High‐Oxidation‐State Palladium Catalysis: New Reactivity for Organic Synthesis

Recent years have seen the rapid development of a new field of palladium catalysis in organic synthesis. This chemistry takes place outside the usually encountered Pd⁰/Pd^II cycles. It is characterized by the presence of strong oxidants, which prevent further palladium(II)‐promoted reactions at a given point of the catalytic cycle by selective metal oxidation. The resulting higher‐oxidation‐state palladium complexes have been used to develop a series of new synthetic transformations that cannnot be realized within conventional palladium catalysis. This type of catalysis by palladium in a higher oxidation state is of significant synthetic potential.     

Synthesis of small tripeptide molecules through a catalysis sequence comprising metathesis and aminohydroxylation

Tripeptidic structures were synthesized by using a combination of two independent consecutive catalytic procedures. Cross-metathesis of N-acroyl amino acid esters yields fumaric amide compounds with exclusive E double-bond geometry. This represents an unprecedented example of complete double-bond selectivity in this kind of reaction. A subsequent asymmetric aminohydroxylation of the chiral fumaric amides was carried out without the need of any further ligand and gave high yields and no side products. This reaction transforms the central fumaric amide unit into a hydroxy aspartic acid moiety and relies on the inherent stereochemistry of the starting fumaric diamides. An additional feature of our sequence is the ease of generating stereochemical diversification within the aminohydroxylation reaction. As a consequence, rapid conformational and configurational diversification can be achieved from the overall two-step catalytic sequence. The versatility of this approach is demonstrated by starting from two different N-acroyl amino esters, which led to the synthesis of eight structurally and stereochemically different tripeptides that could all be identified individually. As such, the present two-step catalytic approach should serve to efficiently synthesize large families of tripeptidic molecular probes.     

Multiplexed analyte and oligonucleotide detection on microarrays using several redox enzymes in conjunction with electrochemical detection

We show that multiple enzyme tags may be used in an immunoassay format or for the detection of sequence-specific DNA on microarrays. The assays may be multiplexed and monitored under separate solution and voltage differences. Thus, the detection method relies on an electrochemical detection format, whereby multiple enzymes can be sensed. In our case we utilize horseradish peroxidase, laccase, and glucose dehydrogenase as enzymes attached to specific antibodies or to streptavidin.     

Preparation and structures of 1,2-dihydro-1,2-diphosphaacenaphthylenes and rigid backbone stabilized triphosphenium cation

The effect of the special peri-geometry of rigid naphthalene-1,8-diyl backbone in phosphenium formation reaction was investigated. 1,8-Bis(diphenylphosphino) naphthalene and P2I4 afforded triphosphenium iodide in a clean reaction. The reaction of 1,8-bis(dimethylaminophosphino) naphthalene with P2I4 is complex, it afforded four products, all containing the 1,2-dihydro-1,2-diphosphaacenaphthylene motif and heterophosphonium functionalities. Two examples of the rare structural motif of two acenaphthylene units connected head to head and thus a contiguous chain of four phosphorus atoms were also isolated, one compound showing diastereomerization in the solution. All new compounds were fully characterised including single crystal X-ray diffraction.     

The semi-phenomenological model of antiferroelectricity in chiral smectic liquid crystals II. The phase transitions and phase diagrams

In the framework of the model of short pitch modes (SPM) developed for chiral smectics with inclined molecules, the phase transitions and diagrams in antiferroelectric systems are described. It is shown that the families of antiferro- and ferri-electric phases are controlled by a few physical parameters such as the smectic correlation length and the chirality parameter. The sequences of antiferro- and ferri-electric states are explained as being dependent on the interactions between SPM and the conventional long pitch mode (LPM), the ferrielectric states being described in terms of the obvious coexistence of LPM and several SPM.     

The semi-phenomenological model of antiferroelectricity in chiral smectic liquid crystals III. Dielectric spectroscopy

In the framework of the model of short pitch modes (SPM) developed for antiferroelectric liquid crystals, the sets of various relaxation modes related to ferro-, antiferro- and ferrielectric phases are explained. The 'soft-like' modes describe the amplitude perturbations of short pitch modes, while the Goldstone modes describe the azimuthal perturbations of the molecular packings related to short pitch modes. The frequencies of the Goldstone modes are mainly determined by the chirality parameter, depending on the number of short pitch modes. The relaxation modes described correspond to the observed phase diagrams in liquid crystal materials for which the measurements of dielectric spectra are presented.     

On the decisive role of finite chain extensibility and global interactions in networks

The stress-strain dependence of dry networks at unidirectional extension and compression is studied. The phenomenological van der Waals equation of state is compared with different molecular models in order to provide an interpretation of the van der Waals corrections. It is shown that the stress-strain behavior predicted by the phantom, Langevin, and constrained junction fluctuation models are altogether covered by the van der Waals approach. The relationship between the suppression of junction fluctuation parameter introduced by Dossin and Graessley and the van der Waals corrections has been worked out. The effect of junction functionality on the small strain modulus as well as on the second Mooney-Rivlin coefficient is also presented.