Classes Of Hydrocarbons Research Articles

On-Surface Synthesis and Characterization of Pentadecacene and Its Gold Complexes.

Acenes are an important class of polycyclic aromatic hydrocarbons that have gained considerable attention from chemists, physicists, and material scientists, due to their exceptional potential for organic electronics. They serve as an ideal platform for studying the physical and chemical properties of sp2 carbon frameworks in the one-dimensional limit and also provide a fertile playground to explore magnetism in graphenic nanostructures due to their zigzag edge topology. While higher acenes up to tridecacene have been successfully generated by means of on-surface synthesis, it is imperative to extend their synthesis toward even longer homologues to comprehensively understand the evolution of their electronic ground state. Here, we demonstrate the on-surface synthesis of pentadecacene (15ac) from a trietheno-bridged precursor via the atom-manipulation-induced dissociation of protecting groups or the elimination of adatoms in a gold-pentadecacene complex. The generated 15ac was investigated by scanning tunneling microscopy (STM)/spectroscopy (STS) and noncontact atomic force microscopy (nc-AFM), in combination with first-principles spin-polarized density functional theory (DFT) calculations. We found that 15ac exhibits an open-shell singlet ground state with an experimental singlet-triplet gap of 124 meV and an STS transport gap of ∼1.12 eV. The formation of Au-pentadecacene complexes suggested a considerable contribution of polyradical character to the electronic ground state of 15ac. Our work contributes to a fundamental understanding of the electronic properties of long acenes and to the development of a versatile STM tip-assisted methodology for the synthesis of elusive compounds.

Physicochemistry and comparative metagenomics of a tropical estuary persistently inundated with anthropogenic pollutants.

The physicochemistry, metabolic properties, and microbial community structure of a tropical estuary persistently inundated with anthropogenic pollutants were elucidated using diverse analytical tools and a shotgun metagenomics approach. The physicochemistry of the Awoye estuary surface water (AEW) and sediment (AES) revealed higher values in the sediment for most of the parameters analyzed, while aside from copper and zinc, the concentrations of the detected heavy metals (Cd, Cr, Pb, Fe, As, Ni, Hg, Mn, Se) in the water and sediment were higher than the acceptable thresholds. Hydrocarbon content analysis revealed increasingly high concentrations of high molecular weight polycyclic aromatic hydrocarbons (HMW PAHs) in the sediment. Structurally, the predominant taxa in the AEW metagenome are Proteobacteria (50.35%), Alphaproteobacteria (43.31%), Brevundimonas (49.96%), and Leptolyngbya boryana (14.93%), while in the sediment (AES) metagenome, Proteobacteria (53.03%), Gammaproteobacteria (28.66%), Azospirillum (6.51%), and Acidihalobacter prosperus (7.56%) were preponderant. Statistical analysis of the two microbiomes (AEW, AES) revealed significant statistical differences (P < 0.05) at all the hierarchical levels. Functional characterization of the two metagenomes revealed extensive adaptations of the sediment microbiome to various environmental stressors as evident in the high numbers of putative genes involved in the degradation of diverse classes of aromatic hydrocarbons, efflux, detoxification, and transport of heavy metals, and metabolism of organic/inorganic nutrients. Findings from this study revealed that the estuary sediment is the sink for most of the anthropogenic pollutants and harbors the more adapted microbiome that could serve as a potential bioresource for the bioremediation of the perturbed estuary.

Excited-State Hund's Rule Violations in Bridged [10]- and [14]Annulene Perimeters.

Molecules with Hund's rule violations between low-lying singlet and triplet states may enable a new generation of fluorescent emitters. However, only a few classes of molecules are known with this property at the current time. Here, we use a high-throughput screening algorithm of the FORMED database to uncover a class of compounds where the first excited state violates Hund's rule. We examine this class of bridged [10]- and [14]annulene perimeters with saturated bridges, and relate them to known conjugated polycyclic systems with Hund's rule violations. Despite the structural similarities with the related class of nonalternant polycyclic hydrocarbons, the mechanism is different in these bridged annulene perimeters. Here, two molecular orbital configurations contribute to each excited state. Consequently, a Hund's rule violation can only be unambiguously assigned based on the symmetry of the lowest excited singlet and triplet states. With several examples of synthetically realistic molecules, the class of bridged [10]- and [14]annulenes thus provides a structural link between the known nonalternant and alternant (azaphenalene) classes of molecules violating Hund's rule. These design principles may open avenues for the identification of new types of molecules where the order of the photophysically relevant first excited singlet and triplet states are inverted.

Recent Advances in the Cascade Cyclization of Alkyne Units for the Construction of Benzofluorenes

AbstractBenzofluorenes are an important class of polycyclic aromatic hydrocarbons (PAHs), which are widely used in materials science for light‐sensitive electronic components. In addition, the benzofluorene skeleton also serves as a key structural unit in various natural products. Therefore, the development of synthetic strategies for the construction of benzofluorenes has been a prominent research topic in synthetic chemistry. Over the past few decades, numerous efforts have been made for the construction of benzofluorenes via cascade cyclization of alkyne units. This review aims to summarize recent advances in the cascade cyclization of alkyne units for the construction of Based on the different reaction mechanisms underlying these transformations, this review can be divided into four categories: (1) thermal‐induced cascade cyclization of alkyne units for the construction of benzofluorenes, (2) metal‐catalyzed cascade cyclization of alkyne units for the construction of benzofluorenes, (3) acid‐promoted/catalyzed cyclization of alkyne units for the construction of benzofluorenes, and (4) base‐promoted cascade cyclization of alkyne units for the construction of benzofluorenes.

Unveiling Structural Variations in Armchair-Edge Coronoids by Spectroscopies.

This study explores the electronic and vibrational properties of armchair coronoids (ACs), a unique class of polycyclic aromatic hydrocarbons with varying molecular and cavity sizes. Through density functional theory simulations, we investigated the X-ray photoelectron spectroscopy (XPS) and Raman spectra of C222, C114, C42, and their derivatives with different cavity sizes. The results reveal that band gaps and electronic properties of ACs can be precisely tuned by adjusting the molecular and cavity dimensions. XPS spectra demonstrated shifts in binding energy correlating with bandgap variations, while Raman spectra exhibited distinct C-C stretching and breathing modes. Notably, the introduction of cavities led to shifts in the breathing mode band, providing insights into the structural identification of ACs through Raman spectroscopy. The findings suggest that combining XPS and Raman spectroscopy can effectively characterize ACs, offering a comprehensive understanding of their structure-property relationships. This research lays the groundwork for future experimental and theoretical studies on the potential applications of ACs in electronic materials.

Solubility Study of a Ladder-Like Polyphenylsilsesquioxane for Membrane Application

In this work, the solubility of a high-molecular-weight homopolymer, a ladder polyphenylsilsesquioxane, was studied in different classes of solvents, including alcohols, aprotic solvents, ketones, alkanes, and aromatic hydrocarbons. The Hansen parameters and the parameter of long-range interaction between the polymer and the solvent were analyzed. The insolubility of L-PPSQ in a wide range of solvents allows for expecting that the properties of a membrane on its basis would be stable during operation in these media. At the same time, aprotic solvents are well suited for the preparation of membranes based on L-PPSQ by the solution phase inversion method.

The Magnetic Properties of Fluorenyl and tert-Butyl-nitroxyl Acene-Based Derivatives: A Quantum Chemical Insight

Acenes, as a class of polycyclic aromatic hydrocarbons, attract considerable attention due to their remarkable nonlinear optical and magnetic properties. The aim of this work was the elucidation of the capability of radical-substituted acene derivatives to undergo spin-state-switching rearrangements. For this purpose, a series of acene-based (anthracene, pentacene, heptacene) molecules bearing fluorenyl and tert-butyl-nitroxyl radicals were investigated through comprehensive quantum chemical modeling of their electronic structures, isomerization and magnetic properties. A possible mechanism of the transformation of the closed-shell folded isomer into the biradical twisted structure of the bis-fluorenyl anthracene has been ascertained by applying the procedure of searching for the Minimum Energy Crossing Point. The conditions favoring the occurrence of spin-state-switching in such classes of polycyclic aromatic hydrocarbon derivatives have been formulated. By varying the size of an acene core and the type of radical substituent, the compounds capable of changing their magnetic properties have been revealed. Considering the unique features of radical-bearing acene-based derivatives, the proposed molecules can be used as functional materials in photonics and electronics.

Phase distribution and probabilistic risk assessment of polycyclic aromatic hydrocarbons in indoor air of coffee shops at Zahedan, Iran

Polycyclic aromatic hydrocarbons (PAHs) are a class of hydrocarbons, some of which are established human carcinogens. Human exposure to these chemicals is complex and originates from both indoor and outdoor sources. This study measured the concentration of PAHs in the gaseous and particulate phases during the cold months of 2022 using XAD-2 sorbent tubes and Polytetrafluoroethylene (PTFE) filters in the indoor air of coffee shops in Zahedan, Iran (n = 23). The average concentrations of particulate-bound PAHs and gaseous PAHs were 13,411.86 ± 6517.24 ng/m³ and 6432.76 ± 4311.72 ng/m³, respectively. Source apportionment analyses indicated that the primary sources of PAHs in coffee shops were fossil fuel combustion and environmental tobacco smoke (ETS), commonly referred to as second and third-hand smoke. The lifetime cancer risk (LTCR) of inhaled PAHs was calculated using the Monte Carlo simulation method. The mean LTCR for adults and children from inhaling these substances were 9.43 × 10-6 ± 5.06 × 10-6 and 5.34 × 10-6 ± 2.87 × 10-6, respectively. The hazard quotient (HQ) of PAHs exceeded 1. These findings highlight the need to reduce PAHs exposure in public spaces through proper health warning labels and regulated indoor smoking policies.

Heavy Heterodendralenes: Structure and Reactivity of Phosphabora[3]dendralenes.

The incorporation of phosphorus and boron into [3]dendralenes provides access to heavy heterodendralenes, a new class of main-group precursor to "doped" polycyclic hydrocarbons. [n]Dendralenes are a core class of unsaturated hydrocarbons built from geminally connected polyenes; the resulting arrangement of conjugated C═C bonds enables [n]dendralenes to undergo reactions that allow rapid access to complex polycyclic compounds. The increasing technological and synthetic importance of main-group-containing polycyclic hydrocarbons and their analogues makes new routes to access such systems highly attractive. Here we report the preparation of the first heavy heterodendralenes in the form of phosphorus- and boron-containing [3]dendralenes, prepared by a ring-opening reaction of a 1,2-phosphaborete. We reveal the electronic effect of P/B incorporation and demonstrate that, like their hydrocarbon analogues, phosphabora[3]dendralenes undergo diene-transmissive cycloaddition chemistry.

Pollution Characteristics and Ecological Impact of Screening Analysis of Fishing Port Sediments from Dalian, North China.

Environmental pollution from synthetic chemical mixtures has significant adverse impacts on marine ecosystems. However, identifying the main constituents of chemical mixtures that pose ecological threats is challenging due to the necessity of an integrated workflow for comprehensive identification and toxicological prioritization of pollutants. Here, an all-in-one mass spectrometric strategy integrating target, suspect, and nontarget analysis was used to investigate organic pollutants of concern in fishing port sediments, with 355 pollutants (32 from target analysis, 118 from suspect screening and 205 from nontarget analysis) identified in 11 categories. The chemical classes of polycyclic aromatic hydrocarbons (PAHs), pesticides, and intermediates were the extensively detected chemical classes. The ecological risks of absolutely quantified pollutants (i.e., 16 parent PAHs, 7 organophosphate esters (OPEs), 10 pesticides and 4 benzotriazole ultraviolet absorbers) were assessed using toxicity-weighted concentration ranking, with o,p'-DDT being the major contributor. Under the toxicological priority index (ToxPi) framework, an extended ranking of all identified pollutants was achieved by combining instrument response and detection frequency, with a priority control list of 15 pollutants obtained, of which benzo[ghi]perylene (BghiP) and p,p'-DDE had the highest risk priority. Due to frequent detection rates and significant environmental risks, routine monitoring of petroleum pollutants is considered essential. This study presents a general workflow that includes comprehensive identification and prioritization of pollutants, facilitating chemical management and ecological risk assessment.

Generation of abnormal distributions of inter- and intramolecular δ13C compositions in hydrocarbons from gold tube pyrolysis of an Australian torbanite

Abnormal stable carbon isotopic (δ13C) compositions, deviating from the conventional order of δ13C1 < δ13C2 < δ13C3, are frequently observed in natural gas reservoirs. For thermogenic gas, these anomalies, such as δ13C1 < δ13C3 < δ13C2 or δ13C1 > δ13C2 > δ13C3, have multiple formation mechanisms including gas mixing in conventional systems and desorption processes of gaseous hydrocarbons in unconventional shale gas systems due to their inconsistency with Rayleigh fractionation processes. Considering distinct reaction pathways (e.g., C1 polymerized to C2), these aberrant δ13C signatures are often construed as intrinsic hallmarks of extensively evolved natural gas. However, on the basis of gas generation simulation, not all findings exhibit abnormal δ13C values, hinting at multifaceted and intricate mechanisms governing the isotopic fractionation of alkane gas components. This study conducted gold tube pyrolysis of an Australian torbanite, revealing four distinct types of δ13C anomalies in hydrocarbon classes. Polycyclic aromatic hydrocarbons (PAHs) exhibited δ13C values more negative than co-occurring n-alkanes. δ13C3 displayed a negative trend shift from EasyRo = 3.5 %, resulting in a partially δ13C-reversed gas (δ13C1 < δ13C3 < δ13C2) formed at EasyRo ≈ 4.1 %. Moreover, intramolecular δ13C3 (both terminal and central carbons, termed δ13Ca and δ13Cb, respectively) reversed alongside the overall δ13C3 trend. Additionally, the evolution of site preference in δ13C3 (termed ‰SP = δ13Ca – δ13Cb) transitioned from progressively negative to positive. The results of this study demonstrate that the potential conversion between saturated hydrocarbons, aromatic hydrocarbons, and alkane gases is at least partially responsible for δ13C anomalies, but also that gaseous hydrocarbons formed from other fractions at high maturity cannot be ruled out, such as kerogen and pyrobitumen.

Cladanthus scariosus Essential Oil and Its Principal Constituents with Cytotoxic Effects on Human Tumor Cell Lines.

Cladanthus is a small genus of the Asteraceae family comprising just five species that, apart from Cladanthus mixtus (L.) Chevall., has a large distribution in all the Mediterranean countries, mainly in the North Africa area. Several ethnopharmacological uses have been reported for species of this genus. Notably, Cladanthus scariosus (Ball) Oberpr. & Vogt is endemic to Morocco. Seeking to delve deeper into the phytochemistry and pharmacological aspects of this species, in this work, we investigated the essential oil (EO) obtained from the aerial parts of a locally sourced accession, hitherto unexplored, growing wild near Tizi n'Ticha, Morocco. The chemical composition of the EO, obtained by the hydrodistillation method, was evaluated by GC and GC-MS. The most abundant EO constituent was germacrene D (13.2%), the principal representative of the sesquiterpene hydrocarbons class (27.2%). However, the major class of constituents was monoterpene hydrocarbons (43.0%), with α-pinene (11.9%), sabinene (10.2%), p-cymene (8.5%), and α-phellandrene (5.2%) as the most abundant. The EO and its main constituents have been tested for their possible cytotoxic activity against three human tumor cell lines (MDA-MB 231, A375, and CaCo2) using the MTT assay, with corresponding IC50 values of 13.69, 13.21, and 22.71 µg/mL, respectively. Germacrene D and terpinen-4-ol were found to be the most active constituents with IC50 values between 3.21 and 9.53 µg/mL. The results demonstrate remarkable cytotoxic activity against the three human tumor cell lines studied, and in the future, further analyses could demonstrate the excellent potential of C. scariosus EO as an antitumor agent.

Dissecting the long-term neurobehavioral impact of embryonic benz[a]anthracene exposure on zebrafish: Social dysfunction and molecular pathway activation

Benz[a]anthracene (BaA), a prevalent environmental contaminant within the polycyclic aromatic hydrocarbon class, poses risks to both human health and aquatic ecosystems. The impact of BaA on neural development and subsequent social behavior patterns remains inadequately explored. In this investigation, we employed the zebrafish as a model to examine the persisting effects of BaA exposure on social behaviors across various developmental stages, from larvae, juveniles to adults, following embryonic exposure. Our findings indicate that BaA exposure during embryogenesis yields lasting neurobehavioral deficits into adulthood. Proteomic analysis highlights that BaA may impair neuro-immune crosstalk in zebrafish larvae. Remarkably, our proteomic data also hint at the activation of the aryl hydrocarbon receptor (AHR) and cytochrome P450 1A (CYP1A) pathway by BaA, leading to the hypothesis that this pathway may be implicated in the disruption of neuro-immune interactions, contributing to observable behavioral disruptions. In summary, our findings suggest that early exposure to BaA disrupts social behaviors, such as social ability and shoaling behaviors, from the larval stage through to maturity in zebrafish, potentially through the detrimental effects on neuro-immune processes mediated by the AHR-CYP1A pathway.

Current Ecological State of the Volga-Akhtuba Floodplain Water Bodies (Using the Example of Dudachenok Shallow Channel)

Current ecological state assessment of the water body located on the Volga-Akhtuba floodplain territory (Dudachenok shallow channel) after its environmental rehabilitation was carried out. It was found that almost all the studied indicators correspond to the approved quality standards with the exception of strontium – 4.5 mg/l (MPC – 0.4 mg/l (Order No. 552 dated December 13, 2016), MPC – 7 .0 mg/l (SanPiN 1.2.3685-21 No. 2 dated January 28, 2021)) and barium – 1.25 mg/l (MPC– 0.74 mg/l (Order No. 552 dated December 13, 2016), MPC – 0.7 mg/l (SanPiN 1.2.3685-21 No. 2 dated January 28, 2021)). It is concluded that it is possible to assign a hydrocarbonate class (predominant anion), calcium group (predominant cation) and second type to a water body. A study of bottom sediments revealed that chloride (36 mg/kg) is one of the predominant anions, calcium (27 mg/kg) and sodium (27 mg/kg) are the predominant cations, which agrees with the obtained water chemical composition data. Chemical and toxicological parameters of bottom sediments were analyzed. It was determined that the quantitative content of metals and pesticides does not exceed the maximum permissible concentrations.

Investigation of the Behavior of Hydrocarbons during Crude Oil Fouling by High-Resolution Electrospray Ionization Mass Spectrometry

Crude oil is probably the most complex natural chemical mixture processed in various ways to make fuel and fine chemicals among a wide range of products in industrial processing. The conditions of those industrial processes often include high temperatures, which often cause undesired chemical reactions. One of those reaction sequences is crude oil fouling, which finally results in the formation of undesired solid deposits of carbon material, a calamity that costs millions of dollars worldwide each year and produces toxic waste. However, the compounds involved in fouling, let alone the underlying reaction mechanisms, are not understood to date. Here, in order to investigate chemical fouling, the process was simulated under laboratory conditions, focusing on hydrocarbons as the main constituents of crude oil. The results demonstrate large differences within the hydrocarbon class of compounds before and after thermal treatment, even for a very light crude oil fraction, which initially does not contain any bigger or heavier compounds. Here, the fouling reaction is simulated and studied on the molecular level using high-resolution mass spectrometry. After thermal treatment, new, higher molecular weight hydrocarbon compounds with high aromaticity were detected. Results indicate that a radical reaction leads to the formation of larger and more aromatic compounds. The findings were verified by the use of a model hydrocarbon compound to study the mechanism.

Chemometric Analysis Combined with GC × GC-FID and ESI HR-MS to Evaluate Ultralow-Sulfur Diesel Stability.

Diesel has been the most employed fuel in highway and nonhighway transportation systems. Many studies over the past years have attempted to classify diesel as a stable or unstable composition since this fuel can still degrade during storage or thermal oxidative processes. Products generated because of such degradation are the reason for the formation of soluble gums and insoluble organic particulates, which in turn cause a negative influence on engine performance. This work reports a detailed composition of nonpolar and polar compounds in many ultralow-sulfur diesel (ULSD) samples by comprehensive two-dimensional gas chromatography with a flame ionization detector (GC × GC-FID) and electrospray ionization high-resolution mass spectrometry (ESI HR-MS). In addition, chemometric approaches were applied for ULSD storage stability investigation. GC × GC-FID experiments achieved the nonpolar chemical characterization for the ULSD samples, including all main hydrocarbon classes: paraffins, mono- and dinaphthenics and olefins, and aromatics. The GC × GC-FID data combined with principal component analysis (PCA) described that the separation of the samples' concerning storage stability was mainly due to the contents of mono- and diaromatic compounds in the unstable ULSD samples. Moreover, PCA was also applied to the ESI (±) data set, and the results highlight the presence of compounds belonging to O class (natural antioxidants), which decrease the rate of oxygen consumption in the fuel, characterizing it as stable composition. The basic nitrogen compounds are mostly present in the stable ULSD samples indicating that they did not affect the stability of the fuel. On the other hand, the HC classes presented pronounced abundance among unstable ULSD samples suggesting that the fuel degradation may go through the oxidation of hydrocarbons and the formation of Ox compounds as byproducts. Furthermore, MS/MS experiments point to the formation of CcHhNnOo-like precursor species, which can react with each other and lead to the formation of gums and insoluble sediments in the fuel. In summary, the results express the potential of using the GC × GC-FID and ESI (±) Orbitrap MS techniques as valuable tools for diesel stability evaluations.

1.4-Dioxane and the Phenolic Compound Against UV Irradiation of Diesel

During storage and transportation, some classes of hydrocarbons in diesel fuel can undergo chemical transformations over time due to ambient temperature, sunlight, and oxygen in the air. As a result of these reactions, there are changes in the composition of the fuel, such as sediment, color change, turbidity, which have a negative effect on the physico-chemical indicators of the fuel. Such a change can cause engine wear and adversely affect engine efficiency, performance, emissions, and durability. The main objective of this study is to investigate antioxidant additives to delay the aging process in diesel fuels. The compounds 1,4 dioxane and 3-hydroxy-1-(2-hydroxyphenyl)-3-(4-nitrophenyl)-propane-1- one were selected for this study. UV rays have been used to stimulate the aging process. As a result of research, the use of 1,4-dioxane has significantly improved the chemical stability, density, and kinematic viscosity of fuel and its use in diesel fuel has shown greater stabilization potential.

Development of a Compact Skeletal Mechanism for Thermally Cracked Hydrocarbon Fuels

ABSTRACT The construction of a compact kinetic mechanism for thermally cracked hydrocarbon fuels holds great importance for developing advanced engine with regenerative cooling. In the present study, a skeletal oxidation mechanism consisting of 104 species and 373 reactions, which can be divided into two parts, i.e. a core mechanism for pyrolysis gas, and a skeletal sub-mechanism for pyrolysis liquid, was developed by a decoupling method. The combustion process of pyrolysis gas and its pure constituents was depicted by incorporating detailed reaction pathways of H2/CO/C1-C4 molecules, and variations of hydrocarbon classes, as well as carbon number distributions were also considered by introducing eight skeletal sub-mechanisms for heavy hydrocarbons which covered chain alkanes, cycloalkanes, and monocyclic aromatics in pyrolysis liquid, thus the newly developed mechanism was suitable for thermally cracked hydrocarbon fuels over a wide range of pyrolysis temperatures. The skeletal mechanism was extensively validated by experimental data of laminar burning velocities and ignition delay times, confirming its applicability for reproducing the flame characteristics of pyrolysis gases, pyrolysis liquids, and thermally cracked fuels. Sensitivity analyses showed that laminar burning velocities of thermally cracked fuels were only affected by reactions involving small radicals when the pyrolysis temperature was lower than 600°C, while reactions involving benzene rings started to dominate the flame propagation of thermally cracked fuel at 650°C under fuel-lean, stoichiometric, and fuel-rich conditions. Reactions of small radicals and heavy hydrocarbons both affected the ignition process of thermally cracked fuels.

Synthesis of Tridecacene by Multistep Single-Molecule Manipulation.

Acenes represent a unique class of polycyclic aromatic hydrocarbons that have fascinated chemists and physicists due to their exceptional potential for use in organic electronics. While recent advances in on-surface synthesis have resulted in higher acenes up to dodecacene, a comprehensive understanding of their fundamental properties necessitates their expansion toward even longer homologues. Here, we demonstrate the on-surface synthesis of tridecacene via atom-manipulation-induced conformational preparation and dissociation of a trietheno-bridged precursor on a Au(111) surface. The generated tridecacene has been investigated by scanning tunneling microscopy and spectroscopy (STM/STS), combined with first-principles calculations. We observe that the STS transport gap (1.09 eV) shrinks again following the gap reopening of dodecacene (1.4 eV). Spin-polarized density functional theory calculations confirm an antiferromagnetic open-shell ground-state electronic configuration for tridecacene in the gas phase. Interestingly, tridecacene's open-shell character is significantly reduced upon interaction with the Au(111) surface despite being only physisorbed. The interaction with the surface leads to a lowering of the magnetization of tridecacene, a reduced gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), compared to the gas phase, and a reduced relative energy to the nonmagnetic state, making it nearly isoenergetic. These observations show qualitatively that the influence of the Au(111) substrate on the properties of long acenes is significant, which is important for interpreting the measured STS transport gaps. Our work contributes to a fundamental understanding of the electronic properties of long acenes, confirming a nonmonotonous length-dependent HOMO-LUMO gap, and to the development of multistep tip-assisted synthesis of elusive compounds.

Effect of Solute on Interfacial Properties and Micelle Structure of Dodecylbenzenesulfonate (DBS): Experimental and Molecular Dynamics Studies.

A combined experimental and molecular dynamic simulation approach was used to examine the structure and interfacial properties of solute-saturated micelles. The properties of dodecylbenzenesulfonate (DBS) micelles were examined in dodecane and benzene hydrocarbon systems. Pyrene fluorescence was used to determine the aggregation number of surfactant monomers in the micelle systems. Molecular dynamic (MD) simulations using energy minimization applying the CHARMm force field with the TIP3P model for water. Comparison of the DBS/benzene and DBS/Dodecane micelles equilibrium structures via radial distribution function (RDF) and probability distribution function (PDF) analysis indicates that the area per head group for the DBS/Benzene micelle interface is significantly larger than that of the DBS/Dodecane at the interface. It was also determined that benzene molecules can move freely within the micelle while dodecane is strictly confined in the core of the micelle. The increased interfacial area per monomer caused by the insertion of benzene also reduces the effectiveness of the surfactant, which has implications for use in various environmental applications. However, the DBS/benzene micelle can solubilize many more hydrocarbon molecules in one micelle with less surfactant monomer (i.e., lower aggregation number) per micelle due to the increased available packing positions within the micelle. This, in turn, increases the efficiency of the surfactant in real-world applications which is consistent with previous laboratory results. Understanding the differing solubilization characteristics of surfactants against various classes of hydrocarbons in single solute systems is a necessary step to beginning to understand their solubilization properties in the mixed waste systems prevalent in most surfactant enhanced remediation (SEAR) strategies.