bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Expansion of Thin Diblock Copolymer Films
Authors: Bassereau P. , Russell T.P.
Published: November 2013

The thermal expansion of thin films of symmetric diblock copolymers of polystyrene (PS) and poly(methyl methácrylate) (PMMA) was investigated by X‐ray reflectivity. The confinement of the copolymer to the substrate, coupled with the multilayering of the copolymer where PS and PMMA layers are oriented parallel to the substrate, gives rise to unusual thermal expansion characteristics. The total thickness of the film increases as 3αL, where αL is the linear thermal expansion coefficient of the copolymer. Unlike homopolymer films, the thermal expansion of an ordered block copolymer film results in an excessive stretching of the copolymer chains at the interface between the PS and PMMA layers. This excess stretching is a result of the confinement of the junction points of the copolymer chains to the interfaces and the suppression of the lateral expansion of the copolymer. When the stretching of the chains becomes too high, relaxation occurs by transporting copolymer chains to the surface. This is evidenced by a reduction in the period of the multilayer. After the copolymer chains have relaxed, the change in the multilayer period with temperature closely follows αL.
Pattern Formation in the Evaporation of Thin Liquid Films
Authors: Elbaum M. , Lipson S.G.
Published: November 2013

We investigate the patterns formed by thin liquid films evaporating from clean substrates. The system in equilibrium is entirely homogeneous, yet a remarkably regular, symmetric pattern is generated by a change in an isotropic parameter: the vapor pressure. The hydrodynamic instabilities which come into play display strong nonlinearities, distinguishing them from the classical capillary instabilities described by Rayleigh.
“Chrysanthemums”: Weak Micellization
Authors: De Gennes P.G.
Published: November 2013

A statistical copolymer (A/B, with 50%–50% composition) immersed in a B polymer matrix, should display a novel form of micellization: portions which are slightly B‐rich protruding outward, and portions which are slightly A‐rich concentrating in a core. The average length of one portion is Neff ≅ 16χ−2, where χ is the AB Flory parameter. The total length N of the copolymer may range between Neff and Neff3/2. The limit N ‐ Neff corresponds to weak association, while N ˜ Neff3/2 corresponds to very few chains/micelle. Systems of this type should micellize equally well in B or A polymer solvents.
Diffusion‐Limited Segregation of Diblock Copolymers to a Homopolymer Surface
Authors: Budkowski Andrzej , Losch Andreas , Klein Jacob
Published: November 2013

Using nuclear reaction analysis, we have measured the rate of surface segregation of an asymmetric diblock polyisoprene–polystyrene (PIPS) copolymer to the free surface of polystyrene (PS) homopolymers within which it is incorporated at low bulk concentrations. We have also measured the tracer diffusion coefficient of PIPS in PS under similar conditions, and shown it to equal, within error, the self‐diffusion coefficient of PS of a similar length. The equilibrium surface excess Γ of the diblock is low (<Rg, the radius of gyration of the PS block of the copolymer), so that the diffusion rate is not expected to be significantly reduced by energy barrier effects. The rate of segregation appears considerably slower than a diffusion‐limited picture based on a sink‐boundary condition for the PIPS molecules at the PS surface would suggest. A much better description of our data is provided by a simple kinetic model which assumes local equilibrium between unattached and tethered diblocks at the free PS surface.
Thermoluminescence Dating and the Problem of Geochemical Evolution of Sediments — A Case Study: The Mousterian Levels at Hayonim
Authors: Mercier N. , Valladas H. , Joron J.L. , Schiegl S. , Bar Yosef O. , Weiner S.
Published: November 2013

The thermoluminescence dating of burnt flints has become a major tool in the elaboration of the chronology of human settlements of the last half a million years. The reliability of an age estimate depends to a great extent on the accuracy with which the internal and external radiation dose rates prevailing during the duration of burial can be determined. While determining the internal dose rate is relatively straightforward, the same cannot be said of the external, particularly if the sediment surrounding the flints is mineralogically heterogeneous or has undergone diagenetic changes during prolonged burial. In this article we show some examples of the problems confronted when one attempts to determine the external dose rates experienced by flints buried in a relatively heterogeneous environment of sediments, such as those sampled at the Middle Paleolithic occupation levels at Hayonim (Israel) which show evidence of past mineralogical evolution. The impact of changes produced by leaching and chemical reactions between the components of hearth ashes on the radioisotopic composition of the sediment and consequently the environmental dose rates were examined by subjecting several distinct sediment layers to thorough mineralogical, radiochemical, and dosimetric analyses. The problems of external dose‐rate determinations in mineralogically heterogeneous sediments are examined, particularly in those consisting of variable amounts of siliceous aggregates, apatite, and other phosphorus‐rich minerals produced by diagenetic reactions with bone residues.
On Early Myths and Formative Technologies: A Study of Pre‐Pottery Neolithic B Sculptures and Modeled Skulls From Jericho
Authors: Goren Yuval , Segal Irena
Published: November 2013

During the last two decades, considerable interest has been expressed in the development of lime and lime plaster products in the Near Eastern Pre‐Pottery Neolithic B. The occurrences of lime products in numerous Levantine sites have raised questions concerning their methods of production, their role in the development of craft specialization, and their social and economic implications. Lime plaster was the first product that entailed the intentional chemical alteration of materials and the complete control over their properties. This was probably the reason for the wide spectrum of uses to which it was put, amongst which “daily” architectural functions appear to coexist with the symbolic or spiritual applications of this material.

Amongst the variety of plaster products which appeared in the PPNB, it seems that the practice of skull plastering and sculpture production was the most “socially oriented” one, lacking any apparent relation to daily, functional use. In the present study two modeled skulls and a collection of plaster sculptures from Jericho were examined by means of thin section petrographic analysis, inductively coupled plasma atomic emission spectrometry, scanning electron microscopy, X‐ray diffraction, and Fourier‐transform infrared spectrometry. The results of the mineralogical and chemical analyses, when compared to data obtained from similar artifacts from other sites, demonstrate pronounced intersite variability in the methods of production of the skull and sculpture modeling. The full implications of this issue are discussed in detail in the paper.
Structure and Function of Activated Rhodopsin
Authors: Hofmann Klaus P. , Jäger Stefan , Ernst Oliver P.
Published: November 2013

Aftercis/transisomerization of retinal and early photoproducts, activated rhodopsin (R*) develops signaling states for different proteins in a time‐ordered sequence. Rhodopsin kinase binds all Meta forms, including the early Meta I, while interaction with transducin (Gt) or arrestin requires the deprotonated Schiff base form, Meta II (MII). Gtrecognizes a specific conformation, termed MIIb, which arises from an additional, spectrally silent conversion, linked to proton uptake. Collisional coupling with the GDP‐bound Gtholoprotein induces the release of GDP and formation of a stable R*—Gtcomplex, in which the nucleotide binding site of Gtis empty. The empty site complex, once formed, remains stable, even if the retinal is re‐isomerized to thecisconfiguration. The cytoplasmic surface of rhodopsin appears to provide the majority of interaction sites for other proteins. Physical analyses and mutagenesis have emphasized the loops connecting helices C/D and E/F of the seven‐helix structure. Any interaction between R* and Gtdepends on a conserved charge pair at the interface between the helix C and the adjacent loop CD. Replacements or deletions in loops CD and EF were found to cause more specific functional defects, including slow release of GDP or failure of GTP‐induced complex dissociation. In the dark, signaling states with low activity can be generated by reversible binding of all‐trans‐retinal to opsin. These light‐independent signaling states are different from the Meta forms.
Catalytic Properties of the Antibody H11
Authors: Pitt Andrew R. , Stimson William H. , Suckling Colin J. , Marrero‐Tellado Jose J. , Vazzana Caterina
Published: November 2013

The catalytic activity of the antibody H11 is shown to reside chiefly in its ability to hydrolyze 1‐acetoxybutadiene to crotonaldehyde and to promote the cycloaddition of the intermediate enol with N‐alkylmaleimides. This conclusion is based upon the demonstration that the enol tautomerizes too rapidly in solution to be a competent intermediate and that under the reaction conditions for H11, no cycloaddition occurs with crotonaldehyde and N‐ethylmaleimide. As a first step towards a structural understanding of the chemistry of H11, chemical modification experiments have shown that reactions of acidic amino acids, tyrosine, lysine, and histidine, but not arginine, inhibit the reactions mediated by H11.
Proteolytic Antibodies
Authors: Paul Sudhir
Published: November 2013

Catalytic activities are known to arise naturally in antibodies. Several naturally‐occurring peptides, synthetic protease substrates, DNA, and esters are known to be cleaved by antibodies. There is increased production of antigen‐specific catalytic antibodies in autoimmune disease. Polyreactive catalytic antibodies are present in unimmunized donors. Antibody light chains isolated from multiple myeloma patients frequently express proteolytic activity. Immunization protocols using as immunogens the ground state of a naturally‐occurring polypeptide, anti‐enzyme antibodies, or the enzyme itself are known to provoke catalytic antibody synthesis. Active site residues in the light chain subunit serve as the catalytic residues in a model antibody with peptide bond cleaving activity. A split‐site model in which distinct amino acids serve as the essential catalytic residues and substrate ground‐state recognition residues has been developed from mutagenesis studies. Engineering of the available antibodies could potentially generate improved catalysts. The possible mechanisms underlying proteolysis by natural antibodies and evolution of the catalytic activity are reviewed.
The Pyrolysis of 3‐Picoline: Ab Initio Quantum Chemical and Experimental (Shock Tube) Kinetic Studies
Authors: Jones Jeffrey , Bacskay George B. , Mackie John C.
Published: November 2013

The pyrolysis of 3‐picoline dilute in argon was investigated using a single‐pulse shock tube over the temperature range of 1400–1650 K and total pressures of 12–13 atm. The principal products observed were HCN, acetylene, benzene, cyanoacetylene, methane, and pyridine. Assuming that 3‐picoline decomposes according to first‐order kinetics, the rate constant for its overall disappearance was determined to be kdis = 1016.9 (±0.8) exp[–99 (±6) kcal mol−1/RT] s−1. The principal initial decomposition routes were found to be via the formation of the 3‐picolyl and m‐pyridyl radicals whose subsequent ring‐opening led to the observed products. A 68‐step kinetic model was developed that successfully fits the experimental data. The dominant reactions, i.e., the formation of picolyl and pyridyl radicals and their subsequent chain‐opening reactions, were studied using ab initio quantum chemical techniques. The ab initio data were also incorporated into the kinetic model in the form of energies and A‐factors for reactions for which no kinetic or thermochemical data were previously available. Optimization of the kinetic model yields a value of 64 ± (3) kcal mol−1 for the heat of formation of 3‐picolyl, a value lower than that for 2‐picolyl, suggesting that the decomposition of 3‐picoline more closely resembles that of toluene, rather than its isomer 2‐picoline.
Shock Tube Study of High‐Temperature Reactions of Cyclopentadiene
Authors: Roy Karin , Frank Peter , Just Thomas
Published: November 2013

The thermal decomposition of cyclopentadiene has been studied in the temperature range 1260–1530 K behind reflected shocks. The total pressure ranged from 1.5 to 2.3 bar. Resonance absorption was used to record the temporal concentration profiles of H atoms. This sensitive technique allowed the study of the reaction systems under favorable conditions by applying very low initial concentrations (0.5–8 ppm). For cyclopentadiene decomposition R1, C5H6 → C5H3‐c + H, a rate expression of k1 = 1.1 × 1015 exp(–38760/T) s−1 was deduced. In a separate series of experiments the consumption by cyclopentadiene of H atoms, which had been generated by the thermal decay of ethyl iodide, was investigated. A preliminary value of k2 = 1.4 × 1014 exp(–2739/T) cm3 mol−1 s−1 was deduced for the total rate of H‐atom consumption by cyclopentadiene R2, C5H6 + H → products.
Kinetics of Hexane Combustion in a Shock Tube
Authors: Burcat Alexander , Olchanski Erna , Sokolinski Chara
Published: November 2013

A detailed shock tube investigation on the ignition delay times in mixtures containing n‐hexane and oxygen diluted in argon is reported. The product distribution of the pre‐ignited mixtures was also investigated and a computer modeling of the combustion kinetics was performed. The experiments covered the temperature range 1020–1725 K at pressures of 1–7 atm. A computer simulation was performed with a large number of elementary reactions (386), which was then reduced to a scheme containing only 76 reactions.
Development of Molecules for All‐Optical Switching Devices
Authors: Bjørnholm Thomas
Published: November 2013

The prospects for developing efficient molecular devices for all‐optical switching are discussed on the basis of measurements of the second molecular hyperpolarizability coefficient, γ, responsible for third harmonic generation. More than twenty structurally different organic compounds comprising organic metal complexes, polyenes, cyanines, and derivatives of triarylmethyl cations have been examined. The dependence of γon the number of π‐electrons in the nonlinear chromophore leads to a classification of the data in four categories; (i) the polyene ‐ like, (ii) the cyanine‐like, (iii) the bis‐1,2‐dithiole metal complexes, and (iv) a new category comprising molecules with significant ligand‐to‐metal or other “periphery‐to‐center” charge transfer transitions. Values of γ as high as 3 × 10−32 esu are reported in this new category. The importance of changes in higher multipole moments such as quadrupole and octupole moments upon electronic excitation is addressed. Strategies for improved molecular and materials design are discussed.
Tailoring of Surfaces with Ultrathin Layers for Controlled Binding of Biopolymers and Adhesion and Guidance of Cells
Authors: Knoll Wolfgang , Matsuzawa Mieko , Offenhäusser Andreas , Rühe Jürgen
Published: November 2013

Various strategies are described for the bio‐functionalization of solid substrates by design of interfacial architectures. The first approach is based on the self‐assembly process of long‐chain thiol molecules from solution to a (noble) metal surface. If some of these building blocks carry a binding site (ligand) for proteins (receptors, antibodies, etc.) the metal surface can be tailored for maximum specific binding while simultaneously minimizing nonspecific adsorption.

The second concept is based on polymers that are covalently attached to (oxide) surfaces. The preparation of these (end‐) grafted functional polymers involves either the binding of preformed macromolecules to corresponding sites at the surface of the support or the recently introduced “grafting‐from” method, by which an initiator molecule is first covalently bound to the surface and then activated — either by heat or light — in the presence of suitable monomer units such that a polymer chain grows from the solid/solution interface.

Finally, the functionalization of patterned surfaces by peptide chains that mimic the binding domains of cell adhesion proteins is summarized. It is demonstrated that not only the selective adhesion of neuronal cells can then be controlled, but also their development with the outgrowth of dendrites and axons.
Controlling Stereoselection in Aza‐Cope‐Mannich Reactions
Authors: Overman Larry E. , Trenkle William C.
Published: November 2013

The synthesis of 2‐substituted cis‐octahydroindolones from the reaction of cis‐2‐amino‐1‐alkenylcyclopentanols with aldehydes was studied to examine whether stereoselection in the aza‐Cope–Mannich reaction could be controlled by the nature of the nitrogen substituent. 2‐Alkylamino‐1‐(1‐phenylethenyl)cyclopentanols 7 and 8, which contain nitrogen substituents of widely differing size (Me and CHPh2), were condensed with four aldehydes to give oxazolidines 9a–d and 10a‐c. Rearrangement of these intermediates at 23–60 °C, in the presence of 0.9 equiv of (±)‐10‐camphorsulfonic acid in acetonitrile, gave cis‐octahydroindolones 11a‐d and 12a–c in yields of 77–95%. Using a combination of single‐crystal X‐ray crystallography, 1H nOe measurements, and comparisons with known materials it was established that the N‐methyl oxazolidines 9a–d provided exclusively cis‐octahydroindolones having the 2‐substituent trans to the angular substituents, while N‐benzhydryl analogs 10a–c provided exclusively the all‐cis products 12a–c. These results are interpreted to mean: (1) When the nitrogen substituent is small (Me), the stereochemistry‐determining [3,3]‐sigmatropic rearrangement occurs preferentially through a transition‐state topography having the R2 substituent oriented quasiequatorially (14 → 15 → 16); (2) When this substituent is large (CHPh2), destabilizing steric interactions between the vicinal R1 and R2 substituents causes the rearrangement to occur preferentially through the alternate iminium ion stereoisomer (17 → 18 → 19).
Two‐Dimensional Ordering of Coumarin at the Indium Amalgam–Electrolyte Interface
Authors: Freymann Marco , Poelman Mireille , Buess‐Herman Claudine
Published: November 2013

The two‐dimensional condensation of coumarin was investigated at the indium amalgam‐aqueous solution interface by capacitance‐potential and charge‐time measurements. Two distinct adsorption states were found for saturated coumarin solutions in 0.5 M NaF at 10 °C. Similar to the adsorption behavior on mercury, coumarin molecules can form a monolayer presenting the characteristics of a two‐dimensional condensed layer. An increase of the indium content of the amalgam leads to an extension of the stability range of the condensed monolayer at most negative potentials. The shift of the transition potential parallels the variation of the pzc of the amalgams. The kinetics of condensation of coumarin were investigated by the potential step technique at a 50% In‐Hg electrode. Mononuclear transients leading to the condensed film are observed in a wide range of the overvoltage. A comparison of the data obtained at the amalgam and mercury electrodes shows that the growth rate is independent of the nature of the electrode and that the detection of a single event takes place at lower supersaturations at the amalgam electrode.
Channel Mimetic Sensing Membranes for Nucleotides Based on Multitopic Hydrogen Bonding
Authors: Tohda Koji , Amemiya Shigeru , Ohki Tohru , Nagahora Shinichiro , Tanaka Shunitz , Bühlmann Philippe , Umezawa Yoshio
Published: November 2013

Nucleotide‐induced permeability changes of oriented monolayers composed of the nucleotide receptors 4‐amino‐1‐octadecyl‐2‐(1H)‐pyrimidinone (1), 5‐methyl‐1‐octadecyl‐2,4(1H,3H)‐pyrimidinedione (2), and 1‐(2‐heptylundecyl)‐4‐(8‐(3‐methylureido)‐2‐naphthyl)‐amide‐2‐(1H)‐pyrimidinone (3) were examined. These molecules are capable of binding guanosine, adenosine, and guanosine nucleotides, respectively, by multitopic hydrogen bonding. Monolayers were first formed at the air/water interface and then directly contacted with a highly oriented pyrolytic graphite (HOPG) electrode. The permeabilities of these membranes were evaluated with cyclic voltammetry, using [Fe(CN)6]4– as permeability marker. Selectively 5′‐GMP‐induced decreases in the permeability of the membranes based on receptor 1 or 3 were observed. On the other hand, decreases in the permeability of membranes based on receptor 2 were larger in the presence of 5′‐AMP than of 5′‐GMP. The permeability changes thus observed can be ascribed to repulsive electrostatic interaction between the marker anions and the negatively charged nucleotides that selectively bind to the electrically neutral membrane receptors. The ratios of the oxidation current decreases for solutions containing 3.0 mM 5′‐GMP and for solutions containing 3.0 mM 5′‐AMP were 1.30, 0.76, and 1.85 for monolayers based on receptors 1, 2, or 3, respectively. The monolayer based on receptor 3, which is capable of binding the guanine base by five hydrogen bonds, showed a higher 5′‐GMP selectivity than the monolayer of receptor 1 with the cytosine residue. Similar nucleotide‐induced permeability changes were observed for mixed multilayers of receptor 1 and octadecanol (4), as well as for mixed monolayers with receptor 2 and 4.
Electron Emission from Diamond Films
Authors: Hatta Akimitsu , Ito Toshimichi , Hiraki Akio
Published: November 2013

Recent studies on electron emission from diamond and related materials are reviewed. The properties of the diamond surface have been carefully investigated with well‐defined treatments and it has been confirmed that the hydrogenated diamond surface has a negative electron affinity (NEA). The field electron emission properties of a variety of carbon materials were investigated and remarkable results of high emissivity at low fields were documented. The mechanism for the low field emission was partly attributed to an NEA nature although the emission surface was not always confirmed to have NEA properties.

Electron emission devices with NEA diamond surfaces have been developed. An emission device of metal‐insulator‐semiconductor structure was designed and built and its performance was investigated.
Modeling of the Low‐Frequency Noise in Thermal Lens Spectrometry
Authors: Martín‐Biosca Yolanda , Rozé Claude , Ramis‐Ramos Guillermo
Published: November 2013

The low‐frequency noise observed in thermal lens spectrometry (TLS) can be modeled by assuming that the heated region, constituted by the thermal lens gradient and associated convective stream, behaves as a weakly damped harmonic oscillator with a natural frequency, vo, which is forced to move at an externally imposed pump frequency, vp. Out‐of‐phase lower‐frequency oscillations of the TLS signal can be produced both by transient events, such as the beginning of the TLS experiment and small changes in the pump beam stability, and by drift of boundary conditions, such as the temperature of the surroundings. A model is developed and checked using 1‐(2‐pyridylazo)‐2‐napthol (PAN) solutions in silicone oil. Consequences of analytical interest are drawn; e.g., the signal‐to‐noise ratio of the TLS experiments is improved by pumping at the resonance frequency, where vp = vo.
Picosecond Time‐Resolved Dispersion Spectroscopy Using the Interference between Population and Thermal Phase Gratings
Authors: Högemann Claudia , Vauthey Eric
Published: November 2013

A new method is presented for measuring directly the dispersion spectrum of short‐lived transients, based on heterodyne transient grating spectroscopy. The light diffracted from a preformed thermal phase grating is used as a local oscillator, in phase with the light diffracted from the population phase grating. Time‐resolved dispersion spectra measured upon photoinduced electron transfer reaction between 9,10‐dicyano‐anthracene and anisole in acetonitrile are presented. These spectra and the corresponding absorption spectra obtained by Kramers‐Kronig transformation are compared with those deduced from the homodyne transient grating spectra. Potential applications of this technique are discussed.
Calibrating Picosecond Time Resolved Optical Calorimetry: Absolute Enthalpies from Investigations of Mixtures
Authors: Vath Peter A. , Zimmt Matthew B.
Published: November 2013

A method for quantifying the absolute enthalpy release detected in picosecond optical calorimetry (transient grating spectroscopy) is described. Excitation and analysis of thermal phase grating waveforms from mixtures containing both a fully characterized calibration compound and a precursor to a reactive intermediate of interest provides a value of the total heat release attending formation and decay of the reactive intermediate, within the time window of the experiment. This information can be used to obtain the absolute reaction enthalpies accompanying formation and decay of the reactive intermediate. The calibration method is demonstrated using tetraphenylethylene as the ground‐state precursor to its zwitterionic, twisted excited state and copper (II) bis(2,2,6,6‐tetramethyl‐3,5‐heptanedionate) as the calibration compound. The results suggest that 96 ± 6% of the exciting photon's energy (284 nm, 101 kcal/mole) is released within 10 ns. This is in reasonable agreement with the literature lower limit of 97.5% energy release. Limitations of the mixture method for calibration and relevant control experiments are described.
Determination of the pKa of the Aci‐Nitro Intermediate in o‐Nitrobenzyl Systems
Authors: Carcelli Mauro , Pelagatti Paolo , Viappiani Cristiano
Published: November 2013

The structural volume changes following photoexcitation of o‐nitrobenzyl systems are used to estimate the excited state pKa of the aci‐nitro intermediate in aqueous solutions. The rather large contractions induced in solution by UV excitation are due to the rapid deprotonation of the short‐lived aci‐nitro intermediate, which leads to the formation of two charged species. The magnitude of the measured contraction as a function of the pH in acidic solutions follows a sigmoidal curve, from which it is possible to extract the pKa of the aci‐nitro intermediate. This method is generally applicable to short‐lived intermediates with stronger acid character than the parent compound, provided they undergo irreversible chemical transformations to a product that cannot rebind the photodetached proton. The reaction volume for water formation from its ionic constituents at basic pH allows the determination of the deprotonation quantum yields.
Discriminating between Phytoplankton Taxa by Photoacoustics
Authors: Mauzerall David C. , Feitelson Jehuda , Dubinsky Zvy
Published: November 2013

We present here an application of the photoacoustic method for studying and discriminating between important phytoplankton taxa in suspension. The photosynthetic activity was studied by measuring the photoacoustic signal with and without background illumination. A linear dependence of the photoacoustic signal on the biomass of different algae was observed along with wavelength‐dependent differences between the various phytoplankton taxa. The photoacoustic signals from mixtures of pairs of taxa were measured at different ratios of the mixture components and at selected wavelengths at which the differences in absorption among the species were maximal. A linear dependence of the photoacoustic signal on the composition of each pair at the wavelengths studied was found. The results indicate the potential of the procedure for determining the composition of phytoplankton communities and following the effects of environmental parameters such as irradiance and nutrient status on the photosynthetic activity of phytoplankton.
Attenuation of the Photobaric‐Photoacoustic Signal in Leaves by Oxygen‐Consuming Processes
Authors: Malkin Shmuel
Published: November 2013

Charland et al. (Biochim. Biophys. Acta 1992, 1098, 261–265) obtained photoacoustic data from sugar maple tree leaves, in which the photobaric part of the photoacoustic signal declined in time following a transition from high light to low light level, which they interpreted as indicating stromal and plasmal oxygen‐consuming processes. Here, a simple mathematical model of oxygen diffusion, which includes a continuous distribution of oxygen‐consuming sinks in the diffusion path from the photosynthetic membrane to the inner air phase, is presented. The model explains the main features of the dependence of the steady‐state signal on the modulation frequency and the light intensity, although the numerical agreement between the data and the results of the model is only semi‐quantitative, which is discussed. It turns out that at sufficiently high light intensity, or at a short time after a previous exposure to a high light level, the effect of oxygen consumption tends to zero because a high stromal oxygen concentration is built up which is saturating for the uptake process. Within this limitation, the merit of the photoacoustic signal as an indicator for photosynthetic oxygen evolution is preserved, answering recent doubts.
Reversible Charge Transfer in Liquids at High Excitation Power
Authors: Mikhelashvili Meir S. , Dodu Marian
Published: November 2013

We discuss the influence of high excitation power on reversible charge transfer kinetics. The kinetics depends on the excited donor concentration, on the parameters of the rate constants, and on the boundary conditions for the Smoluchowski equation in liquids. The nonlinear effects of the excitation power are determined by the geometry of molecular spectra of emission and absorption. They disappear with the acceptor concentration, with the decrease in the forward rate constant. The role of Coulomb interaction of ions increases with increase of diffusion constant. Nonlinear effects for our theory of reversible charge transfer in liquids are compared with those of Dorfman and coworkers (J. Chem. Phys. 1989, 90, 159). The difference of the effects between the two theories vanishes when the probability of the donor's excited state approaches unity.
Velocity Distributions after Laser‐Induced Desorption of NO from NiO(100)—The Role of the Angular Coordinate
Authors: Thiel Stephan , Klüner Thorsten , Freund Hans‐Joachim , Kosloff Ronnie
Published: November 2013

The experimental velocity distributions of NO desorbing from a NiO(100)‐surface are simulated using a time‐dependent wave packet method. Including the polar angle between the surface normal and the adsorbate molecular axis yields bimodal distributions in the correct velocity range and reasonable desorption probabilities if a resonance lifetime on the order of 25 fs is assumed. For two‐dimensional simulations, an angular‐independent charge‐transfer‐state was chosen as excited state in order to investigate the influence of the electronic ground‐state on the final state distributions. We compare our results with wave packet calculations using a representative ab initio angular‐dependent excited‐state potential energy surface using a three‐dimensional Hamiltonian.
The Adsorption Sites of CO and NO Molecules on Metal Surfaces
Authors: van Hove Michel A.
Published: November 2013

This article briefly reviews recent structural results obtained for the adsorption of CO and NO on the closest‐packed single‐crystal metal surfaces. We discuss mainly the question of adsorption sites (top, bridge, hollow), in connection with site assignments based on C–O and N–O vibrational stretch frequencies. It is by now well established that, especially for high‐coverage molecular structures (i.e., high‐density monolayers), one cannot rely on simple site assignments based on these frequencies: molecular interactions change the frequencies, such that the frequency ranges deduced for carbonyl and nitrosyl cluster compounds are in some cases violated.
Probing the Influence of Alloyed Sn on Pt(100) Surface Chemistry by CO Chemisorption
Authors: Panja Chameli , Koel Bruce E.
Published: November 2013

The chemisorption properties of the c(2×2) and (3√2×√2)R45° Sn/Pt(100) alloy surfaces, along with the clean Pt(100) surface, were investigated using CO as a probe molecule. Temperature‐programmed desorption (TPD) studies revealed a reduction in CO desorption peak temperature, and thus the chemisorption bond energy, by alloying Sn into the Pt(100) surface. A large decrease was observed in the saturation coverage of CO on these alloyed surfaces at 150 K compared to the Pt(100) surface. The initial sticking coefficient of CO was found, however, to be nearly independent of the surface Sn concentration. High‐resolution electron energy loss spectroscopy (HREELS) studies showed that CO was only chemisorbed on atop sites on both alloys. Sn incorporation results in isolated Pt atoms at the surface of these two Sn/Pt(100) alloys and eliminates the possibility of CO bonding to multiple Pt centers, i.e., to pure‐Pt 2‐ and 3‐fold bridging sites.
Selective Oxidation of Propene at Cesium and Cesium‐modified Ag(100) Surfaces
Authors: Carley Albert F. , Chambers Alan , Roberts M. Wyn , Santra Ashok K.
Published: November 2013

The oxidation of propene at Ag(100), Ag(100)–Cs, and Cs surfaces has been investigated by X‐ray photoelectron spectroscopy in the temperature range 80–298 K. The atomically clean Ag(100) surface is unreactive, while cesium surfaces effect mainly dehydrogenation or selective oxidation with some metal–carbon bond formation, but with complete oxidation a minor pathway. Partially cesiated Ag(100) surfaces, on the other hand, result in complete oxidation to give surface carbonate at 160 K. Two key intermediates responsible for the alternative reaction pathways have been delineated through their very different, but characteristic, C(1s) spectra at 80 K.
Dynamic Monte Carlo Simulations of Oscillatory Reactions
Authors: Gelten Ronald J. , Jansen Tonek P.J. , van Santen Rutger A. , Lukkien Johan J. , Segers John P.L. , Hilbers Peter A.J.
Published: November 2013

The dynamic Monte Carlo method has been used to simulate the 2 A + B2 → 2 AB reaction catalyzed by a reconstructing substrate. Oscillatory behavior and spatio‐temporal is studied as a function of grid size. Spatio‐temporal pattern formation has been simulated in various forms: cellular patterns, target patterns, rotating spirals, and turbulent patterns. Cellular patterns are a manifestation of a local synchronization mechanism in which all reaction fronts periodically extinguish each other. This illustrates that dynamic Monte Carlo simulations form a promising technique and can be used to predict macroscopic kinetic phenomena on a molecular basis.
Laser and Probe Diagnostics in Fundamental Combustion Research
Authors: Kohse‐Höinghaus Katharina
Published: November 2013

Combustion diagnostics using lasers has matured considerably during the last decade. By now, lasers are routinely relied upon in many practical applications where direct inspection of the combustion process is necessary. Quantitative information, however, may still be a major challenge. In this article, some essential features of laser techniques for fundamental combustion research are discussed in view of their potential and limitations. Laser methods are complemented by molecular beam mass spectrometry. Applications include diagnostics in laminar and turbulent diffusion flames, in fuel‐rich and sooting flames, and in combustion chemical vapor deposition (CVD) of thin diamond films. Avenues for further research will be discussed.
CH, NH, and NH2 Concentration Profiles in Methane/Air Flames Doped with N2O
Authors: Derzy Igor , Lozovsky Vladimir A. , Cheskis Sergey
Published: November 2013

Intracavity Laser Absorption Spectroscopy (ICLAS) and Cavity Ring‐Down Spectroscopy (CRDS) were used to measure concentration profiles of the CH, NH, and NH2 radicals in a low‐pressure (30 Torr) stoichiometric methane/oxygen/nitrogen flat flame doped with a small amount of nitrous oxide (1.7%). Concentration profiles of the CH and NH radicals were measured by CRDS, whereas the NH2 radical profile was measured by ICLAS. Temperature profiles were obtained using measured CRDS spectra of the OH radical. The radical absorption spectra were recorded with good signal‐to‐noise ratio. For the first time, absolute concentrations of NH and NH2 were measured in flames of this kind. The obtained experimental profiles and peak amounts agree well with model predictions based on GRI‐Mech 2.11 (Gas Research Institute Mechanism). The mechanism also describes well the observed decreasing CH concentration with addition of N2O.
Synthesis and Structure of New Dimeric Cyclopentadienyl Titanium Fluorine–Oxygen Systems: [Cp*TiF(μ‐F)(μ‐OPOPh2)]2, [Cp*TiF(μ‐F)(μ‐OSO2‐p‐C6H4Me)]2 and [Cp*TiF2(μ‐OMe)]2
Authors: Gindl Judith , Said Musa A. , Yu Peihua , Roesky Herbert W. , Noltemeyer Mathias , Schmidt Hans‐Georg
Published: November 2013

The reactions of Cp*TiF3 with Me3SiOPOPh2, Me3SiOSO2‐p‐C6H4Me, and Al(OMe)3 resulted in the formation of the dimers [Cp*TiF(μ‐F)(μ‐OPOPh2)]2 1, [Cp*TiF(μ‐F)(μ‐OSO2‐p‐C6H4Me)]2 2, and [Cp*TiF2(μ‐OMe)]2 3, respectively, in good yields. In contrast to the formation of 3, Cp*TiF3 reacts with Al(OH)3 to afford the known tetramer [Cp*TiF(μ‐O)]4 4. The structures of 1–3 have been determined by X‐ray crystallography; compounds 1 and 3 crystallize in the monoclinic space group P21/c and compound 2 in the monoclinic space group P2/n. Compound 1 is the first example of a dimeric Cp*‐titanium phosphinate containing a fluorine ligand. The core of the dimeric structure of both 1 and 2 consists of two Ti atoms bridged by two fluorine atoms and two bidentate groups. In contrast, the dimeric structure of 3 consists of two Ti atoms bridged only by two methoxy groups. An equilibrium of isomers of 1 and 2 has been observed in solution by 1H and 19F NMR. The 19F NMR spectra of 1–3 are discussed in detail.
Electrochemical Direct Fluorination of Lactams
Authors: Sawaguchi Masanori , Hara Shoji , Fukuhara Tsuyoshi , Yoneda Norihiko
Published: November 2013

The electrochemical fluorination of a variety of N‐protected lactams was carried out and Et3N–5HF was found to be superior to Et3N–3HF as the electrolyte. When 5‐ and 6‐membered N‐acetyl or ethoxycarbonyl lactams were used as substrates, the fluorination reaction selectively took place at the α‐position of the lactam nitrogen and the corresponding monofluoro products could be obtained in good yields.
Electrophilic Fluorination of Aromatics with Selectfluor™ and Trifluoromethanesulfonic Acid1
Authors: Shamma Tatyana , Buchholz Herwig , Prakash G.K. Surya , Olah George A.
Published: November 2013

1‐(chloromethyl)‐4‐fluoro‐1,4‐diazabicyclo[2.2.2]octane bis (tetrafluoroborate) [Selectfluor™ F‐TEDA‐BF4 (TEDA = triethylenediamine)] in the presence of trifluoromethanesulfonic acid has been found to be a very effective reagent system for the direct electrophilic fluorination of a wide variety of aromatic compounds under mild reaction conditions to the corresponding fluoroaromatics in good to excellent yields.
Consequences of Protonation of Diamines in the Gas Phase and the Solid State
Authors: Woźniak Krzysztof , Raczyñska Ewa D. , Korybut‐Daszkiewicz Bogdan
Published: November 2013

An interesting model class of compounds are proton sponges—aromatic diamines characterized by exceptional basicity, such as 1,8‐bis(dimethylamino)naphthalene (DMAN). For these compounds, protonation causes substantial redistribution of electron density which may be traced by observing the changes of structural parameters as well as of the properties of electron density at bond critical points. On protonation, electron density in DMAN goes from the terminal atoms towards the center of the molecule. This redistribution can also be confirmed by good quality neutron structural data.

An ionic complex of DMAN with triformylmethane (TFM) acid has been studied by X‐ray diffraction. We propose a multicenter model of hydrogen bonding {[Me2N–H0.5….0.5H–NMe2]+… X−} in this complex. The influence of weak intermolecular interactions of the DMANH+cation with the nearest electronegative atom from the counterion on the strong intramolecular [N–H···N]+hydrogen bonding has been demonstrated. Such interactions affect the localization of the proton in the intramolecular [N–H···N]+hydrogen bridge.
Acid Ionization of HBr in a Small Water Cluster
Authors: Gertner Bradley J. , Peslherbe Gilles H. , Hynes James T.
Published: November 2013

The acid ionization by which HBr transfers a proton to a water molecule is studied for HBr in small water clusters as a first stage in a study of the corresponding Arctic atmospheric process. Electronic structure calculations, involving relatively large basis sets and including electron correlation effects, indicate that HBr is acid‐ionized in a cluster of four water molecules. The most stable structure in the general HBr(H2O)4 system is a diamond‐like (trigonal bipyramidal) structure in which the bromide and hydronium ion species are bridged by three water molecules, and infrared spectral and ionization potential characteristics potentially useful for experimental study are provided. This structure is calculated to remain the thermodynamically most stable one up to about 180 K, where HBr + (H2O)4 becomes more stable. Aspects of the formation of the acid‐ionized cluster from both HBr + (H2O)4 and H2O + HBr(H2O)3 are discussed. Possible implications for HBr acid ionization at the surface of ice, believed to be important for Arctic atmosphere ozone depletion mechanisms, are briefly discussed.
Hydrogen‐Bond Dynamics and Solvation of Electronically Excited States as Determined by Femtosecond Vibrational Spectroscopy
Authors: Nibbering Erik T.J. , Chudoba Christian , Elsaesser Thomas
Published: November 2013

The ultrafast dynamics of site‐specific hydrogen bonds between an organic chromophore serving as hydrogen acceptor and a hydrogen‐donating species in solution is studied by femtosecond vibrational spectroscopy. This new method gives specific insight into microscopic structural changes of hydrogen bonds initiated by electronic excitation of the chromophore. We study H‐bonded complexes of coumarin 102 with the solvent CHCl3, and with phenol. Upon electronic excitation, the intermolecular hydrogen bond between proton donor and acceptor is cleaved within 200 fs, followed by a slower reorientation dynamics of the donor molecules extending into the picosecond regime. For CHCl3, this slower rearrangement is interpreted in terms of polar solvation. In complexes consisting of a coumarin molecule and two phenol moieties, the slower dynamics is related to geometry changes of the phenol–phenol hydrogen bond. The consequences of those results for a microscopic picture of polar solvation are discussed.
An Extended Empirical Valence Bond Model for Describing Proton Mobility in Water
Authors: Vuilleumier Rodolphe , Borgis Daniel
Published: November 2013

In order to study the microscopic nature of the hydrated proton and its transport mechanism, we have introduced a multistate empirical valence bond model, fitted to ab initio results. This model was applied to the study, at low computational cost, of the structure and dynamics of an excess proton in liquid water. The quantum character of the proton is included by means of an effective parametrization of the model using preliminary path‐integral calculations. The mechanism of proton transfer is interpreted as the translocation of a special O–H+–O bond along the hydrogen network, i.e., a series of reactions of the form H5O2+ + H2O ⇌ H2O + H5O2+, rather than H3O+ + H2O → H2O + H3O+ as usually described. The translocation of the special bond can be described as a diffusion process with a jump time of 1 ps. A time‐dependent correlation function analysis of the special pair relaxation yields two timescales, 0.3 and 3.5 ps. The first time is attributed to the interconversion between a delocalized (H5O2+‐like) and a localized (H9O4+‐like) form of the hydrated proton within a given special pair. The second one is the relaxation time of the special pair, including return trajectories. The computed diffusion constant, as well as the isotopic substitution effect, are in good agreement with experiment. The hydration structure around the excess proton is discussed in terms of various radial distribution functions around the water molecules involved in the special pair and those in the first solvation shell. The hydrogen‐bond‐dynamics which accompanies the translocation process is studied statistically. The “Moses mechanism” proposed by Noam Agmon for proton mobility in water is partially verified by our simulations.
Quantum Properties of the Excess Proton in Liquid Water
Authors: Schmitt Udo W. , Voth Gregory A.
Published: November 2013

The classical and quantum equilibrium properties of an excess proton in bulk phase water are examined computationally with a special emphasis on the influence of an explicit quantum dynamical treatment of the nuclei on the calculated observables. The potential model used, our recently developed multistate empirical valence bond (MS‐EVB) approach is described. The MS‐EVB model takes into account the interaction of an exchange charge distribution of the charge‐transfer complex with the polar solvent, which qualitatively changes the nature of the solvated complex. The impact and importance of the exchange term on the stability of the solvated H5O2+ (Zundel) cation relative to the H9O4+ (Eigen) cation in the liquid phase is demonstrated. Classical and quantum path‐integral molecular dynamics (PIMD) simulations of an excess proton in bulk phase water reveal that quantization of the nuclear degrees of freedom results in an increased stabilization of the solvated Zundel cation relative to the Eigen cation, and that species intermediate between the two are also probable. Quantum effects lead to a significant broadening of the probability distributions used to characterize the two species, and a definite differentiation and sharp characterization of the species connected to the excess proton in liquid water is found to be difficult.
Comparative analysis of in vitro oxidative degradation of poly(carbonate urethanes) for biostability screening
Authors: Dempsey David K. , Carranza Christopher , Chawla Chander P. , Gray Patrick , Eoh Joon H. , Cereceres Stacy , Cosgriff‐Hernandez Elizabeth M.
Published: November 2013

The resistance to oxidation and environmental stress cracking of poly(carbonate urethanes) (PCUs) has generated significant interest as potential replacements of poly(ether urethanes) in medical devices. Several in vitro models have been developed to screen segmented polyurethanes for oxidative stability. High concentrations of reactive oxygen intermediates produced by combining hydrogen peroxide and dissolved cobalt ions has frequently been used to predict long‐term oxidative degradation with short‐term testing. Alternatively, a 3% H2O2 concentration without metal ions is suggested within the ISO 10993‐13 standard to simulate physiological degradation rates. A comparative analysis which evaluates the predictive capabilities of each test method has yet to be completed. To this end, we have utilized both systems to test three commercially available PCUs with low and high soft segment content: Bionate® PCU and Bionate® II PCUs, two materials with different soft segment chemistries, and CarboSil® TSPCU, a thermoplastic silicone PCU. Bulk properties of all PCUs were retained with minor changes in molecular weight and tensile properties indicating surface oxidative degradation in the accelerated system after 36 days. Soft segment loss and surface damage were comparable to previous in vivo data. The 3% H2O2 method exhibited virtually no changes on the surface or in bulk properties after 12 months of treatment despite previous in vivo results. These results indicate the accelerated test method more effectively characterized the oxidative degradation profiles than the 3% H2O2 treatment system. The lack of bulk degradation in the 12‐month study also supports the hydrolytic stability of these PCUs. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 3649–3665, 2014.