Stability and Reactivity of Aromatic Radical Anions in Solution with Relevance to Birch Reduction.

We investigate the electronic structure of aromatic radical anions in the solution phase employing a combination of liquid-jet (LJ) photoelectron (PE) spectroscopy measurements and electronic structure calculations. By using recently developed protocols, we accurately determine the vertical ionization energies of valence electrons of both the solvent and the solute molecules. In particular, we first characterize the pure solvent of tetrahydrofuran (THF) by LJ-PE measurements in conjunction with ab initio molecular dynamics simulations and GW calculations.

Photoelectron spectroscopy from a liquid flatjet.

We demonstrate liquid-jet photoelectron spectroscopy from a flatjet formed by the impingement of two micron-sized cylindrical jets of different aqueous solutions. Flatjets provide flexible experimental templates enabling unique liquid-phase experiments that would not be possible using single cylindrical liquid jets. One such possibility is to generate two co-flowing liquid-jet sheets with a common interface in vacuum, with each surface facing the vacuum being representative of one of the solutions, allowing face-sensitive detection by photoelectron spectroscopy.

Bridging Electrochemistry and Photoelectron Spectroscopy in the Context of Birch Reduction: Detachment Energies and Redox Potentials of Electron, Dielectron, and Benzene Radical Anion in Liquid Ammonia.

Birch reduction is a time-proven way to hydrogenate aromatic hydrocarbons (such as benzene), which relies on the reducing power of electrons released from alkali metals into liquid ammonia. We have succeeded to characterize the key intermediates of the Birch reduction process─the solvated electron and dielectron and the benzene radical anion─using cyclic voltammetry and photoelectron spectroscopy, aided by electronic structure calculations. In this way, we not only quantify the electron binding energies of these species, which are decisive for the mechanism of the reaction, but also use Birch reduction as a case study to directly connect the two seemingly unrelated experimental techniques.

Observation of intermolecular Coulombic decay and shake-up satellites in liquid ammonia.

We report the first nitrogen 1s Auger-Meitner electron spectrum from a liquid ammonia microjet at a temperature of ∼223 K (-50 °C) and compare it with the simultaneously measured spectrum for gas-phase ammonia. The spectra from both phases are interpreted with the assistance of high-level electronic structure and molecular dynamics calculations. In addition to the regular Auger-Meitner-electron features, we observe electron emission at kinetic energies of 374-388 eV, above the leading Auger-Meitner peak (3a ).

High Versatility of IPP and DMAPP Methyltransferases Enables Synthesis of C , C and C Terpenoid Building Blocks.

The natural substance class of terpenoids covers an extremely wide range of different structures, although their building block repertoire is limited to the C compounds DMAPP and IPP. This study aims at the characterization of methyltransferases (MTases) that modify these terpene precursors and the demonstration of their suitability for biotechnological purposes. All seven enzymes tested accepted IPP as substrate and altogether five C compounds and six C compounds were formed within the reactions.

Spectroscopic characterization of singlet-triplet doorway states of aluminum monofluoride.

Aluminum monofluoride (AlF) possesses highly favorable properties for laser cooling, both via the AΠ and aΠ states. Determining efficient pathways between the singlet and the triplet manifold of electronic states will be advantageous for future experiments at ultralow temperatures. The lowest rotational levels of the AΠ, v = 6 and bΣ, v = 5 states of AlF are nearly iso-energetic and interact via spin-orbit coupling.

Imaging of Chemical Kinetics at the Water-Water Interface in a Free-Flowing Liquid Flat-Jet.

We present chemical kinetics measurements of the luminol oxidation chemiluminescence (CL) reaction at the interface between two aqueous solutions, using liquid jet technology. Free-flowing liquid microjets are a relatively recent development that have found their way into a growing number of applications in spectroscopy and dynamics. A variant thereof, called flat-jet, is obtained when two cylindrical jets of a liquid are crossed, leading to a chain of planar leaf-shaped structures of the flowing liquid.

Photoelectron Spectroscopy of Benzene in the Liquid Phase and Dissolved in Liquid Ammonia.

We report valence band photoelectron spectroscopy measurements of gas-phase and liquid-phase benzene as well as those of benzene dissolved in liquid ammonia, complemented by electronic structure calculations. The origins of the sizable gas-to-liquid-phase shifts in electron binding energies deduced from the benzene valence band spectral features are quantitatively characterized in terms of the Born-Haber solvation model. This model also allows to rationalize the observation of almost identical shifts in liquid ammonia and benzene despite the fact that the former solvent is polar while the latter is not.

Spectroscopic evidence for a gold-coloured metallic water solution.

Insulating materials can in principle be made metallic by applying pressure. In the case of pure water, this is estimated to require a pressure of 48 megabar, which is beyond current experimental capabilities and may only exist in the interior of large planets or stars. Indeed, recent estimates and experiments indicate that water at pressures accessible in the laboratory will at best be superionic with high protonic conductivity, but not metallic with conductive electrons.

Identification of Fungal Limonene-3-Hydroxylase for Biotechnological Menthol Production.

More than 30,000 tons of menthol are produced every year as a flavor and fragrance compound or as a medical component. So far, only extraction from plant material and chemical synthesis are possible. An alternative approach for menthol production could be a biotechnological-chemical process with ideally only two conversion steps, starting from (+)-limonene, which is a side product of the citrus processing industry.

Photoelectron spectra of alkali metal-ammonia microjets: From blue electrolyte to bronze metal.

Experimental studies of the electronic structure of excess electrons in liquids-archetypal quantum solutes-have been largely restricted to very dilute electron concentrations. We overcame this limitation by applying soft x-ray photoelectron spectroscopy to characterize excess electrons originating from steadily increasing amounts of alkali metals dissolved in refrigerated liquid ammonia microjets. As concentration rises, a narrow peak at ~2 electron volts, corresponding to vertical photodetachment of localized solvated electrons and dielectrons, transforms continuously into a band with a sharp Fermi edge accompanied by a plasmon peak, characteristic of delocalized metallic electrons.

Deeply cooled and temperature controlled microjets: Liquid ammonia solutions released into vacuum for analysis by photoelectron spectroscopy.

A versatile, temperature controlled apparatus is presented, which generates deeply cooled liquid microjets of condensed gases, expelling them via a small aperture into vacuum for use in photoelectron spectroscopy (PES). The functionality of the design is demonstrated by temperature- and concentration-dependent PES measurements of liquid ammonia and solutions of KI and NHI in liquid ammonia. The experimental setup is not limited to the usage of liquid ammonia solutions solely.

Investigation of monoterpenoid resistance mechanisms in Pseudomonas putida and their consequences for biotransformations.

Monoterpenoids are widely used in industrial applications, e.g. as active ingredients in pharmaceuticals, in flavor and fragrance compositions, and in agriculture.

Investigation of fatty aldehyde and alcohol synthesis from fatty acids by αDox- or CAR-expressing Escherichia coli.

Fatty aldehydes are among the most important flavor and fragrance compounds. Most biotechnological production approaches make use of the one step conversion of fatty acids from renewable sources by the enzymes α-dioxygenase (αDox) or carboxylic acid reductase (CAR). Their reaction mechanisms and cofactor dependencies are very different.

Investigation of plasmid-induced growth defect in Pseudomonas putida.

Genetic engineering in bacteria mainly relies on the use of plasmids. But despite their pervasive use for physiological studies as well as for the design and optimization of industrially used production strains, only limited information about plasmid induced growth defects is available for different replicons and organisms. Here, we present the identification and characterization of such a phenomenon for Pseudomonas putida transformants carrying the pBBR1-derived plasmid pMiS1.

Efficient hydroxylation of 1,8-cineole with monoterpenoid-resistant recombinant Pseudomonas putida GS1.

In this work, monoterpenoid hydroxylation with Pseudomonas putida GS1 and KT2440 were investigated as host strains, and the cytochrome P450 monooxygenase CYP176A1 (P450cin) and its native redox partner cindoxin (CinC) from Citrobacter braakii were introduced in P. putida to catalyze the stereoselective hydroxylation of 1,8-cineole to (1R)-6β-hydroxy-1,8-cineole. Growth experiments in the presence of 1,8-cineole confirmed pseudomonads' superior resilience compared to E.

Stark Interference of Electric and Magnetic Dipole Transitions in the A-X Band of OH.

An experimental method is demonstrated that allows determination of the ratio between the electric (E1) and magnetic (M1) transition dipole moments in the A-X band of OH, including their relative sign. Although the transition strengths differ by more than 3 orders of magnitude, the measured M1-to-E1 ratio agrees with the ratio of the ab initio calculated values to within 3%. The relative sign is found to be negative, also in agreement with theory.

Rotationally inelastic scattering of OH by molecular hydrogen: Theory and experiment.

We present an experimental and theoretical investigation of rotationally inelastic transitions of OH, prepared in the X(2)Π, v = 0, j = 3/2 F1f level, in collisions with molecular hydrogen (H2 and D2). In a crossed beam experiment, the OH radicals were state selected and velocity tuned over the collision energy range 75-155 cm(-1) using a Stark decelerator. Relative parity-resolved state-to-state integral cross sections were determined for collisions with normal and para converted H2.

Bioprocess engineering for microbial synthesis and conversion of isoprenoids.

Isoprenoids represent a natural product class essential to living organisms. Moreover, industrially relevant isoprenoid molecules cover a wide range of products such as pharmaceuticals, flavors and fragrances, or even biofuels. Their often complex structure makes chemical synthesis a difficult and expensive task and extraction from natural sources is typically low yielding.

De novo production of the monoterpenoid geranic acid by metabolically engineered Pseudomonas putida.

Background: Production of monoterpenoids as valuable chemicals using recombinant microbes is a growing field of interest. Unfortunately, antimicrobial activity of most monoterpenoids hampers a wide application of microorganisms for their production. Strains of Pseudomonas putida, a fast growing and metabolically versatile bacterium, often show an outstanding high tolerance towards organic solvents and other toxic compounds.

Multiple improvement of astaxanthin biosynthesis in Xanthophyllomyces dendrorhous by a combination of conventional mutagenesis and metabolic pathway engineering.

Xanthophyllomyces dendrorhous (Phaffia rhodozyma) is the only yeast or fungus that synthesizes the commercially attractive carotenoid astaxanthin. For a suitable bioprocess, the wild type has to be modified for increasing biomass content. To achieve this, a two step strategy has been followed.

Quantum-state resolved bimolecular collisions of velocity-controlled OH with NO radicals.

Whereas atom-molecule collisions have been studied with complete quantum-state resolution, interactions between two state-selected molecules have proven much harder to probe. Here, we report the measurement of state-resolved inelastic scattering cross sections for collisions between two open-shell molecules that are both prepared in a single quantum state. Stark-decelerated hydroxyl (OH) radicals were scattered with hexapole-focused nitric oxide (NO) radicals in a crossed-beam configuration.

Coherent reflection of he atom beams from rough surfaces at grazing incidence.

We report coherent reflection of thermal He atom beams from various microscopically rough surfaces at grazing incidence. For a sufficiently small normal component k(z) of the incident wave vector of the atom the reflection probability is found to be a function of k(z) only. This behavior is explained by quantum reflection at the attractive branch of the Casimir-van der Waals interaction potential.

Biotechnological production of astaxanthin with Phaffia rhodozyma/Xanthophyllomyces dendrorhous.

The oxygenated β-carotene derivative astaxanthin exhibits outstanding colouring, antioxidative and health-promoting properties and is mainly found in the marine environment. To satisfy the growing demand for this ketocarotenoid in the feed, food and cosmetics industries, there are strong efforts to develop economically viable bioprocesses alternative to the current chemical synthesis. However, up to now, natural astaxanthin from Haematococcus pluvialis, Phaffia rhodozyma or Paracoccus carotinifaciens has not been cost competitive with chemically synthesized astaxanthin, thus only serving niche applications.

P450(BM-3)-catalyzed whole-cell biotransformation of alpha-pinene with recombinant Escherichia coli in an aqueous-organic two-phase system.

A recombinant Escherichia coli BL21 (DE3) strain overexpressing a variant of P450(BM-3) (V26T/R47F/A74G/F87V/L188K; abbreviated: BL21 (P450(BM-3) QM)) oxyfunctionalizes the bicyclic monoterpene alpha-pinene to alpha-pinene oxide, verbenol, and myrtenol. To address the low water solubility and the toxicity of terpenoids, an aqueous-organic two-phase bioprocess was developed. Diisononyl phthalate was selected as a biocompatible organic carrier solvent capable of masking the toxic effects mediated by alpha-pinene and of efficiently extracting the products enabling scale-up to the bioreactor.