Effects of Cyclodextrin Derivatives on the Catalytic Activity of Tyrosine Phenol-Lyase

The impact of permethylated α-, β-, γ-cyclodextrin (TMα-CD, TMβ-CD, TMγ–CD, respectively) on TPL-catalysed decomposition of L-tyrosine was investigated by means of spectrophotometric measurements. The inhibitory effects of TM-CDs on the catalytic activity of the enzyme were shown. This phenomenon is supposed to be connected with the host–guest complex formation. CDs were found to have impact on maximal velocity and on Michaelis constant of described catalysis.     

Asymptotic and spectral analysis of non‐selfadjoint operators generated by a filament model with a critical value of a boundary parameter

We consider a class of non‐selfadjoint operators generated by the equation and the boundary conditions, which govern small vibrations of an ideal filament with non‐conservative boundary conditions at one end and a heavy load at the other end. The filament has a non‐constant density and is subject to a viscous damping with a non‐constant damping coefficient. The boundary conditions contain two arbitrary complex parameters. In our previous paper (Mathematical Methods in the Applied Sciences 2001; 24 (15) : 1139–1169), we have derived the asymptotic approximations for the eigenvalues and eigenfunctions of the aforementioned non‐selfadjoint operators when the boundary parameters were arbitrary complex numbers except for one specific value of one of the parameters. We call this value the critical value of the boundary parameter. It has been shown (in Mathematical Methods in the Applied Sciences 2001; 24 (15) : 1139–1169) that the entire set of the eigenvalues is located in a strip parallel to the real axis. The latter property is crucial for the proof of the fact that the set of the root vectors of the operator forms a Riesz basis in the state space of the system. In the present paper, we derive the asymptotics of the spectrum exactly in the case of the critical value of the boundary parameter. We show that in this case, the asymptotics of the eigenvalues is totally different, i.e. both the imaginary and real parts of eigenvalues tend to ∞as the number of an eigenvalue increases. We will show in our next paper, that as an indirect consequence of such a behaviour of the eigenvalues, the set of the root vectors of the corresponding operator is not uniformly minimal (let alone the Riesz basis property). Copyright © 2003 John Wiley & Sons, Ltd.     

A von Neumann theorem for uniformly distributed sequences of partitions

In this paper we consider permutations of sequences of partitions, obtaining a result which parallels von Neumann’s theorem on permutations of dense sequences and uniformly distributed sequences of points.     

Manganese silicide single crystal and films deposited on Si(1 1 1): A comparative spectroscopic study

A comparative experimental study is presented of the electronic properties of MnSi films grown on Si(1 1 1) and of MnSi single crystals, using X-ray absorption spectroscopy (XAS), and core level and valence band photoemission spectroscopy (PES). No significant differences in the electronic structure of the two systems can be found.Absorption measurements on the Mn 2p threshold show a mixed valence ground state, where the multiplet structure is washed out by the hybridisation of the Mn 3d states with the Si sp states. These results are also confirmed by photoemission (PE) spectra from the valence band and the Mn 3s, 3p and 2p core levels.Strong attention has been paid to the effect of contamination. The occurrence of multiplet effects in the absorption spectra indicates unambiguously the localisation of the Mn 3d electrons in Mn-O bonds, which strongly influences the electronic properties of these systems.     

Internal derivatization of oligonucleotides with selenium for X-ray crystallography using MAD.

We have developed a route for the synthesis of 2'-selenium uridine analogues and oligonucleotides containing selenium labels, and have demonstrated for the first time a new strategy to covalently derivatize nucleotides with selenium for phase and structure determination in X-ray crystallography.     

Nonlinear dynamics of inviscid reduced MHD plasmas: the appearance of Quasi-Single-helicity states

The nonlinear dynamics of an inviscid magnetohydrodynamic system in a low-beta plasma is investigated through a simplified model obtained by a Galerkin projection. We show that a single Fourier mode dominates over the whole energy spectrum, a self-organization mechanism of turbulence being responsible for this nonlinear effect. Our results are in agreement with observations of an analogous phenomenon, say, the emergence of a quasi-single-helicity state both in numerical simulations and real experiments in reversed field pinch laboratory plasmas.     

Aspects of cell production in mantle tissue of Ciona intestinalis L. (Tunicata, Ascidiacea)

Renewal of cell population is needed in the tunic of ascidians, as the tunic cells are involved in many biological functions. Tunic cells are thought to arrive by migrating across the mantle epithelium into the tunic from the blood lacunae or the mesenchymal space. Electron microscope observations show that the mantle epithelium of Ciona intestinalis shares some proliferative characteristics, releasing cells into the tunic and thus providing an increase renewal of tunical cells in restricted zones of adult animals.     

Coordination properties of 3-functionalized beta-cyclodextrins. Thermodynamic stereoselectivity of copper(II) complexes of the A,B-diamino derivative and its exploitation in LECE

The bis-amino AB derivative of beta-cyclodextrin on the secondary rim was synthesised and spectroscopically characterised by different techniques. Its binary systems both with protons and copper(II) were thermodynamically characterised by pH-metric potentiometry. In addition the ternary systems with each of the enantiomers of tryptophan and alanine were investigated. A thermodynamic stereoselectivity was observed for the tryptophan enantiomers and this was exploited to separate them by capillary electrophoresis through a ligand exchange mechanism (LECE). LECE separation of racemates of phenylalanine and tyrosine was also obtained.     

Electron spectroscopic investigation of metal-insulator transition in Ce1-xSrxTiO3

We have carried out detailed electron spectroscopic investigation of Ce_1−x Sr_xTiO₃ exhibiting insulator-metal transition withx. Core level X-ray photoelectron spectra of Ce3d as well as resonant photoemission spectra obtained at the Ce4d→4f resonant absorption threshold establish Ce as being in the trivalent state throughout the series. Using the ’off-resonance’ condition for Ce 4f states, we obtain the Ti3d dominated spectral features close toE _F , exhibiting clear signatures of coherent and incoherent peaks. We discuss the implications of our findings in relation to the metalinsulator transition observed in this series of compounds. Dedicated to Professor C N R Rao on his 70th birthday