Supramolecular click chemistry for the self-assembly of a stable Zn(II)-porphyrin-C60 conjugate

Owing to the complementarity between a bis-Zn(II)-porphyrin receptor and a fullerene ligand bearing two pyridine substituents, the substrate can be clicked onto the ditopic receptor, thus leading to a stable non-covalent macrocyclic 1 ratio 1 complex.     

Resonance Raman detection of a ferrous five-coordinate nitrosylheme b(3) complex in cytochrome cbb(3) oxidase from Pseudomonas stutzeri

Understanding the chemical nature of the nitric oxide (NO) moiety of nitrosylheme copper oxidases is crucial for elucidation of the NO activation process. In the present work, direct resonance Raman spectroscopic observation of both the Fe(2+)-NO and the N-O stretching modes unambiguously establishes the vibrational characteristics of the NO-bound heme moiety in cytochrome cbb(3) from Pseudomonas stutzeri. Addition of NO to fully reduced enzyme causes the rupture of the proximal His-heme b(3) bond resulting in the formation of a five-coordinate heme b(3)(2+)-NO species with nu(Fe-NO) and nu(NO) at 524 and 1679 cm(-1), respectively. The frequencies of the nitrosyl species we detect are very similar to those obtained in other model- and protein heme-NO complexes. To account for this observation, we propose a model describing the oxidation and ligand-binding states in fully reduced cytochrome cbb(3) upon addition of NO.     

Restricted rotation in a tetrakis(para-substituted phenyl) porphyrin bearing four porphyrin-fullerene substituents

A porphyrin substituted with four porphyrin-fullerene moieties has been prepared and variable-temperature NMR studies revealed a high barrier to free rotation about the four para-substituted phenyl groups of the central porphyrin core.     

Preparation, characterization, and heck reaction of siloxane films derived from carbosilane dendrons with a bromophenyl group at the focal point and up to 27 SiCl3 groups at the periphery

Multidentate organosiloxane thin films were prepared on SiO2/Si surfaces by solution phase deposition of carbosilane dendrons containing a bromophenyl group at the focal point and 3 (Br-G0), 9 (Br-G1), and 27 (Br-G2) SiCl3 groups at the periphery. The films were characterized by contact angle goniometry, ellipsometry, and X-ray photoelectron spectroscopy (XPS). The results indicated that about six Br-G0 molecules covered the same surface area as three Br-G1 molecules and one Br-G2 molecule. Hence, the density of the bromophenyl groups in the films could be defined by the size (generation) of the dendron adsorbates. We also demonstrated that the bromophenyl groups on the film surfaces could serve as a handle for attaching conjugated molecules via formation of C-C bonds. Thus, upon treatment of the films with 4-fluorostyrene under Heck reaction conditions, XPS analysis showed that about 90, 66, and 51% of the bromine atoms in the films prepared from Br-G0, Br-G1, and Br-G2 were consumed, and 94, 82, and 58% of the consumed bromine atoms were replaced by fluorostyryl groups. The remaining bromophenyl groups were probably not accessible to the reactants because of their unfavorable orientation. The overall yields for the surface Heck reaction were estimated to be 84, 54, and 30% for the films prepared from Br-G0, Br-G1, and Br-G2, respectively.     

Tracking quasiclassical chaos in ultracold boson gases

We study the dynamics of an ultracold boson gas in a lattice submitted to a constant force. We track the route of the system towards chaos created by the many-body-induced nonlinearity and show that relevant information can be extracted from an experimentally accessible quantity, the gas mean position. The threshold nonlinearity for the appearance of chaotic behavior is deduced from Kolmogorov-Arnold-Moser arguments and agrees with the value obtained by calculating the associated Lyapunov exponent.     

NMR study of water bound to soft segments in thermoplastic elastomers

The interaction between water absorbed in four hard-soft segment block-copolymers and the polymer chains is investigated by pulsed field gradient echo NMR spectroscopy and Nuclear Overhauser NMR spectroscopy. The results show, depending on the structure and mass fraction of the soft segments, a strong interaction between water and the soft segments. Most likely this is due to a hydrogen bond between water and the ether groups. The self-diffusion of water has been determined and is described as a jumping process between the ether sites with a residence time t and a time between sites t. It is found that the residence time is of the order of a few ns and also that the ratio t/τ decreases with increasing soft segment rigidity.