Gold(II) Porphyrins as Key Intermediates in Novel Artificial Photosynthetic Systems

Over the past years, a promising approach to illuminate the first steps of photosynthesis was achieved by the design and preparation of artificial photosynthetic RCs, composed of donor-acceptor model compounds, mimicking the energy conversion process. In this context, this work aims to elucidate the role of gold(III) porphyrins as a potent cationic electron acceptor in such artificial photosynthetic systems. Particularly, the site of gold(III) porphyrin reduction is discussed controversially in the literature, since it could be ligand centred or metal centred. The approach chosen here was the preparation and characterisation of a meso-tetraarylporphyrinato gold(III) cation reference system, bearing functional groups at the aryl substituents with variable electron-donating and electron-withdrawing behaviour (COOMe, COOH, NO2, NH2, NHAc, H, OnBu, CF3) to examine their influence on the site of gold(III) porphyrin reduction. The obtained gold(III) porphyrins were treated with the reducing agent cobaltocene and probed by electron paramagnetic resonance (EPR) spectroscopy to determine the preferred location of the spin density (AuII: 5d9 metallo radical; (P●−): organic -radical anion). Gratifyingly, the chemical one-electron reduction of the gold(III) porphyrins yielded the corresponding gold(II) porphyrin complexes with a characteristic EPR pattern revealing hyperfine coupling to 197Au and 14N and is therefore clearly preferred over the porphyrin pi-radical anion. Encouraged by the unexpected high stability of the aforementioned gold(II) porphyrin complexes and to further investigate this usually elusive species, a mononuclear gold(II) porphyrin was successfully synthesized. This has been achieved via chemical reduction of a gold(III) porphyrin with stoichiometric amounts of KC8 or cobaltocene and by an excess of 1-benzyl-1,4-dihydronicotinamide (BNAH) in the presence of a base. The latter was employed as an NADH model compound to illustrate the potential mode-of-action of gold(III) porphyrins inside tumor cells, since they are used as potent anti-cancer drugs. Furthermore, it was possible to isolate and purify this mononuclear gold(II) complex by means of recrystallization or sublimation. This enabled the first thorough investigation of a thermodynamically stable mononuclear gold(II) species by using a combination of spectroscopic and theoretical methods. Further, the knowledge obtained from the aforementioned studies has been exploited for the synthesis and examination of three novel amide-bridged donor-acceptor dyads designed to undergo ultrafast PET. For this purpose, zinc(II) porphyrin amino acid derivatives were utilised as chromophores and electron donors and gold(III) porphyrin amino acid derivatives as electron acceptors [Zn(P)-AuIII(P)][PF6]. The individual building blocks were equipped with electron-donating and electron-withdrawing meso-aryl groups (4-C6H4OnBu, 4-C6H4CF3) with the intent to influence the driving force of the forward PET and the backward electron transfer (BET). The PET processes were successfully investigated via time-resolved spectroscopic techniques and they revealed a charge-shifted (CSh) state [Zn(P● )-AuII(P)] featuring a gold(II) core for all the dyads. Since the transferred electron is located in a sigma-type orbital of gold (5dx2-y2) relative to the porphyrine plane, the direct back-electron transfer to the a2u SOMO of the zinc(II) porphyrin is hindered, resulting in a relatively long lifetime of the CSh state. As a consequence, the CSh states have been successfully exploited for bimolecular reactions with amines as sacrificial electron donors yielding a stable gold(II) species Zn(P)-AuII(P) as confirmed by using a combination of spectroscopic and theoretical methods. Furthermore, this stable gold(II) species was competent to reduce aromatic azides to amines during a photoredox experiment, whereby the initial gold(III) dyad was restored and thus a catalytic cycle was closed.Ein vielversprechender Ansatz zur Aufklärung der ersten Schritte des photosynthetischen Prozesses wurde in den vergangenen Jahren mit Hilfe von künstlichen RCs ermöglicht. Diese bestehen aus Donor-Akzeptor-Modellverbindungen und können den Energieumwandlungsprozess nachahmen. In diesem Zusammenhang soll in dieser Arbeit die Rolle von Gold(III)-Porphyrinen als potenter kationischer Elektronenakzeptor in solchen künstlichen Photosynthese-Systemen untersucht werden. Insbesondere wird der Charakter der Gold(III)-Porphyrin-Reduktion in der Fachliteratur bisher kontrovers diskutiert, da diese liganden- oder metallzentriert ablaufen kann. Der hier gewählte Ansatz basiert auf der Darstellung und Charakterisierung eines meso-Tetraarylporphyrinato-Gold(III)-Kation Bezugssystems. Dieses besitzt funktionelle Gruppen mit unterschiedlichen elektronenziehenden und -schiebenden Eigenschaften an den Aryl-Substituenten (COOMe, COOH, NO2, NH2, NHAc, H, OnBu, CF3), um deren Einfluss auf den Ort der Gold(III)-Porphyrin Reduktion untersuchen zu können. Die so erhaltenen Gold(III)-Porphyrine wurden mit dem Reduktionsmittel Cobaltocen versetzt und mittels elektronenparamagnetischer Resonanzspektroskopie (EPR) untersucht, um die bevorzugte Lage der Spindichte zu bestimmen (AuII: 5d9-Metallradikal; (P●−): organisches pi-Radikalanion). Erfreulicherweise ergab die chemische Einelektronen-Reduktion der Gold(III)-Porphyrine die entsprechenden Gold(II)-Porphyrin-Komplexe mit einem charakteristischen EPR-Muster, sowie Hyperfeinkopplungen zu 197Au und 14N und ist somit gegenüber einem Porphyrin--Radikalanion klar bevorzugt. Ermutigt durch die unerwartet hohe Stabilität der zuvor genannten Gold(II)-Porphyrin-Komplexe, und zur weiteren Untersuchung dieser normalerweise schwer fassbaren Spezies, wurde ein mononuklearer Gold(II)-Porphyrin Komplex synthetisiert. Dies gelang mittels chemischer Reduktion eines Gold(III)-Porphyrins mit stöchiometrischen Mengen an KC8, Cobaltocen oder durch einen Überschuss an 1-Benzyl-1,4-dihydronicotinamid in Gegenwart einer Base. Letzteres wurde als NADH-Modellverbindung eingesetzt, um die mögliche Wirkungsweise von Gold(III)-Porphyrinen in Tumorzellen zu veranschaulichen, da diese als wirksame Krebsmedikamente eingesetzt werden. Außerdem konnte dieser einkernige Gold(II)-Komplex mittels Sublimation oder Rekristallisation isoliert und gereinigt werden. Dies ermöglichte die erste tiefgehende Untersuchung einer thermodynamisch stabilen mononuklearen Gold(II)-Spezies mittels spektroskopischer und theoretischer Methoden. Die Erkenntnisse aus den oben genannten Studien wurden für die Synthese und Untersuchung von drei neuartigen Amid-verbrückten Donor-Akzeptor Dyaden genutzt, um einen sehr schnellen PET zu ermöglichen. Zu diesem Zweck wurden Zink(II)-Porphyrin-Aminosäurederivate als Chromophore und Elektronendonatoren und Gold(III)-Porphyrin-Aminosäurederivate als Elektronenakzeptoren verwendet [Zn(P)-AuIII(P)][PF6]. Die einzelnen Bausteine wurden mit elektronenschiebenden und -ziehenden meso-Aryl-Gruppen (4-C6H4OnBu, 4-C6H4CF3) ausgestattet, um die Triebkraft des vorwärts gerichteten PETs und des rückwärts gerichteten Elektronentransfers (BET) beeinflussen zu können. Die PET-Prozesse wurden erfolgreich mittels zeitaufgelösten spektroskopischen Methoden verfolgt und offenbarten für alle Dyaden einen ladungsverschobenen (CSh) Zustand [Zn(P● )-AuII(P)] mit einem Gold(II)-Kern. Da sich das transferierte Elektron in einem -artigen Orbital (5dx2-y2) von Gold (relativ zur Porphyrin-Ebene) befindet, ist der direkte Elektronen-Rücktransport zum a2u SOMO des Zink(II)-Porphyrins gehemmt, was zu einer relativ langen Lebensdauer des CSh-Zustands führt. Infolgedessen wurden die CSh-Zustände erfolgreich für bimolekulare Reaktionen mit Aminen als Opferelektronendonatoren eingesetzt, was in einer stabilen Gold(II)-Spezies Zn(P)-AuII(P) resultierte. Darüber hinaus konnte diese Gold(II)-Dyade erfolgreich für die Reduktion von aromatischen Aziden während eines Photoredox-Experimentes verwendet werden, wobei die anfängliche Gold(III)-Dyade regeneriert und somit ein katalytischer Zyklus geschlossen wurde

Mobility in a Globalised World 2013

The term mobility has different meanings in the following science disciplines. In economics, mobility is the ability of an individual or a group to improve their economic status in relation to income and wealth within their lifetime or between generations. In information systems and computer science, mobility is used for the concept of mobile computing, in which a computer is transported by a person during normal use. Logistics creates by the design of logistics networks the infrastructure for the mobility of people and goods. Electric mobility is one of today‘s solutions from engineering perspective to reduce the need of energy resources and environmental impact. Moreover, for urban planning, mobility is the crunch question about how to optimise the different needs for mobility and how to link different transportation systems. In this publication we collected the ideas of practitioners, researchers, and government officials regarding the different modes of mobility in a globalised world, focusing on both domestic and international issues. We are grateful for the academic hospitality at the Stuttgart Media University for our conference 2013 "Mobility in a globalised world" in September 2013. We would like to thank Prof. Dr Johannes Maucher and Dr. Heiko Roßnagel for their technical support during our sojourn in Stuttgart

Wireless Sensor Network-Based Asset Management for Mobile Measurement Devices

The maturity level of Wireless Sensor Networks (WSN) has grown constantly and the market offers first components and products. Nevertheless the commercial breakthrough in industries has not yet happened due to the lack of economically justifiable applications. This paper presents the management of assets as one promising field of application for WSN. In particular we show how the existing asset management process for mobile measurement devices at Fraunhofer IIS is optimized with a WSN-based asset management system

Facile access to foldable redox-active flavin-peptide conjugates

A convenient approach for the synthesis of foldable redox-active flavin peptide conjugates was established. A model β-hairpin oligopeptide motif was utilized to demonstrate that azidolysine side-chains are readily functionalised with an alkyne-bearing flavine derivative. The folding equilibrium of the peptide backbone as well as the redox behaviour of the flavin moieties remains intact after the conjugation

Chirality enriched carbon nanotubes with tunable wrapping via corona phase exchange purification (CPEP)

Single-walled carbon nanotubes (SWCNTs) have unique photophysical properties and serve as building blocks for biosensors, functional materials and devices. For many applications it is crucial to use chirality-pure SWCNTs, which requires sophisticated processes. Purification procedures such as wrapping by certain polymers, phase separation, density gradient centrifugation or gel chromatography have been developed and yield distinct SWCNT species wrapped by a specific polymer or surfactant. However, many applications require a different organic functionalization (corona) around the SWCNTs instead of the one used for the purification process. Here, we present a novel efficient and straightforward process to gain chirality pure SWCNTs with tunable functionalization. Our approach uses polyfluorene (PFO) polymers to enrich certain chiralities but the polymer is removed again and finally exchanged to any desired organic phase. We demonstrate this concept by dispersing SWCNTs in poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6'-{2,2'-bipyridine})] (PFO-BPy), which is known to preferentially solubilize (6,5)-SWCNTs. Then PFO-BPy is removed and recycled, while letting the SWCNTs adsorb/agglomerate on sodium chloride (NaCl) crystals, which act as a toluene-stable but water-soluble filler material. In the last step these purified SWCNTs are redispersed in different polymers, surfactants and ssDNA. This corona phase exchange purification (CPEP) approach was also extended to other PFO variants to enrich and functionalize (7,5)-SWCNTs. CPEP purified and functionalized SWCNTs display monodisperse nIR spectra, which are important for fundamental studies and applications that rely on spectral changes. We show this advantage for SWCNT-based nIR fluorescent sensors for the neurotransmitter dopamine and red-shifted sp3 defect peaks . In summary, CPEP makes use of PFO polymers for chirality enrichment but provides access to chirality enriched SWCNTs functionalized in any desired polymer, surfactant or biopolymer

Structure and reactivity of a mononuclear gold(II) complex

Mononuclear gold(II) complexes are very rare labile species. Transient gold(II) species have been suggested in homogeneous catalysis and in medical applications, but their geometric and electronic structures have remained essentially unexplored: even fundamental data, such as the ionic radius of gold(II), are unknown. Now, an unprecedentedly stable neutral gold(II) complex of a porphyrin derivative has been isolated, and its structural and spectroscopic features determined. The gold atom adopts a 2+2 coordination mode in between those of gold(III) (four-coordinate square planar) and gold(I) (two-coordinate linear), owing to a second-order Jahn–Teller distortion enabled by the relativistically lowered 6s orbital of gold. The reactivity of this gold(II) complex towards dioxygen, nitrosobenzene and acids is discussed. This study provides insight on the ionic radius of gold(II), and allows it to be placed within the homologous series of nd$^9$ Cu/Ag/Au divalent ions and the 5d$^{8/9/10}$ Pt/Au/Hg ‘relativistic’ triad in the periodic table

The emergent Yo-yo movement of nuclei driven by collective cytoskeletal remodeling in pseudo-synchronous mitotic cycles

Many aspects in tissue morphogenesis are attributed to the collective behavior of the participating cells. Yet, the mechanism for emergence of dynamic tissue behavior is not understood completely. Here we report the “yo-yo”-like nuclear drift movement in Drosophila syncytial embryo displays typical emergent feature of collective behavior, which is associated with pseudo-synchronous nuclear division cycle. We uncover the direct correlation between the degree of asynchrony of mitosis and the nuclear collective movement. Based on experimental manipulations and numerical simulations, we find the ensemble of spindle elongation, rather than a nucleus’ own spindle, is the main driving force for its drift movement. The cortical F-actin effectively acts as a viscoelastic material dampening the drift movement and ensuring the nuclei return to the original positions. Our study provides insights into how the interactions between cytoskeleton as individual elements leads to collective movement of the nuclear array on a macroscopic scale