Determination of Total Petroleum Hydrocarbon (TPH) and Polycyclic Aromatic Hydrocarbon (PAH) in Soils: A Review of Spectroscopic and Nonspectroscopic Techniques

Abstract: In the analysis of petroleum hydrocarbon–contaminated soils for total petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons (PAHs), the roles of spectroscopic and nonspectroscopic techniques are inseparable. Therefore, spectroscopic techniques cannot be discussed in isolation. In this report, spectroscopic techniques including Raman, fluorescence, infrared, and visible and near-infrared (Vis-NIR) spectroscopies, as well as mass spectroscopy (coupled to a gas chromatograph) and nonspectroscopic techniques such as gravimetry, immunoassay, and gas chromatography with flame ionization detection are reviewed. To bridge the perceived gap in coverage of the quantitative applications of Vis-NIR spectroscopy in the rapid determination of TPHs and PAHs in soils, a detailed review of studies from the period 1999–2012 are presented. This report also highlights the strengths and limitations of these techniques and evaluates their performance from the perspective of their attributes of general applicability, namely economic portability, operational time, accuracy, and occupational health and safety considerations. Overall, the fluorescence spectroscopic technique had the best performance (85% total score) in comparison to the others, and the gravimetric technique performed the least (60% total score). Method-specific solutions geared toward performance improvement are also suggested.     

Effect of isotopically sensitive branching on product distribution for pentalenene synthase: support for a mechanism predicted by quantum chemistry

Mechanistic proposals for the carbocation cascade reaction leading to the tricyclic sesquiterpene pentalenene are assessed in light of the results of isotopically sensitive branching experiments with the H309A mutant of pentalenene synthase. These experimental results support a mechanism for pentalenene formation involving a 7-protoilludyl cation whose intermediacy was first predicted using quantum-chemical calculations.     

S-oxygenation of thiocarbamides IV: Kinetics of oxidation of tetramethylthiourea by aqueous bromine and acidic bromate

The kinetics and mechanism of oxidation of tetramethylthiourea (TTTU) by bromine and acidic bromate has been studied in aqueous media. The kinetics of reaction of bromate with TTTU was characterized by an induction period followed by formation of bromine. The reaction stoichiometry was determined to be 4BrO(3)(-) + 3(R)(2)C═S + 3H(2)O → 4Br(-) + 3(R)(2)C═O + 3SO(4)(2-) + 6H(+). For the reaction of TTTU with bromine, a 4:1 stoichiometric ratio of bromine to TTTU was obtained with 4Br(2) + (R)(2)C═S + 5H(2)O → 8Br(-) + SO(4)(2-) + (R)(2)C═O + 10H(+). The oxidation pathway went through the formation of tetramethythiourea sulfenic acid as evidenced by the electrospray ionization mass spectrum of the dynamic reaction solution. This S-oxide was then oxidized to produce tetramethylurea and sulfate as final products of reaction. There was no evidence for the formation of the sulfinic and sulfonic acids in the oxidation pathway. This implicates the sulfoxylate anion as a precursor to formation of sulfate. In aerobic conditions, this anion can unleash a series of genotoxic reactive oxygen species which can explain TTTU's observed toxicity. A bimolecular rate constant of 5.33 ± 0.32 M(-1) s(-1) for the direct reaction of TTTU with bromine was obtained.     

A Tunable Multicolor Photoluminescent Nanocarbon Prepared from Castor Oil Soot

We herein report a straightforward soot‐based synthesis and characterization of the negatively charged, hydrophilic, photoluminescent nanocarbon. The photoluminescent nanocarbon was prepared by refluxing castor oil soot in nitric acid. The as‐obtained fluorescent nanocarbon shows multiple colors under UV exposure and was characterized with surface morphological and spectral studies. Additionally, the photoluminescence nature of the nanocarbon was tunable by changing the pH or the dilution factor. During the course of the investigation, it has been found that, the photoluminescence nature observed here is not attributed to the presence of poly aromatic hydrocarbons, but solely due to the trait of the fluorescent nanocarbon. These results indicate that interparticle surface plasmon resonance plays a key role in the exhibition of photoluminescence. Furthermore, the feasibility of photoluminescent nanocarbon as a plausible tool for cell imaging and electrochemical application of the oxidized nanocarbon has also been examined.     

Field-driven super/subradiant lasing without inversion in three-level ladder scheme

A model of a superradiant laser comprising of N three-level systems driven by two pumping lasers is considered in semiclassical approximation. Steady-state equations for density matrix elements are solved both analytically and numerically. Various properties of generated light are investigated. It is found that such a laser can exhibit both superradiance, when the intensity scales as N(2), and subradiance when the intensity does not depend on N. The phase of the laser field is locked to the relative phase of the pumping lasers.     

Pulsed laser deposition of BiCuOSe thin films

Undoped and 10% Ca-doped BiCuOSe thin films are prepared by pulsed laser deposition without ex-situ processing. The influence of the preparation conditions on structure and properties of Bi_0.9Ca_0.1CuOSe thin films on amorphous silica substrates is studied. The highest achieved concentration and mobility of free holes (3.9×10²⁰ cm⁻³ and 3.5 cm²/Vs) was close to that measured in strongly c-axis oriented samples on SrTiO₃ substrates (4.0×10²⁰ cm⁻³ and 7.5 cm²/Vs). The Bi_0.9Ca_0.1CuOSe films on SrTiO₃ show almost temperature-independent Seebeck coefficient and their resistivity increases with increasing temperature. The Seebeck coefficient of undoped BiCuOSe films on SrTiO₃ increases below 150°K, and the resistivity shows a flat plateau centered at this temperature. Optical measurements suggest that BiCuOSe has an indirect bandgap of 0.8 eV and a strong absorption edge at 1.45 eV. Ab-initio calculations of the electronic band structure, effective masses and optical properties of BiCuOSe are also presented.     

A novel organozinc reagent 4-coumarinylzinc bromide; preparation and application in the synthesis of 4-substituted coumarin derivatives

A novel organozinc reagent, 4-coumarinylzinc bromide, was prepared by the direct oxidative addition of active zinc to 4-bromocoumarin. The resulting organozinc bromide underwent the palladium-catalyzed cross-coupling reactions with a variety of aryl halides and acid chlorides affording the corresponding coupling products in good yields under mild conditions.     

Cyclopropanation of diazoesters with styrene derivatives catalyzed by magnetically recoverable copper-plated iron nanoparticles

Simple bare copper-plated iron nanoparticles catalyzed the cyclopropanation of diazoesters with styrene derivatives. The reaction proceeded smoothly and provided the desired products in moderate to good yields, with selectivity for the trans isomer in neat conditions. The reaction scope was explored and di or tri-substituted cyclopropanes were synthesized. The catalysts could be magnetically separated and reusable up to five times. It was also characterized by TEM, XPS, and ICP-MS. A gram-scale reaction was performed with a yield of 72%.     

A Convenient Preparation of 2-Ethyl-4-Carboxycyclohexanone

Several years ago in the course of work directed toward the total synthesis of the iboga alkaloids¹, we required relatively large quantities of 2-ethyl-4-carboxycyclonhexanone (1) and its methyl ester as precursors to 3-ethyl-5-carbomethoxycyclohexene. Although it was possible to prepare keto acid 2 from 1,3,5-tricarbomethoxypentane (3) following the published synthesis of 2-methyl-4-carboxycyclohexanone², the overall yield was only 52%. ³ In addition, the isolation and purification of intermediates 4 renders the synthesis rather tedious.