Proline zwitterion dynamics in solution, glass, and crystalline state

Raman and Raman optical activity spectra of L- and D-proline zwitterionic (PROZW) forms were recorded for H(2)O and D(2)O solutions in a wide frequency range and analyzed with respect to the motion of the proline ring and rotation of the carbonyl group. The solution spectra were additionally compared to Raman scattering of glass and crystalline powder proline. Solution and glass spectral band broadenings are similar and reveal information about the extent of internal molecular motion. Two distinct but equally populated flexible forms were found in the glass and the solution. The equal population is consistent with NMR data, temperature, and concentration dependencies. The molecular flexibility is reduced significantly in the crystal, however, where only one conformer is present. Consequently, the crystal bands are narrow and exhibit minor frequency shifts. The spectra were interpreted with the aid of density functional theory computations involving both continuum and explicit solvent. A two-dimensional potential energy surface pertaining to the five-member ring puckering coordinates was constructed and used for dynamical averaging of spectral properties. Comparison of the computed and experimental bandwidths suggests that the puckering is strongly correlated with the carbonyl rotation. An averaging over these two motions produces similar results. The interpretation of the Raman experiments with the aid of the simulation techniques also indicates that the environment modulates properties of the hydrophobic part of the molecule indirectly by interacting with the ionic group. Such behavior may be important for the reactivity and biological activity of proline-containing peptides and proteins.     

The Howe Duality for the Dunkl Version of the Dirac Operator

The classical Fischer decomposition of polynomials on Euclidean space makes it possible to express any polynomial as a sum of harmonic polynomials multiplied by powers of |x|². A deformation of the Laplace operator was recently introduced by Ch.F. Dunkl. It has the property that the symmetry with respect to the orthogonal group is broken to a finite subgroup generated by reflections (a Coxeter group). It was shown by B. ?rsted and S. Ben Said that there is a deformation of the Fischer decomposition for polynomials with respect to the Dunkl harmonic functions. In Clifford analysis, a Dunkl version of the Dirac operator was introduced and studied by P. Cerejeiras, U. K?hler and G. Ren. The aim of the article is to describe an analogue of the Fischer decomposition for solutions of the Dunkl Dirac operator. The main methods used are coming from representation theory, in particular, from ideas connected with Howe dual pairs. This paper is dedicated to the memory of our friend and colleague Jarolim Bureš to recall our long lasting cooperation on many topics in mathematics The work presented here is a part of the research project MSM 0021620839 and was supported also by the grant GA ČR 201/05/2117. Received: October, 2007. Accepted: February, 2008.     

Tantalum induced butterfly-like clusters on Si (111)-7 × 7 surface: STM/STS study at low coverage

The adsorption of the small amounts of tantalum on Si (111)-7 × 7 reconstructed surface is investigated systematically using scanning tunneling microscopy and tunneling spectroscopy combined with first-principles density functional theory calculations. We find out that the moderate annealing of the Ta covered surface results in the formation of clusters of the butterfly-like shape. The clusters are sporadically distributed over the surface and their density is metal coverage dependent. Filled and empty state STM images of the clusters differ strongly suggesting the existence of covalent bonds within the cluster. Tunneling spectroscopy measurements reveal small energy gap, showing semiconductor-like behavior of the constituent atoms. The cluster model based on experimental images and theoretical calculations has been proposed and discussed. Presented results show that Ta joins the family of adsorbates, that are known to form magic clusters on Si (111)-7 × 7, but its magic cluster has the structural and electronic properties that are different from those reported before.     

Injectable Hyaluronic Acid Hydrogel Containing Platelet Derivatives for Synovial Fluid Viscosupplementation and Growth Factors Delivery

Osteoarthritisis a highly prevalent musculoskeletal disorder characterized by degradation of cartilage and synovial fluid (SF). Platelet derivatives as platelet-rich plasma (PRP) and platelet lysate have great potential in the treatment of osteoarthritis because they contain biologically active substances including growth factors (GFs). Rapid release of GFs and their short biological half-life are factors that can limit the therapeutic impact of PRP therapy. Herein, the first work that describes hydrogels based on polyaldehyde derivative of hyaluronic acid (HA-OX) as carriers of platelet derivatives for in situ applications is presented, which can be a possible solution to the problem. HA-OX hydrogels containing 50% (w/w) of PRP or platelet lysate can be injected using a syringe due to low viscosity(<10 Pa s) and injection force (<20 N), and reach elastic modulus up to 2000 Pa. Insulin-like GF-1 and Platelet-derived GF-AB release from HA-OX hydrogels (mesh size 297–406 nm) by Fickian and non-Fickian diffusion respectively. The released PRP GFs maintain their ability to induce cell proliferation (87%–92%). Based on the obtained results, the unique concept of a new material that can restore viscoelastic properties of SF and at the same time gradually deliver GFs from platelet derivatives is designed.     

Concise Synthesis,Conformational Study,and Aroma Properties of Carba-Homologues of Helvetolide and Serenolide

We have designed, prepared, and evaluated a set of racemic (un)saturated carba-homologues of prominent musks Helvetolide and Serenolide. The short synthesis employs commercially available Artemone and/or Herbac, that are transformed in three steps to the target compounds. Their qualitative olfactory analysis revealed that incorporation of methylene bridge into the backbone chain of parent compounds completely erases the original musk scent and such new derivatives exhibit a pleasant and often intense sweet(ish) aroma of fruit with floral and herbal aspects. The results of computational modelling suggest that previously postulated horseshoe shape conformation might be necessary but not sufficient prerequisite for musk-scented compounds. Thus, we offer an alternative hypothesis based on the structural differences between metallocomplexes of Helvetolide and/or Serenolide vs. their (un)saturated carba-homologues with zinc-atom as a model for the putative metal-binding site in human olfactory receptors.