Measurement of the Seperation between Atoms beyond Diffraction Limit

We propose a scheme to obtain the distance of two identical atoms placed inside the standing wave field by monitoring the collective resonance fluorescence spectrum emitted by the two particles. We find three different parameter ranges, depending on the distance of the atoms as compared to the transition wavelength. For large interparticle distances, dipole-dipole coupling is negligible, and the main system evolution arises from the interaction with the standing wave field. In the small-distance limit, the dynamics is dominated by the dipole-dipole interaction. Finally, in the intermediate region, a rich interplay of the various couplings arises, which however is lifted for strong driving laser fields. The present measurement procedure allows us to distinguish the three cases. In each of the cases, we show how to determine the distance of the two particles and their respective positions relative to the nodes of the standing wave field with fractional-wavelength precision.     

Analysis of metabolites of glucose pathways in human erythrocytes by analytical isotachophoresis

A method for the quantitative determination of the major anionic constituents of fountain solutions, typically mono-, di- and hydroxycarboxylates, alkylbenzenesulfonates, and inorganic anions, including orthophosphate and polyphosphates, is presented here for the first time. The analytical problems arising from extensive co-elution of many of these analytes on an ion-exchange column have been resolved through a combination of (i) careful selection of the concentration gradient of the sodium hydroxide eluent; (ii) parallel analysis by ion-exclusion chromatography; and (iii) determination of total phosphorus by inductively coupled plasma atomic emission spectrometry.     

Neutron diffraction study of [H(4)Co(4)(C(5)Me(4)Et)(4)], a tetrahedral metal cluster complex with four face-bridging hydride ligands

A single-crystal neutron diffraction analysis of the cluster complex [H(4)Co(4)(C(5)Me(4)Et)(4)] was carried out on the new quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin. The structure consists of four face-bridging hydrides attached to a tetrahedral cobalt metal core. Average distances and angles in the core of the molecule are as follows: Co-Co = 2.571(8), Co-C = 2.158(6), Co-H = 1.749(7), H.H = 2.366(9) A; Co-H-Co = 94.6(3), H-Co-H = 85.1(3) degrees. The hydride ligands are located off the Co-Co-Co planes by an average distance of 0.923(8) A. It is suggested that the dimensions of the HCo(3) fragments found in this molecule provide reasonable estimates for analogous distances and angles associated with chemisorbed H atoms situated on the 3-fold hollows of a cobalt surface. Crystallographic details: space group P2(1)/a (monoclinic); a = 21.979(2), b = 10.924(1), c = 34.406(2) A; beta = 90.81(1) degrees; Z = 8. Final agreement factor: R(F) = 0.099 for 3779 reflections [I > 2sigma(I)] collected at 20 K.     

Isotachophoretic analysis of the dihydrofolate reductase reaction in the presence of methotrexate and ascorbic acid

The antifolate methotrexate (MTX) is widely used in cancer chemotherapy. In this study, we show that MTX (MTX-Glu1) and MTX-polyglutamates (MTX-Glu2-5) strongly inhibited the growth of the leukemic cell line MOLT-4. This effect, however, was mitigated by ascorbic acid. We investigated whether ascorbic acid is able to reduce dihydrofolic acid (DHF) to tetrahydrofolic acid (THF) directly or by circumventing the MTX inhibition of dihydrofolate reductase (DHFR). The inhibition of this NADPH-dependent reduction of DHF by MTX-Glun in the absence or presence of ascorbate, was determined by analytical isotachophoresis. Using 0.01 M HCl/histidine, pH 6.0, as a leading electrolyte (L) and 0.005 M 2-(N-morpholino)ethanesulfonic acid (MES)/histidine, pH 6.0, as a terminating electrolyte (T), MTX-Glun derivatives including MTX-Glu1 could be easily separated, whereas the quantitative estimation of THF was not possible. A quantitative characterization of the DHFR reaction by measuring NADPH, NADP+ and ascorbate was achieved with another system (L: 0.01 M HCI/beta-alanine, pH 3.73; T: 0.01 M caproic acid, pH 3.27). Nanomolar concentrations of MTX-Glu1-5 inhibited consumption of NADPH and production of NADP+. Ascorbic acid was not able to reduce DHF, neither directly nor after inhibition of DHFR by MTX. However, ascorbic acid seemed to diminish the oxidation of THF and this may account for its capacity to reduce the inhibitory effect of MTX on MOLT-4 cells.     

Mechanisms of reduced human vascular cell migration after photodynamic therapy

Restenosis results from intimal hyperplasia and constrictive remodeling following cardiovascular interventions. Photodynamic therapy (PDT) has been shown to inhibit intimal hyperplasia in vivo by preventing neointimal repopulation of the treated vessel. This study was undertaken in an attempt to further dissect the mechanisms by which PDT acts on secreted and extracellular matrix proteins to inhibit migration of cultured human vascular cells. PDT of three-dimensional collagen gels inhibited invasive human smooth muscle cell (SMC) migration, whereas cell-derived matrix metalloproteinase production remained unaltered. Additionally, PDT generated cross-links in the collagen gels, a result substantiated in an ex vivo model whereby PDT rendered the treated vessels resistant to pepsin digestion and inhibited invasive migration of SMC and fibroblasts. These data support the premise that by inducing matrix protein cross-links, rendering the vessel resistant to degradation, in vivo PDT inhibits repopulation of the vessel and therefore intimal hyperplasia.