Wie Nanopartikel interne Struktur von Flüssigkeiten umordnen

Fast unbemerkt sind sie Teil unseres täglichen Lebens geworden: Nanopartikel führen in Kosmetika, Nahrungsmitteln und Medikamenten, aber auch in Katalysatoren zu besonderen Eigenschaften der Produkte. In den meisten Anwendungsgebieten werden die Nanopartikel in Flüssigkeiten aufgelöst, denn viele ihrer Eigenschaften entstehen an den Grenzflächen. Bisher konnten Wissenschaftler jedoch nur theoretisch modellieren, ob und wie sich die interne Struktur einer Flüssigkeit an der Oberfläche eines Nanopartikels verändert. Physikern der Universität Erlangen-Nürnberg ist nun erstmals der experimentelle Nachweis gelungen. Ihre Ergebnisse haben sie in dem Wissenschaftsjournal veröffentlicht ("Universal solvent restructuring induced by colloidal nanoparticles"). >Mirijam Zobel und Reinhard Neder während eines Experiments Mirijam Zobel und Prof. Dr. Reinhard Neder während des Experiments an der European Synchroton Research Facility in Grenoble. Flüssigkeiten wie Wasser oder Alkohole besitzen eine interne Struktur: Sauerstoffelemente wechselwirken mit Wasserstoffatomen, wodurch sich Strukturen wie beispielsweise Ringmotive oder Ketten innerhalb der Flüssigkeit bilden. Diese Struktur bricht in der Nähe von glatten Oberflächen – wie beispielsweise Gefäßwänden – auf. Für Nanopartikel sagten Wissenschaftler eine ähnliche Verhaltensweise voraus, es fehlte bisher jedoch der experimentelle Nachweis. Den haben nun die FAU-Wissenschaftler Prof. Dr. Reinhard Neder und Mirijam Zobel von der Professur für Allgemeine Mineralogie/Kristallographie geliefert. Für den Nachweis benutzen die FAU-Wissenschaftler die Pair Distribution Function (PDF; deutsch: Paarverteilungsfunktion). Da weltweit nur wenige Geräte die präzisen PDF-Messungen erlauben, reisten die FAU-Wissenschaftler zur European Synchroton Radiation Facility ins französische Grenoble. Dort bestrahlten die Wissenschaftler die Proben – eine Vielzahl selbst hergestellter und käuflich erworbener Nanopartikel wie beispielsweise Zinkoxid oder Silber aufgelöst in verschiedenen Lösungsmitteln – mit hochenergetischen Röntgenstrahlen. Die Strahlen erzeugten ein Röntgenbild sobald sie auf die Elektronen des Nanopartikels und des Lösungsmittels treffen. Mithilfe dieser Aufnahme berechneten die Wissenschaftler, wie weit die einzelnen Atome voneinander entfernt sind – und wiesen so nach, dass sich die Moleküle an der Grenzfläche von Nanopartikel und Flüssigkeit neu ordnen. Diese Umordnung ist direkt an der Grenzfläche am stärksten und erstreckt sich über etwa fünf Molekülschichten, bis weiter von der Grenzfläche entfernt wieder die Eigenschaften der reinen Flüssigkeiten angenommen werden. "Wir erwarten, dass unsere allgemeingültigen Ergebnisse die Modellierung von chemischen Reaktionen an Oberflächen maßgeblich beeinflussen," erklärt Mirijam Zobel.
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Nanotechnology for clean drinking water

One way of removing harmful nitrate from drinking water is to catalyse its conversion to nitrogen. This process suffers from the drawback that it often produces ammonia. By using palladium nanoparticles as a catalyst, and by carefully controlling their size, this drawback can be partially eliminated. It was research conducted by Yingnan Zhao of the University of Twente’s MESA+ Institute for Nanotechnology that led to this discovery. nanoparticle catalyst for nitrate removal Nanoparticle catalyst for nitrate removal. Due to the excessive use of fertilizers, our groundwater is contaminated with nitrates, which pose a problem if they enter the mains water supply. Levels have fallen significantly in recent years, as a result of various European directives. In addition, the Integrated Approach to Nitrogen programme was launched in various Dutch nature reserves at the start of January. Tackling the problem at source is one thing, but it will still be necessary to treat the mains water supply. While this can be achieved through biological conversion (using bacteria to convert the nitrate to nitrogen gas), this is a slow process. Using palladium to catalyse the conversion of nitrate to nitrogen speeds up the process enormously. However, this reaction suffers from the drawback that it produces a harmful by-product – ammonia. Exposed surface The amount of ammonia produced appears to depend on the method used to prepare the palladium and on the catalyst’s physical structure. Yingnan Zhao decided to use nanometre-sized colloidal palladium particles, as their dimensions can be easily controlled. These particles are fixed to a surface, so they do not end up in the mains water supply. However, it is important to stop them clumping together, so stabilizers such as polyvinyl alcohol are added. Unfortunately, these stabilizers tend to shield the surface of the palladium particles, which reduces their effectiveness as a catalyst. By introducing additional treatments, Yingnan Zhao has managed to fully expose the catalytic surface once again or to manipulate it in a controlled manner. This has resulted in palladium nanoparticles that can catalyse the conversion to nitrogen, while producing very little ammonia. This has brought the further development of catalytic water treatment (in compact devices for home use, for example) one step closer. Yingnan Zhao, who is from Heze, Shandong, China, conducted his research in Prof. Leon Lefferts’ Catalytic Processes and Materials group. He defended his thesis, which is entitled “Colloidal Nanoparticles as Catalysts and Catalyst Precursors for Nitrite Hydrogenation” on Thursday 15 January.
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New triggered-release nanoparticle mechanism could improve drug delivery

More efficient medical treatments could be developed thanks to a new method for triggering the rearrangement of chemical particles. The new method, developed at the University of Warwick, uses two ‘parent’ nanoparticles that are designed to interact only when in proximity to each other and trigger the release of drug molecules contained within both. The release of the drug molecules from the ‘parent’ nanoparticles could subsequently form a third ‘daughter’ particle, which comprises molecules from both ‘parent’ nanoparticles. TEM image of cylindrical micelles TEM image of cylindrical micelles. Scale bars = 500nm The researchers, led by Professors Andrew Dove and Rachel O’Reilly, suggest that this new mechanism could potentially limit side-effects by only releasing the drug where required: “We conceive that in the blood stream the particles would not be able to interact sufficiently to lead to release, only when they are taken into cells would the release be able to happen”, says Professor Dove. “In this way, the drug can be targeted to only release where we want it to and therefore be more effective and reduce side effects”. The chemical composition of the two ‘parent’ nanoparticles is crucial to the new method. Professor Dove explains: “The two ‘parent’ nanoparticles used in the new mechanism are cylindrical in shape and are made from polymer chains that differ only by the way in which chemical bonds are directed within a part of the structure. “When the two ‘parent’ nanoparticles are in close enough proximity the polymer chains are driven to come together to form a new ‘daughter’ nanoparticle by a phenomenon known as stereocomplexation. “In the process of this rearrangement, we propose that any molecules, such as drug molecules, that are encapsulated within the parent particles will be released.” Published in journal the research, "Structural reorganisation of cylindrical nanoparticles triggered by polylactide stereocomplexation", could “raise new possibilities in how we can administer medical treatments”, says Professor Dove. “We’re planning to study this as a new treatment for cancer but the principle could potentially be applied to a wide range of diseases.”
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