A comparison method for ordinary differential systems

We study the existence, uniqueness and continuous dependence of solutions for systems of ordinary differential equations including also delay problems with initial and periodic conditions. Results are obtained by using the comparison method and the theory of differential inequalities. This revised version was published online in June 2006 with corrections to the Cover Date.     

Acetylcholinesterase-inhibiting alkaloids from Zephyranthes concolor

The bulbs and aerial parts of Zephyranthes concolor (Lindl.) Benth. & Hook. f. (Amaryllidaceae), an endemic species to Mexico, were found to contain the alkaloids chlidanthine, galanthamine, galanthamine N-oxide, lycorine, galwesine, and epinorgalanthamine. Since currently only partial and low resolution (1)H-NMR data for chlidanthine acetate are available, and none for chlidanthine, its 1D and 2D high resolution (1)H- and (13)C-NMR spectra were recorded. Unambiguous assignations were achieved with HMBC, and HSQC experiments, and its structure was corroborated by X-ray diffraction. Minimum energy conformation for structures of chlidanthine, and its positional isomer galanthamine, were calculated by molecular modelling. Galanthamine is a well known acetylcholinesterase inhibitor; therefore, the isolated alkaloids were tested for this activity. Chlidanthine and galanthamine N-oxide inhibited electric eel acetylcholinesterase (2.4 and 2.6 × 10(-5) M, respectively), indicating they are about five times less potent than galanthamine, while galwesine was inactive at 10(-3) M. Inhibitory activity of HIV-1 replication, and cytotoxicity of the isolated alkaloids were evaluated in human MT-4 cells; however, the alkaloids showed poor activity as compared with standard anti-HIV drugs, but most of them were not cytotoxic.     

Synthesis and inclusion properties study of some mono 6-amino ??-cyclodextrin dimers bridged by N,N-succinyldiamide linkers

Methylated and partially methylated cyclodextrin homo- and heterodimers linked by diamidosuccinic bridges were synthesised and their inclusion properties were evaluated using NMR and isothermic microcalorimetric measurements ITC. The selective binding of ligands, such as bisadamantyl derivatives, to the cavities of unprotected cyclodextrin dimers showed the equimolar formation of bidendate inclusion complexes (2:2, two ligand guest to two cavities host).     

Effect of electron correlation on the forced electric dipole transition probabilities in fn systems

A method for the investigation of the effects of electron correlation on the forced electric dipole transition probabilities between levels of the fⁿ configuration is presented. The approach is based on double perturbation theory and on the application of effective operators. Effective operators describing the correlation effects are generated for various classes of perturbing configurations in terms of generalized unit tensor operators. A classification scheme for the possible operators is presented. In general, one- and two- particle operators are obtained. The latter do not appear in the standard Judd-Ofelt theory. One-particle operators dependent on unit tensor operators of odd rank are also new. The other one-particle operators are of the form considered in the Judd-Ofelt theory. However, the present results indicate that the interpretation of the empirical parameters of this theory should be modified to take into account electron correlation effects.     

Electron-correlation third-order contributions to the electric dipole transition amplitudes of rare earth ions in crystals

In ab initio studies of the impact of electron correlation effects of f ? f transition probabilities much numerical work is concerned with evaluating radial factors. These terms are expressed as products of the radial integrals summed over all excited orbitals including those in the continuum. To simplify the evaluation of these sums, for the first time in f ? f transition theory, the perturbed-function approach has been applied. The detailed analysis of numerical results obtained for the radial factors contributing to the transition amplitudes for Pr³⁺ are presented. Special attention is paid to studying the impact of the incompleteness of the radial basis set upon the radial factors occurring in f ? f electric-dipole transition theory.     

FAB of peptides study: Deuterated glycerol matrix and selectively deuterated peptides. Part II

Abstract

Two peptides, H-Gly-Lys-Thr-Gly-Pro-Gly-OH (1) and Leu-enkephalin (2) FAB-PI spectra in normal and deuterated glycerol have been studied. Two C-deuterated and D₂O exchanged analogs have been used to compare their fragmentation to unlabelled peptides.

The mass spectrometry of peptides has become a particularly interesting field with the wide spread adoption of the FAB technique. This technique enables one to record the quasi-molecular ion (in both positive and negative modes as M+1 or M?1 respectively) and to extract from the spectrum valuable information on the peptide sequence.     

Infrared and Raman spectroscopic studies of the charge localization in one‐dimensional organic metals (DMtTTF)2X (X = ReO4, ClO4) with regular organic stacks

A novel selective synthesis of the unsymmetrically substituted tetrathiafulvalene dimethyltrimethylene‐tetrathiafulvalene (DMtTTF) is described together with its electrocrystallization to the known conducting mixed‐valence ClO₄^– and ReO₄^– salts. Infrared (IR) and Raman spectra of the two isostructural quasi‐one‐dimensional cation radical salts (DMtTTF)₂X (X = ReO₄^–, ClO₄^–) are investigated as a function of temperature (T = 5–300 K). At ambient temperature, these salts show metallic‐like properties and below T_ρ = 100–150 K, they undergo a smeared transition to semiconducting state. To study this charge localization, we measured temperature dependence of polarized IR reflectance spectra (700–16 000 cm^–1) and Raman spectra (150–3500 cm^–1, excitation λ = 632.8 nm) of single crystals. For both compounds, the Raman data and especially the bands related to the C=C stretching vibration of the DMtTTF molecule show that the charge distribution on molecules is uniform down to the lowest temperatures. Similarly, IR data confirm that down to the lowest temperatures, there is neither charge ordering nor important modification of the electronic structure. However, the temperature dependence of Raman spectra of both salts reveals a regime change at about 150 K. Additionally, using Density Functional Theory (DFT) methods, the normal vibrational modes of the neutral DMtTTF⁰ and cationic DMtTTF⁺ species and also their theoretical IR and Raman spectra were calculated. The theoretical data were compared with the experimental IR and Raman spectra of neutral DMtTTF⁰ molecule. Copyright © 2013 John Wiley & Sons, Ltd.     

Fractional equations of Volterra type involving a Riemann–Liouville derivative

In this paper, we will discuss the existence of solutions of fractional equations of Volterra type with the Riemann–Liouville derivative. Existence results are obtained by using a Banach fixed point theorem with weighted norms and by a monotone iterative method too. An example illustrates the results.     

Positive solutions for three-point one-dimensional p-Laplacian boundary value problems with advanced arguments

This paper considers the existence of positive solutions for advanced differential equations with one-dimensional p-Laplacian. To obtain the existence of at least three positive solutions we use a fixed point theorem due to Avery and Peterson.