Electron deficiency in tetrahedral transition-metal clusters: electronic structure and magnetic properties of [Ru4(eta6-C6H6)4(mu3-H)4](2+)

Analysis of the electronic structure of the electron-deficient cluster cation [Ru4(eta6-C6H6)4H4](2+) (1(2+)) by density functional theory calculations shows a very small energy gap (0.06 eV) between the diamagnetic singlet state and the paramagnetic triplet state, as a consequence of the absence of a significant Jahn-Teller distortion in the molecular structure of 1(2+). Magnetic measurements of [1]Cl2, [1][BF4]2, and [1][PF6]2 show 1(2+) to be diamagnetic in the fundamental state, with some weak temperature-independent paramagnetism, depending upon the nature of the counterion.     

Adsorption of atomic hydrogen at a nanostructured electrode of polyacrylate-capped Pt nanoparticles in polyelectrolyte

Atomic hydrogen electrosorption is reported at crystallite sites of polyacrylate-capped Pt nanoparticles (d = 2.5 +/- 0.6 nm), by assembling nanostructured electrodes of polyacrylate-Pt nanocrystallites layer-by-layer in a cationic polyelectrolyte, poly(diallyldimethylammonium chloride). Cyclic voltammetry in 1 M H2SO4 revealed a strongly adsorbed hydrogen state and a weakly adsorbed hydrogen state assigned to adsorption at (100) and (110) sites of the modified nanocrystallites, respectively. Resolving hydrogen adsorption states signifies that surface capping by the carboxylate groups is not irreversibly blocking hydrogen adsorption sites at the modified Pt nanoparticle surface. Adsorption peak currents increased with increasing the number of layers up to 16 bilayers, indicating the feasibility of nanoparticle charging via interparticle charge hopping and the accessibility of adsorption states within the thickness of the nanoparticle/polyelectrolyte multilayers. Despite similarity in hydrogen adsorption in the cyclic voltammorgrams in 1 M H2SO4, negative shifts in adsorption potentials were measured at the nanocrystallite Pt-polyelectrolyte multilayers relative to a polycrystalline bulk Pt surface. This potential shift is attributed to a kinetic limitation in the reductive hydrogen adsorption as a result of the Pt nanoparticle surface modification and the polyelectrolyte environment.     

Evaluations of solid electrodes for use in voltammetric monitoring of heavy metals in samples from metallurgical nickel industry

Evaluation of different solid electrode systems for detection of zinc, lead, cobalt, and nickel in process water from metallurgical nickel industry with use of differential pulse stripping voltammetry has been performed. Zinc was detected by differential pulse anodic stripping voltammetry (DPASV) on a dental amalgam electrode as intermetallic Ni–Zn compound after dilution in ammonium buffer solution. The intermetallic compound was observed at –375 mV, and a linear response was found in the range 0.2–1.2 mg L^–1 (r²=0.98) for 60 s deposition time. Simultaneous detection of nickel and cobalt in the low g L^–1 range was successfully performed by use of adsorptive cathodic stripping voltammetry (AdCSV) of dimethylglyoxime complexes on a silver–bismuth alloy electrode, and a good correlation was found with corresponding AAS results (r²=0.999 for nickel and 0.965 for cobalt). Analyses of lead in the g L^–1 range in nickel-plating solution were performed with good sensitivity and stability by DPASV, using a working electrode of silver together with a glassy carbon counter electrode in samples diluted 1:3 with distilled water and acidified with H₂SO₄ to pH 2. A new commercial automatic at-line system was tested, and the results were found to be in agreement with an older mercury drop system. The stability of the solid electrode systems was found to be from one to several days without any maintenance needed.     

Optical Alignment of Organic Dopants in a Solid Gel Matrix: Dispersed and Grafted Rhodamine B Molecules

We study herein the rotational mobility of organic dye molecules and their ability to align on a strong optical electric field when they are encaged in the pores of an inorganic silica xerogel matrix. We compare the case of dye molecules simply dispersed in the pores of the gel—and possibly held by hydrogen bonds—to the case of molecules chemically grafted on the inner surface of these pores through covalent bonds. The study is led on hybrid silicon-zirconium based inorganic matrices doped with organic rhodamine B molecules. The stronger holding of the dopants when these are grafted to the matrix enhances the molecular alignment—and thus the induced anisotropy—as well as the remanence of this alignment. Furthermore, we show that submitting the samples to a supplementary drying at higher temperature tends to increase both the alignment anisotropy and its stability. We explain these results in terms of mobility of the molecules, in relation to their immediate environment.     

Beiträge zur Gewinnung von Hirudin,der Wirksubstanz des medizinischen Blutegels (Hirudo medicinalis L.)

Zusammenfassung Bei den vorliegenden Untersuchungen wurde Hirudin, die blutgerinnunghemmende Wirksubstanz von Hirudo medicinalis L., dadurch gewonnen, daß man Blutegel physiologische Kochsalzlösung, mit oder ohne Zusatz von roten Blutkörperchen, saugen ließ und den Darminhalt künstlich entnahm. Außer dem Darminhalt enthält auch die Futterrestlösung Hirudin, wodurch bewiesen wurde, daß der Egel diesen Wirkstoff auch in die Bißwunde abgibt. Das angereicherte Rohhirudin wurde auf seine gerinnunghemmende Wirkung mit Kaninchenblut und Pferdeblut getestet und seine Antithrombinwirkung, Wirkung auf die Rekalzifikationszeit, Prothrombinzeit und Thrombingerinnungszeit von Oxalatplasma untersucht. Die Untersuchungen zeigen, daß die II. Phase der Blutgerinnung beeinflußt wird. Der Temperatureinfluß (100°, 70° und 37°) auf Lösungen der Wirksubstanz wurde untersucht, ebenso die Wirkung angereicherter Rohprodukte auf das lebende Kaninchen. Bei wiederholter Injektion trat kein anaphylaktischer Schock auf.Die Reinigung des angereicherten Rohproduktes durch Papierelektrophorese wird beschrieben.Herrn Prof. Dr.A. Wacek zum 60. Geburtstag mit den besten Wünschen gewidmet (O. H.).     

(Eta5-pentamethylcyclopentadienyl)rhodium and -iridium complexes with weakly and strongly coordinating anions: isolation and first X-ray molecular structures of the tris(solvent) complexes [(C5Me5)M(acetone)2(H2O)][BF4]2 (M = Rh, Ir)

Several novel pentamethylcyclopentadienyl complexes of general formula [(C5Me5)IrL3][BF4]2 were prepared including the tris(solvent) precursors [(C5Me5)M(acetone)2(H2O)][BF4]2 (M = Rh, Ir) (1a,b). The X-ray molecular structures of 1a,b were determined at low temperature. Complexes 1a,b are isostructural, and both compounds crystallize in the monoclinic space group P2(1)/c with a = 10.157(3) A, b = 14.038(9) A, c = 16.335(2) A, beta = 99.73(2) degrees, and Z = 4 for 1a and with a = 10.107(9) A, b = 13.994(16) A, c = 15.996(34) A, beta = 99.61(12) degrees, and Z = 4 for 1b. The coordinated water molecule is hydrogen bonded to both BF4(-) anions. Reaction of 1a,b with pyridine (py) afforded the related tris(pyridine) complexes [(C5Me5)M(eta1-(N)-py)3][BF4]2 (M = Rh, Ir) (2a,b). Complex 2b was characterized by X-ray crystallography, monoclinic space group P2(1)/c with a = 8.665(3) A, b = 19.687(7) A, c = 18.408(5) A, beta = 94.17(3) degrees, and Z = 4. Moreover, we prepared the novel neutral compounds (C5Me5)M(eta2-NO3)(eta1-NO3) (M = Rh, Ir) (4a,b) where the anions are bonded to the metal center instead of a coordinating solvent as confirmed by X-ray study on the iridium complex 4b. The latter crystallizes in the orthorhombic space group Pcab with a = 13.032(4) A, b = 14.370(11) A, c = 14.839(18) A, and Z = 8.     

Topographical properties of polymer films deposited in capillaries for electrophoretic separations of large organic molecules

Topography and thickness of hydrophilic polymer coatings of fused-silica capillaries for capillary electrophoresis (CE) were investigated using atomic force microscopy (AFM), scanning electron microscopy (SEM), and profilometry. Three hydrogels, poly(2-hydroxyethyl methacrylate) [poly(HEMA)], poly(diethylene glycol monomethacrylate) [poly(DEGMA)], and poly(triethylene glycol monomethacrylate) [poly(TEGMA)], were deposited using two procedures, either by simple physical sorption of the polymers, or by derivatization of the capillary wall surface with glycidyl methacrylate (EPMA) followed by polymerization of the appropriate monomers. The performance of the modified capillaries was tested under CE conditions (decrease in the electroosmotic flow, EOF dependence on pH, separation of milk and standard proteins). It has been found that the most important property of the polymer coating is its thickness, whereas its topography and the degree of its hydrophobicity are less significant. Film deposition by physical adsorption is preferable to polymerization on the derivatized surface.     

Thioacylation reactions for the surface functionalization of phosphorus-containing dendrimers

The functionalization of phosphorus-containing dendrimers was easily achieved through thioacylation reactions involving new dendrimers capped with dithioester end groups and various functionalized amines. These reactions were successfully applied to the first generation (12 end groups) and the third generation of the dendrimer (48 end groups) and allowed their functionalization by various primary or secondary amines, alcohols, glycols, and azides. [reaction: see text]     

Development of cross-linked polystyrene-supported chiral amines featuring a fluorinated linker for gel-phase 19F NMR spectrometry monitoring of reactions

Ten cross-linked polystyrene-supported, protected chiral amines featuring both a spacer, comprising from 5 to 15 atoms, and a fluorinated linker have been successfully prepared. The development of the monitoring technique by gel-phase 19F NMR spectrometry on cross-linked polystyrene derivatives proved to be of high value in four steps of the process, as shown by the comparison of data gathered from both a classic NMR spectrometer and elemental analysis. Gel-phase 19F NMR spectrometry, thus, constitutes a useful technique that complements IR and 13C NMR spectrometries for the qualitative monitoring of reactions. In addition, quantitative determination of the conversion in a given transformation is possible, provided that 19F chemical shifts of the substrate and the product be different enough (Deltadelta>base width), as illustrated by the Mitsunobu coupling process (16-->17). The technique is nondestructive, and the samples used to monitor the reactions may be returned to the reaction medium. Deprotection of the above amines was achieved and furnished eight of the final resins in good to acceptable purity for future applications.     

Influence of response factors on determining equilibrium association constants of non-covalent complexes by electrospray ionization mass spectrometry

A method for determining the equilibrium association constant of a complexation reaction A + B left harpoon over right harpoon AB by electrospray ionization mass spectrometry is described. The method consists in measuring the relative intensities of the peaks corresponding to A and to AB in equimolar A-B solutions at different concentrations C(0). The results are fitted by a non-linear least-squares procedure, with the two variable parameters being the equilibrium association constant K(a) and a factor R, defined by I(AB)/I(A) = R x [AB]/[A]. The factor R is the ratio between the response factors of AB and A, and corrects for the relative electrospray responses of the complex and the free substrate A, mass discrimination of instrumental origin and/or moderate in-source dissociation. The method is illustrated with the following two systems: complexes between a double-stranded 12-base pair oligonucleotide and minor groove binders, and cyclodextrin complexes with alpha,omega-dicarboxylic acids. For the oligonucleotide complexes, it is found that the response of the complex is not dramatically different to the response of the free oligonucleotide duplex, as the double helix conformation is disturbed by the drug only to a minor extent. In the case of cyclodextrin complexes, these complexes were found to have a much higher response than free cyclodextrin. This may be due to the fact that cyclodextrin is neutral in solution, whereas the complex is charged, but it can also stem from the fact that a significant proportion of the complex is in a non-inclusion geometry. The present method requires the exact determination of the concentrations of the reactants and is applicable to 1 : 1 complexes.