Synthesis and aggregation behaviour of amphiphilic block copolymers with random middle block

The effect of microstructure on the aggregation behaviour of symmetrical di- and triblock copolymers P(BMA)-b-P(MAA) and P(BMA)-b-P(BMA-co-MAA)-b-P(MAA) with a molecular weight of 40,000 g/mol was studied. The critical micelle concentration, hydrodynamic radius and morphology of the micelles were determined by fluorescence spectroscopy, dynamic light scattering and scanning force microscopy (SFM). Whereas no effect of the microstructure on the critical micelle concentration could be detected, the hydrodynamic radius decreased from di- to triblock copolymer from 53 to 36 nm. The decrease of about 32% corresponds to the length of the random middle block within the triblock copolymer so that the reduction in hydrodynamic radius was caused by a complete orientation of the random middle block at the core corona interface. Finally, the SFM investigation showed that dehydration of micelles on a substrate is accompanied by formation of a physisorbed monolayer with a thickness of 2 nm on which the micelles are deposited.     

Apoenzyme Reconstitution as a Chemical Tool for Structural Enzymology and Biotechnology

Enzymes with artificial cofactors : Nondiffusible organic cofactors of enzymes can often be replaced by artifical analogues to generate semisynthetic enzymes (see scheme). This approach can be used to study structure–function relationships in enzymology and to produce novel enzymes with enhanced or even entirely new functions that are useful for biosensing, biocatalysis, and materials science applications.

     

Growth Mechanism of Metal–Organic Frameworks: Insights into the Nucleation by Employing a Step‐by‐Step Route

One step at a time : The in situ monitoring of the step‐by‐step formation of metal–organic frameworks (MOFs) by using surface plasmon resonance (SPR), allows the nucleation process and the formation of the secondary building units to be investigated. Growth rates on functionalized organic surfaces with different crystallographic orientations can also be studied.

     

Surface-enhanced Raman scattering as a tool to probe cytochrome P450-catalysed substrate oxidation

Surface-enhanced Raman scattering was used as a spectroscopic tool to investigate the changes brought upon cytochrome P450BSß after fatty acid binding. Differences in the spectra of substrate-free and substrate-bound enzyme were observed indicating the potential for this method to be used in the screening of P450 substrates. In particular, the binding characteristics of myristic acid, an inherent substrate, and hydroxylauric acid, a product of fatty acid oxidation, towards P450BSß in the presence of H₂O₂ were investigated. Specific spectral changes could be assigned to changes in the heme environment only for myristic acid, indicating an occurrence of oxidation process characteristic for the enzymatic substrate.     

Illustration of transition path theory on a collection of simple examples

Transition path theory (TPT) has been recently introduced as a theoretical framework to describe the reaction pathways of rare events between long lived states in complex systems. TPT gives detailed statistical information about the reactive trajectories involved in these rare events, which are beyond the realm of transition state theory or transition path sampling. In this paper the TPT approach is outlined, its distinction from other approaches is discussed, and, most importantly, the main insights and objects provided by TPT are illustrated in detail via a series of low dimensional test problems.     

Barrelane-like germanium clusters in Eu3Ge5: Crystal structure, chemical bonding and physical properties

Formation and crystal structure of the binary germanide Eu₃Ge₅ were investigated in detail. The compound forms peritectically at 1008 °C and does not undergo any phase transition down to room temperature. The crystal structure was determined first from X-ray powder diffraction data and was later confirmed by single-crystal X-ray diffraction: structure type Pu₃Pd₅, space group Cmcm (no. 63), , , . The main building blocks are Ge₅⁶⁻ cluster anions surrounded by Eu²⁺ cations. The nearly tetragonal-pyramidal shape is suggested by the interatomic distances. Contrary to that, the bonding analysis with the electron localization function (ELF) reveals only two- and three-bonded germanium atoms forming a strongly distorted [1.1.1]-barrelane-like cluster. Despite the formal electron deficiency, compared to the barrelane C₅H₈, the electron counting in the cluster anion and its conformation cannot be interpreted applying the Wade's rules. In accordance with the calculated electronic density of states, Eu₃Ge₅ shows a metal-like temperature dependence of the electrical resistivity with a sharp change of ρ(T) slope at the Néel point. Above the Néel point the inverse magnetic susceptibility reveals Curie-Weiss behavior with an effective moment of 8.11 μ_B (Eu²⁺, 4f⁷ configuration) in agreement with the analysis of the chemical bonding. The 4f⁷ electronic configuration of europium is confirmed by Eu-L_III X-ray absorption spectroscopy.     

Statistical Analysis of the First Passage Path Ensemble of Jump Processes

The transition mechanism of jump processes between two different subsets in state space reveals important dynamical information of the processes and therefore has attracted considerable attention in the past years. In this paper, we study the first passage path ensemble of both discrete-time and continuous-time jump processes on a finite state space. The main approach is to divide each first passage path into nonreactive and reactive segments and to study them separately. The analysis can be applied to jump processes which are non-ergodic, as well as continuous-time jump processes where the waiting time distributions are non-exponential. In the particular case that the jump processes are both Markovian and ergodic, our analysis elucidates the relations between the study of the first passage paths and the study of the transition paths in transition path theory. We provide algorithms to numerically compute statistics of the first passage path ensemble. The computational complexity of these algorithms scales with the complexity of solving a linear system, for which efficient methods are available. Several examples demonstrate the wide applicability of the derived results across research areas.     

Visualization of Protein‐Specific Glycosylation inside Living Cells

Protein glycosylation is a ubiquitous post‐translational modification that is involved in the regulation of many aspects of protein function. In order to uncover the biological roles of this modification, imaging the glycosylation state of specific proteins within living cells would be of fundamental importance. To date, however, this has not been achieved. Herein, we demonstrate protein‐specific detection of the glycosylation of the intracellular proteins OGT, Foxo1, p53, and Akt1 in living cells. Our generally applicable approach relies on Diels–Alder chemistry to fluorescently label intracellular carbohydrates through metabolic engineering. The target proteins are tagged with enhanced green fluorescent protein (EGFP). Förster resonance energy transfer (FRET) between the EGFP and the glycan‐anchored fluorophore is detected with high contrast even in presence of a large excess of acceptor fluorophores by fluorescence lifetime imaging microscopy (FLIM).