Phenanthrene Crystals Research Articles

Aromatic superconductors: Electron-phonon coupling and electronic correlations

<sec>Aromatic superconductors are a new type of high-temperature superconductor discovered in recent years. The superconducting transition temperature (<i>T</i><sub>c</sub>) increases with the size of aromatic molecule increasing, which has attracted widespread attention of experimental and theoretical researchers. The driving mechanism for such a superconductivity, whether it is dominated by electron-phonon coupling or electronic correlation effects, has aroused great interest of many research groups. This paper briefly introduces the rich superconducting phenomena of metal doped aromatic compounds. From the perspectives of electron-phonon coupling or electronic correlations, the superconductivity of aromatic compounds is discussed, which is helpful in exploring aromatic superconductors with higher <i>T</i><sub>c</sub>. The challenges currently faced in the field are also introduced.</sec><sec>The rest of this paper is organized as follows. We first introduce the existence of abundant superconducting phases in the experiment of metal doped aromatic compounds. Different doping concentrations of metal cause superconducting phases with different <i>T</i><sub>c</sub> values, especially the highest <i>T</i><sub>c</sub> value of the superconducting phase increases with the size of aromatic molecule increasing. Theoretical prediction shows that all aromatic hydrocarbon superconductors have a low-<i>T</i><sub>c</sub> superconducting phase in a range of 5–7 K, which is a common feature. For systems with few benzene rings (such as benzene, naphthalene, and phenanthrene crystals), only low-<i>T</i><sub>c</sub> phase of 5–7 K exists, while in systems with multiple benzene rings (such as picene, dibenzopentacene, and others with the number of benzene rings more than 5), there are multiple superconducting phases; the highest <i>T</i><sub>c</sub> in long-benzene-ring system depends not only on the number of benzene rings, but also on the chain size of organic molecule. Further research indicates that low-<i>T</i><sub>c</sub> phase is induced by doping about 2 electrons and has good stability, while high-<i>T</i><sub>c</sub> phase results from doping 3 electrons and has slightly poorer stability.</sec><sec>Then, the electron-phonon coupling characteristics and electron-electron exchange correlation effects in aromatic compound superconductors are discussed. For low-<i>T</i><sub>c</sub> phases, the values of electronic density of states at the Fermi level are comparable to each other and relatively low, resulting in weak electron-phonon interactions. However, the <i>T</i><sub>c</sub> value predicted by this electron-phonon coupling mechanism is in good agreement with experimental value, indicating that the electron-phonon coupling is sufficient to describe the superconductivity of low-<i>T</i><sub>c</sub> phases. For high-<i>T</i><sub>c</sub> phases, the big values of electron density of states at the Fermi level imply strong electron-phonon interactions, and this electron-phonon coupling increases with the size of organic molecule increasing. However, the <i>T</i><sub>c</sub> value predicted only by the electron-phonon mechanism is lower than the experimental value. The study of electron-electron exchange correlation effect of aromatic compounds shows that the electronic correlation effect increases with the size of aromatic molecule increasing, which is consistent with the increase of <i>T</i><sub>c</sub> maximum value with the size of aromatic molecule increasing in a long-benzene-ring system. This indicates that the superconductivity of high<i>-T</i><sub>c</sub> phase is driven by both the electron-phonon mechanism and the electronic correlation effect. This understanding of superconductivity is significant for exploring and discovering aromatic superconductors with higher transition temperatures.</sec><sec>Finally, comprehensive physical models and methods are required in this paper in order to gain a thorough understanding of the superconductivity of aromatic compound.</sec>

Adsorptive separation of para-xylene by nonporous adaptive crystals of phenanthrene[2]arene.

In this work, we developed a new method for the preparation of phenanthrene[2]arene on a large-scale. Meanwhile, the synthetic phenanthrene[2]arene has been successfully used as nonporous adaptive crystals for the separation of para-xylene (pX) from xylene isomers. The crystal structure revealed that one host molecule can adsorb one pX molecule to form the 1@pX complex, in which pX is located in the cavity of the host.

Crystal growth and luminescence properties of phenanthrene for neutron detection

Phenanthrene crystals were grown by the self-seeding vertical Bridgman technique as a neutron scintillation material and their luminescence properties were evaluated. As-grown crystals had no secondary phases from the results of the powder X-ray Diffraction and Fourier transform infrared spectrometer measurements. The radioluminescence emission spectrum had a peak at 408 nm and its profile was similar to that of the photoluminescence emission spectrum. The relative light yield under 5.5-MeV alpha-ray was 1.15 times higher than that of lithium glass GS-20. The light yield of phenanthrene under 662 keV gamma-ray is estimated to be 38 ± 2% of NaI:Tl. The scintillation decay time under neutron excitation was estimated to be 7.30 ± 0.14 ns.

Biofilms of Halobacterium salinarum as a tool for phenanthrene bioremediation

The use of hyperhalophilic microorganisms is emerging as a sustainable alternative to clean hydrocarbon-polluted hypersaline water bodies. In line with this practice, this work reports on the ability of the archaeon Halobacterium salinarum to develop biofilms on a solid surface conditioned by the presence of phenanthrene crystals, which results in the removal of the contaminating compound. The cell surface hydrophobicity does not change during the removal process and this organism is shown to constitutively produce a surfactant molecule with specific action on aromatic hydrocarbons, both indicating that phenanthrene removal might proceed through a non-contact mechanism. A new approach is presented to follow the process in situ through epifluorescence microscopy by monitoring phenanthrene auto-fluorescence.

Isolation and Characterization of Phenanthrene Degrading Bacteria from Diesel Fuel-Contaminated Antarctic Soils.

Antarctica is an attractive target for human exploration and scientific investigation, however the negative effects of human activity on this continent are long lasting and can have serious consequences on the native ecosystem. Various areas of Antarctica have been contaminated with diesel fuel, which contains harmful compounds such as heavy metals and polycyclic aromatic hydrocarbons (PAH). Bioremediation of PAHs by the activity of microorganisms is an ecological, economical, and safe decontamination approach. Since the introduction of foreign organisms into the Antarctica is prohibited, it is key to discover native bacteria that can be used for diesel bioremediation. By following the degradation of the PAH phenanthrene, we isolated 53 PAH metabolizing bacteria from diesel contaminated Antarctic soil samples, with three of these isolates exhibiting a high phenanthrene degrading capacity. In particular, the Sphingobium xenophagum D43FB isolate showed the highest phenanthrene degradation ability, generating up to 95% degradation of initial phenanthrene. D43FB can also degrade phenanthrene in the presence of its usual co-pollutant, the heavy metal cadmium, and showed the ability to grow using diesel-fuel as a sole carbon source. Microtiter plate assays and SEM analysis revealed that S. xenophagum D43FB exhibits the ability to form biofilms and can directly adhere to phenanthrene crystals. Genome sequencing analysis also revealed the presence of several genes involved in PAH degradation and heavy metal resistance in the D43FB genome. Altogether, these results demonstrate that S. xenophagum D43FB shows promising potential for its application in the bioremediation of diesel fuel contaminated-Antarctic ecosystems.

Mechanism of order–disorder phase transition in phenanthrene crystals: an interpretation based on the rotational potential energy surface for a phenanthrene molecule in a phenanthrene crystal

Crystals of phenanthrene undergo an order–disorder phase change at 72°C. High temperature phase was found to be disordered with two possible molecular positions. In order to understand the fundamental mechanism of the phase transition, we have modeled the molecular movement within the phenanthrene crystal and estimated the rotational potential energy surface for a phenanthrene molecule, as it undergoes this flip-flop motion. The situation in phenanthrene crystal is explained by a model where the molecules exhibit large amplitude librations having been trapped in the potential wells. Fluctuations in the orientation of the neighboring molecules result in changes in the shape of the potential well and consequently giving rise to angular motions of molecules with large amplitude. The calculations show that the two minima of the potential energy surface are not equivalent, as a result, the occupancy of the two possible molecular positions will not be the same, hence the space group of the disorder phase will remain P21 and not change to P21/a.

Emulsion crystallization of phenanthrene by supercritical fluid extraction of emulsions

The emulsion crystallization of phenanthrene has been investigated by solvent extraction from oil in water emulsions through dilution with water and through supercritical fluid extraction of emulsions (SFEE). In order to contribute to an improved understanding of this process, different physical mechanisms involved in particle formation have been explored by observation of crystallizing emulsion samples progressing towards equilibrium. Phenanthrene crystals are formed either by self-nucleation of single emulsion droplets, or through contact of emulsion droplets with already existing crystals. On the other hand, emulsion droplets are mainly consumed by the growth of phenanthrene crystals, involving mass transfer through the continuous water phase. Furthermore, the influence of various process parameters on the crystallization of phenanthrene has been investigated experimentally. When increasing the temperature, the average median x50 of the particle size distribution increased from 15μm at 20°C to 103μm at 60°C. Other parameters investigated were the stirring rate and the suspension density, which could be increased through solvent removal by SFEE. The latter method yielded the smallest particles, exhibiting a median x50 of 3.0μm. Emulsion crystallization enables the formation of crystals through the liquid–liquid two phase region instead of avoiding it, and may ultimately lead to the development of crystallization processes that can be carried out faster and at higher solid densities, thus at a more intensive level. The present study demonstrates that this process exhibits good reproducibility and enables controlling the particle size in a rather wide range, thus further underlining the potential of this technique for applications both in research and in the pharmaceutical industry.

Difference in optical properties of anthracene molecule aggregates in fluorene and phenanthrene crystals

AbstractOptical properties of anthracene molecules in phenanthrene crystals with anthracene concentration of 0.03% to 8.4% were investigated and compared with those in fluorene crystals. In contrast to fluorene system where two kinds of dimers, one of which is accompanied by lattice relaxation, are observed, it was found that only one kind of dimers without lattice relaxation are observed in phenanthrene system. Also in aggregates of anthracene in higher concentration samples, the luminescence is a ‘free exciton’‐type in phenanthrene crystals in contrast to a ‘self‐trapped exciton’‐type in fluorene crystals. With reference to the variation of the magnitude of exciton–phonon coupling constant on nearest neighbour distance of molecules known for bulk crystals of aromatic molecules, the difference is attributed to longer inter molecular distance between anthracene molecules in phenanthrene matrix in comparison to those in fluorene matrix (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A non-invasive fluorescent staining procedure allows Confocal Laser Scanning Microscopy based imaging of Mycobacterium in multispecies biofilms colonizing and degrading polycyclic aromatic hydrocarbons

To study the micro scale interactions of Mycobacterium with bacteria belonging to other genera by means of Confocal Laser Scanning Microscopy (CLSM), a procedure was developed to non-invasively and fluorescently stain Mycobacterium without compromising the signal produced by commonly used fluorescent reporter genes. The procedure makes use of the commercial non-specific nucleic acid stain Syto62 and was optimized to efficiently stain Mycobacterium cells in suspensions and biofilms. The staining procedure was found non-invasive towards overall cell viability, biofilm architecture and fluorescence signals emitted by other organisms expressing the fluorescent reporter genes gfp and dsRed. The procedure was successfully applied to visualize the comportment of the PAH-degrading Mycobacterium sp. VM552 in triple species biofilms containing, in addition to strain VM552, the GFP labeled PAH-degrading Sphingomonas sp. LH128-GFP and DsRed-labeled Pseudomonas putida OUS82(RF), and colonizing a glass substrate coated with phenanthrene crystals in flow chambers. CLSM imaging and subsequent appropriate image processing of the biofilms show that the comportment of strain Mycobacterium sp. VM552 was largely affected by the presence of the other organisms. The data support the value of the staining procedure to study ecological questions about micro scale behavior and niche occupation of Mycobacterium in multi-species systems.

Study of the Degradation Activity and the Strategies to Promote the Bioavailability of Phenanthrene by Sphingomonas paucimobilis Strain 20006FA

The present study describes the phenanthrene-degrading activity of Sphingomonas paucimobilis 20006FA and its ability to promote the bioavailability of phenanthrene. S. paucimobilis 20006FA was isolated from a phenanthrene-contaminated soil microcosm. The strain was able to grow in liquid mineral medium saturated with phenanthrene as the sole carbon source, showing high phenanthrene elimination (52.9% of the supplied phenanthrene within 20 days). The accumulation of 1-hydroxy-2-naphthoic acid and salicylic acid as major phenanthrene metabolites and the capacity of the strain to grow with sodium salicylate as the sole source of carbon and energy indicated that the S. paucimobilis 20006FA possesses a complete phenanthrene degradation pathway. However, under the studied conditions, the strain was able to mineralize only the 10% of the consumed phenanthrene. Investigations on the cell ability to promote bioavailability of phenanthrene showed that the S. paucimobilis strain 20006FA exhibited low cell hydrophobicity (0.13), a pronounced chemotaxis toward phenanthrene, and it was able to reduce the surface tension of mineral liquid medium supplemented with phenanthrene as sole carbon source. Scanning electron micrographs revealed that: (1) in suspension cultures, cells formed flocks and showed small vesicles on the cell surface and (2) cells were also able to adhere to phenanthrene crystals and to produce biofilms. Clearly, the strain seems to exhibit two different mechanisms to enhance phenanthrene bioavailability: biosurfactant production and adhesion to the phenanthrene crystals.

A new green fluorescent protein‐based bacterial biosensor for analysing phenanthrene fluxes

The polycyclic aromatic hydrocarbon (PAH)-degrading strain Burkholderia sp. RP007 served as host strain for the design of a bacterial biosensor for the detection of phenanthrene. RP007 was transformed with a reporter plasmid containing a transcriptional fusion between the phnS putative promoter/operator region and the gene encoding the enhanced green fluorescent protein (GFP). The resulting bacterial biosensor--Burkholderia sp. strain RP037--produced significant amounts of GFP after batch incubation in the presence of phenanthrene crystals. Co-incubation with acetate did not disturb the phenanthrene-specific response but resulted in a homogenously responding population of cells. Active metabolism was required for induction with phenanthrene. The magnitude of GFP induction was influenced by physical parameters affecting the phenanthrene flux to the cells, such as the contact surface area between solid phenanthrene and the aqueous phase, addition of surfactant, and slow phenanthrene release from Model Polymer Release System beads or from a water-immiscible oil. These results strongly suggest that the bacterial biosensor can sense different phenanthrene fluxes while maintaining phenanthrene metabolism, thus acting as a genuine sensor for phenanthrene bioavailability. A relationship between GFP production and phenanthrene mass transfer is proposed.

Molecular Modelling of the Morphology of Organic Crystals in the Presence of Impurity Species: Recent Applications to Naphthalene, Phenanthrene, and Caprolactam Crystals

ABSTRACT A molecular modelling capability for predicting the purity and morphology of solids manufactured via crystallisation is important in the realisation of a ‘molecule-up’ or product-centred, approach for the optimisation of chemical processes. Recent work on producing the morphology of molecular solids based upon the molecular and crystal chemistry is presented. The approach is based on the atom-atom method for calculating surface attachment energies, and from these relative crystal growth rates as a function of crystallographic growth direction. The computations have been recently [213-15] developed to be able to treat the effects of impurity species that influence morphology. Molecular modelling procedures include an optimisation of the position and orientation of the adsorbed additive within the host lattice hence, simulating the crystal chemistry of the hetero-species within the host lattice. Case studies include naphthalene and phenanthrene in the presence of biphenyl impurity and caprolactam in the presence of synthesis impurities.

Three-dimensional distribution of GFP-labeled Pseudomonas putida during biofilm formation on solid PAHs assessed by confocal laser scanning microscopy

Confocal laser scanning microscopy was used to monitor the colonization pattern of the gfp-labeled derivative strain of Pseudomonas putida ATCC 17514 on fluorene and phenanthrene crystals. The in situ experiments showed that P. putida tends to grow directly on phenanthrene, forming a biofilm on accessible crystalline surfaces. On the other hand, no significant biofilm formation was observed in the presence of fluorene. The results obtained showed that substrate properties affected bacterial strategy regarding uptake.

Bioavailability of solid and non-aqueous phase liquid (NAPL)-dissolved phenanthrene to the biosurfactant-producing bacterium Pseudomonas aeruginosa 19SJ.

The biodegradation of phenanthrene by the biosurfactant-producing strain Pseudomonas aeruginosa 19SJ was investigated in experiments with the compound present either as crystals or dissolved in non-aqueous phase liquids (NAPLs). Growth on solid phenanthrene exhibited an initial phase not limited by dissolution rate and a subsequent, carbon-limited phase caused by exhaustion of the carbon source. Rhamnolipid biosurfactants were produced from solid phenanthrene and appeared in solution and particulate material (cells and phenanthrene crystals). During the carbon-limited phase, the concentration of rhamnolipids detected in culture exceeded the critical micelle concentration (CMC) determined with purified rhamnolipids. The biosurfactants caused a significant increase in dissolution rate and pseudosolubility of phenanthrene, but only at concentrations above the CMC. Externally added rhamnolipids at a concentration higher than the CMC increased the biodegradation rate of solid phenanthrene. Mineralization curves of low concentrations of phenanthrene initially dissolved in two NAPLs [2,2,4,4,6,8,8-heptamethylnonane and di(2-ethylhexyl)phthalate] were S-shaped, although no growth was observed in the population of suspended bacteria. Biosurfactants were not detected in solution under these conditions. The observed mineralization was attributed not only to suspended bacteria, but also to bacterial populations growing at the NAPL-water interface, mineralizing the compound at higher rates than predicted by abiotic partitioning. We suggest that rhamnolipid production and attachment increased the bioavailability of phenanthrene, so promoting biodegradation activity.

Knoop hardness anisotropy in anthracene and phenanthrene single crystals

Microhardness anisotropy in single crystals of anthracene and phenanthrene has been observed by the Knoop indentation technique. The Knoop hardness variation with respect to the [010] direction shows opposite trends. Both these crystals have the same crystal structure and space group. The present observations are explained in terms of orientation and disposition of molecules in the unit cells.

PHOTOCONDUCTIVITY OF PHENANTHRENE SINGLE CRYSTALS

Single crystals of phenanthrene were grown from the melt in specially designed crystal growth tubes. Over the wavelength range studied: 200–650 nm, surface photoconductivity at room temperature is independent of photon energy >3.5 eV for applied bias fields ~10 kV cm−1. This is interpreted as saturation of the generation process for both electron and hole carriers. However, bulk photoconductivity for photon energy <3.5 eV at room temperature is dependent on photon energy and applied bias fields and generation mechanism involved in this case is attributed to exciton-exciton collisions and photoionization of excitons.

Crystallization of phenanthrene from toluene with carbon dioxide by the GAS process

AbstractThe crystallization of phenanthrene from toluene with carbon dioxide as the antisolvent gas is described. In the GAS process, a pressurized gas is dissolved into a liquid solvent, where it causes a volumetric expansion and lowers the solubility of the solute. Theoretical models are presented for the liquid‐phase expansion and the solubility as a function of pressure and temperature. The Nývlt theory for batch crystallization is adapted to predict the pressure profile in the crystallizer needed to maintain a constant supersaturation and growth rate. Generation of seeds is accomplished via a pressure pulse at the saturation pressure. The average particle size of the phenanthrene could be varied from 160 to 540 μm. Creation of seeds doubles the particle size and reduces the coefficient of variation significantly. The residual amount of toluene in the crystals without treatment is approximately 70 ppm. The particles are agglomerates of phenanthrene crystals.

Structure, disorder, and phase transition in ternary crystals of anthracene, phenanthrene, and tetracyanobenzene, AxPh1−xTCNB

The structure of ternary, charge-transfer crystals of anthracene, phenanthrene, and tetracyanobenzene, AxPh1−xTCNB, in a wide range of concentrations has been studied. We have focused on the problem of substitutional and orientational disorder of anthracene and phenanthrene molecules and its influence on the orientational instability. The crystal structure determination has been performed at room temperature and 120 K, and the refinement procedures allowed us to determine the orientational disorder for different concentrations. The phase diagram for the orientational phase transition with symmetry change, C2/m to P21/a, has been determined and a critical concentration (xc=0.74) was found. The disorder and the phase diagram has been successfully modeled by a minimization of the crystal energy using the ‘‘split molecule’’ concept and the virtual crystal approximation to mimic both orientational and substitutional disorders. The ternary crystals, their structure, disorder, and phase transitions are well understood in terms of a competition between orientational disorder of anthracene molecules and local stresses created by the substitutional disorder (with statistical orientations) of phenanthrene molecules. A possibility for an existence of molecular orientational glassy state is suggested for concentrations below the critical one.

Comparative physiology of phenanthrene degradation by two dissimilar pseudomonads isolated from a creosote-contaminated soil

Two species of bacteria, identified as Pseudomonas stutzeri (P-16) and Pseudomonas saccharophila (P-15) by fatty acid methyl ester analysis, were found in a phenanthrene enrichment culture of a creosote-contaminated soil. The organisms are shown to be physiologically dissimilar, and their genetic relatedness is discussed. Phenanthrene degradation by both organisms followed Michaelis-Menten kinetics, allowing for the determination of half-saturation (Ks) and maximum activity coefficients, using nonlinear regression. Both organisms utilized kinetically similar enzymes for phenanthrene uptake and oxidation, as evidenced by similar Ks coefficients of approximately 0.2 mg/L and temperature optima of 40 degrees C, but levels of expression differed with different media. Each organism degraded phenanthrene via salicylic acid, but patterns of intermediate metabolism were shown to differ. P-15 excreted 1-hydroxy-2-naphthoic acid during growth on phenanthrene and demonstrated Michaelis-Menten kinetics for the oxidation of 1-hydroxy-2-naphthoic acid by resting cells. P-16 excreted only trace amounts of 1-hydroxy-2-naphthoic acid and demonstrated linear kinetics in response to 1-hydroxy-2-naphthoic acid concentration. P-15 was found to form thick biofilms on phenanthrene crystals and was characterized by a hydrophobic cell surface, whereas P-16 grew mostly in suspension and was hydrophilic. Neither organism produced significant amounts of biosurfactants when grown on phenanthrene. The implications of these findings for the design of systems to remediate contaminated soil are discussed.

Enhanced biodegradation of phenanthrene in a biphasic culture system

Degradation of phenanthrene byPseudomonas aeruginosa AK1 was examined in (i) an aqueous mineral salts medium to which phenanthrene particles of varying size (i.e. diameter) were added, and (ii) an aqueous/organic biphasic culture system consisting of mineral salts medium supplemented with 2,2,4,4,6,8,8-heptamethylnonane (HMN) as the phenanthrene-carrying organic phase. In both systems, the rate of phenanthrene biodegradation could be significantly enhanced by manipulations leading to improved phenanthrene mass transfer into the aqueous phase. With crystalline phenanthrene, the rate of biodegradation was found to be directly correlated to the particle surface area, whereas in the biphasic system the rate of biodegradation of the dissolved phenanthrene was mainly governed by the HMN/water interface area. In the latter system, exponential growth with a doubling time t d of 6–8 hours has been achieved under conditions of intensive agitation of the medium indicating that phenanthrene degradation by strain AK1 is limited mainly by physicochemical parameters. Addition of selected surfactants to the culture medium was found to accelerate phenanthrene degradation by strain AK1 only under conditions of low agitation (in the presence of HMN) and after pretreatment of phenanthrene crystals by ultrasonication (in the absence of HMN). Evidence is presented that the stimulating effect of the surfactants was primarily due to improved dispersion of phenanthrene particle agglomerates (in the aqueous mineral salts medium supplemented with phenanthrene crystals) or of the phenanthrene-carrying lipophilic solvent drops (in the aqueous/organic biphasic culture system) whereas the solubilizing activity towards phenanthrene was neglectible. Under conditions of intensive mixing of the culture medium (i.e. if a high particle surface area or HMN/water interface area, respectively, is provided), the addition of surfactants did not enhance phenanthrene biodegradation.