Homo- and heterogeneous Ru-based metathesis catalysts in cross-metathesis of 15-allylestrone—towards 17β-hydroxysteroid dehydrogenase type 1 inhibitors

The cross-metathesis of allylestrone with acrylic acid derivatives using homogeneous and heterogenized Ru-catalysts was evaluated for the synthesis of a new 17β-hydroxysteroid dehydrogenase type 1 inhibitor. Hoveyda-type catalyst containing an additional diethylamino group turned out to be comparably active as homogeneous Grubbs II catalyst after immobilization on an acidic ion exchange resin which greatly facilitated workup.     

Gold polycarbonate microchannels for electrochemical applications

In this paper, we present gold-plating polycarbonate (PC) microchannels. The fabrication of the gold microfluidic channels is achieved by tuning the sequence of reagent insertion into milled and closed submillimeter PC system channels. The resulting gold surface can be utilized in many applications where the benefits of microfluidics, (bio)chemistry of surfaces, and electrochemistry can be combined. Here, we combine the advantages of electrochemistry with microfluidics by mixing the gold sensor with microfluidics. This approach differs from the classic one – the sensor will undergo modifications (e. g., shape and size) depending on the specific scientific problem and will be designed individually; hence its characteristics will be changed. Our goal in this work is to indicate new possibilities for combining two methodologies – electrochemistry and microfluidics. In our work, we emphasize that it confirms the validity of our chosen concept (proof-of-concept). In this work, we present one such application, the use of a gold microfluidic channel as a working electrode (WE). We describe the microchip‘s construction and electrochemical characterization, including the gold flow-through WE, the Ag/AgCl wire pseudo-reference, and the Pt auxiliary electrode. The measured current is the result of the flow through a rectangular duct of the gold microchannel electrode embedded in the four walls of the chip.     

Synchronization in arrays of coupled self-induced friction oscillators

We investigate synchronization phenomena in systems of self-induced dry friction oscillators with kinematic excitation coupled by linear springs. Friction force is modelled according to exponential model. Initially, a single degree of freedom mass-spring system on a moving belt is considered to check the type of motion of the system (periodic, non-periodic). Then the system is coupled in chain of identical oscillators starting from two, up to four oscillators. A reference probe of two coupled oscillators is applied in order to detect synchronization thresholds for both periodic and non-periodic motion of the system. The master stability function is applied to predict the synchronization thresholds for longer chains of oscillators basing on two oscillator probe. It is shown that synchronization is possible both for three and four coupled oscillators under certain circumstances. Our results confirmed that this technique can be also applied for the systems with discontinuities.     

High-resolution NMR characterization of a gel-like surfactant mesophase

The addition of phosphatidylcholine to AOT water-in-oil microemulsions leads to the formation of a rigid gel as the water content is increased above a specific threshold. This system is a gel-like crystalline phase where the microstructure evolves from reverse hexagonal to lamellar with increasing water content and/or temperature. Couette sheared (1)H and (31)P NMR experiments carried out at varying temperature and water content show distinct signatures with microstructure evolution. Because the system has been fully characterized through small-angle neutron scattering, it is possible to relate the NMR signatures to the microstructure. The NMR technique therefore complements scattering techniques but is additionally useful because the technique also picks up isotropic signatures from concurrently occurring noncrystalline phases. The use of NMR to identify such lyotropic gel-like crystalline phases allows easy correlation between templated materials synthesis in these phases and phase microstructure. NMR can therefore be used as a probe to understand microstructure in specific surfactant systems and to characterize the retention of microstructure during materials synthesis.     

4-Methylpseudoproline derived from α-methylserine - synthesis and conformational studies

This paper presents the synthesis and solution conformational studies of the tripeptides Fmoc-Ala-(R)-(αMe)Ser(Ψ(H,H)Pro)-Ala-OBu(t) (6a) and Fmoc-Ala-(S)-(αMe)Ser(Ψ(H,H)Pro)-Ala-OBu(t) (6b). Additionally, the X-ray structure of 6a is given. NMR analysis corroborated by theoretical calculations (XPLOR) shows that in both peptides the amide bond between pseudoproline and the preceding amino acid is in the trans conformation. The same amide bond geometry was observed in the crystal state of 6a. The latter is additionally influenced by the presence of two symmetrically independent molecules in an asymmetric unit. Both molecules adopt a conformation which resembles β-turn type II, stabilized by hydrogen bonding. The conformational preferences and prolyl cis-trans isomerization of Ac-(αMe)Ser(Ψ(H,H)Pro)-NHMe (7) were explored at the IEFPCM/B3LYP/6-31+G(d) level of theory in vacuum, water and chloroform. It has been shown that the trans isomer predominates in water solutions and the cis isomer is preferred in chloroform. The conformation of 7 is down-puckered independently of the geometry of the amide bonds, with lower puckering in the transition state of the cis-trans isomerization.     

Chiroptical dissymmetries in fluorescence excitation from single molecules of (M-2) helicene dimers

We report on the single-molecule chiroptical properties of "right"-handed bridged triaryl amine helicene dimers, MH2. Using an experimental setup to precisely define the circular excitation polarization at the sample plane, we investigated the circular dichroic response in luminescence from individual molecules in which induced ellipticity from microscope optics is minimized. Our results comparing circular anisotropies in fluorescence excitation from MH2 and perylene diimide (PDI), an achiral, centrosymmetric chromophore, demonstrate a significant reduction in the breadth of the distribution of circular dissymmetry parameters obtained from modulation of the circularly polarized excitation source (457 nm). For PDI, we observe a symmetric distribution of circular anisotropy parameters centered about zero, with a fwhm of 0.25. For MH2, we observe an asymmetric distribution peaked at g = -0.09, with a slightly larger width as the corresponding PDI distribution. These results indicate that the large dissymmetry parameters (|g| > 0.5) in fluorescence excitation described in our original report (Hassey, R.; et al. Chirality 2008, 20, 1039-1046 and Hassey, R.; et al. Science 2006, 314, 1437-1439) were indeed affected by (at the time, unknown) linear polarization artifacts. However, the present results on MH2 provide compelling evidence for single-molecule circular dissymmetries much larger than solution or thin-film ensemble values, defined primarily by the enhanced rotatory strength (relative to the monomer), and restricted orientation at the sample surface.     

Theoretical determination of the infrared spectra of amorphous polymers

The simple procedure of calculating the infrared spectra of polymers is presented. It is based on selecting the relevant, medium-size representative fragments of a polymer, for which the vibrational frequencies are computed within the harmonic approximation, in conjunction with the multiparameter scaling techniques. Scaling is necessary to predict the reliable fundamentals, which, along with the calculated intensities and properly chosen band widths, reproduce the observed band shapes with high accuracy. Applications to the three polymers: poly(methyl methacrylate), poly(vinyl acetate), and poly(isopropenyl acetate) are presented. The simulated spectra are in good agreement with the experiment. The assignment of bands is reported. The obtained results indicate strong delocalization of the vibrational modes within polymers, which is in accord with the most recent experimental finding [Macromolecules2008, 41, 2494-2501]. Good agreement between the observed and the calculated spectra of deuterated PMMA confirms the correctness of our approach. The preliminary results obtained for the highly irregular macromolecular compound (vinyl-functionalized silica) are also shown.     

A highly selective synthesis of dialkenyl sulfones via cross-metathesis of divinyl sulfone

Catalytic cross-metathesis of commercial divinyl sulfone allowed direct access to novel (E)-alkenylvinyl sulfones and (E,E)-dialkenyl sulfones with excellent stereoselectivity. These compounds are useful building blocks, e.g., in the synthesis of substituted thiomorpholine 1,1-dioxide derivatives. [reaction: see text]