Simulation of Deposition of Wax to Iron Oxide Surfaces

Abstract

Molecular dynamics techniques have been used to model the processes associated with the deposition of alkanes on a hematite surface, and the subsequent growth of an alkane crystal. First we have obtained a relaxed (0001)-hematite surface; this is believed to be the most common surface exhibited on the pipeline walls. Subsequently, the adsorption of two different linear alkanes has been examined: C₁₂ and C₂₈. The principal adsorption site for both has been determined and consisted of the molecule lying between two parallel rows of iron atoms. The subsequent addition of alkane molecules generates a crystalline structure, which corresponds closely with C₂₈ crystal growth along the (010) direction.     

Impact of C60 Adsorption on Surface Plasmon Polaritons on Self-Assembled Ag(111) Islands on Si(111)

The influence of C₆₀ adsorption on the properties of surface plasmon polaritons on small Ag islands is discussed. Under illumination with UV light as well as under illumination with femtosecond laser pulses, a decrease of the photoemission yield with increasing C₆₀ coverage is observed. With angular resolved measurements, changes of the band structure during deposition are studied. Based on these experiments, an increase of the work function with increasing coverage is measured. In two photon photoemission, the surface plasmons are imaged as a periodic moiré pattern, the wavelength of which changes because of a modified effective surface dielectric function. Our findings imply that the wavelength of the plasmon wave becomes shorter as a result. Finally, a decrease of the intensity of the moiré pattern maxima compared with the intensity of the first maximum with increasing C₆₀ coverage has been observed. Accordingly, the damping of the plasmon wave becomes stronger.     

Geometrical deformation and failure behavior of C60 fullerene dimer under applied external electric field

By the quantum-molecular dynamics (QMD) technique based on the Roothaan–Hall equation and the Newton motion law, geometrical deformation and failure behavior of C₆₀ fullerene dimer (2C₆₀) as well as single C₆₀ fullerene under applied external electric field are simulated. Further, the effects of the electric field direction on the electric field-induced deformation, polarization-charge distribution and dipole moment of the fullerene molecules are discussed systemically. It is found that the geometrical configuration and failure behavior of the 2C₆₀ molecule are sensitive to the electric field direction, that when the electric field direction is parallel to the bridging C–C bonds of the 2C₆₀ molecule the 2C₆₀ fails easily, and that when the electric field direction is perpendicular to the 2C₆₀ fails difficultly and has the same polarization and failure mechanism as the single C₆₀.     

Growth and Potential Damage of Human Bone-Derived Cells Cultured on Fresh and Aged C60/Ti Films

Thin films of binary C₆₀/Ti composites, with various concentrations of Ti ranging from ~ 25% to ~ 70%, were deposited on microscopic glass coverslips and were tested for their potential use in bone tissue engineering as substrates for the adhesion and growth of bone cells. The novelty of this approach lies in the combination of Ti atoms (i.e., widely used biocompatible material for the construction of stomatological and orthopedic implants) with atoms of fullerene C₆₀, which can act as very efficient radical scavengers. However, fullerenes and their derivatives are able to generate harmful reactive oxygen species and to have cytotoxic effects. In order to stabilize C₆₀ molecules and to prevent their possible cytotoxic effects, deposition in the compact form of Ti/C₆₀ composites (with various Ti concentrations) was chosen. The reactivity of C₆₀/Ti composites may change in time due to the physicochemical changes of molecules in an air atmosphere. In this study, we therefore tested the dependence between the age of C₆₀/Ti films (from one week to one year) and the adhesion, morphology, proliferation, viability, metabolic activity and potential DNA damage to human osteosarcoma cells (lines MG-63 and U-2 OS). After 7 days of cultivation, we did not observe any negative influence of fresh or aged C₆₀/Ti layers on cell behavior, including the DNA damage response. The presence of Ti atoms resulted in improved properties of the C₆₀ layers, which became more suitable for cell cultivation.     

Effect of different water-soluble forms of fullerene C<Subscript>60</Subscript> on the metabolic activity and ultrastructure of cells in culture

In view of contradictory data on the toxicity of fullerenes for living organisms we studied the effect of water-soluble complexes of C₆₀ with N-polyvinylpyrrolidone (C₆₀/PVP) and γ-cyclodextrin (C₆₀/γ-CD) on MA-104 cells in culture. Both complexes proved to be nontoxic for cultured cells in the dark in a wide range of concentrations. Both complexes provoke changes of cell ultrastructure that reflect enhancement of metabolic activity. At the same time only the exposition with C₆₀/PVP leads to substantial growth of the number and size of mitochondria. However, the effect of two studied water-soluble forms of C₆₀ under intense UV irradiation of cells proved to be opposite: C₆₀/PVP had a cytoprotective action while C₆₀/γ-CD caused a significant growth of phototoxicity. Possible reasons of the differences in the action of different forms of C₆₀ on living organisms are discussed.     

Hatch opening and closing on oxygenation and deoxygenation of C60 bathysphere

The structures and stabilities of C₆₀O_n, where n=1-6, 9, have been calculated using the AM1 Hamiltonian and the program mopac 6.0, and by the density functional technique B3LYP/6-31G* at the AM1 geometry using Gaussian 98. Modes of oxygen addition considered were ethers, epoxides, ketones and ketenes. It is confirmed that in C₆₀O a carbon-carbon bond on a pent-hex edge is replaced by an ether linkage. For higher levels of oxygen addition the replacement of a carbon-carbon bond by two ketone groups becomes important. Particularly stable structures are formed if the additions are on the same, or adjacent, C₆ rings of the C₆₀ structure where the oxygen atoms cooperate in opening up large holes in the molecule. Molecules of greatest stability have a mixture of ether oxygen atoms on pent-hex edges and diketone additions on hex-hex edges. A particularly important stable structure is the mixed ether/ketone isomer of C₆₀O₆ in which a hinged C₅O₂ hatch lid containing two ketone oxygen atoms is opened revealing a hatch 4-5 Å in diameter. An even larger hole of approximately 6 Å in diameter is opened up in a particularly stable isomer of C₆₀O₉ which contains three ether and six ketone groups. Removal of the oxygen atoms from these structures and reoptimisation leads to hatch closing and C₆₀ is reformed.     

A computer simulation of surface microcolony formation during microbial colonization

Several models of microbial surface colonization have been devised to quantitate growth and attachment rates on surfaces. One of these, the surface growth rate equation, is based on the assumption that the number of microcolonies of a given size (C_i) reaches a constant value (C_max) that is equal to the attachment rate (A) divided by the specific growth rate (Μ). In this study, a computer simulation was used to determine the time required to reach C_max. It was shown that C_i approaches C_max asymptotically. The time required is dependent solely upon the growth rate and size of microcolonies. The number of one-celled microcolonies reaches 95% of C_max after 4.3 generations. At low growth rates, a relatively long incubation period is required. Alternate methods that shorten the incubation time are considered.     

Enhanced Nucleation of Atomic Layer Deposited Contacts Improves Operational Stability of Perovskite Solar Cells in Air

Metal‐halide perovskites show promise as highly efficient solar cells, light‐emitting diodes, and other optoelectronic devices. Ensuring long‐term stability is now a major priority. In this study, an ultrathin (2 nm) layer of polyethylenimine ethoxylated (PEIE) is used to functionalize the surface of C₆₀ for the subsequent deposition of atomic layer deposition (ALD) SnO₂, a commonly used electron contact bilayer for p–i–n devices. The enhanced nucleation results in a more continuous initial ALD SnO₂ layer that exhibits superior barrier properties, protecting Cs_0.25FA_0.75Pb(Br_0.20I_0.80)₃ films upon direct exposure to high temperatures (200 °C) and water. This surface modification with PEIE translates to more stable solar cells under aggressive testing conditions in air at 60 °C under illumination. This type of “built‐in” barrier layer mitigates degradation pathways not addressed by external encapsulation, such as internal halide or metal diffusion, while maintaining high device efficiency up to 18.5%. This nucleation strategy is also extended to ALD VO_x films, demonstrating its potential to be broadly applied to other metal oxide contacts and device architectures.     

C<Subscript>60</Subscript> fullerene affects elastic properties and osmoregulation reactions of human lymphocytes

The influence of aqueous solution of pristine C₆₀ fullerene (C₆₀FAS) on functional activity of lymphocytes from a healthy person was studied for the first time. By means of atomic force microscopy, it was found that C₆₀FAS in a concentration of 0.1 mg/ml increases the stiffness of the lymphocyte membrane by 41 % (p < 0.05) and lowers the functional activity of the plasmalemma surface, thereby constraining the use of its membrane material in physiological reactions using a hypotonic model in vitro. However, a cell retains the ability to regulate its volume and demonstrates relative resistance to hypo-osmotic stress. The resistance of lymphocytes in hypo-osmotic medium is facilitated by activation of the nucleus by C₆₀ fullerene particles, which regulates the implementation of two consistent phases of an increase and decrease of cell volume, thereby retaining cell viability. All these indicate the impact of C₆₀ fullerene on the cellular nucleus.     

Tuning the Optical and Rheological Properties of Fullerene C<Subscript>60</Subscript>/Poly (Vinyl Pyrrolidone) Nanofluids via Inclusion of Nanogold

In this article, development of nanogold (NG) containing fullerene C₆₀ nanofluids (NFs) with poly (vinyl pyrrolidone) PVP polymer in water via a wet chemical route is reported and studied their rheo-optical properties. An inclusion of NG into a C₆₀:PVP nanofluid thus results in a gold (Au) surface plasmon resonance (SPR) enhanced π?→?π* C₆₀ (sp²) electron transition over 250–450 nm of absorption spectrum in water. Evolution of a broad Au-SPR band in the 450–750 nm region signifies that a controlled Au³⁺?→?Au reduction reaction had occurred on it and was carried in C₆₀:PVP NFs. The average maximum wavelength value has thus varied along with a molar extinction coefficient in a function of the Au-uploads and shape and size of the flocculates in the resulting Au:C₆₀-PVP NFs. A systematic rheological study performed on the Au:C₆₀-PVP NFs in water by varying the NG content up to 85.0 μM reveals a non-Newtonian behavior with an enhanced yield stress is a signature of Bingham flow. NG of different shapes serves as filler in C₆₀:PVP NFs so as it adapts tailored shear viscosity. The shear viscosity relaxes slowly to the base value on increasing the shear rate from 10 to 100 s^?1 as it leads to breaking up of soft Au:C₆₀-PVP assemblies into a fine structures. Synthesis of Au:C₆₀-PVP NFs with various Au-contents could be potential nanostructure hybrid composite materials for development of photovoltaic nanodevices.     

Tissue Sites of Uptake ofC-Labeled C60

This paper describes thein vivobehavior and potential metabolism of C₆₀and a more water-soluble quaternary ammonium salt-derivatized C₆₀. In both cases, a¹⁴C-labeled fullerene core was utilized for the target molecules that were intravenously injected into female Sprague–Dawley rats. The¹⁴C-labeled C₆₀(*C₆₀) was rapidly (within 1 min) cleared from the circulation and the majority of the *C₆₀accumulated in the liver (90–95%). *C₆₀was not eliminated from the liver over the 120-h period of this study. Our results also suggest that C₆₀is not metabolized by the typical oxidative patterns characteristic of other polycyclic aromatics. Therefore, although not acutely toxic, use of C₆₀, or its derivatives that could be cleaved back to the parent C₆₀in vivo, would likely lead to long-term fullerene accumulation in the liver. The uptake of *C₆₀and¹⁴C-labeled ammonium salt-derivatized C₆₀(1)by human keratinocytesin vitroshowed that while both *C₆₀and1are readily taken up by cells,1accumulates more slowly. Additionally, while C₆₀, at rather high concentrations (2.0 μM) and over extended periods of time (8 days), is able to inhibit the growth of human keratinocytes by about 50%, this effect showed little, if any, photoinducability.     

Co-Exposure with Fullerene May Strengthen Health Effects of Organic Industrial Chemicals

In vitro toxicological studies together with atomistic molecular dynamics simulations show that occupational co-exposure with C₆₀ fullerene may strengthen the health effects of organic industrial chemicals. The chemicals studied are acetophenone, benzaldehyde, benzyl alcohol, m-cresol, and toluene which can be used with fullerene as reagents or solvents in industrial processes. Potential co-exposure scenarios include a fullerene dust and organic chemical vapor, or a fullerene solution aerosolized in workplace air. Unfiltered and filtered mixtures of C₆₀ and organic chemicals represent different co-exposure scenarios in in vitro studies where acute cytotoxicity and immunotoxicity of C₆₀ and organic chemicals are tested together and alone by using human THP-1-derived macrophages. Statistically significant co-effects are observed for an unfiltered mixture of benzaldehyde and C₆₀ that is more cytotoxic than benzaldehyde alone, and for a filtered mixture of m-cresol and C₆₀ that is slightly less cytotoxic than m-cresol. Hydrophobicity of chemicals correlates with co-effects when secretion of pro-inflammatory cytokines IL-1β and TNF-α is considered. Complementary atomistic molecular dynamics simulations reveal that C₆₀ co-aggregates with all chemicals in aqueous environment. Stable aggregates have a fullerene-rich core and a chemical-rich surface layer, and while essentially all C₆₀ molecules aggregate together, a portion of organic molecules remains in water.     

Top‐illuminated Organic Photovoltaics on a Variety of Opaque Substrates with Vapor‐printed Poly(3,4‐ethylenedioxythiophene) Top Electrodes and MoO3 Buffer Layer

Organic photovoltaics devices typically utilize illumination through a transparent substrate, such as glass or an optically clear plastic. Utilization of opaque substrates, including low cost foils, papers, and textiles, requires architectures that instead allow illumination through the top of the device. Here, we demonstrate top‐illuminated organic photovoltaics, employing a dry vapor‐printed poly(3,4‐ethylenedioxythiophene) (PEDOT) polymer anode deposited by oxidative chemical vapor deposition (oCVD) on top of a small‐molecule organic heterojunction based on vacuum‐evaporated tetraphenyldibenzoperiflanthene (DBP) and C₆₀ heterojunctions. Application of a molybdenum trioxide (MoO₃) buffer layer prior to oCVD deposition increases the device photocurrent nearly 10 times by preventing oxidation of the underlying photoactive DBP electron donor layer during the oCVD PEDOT deposition, and resulting in power conversion efficiencies of up to 2.8% for the top‐illuminated, ITO‐free devices, approximately 75% that of the conventional cell architecture with indium‐tin oxide (ITO) transparent anode (3.7%). Finally, we demonstrate the broad applicability of this architecture by fabricating devices on a variety of opaque surfaces, including common paper products with over 2.0% power conversion efficiency, the highest to date on such fiber‐based substrates.     

The Roles of Structural Order and Intermolecular Interactions in Determining Ionization Energies and Charge‐Transfer State Energies in Organic Semiconductors

The energy landscape in organic semiconducting materials greatly influences charge and exciton behavior, which are both critical to the operation of organic electronic devices. These energy landscapes can change dramatically depending on the phases of material present, including pure phases of one molecule or polymer and mixed phases exhibiting different degrees of order and composition. In this work, ultraviolet photoelectron spectroscopy measurements of ionization energies (IEs) and external quantum efficiency measurements of charge‐transfer (CT) state energies (E_CT) are applied to molecular photovoltaic material systems to characterize energy landscapes. The results show that IEs and E_CT values are highly dependent on structural order and phase composition. In the sexithiophene:C₆₀ system both the IEs of sexithiophene and C₆₀ shift by over 0.4 eV while E_CT shifts by 0.5 eV depending on molecular composition. By contrast, in the rubrene:C₆₀ system the IE of rubrene and C₆₀ vary by ≤ 0.11 eV and E_CT varies by ≤ 0.04 eV as the material composition varies. These results suggest that energy landscapes can exist whereby the binding energies of the CT states are overcome by energy offsets between charges in CT states in mixed regions and free charges in pure phases.     

DFT studies of acrolein molecule adsorption on pristine and Al- doped graphenes

The ability of pristine graphene (PG) and Al-doped graphene (AlG) to detect toxic acrolein (C₃H₄O) was investigated by using density functional calculations. It was found that C₃H₄O molecule can be adsorbed on the PG and AlG with adsorption energies about ?50.43 and – v30.92 kcal mol^?1 corresponding to the most stable configurations, respectively. Despite the fact that interaction of C₃H₄O has no obvious effects on the of electronic properties of PG, the interaction between C₃H₄O and AlG can induce significant changes in the HOMO/LUMO energy gap of the sheet, altering its electrical conductivity which is beneficial to sensor designing. Thus, the AlG may be sensitive in the presence of C₃H₄O molecule and might be used in its sensor devices. Also, applying an external electric filed in an appropriate orientation (almost stronger than 0.01 a.u.) can energetically facilitate the adsorption of C₃H₄O molecule on the AlG.     

Graphitic Carbon Nitride Induced Micro‐Electric Field for Dendrite‐Free Lithium Metal Anodes

Uncontrolled dendrites resulting from nonuniform lithium (Li) nucleation/growth and Li volume expansion during charging cause serious safety problems for Li anode‐based batteries. Here the coating of nickel foam with graphitic carbon nitride (g‐C₃N₄) to have a 3D current collector (g‐C₃N₄@Ni foam) for dendrite‐free Li metal anodes is reported. The lithiophilic g‐C₃N₄ coupled with the 3D framework is demonstrated to be highly effective for promoting the uniform deposition of Li and suppressing the formation of dendrites. Both density functional theory calculations and experimental studies indicate the formation of a micro‐electric field resulting from the tri‐s‐triazine units of g‐C₃N₄, which induces numerous Li nuclei during the initial nucleation stage, effectively guiding the following Li growth on the 3D Ni foam to be well distributed. Furthermore, the 3D porous framework is favorable for absorbing any volume change and stabilizing the solid–electrolyte interphase layer during repeated Li plating/stripping. As such, a Li metal anode based on the g‐C₃N₄@Ni foam has a remarkable electrochemical performance with a high Coulombic efficiency (98% retention after 300 cycles), an ultralong lifespan up to 900 h, as well as a low overpotential (<15 mV at 1.0 mA cm^?2) at a Li deposition of 9.0 mA h cm^?2.     

Global forest carbon uptake due to nitrogen and phosphorus deposition from 1850 to 2100

Spatial patterns and temporal trends of nitrogen (N) and phosphorus (P) deposition are important for quantifying their impact on forest carbon (C) uptake. In a first step, we modeled historical and future change in the global distributions of the atmospheric deposition of N and P from the dry and wet deposition of aerosols and gases containing N and P. Future projections were compared between two scenarios with contrasting aerosol emissions. Modeled fields of N and P deposition and P concentration were evaluated using globally distributed in situ measurements. N deposition peaked around 1990 in European forests and around 2010 in East Asian forests, and both increased sevenfold relative to 1850. P deposition peaked around 2010 in South Asian forests and increased 3.5‐fold relative to 1850. In a second step, we estimated the change in C storage in forests due to the fertilization by deposited N and P (?C_{ν dep}), based on the retention of deposited nutrients, their allocation within plants, and C:N and C:P stoichiometry. ?C_{ν dep} for 1997–2013 was estimated to be 0.27 ± 0.13 Pg C year^?1 from N and 0.054 ± 0.10 Pg C year^?1 from P, contributing 9% and 2% of the terrestrial C sink, respectively. Sensitivity tests show that uncertainty of ?C_{ν dep} was larger from P than from N, mainly due to uncertainty in the fraction of deposited P that is fixed by soil. ?C_{P dep} was exceeded by ?C_{N dep} over 1960–2007 in a large area of East Asian and West European forests due to a faster growth in N deposition than P. Our results suggest a significant contribution of anthropogenic P deposition to C storage, and additional sources of N are needed to support C storage by P in some Asian tropical forests where the deposition rate increased even faster for P than for N.     

Syntheses of water-soluble [60]fullerene derivatives and their enhancing effect on neurite outgrowth in NGF-treated PC12 cells

Water-soluble [60]fullerene (C₆₀) derivatives were synthesized to examine their bioactivities. PC12 cells were used as a model of nerve cells and the bioactivities of synthesized C₆₀ derivatives together with some reported ones were tested. Among the compounds tested, C₆₀/(γ-CyD)₂, C₆₀-bis(γ-CyD) (5) containing C₆₀-mono(γ-CyD) (5′), and C₆₀/PVP were sufficiently soluble in water and showed an enhancing effect on the neurite outgrowth of NGF-treated PC12 cells.     

Can soil organic carbon isotopes be used to describe grass-tree dynamics at a savanna-grassland ecotone and within the savanna?

Abstract. We evaluated the use of soil organic carbon (SOC) isotopes to describe grass-tree dynamics at locations at the savanna-C₄ grassland ecotone and within a temperate semiarid Quercus savanna in southeastern Arizona, USA. SOC will not describe grass-tree dynamics at locations within the savanna because isotope composition near the soil surface does not correspond with the overlying vegetation and recent C₃ carbon has been deposited at deep soil depths with no C₄analog. In contrast, SOC can describe grass-tree dynamics at the savanna-grassland ecotone because isotope composition near the soil surface corresponds with overlying vegetation and significant deep soil deposition of C₃ carbon was not apparent. At the ecotone, trees became established in the last 700–1700 years. There is no evidence to suggest an unstable grass-tree mixture at the ecotone since that time.     

Parallel Computation of the Matrix of the Chemical Distances on the Connection Machine

Abstract

We report here the parallel implementation of an original algorithm allowing a fast calculation of the distance matrix D of a graph representing a given chemical structure (molecule, polymer, crystal, etc.). Our algorithm fits perfectly in the SIMD parallel architecture of the Connection Machines CM-200 as we shall show. After discussing the performances of the parallel evaluation of D, we will end with a relevant application concerning C₆₀ and C₇₀ fullerenes. The present study applies to a generic globally connected graph without any restriction on the local connectivity of each graph's vertex.