The effects of season and soil type on microbial degradation of gasoline residues from incendiary devices

The primary task of a fire debris chemist is to determine if there is an ignitable liquid present in a fire debris sample and, if so, to classify it according to its boiling point and carbon number range. However, in organic-rich substrates such as soil, the ignitable liquid residue is subject to microbial degradation due to the ease with which bacteria can metabolize the various hydrocarbons present. This is a rapid process which is problematic in many forensic laboratories as fire debris is often stored for extended periods of time due to case backlog. Although microbial degradation has been studied in laboratory samples, it has not been well-studied in “real-world” samples, which have not only been exposed to microbial degradation but have also suffered the effects of weathering due to the intense heat of the fire. In this work, the effects of microbial degradation of gasoline from an incendiary device have been evaluated over time. In addition to visually monitoring chromatographic changes, this work also utilizes multivariate statistical techniques to simplify the complex data set and elucidate trends that might not otherwise be observed. Results indicate a clear difference between glass samples, which suffered the loss of low boiling compounds, and soil, which suffered the loss of the normal alkanes and lesser substituted aromatics. Also, devices deployed on lawn soil and in the winter season appear to show the most extensive degradation of gasoline. Finally, while the ratio of the C₃-alkylbenzenes is significantly altered in soil samples recovered from large devices, the overall chromatographic profile of gasoline recovered from smaller incendiary devices is significantly lower.

Methanol dehydrogenation and oxidation on Pt(111) in alkaline solutions

Adsorption, dehydrogenation, and oxidation of methanol on Pt(111) in alkaline solutions has been examined from a fundamental mechanistic perspective, focusing on the role of adsorbate-adsorbate interactions and the effect of defects on reactivity. CO has been confirmed as the main poisoning species, affecting the rate of methanol dehydrogenation primarily through repulsive interactions with methanol dehydrogenation intermediates. At direct methanol fuel cell (DMFC)-relevant potentials, methanol oxidation occurs almost entirely through a CO intermediate, and the rate of CO oxidation is the main limiting factor in methanol oxidation. Small Pt island defects greatly enhance CO oxidation, though they are effective only when the CO coverage is 0.20 ML or higher. Large Pt islands enhance CO oxidation as well, but unlike small Pt islands, they also promote methanol dehydrogenation. Perturbations in electronic structure are responsible for the CO oxidation effect of defects, but the role of large Pt islands in promoting methanol dehydrogenation is primarily explained by surface geometric structure.     

A Simple, Exact Density-Functional-Theory Embedding Scheme

Density functional theory (DFT) provides a formally exact framework for quantum embedding. The appearance of nonadditive kinetic energy contributions in this context poses significant challenges, but using optimized effective potential (OEP) methods, various groups have devised DFT-in-DFT methods that are equivalent to Kohn-Sham (KS) theory on the whole system. This being the case, we note that a very considerable simplification arises from doing KS theory instead. We then describe embedding schemes that enforce Pauli exclusion via a projection technique, completely avoiding numerically demanding OEP calculations. Illustrative applications are presented using DFT-in-DFT, wave-function-in-DFT, and wave-function-in-Hartree-Fock embedding, and using an embedded many-body expansion.     

Operator algebras and a theorem of Dieudonne

LetA be aC*-algebra with second dualA″. Let (φ _n)(n=1,...) be a sequence in the dual ofA such that limφ _n(a) exists for eacha εA. In general, this does not imply that limφ _n(x) exists for eachx εA″. But if limφ _n(p) exists whenever p is the range projection of a positive self-adjoint element of the unit ball ofA, then it is shown that limφ _n(x) does exist for eachx inA″. This is a non-commutative generalisation of a celebrated theorem of Dieudonné. A new proof of Dieudonné’s theorem, for positive measures, is given here. The proof of the main result makes use of Dieudonné’s original theorem.     

The effects of microbial degradation on ignitable liquids

The identification of ignitable liquid residues in fire debris is a key finding for determining the cause and origin of a suspicious fire. However, the complex mixtures of organic compounds that comprise ignitable liquids are susceptible to microbiological attack following collection of the sample. Biodegradation can result in selective removal of many of the compounds required for identification of an ignitable liquid. Such degradation has been found to occur rapidly in substrates such as soil, rotting wood, or other organic matter. Furthermore, fire debris evidence must often be stored for extended periods at room temperature prior to analysis due to case backlogs and available evidence storage. Hence, extensive damage to ignitable liquid residues by microbes poses a significant threat to subsequent laboratory work. In this work, the effects of microbial degradation of ignitable liquids in soil have been evaluated as a function of time. Key findings include the loss of n-alkanes, particularly C₉–C₁₆, which showed the most dramatic decrease in gasoline as well as the petroleum distillates, while branched alkanes remained unchanged. Monosubstituted benzenes also showed the most dramatic loss in gasoline. In the heavy petroleum distillates, n-alkanes with even carbon numbers were degraded more than n-alkanes with odd carbon numbers. Figure A “fully involved” house fire in Indianapolis, IN

Mechanism of CO oxidation on Pt(111) in alkaline media

Electrochemical techniques, coupled with in situ scanning tunneling microscopy, have been used to examine the mechanism of CO oxidation and the role of surface structure in promoting CO oxidation on well-ordered and disordered Pt(111) in aqueous NaOH solutions. Oxidation of CO occurs in two distinct potential regions: the prepeak (0.25-0.70 V) and the main peak (0.70 V and higher). The mechanism of reaction is Langmuir-Hinshelwood in both regions, but the OH adsorption site is different. In the prepeak, CO oxidation occurs through reaction with OH that is strongly adsorbed at defect sites. Adsorption of OH on defects at low potentials has been verified using charge displacement measurements. Not all CO can be oxidized in the prepeak, since the Pt-CO bond strength increases as the CO coverage decreases. Below theta(CO) = 0.2 monolayer, CO is too strongly bound to react with defect-bound OH. Oxidation of CO at low coverage occurs in the main peak through reaction with OH adsorbed on (111) terraces, where the Pt-OH bond is weaker than on defects. The enhanced oxidation of CO in alkaline media is attributed to the higher affinity of the Pt(111) surface for adsorption of OH at low potentials in alkaline media as compared with acidic media.