Tailored silica coated Ag nanoparticles for non-invasive surface enhanced Raman spectroscopy of biomolecular targets

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Silica coated Ag nanoparticles with defined surface plasmon resonances are used to selectively detect and analyze protein cofactors in solution and on interfaces via surface enhanced resonance Raman spectroscopy. The silica coating has a surprisingly small effect on optical amplification but minimizes unwanted interactions between the protein and the nanoparticle.DFG, EXC 314, Unifying Concepts in Catalysi

Functionalized Ag nanoparticles with tunable optical properties for selective protein analysis

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.We present a preparation procedure for small sized biocompatibly coated Ag nanoparticles with tunable surface plasmon resonances. The conditions were optimised with respect to the resonance Raman signal enhancement of heme proteins and to the preservation of the native protein structure.DFG, EXC 314, Unifying Concepts in Catalysi

A High-Rate Two-Dimensional Polyarylimide Covalent Organic Framework Anode for Aqueous Zn-Ion Energy Storage Devices

Rechargeable aqueous Zn-ion energy storage devices are promising candidates for next-generation energy storage technologies. However, the lack of highly reversible Zn2+-storage anode materials with low potential windows remains a primary concern. Here, we report a two-dimensional polyarylimide covalent organic framework (PI-COF) anode with high-kinetics Zn2+-storage capability. The well-organized pore channels of PI-COF allow the high accessibility of the build-in redox-active carbonyl groups and efficient ion diffusion with a low energy barrier. The constructed PI-COF anode exhibits a specific capacity (332 C g–1 or 92 mAh g–1 at 0.7 A g–1), a high rate capability (79.8% at 7 A g–1), and a long cycle life (85% over 4000 cycles). In situ Raman investigation and first-principle calculations clarify the two-step Zn2+-storage mechanism, in which imide carbonyl groups reversibly form negatively charged enolates. Dendrite-free full Zn-ion devices are fabricated by coupling PI-COF anodes with MnO2 cathodes, delivering excellent energy densities (23.9 ∼ 66.5 Wh kg–1) and supercapacitor-level power densities (133 ∼ 4782 W kg–1). This study demonstrates the feasibility of covalent organic framework as Zn2+-storage anodes and shows a promising prospect for constructing reliable aqueous energy storage devices

Thiophene-Based Conjugated Acetylenic Polymers with Dual Active Sites for Efficient Co-Catalyst-Free Photoelectrochemical Water Reduction in Alkaline Medium

Although being attractive materials for photoelectrochemical hydrogen evolution reaction (PEC HER) under neutral or acidic conditions, conjugated polymers still show poor PEC HER performance in alkaline medium due to the lack of water dissociation sites. Herein, we demonstrate that tailoring the polymer skeleton from poly(diethynylthieno[3,2-b]thiophene) (pDET) to poly(2,6-diethynylbenzo[1,2-b:4,5-b′]dithiophene (pBDT) and poly(diethynyldithieno[3,2-b:2′,3′-d]thiophene) (pDTT) in conjugated acetylenic polymers (CAPs) introduces highly efficient active sites for water dissociation. As a result, pDTT and pBDT, grown on Cu substrate, demonstrate benchmark photocurrent densities of 170 μA cm−2 and 120 μA cm−2 (at 0.3 V vs. RHE; pH 13), which are 4.2 and 3 times higher than that of pDET, respectively. Moreover, by combining DFT calculations and electrochemical operando resonance Raman spectroscopy, we propose that the electron-enriched Cβ of the outer thiophene rings of pDTT are the water dissociation active sites, while the −C≡C− bonds function as the active sites for hydrogen evolution. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH Gmb

Thiophen-basierte konjugierte acetylenische Polymere mit dualen aktiven Zentren für effiziente Cokatalysator-freie photoelektrochemische Wasserreduktion im alkalischen Medium

AbstractKonjugierte Polymere sind attraktive Materialien für die photoelektrochemische Wasserstoffentwicklungsreaktion (PEC‐HER) unter neutralen oder sauren Bedingungen. Jedoch zeigen sie im alkalischen Medium immer noch eine geringe PEC‐HER‐Leistung aufgrund des Fehlens von Wasserdissoziations‐Zentren. Hier zeigen wir, dass durch Anpassung des konjugierten acetylenischen Polymers (CAPs) von Poly(diethinylthieno[3,2‐b]thiophen) (pDET) zu Poly(2,6‐diethinylbenzo[1,2‐b:4,5‐b′]dithiophen (pBDT) und Poly(diethinyldithieno[3,2‐b:2′,3′‐d]thiophen) (pDTT) hocheffiziente aktive Wasserdissoziations‐Zentren in CAPs eingeführt werden können. Infolgedessen zeigen auf Cu‐Substrat gewachsene pDTT und pBDT Benchmark‐Photostromdichten von 170 μA cm−2 und 120 μA cm−2 (bei 0,3 V vs. RHE; pH 13), die 4,2‐ bzw. 3‐mal höher sind als die von pDET. DFT‐Rechnungen und elektrochemische Operando‐Resonanz‐Raman‐Spektroskopie zeigen, dass die elektronenangereicherten Cβ der äußeren Thiophenringe von pDTT die aktiven Zentren für die Wasserdissoziation sind, während die ‐C≡C‐Bindungen als aktive Zentren für die Wasserstoffentwicklung fungieren

Safety and efficacy of fluoxetine on functional outcome after acute stroke (AFFINITY): a randomised, double-blind, placebo-controlled trial

Background Trials of fluoxetine for recovery after stroke report conflicting results. The Assessment oF FluoxetINe In sTroke recoverY (AFFINITY) trial aimed to show if daily oral fluoxetine for 6 months after stroke improves functional outcome in an ethnically diverse population. Methods AFFINITY was a randomised, parallel-group, double-blind, placebo-controlled trial done in 43 hospital stroke units in Australia (n=29), New Zealand (four), and Vietnam (ten). Eligible patients were adults (aged ≥18 years) with a clinical diagnosis of acute stroke in the previous 2–15 days, brain imaging consistent with ischaemic or haemorrhagic stroke, and a persisting neurological deficit that produced a modified Rankin Scale (mRS) score of 1 or more. Patients were randomly assigned 1:1 via a web-based system using a minimisation algorithm to once daily, oral fluoxetine 20 mg capsules or matching placebo for 6 months. Patients, carers, investigators, and outcome assessors were masked to the treatment allocation. The primary outcome was functional status, measured by the mRS, at 6 months. The primary analysis was an ordinal logistic regression of the mRS at 6 months, adjusted for minimisation variables. Primary and safety analyses were done according to the patient's treatment allocation. The trial is registered with the Australian New Zealand Clinical Trials Registry, ACTRN12611000774921. Findings Between Jan 11, 2013, and June 30, 2019, 1280 patients were recruited in Australia (n=532), New Zealand (n=42), and Vietnam (n=706), of whom 642 were randomly assigned to fluoxetine and 638 were randomly assigned to placebo. Mean duration of trial treatment was 167 days (SD 48·1). At 6 months, mRS data were available in 624 (97%) patients in the fluoxetine group and 632 (99%) in the placebo group. The distribution of mRS categories was similar in the fluoxetine and placebo groups (adjusted common odds ratio 0·94, 95% CI 0·76–1·15; p=0·53). Compared with patients in the placebo group, patients in the fluoxetine group had more falls (20 [3%] vs seven [1%]; p=0·018), bone fractures (19 [3%] vs six [1%]; p=0·014), and epileptic seizures (ten [2%] vs two [<1%]; p=0·038) at 6 months. Interpretation Oral fluoxetine 20 mg daily for 6 months after acute stroke did not improve functional outcome and increased the risk of falls, bone fractures, and epileptic seizures. These results do not support the use of fluoxetine to improve functional outcome after stroke

Anwendung von oberflächenverstärkter Raman-Spektroskopie in biologischen Systemen

In dieser Arbeit wurden die Resonanz-Raman-Spektroskopie (RR-Spektroskopie) sowie die oberflächenverstärkte Resonanz-Raman-Spektroskopie (SERR-Spektroskopie) verwendet, um biologische Systeme, insbesondere Hämproteine, zu untersuchen. Der elektronische Übergang der Hämgruppe kann ausgenutzt werden, um über gezielte Lichtanregung ausschließlich stark verstärkte Raman-Streusignale des Kofaktors zu erhalten. Adsorbiert an aufgerauten Silberelektroden kommt der Oberflächenverstärkungseffekt zum Tragen, der es ermöglicht, Proteine selbst bei Submonolagen-Beschichtung zu untersuchen. Darüber hinaus ermöglicht die Elektrode die Ansteuerung von Oberflächenredoxreaktionen, was ausgenutzt werden kann, um Informationen über die Redox-Eigenschaften und Dynamik von Hämproteinen zu erhalten. Dieser experimentelle Ansatz wurde verwendet, um die Elektronentransferkinetik des Proteins Cytochrom c - ein kleines, redox-aktives Hämprotein in der mitochondrialen Atmungskette – zu untersuchen. Cytochrom c wurde dafür auf einer rauen Silberelektrode, beschichtet mit einer biomimetischen Monoschicht aus carboxyl-terminierten Alkanthiolen, immobilisiert und mit stationärer und zeitaufgelöster SERR-Spektroskopie untersucht. Besonderes Augenmerk wurde auf die Elektronentransfereigenschaften des Proteins bei kleinen Abständen zur Elektrode gelegt. Die Ergebnisse der Untersuchungen geben neue Aufschlüsse über den heterogenen Elektronentransfer und deuten dabei auf eine besondere Rolle des elektrischen Feldes an Grenzflächen hin. Dieses beeinflusst die Oberflächenorientierungsdynamik, die Elektronentunnel-Wahrscheinlichkeit und die Umstrukturierung der Wasserstoffbrückennetzwerke des Protein und an der Grenzfläche. Neben der Rolle als Elektronenüberträger in der Atmungskette fungiert Cytochrom c ebenso als Signalprotein in der Apoptose, dem programmierten Zelltod. Dafür muss es die mitochondriale Membran, an die es normalerweise gebunden ist, verlassen und ins Zellplasma übergehen. Die Ursache für diese Migration ist noch weitestgehend ungeklärt. Als ein Faktor, der den damit verbundenen Verlust an Redox- und die Zunahme an Peroxidase-Aktivität erklärt, wird die post-translationale Nitrierung von Tyrosinresten des Proteins diskutiert. Folglich wurde mittels RR-Spektroskopie der Einfluss von post-translationaler Tyrosin-Nitrierung auf die Integrität der Hämtasche untersucht. Es zeigte sich, dass die Destabilisierungen, hervorgerufen durch die Nitrierung verschiedener Tyrosinreste, nicht mit der jeweiligen gesteigerten Peroxidase-Aktivität korrelieren. Experimente, bei denen die verschiedenen Tyrosin-Mutanten auf eine Elektrode adsorbiert wurden, zeigten außerdem, dass die Grenzflächen bedingte Destabilisierung der Hämtasche unabhängig von der Nitrierung wirkt. Des Weiteren wurde die Anwendbarkeit der zeitaufgelösten SERR-Spektroskopie zur kinetischen Untersuchung von Biofilmen des Bakteriums Geobacter Sulfurreducens demonstriert. Dies ist möglich, da das Bakterium eine Reihe von Multihämproteinen, sogenannten "outer membrane cytochromes" (Omcs), besitzt, die für den extrazellulären Elektronentransfer verantwortlich sind. Besonders stark sind diese Cytochrome an der Grenzfläche zwischen Biofilm und Elektrode akkumuliert. Durch Anwendung von stationärer und zeitaufgelöster SERR-Spektroskopie konnte die besondere Rolle der Omcs als "Elektronenschleuse" zwischen Biofilm und Elektrode nachgewiesen und eine gemittelte heterogene Elektronentransferratenkonstante bestimmt werden. Weiter deuten die Experimente zusammen mit kinetischen Simulationen darauf hin, dass der heterogene Elektronentransfer der geschwindigkeitsbestimmende Schritt beim Elektronenaustausch Biofilm-Elektrode ist. Der letzte Teil der Arbeit ist der methodischen Entwicklung der oberflächenverstärkten Raman-Spektroskopie zur Ausdehnung auf Nicht-Münzmetalle gewidmet. Dazu wurde eine Pt-Ag-Hybrid-Elektrode konstruiert, die aus einem nanoskopisch rauen Silberuntergrund, welcher zuerst mit einem dielektrischen Material beschichtet und anschließend mit einem Platinfilm überzogen wurde. Während der abgeschottete Silberuntergrund für die notwendige Oberflächenverstärkung sorgt, laufen an der Pt-Oberfläche die zu untersuchenden Grenzflächenreaktionen ab. Die Hybrid-Elektrode wurde in Bezug auf ihre Stabilität und ihre Signalverstärkungseigenschaften bei verschiedenen Wellenlängen untersucht. Die Resultate zeigen, dass starke Raman-Signale von Probenmolekülen, adsorbiert auf der äußeren Pt-Schicht, erhalten werden können. Die Signale sind nur geringfügig schwächer im Vergleich zu einer direkten Adsorption auf Ag.In this thesis, resonance Raman (RR) and surface enhanced resonance Raman (SERR) spectroscopy were applied to investigate biological systems, articularly heme containing proteins. The electronic transition of the heme group can be exploited so that, with a properly tuned light excitation, highly intense Raman signals solely of the cofactor are obtained. If the proteins are adsorbed on a rough silver surface, then the resonance effect can be combined with the surface enhancement effect to yield a highly sensitive technique that allows probing of molecules even at sub-monolayer coverage. Additionally, if the surface is constituted by an electrode, surface redox reactions and kinetics of adsorbed molecules can be investigated. Such a setup was used to study the electron transfer (ET) properties of cytochrome c (cytc), a small soluble redox protein that acts as an electron shuttle in the respiratory chain. Cytc was immobilized on a rough silver electrode coated with a biomimetic monolayer of w-carboxylated alkanethiols and investigated by stationary and time resolved SERR spectroscopy. Specifically, the ET kinetics of the protein at short distances to the electrode was monitored. The results provide new insights into the heterogeneous protein ET and indicate a central role of the interfacial electric field, which has influence on the protein orientational dynamics as well as on the electronic coupling and the rearrangement of hydrogen bond networks at the protein-monolayer interface. Beside its function in bioenergetics, cytc also plays a key role as a signal transducer in the apoptosis, the programmed cell death. To exert this function, it has to be detached from the inner mitochondrial membrane, where it is bound to under normal conditions and released to the cytosol. The factors that control the transfer of cytc are still under debate. In this respect, a possible influence of posttranslational Tyr nitration to switch cytc’s function from ET to peroxidation, which is considered to be the first step in initiating apoptosis, is discussed. Therefore, mono-tyrosine and nitrated mono-tyrosine mutants were investigated using RR spectroscopy in order to evaluate the impact of tyrosine nitration on the integrity of the heme pocket. It could be shown that the destabilization caused by nitration is not directly correlated with the respective peroxidase activity of the mutant. Moreover, experiments in which the mutants were immobilized on a monolayer coated electrode showed that the destabilization, promoted by the interfacial electric field, did not depend on the nitration. Furthermore, the applicability of time resolved SERR spectroscopy for kinetic investigations of biofilms of the bacterium Geobacter Sulfurreducens, grown on rough silver electrodes, was demonstrated. The bacterium possesses a large number of multi-heme proteins, so-called outer membrane cytochromes (Omcs), which facilitate the extracellular ET. These cytochromes are accumulated at the biofilm-electrode interface and therefore can be probed using SERR spectroscopy. By applying stationary and time resolved SERR spectroscopy, it could be shown that these cytochromes function as electron ’gates’ between the biofilm and the electrode, and an average heterogeneous ET rate constant could be determined. Finally, results obtained from kinetic simulations indicate that the interfacial ET is the bottleneck of the biofilm-electrode ET process. The last part of the thesis is dedicated to methodological developments to expand the applicability of surface enhanced Raman (SER) spectroscopy to non-coinage metals. Here, a Pt-Ag device was fabricated, using a nanostructured Ag support that was coated by a dielectric layer and subsequently covered by a Pt island film. The idea is that the isolated underlying Ag support should provide the necessary surface enhancement, while the top metal layer promotes the interfacial reactions to be studied. The fabricated hybrid device was tested in terms of stability and SER performance

Direct Observation of the Gating Step in Protein Electron Transfer: Electric-Field-Controlled Protein Dynamics

Heterogeneous electron transfer of proteins at biomimetic interfaces is characterized by unusual distance dependences of the electron-transfer rates, whose origin has been elusive and controversial. Using a two-color, time-resolved, surface-enhanced resonance Raman spectroelectrochemical approach, we have been able to monitor simultaneously and in real time the structure, electron-transfer kinetics, and configurational fluctuations of cytochrome c electrostatically adsorbed to electrodes coated with selfassembled monolayers. Our results show that the overall electron-transfer kinetics is determined by protein dynamics rather than by tunnelling probabilities and that the protein dynamics in turn is controlled by the interfacial electric field. Implications for interprotein electron transfer at biological membranes are discussed.Fil: Kranich, Anja. Technische Universitat Berlin; AlemaniaFil: Ly, Hoang Khoa. Technische Universitat Berlin; AlemaniaFil: Hildebrandt, Peter. Technische Universitat Berlin; AlemaniaFil: Murgida, Daniel Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentin

Proton activation in the presence of a weak acid facilitated via second coordination effects in iron porphyrins

The catalytic activity of two iron-based porphyrin complexes containing pyridine-functionalized second coordination spheres, referred to as Py2XPFe and CuPy2XPFe have been investigated for the hydrogen evolution reaction (HER) and compared with the unsubstituted analog TMPFe in MeCN. The CuPy2XPFe incorporates a second metal center within the pyridine residues and represents a heterodinuclear system, while the structurally analogous Py2XPFe lacks an additional metal in the second coordination sphere. Both the Py2XFe and CuPy2XPFe complexes are observed to activate the weak acid, acetic acid (AcOH) at the FeII/I couple rather than at the more energy intensive FeI/0 couple observed for the TMPFe species at low acid concentrations. The ability of the monometallic Py2XPFe complex to activate the weak proton source at the FeII/I couple manifests as an ECEC(E) type electrochemical mechanism, rather than an EECC(E) type mechanism as observed for the unsubstituted TMPFe. The CuPy2XPFe displays improved reactivity compared with the Py2XPFe and TMPFe under the same substrate conditions; however the mechanistic nuances into the bimetallic CuPy2XPFe system are currently unclear. The concentration of AcOH was incrementally increased and the rate constants of the initial protonation step i.e. formation of a hydridic species (k1,app), as well as of the protonation of the hydric species to produce dihydrogen (k2,app) were calculated using the Foot-of-the-wave and KS zone rate equation methodologies, respectively. The kinetic analysis indicates that the activation of protons through the ECEC(E) type mechanism results in a system in which k1,app < k2,app. As both the monometallic Py2XPFe and bimetallic CuPy2XPFe activate the AcOH at less cathodic potentials than the TMPFe under identical conditions, the overpotential (TOF/2) for these complexes is thus dramatically lower. The reactivity difference of the Py2XPFe when compared to the TMPFe due to the hanging groups influence is postulated to be either a result of the pyridine residues acting as hydrogen bonding promoters to the active site or aiding to stabilize a catalytic intermediate species during catalysis. Interestingly, a mechanistic change for the TMPFe is also observed at higher AcOH concentrations, underlying perhaps an increased HER reactivity of iron-porphyrins in MeCN