Low-Temperature Miniemulsion-Based Routes for Synthesis of Metal Oxides

Dedicated to Professor Gerhard Wegner on the occasion of his 80th anniversar

Triple-target stimuli-responsive anti-COVID-19 face mask with physiological virus-inactivating agents

Conventional face masks to prevent SARS-CoV-2 transmission are mostly based on a passive filtration principle. Ideally, anti-COVID-19 masks should protect the carrier not only by size exclusion of virus aerosol particles, but also be able to capture and destroy or inactivate the virus. Here we present the proof-of-concept of a filter mat for such a mask, which actively attracts aerosol droplets and kills the virus. The electrospun mats are made of polycaprolactone (PCL) a hydrophilic, functionalizable and biodegradable polyester, into which inorganic polyphosphate (polyP) a physiological biocompatible, biodegradable and antivirally active polymer (chain length, ∼40 P(i) units) has been integrated. A soluble Na-polyP as well as amorphous calcium polyP nanoparticles (Ca-polyP-NP) have been used. In this composition, the polyP component of the polyP-PCL mats is stable in aqueous protein-free environment, but capable of transforming into a gel-like coacervate upon contact with divalent cations and protein like mucin present in (virus containing) aerosol droplets. In addition, the Ca-polyP-NP are used as a carrier of tretinoin (all-trans retinoic acid) which blocks the function of the SARS-CoV-2 envelope (E) protein, an ion channel forming viroporin. The properties of this novel mask filter mats are as follows: First, to attract and to trap virus-like particles during the polyP coacervate formation induced in situ by aerosol droplets on the spun PCL fibers, as shown here by using SARS-CoV-2 mimicking fluorescent nanoparticles. Second, after disintegration the NP by the aerosol-mucus constituents, to release polyP that binds to and abolishes the function of the receptor binding domain of the viral spike protein. Third, to destroy the virus by releasing tretinoin, as shown by the disruption of virus-mimicking liposomes with the integrated recombinant viral viroporin. It is proposed that these properties, which are inducible (stimuli responsive), will allow the design of antiviral masks that are smart

Synthesis of (cinnamate-zinc layered hydroxide) intercalation compound for sunscreen application

Background: Zinc layered hydroxide (ZLH) intercalated with cinnamate, an anionic form of cinnamic acid (CA), an efficient UVA and UVB absorber, have been synthesized by direct method using zinc oxide (ZnO) and cinnamic acid as the precursor. Results: The resulting obtained intercalation compound, ZCA, showed a basal spacing of 23.9 Å as a result of cinnamate intercalated in a bilayer arrangement between the interlayer spaces of ZLH with estimated percentage loading of cinnamate of about 40.4 % w/w. The UV–vis absorption spectrum of the intercalation compound showed excellent UVA and UVB absorption ability. Retention of cinnamate in ZLH interlayers was tested against media usually came across with sunscreen usage to show low release over an extended period of time. MTT assay of the intercalation compound on human dermal fibroblast (HDF) cells showed cytotoxicity of ZCA to be concentration dependent and is overall less toxic than its precursor, ZnO. Conclusions: (Cinnamate-zinc layered hydroxide) intercalation compound is suitable to be used as a safe and effective sunscreen with long UV protection effect

Surface-functionalized latex particles as additives in the mineralization of zinc oxide

Polystyrene latex particles modified at the surface with different hydrophilic functional groups were prepared by miniemulsion polymerization and applied to control the crystallization of zinc oxide in aqueous medium. The effects of both latex structure and concentration on the crystal growth, morphology, crystalline structure, and properties of the resulting zinc oxide were analyzed. Depending on the latex additive used, micro- and submicrosized crystals with a broad variety of morphologies were obtained. Among the studied latexes, the carboxyl-derived particles were shown to be a convenient system for further quantitative investigations. In this case, as the additive concentration increases, the aspect ratio of the crystals decreases systematically. Latex particles are assumed to adsorb preferentially onto the fast growing {001} faces of ZnO, interacting with the growth centers and reducing the growth rate in [001]. When zinc oxide is precipitated in the presence of latex, the polymer particles become incorporated into the growing crystals and polymer–inorganic hybrid materials are obtained. These materials are composed of an inorganic and largely undisturbed crystalline matrix in which organic latex particles are embedded. Increasing amounts of latex become incorporated into the growing crystals at increasing overall concentration in the crystallizing system. Photoluminescence (PL) spectra were measured to obtain information on defect centers. Emission spectra of all samples showed a narrow UV peak and a broad band in the green-yellow spectral region. The former emission is attributed to exciton recombination, whereas the latter seems to be related with deep-level donors. Latex appears to be a quencher of the visible emission of zinc oxide. Thus, compared to pure zincite, ZnO–latex hybrid materials show a significantly lower PL intensity in the visible range of the spectrum. Under continuous photoexcitation, a noticeable dynamic behavior of the PL is observed, which can be related to a photodesorption of adsorbed oxygen. These surface-adsorbed oxygen species seem to play a crucial role for the optical properties of the materials and may mediate the tunneling of electrons from the conduction band to preexisting deep-level traps, probably related to intrinsic defects (oxygen vacancies or interstitial zinc). The polymer particles can block the sites where oxygen adsorbs, and the disappearance of the “electron-shuttle” species leads to the observed quenching of the visible emission. Electron paramagnetic resonance (EPR) provided additional information about crystal defects with unpaired electrons. Spectra of all samples exhibit a single signal at g ≈ 1.96, typical for shallow donors. Contrary to the results of other authors, no correlation was possible between the EPR signal and the visible range of PL spectra, which suggests that centers responsible for the visible emission and the EPR signal are different. -------------------------------------------------------------------------------- Inhaltszusammenfassung in einer weiteren Sprache (deutsch) Polystyrollatexteilchen, modifiziert an der Oberfläche mit unterschiedlichen hydrophilen Gruppen, wurden durch Miniemulsionspolymerisation hergestellt und zur Kontrolle der Zinkoxid-Kristallisation in wässrigem Medium verwendet. Effekte der Latexfunktionalisierung und -konzentration auf das Kristallwachstum, die Morphologie, die Struktur und die Eigenschaften des Zinkoxids wurden untersucht. Durch die Benutzung unterschiedlicher Latexadditive gewinnt man Kristalle im Mikron- und Submikron-Bereich mit einer breiten morphologischen Vielfalt. Latexteilchen, deren Oberfläche mit Carboxylgruppen funktionalisiert waren, eignet sich besonders gut für weitere quantitative Untersuchungen. In diesem Fall nimmt mit steigender Additivkonzentra¬tion das Aspektverhältnis der Kristallen ab. Es wird angenommen, dass Latexteilchen vorzugsweise an den schnell wachsenden {001}-Flächen des Zinkoxids adsorbieren, wobei sie mit den Wachstumszentren in Wechselwirkung stehen und die Wachstumsrate in [001] reduzieren. Wenn Zinkoxid in Gegenwart von Latex hergestellt wird, werden die Polymerpartikel in die wachsende Kristalle eingebaut und polymer–anorganische Hybridmaterialien dabei erhalten. Solche Materialien bestehen aus einer weitgehend ungestörten anorganischen Matrix, in der die organischen Latexteilchen eingebetet sind. Steigende Mengen von Latex werden eingebaut, wenn die Gesamtlatexkonzentration erhöht wird. Photolumineszenzspektren wurden gemessen, um Information über Defektzentren zu bekommen. Emissionsspektren aller Proben zeigten einen schmalen UV-Peak und ein breites Band im grün-gelbes Spektralbereich. Die ersterwähnte Emission wird der Exziton-Rekombination zugeschrieben, während die zweite mit tiefen Donatornieveaus zusammenzuhängen scheint. Latex zeigt sich als Löscher der sichtbaren Emission in Zinkoxid. Somit zeigen ZnO–Latex Hybride eine deutlich geringere Photolumineszenzintensität (im Vergleich mit reinem Zinkit) im sichtbaren Bereich des Spektrums. Unter kontinuierlicher Photoanregung wird ein erkennbares dynamisches Verhalten der Photolumineszenz beobachtet, das in Zusammenhang mit einer Photodesorption von adsorbiertem Sauerstoff stehen kann. Solche oberflächenadsorbierten Sauerstoffspezies scheinen eine Rolle in den optischen Eigenschaften der Materialien zu spielen. Sie können das Tunneln der Elektronen vom Leitungsband zu bereits bestehenden tiefen Störstellen vermitteln, die wahrscheinlich mit intrinsischen Defekten (Sauerstoff-Fehlstellen oder Zink in Zwischengitterplätze) in Verbindung stehen. Polymerteilchen können die Stellen, an denen Sauerstoffadsorption stattfindet, blockieren und damit zu der beobachteten Löschung der sichtbaren Emission beitragen. Elektronenparamagnetische Resonanz (EPR) ergab weitere Informationen über Kristalldefekte mit ungepaarten Elektronen. Spektren der Proben weisen ein einzelnes Signal bei g ≈ 1.96 auf, typisch für Donatoren nahe der Bandkante („shallow donors“). Im Gegensatz zu Ergebnissen anderer Autoren, korrelierten die EPR-Signale und die sichtbare Photolumineszenz nicht, was darauf hinweist, dass die verantwortlichen Zentren für die sichtbare Emission und die EPR-Signal unterschiedlichen Ursprungs sein müssen. -------------------------------------------------------------------------------

Ceria/polymer nanocontainers for high-performance encapsulation of fluorophores

We report the synthesis of high-performance organic–inorganic hybrid fluorescent nanocapsules comprising a polymer shell armored with an inorganic layer and a liquid core containing a fluorophore. The polymeric capsules are synthesized by free radical miniemulsion polymerization and contain covalently bound carboxylate surface functionalities that allow for the binding of metal ions through electrostatic interaction. A cerium(IV) oxide nanoparticle layer, formed in situ at the surface of the hybrid nanocapsules, acts as oxygen scavenger and keeps external reactive molecular oxygen from entering into the capsules, eventually resulting in a reduction of the photooxidation of encapsulated fluorescent molecules. This approach shows an increase in the fluorescence of the model organic fluorophore terrylene diimide by avoiding the ground-state molecular oxygen to react with electronically excited states of the fluorescent hydrocarbon molecule