Technical University of Berlin

About: Technical University of Berlin is a education organization based out in Berlin, Germany. It is known for research contribution in the topics: Quantum dot & Laser. The organization has 27292 authors who have published 59342 publications receiving 1414623 citations. The organization is also known as: Technische Universität Berlin & TU Berlin.

Hydrogen bonding of water confined in mesoporous silica MCM-41 and SBA-15 studied by 1H solid-state NMR.

Abstract: The adsorption of water in two mesoporous silica materials with cylindrical pores of uniform diameter, MCM-41 and SBA-15, was studied by 1H MAS (MAS=magic angle spinning) and static solid-state NMR spectroscopy. All observed hydrogen atoms are either surface -SiOH groups or hydrogen-bonded water molecules. Unlike MCM-41, some strongly bound water molecules exist at the inner surfaces of SBA-15 that are assigned to surface defects. At higher filling levels, a further difference between MCM-41 and SBA-15 is observed. Water molecules in MCM-41 exhibit a bimodal line distribution of chemical shifts, with one peak at the position of inner-bulk water, and the second peak at the position of water molecules in fast exchange with surface -SiOH groups. In SBA-15, a single line is observed that shifts continuously as the pore filling is increased. This result is attributed to a different pore-filling mechanism for the two silica materials. In MCM-41, due to its small pore diameter (3.3 nm), pore filling by pore condensation (axial-pore-filling mode) occurs at a low relative pressure, corresponding roughly to a single adsorbed monolayer. For SBA-15, owing to its larger pore diameter (8 nm), a gradual increase in the thickness of the adsorbed layer (radial-pore-filling mode) prevails until pore condensation takes place at a higher level of pore filling.

Carrier Multiplication in Graphene

Abstract: Graphene as a zero-bandgap semiconductor is an ideal model structure to study the carrier relaxation channels, which are inefficient in conventional semiconductors. In particular, it is of fundamental interest to address the question whether Auger-type processes significantly influence the carrier dynamics in graphene. These scattering channels bridge the valence and conduction band allowing carrier multiplication, a process that generates multiple charge carriers from the absorption of a single photon. This has been suggested in literature for improving the efficiency of solar cells. Here we show, based on microscopic calculations within the density matrix formalism, that Auger processes do play an unusually strong role for the relaxation dynamics of photoexcited charge carriers in graphene. We predict that a considerable carrier multiplication takes place, confirming the potential of graphene as a new material for high-efficiency photodevices.

Palladium-catalysed hydroxylation and alkoxylation

Abstract: The formation of oxygen–carbon bonds is one of the fundamental transformations in organic synthesis. In this regard the application of palladium-based catalysts has been extensively studied during recent years. Nowadays it is an established methodology and the success has been proven in manifold synthetic procedures. This tutorial review summarizes the advances on palladium-catalysed C–O bond formation, means hydroxylation and alkoxylation reactions.

Matrix-assisted laser desorption ionization--time of flight mass spectrometry of lipopeptide biosurfactants in whole cells and culture filtrates of Bacillus subtilis C-1 isolated from petroleum sludge.

Abstract: An innovative method was developed for rapid sensitive detection and efficient structural characterization of lipopeptide biosurfactants by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry by using whole microbial cells and crude culture filtrates as targets in combination with surface tension measurements. This was done for a bacterial strain that was isolated from petroleum sludge and efficiently produces biosurfactants. This organism was identified by using biochemical, physiological, and genetic parameters as a Bacillus subtilis strain, designated B. subtilis C-1. This assignment was supported by a mass spectrometric investigation of the secondary metabolite spectrum determined by whole-cell MALDI-TOF mass spectrometry, which revealed three lipopeptide complexes, the surfactins, the iturins, and the fengycins, which are well-known biosurfactants produced by B. subtilis strains. These compounds were structurally characterized by in situ structure analysis by using postsource decay MALDI-TOF mass spectrometry. The isoforms were separated by miniaturized high-resolution reversed-phase high-performance liquid chromatography for mass spectrometric characterization. Iturin compounds which contain unusual fatty acid components were detected.