@article{SchulzeKoetz2017, author = {Schulze, Nicole and Koetz, Joachim}, title = {Kinetically controlled growth of gold nanotriangles in a vesicular template phase by adding a strongly alternating polyampholyte}, series = {Journal of dispersion science and technology}, volume = {38}, journal = {Journal of dispersion science and technology}, number = {8}, publisher = {Taylor \& Francis}, address = {Philadelphia}, issn = {0193-2691}, doi = {10.1080/01932691.2016.1220318}, pages = {1073 -- 1078}, year = {2017}, abstract = {This paper is focused on the temperature-dependent synthesis of gold nanotriangles in a vesicular template phase, containing phosphatidylcholine and AOT, by adding the strongly alternating polyampholyte PalPhBisCarb. UV-vis absorption spectra in combination with TEM micrographs show that flat gold nanoplatelets are formed predominantly in the presence of the polyampholyte at 45°C. The formation of triangular and hexagonal nanoplatelets can be directly influenced by the kinetic approach, i.e., by varying the polyampholyte dosage rate at 45°C. Corresponding zeta potential measurements indicate that a temperature-dependent adsorption of the polyampholyte on the {111} faces will induce the symmetry breaking effect, which is responsible for the kinetically controlled hindered vertical and preferred lateral growth of the nanoplatelets.}, language = {en} } @article{IhlenburgMaiThuenemannetal.2021, author = {Ihlenburg, Ramona and Mai, Tobias and Th{\"u}nemann, Andreas F. and Baerenwald, Ruth and Saalw{\"a}chter, Kay and Koetz, Joachim and Taubert, Andreas}, title = {Sulfobetaine hydrogels with a complex multilength-scale hierarchical structure}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {125}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, number = {13}, publisher = {American Chemical Society}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.0c10601}, pages = {3398 -- 3408}, year = {2021}, abstract = {Hydrogels with a hierarchical structure were prepared from a new highly water-soluble crosslinker N,N,N',N'-tetramethyl-N,N'-bis(2-ethylmethacrylate)-propyl-1,3-diammonium dibromide and from the sulfobetaine monomer 2-(N-3-sulfopropyl-N,N-dimethyl ammonium)ethyl methacrylate. The free radical polymerization of the two compounds is rapid and yields near-transparent hydrogels with sizes up to 5 cm in diameter. Rheology shows a clear correlation between the monomer-to-crosslinker ratio and the storage and loss moduli of the hydrogels. Cryo-scanning electron microscopy, low-field nuclear magnetic resonance (NMR) spectroscopy, and small-angle X-ray scattering show that the gels have a hierarchical structure with features spanning the nanometer to the sub-millimeter scale. The NMR study is challenged by the marked inhomogeneity of the gels and the complex chemical structure of the sulfobetaine monomer. NMR spectroscopy shows how these complications can be addressed via a novel fitting approach that considers the mobility gradient along the side chain of methacrylate-based monomers.}, language = {en} } @article{GharabekyanKoetzPoghosyan2021, author = {Gharabekyan, Hrant H. and Koetz, Joachim and Poghosyan, Armen H.}, title = {A protonated L-cysteine adsorption on gold surface}, series = {Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects}, volume = {629}, journal = {Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0927-7757}, doi = {10.1016/j.colsurfa.2021.127452}, pages = {7}, year = {2021}, abstract = {The adsorption of protonated L-cysteine onto Au(111) surface was studied via molecular dynamics method. The detailed examination of trajectories reveals that a couple of picoseconds need to be strongly adsorbed at the gold surface via L-cysteine's sulfur and oxygen atoms. The average distances of L-cysteine's adsorbed sulfur and oxygen from gold plane are-2.7 angstrom and-3.2 angstrom, correspondingly. We found that the adsorption of L-cysteine takes place preferentially at bridge site with possibility of-82\%. Discussing the conformation features of protonated L-cysteine, we consider that the most stable conformation of protonated L-cysteine is "reverse boat" position, where sulfur and oxygen pointed down to the gold surface, while the amino group is far from the gold surface.}, language = {en} } @article{LiebigSarhanSchmittetal.2020, author = {Liebig, Ferenc and Sarhan, Radwan Mohamed and Schmitt, Clemens Nikolaus Zeno and Th{\"u}nemann, Andreas F. and Prietzel, Claudia Christina and Bargheer, Matias and Koetz, Joachim}, title = {Gold nanotriangles with crumble topping and their influence on catalysis and surface-enhanced raman spectroscopy}, series = {ChemPlusChem}, volume = {85}, journal = {ChemPlusChem}, number = {3}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {2192-6506}, doi = {10.1002/cplu.201900745}, pages = {519 -- 526}, year = {2020}, abstract = {By adding hyaluronic acid (HA) to dioctyl sodium sulfosuccinate (AOT)-stabilized gold nanotriangles (AuNTs) with an average thickness of 7.5 +/- 1 nm and an edge length of about 175 +/- 17 nm, the AOT bilayer is replaced by a polymeric HA-layer leading to biocompatible nanoplatelets. The subsequent reduction process of tetrachloroauric acid in the HA-shell surrounding the AuNTs leads to the formation of spherical gold nanoparticles on the platelet surface. With increasing tetrachloroauric acid concentration, the decoration with gold nanoparticles can be tuned. SAXS measurements reveal an increase of the platelet thickness up to around 14.5 nm, twice the initial value of bare AuNTs. HRTEM micrographs show welding phenomena between densely packed particles on the platelet surface, leading to a crumble formation while preserving the original crystal structure. Crumbles crystallized on top of the platelets enhance the Raman signal by a factor of around 20, and intensify the plasmon-driven dimerization of 4-nitrothiophenol (4-NTP) to 4,4 '-dimercaptoazobenzene in a yield of up to 50 \%. The resulting crumbled nanotriangles, with a biopolymer shell and the absorption maximum in the second window for in vivo imaging, are promising candidates for biomedical sensing.}, language = {en} } @article{FortesMartinThuenemannStockmannetal.2021, author = {Fortes Mart{\´i}n, Rebeca and Th{\"u}nemann, Andreas F. and Stockmann, J{\"o}rg M. and Radnik, J{\"o}rg and Koetz, Joachim}, title = {From nanoparticle heteroclusters to filament networks by self-assembly at the water-oil interface of reverse microemulsions}, series = {Langmuir : the ACS journal of surfaces and colloids / American Chemical Society}, volume = {37}, journal = {Langmuir : the ACS journal of surfaces and colloids / American Chemical Society}, number = {29}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.1c01348}, pages = {8876 -- 8885}, year = {2021}, abstract = {Surface self-assembly of spherical nanoparticles of sizes below 10 nm into hierarchical heterostructures is under arising development despite the inherent difficulties of obtaining complex ordering patterns on a larger scale. Due to template-mediated interactions between oil-dispersible superparamagnetic nanoparticles (MNPs) and polyethylenimine- stabilized gold nanoparticles (Au(PEI)NPs) at the water-oil interface of microemulsions, complex nanostructured films can be formed. Characterization of the reverse microemulsion phase by UV-vis absorption revealed the formation of heteroclusters from Winsor type II phases (WPII) using Aerosol-OT (AOT) as the surfactant. SAXS measurements verify the mechanism of initial nanoparticle clustering in defined dimensions. XPS suggested an influence of AOT at the MNP surface. Further, cryo-SEM and TEM visualization demonstrated the elongation of the reverse microemulsions into cylindrical, wormlike structures, which subsequently build up larger nanoparticle superstructure arrangements. Such WPII phases are thus proven to be a new form of soft template, mediating the self-assembly of different nanoparticles in hierarchical network-like filaments over a substrate during solvent evaporation.}, language = {en} } @article{HenningLiebigPrietzeletal.2020, author = {Henning, Ricky and Liebig, Ferenc and Prietzel, Claudia Christina and Klemke, Bastian and Koetz, Joachim}, title = {Gold nanotriangles with magnetite satellites}, series = {Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects}, volume = {600}, journal = {Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0927-7757}, doi = {10.1016/j.colsurfa.2020.124913}, pages = {7}, year = {2020}, abstract = {This work describes the synthesis of hybrid particles of gold nanotriangles (AuNTs) with magnetite nanoparticles (MNPs) by using 1-mercaptopropyl-3-trimethoxysilan (MPTMS) and L-cysteine as linker molecules. Due to the combination of superparamagnetic properties of MNPs with optical properties of the AuNTs, nanoplatelet-satellite hybrid nanostructures with combined features become available. By using MPTMS with silan groups as linker molecule a magnetic "cloud" with embedded AuNTs can be separated. In presence of L-cysteine as linker molecule at pH > pH(iso) a more unordered aggregate structure of MNPs is obtained due to the dimerization of the L-cysteine. At pH < pH(iso) water soluble positively charged AuNTs with satellite MNPs can be synthesized. The time-dependent loading with MNP satellites under release of the extinction and magnetization offer a hybrid material, which is of special relevance for biomedical applications and plasmonic catalysis.}, language = {en} } @article{RajuKoetz2022, author = {Raju, Rajarshi Roy and Koetz, Joachim}, title = {Pickering Janus emulsions stabilized with gold nanoparticles}, series = {Langmuir : the ACS journal of surfaces and colloids / American Chemical Society}, volume = {38}, journal = {Langmuir : the ACS journal of surfaces and colloids / American Chemical Society}, number = {1}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.1c02256}, pages = {147 -- 155}, year = {2022}, abstract = {We report a modified approach to the batch scale preparation of completely engulfed core-shell emulsions or partially engulfed Janus emulsions with colorful optical properties, containing water, olive oil, and silicone oil. The in situ reduction of gold chloride, forming gold nanoparticles (AuNPs) at the olive oil interface in the absence or presence of chitosan, leads to the formation of compartmentalized olive-silicone oil emulsion droplets in water. In the absence of additional reducing components, time-dependent morphological transformations from partial engulfment to complete engulfment were observed. Similar experiments in the presence of chitosan or presynthesized AuNPs show an opposite time-dependent trend of transformation of core-shell structures into partially engulfed ones. This behavior can be understood by a time-dependent rearrangement of the AuNPs at the interface and changes of the interfacial tension. The Pickering effect of AuNPs at oil-water and oil-oil interfaces brings not only color effects to individual microdroplets, which are of special relevance for the preparation of new optical elements, but also a surprising self-assembly of droplets.}, language = {en} } @article{FortesMartinPrietzelKoetz2021, author = {Fortes Mart{\´i}n, Rebeca and Prietzel, Claudia Christina and Koetz, Joachim}, title = {Template-mediated self-assembly of magnetite-gold nanoparticle superstructures at the water-oil interface of AOT reverse microemulsions}, series = {Journal of colloid and interface science}, volume = {581}, journal = {Journal of colloid and interface science}, number = {Part A}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0021-9797}, doi = {10.1016/j.jcis.2020.07.079}, pages = {44 -- 55}, year = {2021}, abstract = {Hypothesis: Bimetallic magnetite-gold nanostructures are interesting candidates to combine and enhance individual properties of each metal element in catalytic and analytical applications. Microemulsions have been employed in templated synthesis of nanoparticles, and their combination with different types of nanoparticles can further mediate interactions at the water-oil interface, providing new forms of hybrid nanostructures. Experiments: Reverse water-in-oil microemulsions of droplet sizes below 50 nm were prepared from ternary mixtures of Aerosol-OT (AOT) as surfactant, incorporating 4 nm sized superparamagnetic nanoparticles (MNPs) to the hexane-pentanol oil phase and 5 nmsized polyethyleneimine-stabilized gold nanoparticles (Au(PEI)-NPs) to the water phase. The resulting isotropic L-2 phase, Winsor phases and organized nanostructures were investigated using conductometry, calorimetry, UV-Vis spectroscopy, cryoSEM and HRTEM. Findings: Droplet-droplet interactions, morphology and surfactant film properties of AOT microemulsions could be modulated in different ways by the presence of the different nanoparticles from each liquid phase. Additionally, phase separation into Winsor phases allows the formation upon solvent evaporation of films with bimetallic heterostructures on the micrometer scale. This demonstrates a new way of nanoparticle templated assembly at liquid interfaces by assisted interactions between microemulsions and nanoparticles, as a promising strategy to obtain thin films of small, isotropic nanoparticles with hierarchical ordering.}, language = {en} } @article{BourgatTierschKoetzetal.2020, author = {Bourgat, Yannick and Tiersch, Brigitte and Koetz, Joachim and Menzel, Henning}, title = {Enzyme degradable polymersomes from chitosan-g-[poly-l-lysine-block-epsilon-caprolactone] copolymer}, series = {Macromolecular bioscience}, volume = {21}, journal = {Macromolecular bioscience}, number = {1}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1616-5187}, doi = {10.1002/mabi.202000259}, pages = {1 -- 9}, year = {2020}, abstract = {The scope of this study includes the synthesis of chitosan-g-[peptide-poly-epsilon-caprolactone] and its self-assembly into polymeric vesicles employing the solvent shift method. In this way, well-defined core-shell structures suitable for encapsulation of drugs are generated. The hydrophobic polycaprolactone side-chain and the hydrophilic chitosan backbone are linked via an enzyme-cleavable peptide. The synthetic route involves the functionalization of chitosan with maleimide groups and the preparation of polycaprolactone with alkyne end-groups. A peptide functionalized with a thiol group on one side and an azide group on the other side is prepared. Thiol-ene click-chemistry and azide-alkyne Huisgen cycloaddition are then used to link the chitosan and poly-epsilon-caprolactone chains, respectively, with this peptide. For a preliminary study, poly-l-lysin is a readily available and cleavable peptide that is introduced to investigate the feasibility of the system. The size and shape of the polymersomes are studied by dynamic light scattering and cryo-scanning electron microscopy. Furthermore, degradability is studied by incubating the polymersomes with two enzymes, trypsin and chitosanase. A dispersion of polymersomes is used to coat titanium plates and to further test the stability against enzymatic degradation.}, language = {en} } @article{vonKlitzingStehlPogrzebaetal.2017, author = {von Klitzing, Regine and Stehl, Dimitrij and Pogrzeba, Tobias and Schoma{\"a}cker, Reinhard and Minullina, Renata and Panchal, Abhishek and Konnova, Svetlana and Fakhrullin, Rawil and Koetz, Joachim and Moehwald, Helmuth and Lvov, Yuri}, title = {Halloysites Stabilized Emulsions for Hydroformylation of Long Chain Olefins}, series = {Advanced materials interfaces}, volume = {4}, journal = {Advanced materials interfaces}, number = {1}, publisher = {Wiley}, address = {Hoboken}, issn = {2196-7350}, doi = {10.1002/admi.201600435}, pages = {8}, year = {2017}, abstract = {Halloysites as tubular alumosilicates are introduced as inexpensive natural nanoparticles to form and stabilize oil-water emulsions. This stabilized emulsion is shown to enable efficient interfacial catalytic reactions. Yield, selectivity, and product separation can be tremendously enhanced, e.g., for the hydroformylation reaction of dodecene to tridecanal. In perspective, this type of formulation may be used for oil spill dispersions. The key elements of the described formulations are clay nanotubes (halloysites) which are highly anisometric, can be filled by helper molecules, and are abundantly available in thousands of tons, making this technology scalable for industrial applications.}, language = {en} }