Hydrogen concentrations in methane-forming cells probed by the ratios of reduced and oxidized coenzyme F420

Coenzyme F420 is the central low-redox-potential electron carrier in methanogenic metabolism. The coenzyme is reduced under hydrogen by the action of F420-dependent hydrogenase. The standard free-energy change at pH 7 of F420 reduction was determined to be −15 kJ mol−1, irrespective of the temperature (25–65 °C). Experiments performed with methane-forming cell suspensions of Methanothermobacter thermautotrophicus incubated under various conditions demonstrated that the ratios of reduced and oxidized F420 were in thermodynamic equilibrium with the gas-phase hydrogen partial pressures. During growth in a fed-batch fermenter, ratios changed in connection with the decrease in dissolved hydrogen. For most of the time, the changes were as expected for thermodynamic equilibrium between the oxidation state of F420 inside the cells and extracellular hydrogen. Also, methanol-metabolizing, but not acetate-converting, cells of Methanosarcina barkeri maintained the ratios of reduced and oxidized coenzyme F420 in thermodynamic equilibrium with external hydrogen. The results of the study demonstrate that F420 is a useful probe to assess in situ hydrogen concentrations in H2-metabolizing methanogens.

Download Full-text

UV Enhancement of Surface Catalytic Polymerization of Ethylene

MRS Proceedings ◽

10.1557/proc-129-259 ◽

1988 ◽

Vol 129 ◽

Author(s):

Parul Vora Purohit ◽

Mordechai Rothschild ◽

Daniel J. Ehrlich

Keyword(s):

Thin Film ◽

Fourier Transform ◽

Gas Phase ◽

Solid Phase ◽

Catalytic Polymerization ◽

Saturation Thickness ◽

Partial Pressures ◽

Rate Of Polymerization ◽

Phase Chemical

ABSTRACTThe polymerization of ethylene on surfaces sequentially dosed with TiC14 and trimethylaluminum was studied by Fourier transform infrared spectroscopy. The polymer film was observed in situ as a function of time and under the influence of 254-nm cw radiation. The rate of polymerization and the saturation thickness of the polyethylene are strongly dependent on the order of dosing and the partial pressures of the reactants that form the catalyst. UV enhancement of polymerization was demonstrated to occur through two separate photochemical channels: gas-phase photolysis of the reactants and solid-phase chemical transformation of a noncatalytic thin film.

Download Full-text

A polycentric growth model of gallium arsenide epitaxial layers from the gas phase with simultaneous diffusion, adsorption and chemical reaction

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19882995 ◽

1988 ◽

Vol 53 (12) ◽

pp. 2995-3013

Author(s):

Emerich Erdös ◽

Jindřich Leitner ◽

Petr Voňka ◽

Josef Stejskal ◽

Přemysl Klíma

Keyword(s):

Growth Rate ◽

Gallium Arsenide ◽

Epitaxial Growth ◽

Gas Phase ◽

Surface Reaction ◽

Quantitative Description ◽

The Other ◽

Rate Equations ◽

Impact Interaction ◽

Partial Pressures

For a quantitative description of the epitaxial growth rate of gallium arsenide, two models are proposed including two rate controlling steps, namely the diffusion of components in the gas phase and the surface reaction. In the models considered, the surface reaction involves a reaction triple - or quadruple centre. In both models three mechanisms are considered which differ one from the other by different adsorption - and impact interaction of reacting particles. In every of the six cases, the pertinent rate equations were derived, and the models have been confronted with the experimentally found dependences of the growth rate on partial pressures of components in the feed. The results are discussed with regard to the plausibility of individual mechanisms and of both models, and also with respect to their applicability and the direction of further investigations.

Download Full-text

In Situ Observation of Electron-Beam-Induced Formation of Nano-Structures in PbTe

Nanomaterials ◽

10.3390/nano11010163 ◽

2021 ◽

Vol 11 (1) ◽

pp. 163

Author(s):

Iryna Zelenina ◽

Igor Veremchuk ◽

Yuri Grin ◽

Paul Simon

Keyword(s):

Electron Beam ◽

Gas Phase ◽

Threshold Current ◽

Threshold Current Density ◽

Atomic Scale ◽

In Situ Observation ◽

Nano Structures ◽

Transmission Electron ◽

Initial Crystal

Nano-scaled thermoelectric materials attract significant interest due to their improved physical properties as compared to bulk materials. Well-shaped nanoparticles such as nano-bars and nano-cubes were observed in the known thermoelectric material PbTe. Their extended two-dimensional nano-layer arrangements form directly in situ through electron-beam treatment in the transmission electron microscope. The experiments show the atomistic depletion mechanism of the initial crystal and the recrystallization of PbTe nanoparticles out of the microparticles due to the local atomic-scale transport via the gas phase beyond a threshold current density of the beam.

Download Full-text

An Atmospheric Origin for HCN-Derived Polymers on Titan

Processes ◽

10.3390/pr9060965 ◽

2021 ◽

Vol 9 (6) ◽

pp. 965

Author(s):

Zoé Perrin ◽

Nathalie Carrasco ◽

Audrey Chatain ◽

Lora Jovanovic ◽

Ludovic Vettier ◽

...

Keyword(s):

Chemical Composition ◽

Gas Phase ◽

Formation Process ◽

Upper Atmosphere ◽

Gas Mixture ◽

Space Probe ◽

Atmospheric Haze ◽

Formation And Evolution ◽

Haze Formation

Titan’s haze is strongly suspected to be an HCN-derived polymer, but despite the first in situ measurements by the ESA-Huygens space probe, its chemical composition and formation process remain largely unknown. To investigate this question, we simulated the atmospheric haze formation process, experimentally. We synthesized analogues of Titan’s haze, named Titan tholins, in an irradiated N2–CH4 gas mixture, mimicking Titan’s upper atmosphere chemistry. HCN was monitored in situ in the gas phase simultaneously with the formation and evolution of the haze particles. We show that HCN is produced as long as the particles are absent, and is then progressively consumed when the particles appear and grow. This work highlights HCN as an effective precursor of Titan’s haze and confirms the HCN-derived polymer nature of the haze.

Download Full-text

In Situ Optical Analysis of the Gas Phase during the Deposition of Silicon Carbide from Methyltrichlorosilane

Journal of The Electrochemical Society ◽

10.1149/1.1836694 ◽

1996 ◽

Vol 143 (5) ◽

pp. 1654-1661 ◽

Cited By ~ 25

Author(s):

M. Ganz ◽

N. Dorval ◽

M. Lefebvre ◽

M. Péalat ◽

F. Loumagne ◽

...

Keyword(s):

Silicon Carbide ◽

Gas Phase ◽

Optical Analysis

Download Full-text

In situ analysis of gas phase reaction processes within monolithic catalyst supports by applying NMR imaging methods

Catalysis Today ◽

10.1016/j.cattod.2016.02.062 ◽

2016 ◽

Vol 273 ◽

pp. 91-98 ◽

Cited By ~ 6

Author(s):

Jürgen Ulpts ◽

Wolfgang Dreher ◽

Lars Kiewidt ◽

Miriam Schubert ◽

Jorg Thöming

Keyword(s):

Gas Phase ◽

In Situ Analysis ◽

Catalyst Supports ◽

Nmr Imaging ◽

Phase Reaction ◽

Imaging Methods ◽

Monolithic Catalyst ◽

Gas Phase Reaction ◽

Reaction Processes

Download Full-text

Open-path, quantum cascade-laser-based sensor for high-resolution atmospheric ammonia measurements

Atmospheric Measurement Techniques ◽

10.5194/amt-7-81-2014 ◽

2014 ◽

Vol 7 (1) ◽

pp. 81-93 ◽

Cited By ~ 57

Author(s):

D. J. Miller ◽

K. Sun ◽

L. Tao ◽

M. A. Khan ◽

M. A. Zondlo

Keyword(s):

Gas Phase ◽

Quantum Cascade Laser ◽

High Temporal Resolution ◽

Reduced Pressure ◽

Total Uncertainty ◽

Atmospheric Ammonia ◽

Quantum Cascade ◽

Open Path ◽

Time Calibration

Abstract. We demonstrate a compact, open-path, quantum cascade-laser-based atmospheric ammonia sensor operating at 9.06 μm for high-sensitivity, high temporal resolution, ground-based measurements. Atmospheric ammonia (NH3) is a gas-phase precursor to fine particulate matter, with implications for air quality and climate change. Currently, NH3 sensing challenges have led to a lack of widespread in situ measurements. Our open-path sensor configuration minimizes sampling artifacts associated with NH3 surface adsorption onto inlet tubing and reduced pressure sampling cells, as well as condensed-phase partitioning ambiguities. Multi-harmonic wavelength modulation spectroscopy allows for selective and sensitive detection of atmospheric pressure-broadened absorption features. An in-line ethylene reference cell provides real-time calibration (±20% accuracy) and normalization for instrument drift under rapidly changing field conditions. The sensor has a sensitivity and noise-equivalent limit (1σ) of 0.15 ppbv NH3 at 10 Hz, a mass of ~ 5 kg and consumes ~ 50 W of electrical power. The total uncertainty in NH3 measurements is 0.20 ppbv NH3 ± 10%, based on a spectroscopic calibration method. Field performance of this open-path NH3 sensor is demonstrated, with 10 Hz time resolution and a large dynamic response for in situ NH3 measurements. This sensor provides the capabilities for improved in situ gas-phase NH3 sensing relevant for emission source characterization and flux measurements.

Download Full-text

The Equilibrium and the Determination of D00 (H—CN)

Canadian Journal of Chemistry ◽

10.1139/v75-333 ◽

1975 ◽

Vol 53 (16) ◽

pp. 2365-2370 ◽

Cited By ~ 15

Author(s):

Don Betowski ◽

Gervase Mackay ◽

John Payzant ◽

Diethard Bohme

Keyword(s):

Free Energy ◽

Standard Enthalpy ◽

Transfer Reaction ◽

Standard Free Energy ◽

Proton Transfer Reaction ◽

Enthalpy Change ◽

Standard Free Energy Change ◽

Flowing Afterglow ◽

Standard Enthalpy Change

The rate constants and equilibrium constant for the proton transfer reaction [Formula: see text] have been measured at 296 ± 2 K using the flowing afterglow technique: kforward = (2.9 ± 0.6) × 10−9 cm3molecule−1s−1, kreverse = (1.8 ± 0.4) × 10−10 cm3 molecule1 s−1, and K = 16 ± 2. The measured value of K corresponds to a standard free energy change, ΔG296°, of −1.6 ± 0.1 kcal mol−1 which provides values for the standard enthalpy change, ΔH298°= −1.0 ± 0.2 kcal mol−1, the bond dissociation energy, D00(H—CN) = 124 ± 2 kcal mol−1, and the proton affinity, p.a.(CN−) = 350 ± 1 kcal mol−1.

Download Full-text