(methyl acrylate-co-methyl methacrylate)] blends in miscible and phase separated regimes of various morphologies. Part IV: Influence of the morphology on the mechanical properties (IUPAC Technical Report)
Authors: Altstädt V. , de Freitas L. Lucca , Schubert D. W.
Published: October 2007

Influences of the morphology on the thermal and mechanical properties of poly(α-methylstyrene-co-acrylonitrile)/poly[(methyl acrylate-co-methyl methacrylate)] (PαMSAN/PMMA) blends have been investigated. DSC measurements confirm that all blends were phase-separated due to the temperature at which they have been extruded and squeeze-molded. Based on the cloudpoints of 17 blends and TEM micrographs, the interaction parameters as a function of temperature and composition were calculated for the lower critical solution temperature (LCST) system. Varying the morphology by annealing without changing the composition of the system resulted in a finer morphology for the 85/15 blends, while the 40/60 blend showed an increase in the domain size with annealing time. Tensile strength and fracture toughness indicate that the PαMSAN domains in the tougher PMMA matrix cause a deterioration in the mechanical properties of the blends, while the PMMA domains in the PαMSAN matrix improve the mechanical properties. No clear conclusions on the influence of morphology on fracture toughness could be drawn because in one case (40/60 blend) the fracture toughness decreases slightly by annealing and in the other case (85/15 blend) fracture toughness values increase slightly with decreasing phase separation by annealing. In situ strained thin sections in the TEM indicated no effect of annealing on the micromechanical behavior. Shear deformation was observed as the prevailing deformation mechanism in the PαMSAN and fibrillized crazing in the PMMA-rich blends. From fatigue crack growth experiments it was concluded that the fatigue crack propagation threshold is higher for PMMA than for PαMSAN. Tests on the annealed samples of PαMSAN/PMMA 85/15 and 40/60 showed that the differences in morphology did not affect the fatigue crack growth resistance significantly. From the features of the fracture surface investigated by SEM, the conclusion can be drawn that the fatigue crack propagates faster in the more brittle PαMSAN phase, but the overall advance of the crack front is controlled at the interphases, resulting in a crack propagation gradient along the interphase.
Determination of trace elements bound to soil and sediment fractions (IUPAC Technical Report)
Authors: Hlavay József , Prohaska T. , Weisz M. , Wenzel W. W. , Stingeder G. J.
Published: October 2007

This paper presents an overview of methods for chemical speciation analysis of elements in samples of sediments and soils. The sequential leaching procedure is thoroughly discussed, and examples of different applications are shown. Despite some drawbacks, the sequential extraction method can provide a valuable tool to distinguish among trace element fractions of different solubility related to mineralogical phases. The understanding of the speciation of trace elements in solid samples is still rather unsatisfactory because the appropriate techniques are only operationally defined. The essential importance of proper sampling protocols is highlighted, since the sampling error cannot be estimated and corrected by standards. The Community Bureau of Reference (BCR) protocols for sediment and soil give a good basis for most of the solid samples, and the results can be compared among different laboratories.
Terminology for analytical capillary electromigration techniques (IUPAC Recommendations 2003)
Authors: Riekkola M.-L. , Jönsson J. Å. , Smith R. M.
Published: October 2007

This paper presents terms and definitions for capillary electromigration techniques for separation, qualitative and quantitative analysis and physico-chemical characterization. Names and descriptions for such techniques (e.g., capillary electrophoresis and capillary electrochromatography) as well as terms for the phenomenon of electroosmotic flow are included.
Metal cyclopropyl carbenes in the reactions of alkynes with alkenes and furans
Authors: Echavarren Antonio M. , Méndez María , Muñoz M. P. , Nevado C. , Martín-Matute Belén , Nieto-Oberhuber C. , Cárdenas D. J.
Published: October 2007

Electrophilic transition-metal complexes catalyze the reaction of enynes in the presence of water or alcohols to give hydroxy- or alkoxycyclization derivatives. The reaction proceeds by the anti addition of the alkene and the metal to the alkyne. The key intermediates in this reaction are cyclopropyl metal carbenes, which are also probably involved in the metathesis-type rearrangement of enynes. A general scheme is proposed for the cyclization of enynes initiated by the coordination of the metal to the enyne by transition metals, which included 5-exo -dig and 6-endo -dig pathways. The intramolecular reaction of furans with alkynes also proceeds via cyclopropyl metal carbenes.
Rhodium-catalyzed asymmetric addition of aryl- and alkenylboron reagents to electron-deficient olefins
Authors: Hayashi T.
Published: October 2007

Asymmetric 1,4-arylation and -alkenylation was achieved by use of organoboronic acids or their derivatives in the presence of a rhodium catalyst coordinated with binap or its related ligands. The scope of this asymmetric addition is very broad, α, β-unsaturated ketones, esters, amides, 1-alkenylphosphonates, and 1-nitroalkenes being efficiently converted into the corresponding 1,4-addition products with over 95% enantioselectivity. The catalytic cycle in water is proposed to involve three intermediates [aryl-or alkenyl-rhodium (oxa-π-allyl) rhodium, and hydroxo-rhodium] by NMR studies on the rhodium intermediates.
Synthetic applications of planar chiral cationic η3-allylmolybdenum complexes
Authors: Kocienski P. , Bell Richard , Bourque Elyse , Christopher J. A. , Cooksey John , Gunn Andrew , Kuhl Alexander , Li Y. , Uppal S. , Yuen Josephine
Published: October 2007

The synthesis of planar chiral η3-allylmolybdenum complexes is described together with some examples of the nucleophilic addition of organocopper(I) reagents.
Application of allylic substitutions in natural products synthesis
Authors: Helmchen G. , Ernst Martin , Paradies G.
Published: October 2007

Synthesis routes are described, allowing all known jasmonoids as well as their enantiomers to be synthesized in enantiomerically and diastereomerically pure form. The routes are based on a set of closely related lactones containing an electrophilic allylic moiety, which are accessible via asymmetric Pd-catalyzed allylic alkylation. Regio- and diastereoselective SN2'-anti-reactions of the electrophilic lactones with organocopper compounds furnished 2,3-cis-disubstituted cyclopentenones, which were further transformed into the target compounds, i.e., 12-oxophytodienoic acid (12-OPDA) in excellent overall yields. The methodology also allowed iridoids and isoprostanes to be prepared. The configuration of an Archaea membrane lipid constituent containing cyclopentane rings was determined by total synthesis of a diol that was also obtained by degradation of the natural product.
Development of catalysts for the hydroamination of olefins
Authors: Hartwig J. F.
Published: October 2007

Studies on the development of palladium, nickel, and rhodium catalysts for the hydroamination of dienes and vinylarenes are described. Enantioselective catalysts based on palladium have been developed for the addition of arylamines to dienes and for Markovnikov addition of arylamines to vinylarenes. In addition, nickel catalysts for the addition of aliphatic amines to dienes have been developed, and rhodium catalysts for the first transition metal-catalyzed aminations of vinylarenes that generate terminal amines as the major product are described. Mechanistic data on the hydroamination of vinylarenes with palladium and rhodium is also provided.
New regio-, stereo-, diastereo- and enantioselective one-pot reactions mediated by organometallic derivatives
Authors: Chinkov Nicka , Sklute G. , Chechik Helena , Abramovitch Adi , Amsallem Deborah , Varghese J. , Majumdar Swapan , Marek I.
Published: October 2007

In the first part of the lecture, we will discuss the one-pot preparation of chiral homoallylic alcohol and amine derivatives by a copper-catalyzed four-component reaction. In this process, three new carbon-carbon bonds as well as a quaternary and a tertiary chiral center are created with excellent regio- and diastereoselectivities. When the reaction was performed without adding external electrophiles, a β-elimination reaction took place to give polysubstituted allenes in good overall yields. This strategy of zinc-homologation followed by a β-elimination reaction was also synthetically used for the transformation of sp3 sulfoxides into olefins with potential application in asymmetric synthesis. Finally, in the second part of this lecture, the stereoselective preparation of metallated dienes in only two chemical steps from commercially available products will be described. This new strategy is based on a tandem allylic C-H bond activation of a remote ω-double bond followed by an elimination reaction.
Negative nonlinear effect in aquo palladium catalysis depending on tropos biphenylphosphine ligand chirality controlled by chiral diaminobinaphthyl activator
Authors: Mikami K. , Aikawa Kohsuke , Yamanaka Masahiro
Published: October 2007

Asymmetric activation of aquo Pd catalysts with tropos biphenylphosphine (BIPHEP) ligands by a chiral diaminobinaphtyl (DABN) activator exhibits a remarkable negative nonlinear effect, (–)-NLE, with higher catalytic efficiency than that achieved by enantiopure atropos BINAP- or tropos BIPHEP-Pd catalysts without DABN activator.
Asymmetric catalytic synthesis of polyketones and polycarbonates
Authors: Nozaki K.
Published: October 2007

Two examples are presented for the synthesis of optically active polymers with main-chain chirality from achiral monomers using chiral metal-complexes as catalysts. Asymmetric alternating copolymerization of α-olefins with carbon monoxide provided optically active polyketones when catalyzed by an (R,S)-BINAPHOS-Pd complex. From propene and CO, highly isotactic polyketone with high enantioselectivity (>97 % like diad and >95 % ee). Spectroscopic and theoretical studies revealed that the olefin insertion is the key step for the enantiofacial selection and that this step takes place at cis to the phosphine part of (R,S)-BINAPHOS. The catalyst is applicable not only to propene/CO but also to styrene/CO, which enabled the first asymmetric terpolymerization of propene/styrene/CO. The catalyst tolerates funational groups such as fluorocarbons and a nitrile group so that they can be incorporated in the side chain. Optically active polycarbonate was also synthesized by the alternating copolymerization of cyclohexene oxide with carbon dioxide via the desymmetrization of the meso-epoxide. Dinuclei zinc species prepared from diethylzinc, ethanol, and α,α'-diphenylprolinol, was revealed to be the real active species.
Development of a new methodology for the preparation of optically active alcohols
Authors: Andersson P. G.
Published: October 2007

This article summarizes our recent achievements in the asymmetric catalytic formation of chiral alcohols using 3-substituted, 2-azanorbornyl-based ligands. The use of this structural unit in ligand synthesis offers several advantages over the analogous proline chemistry, such as equal availability of both enantiomers and increased rigidity of the catalysts. This ligand has been found to be very useful for the two reactions described in this paper: the ruthenium-catalyzed transfer hydrogenation of ketones, and the base-mediated rearrangement of epoxides.
Stereochemistry of epoxide carbonylation using bimetallic Lewis acid/metal carbonyl complexes
Authors: Getzler Y. D. Y. L. , Mahadevan Viswanath , Lobkovsky E. B. , Coates G. W.
Published: October 2007

The stereochemistry of epoxide carbonylation using bimetallic [Lewis acid]+[Co(CO)4]- complexes is reported. The achiral complex [(salph)Al(THF)2][Co(CO)4] stereospecifically carbonylates cis- and trans-2-butene oxide to the trans- and cis-β-lactones, respectively. Preliminary experiments regarding the carbonylative kinetic resolution of racemic trans-2-butene oxide using the enantiomerically pure complex [(R,R-salcy)Al(THF)2][Co(CO)4] are also reported.
Dual role of nucleophiles in palladium-catalyzed Heck, Stille, and Sonogashira reactions
Authors: Jutand Anny
Published: October 2007

In palladium-catalyzed Heck, Stille, or Sonogashira reactions, the nucleophiles-respectively, alkenes, vinylstannanes, or alkynes-are involved in carbopalladation or transmetallation steps that follow the oxidative addition of an aryl halide or triflate to a Pd0 complex. As soon as the nucleophiles possess a C=C or a C 'triple-bond' C bond capable of coordinating the Pd0 complex active in the oxidative addition, they play a dual role since they interfere in the oxidative addition by a decelerating effect due to a partial coordination of the active Pd0 complex. Indeed, its concentration decreases due to the formation of either unreactive complexes (η2-RCH=CH2)Pd0L2 (R = Ph, CO2Et, L = PPh3 ; R = Bu3Sn, L = AsPh3), (η2-RCH=CH2)Pd0L2(OAc)- (R = Ph, L = PPh3), (η2-R-C 'triple-bond' CH)Pd0L2 (R = Ph, L = PPh3) or more slowly reactive complexes (η2-R-C 'triple-bond' CH)Pd0L2 (R = CO2Et, L = PPh3), (η2-RCH=CH2)Pd0L2 (R= CO2Me, L2 = dppf). Whenever the oxidative addition is faster than the ensuing carbopalladation or transmetallation, the decelerating effect of the nucleophiles in the oxidative addition is in favor of a better efficiency for the catalytic cycle by bringing the rate of the fast oxidative addition closer to that of the slow carbopalladation or transmetallation steps.
Application of C-H and C-C bond activation in organic synthesis
Authors: Jun C.-H. , Lee J. H.
Published: October 2007

Herein we describe the chelation-assisted C-H and C-C bond activation by Rh(I) catalysts and its application directed toward the formation of C-C bonds in organic synthesis.
Coordination of the Trost modular ligand to palladium allyl fragments: Oligomers, monomers and memory effects in catalysis
Authors: Lloyd-Jones G. C. , Stephen S. C. , Fairlamb I. J. S. , Martorell Aina , Dominguez Beatriz , Tomlin P. M. , Murray M. , Fernandez J. M. , Jeffery J. C. , Riis-Johannessen T. , Guerziz Toufik
Published: October 2007

Reaction of the C
2-symmetric "Trost modular ligand" with cationic Pd(II) allyl fragments allows isolation of air- and bench-stable pro-catalysts for the asymmetric allylic alkylation of racemic cycloalkenyl esters. In solution, three distinct complexation modes are observed. When mixed in a ligand/Pd ratio of 1/2, a binuclear bis-P,O-chelate complex is generated. This species does not induce enantioselectivity in the reaction. In contrast, with a ligand/Pd ratio of 1/1, a highly enantioselective, P,P-coordinated pro-catalyst system is generated in which there are two basic coordination modes: monomeric and oligomeric. The monomeric form is mononuclear and exists as two 13-membered chelates, isomeric through loss of C
2-symmetry in the ligand. The oligomeric form is polynuclear and forms chains and rings of alternating ligand and cationic Pd(allyl) units, one of which was identified by single-crystal X-ray diffraction. In solution, the monomeric and oligomeric species are in dynamic equilibrium with populations and interconversion rates controlled by concentration, temperature, and counterion. Isotopic desymmetrization analysis suggests that the monomer-oligomer equilibrium plays a crucial role in both the selectivity and efficiency of the asymmetric allylic alkylation reaction.
New methods for the synthesis of heterocyclic compounds
Authors: Caiazzo Aldo , Dalili Shadi , Picard C. , Sasaki M. , Siu T. , Yudin A. K.
Published: October 2007

Due to frequent occurrence of nitrogen-containing groups among the biologically active compounds, chemoselective functionalization of organic molecules with nitrogen-containing functional groups is an important area of organic synthesis. We have proposed and implemented a new strategy toward design of nitrogen-transfer reactions on inert electrode surfaces with a particular focus on the generation and trapping of highly reactive nitrogen-transfer agents. A wide range of structurally dissimilar olefins can be readily transformed into the corresponding aziridines. The resulting aziridines are precursors to a range of catalysts via nucleophilic ring-opening with diaryl- and dialkyl phosphines. Another strategy explored in the context of oxidative nitrogen transfer is cycloamination of olefins using NH aziridines.
Mechanistic insights into perfluoroaryl borane-catalyzed allylstannations: Toward asymmetric induction with chiral boranes
Authors: Morrison D. J. , Blackwell J. M. , Piers W. E.
Published: October 2007

The perfluoroaryl borane B(C6F5)3 is an effective catalyst for a variety of organic transformations. In the hydrosilation of carbonyl functions, it activates the silane rather than the carbonyl substrate. In allylstannation reactions, two competing reaction pathways are observed, one involving tin cation catalysis, the other "true" borane catalysis. For B(C6F5)3, the former mechanism dominates, while for the weaker Lewis acid PhB(C6F5)2, the latter pathway is more prominent. Thus, chiral boranes of similar Lewis acid strength to PhB(C6F5)2 have the potential to mediate asymmetric allylstannation of aldehyde substrates.