Covalent display of oligosaccharide arrays in microtiter plates

A covalent array for the display of complex oligosaccharides in microtiter plates has been developed. This strategy is conducive to the display of carbohydrates to proteins of interest such as lectins and antibodies, including the broadly neutralizing antibody 2G12 against HIV envelope oligomannose and can be cleaved from the surface for further characterization by mass spectrometry. The system was used to probe the multivalent interaction of 2G12 with an optimal epitope (Kd 0.1 muM).     

Electron ionization-induced fragmentation of N-(alkoxymethyl)anilides

Electron ionization-induced fragmentation patterns of the series of N-(alkoxymethyl)acetanilides and related formanilides and benzanilides have been studied. The main fragmentation reaction observed for all compounds studied is the loss of an alkyl radical from the N-alkoxymethyl group leading to the appropriate protonated N-acylformanilide derivatives. This reaction is accompanied by unusually high kinetic energy release. Other important fragmentations common for majority of the compounds studied are (i) loss of an aldehyde molecule derived from an alkoxyl group yielding an appropriate N-acyl-N-methylaniline, (ii) elimination of a C(n)H(2n)O(2) fragment derived from N-alkoxymethyl group and carbonyl group oxygen atom and (iii) formation of N-methyleneaniline radical cation.     

Orientation and Restricted Rotation of Lopsided Aromatic Ligands. Octahedral Complexes Derived from cis-RuCl(2)(Me(2)SO)(4)

The solution and solid state structures of two octahedral Ru(II) complexes, cis,cis,cis-RuCl(2)(Me(2)SO)(2)(py)(Me(3)Bzm) (Me(3)Bzm = 1,5,6-trimethylbenzimidazole, py = pyridine) (1) and cis,cis,cis-RuCl(2)(Me(2)SO)(2)(Me(3)Bzm)(2) (2), were compared. 2, the subject of a preliminary report, is described in more detail here. 1 has two possible geometric isomers with py trans to Cl in one (position "a") and trans to Me(2)SO in the other (position "b"), Me(3)Bzm occupying the other position in each isomer. The X-ray structure of 1 revealed that py is at "a". Since Me(3)Bzm is lopsided, each Me(3)Bzm has two possible orientations related by a rotation of approximately 180 degrees about the Ru-N3 bond; there are two possible atropisomers for each geometric isomer of 1 and four for 2. For 1, the solid state structure shows that Me(3)Bzm adopts the orientation with H2 (H on C between the two N's) pointing between the two cis Cl ligands, the same disposition as Me(3)Bzm "b" in 2 in the solid. For 1, the py signals (two broad py alpha and beta signals, a sharp gamma signal) in CDCl(3) show that py "a" is rotating on the NMR time scale and that only one atropisomer is present. This interpretation was supported by ROESY and EXSY (1)H NMR spectra. The (1)H NMR shift pattern and the NOE data can be understood best if Me(3)Bzm "b" remains primarily in the orientation found in the solid. The solution data for 1, with the nonlopsided and sterically less demanding py ligand, provide insight into the more complicated properties of 2. For 2, there is a marked dispersion of (1)H NMR signals of Me(3)Bzm "a" between the two atropisomers, which have nearly equal stability. One atropisomer is a head-to-head (HH) and the other a head-to-tail (HT) species. Me(3)Bzm "a" flips between the two species. Thus, ligand "a" is fluxional in both complexes. The dispersion of Me(3)Bzm "a" signals is due to the effect of Me(3)Bzm "b" anisotropy. For 1 and both atropisomers of 2, Me(3)Bzm "b" prefers one orientation, which appears to be the most hindered orientation. We postulate that the H2 of Me(3)Bzm "b" is electrostatically attracted to the two cis halides, accounting for this surprising result. Crystallographic details for 1 are as follows: C(19)H(29)Cl(2)N(3)O(2)RuS(2), P2(1)/c, a = 10.947(1) ?, b = 9.046(1) ?, c = 24.221(2) ?, D(calcd) = 1.580 g cm(-)(3), Z = 4, R = 0.026 for 4627 independent reflections.     

On the role of the ground state Tb(III)/acetylacetone complex in sensitized emission of Tb(III) in ethanol solution

Summary The Tb(III)-acetylacetone system in ethanol solution has been studied by spectroscopic methods. The formation of a Tb(III)/acetylacetone (1:1) complex in the ground state has been proved and its stability constant determined,K=(0.97±0.06)·10⁴dm³mol^–1. The role of this complex in the spectrofluorimetric determination ofLn(III) ions in the presence of acetylacetone has been discussed.

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Über die Rolle eines Tb(III)-Acetylaceton-Komplexes im Grundzustand in der sensibilisierten Emission von Tb(III) in Ethanol-Lösung

Zusammenfassung Das Tb(III)-Acetylaceton-System in Ethanol-Lösung wurde mit spektroskopischen Methoden untersuchung. Die Bildung eines Tb(III)-Acetylaceton(1:1)-Komplexes im Grundzustand wurde bestätigt und seine Stabilitätskonstante bestimmt,K=(0.97±0.06)·10⁴dm³mol^–1. Die Rolle dieses Komplexes in der spektrofluorimetrischen Bestimmung vonLn(III)-Ionen in Gegenwart von Acetylaceton wurde erörtert.

     

POST-TREATMENT INTERACTIONS OF PHOTODYNAMIC and RADIATION-INDUCED CYTOTOXIC LESIONS

The interaction of chloroaluminum phthalocyanine-sensitized photodynamic treatment and gamma-irradiation was studied in confluent murine L929 fibroblasts. When the cells were given the combined treatments and immediately subcultured for determination of cell survival by colony formation, the data indicate independent actions of each modality. However, when subculture was delayed for 1 h, a substantial fraction of cells treated with a sub-lethal dose of PDT followed by 5 Gy gamma-radiation detached from the monolayer. Most of these detached cells were no longer clonogenic. The mode of photosensitized cell killing was found to be different from that of ionizing radiation-induced cell killing. Photosensitized cell killing was accompanied by morphological changes in the cells and extensive DNA degradation within one hour following the treatment. When chloroaluminum phthalocyanine pretreated cells were exposed to a sublethal fluence of light (6 kJ/m2) and a lethal dose of gamma-radiation (5 Gy), DNA degradation was enhanced, and about 20% of the cell population appeared to undergo the type of cell death typical of photodynamic treatment. Thus, although different initial lethal lesions are induced by photodynamic treatment and by ionizing radiation, interactions may occur during processing of the damage.     

Phenomena related to electron beams in solar flares

Starting from basic observational characteristics of solar flares the flare physical processes are briefly described. The role of electron beams in such a flare scenario is expressed. The observational manifestations of electron beams as, e.g., type III and U radio bursts are presented. Then results of numerical modelling of these processes are shown. Besides the magnetic field-line reconnection process which is considered to be a primary flare one, the main attention is devoted to the evolution of electron beams in flare loops, to the interpretation of U bursts, to the electron beam bombardment of deep and dense layers of the solar atmosphere and to accompanied processes as the evaporation process and the asymmetry of optical chromospheric lines.Presented at 17^th Symposium Plasma Physics and Technology, Prague, June 13–16, 1995.This work was supported by Grant Agency of Academy of Sciences of Czech Republic, Grant No. 303404.     

Morin hydrate as pro-ecological antioxidant and pigment for polyolefin polymers

In our studies, we propose the use of natural, pro-ecological substances, such as flavonoids to protect elastomers against ageing. One of these substances, namely morin hydrate, was incorporated into ethylene–octene rubbers (Engage); then the vulcanisates of Engage containing the antioxidant under investigation were subjected to ageing processes. The changes in deformation energy, colour and cross-linking density and OIT index of the vulcanisates of Engage were measured before and after each ageing process. The test results obtained show that morin hydrate has a very positive influence on the stability of the vulcanisates of Engage, protecting them against the negative effects of ageing. In addition to its anti-oxidative function, morin hydrate changes the colour of the final polymeric product, fulfilling the role of a natural pigment. Thus, morin hydrate is not only a natural antioxidant but also a pigment in the polymers, imparting to them the features of pro-ecological materials.     

Energy efficient iron based electronic field cycling magnet

A new concept for an energy efficient electromagnet for fast field cycling NMR applications as well as its construction and first test results are presented. The magnet, which provides a rectangular sample space of 17 × 25 mm, has an iron yoke and pole pieces optimised with respect to the B₀ homogeneity. The maximum field is 0.66 T at a current of 320 A; its field inhomogeneity for a cylindrical sample (length 7 mm, diameter 6 mm) is about 50 ppm. The power dissipation during polarisation at 0.55 T is as low as 1.4 kW. The magnet is powered by a commercially available power supply and can be rapidly switched with a slew rate of 0.55 T/ms. The system has shown a stability of 50 ppm/h.