Total Carbon Atoms Research Articles

Studies on the characteristics of polycyclic aromatic hydrocarbons accumulation in lipids and the disturbance of lipid metabolism of Ruditapes philippinarum

Polycyclic aromatic hydrocarbons (PAHs) constitute a class of persistent organic pollutants with strong lipophilicity, which readily accumulate within organisms and have the effect to induce disorders in lipid metabolism. The present study aimed to investigate the accumulation localization and pattern of PAHs in Ruditapes philippinarum, and to reveal the association between PAHs and lipids metabolism. The 21-day exposure experiment was conducted using a mixture of phenanthrene, chrysene, and benzo[a]pyrene (the proportion is 1:1:1) at concentrations of 0.4 μg/L, 2 μg/L, and 10 μg/L. The tissue distribution of PAHs indicated that the digestive gland was the primary site of PAHs accumulation. Meanwhile, fluorescence colocalization suggested that PAHs primarily accumulated within the lipid droplets of digestive gland cells. This study further determined the transcriptomic and lipidomic profiles of the digestive gland to analyze the key genes involved in disrupted lipid metabolism and the major lipids affected. Lipidomic analysis identified the key differential metabolites as triglycerides (TGs). Furthermore, TGs were upregulated in the digestive gland had a total carbon atom number of 50–64 and a total number of 3–9 double bonds in the acyl side chains. Biochemical analysis experiments and oil red O stained frozen sections confirmed that the content of TGs steadily increased in various tissues during the experiment, leading to an elevated digestive gland index. Changes of lipid metabolism associated genes expression level also indicated that the synthesis of lipid in digestive gland were up-regulated while the decomposition was down-regulated. This study is the first to demonstrate the cellular localization of PAHs accumulation in bivalves and confirms the pattern of variation in TGs, providing new insights into the mechanisms of PAHs bioaccumulation and lipid metabolism disruption.

High temperature-size exclusion chromatography with triple detection to assess the molecular architecture of low-density polyethylene: Insight into branching and processability correlations.

In this study, three commercially available low-density polyethylene (LDPE) polymers produced via a tubular reactor process, with varying melt flow rates at 190°C/2.16kg (4.0, 1.9, and 0.75g/10min), have been selected and subjected to high temperature-size exclusion chromatography (SEC) analysis coupled with an infrared-5 (IR-5), viscometer (VISCO), and multiangle laser light-scattering detectors. The molecular weight (MW), MW distribution, short-chain branching (SCB), and long-chain branching parameters were investigated. It was found that MW obtained by the universal technique (∼1.57-1.7 times) and multiangle laser light-scattering detection technique is (∼1.43-1.55 times) higher than that of the conventional calibration technique, which could be attributed to structural complexity associated with LDPEs which is not clearly understood by conventional SEC mode alone. The bulk SCB per 1000 total carbon atoms estimated by IR-5 detection was found to range from 16.50 to 17.80. On the other hand, long chain branching frequency per 1000 total carbon atoms obtained by online VISCO and multiangle laser light-scattering detection ranged from 0.46 to 0.54 and 0.65 to 0.94, respectively. Further, the significance of long chain branching parameters on the polymer processing behavior was studied in correlation with rheological property (Die swell ratio).

Explosion characteristics of shale gas in air

In this work, explosion characteristics of stoichiometric shale gas were studied employing a standard 20-L explosion bomb. Shale gas was represented by methane/ethane, methane/propane, and methane/ethane/propane mixtures, and the effect of fuel compositions, the volume fraction of ethane (or propane) increases from 0 to 0.42, on explosion parameters was examined. Results show that the maximum explosion pressure, the maximum explosion pressure rising rate, and the laminar flame speed increase with the volume fraction of ethane (or propane). The reason is that the increment of ethane (or propane) volume fraction increases the mole fraction of [H + O + OH]max. For a given volume fraction, propane provides more heat and H, O, and OH radicals, and consequently, propane shows a more robust incentive function on explosion parameters. Finally, the CH ratio, which is defined as the ratio of total carbon atoms and hydrogen atoms, is used to further study the explosion characteristics of various fuel compositions. There is a robust linear relationship between the CH ratio and explosion parameters. For laminar flame speed, however, the global fit curve provides poor accuracy while the local fitting curves coincide well with the data. This indicates that the laminar flame speed is more sensitive to the gas species.

Interaction of metanil yellow dye with cationic surfactants: Conductometric and spectroscopic studies

Conductometric and spectroscopic methods were used to examine the interactions among the cationic surfactants, tetradecyltrimethylammonium bromide (TTAB) and cetylpyridinium chloride (CPC), and the anionic azo dye metanil yellow (MY) in an aqueous solution. The standard Gibb’s energy (ΔGm0), enthalpy (ΔHm0), and entropy (ΔSm0) of micellization were determined with the help of the equilibrium model. With temperature rise, the critical micelle concentration (cmc) increases because of the interruption of the organized water (WR) molecules enclosing the surfactant’s hydrophobic groups. As the total carbon atoms of the hydrophobic group are more in CPC than TTAB, a considerable fall in cmc value was observed. The presence of MY caused a higher degree of ionization (α) of micelles of TTAB and CPC. The negative values of ΔGm0 and ΔHm0 for both the surfactants in WR and aqueous MY solution (WR-MY) show that the micellization process is spontaneous and exothermic. As indicated by the -TΔSm0 values, which were found to be greater than ΔHm0 values, the entropy gain is typically what regulates the micellization process and the micellization was found to have a negative heat capacity (ΔCp,m0). UV–Visible spectra show that CPC has a higher binding constant (Kb) value as compared to TTAB implying that CPC has a comparatively greater binding affinity with MY dye in aqueous media (WR). The decreasing value of ΔGb for CPC indicates that the chance for the MY–CPC complex formation is more than that of the MY–TTAB complex. As shown by the rise in absorbance values as surfactant concentrations increase, a large number of the MY molecules are attracted to TTAB and CPC micelles.

Molecular descriptors-based models for estimating net heat of combustion of chemical compounds

The heating values of fuels are determined by Heat of Combustion (ΔHC∘)in which the higher amount is more lucrative. Moreover, one of the best methods to compare the stabilities of chemical materials is using ΔHC∘. Therefore, improving precise and general models to estimate this property in different areas such as industries and academic perspective should be considered. In this study, three models namely Least Square Support Vector Machine optimized by Coupled Simulated Annealing optimization algorithm (CSA-LSSVM), Genetic Programming (GP) and Adaptive-Neuro Fuzzy Inference System optimized by PSO, and GA methods (PSO-ANFIS and GA-ANFIS) were applied to estimate ΔHC∘ Also, ΔHC∘ can be expressed by the GP model with an equation. The input parameters of the models are total carbon atoms in a molecule (nC), sum of atomic van der Waals volumes (scaled on carbon atom) (Sv), Broto–Moreau autocorrelation of a topological structure (ATS2m), and total Eigenvalue from electronegativity weighted distance matrix (siege). In addition, two parameter models based on measureable variables of nC and Sv are proposed. In a comprehensive set, 1714 data points were used to fulfill and develop the models. Results demonstrate that the models are trustworthy and accurate (especially the PSO-ANFIS model) in comparison with other recently developed literature models.

Efficient hybrid solar-to-alcohol system via synergistic catalysis between well-defined Cu–N4 sites and its sulfide (CuS)

Abstract In order to selectively produce liquid hydrocarbon fuels by photoelectroreduction of carbon dioxide (CO2) with titania (TiO2) photoanode, copper sulfide (CuS) nanoparticles (NPs) anchored on Cu-porphyrin (CuPor)-based metal–organic framework nanosheets (NSs) were used as cathode catalysts to efficiently convert CO2 to hybrid alcohol products, in particular, ethanol. Crystal size of CuS increased from 24.6 to 48.1 nm with partial decomposition of CuPor, when sulfuration-time increased from 2 to 6 h. Fractal dimension of CuS/CuPor catalyst surface first surface first increased from 1.12 to 1.31 with the increase in sulfuration-time to 4 h because of generated CuS NPs, and then decreased to 1.26 at 6 h. Formation of the heterojunction between CuS NPs with crystal surface (1 1 0) and CuPor NSs with crystal surface (0 0 4) contributed to synergistic catalytic effect on efficient reduction of CO2. The total carbon atom conversion rate in CO2 photoelectroreduction over stable CuS/CuPor-4 h cathode catalyst reached 5174 nmol h−1 cm−2 with a high selectivity of 74.4% for ethanol product. Density functional theory calculations indicated that CuS exhibited high catalytic activity by strengthening binding energy to adsorb CO* in S atoms (1.5 eV), and then CO* was gradually converted to alcohol on the surface of CuPor NSs. The remarkable performance in CO2 electroreduction over cathode catalysts was attributed to synergistic catalysis between the structure of Cu-N4 in 2D macroporous CuPor NSs and its sulfide CuS NPs with high binding energy toward CO* intermediate.

Development of an efficient catalyst with controlled sulfur vacancies and high pyridine nitrogen content for the photoelectrochemical reduction of CO2 into methanol

To efficiently and selectively produce liquid hydrocarbon fuels, e.g., methanol, by CO2 photoelectrochemical reduction, CdS nanoparticles (NPs) anchored on the nitrogen-doped carbon particles (NCP) with core-shell dodecahedral porous structure were used as cathode catalysts. Electron paramagnetic resonance (EPR) spectra indicated that CdS/NCP treated at 500 °C had the maximum S-vacancies. The heterojunction generated between CdS with abundant S-vacancies and NCP with a high content of pyridinic N acted as synergistic catalyst for CO2 reduction. CdS/NCP-500 catalyst exhibited a selectivity of 77.3% towards methanol with a total carbon atom conversion rate of 3052 nmol·h−1·cm−2. Density functional theory (DFT) calculations revealed that the S-vacancies decreased the energy barrier for CO2 conversion into methanol product. NCP, exhibiting a high adsorption capacity for CO2, allowed the conversion of COOH* into CO* (ΔE = −3.6 eV), which was then transferred to the CdS surface displaying abundant S-vacancies for the reduction into the methanol product.

Enhanced photoelectrochemical hydrogenation of green-house gas CO2 to high-order solar fuel on coordinatively unsaturated metal-N sites containing carbonized Zn/Co ZIFs

Porous carbon-based catalysts facilitate CO2 photoelectrochemical reduction reaction (CO2PRR) through the high charge transfer ability and CO2 adsorption ability. However, the design of catalysts with high selectivity towards high-order solar fuels (such as ethanol and propanol) remains challenging. Herein, catalysts of carbonized Zn/Co Zeolitic Imidazolat Frameworks with various pyrolysis hours (xh-C-Zn/Co ZIFs) were synthesized and accessed for high selective CO2PRR for the first time. XRD and TEM analyses show that the C containing functional groups in pristine Zn/Co ZIF are carbonized and turned into amorphous porous carbon, while many Co and ZnO nanoparticles are formed during the pyrolysis process. Electrochemical characterizations of the catalysts prove that increasing pyrolysis time of Zn/Co ZIF from 1 h to 3 h, resulting in a decreased light current density from 3.3 mA/cm2 to 2.3 mA/cm2, which is much higher than that of Zn/Co ZIF (1.9 mA/cm2). Meanwhile, increasing pyrolysis time of Zn/Co ZIF from 1 h to 3 h results in decreased BET surface area and CO2 adsorption ability. XPS spectra suggest a decreased content of metal-nitrogen bonds in C–Zn/Co ZIF, which leads to the formation of coordinatively unsaturated metal-nitrogen sites. Density functional theory (DFT) calculations reveal that the coordinatively unsaturated CoN3V sites in C–Zn/Co ZIF had the highest catalytic activity towards high-order organics. The total carbon atom conversion rate reaches 5459 nmol/h·cm2 when 1h-C-Zn/Co ZIF is employed as catalyst in the CO2PRR system and the selectivity towards high-order solar fuel reaches 84%.

Solar driven reduction of CO2 using Pt-Cu/C as a catalyst in a photoelectrochemical cell: experiment and mechanism study.

Carbon supported nano-metal catalysts are expected to improve CO2 reduction selectivity and efficiency due to the addition of more active sites and enhancement of electron transport ability. In this study, HKUST-1 was pyrolyzed and decorated with Pt to prepare Pt–Cu/C catalysts. The catalytic effect of the catalysts with different Pt contents in the CO2 photoeletrochemical reduction reaction (CO2PRR) were compared. The total carbon atom conversion rate in CO2PRR experiments using Pt–Cu/C catalysts first increased to a peak when using 1.6 wt% Pt–Cu/C catalyst and then decreased with the increase of Pt content. The 1.6 wt% Pt–Cu/C catalyst showed good hydrogen evolution reaction (HER) inhibiting ability compared with other Pt–Cu/C catalysts. Density functional theory (DFT) calculations were conducted to give an insight into the CO2PRR mechanism on some possible active sites in Pt–Cu/C catalysts. The result demonstrated that HER was more likely to be inhibited on the Cu/Pt active surface and at the same time CO2PRR was promoted.

Selective reduction of CO2 to alcohol products on octahedral catalyst of carbonized Cu(BTC) doped with Pd nanoparticles in a photoelectrochemical cell

In order to directionally convert CO2 into liquid fuels, Cu(BTC) doped with Pd nanoparticles was carbonized to obtain a novel octahedral catalyst C-Pd/Cu for selective reduction of CO2 to alcohol products. XRD patterns showed that Cu characteristic peak in C-8 wt% Pd/Cu catalyst shifted to the lowest angle at 2θ=43.22°among all the prepared catalysts (2θC-1.6 wt% Pd/Cu = 43.3°, 2θC-4.8 wt% Pd/Cu = 43.29°, 2θC-11.2 wt% Pd/Cu = 43.26°, 2θC-14.4 wt% Pd/Cu = 43.28°). The inter planar distance of Cu nanoparticles in C-8 wt% Pd/Cu catalyst was 2.0915 nm, which was larger than those in other catalysts. XPS spectra showed main peak shift to lower binding energy, representing the influence of Pd doping to Cu. SEM and TEM indicated that many ∼70 nm Cu particles and ∼10 nm Pd nanoparticles uniformly distributed in ∼250 nm porous carbon-based octahedral particles. Raman spectrum implied that C-Pd/Cu catalyst with many defects (band ratio ID/IG = 0.84) provided more active sites for intermediates adsorption and facilitated electron transfer. BET result showed C-Pd/Cu catalyst had many mesporous. It was found by density functional theory (DFT) calculations that C-Pd/Cu catalyst had good selectivity towards alcohol products such as methanol, the reaction energy towards producing CH3OH was 19.5 eV lower than that of producing HCOOH. The pathway CO2 → COOH∗ → CO∗ + H2O → COH∗ → HCOH∗ → CH2OH∗ → CH3OH was the most favored to produce CH3OH. CO2 photoelectrochemical reduction reaction was then conducted in a photoelectrochemical reduction cell (PEC) to verify the calculation result. The total carbon atom conversion rate over C-8 wt% Pd/Cu catalyst reached 2380 nmol·h−1 cm−2 with a high liquid products selectivity towards alcohol products, which was in good agreement with DFT calculation results. And the PEC system was proved to have more energy input under the same applied voltage compared with the electrochemical system.

Applying a vernix caseosa based formulation accelerates skin barrier repair by modulating lipid biosynthesis

Restoring the lipid homeostasis of the stratum corneum (SC) is a common strategy to enhance skin barrier function. Here, we used a ceramide containing vernix caseosa (VC)-based formulation and were able to accelerate barrier recovery in healthy volunteers. The recovery was examined over 16 days by monitoring trans-epidermal water loss (TEWL) after barrier disruption by tape-stripping. Four skin sites were used to examine the effects of both treatment and barrier recovery. After 16 days, samples were harvested at these sites to examine the SC ceramide composition and lipid organization. Changes in ceramide profiles were identified using principal component analysis. After barrier recovery, the untreated sites showed increased levels of ceramide subclass AS and ceramides with a 34 total carbon-atom chain length, while the mean ceramide chain length was reduced. These changes were diminished by treatment with the studied formulation, which concurrently increased the formulated ceramides. Correlations were observed between SC lipid composition, lipid organization, and TEWL, and changes in the ceramide subclass composition suggest changes in the ceramide biosynthesis. These results suggest that VC-based formulations enhance skin barrier recovery and are attractive candidates to treat skin disorders with impaired barrier properties.

Preparation of a Cu(BTC)-rGO catalyst loaded on a Pt deposited Cu foam cathode to reduce CO2 in a photoelectrochemical cell.

To increase the reaction productivity and selectivity of the CO2 photoelectrochemical reduction reaction, a Cu (benzene 1,3,5-tricarboxylic acid [BTC])-reduced graphite oxide (rGO) catalyst was prepared by using a facile hydrothermal method and used in a CO2 photoelectrochemical cell (PEC) as a cathode catalyst. Characterization of the catalyst proved that successfully bonding of rGO to Cu(BTC) not only facilitated faster transfer of electrons on the surface of the catalyst but also created more active sites. CO2 photoelectrochemical reduction experimental results showed that the total carbon atom conversion rate was up to 3256 nmol h−1 cm−2 which was much higher than when pure Cu(BTC) was used as a cathode catalyst. The liquid product's selectivity to alcohols was up to 95% when −2 V voltage was applied to the system with Cu(BTC)-rGO used as the cathode catalyst.

The effect of the length of alkyl side-chains on the molecular aggregation and photovoltaic performance of the isoindigo-based polymers

To investigate the length of the alkyl side-chains on the photovoltaic performance, three isoindigo-based polymers with different-length side chains on the thiophene-benzene-thiophene (TBT) (electron-donating) moiety and isoindigo (electron-withdrawing) moiety have been designed and synthesized, in which the total carbon atom numbers of the side chains in a constitutional repeating unit are completely identical. The results indicate that the polymer with longer branched side chains on the TBT units and shorter linear side chains on the isoindigo units shows stronger interchain interaction and light-harvesting capacity in 1,2-dichlorobenzene solution and thin film, lower band gaps, stronger π−π stacking interaction, more appropriate microphase separation with PC71BM, higher hole mobility and better photovoltaic performance. As a result, the bulk heterojunction (BHJ) device based on PTBTOD-IDB with 2-octyldodecyl on the TBT moiety and n-butyl on the isoindigo moiety exhibits a power conversion efficiency (PCE) of 5.29%, which is almost eight times as high as that of PTBTEH-IDHD with 2-ethylhexyl side chain on TBT moiety and 2-hexyldecyl side chain on isoindigo moiety.

Characterization of Sulfur Compounds in MTBE

A study is carried out on chemical constitution of sulfur compounds in MTBE and their formation mechanisms. These sulfur compounds are classified into three types: common sulfur compounds, newly formed sulfur compounds, and high boiling sulfur compounds. Common sulfur compounds which include mercaptans, low molecule sulfides and disulfides, are directly from C4, one of the stocks for production of MTBE. The newly formed sulfur compounds, with one sulfur atom and five or more total carbon atoms in one molecule, are mainly tert-butyl methyl sulfide and tert-butyl ethyl sulfide, thioetherification products of thiols with butenes. Many high boiling sulfur compounds, including polysulfides such as dimethyl trisulfide, multisulfur heterocyclic compounds such as 3,5-dimethyl-1,2,4-trithiolane, and oxygen-containing sulfur compounds such as 2-methoxy-3-methylthio-butane, are also found newly formed in the processes of LPG refining and succedent etherification reaction for producing MTBE. Polysulfides are additional products of elemental sulfur to disulfides, and other high boiling sulfur compounds may be formed by thiols reacting with dienes.

Carbon isotopic fractionation during biodegradation of phthalate esters in anoxic condition

Here we evaluate the quantitative relationship between carbon isotopic fractionation and anoxic biodegradation of phthalate esters (PAEs), a kind of endocrine disruptors. The stable carbon isotope delta values (δ13C) of 4 PAEs, i.e. di-methyl phthalate (DMP), di-ethyl phthalate (DEP), di-n-butyl phthalate (DBP), and di-iso-butyl phthalate (DiBP), were analyzed during biodegradation by a pure bacteria strain isolated from the shallow aquifer sediment in anoxic condition. Results showed that the carbon isotopic fractionation in the initial degradation of PAEs was well-described by the Rayleigh equation model with R2 from 0.8885 to 0.9821. The carbon isotopic fractionation (ε) for DMP and DEP were −4.6±0.4‰ and −2.9±0.1‰, respectively, while DBP and DiBP showed limited isotopic fractionation. A linear relationship between ε values and the total carbon atoms present in straight-carbon-chain PAE molecules with R2 of 0.9918. The apparent kinetic isotope effects (AKIEs) were calculated for proposed 4 initial transformation pathways of PAEs. The high carbon AKIEs of 1.048 and 1.036 were obtained for single enzymatic hydrolysis of DMP and DEP, respectively, and fell in the expected KIE range of 1.03–1.09. However, the intrinsic carbon isotope effects for enzymatic hydrolysis of DBP and DiBP might be masked.

Selective edge modification in graphene and graphite by chemical oxidation.

The effect of edge structures in graphene sheets has been well investigated theoretically but most experimental demonstrations of the functionalization have been for the bulk structures because of only a few reports on chemical methods to modify the edges selectively. We herein report a chemical method using the Lemieux-von Rudloff reagent that selectively oxidizes only the edges of graphene sheets. The selective oxidation at the edges of the graphene sheet was confirmed by thermogravimetric analysis (TGA), Raman mapping measurements, and X-ray photoelectron spectroscopy (XPS). The TGA result of the oxidized graphite with different particle sizes showed a slight weight loss at approximately 350 degrees C (2.29% for the middle particles (35 microm)), which indicates thermal decomposition of the oxidized edge part. The Raman mapping measurement in the inner part of graphene sheets didn't detect any defects or translational symmetry breaking after the oxidation. The XPS data clearly showed that the total carbon atom content present as C--O, C==O, and O--C==C increased from 4.65 to 6.18% by the oxidation. Using the obtained edge-oxidized graphene as a starting material, various functionalizations of the edge structure are expected in the future.

TMEDA-derived biscationic amphiphiles: An economical preparation of potent antibacterial agents

Bis-alkylated derivatives of N,N,N′,N′-tetramethylethylenediamine (TMEDA) represent a well-known class of versatile biscationic amphiphiles, owing to their low cost and ease of preparation. Asymmetric TMEDA derivatives, however, have been studied significantly less, particularly in regards to their antimicrobial properties. We have thus prepared a series of 36 mono- and bis-alkylated TMEDA derivatives to evaluate their inhibition of bacterial growth. This series of compounds showed low micromolar activity against a panel of four bacteria. Optimal inhibition was observed when the biscationic amphiphiles possessed modest asymmetry and were composed of between 20 and 24 total carbon atoms in the side chains. These amphiphiles were prepared in a simple two-step procedure, utilizing inexpensive materials and atom-economical reactions, making them practical for further development.

Salt-free catanionic surface active ionic liquids 1-alkyl-3-methylimidazolium alkylsulfate: Aggregation behavior in aqueous solution

A series of salt-free catanionic surface active ionic liquids (SAILs), 1-alkyl-3-methylimidazolim alkyl sulfates (denoted as [Cnmim][CmSO4], n=6, 8, 10; m=12 and n=4; m=10, 14) were synthesized by an ion exchange reaction and their surface properties in aqueous solution were examined systematically by surface tension, fluorescence and electrical conductivity measurements. As catanionic surfactants, these SAILs exhibit notably higher surface activity, compared to the cationic or anionic analogues. Increment in both cationic and anionic alkyl chain lengths for [Cnmim][CmSO4] can both improve the amphiphilic character remarkably. This can be ascribed to cooperative interactions as formation of catanionic pairs between alkyl-substituted imidazolium cations and alkyl sulfate anions. The negative micellization Gibbs free energy values prove that the micellization of all the 1-alkyl-3-methylimidazolim alkyl sulfates investigated is a spontaneous process. Any additional CH2 group makes the micellization process easier regardless if it is on a cation or an anion. When keeping the total carbon atom number constant, we find that the [Cnmim][CmSO4] molecules with greater asymmetric alkyl chains display superior surface activity. This work indicates that the self-assembly of these imidazolium-based salt-free catanionic SAILs can be tailored by adjusting the mismatch of alkyl chains. These SAILs are expected to have potential applications in the fields of colloidal and interface and nanomaterial synthesis.

Electronic state of the limited graphene

The limited graphene means that two directions of graphene are limited, one is zigzag type boundary and the other is armchair type boundary. Based on the tight-binding model, the electronic state and band of the limited graphene are given analytically. The results show that there are only two kinds of electronic states, i.e., the standing wave state and edge state. For the standing wave state, the wave function is in the form of sine function in two directions; for the edge state, the wave function is in the form of hyperbolic sine function in the direction of armchair boundary and in the form of sine function in the direction of zigzag boundary. The band is composited of total carbon atom number N discrete eigenvalues. The expression of quantitativly calculating the number of eigenvalues of edge state is deduced. Through the density of states of the limited graphene we analyze the existence of the edge state and the consistency in the infinity case. The results from the analitical method are the same as the numerical resullts. When the width of two restricted boundary goes into infinity, the result of the limited graphene tends to that in the infinity case.

Exploring the Structure–Solubility Relationship of Asphaltene Models in Toluene, Heptane, and Amphiphiles Using a Molecular Dynamic Atomistic Methodology

The solubility parameters, δ, of several asphaltene models were calculated by mean of an atomistic NPT ensemble. Continental and archipelago models were explored. A relationship between the solubility parameter and the molecule structure was determined. In general, increase of the fused-rings number forming the aromatic core and the numbers of heteroatoms such as oxygen, nitrogen, and sulfur produces an increase of the solubility parameter, while increases of the numbers and length of the aliphatic chains yield a systematic decrease of this parameter. Molecules with large total carbon atom number at the tails, n(c), and small aromatic ring number, n(r), exhibit the biggest values of δ, while molecules with small n(c) and large n(r) show the smallest δ values. A good polynomial correlation δ = 5.967(n(r)/n(c)) - 3.062(n(r)/n(c))(2) + 0.507(n(r)/n(c))(3) + 16.593 with R(2) = 0.965 was found. The solubilities of the asphaltene models in toluene, heptane, and amphiphiles were studied using the Scatchard-Hildebrand and the Hansen sphere methodologies. Generally, there is a large affinity between the archipelago model and amphiphiles containing large aliphatic tails and no aromatic rings, while continental models show high affinity for amphiphiles containing an aromatic ring and small aliphatic chains.