bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThe 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

AbstractCatalytic 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractVarious 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

AbstractThe 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

AbstractThe 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

AbstractNucleotide‐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

AbstractRecent 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

AbstractThe 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

AbstractA 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

AbstractA 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

AbstractThe 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

AbstractWe 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

AbstractCharland 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

AbstractWe 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

AbstractThe 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

AbstractThis 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.