Different Types Of Carbon Atoms Research Articles

Development of a new force field for the family of primary aliphatic amines using the three steps systematic parameterization procedure

The applicability of the three steps systematic parametrization procedure (3SSPP) to develop a force field for primary amines was evaluated in the present work. Previous simulations of primary amines show that current force fields (FF) can underestimate some experimental values under room conditions. Therefore, we propose a new set of parameters, for an united atom (UA) model, that can be used for short and long amines which predict correctly thermodynamic and dynamical properties. Following the 3SSPP methodology, the partial charges are chosen to match the experimental dielectric constant whereas the Lennard-Jones (LJ) parameters, ε and σ, are fitted to reproduce the surface tension at the vapor-liquid interface and the liquid density, respectively. Simulations were initially conducted for the propylamine molecule by introducing three different types of carbon atoms, Cα and Cβ, with electric charges, and Cn, without charge. Then, modifying the charges of the carbons and using the transferable LJ parameters, the new set of constants for long amines were found. The results show good agreement for the experimental dielectric constant and mass density with a percentage error less than 1% surface tension the error is up to 4% ethylamine, the new charges were obtained from a fitting function calculated from the long amines results. For these molecules, the values of the dielectric constant and the surface tension present errors of the order of 10% with the experimental data. Miscibility of the amines was also tested with the new parameters and the results show reasonable agreement with experiments.

Heteroatom-doped fullerene C70 as non-metal electrocatalysts for oxygen reduction and oxygen evolution from computational study

Here, we report on computational oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) efficiencies of a series of heteroatom-doped fullerene C70 (X(Cn), with B, N, O or Si as dopant X, replacing five different types of carbon atoms (Cn, n = 1–5) on C70). It is clarified that the X(Cn) is thermodynamically stable. ΔG⁎OH shows a good linear relationship with ΔG⁎OOH and ΔG⁎O. It is worth noting that the ORR overpotential values of N(C1), N(C2), N(C3) and N(C4) are 0.87 V, 0.75 V, 0.67 V and 0.73 V, respectively, which are all greater than Pt (ηORR = 0.45 V), but it shows that ORR can still be catalyzed. Compared with the pristine C70, both B and N doping can reduce OER overpotential value and improve OER performance. In particular, N(C4) (ηOER = 0.55 V) has the closest overpotential to traditional noble metal OER catalysts such as RuO2 (ηOER = 0.42 V), indicating that it can be used as a potential candidate for OER catalysts. According to the volcano plots, the best ORR and OER activities of X(Cn) appear at ΔG⁎OH = 0.56 eV and ΔG⁎O − ΔG⁎OH = 1.78 eV, respectively. This work can provide some clues for the design and discovery of new non-metal carbon-based electrocatalysts.

Electronic Energy Relaxation in a Photoexcited Fully Fused Edge-Sharing Carbon Nanobelt.

Carbon nanobelts are cylindrical molecules composed of fully fused edge-sharing arene rings. Because of their aesthetically appealing structures, they acquire unusual optoelectronic properties that are potentially suitable for a range of applications in nanoelectronics and photonics. Nevertheless, the very limited success of their synthesis has led to their photophysical properties remaining largely unknown. Compared to that of carbon nanorings (arenes linked by single bonds), the strong structural rigidity of nanobelts prevents significant deformations away from the original high-symmetry conformation and, therefore, impacts their photophysical properties. Herein, we study the photoinduced dynamics of a successfully synthesized belt segment of (6,6)CNT (carbon nanotube). Modeling this process with nonadiabatic excited state molecular dynamics simulations uncovers the critical role played by the changes in excited state wave function localization on the different types of carbon atoms. This allows a detailed description of the excited state dynamics and spatial exciton evolution throughout the nanobelt scaffold. Our results provide detailed information about the excited state electronic properties and internal conversion rates that is potentially useful for designing nanobelts for nanoelectronic and photonic applications.

Electronic structures and spectral characteristics of the six C32 fullerene isomers.

In this paper, the six C32 isomers which were of crucial importance in the manufacture of new electronic components were identified by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS). For the discernment, geometry optimizations of the six isomers have been carried out, and the C1s XPS and NEXAFS spectra have been simulated in the frame of density functional theory (DFT). XPS spectra, as accurately reflection of different chemical environments where a particular element was located, provided an effective way to identify the six isomers of C32. The NEXAFS spectra, which were commonly used in the electronic structure detection, captured information of unoccupied orbital and showed many recognizable characteristics. To further investigate the source of spectral features, the spectral components calculated from different types of carbon atoms in each C32 isomer also have been well explored and discussed.

The effects of diamond amorphous layer on the diamond lapping surface

The diamond presents its versatile applications in chemical, electrical, optical, mechanical and thermal field. Until now, mechanical polishing is the efficient and low-cost technology to shape the diamond to the desired geometry. However, the defects, or amorphization, of the diamond surface is inevitable during the lapping process. This amorphization layer has some adverse effects on the application of diamond. In this paper, the effects of diamond amorphous layer on the diamond lapping surface integrity are studied. By molecular dynamics (MD) simulation method, it is investigated that a diamond sample covered with an amorphous layer is scratched by a diamond abrasive particle. The formed amorphous layer on the diamond lapping surface is analyzed in terms of the distribution of different types of carbon atoms and surface stress. Our work gives an atomic insight into the integrity of the diamond surface with amorphous layer, based on which our understanding on the diamond lapping surface is deepened.

Sooting tendencies of diesel fuels, jet fuels, and their surrogates in diffusion flames

Surrogates of transportation fuels are useful design tools for developing engines with cleaner and more efficient combustion. It is important that information about the sooting tendency of the target fuel be incorporated in the formulation of these surrogates. Toward that end, in this work we report experimentally measured sooting tendencies of several diesel and jet fuels, surrogates of these fuels, and pure compounds which are components of these surrogates. These fuels, surrogates, and compounds were separately doped in trace quantities (0.5% by mass) into the fuel of a methane-air laminar coflow flame. The sooting tendencies, expressed as Yield Sooting Indices (YSIs), were quantified from spatially resolved two-dimensional soot volume fraction distributions of these flames as measured with color ratio pyrometry. Previous means of matching the sooting behavior of the surrogate to the fuel, such as by matching the fuel’s hydrogen content or its double bond equivalent, were found to be inadequate because these approaches do not fully account for the effects on the fuel’s sooting tendency of branching in aliphatics and alkyl substitutions in aromatics. A strong correlation was observed between the YSI and the relative abundance of different types of carbon atoms (as quantified by 1H and 13C NMR spectroscopy) in these fuels and compounds, indicating that such NMR characterization can capture essential structure-specific sooting information of relevance to surrogate formulation. Based on these YSI measurements, we demonstrate two approaches to predict the sooting tendency of a fuel surrogate. These approaches, based on (1) the choice of pure compounds that are blended to create a surrogate, or (2) the distribution of carbon atom types in a surrogate, can be used to tune the surrogate’s formulation to match the sooting tendency of its target fuel.

Highly Photoluminescent Carbon Dots for Multicolor Patterning, Sensors, and Bioimaging

Fluorescent carbon-based materials have drawn increasing attention in recent years owing to exceptional advantages such as high optical absorptivity, chemical stability, biocompatibility, and low toxicity. These materials primarily include carbon dots (CDs), nanodiamonds, carbon nanotubes, fullerene, and fluorescent graphene. The superior properties of fluorescent carbon-based materials distinguish them from traditional fluorescent materials, and make them promising candidates for numerous exciting applications, such as bioimaging, medical diagnosis, catalysis, and photovoltaic devices. Among all of these materials, CDs have drawn the most extensive notice, owing to their early discovery and adjustable parameters. However, many scientific issues with CDs still await further investigation. Currently, a broad series of methods for obtaining CD-based materials have been developed, but efficient one-step strategies for the fabrication of CDs on a large scale are still a challenge in this field. Current synthetic methods are mainly deficient in accurate control of lateral dimensions and the resulting surface chemistry, as well as in obtaining fluorescent materials with high quantum yields (QY). Moreover, it is important to expand these kinds of materials to novel applications. Herein, a facile and highoutput strategy for the fabrication of CDs, which is suitable for industrial-scale production (yield is ca. 58%), is discussed. The QY was as high as ca. 80%, which is the highest value recorded for fluorescent carbon-based materials, and is almost equal to fluorescent dyes. The polymer-like CDs were converted into carbogenic CDs by a change from low to high synthesis temperature. The photoluminescence (PL) mechanism (high QY/PL quenching) was investigated in detail by ultrafast spectroscopy. The CDs were applied as printing ink on the macro/micro scale and nanocomposites were also prepared by polymerizing CDs with certain polymers. Additionally, the CDs could be utilized as a biosensor reagent for the detection of Fe in biosystems. The CDs were prepared by a hydrothermal method, which is described in the Supporting Information (Figure 1a; see also the Supporting Information, Figure S1). The reaction was conducted by first condensing citric acid and ethylenediamine, whereupon they formed polymer-like CDs, which were then carbonized to form the CDs. The morphology and structure of CDs were confirmed by analysis. Figure 1b shows transmission electron microscopy (TEM) images of the CDs, which can be seen to have a uniform dispersion without apparent aggregation and particle diameters of 2–6 nm. The sizes of CDs were also measured by atomic force microscopy (AFM; Figure S2), and the average height was 2.81 nm. From the high-resolution TEM, most particles are observed to be amorphous carbon particles without any lattices; rare particles possess well-resolved lattice fringes. With such a low carbon-lattice-structure content, no obvious D or G bands were detected in the Raman spectra of the CDs (Figure S3). The XRD patterns of the CDs (Figure 1c) also displayed a broad peak centered at 258 (0.34 nm), which is also attributed to highly disordered carbon atoms. Moreover, NMR spectroscopy (H and C) was employed to distinguish sp-hybridized carbon atoms from sp-hybridized carbon atoms (Figure S4). In the H NMR spectrum, sp carbons were detected. In the C NMR spectrum, signals in the range of 30–45 ppm, which correspond to aliphatic (sp) carbon atoms, and signals from 100–185 ppm, which are indicative of sp carbon atoms, were observed. Signals in the range of 170– 185 ppm, which correspond to carboxyl/amide groups, were also present. In the FTIR analysis of CDs, the following were observed: stretching vibrations of C OH at 3430 cm 1 and C H at 2923 cm 1 and 2850 cm , asymmetric stretching vibrations of C-NH-C at 1126 cm , bending vibrations of N H at 1570 cm , and the vibrational absorption band of C=O at 1635 cm 1 (Figure S5). Moreover, the surface groups were also investigated by XPS analysis (Figure 1d). C1s analysis revealed three different types of carbon atoms: graphitic or aliphatic (C=C and C C), oxygenated, and nitrous (Table S1). In the UV/Vis spectra, the peak was focused on 344 nm in an aqueous solution of CDs. In the fluorescence spectra, CDs have optimal excitation and emission wavelengths at 360 nm and 443 nm, and show a blue color under a hand-held UV lamp (Figure 2a). Excitation-dependent PL behavior was [*] S. Zhu, Q. Meng, Prof. J. Zhang, Y. Song, Prof. K. Zhang, Prof. B. Yang State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University Changchun, 130012 (P. R. China) E-mail: byangchem@jlu.edu.cn

Modeling the semi‐empirical electrotopological index in QSPR studies for aldehydes and ketones

AbstractThe semi‐empirical electrotopological index, ISET, used for quantitative structure–retention relationship (QSRR) models firstly developed for alkanes and alkenes, was remodeled for organic functions such as ketones and aldehydes. The ISET values for hydrocarbons are calculated through the atomic charge values obtained from a Mulliken population analysis using the semi‐empirical AM1 method and their correlation with the SETi values attributed to the different types of carbon atoms according to experimental data. For ketones and aldehydes the interactions between the molecules and the stationary phase are slowly increased relative to the hydrocarbons, due to the charge redistribution that occurs in the presence of heteroatoms. For these polar molecules the increase in the interactions was included in the calculation of the ISET values through the dipole moment of the whole molecule and also through an equivalent local dipole moment related to the net charges of the atoms of the CO and HCO functional groups. Our findings show that the best definition of an equivalent local dipole moment is clearly dependent on the specific features of the charge distribution in the polar region of the molecules (e.g. ketones and aldehydes), which allows them to be distinguished. Thus, the QSRR models for 15 aldehydes and 42 ketones obtained using the remodeled ISET were of good quality as shown by the statistical parameters. The ability of this remodeled index to include charge distribution and structural details opens a new way to study the correlations between the molecular structure and retention indices in gas chromatography. Copyright © 2009 John Wiley & Sons, Ltd.

On a new semi‐empirical electrotopological index for QSRR models

AbstractA new semi‐empirical electrotopological index, ISET, for quantitative structure–retention relationships (QSRR) models was developed based on the refinement of the previously published semi‐empirical topological index, IET. We demonstrate that the values of Ci fragments that were firstly attributed from the experimental chromatographic retention and theoretical deductions have an excellent relationship with the net atomic charge of the carbon atoms. Thus, the values attributed to the vertices in the hydrogen‐suppressed graph of carbon atoms (Ci) are calculated from the correlation of the net atomic charge in each carbon atom, which is obtained from quantum chemical semi‐empirical calculations, and the Ci fragments for primary, secondary, tertiary and quaternary carbon atoms (1.0, 0.9, 0.8 and 0.7, respectively) obtained from the experimental values. This shows that IET encoded this quantum physical reality and that it is possible to calculate a new ISET (the semi‐empirical electrotopological index) through the net atomic charge values obtained from a Mulliken population analysis using the semi‐empirical AM1 method and their correlation with the values attributed to the different types of carbon atoms. This demonstrates that the ISET encodes information on the charge distribution of the solute on which dispersive and electrostatic interactions between the solute (alkanes and alkenes) and the stationary phase strongly depend. Thus, this new method can be considered as an initial step towards forthcoming QSRR/QSAR studies. Copyright © 2008 John Wiley & Sons, Ltd.

Solid state 13C-NMR spectroscopy and XRD studies of commercial and pyrolytic carbon blacks

Abstract The bulk chemistry of commercial carbon blacks and carbon blacks obtained by vacuum pyrolysis (CBP) of used tires was investigated by 13C-NMR spectroscopy with and without magic angle spinning of the sample. Two different kinds of carbon atoms can be distinguished: Graphite like carbon atoms in poly-condensed aromatic rings and carbon atoms in a less ordered environment. Commercial carbon blacks and CBP obtained under different pyrolysis conditions have practically the same concentrations of the different types of carbon atoms in the bulk, whereas earlier ESCA and SIMS investigations have shown that the surface chemistry of CBP is different from commercial carbon blacks and depends strongly on the pyrolysis conditions. Thus, during the pyrolysis only the carbon black surface chemistry is changed. The carbon black bulk structure was also studied by X-ray diffraction. The XRD results, including the radial distribution function (RDF) indicated, in agreement with the NMR results, that the bulk structure of commercial carbon blacks and of CBP are similar.

Identification and determination of the different types of hydrogen and carbon atoms in the soluble organic matter of the Puertollano oil shale

The soluble organic matter of the Puertollano oil shale has been studied by NMR (nuclear magnetic resonance) techniques. The sample was obtained by extractive sonication with carbon disulfide as solvent. 1H and 13C NMR spectra were recorded, the latter by using inverse gated heteronuclear decoupling pulse sequences and chromium(III)-acetylacetonate as relaxation reagent to avoid the NOE (nuclear Overhauser effect). Furthermore, the DEPT NMR pulse sequence (distortionless enhancement by polarization transfer) was used to assign different types of carbon atoms. The study and quantitative determination of the different kinds of hydrogen and carbon atoms present in the sample show that this bitumen is composed mainly of aliphatic hydrocarbons such as linear, polyisoprenoid and cyclic alkanes. There is a smaller contribution from aromatic hydrocarbons of variable structures.

Regularities in the retention of nonsubstituted polynuclear aromatic hydrocarbons in liquid chromatography on polar adsorbents

The retention of polynuclear aromatic hydrocarbons (PAH) is studied in liquid chromatography, using columns packed with silica gel with a hydroxylated surface and the same silica gel with surface-bonded amine and nitrile groups. A linear relationship was found between retention and the number of π-electrons in the molecule, the size of the molecule and the different types of carbon atoms in the molecule. The different carbon atoms in a PAH molecule contribute differently to the retention and this contribution depends on the nature of the polar functional groups on the adsorbent's surface and on the nature and concentration of a polar modifier present in a non-polar eluent.

The relation of physical properties of alkanes to connectivity indices: a molecular explanation

Additive schemes for calculating the molar volumes and heats of vaporization of liquid alkanes from increments characteristic of the numbers and different types of carbon atoms (primary, secondary, tertiary, quaternary), of the mole fraction Zg of gauche conformations, and (where necessary) of other steric factors have been developed. It is suggested that schemes for correlating physical properties of alkanes with connectivity indices mχt are successful because these indices are also correlated with numbers and types of carbon atoms and with Zg.

Die Strukturen der mittleren Ringverbindungen. X. 1, 6‐trans‐Diaminocyclodecan‐dihydrochlorid, monokline Modifikation

AbstractThe structure of the monoclinic modification of 1,6‐trans‐diaminocyclodecanedihydrochloride has been determined, and refined by full‐matrix least‐squares analysis of three‐dimensional X‐ray data. The cyclodecane skeleton is very similar to that found previously in the triclinic modification, but the substituents are attached to different types of carbon atoms. The two crystal modifications thus correspond to different conformational isomers.

Critical temperatures and pressures of hydrocarbons

AbstractA method has been developed for the calculation of van der Waals' constants both a and b for hydrocarbons usually encountered, including the aliphatic, naphthenic, and aromatic types. With these constants critical temperatures and pressures can be calculated directly.Methods recently made available (12, 13, 14, 15) allow the calculation of these constants through the use of substitution values involving the replacement of hydrogen atoms by methyl groups in a definitely prescribed pattern. In this study van der Waals' constants are directly calculated from a consideration only of the molecular structure of the hydrocarbon. This approach has become possible through the assignment of group contributions to different types of carbon atoms, which can be combined in any manner to produce the van der Waals' constants representative of the molecular structure of the hydrocarbon.