bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface Scattering of Hyperthermal (10–50 eV) C60 Molecules: Kinetic Energy Transfer, Vibrational Excitation, and Initial Vibrational Energy Effects
Authors: Bekkerman Anatoly , Tsipinyuk Boris , Budrevich Andrei , Kolodney Eli 
Published: November 2013

AbstractScattering of neutral C60 molecules from surfaces at hyperthermal impact energies of 10–50 eV was studied as a function of impact energy, scattering angle, surface temperature, and incident vibrational energy. Scattered kinetic energy scaled linearly with impact energy, and kinetic energy losses varied with scattering angle from ∼85% to ∼40% (peak values). Analyzing the results, we found nearly complete decoupling between normal and tangential energy losses. Tangential losses are described in terms of various models of rotational excitation and it is concluded that translational slip is involved during the scattering process. The C60 surface interaction well‐depth was determined from the scattering results and compared with the measured desorption energy. Using a newly developed vibrational thermometry method for C60 we measured kinetic energy losses and collisional vibrational excitation as a function of the average vibrational energy of the incident C60 (<Ev> = 7–15 eV). Kinetic energy loss was independent of initial vibrational energy for both near‐grazing and near‐normal scattering angles, while collisional vibrational excitation showed a weak inverse dependence on initial vibrational energy for both scattering angles. For the lowest incident C60 vibrational energy (<Ev> = 9.8 eV) and near‐normal scattering (30.7 eV in the normal impact energy component), vibrational excitation was 5% of the impact kinetic energy. Our detailed results describe the first real “bouncing” regime for C60 scattering off surfaces.
Lasers and Molecular Beams Applied to the Study of Clusters of Chiral Molecules
Authors: Giardini‐Guidoni Anna , Piccirillo Susanna 
Published: November 2013

AbstractResonance‐enhanced two‐photon ionization time‐of‐flight spectroscopy has been applied in a supersonic beam to study R‐(+)‐1‐phenyl‐1‐propanol (PR) and its diastereomeric clusters with R(–) and S(+) 2‐butanol (BR; BS) and with R(–) and S(+) 2‐butylamine (AR, AS). This mass resolved spectroscopy allowed us to assign a few vibronic frequencies of PR and measure the spectral shift of the diastereomeric clusters PRBR, PRBS, PRAR, and PRAS. The different bathocromic shifts observed in the two pairs indicates the possibility for spectroscopically differentiating the aggregates. Moreover, very reproducible differences in the fragmentation patterns provide an additional tool for their discrimination.
Intramolecular Electronic Energy Transfer in the Naphthalene—Anthracene Bichromophoric Molecular Complex in a Supersonic Jet Expansion
Authors: Rosenblum Gershon , Karni Yoram , Speiser Shammai 
Published: November 2013

AbstractIntramolecular electronic energy transfer (intra‐EET) was investigated in an isolated bichromophoric naphthalene (N) and anthracene (A) 1:1 molecular cluster. Investigation of the spectroscopic properties of these chromophores, separately and loosely bound in a van der Waals complex, helps to understand the dependence of the EET rate on the initially excited vibronic level and on the cluster's interchromophoric orientation.Measurement of fluorescence excitation spectra of anthracene at different anthracene pressures shows bands that can be assigned to dimers of anthracene. From measurement of the anthracene excitation spectrum at increasing naphthalene pressures one can identify other spectral features, characterized by different spectral shifts from excitations of the bare molecule. Some transitions are probably due to a 13.5‐cnr−1 progression associated with an interchromophore cluster bond. Pressure dependence of fluorescence intensity gives evidence for 1:1 cluster composition, and for a slow intra‐EET rate that is associated with an unfavored orientation of the two chromophores in one of the two possible conformers of the A‐N cluster, as supported by a calculation of the cluster geometry and by comparison with a recent study of intra‐EET in the A–(CH2)n‐N bichromophoric molecules.
Mass Spectrometric Studies of Fullerene Ion Beams
Authors: Laskin Julia , Lifshitz Chava 
Published: November 2013

AbstractThe energetics and dynamics of C2 evaporations from carbon cluster ions Cn+ were studied using time‐resolved mass spectrometric techniques. Time‐resolved appearance energies (AEs) were determined for C58+ and C56+ on a double‐focusing mass spectrometer using electron‐space‐charge trapping. The AEs were found to be nearly independent of time for times longer than 80 μs. A large intrinsic kinetic shift, IS=30.5 eV, was observed. This intrinsic shift is due to radiative decay in the visible, which is unusually efficient for fullerenes. Time‐resolved kinetic energy releases (KERs) and metastable fractions (MFs) for Cn+ (n = 48 −62) were measured on an ion trap/reflectron mass spectrometer for trapping times up to 100 μs. The average KER for C2 evaporation from fullerenes was observed to decrease with increasing precursor ion lifetime. This constitutes proof that the KER is due to the non‐fixed energy in the transition state rather than to a reverse activation energy, and the reaction takes place via a loose transition state. The metastable fractions decrease with increasing trapping time, as expected. The results obtained for C58+ → C56+ + C2 are successfully modeled taking into account radiative cooling. The shape of the plot of MFs versus ln(t2/t1) (where t1 and t2 are the times corresponding to the beginning and the end of a metastable time window, respectively) is mainly defined by the relation between dissociative and radiative rate constants.
Nucleation and Initial Growth Stages of Chemical Vapor Deposition (CVD) Diamond
Authors: Shima‐Edelstein Ruth , Gouzman Irina , Hoffman Alon 
Published: November 2013

AbstractNucleation of diamond on non‐diamond virgin substrates is characterized by low nucleation densities and long incubation times. Various methods have been developed to enhance nucleation densities and reduce the duration of incubation. This report describes a number of different but related studies of diamond nucleation on silicon and chemically modified silicon surfaces. The effect on the initial stages of deposition of mechanical abrasion with slurries and in‐situ sample biasing are especially discussed.Substrate abrasion with diamond results in the embeddying of diamond debris into its surface. Destructive ion implantation into this diamond debris is found to prevent subsequent diamond growth, therefore leading to the conclusion that the diamond debris serves as growth centers. Abrasion of the substrate with mixed metal/diamond slurries is reported to further enhance nucleation relative solely to diamond abrasion. It is suggested that during the chemical vapor deposition (CVD) process some metals alter the composition of the gas phase above the growing surface. Also, the role of surface reactions is emphasized.We also introduce the dc‐glow discharge process as a novel, in situ surface pretreatment method for the formation of a precursor for diamond nucleation. Our results show that the promotion of diamond growth by this method is primarily due to formation of nano‐size diamond particles during the pretreatment process. It is suggested that, to some extent, graphitic carbon with a high degree of defects may serve as a diamond nucleation center as well.
Diamond Electronic Devices—The End of a Dream?
Authors: Collins Alan T. 
Published: November 2013

AbstractBecause diamond has a high band gap, high‐thermal conductivity, high‐breakdown voltage, high‐saturated electron velocity, low permittivity, and is exceptionally hard and resistant to chemical attack, it has long been argued that it is the ultimate electronic material. In this article the early history of diamond electronic devices is briefly reviewed. The relevant properties of diamond are then compared with those of silicon, GaAs, SiC, and the group III nitrides, and selected recent research on diamond electronic devices is covered in detail. Although exceptional advances have been made, it is concluded that the prospects for commercially successful electronic devices are poor.
Transient Lens Spectroscopy in a Fast Timescale
Authors: Terazima Masahide 
Published: November 2013

AbstractUsing the thermal lens experimental configuration, many types of fast molecular dynamics besides the density variation (the normal thermal lens signal) are reflected by the lens signal. Various transient lens techniques in a fast timescale are reviewed. By using the population lens signal, excited state dynamics can be studied with a probe light which has less restricted wavelength range over a wide timescale from a few femotoseconds to seconds. From the optical Kerr lens signal, molecular reorientational dynamics in solution can be revealed. The temporal development of the temperature lens signal provides unique information such as the thermalization time after nonradiative transition from the excited state, which is usually very difficult to determine by other spectroscopies. Identification of the lens components and the advantages of the time‐resolved transient lens method are discussed.
Differential Thermal Lens Spectrometry in the Infrared
Authors: Franko Mladen , Bicanic Dane 
Published: November 2013

AbstractThe operational principle and the first application of a novel infrared differential thermal lens spectrometer for optical studies of liquid samples is described. Compared to a conventional double‐beam (pump/probe) configuration, the instrumental setup described here offers the possibility to substantially reduce (as much as 30 times) the background signal caused by the absorption of solvent, and hence to achieve improved limits of detection (LOD).Differential thermal lens spectrometry (TLS) with a CO laser as the excitation source was applied to detect tuberculostearic acid and the insecticide Carbaryl, both extracted into CCl4; the corresponding LOD are 200 μg/L and 150 μg/L, respectively. Results of preliminary studies also suggest the potential use of differential TLS for detection of citric acid dissolved in water.
Copper(II) Mediated Homo‐Coupling of 1,2‐difluorovinylstannanes
Authors: Blumenthal Eric J. , Burton Donald J. 
Published: November 2013

AbstractThe reaction of substituted 1,2‐difluorovinylstannanes with anhydrous Cu(OAc)2 in dimethylformamide, under an oxygen atmosphere, at room temperature stereospecifically gives the corresponding symmetrical 1,3‐dienes in good to excellent yields. Moisture drastically reduces the yield of homo‐coupled product and produces significant amounts of RCF=CFH. The Cu(II) promoted homo‐coupling of the fluorinated vinylstannanes is superior to the Cu(I)Cl mediated homo‐coupling of the corresponding hydrocarbon vinylstannanes. When 1,2‐difluorovinylstannanes are treated with Cu(I)Cl, the reaction is sluggish and significant amounts of RCF=CFH are formed.
Palladium(0)‐Catalyzed Allylation Reaction with Dimethyl 2‐fluoromalonate
Authors: Kawasaki Tomoko , Kitazume Tomoya 
Published: November 2013

AbstractThe palladium(0)‐catalyzed allylation reaction of dimethyl 2‐fluoromalonate with allylic carbonates proceeds smoothly under neutral conditions to give the SN2 allylation product. However, using the nucleophile NaCF(CO2Et)2 under basic conditions increased the chemical yield. Moreover, the SN2′ allylation product was increased up to 75% yield.
Intermolecular Excited‐State Proton Transfer in Clusters of 1‐Naphthol with Water and with Ammonia
Authors: Knochenmuss Richard , Fischer Ingo , Lührs Daniel , Lin Qiong 
Published: November 2013

AbstractThe excited‐state proton transfer reactions of 1‐naphthol(H2O)n and 1‐naphthol(NH3)n clusters are compared. Both exisiting and new data suggest that the two systems may react in strikingly different fashions, roughly corresponding to non‐adiabatic and adiabatic limiting cases, respectively. In water clusters, the reaction is kinetically limited by solvent motion, and there is a strong dynamic interaction involving the water and two lowest electronic excited states, which thereby invert. In ammonia clusters, the excited states appear to be premixed by the the stronger base, and the reaction may proceed in a rapid manner, resembling intracluster vibrational relaxation, with relatively little solvent reorganization.
Hydrogen‐Bond Rearrangement and Intermolecular Proton Transfer in Protonated Methanol Clusters
Authors: Chang Huan‐Cheng , Jiang Jyh‐Chiang , Chang Hai‐Chou , Wang Lillian R. , Lee Yuan T. 
Published: November 2013

AbstractVibrational predissociation spectra (VPS) of hydrogen‐bonded and non‐hydrogen‐bonded (free) OH stretches within the frequency range of 2700–3800 cm−1 are closely analyzed to determine the isomeric structures and proton location in protonated methanol clusters, H+(CH3OH)n. The present report emphasizes protonated methanol tetramers and pentamers, which are predicted by ab initio calculations to exist in linear and cyclic forms. Only one isomer with linear structure was identified in the VPS of protonated methanol tetramers in a supersonic expansion. Both linear and cyclic configurations were found for protonated methanol pentamers, and an isomeric transition between these two structures due to hydrogen‐bond rearrangement was observed at a cluster temperature of 190 K. Ab initio calculations indicated that the excess proton in these clusters can be either localized on one methanol unit, as in cyclic H+(CH3OH)4 and linear H+(CH3OH)5 isomers, or delocalized between two methanol molecules, as in linear H+(CH3OH)4 and cyclic H+(CH3OH)5 isomers. Such unique proton delocalization behavior is revealed in the VPS of cyclic H+(CH3OH)5, which is recognized as a symmetric five‐membered pentamer by its characteristic free‐OH stretching absorption at 3647 cm−1 and hydrogen‐bonded OH stretches at 3448 and 3461 cm−1. Using protonated methanol pentamers as a model system, a proton transfer mechanism is suggested to involve intracluster proton transfer mediated by a sequence of hydrogen‐bond breaking and reforming processes. This appealing mechanism can be closely associated with the exceptionally high proton mobility in liquid methanol.
Effects of Model Protein Environments on the Dynamics of Proton Wires
Authors: Decornez Hélène , Hammes‐Schiffer Sharon 
Published: November 2013

AbstractThe multiconfigurational molecular dynamics with quantum transitions (MC‐MDQT) method is utilized to study the impact of model protein environments on the dynamics of proton wires. The MC‐MDQT method allows the realtime nonequilibrium quantum dynamical simulation of proton transport along water chains and provides a framework for analyzing the detailed dynamical mechanisms of these multiple proton transfer reactions. In this paper, the protein environment is modeled by applying structural restraints to the oxygen atoms of the chain, by applying external electric fields, and by including solvating water molecules hydrogen‐bonded to the ends of the water chain. Our simulations illustrate that the protein environment could strongly impact the dynamics of proton wires through a combination of structural restraints, fluctuating electric fields, solvation, and hydrogen bonding. Our simulations also indicate that quantum effects such as hydrogen tunneling and nonadiabatic transitions play a significant role under certain nonequilibrium conditions.
The Deuterium Isotope Effect as a Tool to Investigate Enzyme Catalysis: Proton‐Transfer Control Mechanisms in Cytochrome c Oxidase
Authors: Karpefors Martin , Ädelroth Pia , Aagaard Anna , Smirnova Irina A. , Brzezinski Peter 
Published: November 2013

AbstractCytochrome c oxidase is a membrane‐bound redox‐driven proton pump. The coupling of the exergonic electron‐transfer reactions from cytochrome c to oxygen to proton translocation across the membrane requires control of internal electron‐ and proton‐transfer reactions. In this work, we focus on the kinetics of electron and proton transfer during those reaction steps that are coupled to proton pumping in cytochrome c oxidase. The results show that during the first pumping step (peroxy → oxoferryl transition), proton transfer regulates intramolecular electron transfer. The proton transfer takes place in two steps: (1) Internal proton transfer from a protonatable group, proposed to be Glu(I‐286), in the so‐called D‐pathway, to an oxygen intermediate at the binuclear center (τ ≅ 100 μs); (2) Rapid re‐protonation of Glu(I‐286) from the bulk solution (τ < 100 μs). Only after proton uptake from solution the last (fourth) electron is transferred “one step closer” towards the binuclear center (from CuA to heme a). During the second proton‐pumping step (oxoferryl → oxidized), this electron is transferred to the binuclear center, linked to the uptake of a proton through the D‐pathway. The electron‐transfer rate displays a kinetic‐isotope effect (kH/kD) of 6 ± 1 (in a pH range in which the pH dependence of the rate is small), which indicates that the electron transfer is rate‐limited by the proton transfer. The entry into the D‐pathway (around Asp(I‐132)) is composed of a cluster of negatively‐charged amino acid residues together with a number of histidines, forming a so‐called proton‐collecting antenna designed to allow rapid protonation of groups within the proton‐transfer pathway.
Quantum–Classical Simulation of Proton Migration in Water
Authors: Zahn Dirk , Brickmann Jürgen 
Published: November 2013

AbstractProton transport in water is treated within a mixed quantum–classical molecular dynamics scheme. Therein the migration of a positive charge is treated as a two‐step process: (i) the displacement of a hydronium ion, followed by (ii) proton transfer between a hydronium ion and an adjacent water molecule. Both the hydronium ion and the water molecules are treated as flexible molecules. In the H5O2+‐complex, the proton no longer belongs to a single water molecule, but is delocalized between the two oxygen atoms. The proton transfer is treated quantum mechanically as a function of a transfer coordinate within a single complex. The quantum description is changed to another pair of water molecules after strong proton localization to one of the water molecules in the complex and according to distance criteria with respect to adjacent water molecules. It is demonstrated that the proposed formalism is well suited for an effective simulation of the proton migration in water. In particular, the lifetimes of Eigen complexes and the proton diffusion coefficient (as obtained from simulations) are in very good agreement with corresponding experimental data.
Reproducible quantification of osteoclastic activity: Characterization of a biomimetic calcium phosphate assay
Authors: Maria Salwa M. , Prukner Christiane , Sheikh Zeeshan , Mueller Frank , Barralet Jake. E. , Komarova Svetlana V. 
Published: November 2013

AbstractOsteoclasts are responsible for bone and joint destruction in rheumatoid arthritis, periodontitis, and osteoporosis. Animal tusk slice assays are standard for evaluating the effect of therapeutics on these cells. However, in addition to batch‐to‐batch variability inherent to animal tusks, their use is clearly not sustainable. Our objective was to develop and characterize a biomimetic calcium phosphate assay based on the use of phase pure hydroxyapatite coated as a thin film on the surface of culture plates, to facilitate the reproducible quantification of osteoclast resorptive activity. Osteoclasts were formed from RAW 264.7 mouse monocyte cell line using a pro‐resorptive cytokine RANKL (50 ng/mL). No change in substrate appearance was noted after culture with media without cells, or undifferentiated monocytes. Only in the presence of osteoclasts localized areas of calcium phosphate dissolution were observed. The total area resorbed positively correlated with the osteoclast numbers (R2 = 0.99). The resorbed area was significantly increased by the addition of RANKL, and decreased after application of known inhibitors of osteoclast resorptive activity, calcitonin (10 μM), or alendronate (100 μM). Thus, calcium phosphate coated substrates allow reliable monitoring of osteoclast resorptive activity and offer an alternative to animal tusk slice assays. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 102B: 903–912, 2014.
Augmentation of engineered cartilage to bone integration using hydroxyapatite
Authors: Dua Rupak , Centeno Jerry , Ramaswamy Sharan 
Published: November 2013

AbstractArticular cartilage injuries occur frequently in the knee joint. Photopolymerizable cartilage tissue engineering approaches appear promising; however, fundamentally, forming a stable interface between the subchondral bone and tissue engineered cartilage components remains a major challenge. We investigated the utility of hydroxyapatite (HA) nanoparticles to promote controlled bone‐growth across the bone‐cartilage interface in an in vitro engineered tissue model system using bone marrow derived stem cells. Samples incorporated with HA demonstrated significantly higher interfacial shear strength (at the junction between engineered cartilage and engineered bone) compared with the constructs without HA (p < 0.05), after 28 days of culture. Interestingly, this increased interfacial shear strength due to the presence of HA was observed as early as 7 days and appeared to have sustained itself for an additional three weeks without interacting with strength increases attributable to subsequent secretion of engineered tissue matrix. Histological evidence showed that there was ∼7.5% bone in‐growth into the cartilage region from the bone side. The mechanism of enhanced engineered cartilage to bone integration with HA incorporation appeared to be facilitated by the deposition of calcium phosphate in the transition zone. These findings indicate that controlled bone in‐growth using HA incorporation permits more stable anchorage of the injectable hydrogel‐based engineered cartilage construct via augmented integration between bone and cartilage. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 102B: 922–932, 2014.
Plasma electrolytic oxidation coatings on γTiAl alloy for potential biomedical applications
Authors: Lara Rodriguez L. , Sundaram P. A. , Rosim‐Fachini E. , Padovani A. M. , Diffoot‐Carlo N. 
Published: November 2013

AbstractIn an attempt to enhance the potential of gamma titanium aluminide intermetallic alloy as a biomaterial, its surface characteristics were successfully modified using a calcium and phosphorous rich electrolyte through the application of plasma electrolytic oxidation. Scanning electron microscopy and atomic force microscopy were used to characterize the morphology and topographical features of the resulting coating while X‐ray diffraction and energy dispersive spectroscopy were used to determine the surface oxide composition. The mechanical properties of the surface coating were characterized by nanoindentation studies. The results observed show the formation of a submicron scale porous structure and a concomitant increase in the surface roughness. The surface oxide was composed of rutile and anatase phases. Composition gradients of Ca and P were also present which can possibly enhance the biomaterial application potential of this treated surface. Nanoindentation measurements indicate the formation of a fairly compact oxide during the process. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 102B: 988–1001, 2014.