Closed-shell polycyclic aromatic hydrocarbon cations: a new category of interstellar polycyclic aromatic hydrocarbons

Density functional theory has been employed to calculate the harmonic frequencies and intensities of a range of polycyclic aromatic hydrocarbon (PAH) cations that explore both size and electronic structure effects on the infrared spectroscopic properties of these species. The sample extends the size range of PAH species considered to more than 50 carbon atoms and includes several representatives from each of two heretofore unexplored categories of PAH cations: (1) fully benzenoid PAH cations whose carbon skeleton is composed of an odd number of carbon atoms (C(odd) PAHs); and (2) protonated PAH cations (HPAH+). Unlike the radical electronic structures of the PAH cations that have been the subject of previous theoretical and experimental work, the species in these two classes have a 'closed'-shell electronic configuration. The calculated spectra of circumcoronene, C54H18, in both neutral and (radical) cationic form are also reported and compared with those of the other species. Overall, the C(odd) PAHs spectra are dominated by strong CC stretching modes near 1600 cm(-1) and display spectra that are remarkably insensitive to molecular size. The HPAH+ species evince a more complex spectrum consistent with the added contributions of aliphatic modes and their generally lower symmetry. Finally, for both classes of closed-shell cations, the intensity of the aromatic CH stretching modes is found to increase with molecular size far out of proportion with the number of CH groups, approaching a value more typical of neutral PAHs for the largest species studied.     

Synthesis of a three-dimensional spiro-annulated polycyclic aromatic hydrocarbon

We describe the results of our investigation on the preparation, structural characterization, and optical properties of a spiro-annulated polycyclic aromatic hydrocarbon prepared by the cyclodehydrogenation of a hexa{2-(9,9′-spirobifluorenyl)}benzene precursor molecule. Single-crystal X-ray diffraction analysis reveals that the anthracene backbone adopts one of the largest end-to-end twists thus far reported.     

Analysis of intermediates from polycyclic aromatic hydrocarbon biodegradation

A major difficulty in assessing bioremediation in hydrocarbon impacted field sites is the determination of the extent and products of contaminant biodegradation. Previously, various analytical techniques, including mass spectrometry and chromatography, have been used to characterize components in mixtures resulting from biodegradation. In this work, the applicability of capillary electrophoresis (CE) to this area of research is demonstrated. CE methods were optimized for analysis of compounds that are known metabolites of polycyclic aromatic hydrocarbon (PAH) biodegradation.     

Suppressing aggregation in a large polycyclic aromatic hydrocarbon

With the approach presented herein, a large aromatic pi-system is synthesized, which shows extraordinarily high solubility and an effective suppression of aggregation. This was due to a distortion of the aromatic core by bulky tert-butyl groups and the solubilizing effects of alkyl chains in the corona of the aromatic core. Therefore not only the processing and cleaning of the materials with standard laboratory techniques became possible, but moreover the first structure-rich UV/vis and a resolved (1)H NMR spectra for an aromatic system two times larger than hexa-peri-hexabenzocoronene were recorded. The bulk properties in an extruded fiber as well as on the surface showed a columnar self-assembly including a phase in which a homeotropic alignment on a substrate was observed, which turns the material into an interesting candidate for future applications in electronic devices.     

Electrochemical DNA biosensor for polycyclic aromatic hydrocarbon detection

Four DNA electrochemical biosensors using four types of DNA (calf thymus ssDNA, calf thymus dsDNA, salmon testis ssDNA and salmon testis dsDNA) were constructed using graphite screen printed electrodes. These biosensors were exploited as analytical tool to detect polycyclic aromatic hydrocarbons-DNA interactions using benzo(a)anthracene and phenantrene as model analytes, the guanine oxidation peak variation being the signal revealing the interaction between PAHs and immobilized DNA. The salmon testis ssDNA biosensor resulted as the most promising device and was further evaluated for benzo(a)anthracene, fluorene, indeno(1,2,3-cd)pyrene, anthracene, and phenanthrene in 5–40 ng mL^?1 solutions, and for benzo(a)pyrene (5–50 ng mL^?1). A concentration dependent variation of the DNA guanine oxidation peak was observed for all compounds. The effect of benzo(a)pyrene ultraviolet (UV) activation on the benzo(a)pyrene (BaP)-DNA interaction was evaluated at concentration levels of 20 and 50 ng mL^?1, and a 3.5- and 2.7-fold increases of the guanine oxidation peak was measured respectively. The salmon testis ssDNA biosensor was examined with PAHs contaminated samples of Mytilus galloprovincialis. Upon UV irradiation of three sample extracts exceeding the BaP maximum level, a positive variation of the DNA guanine oxidation was obtained. An average 2.4-fold increase of the guanine oxidation peak was detected demonstrating that the sensor can be used to detect toxic degradation products of PAHs.     

Model calculations for reactivities of polycyclic aromatic hydrocarbon metabolites

Structure-resonance theory calculations correlate reactivities and mutagenicities of polycylic aromatic hydrocarbon metabolites.     

多环芳烃指纹用于渤海采油平台原油的鉴别

采用气相色谱/质谱方法,对渤海海上4个不同区块、5个平台的6口油井原油进行了烷基化多环芳烃系列化合物和美国环保署（EPA）优先控制多环芳烃系列化合物的准确定性定量分析。通过多环芳烃原始指纹谱图、多环芳烃组分分布模式和特征比值的比较对上述原油进行鉴别。结果证明不同区块的原油中多环芳烃指纹信息不尽相同,即使在同一平台不同油井中所产的原油其指纹也存在一定差异。为确保原油鉴别的准确性,分析过程中必须在仪器的稳定性和样品前处理方面实施严格的质量控制措施。     

Indium-catalyzed construction of polycyclic aromatic hydrocarbon skeletons via dehydration

Polycyclic aromatic compounds can be synthesized from 2-benzylic- or 2-allylbenzaldehydes using a catalytic amount of In(III) or Re(I) complexes. By using this method, polycyclic aza-aromatic compounds can also be prepared efficiently. In these reactions, only water is formed as a side product.     

van der Waals interactions of polycyclic aromatic hydrocarbon dimers

Density functional theory is in principle exact and includes also long-range interactions, such as the van der Waals interactions. These are, however, part of the exchange-correlation energy functional that needs to be approximated, and are absent in the local and semilocal standard implementations. Recently a density functional which includes van der Waals interactions for planar systems has been developed, which we show can be extended to provide a treatment of planar molecules. We use this functional to calculate binding distances and energies for dimers of three of the smallest polycyclic aromatic hydrocarbons (PAHs)--naphthalene, anthracene, and pyrene.     

Gas-chromatographic display of the polycyclic aromatic hydrocarbon fraction of cigarette smoke

High electron-affinity polycyclic aromatic hydrocarbons in cigarette smoke are detected by gas chromatography. The resulting gas chromatograms can be used for "fingerprint" indentification of the hydrocarbon fractions in cigarette smoke.     

Identification and quantification of EPA 16 priority polycyclic aromatic hydrocarbon pollutants by Maximum-Quantum NMR

We demonstrate here that the recently introduced Maximum-Quantum NMR analytical strategy is apt for the identification and quantification of 16 polycyclic aromatic hydrocarbon (PAH) pollutants in a mixture and does not need prior separation. The accuracy of the procedure, the response of which is linear in concentration, was assessed and its feasibility was demonstrated down to a concentration of about 30 μM.     

Reactions of polycyclic aromatic hydrocarbon radical cations with model biological nucleophiles

The determination of gas-phase reactivity of a series of polycyclic aromatic hydrocarbons (PAHs) with nucleophiles is directed at achieving isomer differentiation through ion-molecule reactions and collisionally activated decomposition spectra. A series of PAH isomers form gas-phase [adduci — H]⁺ ions with the reagent nucleophiles pyridine and N-methylimidazole. Collisionally activated decomposition spectra of the [adduct — H]⁺ ions of the pyridine/PAH systems are dominated by products formed by losses of C₅H₄N, C₅H₅N (presumably neutral pyridine), and C₅H₆N. Collisional activation of PAH/N-methylimidazole [adduct — H]⁺ ions causes analogous losses of C₄H₅N₂, C₄H₆N₂ (presumably neutral N-methylimidazole), and C₄H₇N₂. The relative abundances of the ions that result from these losses are highly isomer specific for N-methylimidazole but less so for pyridine. Furthermore, PAH/N-methylimidazole [adduct — H]⁺ ions undergo a series of metastableion decompositions that also provide highly isomer-specific information. The C₄H₇N₂ (from PAH/N-methylimidazole product ions) and C₅H₆N (from PAH/pyridine product ions) losses tend to increase with the ΔH _f of the PAH radical cation. In addition, it is shown that the fragmentation patterns of these gas-phase PAH/nucleophile adducts are similar to fragmentation patterns of PAH/nucleoside adducts generated in solution, which suggests that the structures of products formed in gas-phase reactions are similar to those produced in solution.     

CO2 capture by hydrocarbon surfactant liquids

Here we found that CO(2) has high solubility in low-cost hydrocarbon surfactant liquids.     

Dissociation and multiple ionization energies for five polycyclic aromatic hydrocarbon molecules

We have performed density functional theory calculations for a range of neutral, singly, and multiply charged polycyclic aromatic hydrocarbons (PAHs), and their fragmentation products for H-, H(+)-, C(2)H(2)-, and C(2)H(2)(+)-emissions. The adiabatic and vertical ionization energies follow linear dependencies as functions of charge state for all five intact PAHs (naphthalene, biphenylene, anthracene, pyrene, and coronene). First estimates of the total ionization and fragmentation cross sections in ion-PAH collisions display markedly different size dependencies for pericondensed and catacondensed PAH species, reflecting differences in their first ionization energies. The dissociation energies show that the PAH(q+)-molecules are thermodynamically stable for q ≤?2 (naphthalene, biphenylene, and anthracene), q?≤?3 (pyrene), and q?≤?4 (coronene). PAHs in charge states above these limits may also survive experimental time scales due to the presence of reaction barriers as deduced from explorations of the potential energy surface regions for H(+)-emissions from all five PAHs and for C(2)H(2)(+)-emission from naphthalene--the smallest PAH.     

Ab initio-based intermolecular carbon-carbon pair potentials for polycyclic aromatic hydrocarbon clusters

We derived the carbon-carbon pair potentials for polycyclic aromatic hydrocarbon (PAH) clusters, which exhibited a strikingly similar geometry to that of the two-layer graphite. The binding energy of PAH clusters ranging in size from the benzene dimer to the pyrene dimer obtained by ab initio calculations at the MP2 level was used to extract the pair potentials in the form of the Lennard-Jones and Exponential-6 functions. Identical binding energy and equilibrium interlayer distance were reproduced by these functions to those calculated by the ab initio method. The pair potentials for PAHs yield the same equilibrium C-C distance as the known pair potentials for graphite and fullerenes, but nearly twice the well depth because of the polarization of the C-H bond.     

Lichens as polycyclic aromatic hydrocarbon bioaccumulators used in atmospheric pollution studies

The aim of this work has been to determine the possibility of using lichens as polycyclic aromatic hydrocarbon (PAH) bioaccumulators for the evaluation of atmospheric pollution in the city of Rieti. A lichen sample collected in a remote unpolluted area was divided into 18 sub-samples. These were collocated in nine different stations in the city of Rieti and every 5 months the PAH concentrations were determined. Only phenanthrene, anthracene, fluoranthene, pyrene and chrysene were found at concentrations over the limit of quantification. In the meantime a continuous increase of their concentrations was observed.     

Factors affecting the reversed-phase liquid chromatographic separation of polycyclic aromatic hydrocarbon isomers

Reversed-phase liquid chromatography (LC) on C₁₈ stationary phases provides excellent selectivity for the separation of polycyclic aromatic hydrocarbons (PAH). Recent studies have shown that several factors affect selectivity for the LC separation of PAH including phase type (monomeric or polymeric), pore diameter and surface area of the silica substrate, and surface density of the C₁₈ ligands. In this paper the separation of eleven PAH isomers of molecular weight 278 is used to further illustrate the effect of stationary phase characteristics and shape of the solute (length-to-breadth ratio, L/B) on retention and selectivity. Only polymeric C₁₈ phases with a high C₁₈ surface coverage provided separation of all eleven isomers and the elution order of these isomers generally followed increasing L/B values. The effect of solute nonplanarity on reversed-phase LC retention was investigated on both monomeric and polymeric phases using a series of planar and nonplanar PAH pairs. For each solute pair, the nonplanar solute eluted earlier than the planar solute, the largest selectivity factors being observed on the C₁₈ phase with the highest percent carbon load. Based on these studies, a model is proposed to describe the retention of PAH on polymeric C₁₈ phases.     

Electrostatic potential mapping of polycyclic aromatic hydrocarbon diol epoxides using a dipole

Electrostatic potential maps of benz(a)anthracene diol epoxide, benzphenanthrene diol epoxide, chrysene diol epoxide, and tryphenylene diol epoxide, which are ultimate carcinogens derived from the corresponding polycyclic aromatic hydrocarbons, have been studied using a dipole of length 1 Å and strength 1 Debye. The net charge distributions in the molecules were obtained using the MNDO molecular orbital method. The maps were drawn for two closest distances of approach between the charged ends of the dipole and atoms of the molecules. Using the electric field directions and values of electrostatic potentials, reactive sites and relative reactivities of these molecules have been examined. Existence of a bay region appears to be important for the carcinogenic activity of a diol epoxide in this class of carcinogens.