Browsing by Author "Fyta, Maria"

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Open Access
A complementary experimental and theoretical approach for probing the surface functionalization of ZnO with molecular catalyst linkers
(2023) Kousik, Shravan R.; Solodenko, Helena; YazdanYar, Azade; Kirchhof, Manuel; Schützendübe, Peter; Richter, Gunther; Laschat, Sabine; Fyta, Maria; Schmitz, Guido; Bill, Joachim; Atanasova, Petia
The application of ZnO materials as solid-state supports for molecular heterogeneous catalysis is contingent on the functionalization of the ZnO surface with stable self-assembled monolayers (SAMs) of catalyst linker molecules. Herein, experimental and theoretical methods are used to study SAMs of azide-terminated molecular catalyst linkers with two different anchor groups (silane and thiol) on poly and monocrystalline (0001, ) ZnO surfaces. Angle-resolved and temperature-dependent X-ray photoelectron spectroscopy (XPS) is used to study SAM binding modes, thermal stabilities, and coverages. The binding strengths and atomistic ordering of the SAMs are determined via atom-probe tomography (APT). Density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations provide insights on the influence of the ZnO surface polarity on the interaction affinity and conformational behavior of the SAMs. The investigations show that SAMs based on 3-azidopropyltriethoxysilane possess a higher binding strength and thermal stability than the corresponding thiol. SAM surface coverage is strongly influenced by the surface polarity of ZnO, and the highest coverage is observed on the polycrystalline surface. To demonstrate the applicability of linker-modified polycrystalline ZnO as a catalyst support, a chiral Rh diene complex is immobilized on the azide-terminal of the SAM and its coverage is evaluated via XPS.
Open Access
Confined Ru‐catalysts in a two‐phase heptane/ionic liquid solution : modeling aspects
(2020) Kobayashi, Takeshi; Kraus, Hamzeh; Hansen, Niels; Fyta, Maria
A modeling approach for atomic‐resolution studies of sup‐ ported ionic liquid phase (SILP) catalytic systems in silica mesoporous confinement with surface hydroxyl and functional groups is proposed. First, a force field for the Ru‐based catalyst is developed. Second, its solvation behavior within a bulk two‐phase system of heptane and an IL is studied. Third, static and dynamic properties of the confined system are investigated. Using classical molecular dynamics simulations, experimentally inaccessible properties can thus be studied that are important for an optimization of a SILP system for performing a ring‐closing metathesis reaction.
Open Access
Functionalized nanogap for DNA read‐out : nucleotide rotation and current‐voltage curves
(2020) Maier, Frank C.; Fyta, Maria
Functionalized nanogaps embedded in nanopores show a strong potential for enhancing the detection of biomolecules, their length, type, and sequence. This detection is strongly dependent on the features of the target biomolecules, as well as the characteristics of the sensing device. In this work, through quantum‐mechanical calculations, we elaborate on representative such aspects for the specific case of DNA detection and read‐out. These aspects include the influence of single DNA nucleotide rotation within the nanogap and the current‐voltage (I‐V) characteristics of the nanogap. The results unveil a distinct variation in the electronic current across the functionalized device for the four natural DNA nucleotides with the applied voltage. These also underline the asymmetric response of the rotating nucleotides on this applied voltage and the respective variation in the rectification ratio of the device. The electronic tunneling current across the nanogap can be further enhanced through the proper choice of an applied bias voltage. We were able to correlate the enhancement of this current to the nucleotide rotation dynamics and a shift of the electronic transmission peaks towards the Fermi level. This nucleotide specific shift further reveals the sensitivity of the device in reading‐out the identity of the DNA nucleotides for all different configurations in the nanogap. We underline the important information that can be obtained from both the I‐V curves and the rectification characteristics of the nanogap device in view of accurately reading‐out the DNA information. We show that tuning the applied bias can enhance this detection and discuss the implications in view of novel functionalized nanopore sequencers.
Open Access
Impact of COVID-19 on electricity demand : deriving minimum states of system health for studies on resilience
(2021) Manjunath, Smruti; Yeligeti, Madhura; Fyta, Maria; Haas, Jannik; Gils, Hans-Christian
To assess the resilience of energy systems, i.e., the ability to recover after an unexpected shock, the system’s minimum state of service is a key input. Quantitative descriptions of such states are inherently elusive. The measures adopted by governments to contain COVID-19 have provided empirical data, which may serve as a proxy for such states of minimum service. Here, we systematize the impact of the adopted COVID-19 measures on the electricity demand. We classify the measures into three phases of increasing stringency, ranging from working from home to soft and full lockdowns, for four major electricity consuming countries of Europe. We use readily accessible data from the European Network of Transmission System Operators for Electricity as a basis. For each country and phase, we derive representative daily load profiles with hourly resolution obtained by k-medoids clustering. The analysis could unravel the influence of the different measures to the energy consumption and the differences among the four countries. It is observed that the daily peak load is considerably flattened and the total electricity consumption decreases by up to 30% under the circumstances brought about by the COVID-19 restrictions. These demand profiles are useful for the energy planning community, especially when designing future electricity systems with a focus on system resilience and a more digitalised society in terms of working from home.