Imaging of chemical kinetics at the water-water interface in a free-flowing liquid flat-jet
H. Christian Schewe, Bruno Credidio, Aaron M. Ghrist, Sebastian Malerz, Christian Ozga, André Knie, Henrik Haak, Gerard Meijer, Bernd Winter, Andreas Osterwalder
We present chemical kinetics measurements of the luminol oxydation chemiluminescence reaction at the interface between two aqueous solutions, using liquid jet technology. Free-flowing iquid microjets are a relatively recent development that has found its 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. We here show that in the first leaf of this chain the fluids do not exhibit turbulent mixing, providing a clean interface between the liquids from the impinging jets. We also show, using the example of the luminol chemiluminescence reaction, how this setup can be used to obtain kinetics information from friction-less flow and by circumventing the requirement for rapid mixing but by intentionally suppressing all turbulent mixing and instead relying on diffusion.
An atmospheric plasma torch has been supplied with a gaseous mixture of helium, water vapour and/or oxygen to study the production of reactive species within its flowing post-discharge, in particular hydrogen peroxide. The mechanisms responsible for the production of H2O2 have been investigated by correlating measurements of mass spectrometry and absorption photospectrometry. An absolute quantification of H2O2 has also been achieved and indicated that for 5 mmol of water vapour injected in the He-H2O discharge, approximately 9.5 mol of H2O2 were produced in post-discharge.
This study presents the first direct and quantitative measurements of the nuclear momentum distribution anisotropy and the quantum kinetic energy tensor in stable and metastable (supercooled) water near its triple point using Deep Inelastic Neutron Scattering (DINS). From the experimental spectra accurate lineshapes of the hydrogen momentum distributions are derived using an anisotropic Gaussian and a model independent framework. The experimental results, benchmarked with those obtained for the solid phase, provide the state of the art directional values of the hydrogen mean kinetic energy in …
Based on the trajectories of the separation between water molecule pairs from MD simulations, we investigate the bond breakage dynamics in bulk water. From the spectrum of mean first-passage times, the Fokker-Planck equation allows us to derive the diffusivity profile along the separation coordinate and thus to unambiguously disentangle the effects of free-energy and local friction on the separation kinetics. For tightly coordinated water the friction is six times higher than in bulk, which can be interpreted in terms of a dominant reaction path that involves additional orthogonal coordinates.
This paper presents the results of a theoretical and experimental study of plasma-assisted reforming of ethanol into molecular hydrogen in a new modification of the "tornado" type electrical discharge. Numerical modeling clarifies the nature of the non-thermal conversion and explains the kinetic mechanism of nonequilibrium plasma-chemical transformations in the gas-liquid system and the evolution of hydrogen during the reforming as a function of discharge parameters and ethanol-to-water ratio in the mixture. We also propose a scheme of chemical reactions for plasma kinetics description. It is …
The kinetic energy of H and O nuclei has been studied by path integral molecular dynamics simulations of ice Ih and water at ambient pressure. The simulations were performed by using the q-TIP4P/F model, a point charge empirical potential that includes molecular flexibility and anharmonicity in the OH stretch of the water molecule. Ice Ih was studied in a temperature range between 210-290 K, and water between 230-320 K. Simulations of an isolated water molecule were performed in the range 210-320 K to estimate the contribution of the intramolecular vibrational modes to the kinetic energy. Our …
At room temperature, the quantum contribution to the kinetic energy of a water molecule exceeds the classical contribution by an order of magnitude. The quantum kinetic energy (QKE) of a water molecule is modulated by its local chemical environment and leads to uneven partitioning of isotopes between different phases in thermal equilibrium, which would not occur if the nuclei behaved classically. In this work, we use ab initio path integral simulations to show that QKEs of the water molecules and the equilibrium isotope fractionation ratios of the oxygen and hydrogen isotopes are sensitive pro…
How is Water released in Hydrogen-Based Metal Oxide Reduction? Unraveling the Kinetic Bottleneck in Sustainable Metal Production
ShanghaiTech University（上海科技大学）；Suzhou National Laboratory（苏州国家实验室）；University of Chinese Academy of Sciences（中国科学院大学）；Deutsches Elektronen-Synchrotron DESY（德国电子同步加速器）；Helmholtz-Zentrum hereon GmbH（亥姆霍兹海雷恩中心有限公司）；Technical University of Munich（慕尼黑工业大学）；Delft University of Technology（代尔夫特理工大学）；Max Planck Institute for Sustainable Materials（马克斯·普朗克可持续材料研究所）
Even at room temperature, quantum mechanics plays a major role in determining the quantitative behaviour of light nuclei, changing significantly the values of physical properties such as the heat capacity. However, other observables appear to be only weakly affected by nuclear quantum effects (NQEs): for instance, the melting temperatures of light and heavy water differ by less than 4 K. Recent theoretical work has attributed this to a competition between intra and inter molecular NQEs, which can be separated by computing the anisotropy of the quantum kinetic energy tensor. The principal value…
Picosecond geminate recombination kinetics for electrons generated by multiphoton ionization of liquid water become power dependent when the radiance of the excitation light is greater than 0.3-0.5 TW/cm^2 (the terawatt regime). To elucidate the mechanism of this power dependence, tri- 400 nm photon ionization of water has been studied using pump-probe laser spectroscopy on the pico- and femtosecond time scales. We suggest that the observed kinetic transformations are caused by a rapid temperature jump in the sample. Such a jump is inherent to multiphoton ionization in the terawatt regime, whe…
The picosecond geminate recombination kinetics for hydrated electrons generated by 200 nm two photon absorption (12.4 eV total energy) has been measured in both light and heavy water. The geminate kinetics are observed to be almost identical in both H2O and D2O. Kinetic analysis based upon the independent reaction time approximation indicates that the average separation between the electron and its geminate partners in D2O is 13% narrower than in H2O (2.1 nm vs. 2.4 nm). These observations suggest that, even at this high ionization energy, autoionization of water competes with direct ionizatio…
Water cavitation results from the kinetic competition of bulk, surface and surface-defect nucleation events
Laboratory of Computational Science and Modeling, IMX, École Polytechnique Fédérale de Lausanne（洛桑联邦理工学院计算科学与建模实验室）；Freie Universität Berlin（柏林自由大学）；Jožef Stefan Institute（约瑟夫·斯蒂芬研究所）；Technische Universität Darmstadt（达姆施塔特工业大学）
At the fundamental level, our understanding of water hydrogen-bond dynamics has been largely built on the detailed analysis of classical molecular simulations. The latter served to develop a plethora of hydrogen bond definitions based on different properties, including geometrical distances, topology and energetics. Notwithstanding, no real consensus emerged from these approaches, making the development of a consistent and reliable definition elusive. In this contribution, a framework to study hydrogen bonds in liquid water based purely on kinetics is presented. This approach makes use of the …
The interfacial behaviour of water remains a central question to fields as diverse as protein folding, friction and ice formation[1,2]. While the structural and dynamical properties of water at interfaces differ strongly from those in the bulk, major gaps in our knowledge at the molecular level still prevent us from understanding these ubiquitous chemical processes. Information concerning the microscopic motion of water comes mostly from computational simulation[3,4] but the dynamics of molecules, on the atomic scale, is largely unexplored by experiment. Here we present experimental results co…
We use molecular dynamics simulations to study the thermodynamics and kinetics of alanine dipeptide isomerization at the air-water interface. Thermodynamically, we find an affinity of the dipeptide to the interface. This affinity arises from stablizing intramolecular interactions that become unshielded as the dipeptide is desolvated. Kinetically, we consider the rate of transitions between the alpha-L and beta conformations of alanine dipeptide and evaluate it as a continuous function of the distance from the interface using a recent extension of transition path sampling, TPS+U. The rate of is…
We investigate the impact of water fluctuations on the key-lock association kinetics of a hydrophobic ligand (key) binding to a hydrophobic pocket (lock) by means of a minimalistic stochastic model system. It describes the collective hydration behavior of the pocket by bimodal fluctuations of a water-pocket interface that dynamically couples to the diffusive motion of the approaching ligand via the hydrophobic interaction. This leads to a set of overdamped Langevin equations in 2D-coordinate-space, that is Markovian in each dimension. Numerical simulations demonstrate locally increased frictio…
We report on the effects of electron collision and indirect ionization processes, occurring at photoexcitation and electron kinetic energies well below 30 eV on the photoemission spectra of liquid water. We show that the nascent photoelectron spectrum and, hence, the inferred electron binding energy can only be accurately determined if electron energies are large enough that cross sections for quasi-elastic scattering processes, such as vibrational excitation, are negligible. Otherwise, quasi-elastic scattering leads to strong, down-to-few-meV kinetic energy scattering losses from the direct p…
We use transient absorption spectroscopy to monitor the ionization and dissociation products following two-photon excitation of pure liquid water. The two decay mechanisms occur with similar yield for an excitation energy of 9.3 eV, whereas the major channel at 8.3 eV is dissociation. The geminate recombination kinetics of the H and OH fragments, which can be followed in the transient absorption probed at 267 nm, provide a window on the dissociation dynamics at the lower excitation energy. Modeling the OH geminate recombination indicates that the dissociating H atoms have enough kinetic energy…
Thiol-ene photo-click hydrogels were prepared via step-growth polymerisation using thiol-functionalised type-I collagen and 8-arm poly(ethylene glycol) norbornene terminated (PEG-NB), as a potential injectable regenerative device. Type-I collagen was thiol-functionalised by a ring opening reaction with 2-iminothiolane (2IT), whereby up to 80 Abs% functionalisation and 90 RPN% triple helical preservation were recorded via 2,4,6-Trinitrobenzenesulfonic acid (TNBS) colorimetric assay and circular dichroism (CD). Type, i.e. 2-Hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone (I2959) or li…
Water interactions with organic surfaces are of central importance in biological systems and many Earth system processes. Here we describe experimental studies of water collisions and uptake kinetics on liquid and solid butanol from 160 to 200 K. Hyperthermal D2O molecules (0.32 eV) undergo efficient trapping on both solid and liquid butanol, and only a minor fraction scatters inelastically after an 80% loss of kinetic energy to surface modes. Trapped molecules either desorb within a few ms, or are taken up by the butanol phase during longer times. The water uptake and surface residence time i…
Aqueous solutions provide a medium for many important reactions in chemical synthesis, industrial processes, environmental chemistry, and biological functions. It is an accepted fact that aqueous solvents can be direct participants to the reaction process and not act only as simple passive dielectrics. Assisting water molecules and proton wires are thus essential for the efficiency of many reactions. Here we study the decomposition of urea into ammonia and isocyanic acid by means of enhanced ab initio molecular dynamics simulations. We highlight the role of the solvent molecules and their inte…
A key factor influencing a drug's efficacy is its residence time in the binding pocket of the host protein. Using atomistic computer simulation to predict this residence time and the associated dissociation process is a desirable but extremely difficult task due to the long timescales involved. This gets further complicated by the presence of biophysical factors such as steric and solvation effects. In this work, we perform molecular dynamics (MD) simulations of the unbinding of a popular prototypical hydrophobic cavity-ligand system using a metadynamics based approach that allows direct asses…
Water exchange reactions around ionic solutes are ubiquitous in aqueous solution-phase chemistry. However, the extreme sensitivity of exchange rates to perturbations in the chemistry of an ionic solute is not well understood. We examine water exchange around model ions within the language of dynamic facilitation theory, typically used to describe glassy and other systems with collective, facilitated dynamics. Through the development of a coarse-grained, kinetically-constrained lattice model of water exchange, we show that the timescale for water exchange scales exponentially with the strength …
Rates of conversions of molecular internal energy to and from kinetic energy by means of molecular collision allows to compute collisional line shapes and transport properties of gases. Knowledge of ro-vibrational quenching rates is necessary to connect spectral observations to physical properties of warm astrophysical gasses, including exo-atmospheres. For a system of paramount importance in this context, the vibrational bending mode quenching of H2O by H2, we show here that exchange of vibrational to rotational and kinetic energy remains a quantum process, despite the large numbers of quantu…
We present a ``coarse molecular dynamics'' approach and apply it to studying the kinetics and thermodynamics of a peptide fragment dissolved in water. Short bursts of appropriately initialized simulations are used to infer the deterministic and stochastic components of the peptide motion parametrized by an appropriate set of coarse variables. Techniques from traditional numerical analysis (Newton-Raphson, coarse projective integration) are thus enabled; these techniques help analyze important features of the free-energy landscape (coarse transition states, eigenvalues and eigenvectors, transit…
