Publikationen an der Fakultät für Mathematik und Naturwissenschaften

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Strutynska, Nataliia; Malyshenko, Anna; Tverdokhleb, Nina; Evstigneev, Maxim; Vovchenko, Ludmila; Prylutskyy, Yuriy; Slobodyanik, Nikolai; Ritter, Uwe;
Design, characterization and mechanical properties of new Na+, CO32--apatite/alginate/C60 fullerene hybrid biocomposites. - In: Journal of the Korean Ceramic Society. - [Singapore] : Springer Singapore, ISSN 2234-0491, Bd. 58 (2021), 4, S. 422-429
- Im Titel sind "+" und "2-" hochgestellt, "3" und "60" tiefgestellt

Nanoparticles (20-50 nm) of Na+, CO32--containing calcium phosphate (Na: 1.49 wt% and C: 1.53 wt%) with apatite-type structure were prepared by precipitation method from aqueous solution. According to FTIR spectroscopy data, the partial substitution of phosphate by carbonate (B-type) realized in the apatite-type structure. Obtained Na+, CO32--hydroxyapatite (HAP) was used for the preparation of hybrid biocomposites with Alginate (Alg) with weight ratio HAP: Alg = 1:1 or 2:1 and C60 fullerene (C60; from 0.2 to 4 wt%) and their mechanical properties were determined. It was found, that sample with weight ratio HAP: Alg = 2:1 and containing 4.0 wt% of C60 has the highest Young's modulus 429 MPa comparing with other determined samples. The structure modeling of the investigated system showed that the formation of triple complexes Na+, CO32--HAP-Alg-C60 is stabilized by solvophobic and stacking interactions. The created biocomposites can be used as an effective implant material for bone restoration.
Yao, Jie; Zhang, Chenglin; Yang, Guowei; Sha, Mo; Dong, Yulian; Fu, Qun; Wu, Yuhan; Zhao, Huaping; Wu, Minghong; Lei, Yong;
Bismuth nanoparticles confined in carbonaceous nanospheres as anodes for high-performance potassium-ion batteries. - In: ACS applied materials & interfaces. - Washington, DC : Soc., ISSN 1944-8252, Bd. 13 (2021), 27, S. 31766-31774

Bismuth (Bi) has been considered as a promising alloying-type anode for potassium-ion batteries (PIBs), owing to its high theoretical capacity and suitable working voltage plateaus. However, Bi suffers from dramatic volume fluctuation and significant pulverization during the discharge/charge processes, resulting in fast capacity decay. Herein, we synthesize Bi nanoparticles confined in carbonaceous nanospheres (denoted as BiC) for PIBs by first utilizing BiOCl nanoflakes as a hard template and a Bi precursor. The construction of the loose structure buffers the mechanical stresses resulting from the volume expansion of Bi during the alloying reaction and avoids the fracture of the electrode structure, thus improving the cycling performance. Moreover, the carbonaceous layers increase the electronic conductivity and disperse the Bi nanoparticles, enhancing the charge transportation and ionic diffusion, which further promotes the rate capability of Bi@C. It exhibits a superior capacity (389 mAh g^-1 at 100 mA g^-1 after 100 cycles), excellent cycling stability (206 mAh g^-1 at 500 mA g^-1 over 1000 cycles), and an improved rate capability (182 mAh g^-1 at 2.0 A g^-1). This work provides a new structuring strategy in alloying materials for boosting reversible and stable potassium-ion storage.
Kriesell, Matthias;
A note on uniquely 10-colorable graphs. - In: Journal of graph theory. - New York, NY [u.a.] : Wiley, ISSN 1097-0118, Bd. 98 (2021), 1, S. 24-26

Hadwiger conjectured that every graph of chromatic number k admits a clique minor of order k. Here we prove for k ≤ 10, that every graph of chromatic number k with a unique k-coloring (up to the color names) admits a clique minor of order k. The proof does not rely on the Four Color Theorem.
Chernykh, Mariia; Zavalny, Dmytro; Sokolova, Viktoriya; Ponomarenko, Stanislav; Prylutska, Svitlana; Kuziv, Yuliia; Chumachenko, Vasyl; Marynin, Andrii; Kutsevol, Nataliya; Epple, Matthias; Ritter, Uwe; Piosik, Jacek; Prylutskyy, Yuriy;
A new water-soluble thermosensitive star-like copolymer as a promising carrier of the chemotherapeutic drug doxorubicin. - In: Materials. - Basel : MDPI, ISSN 1996-1944, Bd. 14 (2021), 13, S. 1-13

A new water-soluble thermosensitive star-like copolymer, dextran-graft-poly-N-iso-propilacrylamide (D-g-PNIPAM), was created and characterized by various techniques (size-exclusion chromatography, differential scanning calorimetry, Fourier-transform infrared (FTIR) spectroscopy, and dynamic light scattering (DLS) spectroscopy). The viability of cancer cell lines (human transformed cervix epithelial cells, HeLa) as a model for cancer cells was studied using MTT and Live/Dead assays after incubation with a D-g-PNIPAM copolymer as a carrier for the drug doxorubicin (Dox) as well as a D-g-PNIPAM + Dox mixture as a function of the concentration. FTIR spectroscopy clearly indicated the complex formation of Dox with the D-g-PNIPAM copolymer. The size distribution of particles in Hanks solution was determined by the DLS technique at different temperatures. The in vitro uptake of the studied D-g-PNIPAM + Dox nanoparticles into cancer cells was demonstrated by confocal laser scanning microscopy. It was found that D-g-PNIPAM + Dox nanoparticles in contrast to Dox alone showed higher toxicity toward cancer cells. All of the aforementioned facts indicate a possibility of further preclinical studies of the water-soluble D-g-PNIPAM particles behavior in animal tumor models in vivo as promising carriers of anticancer agents.
Romanyuk, Oleksandr; Paszuk, Agnieszka; Bartoš, Igor; Wilks, Regan George; Nandy, Manali; Bombsch, Jakob; Hartmann, Claudia; Félix, Roberto; Ueda, Shigenori; Gordeev, Ivan; Houdkova, Jana; Kleinschmidt, Peter; Machek, Pavel; Bär, Marcus; Jiříček, Petr; Hannappel, Thomas;
Band bending at heterovalent interfaces: hard X-ray photoelectron spectroscopy of GaP/Si(0 0 1) heterostructures. - In: Applied surface science : a journal devoted to applied physics and chemistry of surfaces and interfaces.. - Amsterdam : Elsevier, Bd. 565 (2021)
Paszuk, Agnieszka; Supplie, Oliver; Brückner, Sebastian; Barrigón, Enrique; May, Matthias M.; Nandy, Manali; Gieß, Aaron; Dobrich, Anja; Kleinschmidt, Peter; Rey-Stolle, Ignacio; Hannappel, Thomas;
Atomic surface control of Ge(100) in MOCVD reactors coated with (Ga)As residuals. - In: Applied surface science : a journal devoted to applied physics and chemistry of surfaces and interfaces.. - Amsterdam : Elsevier, Bd. 565 (2021)

Heteroepitaxy of planar, low-defect III-V semiconductor layers on Ge(100) requires a single-domain substrate surface, where dimer rows are aligned in parallel on atomically well-ordered terraces, which are separated by steps of even numbered atomic height. The presence of Ga and As in the sample ambience crucially impacts the preparation of such Ge(100) surfaces. Ga and As are commonly omnipresent, when applying metalorganic chemical vapor deposition (MOCVD), either directly supplied by precursors, in the form of MOCVD reactor residuals, or both. We study the impact of the growth conditions on the Ge(100) surface formation in situ, in dependence on the reactor pre-conditioning, the type of As supply, and/or temperature, utilizing surface-sensitive reflection anisotropy spectroscopy. We benchmark the in situ spectra to in system X-ray photoelectron spectroscopy, low energy electron diffraction and scanning tunneling microscopy. We find that interaction of tertiarybutylarsine (TBAs) with a coating of the inner MOCVD reactor walls by GaAs residuals favors desorption of As from reactor parts resulting in As-dimers on the Ge(100) surface, which are rotated by 90˚ compared to preparation routes employing TBAs in Ga-free ambience. The optical in situ control enables precise adjustment and switching between distinct Ge(100) surface reconstructions for subsequent III-V heteroepitaxy.
Kriničnij, Viktor I.; Yudanova, Evgeniya I.; Denisov, Nikolay N.; Konkin, Aleksei A.; Ritter, Uwe; Bogatyrenko, Victor R.; Konkin, Alexander L.;
Light-induced electron paramagnetic resonance study of charge transport in fullerene and nonfullerene PBDB-T-based solar cells. - In: The journal of physical chemistry. - Washington, DC : Soc., ISSN 1932-7455, Bd. 125 (2021), 22, S. 12224-12240
Grüne, Lars; Schaller, Manuel; Schiela, Anton;
Abstract nonlinear sensitivity and turnpike analysis and an application to semilinear parabolic PDEs. - In: Control, optimisation and calculus of variations : COCV.. - Les Ulis : EDP Sciences, ISSN 1262-3377, Bd. 27 (2021), S. 1-28

We analyze the sensitivity of the extremal equations that arise from the first order necessary optimality conditions of nonlinear optimal control problems with respect to perturbations of the dynamics and of the initial data. To this end, we present an abstract implicit function approach with scaled spaces. We will apply this abstract approach to problems governed by semilinear PDEs. In that context, we prove an exponential turnpike result and show that perturbations of the extremal equation's dynamics, e.g., discretization errors decay exponentially in time. The latter can be used for very efficient discretization schemes in a Model Predictive Controller, where only a part of the solution needs to be computed accurately. We showcase the theoretical results by means of two examples with a nonlinear heat equation on a two-dimensional domain.
Kluitmann, Jonas; Zheng, Xuejiao; Köhler, Michael;
Tuning the morphology of bimetallic gold-platinum nanorods in a microflow synthesis. - In: Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science.. - Amsterdam [u.a.] : Elsevier Science, Bd. 626 (2021)

An automated microfluidic system with computer-controlled syringe pumps was applied for screening a three-dimensional concentration space for the formation of binary gold-platinum metal nanorods. Leveraging the micro segmented flow technique, precise residence and reactant addition timings as well as concentration spaces were addressed. The density and thickness of quasi-isotropic platinum shells on gold nanorod cores were tuned from isolated spots to a dense arrangement of high-aspect-ratio columns. The changing optical properties of the particles in the platinum deposition were used for monitoring the reaction progress and the products by the means of a fiber based micro flow-through spectrophotometer allowing to optimize process times. From our data, we propose an electrochemical model, postulating a diode-like effect and limitations for the formation of Pt nuclei on the gold surface and the formation of nano local elements. This point of view is supported by the observed decoration effects of gold facets and to the formation of columnar structures of the platinum shell.
Visaveliya, Nikunjkumar R.; Köhler, Michael;
Softness meets with brightness: dye-doped multifunctional fluorescent polymer particles via microfluidics for labeling. - In: Advanced optical materials. - Weinheim : Wiley-VCH, ISSN 2195-1071, Bd. 9 (2021), 13, S. 1-22

Fluorogenic labeling strategies have emerged as powerful tools for in vivo and in vitro imaging applications for diagnostic and theranostic purposes. Free organic chromophores (fluorescent dyes) are bright but rapidly degrade. Inorganic nanoparticles (e.g., quantum dots) are photostable but toxic to biological systems. Alternatively, dye-doped polymer particles are promising for labeling and imaging due to their properties that overcome limitations of photodegradation and toxicity. This progress report, therefore, presents various synthesis techniques for the generation of dye-doped fluorescent polymer particles. Polymer particles are relatively soft compared to inorganic nanoparticles and can be synthesized with characteristics like biocompatibility and stimuli responsiveness. Also, their ability of loading fluorophores through various interactions reveals brightness. Here, a multiscale-multicolor library of bright and soft fluorescent polymer particles is generated hierarchically. Various microfluidic supported strategies have been applied where fluorophores can be linked to polymeric networks noncovalently and covalently in the interior, and at the surface of nanoparticles (60-550 nm). Besides, microfluidic strategies for hydrophilic and hydrophobic fluorescent polymer microparticles (20-800 [my]m) have been performed for systematic tuning in size and color combination. Furthermore, soft and bright particulate assemblies are enabled through interfacial interactions at the intermediate scale (600 nm-3 [my]m) between the nanometer and micrometer lengthscale.