Biofuel Combustion Chemistry: From Ethanol to Biodiesel

Biofuels, such as bio‐ethanol, bio‐butanol, and biodiesel, are of increasing interest as alternatives to petroleum‐based transportation fuels because they offer the long‐term promise of fuel‐source regenerability and reduced climatic impact. Current discussions emphasize the processes to make such alternative fuels and fuel additives, the compatibility of these substances with current fuel‐delivery infrastructure and engine performance, and the competition between biofuel and food production. However, the combustion chemistry of the compounds that constitute typical biofuels, including alcohols, ethers, and esters, has not received similar public attention. Herein we highlight some characteristic aspects of the chemical pathways in the combustion of prototypical representatives of potential biofuels. The discussion focuses on the decomposition and oxidation mechanisms and the formation of undesired, harmful, or toxic emissions, with an emphasis on transportation fuels. New insights into the vastly diverse and complex chemical reaction networks of biofuel combustion are enabled by recent experimental investigations and complementary combustion modeling. Understanding key elements of this chemistry is an important step towards the intelligent selection of next‐generation alternative fuels.     

Uranium speciation in biofilms studied by laser fluorescence techniques

Biofilms may immobilize toxic heavy metals in the environment and thereby influence their migration behaviour. The mechanisms of these processes are currently not understood, because the complexity of such biofilms creates many discrete geochemical microenvironments which may differ from the surrounding bulk solution in their bacterial diversity, their prevailing geochemical properties, e.g. pH and dissolved oxygen concentration, the presence of organic molecules, e.g. metabolites, and many more, all of which may affect metal speciation. To obtain such information, which is necessary for performance assessment studies or the development of new cost-effective strategies for cleaning waste waters, it is very important to develop new non-invasive methods applicable to study the interactions of metals within biofilm systems. Laser fluorescence techniques have some superior features, above all very high sensitivity for fluorescent heavy metals. An approach combining confocal laser scanning microscopy and laser-induced fluorescence spectroscopy for study of the interactions of biofilms with uranium is presented. It was found that coupling these techniques furnishes a promising tool for in-situ non-invasive study of fluorescent heavy metals within biofilm systems. Information on uranium speciation and uranium redox states can be obtained.     

Preparation, IR spectroscopy, and time-of-flight mass spectrometry of halogenated and methylated Si(111)

The preparation of chlorine-, bromine-, and iodine-terminated silicon surfaces (Si(111):Cl, Br, and I) using atomically flat Si(111)-(1×1):H is described. The halogenated surfaces were obtained by photochemically induced radical substitution reactions with the corresponding dihalogen in a Schlenk tube by conventional inert gas chemistry. The nucleophilic substitution of the Si-Cl functionality with the Grignard reagent (CH₃MgCl) resulted in the unreconstructed methylated Si(111)-(1×1):CH₃ surface. The halogenated and methylated silicon surfaces were characterized by Fourier transform infrared (FTIR) spectroscopy and laser-induced desorption of monolayers (LIDOM). Calibration of the desorption temperature via analysis of time-of-flight (TOF) distributions as a function of laser fluence allowed the determination of the originally emitted neutral fragments by TOF mass spectrometry using electron-impact ionization. The halogens were desorbed atomically and as SiX _n (X = Cl, Br) clusters. The methyl groups mainly desorbed as methyl and ethyl fragments and a small amount of ⁺SiCH₃.     

Dielectric properties of thin-film ZrO<Subscript>2</Subscript> up to 50 GHz for RF MEMS switches

The dielectric properties of zirconium dioxide (ZrO₂) ceramic thin films were characterized up to 50 GHz using coplanar waveguides (CPWs) and metal–insulator–metal (MIM) capacitors with top circular electrodes. The ZrO₂ films were deposited using a chemical solution onto high-resistivity Si wafers and metal layers. The real part of the dielectric constant of approximately 22 and 26 was extracted at 50 GHz for CPW and MIM structures, respectively, and the loss tangent was approximately 0.09 at 50 GHz. C–V and I–V measurements were carried out to determine low-frequency and DC dielectric properties. The measurement results indicate that ZrO₂ is a promising material to be used as a dielectric layer for radio-frequency (RF) microelectromechanical systems (MEMS) capacitive switches.     

Strichartz estimates for Schrödinger equations on irrational tori in two and three dimensions

In this paper, we prove new multilinear Strichartz estimates, which are obtained by using techniques of Bourgain. These estimates lead to new critical well-posedness results for the nonlinear Schrödinger equation on irrational tori in two and three dimensions with small initial data. In three dimensions, this includes the energy critical case. This extends recent work of Guo–Oh–Wang.     

Towards peptide-substituted titanocene anticancer drugs

An alkyne-substituted fulvene was transformed via hydridolithiation followed by transmetallation with titanium tetrachloride into bis-[p-(prop-2-ynyloxy)-benzyl-cyclopentadienyl] titanium(IV) dichloride. Single crystals of this titanocene derivative could be obtained and the structure determined by X-ray diffraction. It showed that this compound crystallises in the space group C2/c with four molecules in the monoclinic cell. The alkyne-substituted titanocene dichloride derivative was then subject to a copper-catalysed azide-alkyne cycloaddition with its azide-functionalised methylester-protected phenylalanine reaction partner in order to form a linking triazole. This reaction was performed under anhydrous conditions employing a dichloromethane/acetonitrile solvent mixture with copper(I) iodide and 2,6-lutidine as the catalyst system. Under these conditions the adduct between the protein mimic and the titanocene was formed without hydrolysing the titanium dichloride moiety.