TY  - GEN
A1  - Bringmann, Gerhard
A1  - Mutanyatta-Comar, Joan
A1  - Maksimenka, Katja
A1  - Wanjohi, John M.
A1  - Heydenreich, Matthias
A1  - Brun, Reto
A1  - Müller, Werner E. G.
A1  - Peter, Martin
A1  - Midiwo, Jacob O.
A1  - Yenesew, Abiy
T1  - Joziknipholones A and B : the First Dimeric Phenylanthraquinones, from the Roots of Bulbine frutescens
N2  - From the roots of the African plant Bulbine frutescens (Asphodelaceae), two unprecedented novel dimeric phenylanthraquinones, named joziknipholones A and B, possessing axial and centrochirality, were isolated, together with six known compounds. Structural elucidation of the new metabolites was achieved by spectroscopic and chiroptical methods, by reductive cleavage of the central bond between the monomeric phenylanthraquinone and -anthrone portions with sodium dithionite, and by quantum chemical CD calculations. Based on the recently revised absolute axial configuration of the parent phenylanthraquinones, knipholone and knipholone anthrone, the new dimers were attributed to possess the P-configuration (i.e., with the acetyl portions below the anthraquinone plane) at both axes in the case of joziknipholone A, whereas in joziknipholone B, the knipholone part was found to be M-configured. Joziknipholones A and B are active against the chloroquine resistant strain K1 of the malaria pathogen, Plasmodium falciparum, and show moderate activity against murine leukemic lymphoma L5178y cells.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 104 
KW  - antimalarial activity
KW  - chirality
KW  - joziknipholones
KW  - natural products
KW  - structure elucidation
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-42638
ER  - 
TY  - GEN
A1  - Breternitz, Joachim
A1  - Lehmann, Frederike
A1  - Barnett, Sarah A.
A1  - Nowell, Harriott
A1  - Schorr, Susan
T1  - Zur Rolle der Iodid-Methylammonium-Interaktion in der Ferroelektrizität in CH3NH3PbI3
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Ihre außergewöhnlich hohen Konversionseffizienzen von über 20 % und die einfache Zellherstellung machen Hybridperowskite zu heißen Kandidaten für alternative Solarzellenmaterialien. CH3NH3PbI3 als Archetyp dieser Materialklasse besitzt außergewöhnliche Eigenschaften wie eine sehr effiziente Umwandlung von Solarenergie, wobei besonders Ferroelektrizität als mögliche Erklärung in den Fokus gerückt ist. Diese erfordert allerdings eine nicht-zentrosymmetrische Kristallstruktur als notwendige Voraussetzung. Wir stellen hier eine Erklärung des Symmetriebruchs in diesem Material auf kristallographischem, d. h. fernordnungs-basiertem, Wege vor. Während das Molekülkation CH3NH3+ intrinsisch polar ist, ist es extrem fehlgeordnet und kann deshalb nicht die einzige Erklärung darstellen. Es verzerrt allerdings das umgebende Kristallgitter und ruft dadurch eine Verschiebung der Iod-Atome von den zentrosymmetrischen Positionen hervor.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1199 
KW  - ferroelectricity
KW  - hybrid perovskites
KW  - inorganic chemistry
KW  - photovoltaic materials
KW  - structure elucidation
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-525674
SN  - 1866-8372
IS  - 1
ER  - 
TY  - GEN
A1  - Breternitz, Joachim
A1  - Lehmann, Frederike
A1  - Barnett, Sarah A.
A1  - Nowell, Harriott
A1  - Schorr, Susan
T1  - Role of the Iodide-methylammonium interaction in the ferroelectricity of CH3NH3PbI3
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Excellent conversion efficiencies of over 20% and facile cell production have placed hybrid perovskites at the forefront of novel solar cell materials, with CH3NH3PbI3 being an archetypal compound. The question why CH3NH3PbI3 has such extraordinary characteristics, particularly a very efficient power conversion from absorbed light to electrical power, is hotly debated, with ferroelectricity being a promising candidate. This does, however, require the crystal structure to be non-centrosymmetric and we herein present crystallographic evidence as to how the symmetry breaking occurs on a crystallographic and, therefore, long-range level. Although the molecular cation CH3NH3+ is intrinsically polar, it is heavily disordered and this cannot be the sole reason for the ferroelectricity. We show that it, nonetheless, plays an important role, as it distorts the neighboring iodide positions from their centrosymmetric positions.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1196 
KW  - ferroelectricity
KW  - hybrid perovskites
KW  - inorganic chemistry
KW  - photovoltaic materials
KW  - structure elucidation
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-518227
SN  - 1866-8372
IS  - 1
ER  -