Dipolar recoupling in NOESY-type 1H-1H NMR experiments under HRMAS conditions

[structure: see text]. The concept of dipolar recoupling is introduced to 1H-1H NOESY experiments performed under HRMAS conditions. Dipole-dipole couplings are selectively recoupled during the mixing period, while MAS ensures high resolution in the spectral dimensions. Incoherent dipolar exchange is replaced by amplified coherent processes, such that time scales for polarization transfer are shortened, and dipolar double-quantum techniques become applicable. In this way, dipole-dipole couplings, as well as J-couplings, can be individually measured.     

Intracellular photobleaching of 5,10,15,20-tetrakis(m-hydroxyphenyl) chlorin (Foscan) exhibits a complex dependence on oxygen level and fluence rate

The understanding of photosensitizer photobleaching is important not only for mechanistic studies, but also for the development of monitoring techniques for clinical dosimetry in photodynamic therapy. In this study, we investigated the intracellular photobleaching of 5,10,15,20-tetrakis(m-hydroxyphenyl)chlorin (mTHPC, Foscan) in the murine macrophage cell line J774A.1, using quantitative fluorescence imaging microscopy, microspectrofluorometry and microspectrophotometry. Using 652 nm laser irradiation, it was found that mTHPC exhibits oxygen- and fluence rate-dependent intracellular photobleaching. The kinetics showed an inverse dose-rate behavior, i.e. a reduction of fluence rate resulted in more photobleaching at comparable fluences. The effect of deoxygenation was found to be more complex, with decreased bleaching at low fluence rates and increased bleaching at higher fluence rates. The intracellular formation of reactive oxygen species was measured using 2',7'-dichlorodihydrofluorescein diacetate. The results are analyzed in terms of competitive Type-I and Type-II mechanisms.     

A möbius inversion of the ulam subgraphs conjecture

The generalized Eichinger matrices are defined asE = _j ⁿ ₁( _j S ^T S)^–1, where _j M denotes the matrixM withj th row and column deleted.S is the incidence matrix andM ^T is the transposed matrix. The conjectureS ^T SE = S _K ^TS _K , where SK is the incidence matrix of the complete graph, is proven for trees, simple cycles and complete graphs. The consequence of the conjecture isS _G ^T S _G (E _G -I) = S _G ^TS _G , whereG is the complementary graph ofG. It leads to graphs with imaginary arcs as the complements of graphs with multiple arcs.     

Behavior of heterogeneous macromolecular structures Part I: Microgels and coated microgels

Homopolymeric microgels composed of PMMA were prepared by emulsion polymerization in the presence of 0.5 % 1,4-butanediol divinylether (BVE) in an aqueous medium followed by careful removal of the soap. The microgels were coated with polystyrene (PS) by anionic grafting of living PS chains onto the surface. Both types of microgels were characterized by GPC and by static and dynamic light scattering in several solvents. A special model consisting of a hard core and a seam of dangling chains has been developed and applied to interpreting the light scattering data from the various solvents. The model gives consistent results, e. g. the core radius agrees well with the radius of gyration. In the coated microgels a strong expansion of the core as a result of the PS/ PMMA incompatibility is observed.Dedicated to Prof. Dr. H.-G. Kilian on the occasion of his 60th birthday.     

Production of large sodium clusters (Nax,.x⩽65) by seeded beam expansions

Seeded beam expansions of high-temperature sodium vapour in helium, neon, argon, krypton and nitrogen carrier gases are examined. Photoionization coupled with mass spectroscopic detection is used to determine beam constituents. Contrary to non-seeded supersonic expansions, in which the abundance of sodium clusters observed decreases exponentially with increasing cluster size, large abundances of higher clusters (Na_x, x ?65) are observed. Maxima centered at m/z = 161, m/z = 437 and m/z = 874 occur under certain conditions.     

Silacarbocycles from ring expansion

Ring enlargement of silicon heterocycles is accomplished from derivatives which contain an exocyclic chloromethyl substituent by reaction with aluminum halide catalyst or with potassium fluoride. Tricyclic derivatives with a silicon atom in a central five-, six-, or seven-membered ring form silins, silepins and silocins, respectively, and are isolated by quenching the product chlorosilanes with H₂O, MeOH, Na/MeOH, LiAlH₄, MeMgBr or MeLi. A stoichiometric quantity of fluoride ion also results in conversion of 9-chloromethyl-9-silaanthracene to 5-fluoro-dibenzo[b,e] silepin but the percent conversion of the 9-iodomethyl precursor is higher. The limitations of the two methods are discussed briefly.     

Design of low-toxic and temperature-sensitive anionic microemulsions using short propyleneglycol alkyl ethers as cosurfactants

The phase behavior of anionic microemulsions composed of water, sodium dodecyl sulfate (SDS), dodecane, and short propyleneglycol monoalkyl ethers (C(n)()PO(m)(); n = 3, m = 1 and n = 4, m = 2, 3) is studied. From the pseudoternary phase diagrams, it is inferred that C(n)()PO(m)() compounds have cosurfactant behaviors comparable to those of 1-butanol and 1-pentanol, which are the most efficient and widely used cosurfactants. In contrast to these alcohols, the C(n)()PO(m)() cosurfactants induce high temperature dependences in the SDS microemulsion systems. Furthermore, SDS/C(n)()PO(m)() microemulsions can be formed with small SDS concentrations (SDS/C(4)PO(3) mass ratio of 1/6.26). These have a low toxicity in contrast to systems containing genotoxic short ethyleneglycol ethers (C(n)()EO(m)()) as the cosurfactant. The strong temperature dependence can be favorable in the recovery of reaction products when the microemulsion is used either as a reaction medium or in extraction processes.