We report the synthesis of six new dendrimers built around a [Ru(bpy) 3 ] 2+ -type core (bpy ) 2,2′bipyridine) and bearing up to 24 4′-tert-butylphenyloxy or 48 benzyl units in the periphery. The metallodendrimers were obtained by complexation of ruthenium trichloride or Ru(bpy) 2 Cl 2 with bipyridine ligands carrying dendritic wedges in the 4,4′-positions. The absorption spectra and luminescence properties (spectra and lifetimes at 77 and 298 K; quantum yields at 298 K) of the six novel compounds are reported. All of them show the characteristic luminescence of the [Ru(bpy) 3 ] 2+ -type core unit. The dendritic branches protect the luminescent excited state of the core by dioxygen quenching. For the three compounds containing the 4′-tert-butylphenyloxy peripheral units, the electrochemical behavior and the excited-state quenching via electron transfer were also studied. The electrochemical experiments have evidenced an oxidation and three reduction one-electron processes centered in the [Ru(bpy) 3 ] 2+ -type core and two multielectron oxidation processes involving the dioxybenzeneand oxybenzene-type units of the dendritic branches. The core of the largest dendrimer shows an electrochemical behavior typical of encapsulated electroactive units. The reaction of the luminescent excited state of the [Ru-(bpy) 3 ] 2+ -type core with three electron-transfer quenchers (namely, methyl viologen dication, tetrathiafulvalene, and anthraquinone-2,6-disulfonate anion) was found to take place by a dynamic mechanism in all cases. The quenching rate constants, obtained by Stern-Volmer kinetic analysis, are compared with those found for the simple [Ru(bpy) 3 ] 2+ complex. The results show that, for each quencher, the value of the rate constant decreases with increasing number and size of the dendritic branches. For the second-generation dendrimer containing 24 4′-tert-butylphenyloxy units at the periphery, the rate constant of the reaction with methyl viologen is more than 1 order of magnitude smaller than that of the "naked" [Ru(bpy) 3 ] 2+ complex. All the experiments were performed in acetonitrile solution, except for luminescence experiments at 77 K where butyronitrile was used.
We report the synthesis and the photophysical properties of Ðrst and second generation dendrimers built around a core (bpy \ 2,2@-bipyridine) and bearing 12 and 24 naphthyl units, respectively, in the periphery. The [Ru(bpy) 3 ]2m etallodendrimers were obtained by complexation of ruthenium trichloride with bipyridine ligands carrying dendritic wedges in the 4,4@-positions. Since the chromophoric groups present in the dendritic complexes are separated by aliphatic connections, interchromophoric interactions are weak and the absorption spectra of the metallodendrimers are essentially equal to the summation of the spectra of the chromophoric groups which are present in their structures. The " free Ï wedges show an intense emission band in the region of the naphthyl-type units. Such a band, however, is almost completely absent in the emission spectra of the metallodendrimers, which exhibit the visible emission band characteristic of their unit, regardless of the excitation [Ru(bpy) 3 ]2`-type wavelength. These results show that a very efficient energy-transfer process takes place from the potentially Ñuorescent excited states of the aromatic units of the wedges to the metal-based dendritic core (antenna e †ect). We have also found that the dendrimer branches protect the RuÈbpy based core from dioxygen quenching.
New chiral dendrimers with planar-chiral, cycloenantiomeric and topologically chiral cores were prepared in yields of up to 90% starting from a racemic 4-hydroxy[2.2]paracyclophane, a [2]rotaxane with sulfonamide groups in the wheel and axle positions and [2]catenane with a sulfonamide group in both of its macrocycles. The separation of the racemic mix-
COMMUNICATIONS out in the same way. but without the addition of enzyme. Oxidation of amines: 2-, 3-, or 4-chloroaniline (78 FM), H,O, (44.4 p~) , and 1 M sodium acetate buffer (pH 4.5) The reaction was started by the addition of 0.5 u (determined by the monochlorodimedone assay) CPO-P or CPO-T to 1 mL of the mixture. The reaction was carried out at 30 C (3-chloroaniline: 30 min; 2.. 4-chloroaniiine. 50 min). The products were identified by HPLC-coinjection. O.Yidrriion.s wirh peruci'iii' u c i d Under identical experimental conditions, peracetic acid was used instead of H, O, enzyme. (200 pnol CH,CO,H instead of 150 Fmol H,O,). In the monochlorodimedone assay, peracetic acid was used in a concentration of 72 p~ (instead of 7200 p~ H,O,).'iiiutii irm~forinutioii ofperacetic acid hy mass spectrometry: sectorfield mass spectrometer Jeol JMS-700 MS, high-resolution CI-MS with isobutane as reactant gas. positile ion mode, resolution R = 8000. accumulation of 5-10 scans of the accelerating voltage (m/r 56-90,s s per cycle), quasi-molecular ion [ M + HIi (calcd. for C,H,O, 77.0239, found: 77.0261), internal mass calibration with ions derived from isobutane and the solvent. Aliquots (2.5 mL) of a 37 mM solution of peracetic acid in 1 M \odium acetate buffer (pH 5.5) were a) incubated with 5.5 mg (ca. 50 u) CPO-T for 10 min at room temperature (RT). b) incubated with 5.5 mg trypsin for 1 h at RT. or c) kept at RT without the addition of enzyme. The solutions were then acidified with H,SO, to pH 1 and extracted with ether (1 mL). The extracts were concentrated to approximately 50 pL in a stream of N, and introduced into the mass spectrometer through the reference inlet. Whereas peracetic acid was clearly present in approximately the same concentration in experiments (b) and ( c ) , no peracetic acid could be detected by MS in the extract from (a). Furthermore. whereas the pungent smell of peracetic acid persisted in the experiments (h) and (c). this typical odor vanished immediately after the addition of enzyme in experiment (a) Hydrolow uriiviti f t~~~~i c u l~. i p e r~~n e n / .~~.The enzymes were added to a solution of 0.1 pmol p-nitrophenylacetate in 2.0 mL 1 M sodium acetate buffer (pH 5.5) and 10 pL trri-but$ alcohol. The reaction was followed by the decrease of extinction at i = 317 nm. Inliihifion rrperinimr.\' In a typical experiment, 0.04 u CPO-T (determined by the rnonochlorodimedone assay) in 500 pL of water or sodium acetate buffer (pH 5.5, various concentrations) were incubated with a solution of PMSF (4 pmol) in tertbutyl alcohol (20 wL) at 50 C. The remaining enzymatic activity was determined at various incubation times as described above.
Monofunctionalized Dendrons of Different Generations – as Reagents for the Introduction of Dendritic Substituents In recent years dendrimers become more and more important not only in organic chemistry. They represent a new class of molecules with unique characteristic features. But dendrimers represent not only designed molecular architecture. They stand for a new concept in chemistry. They can be used to alter the properties of already existing molecular skeletons or they can be used to transfer new properties to a classical functional unit. This means that functionalized dendrimers and dendrons (dendritic building blocks) can be regarded as reagents for the preparation of new compounds with dendritic properties. In this article the synthesis and the practical use of appropriate dendritic reagents is explained. Furthermore we introduce the new technical terms „{n} dendryl‐”︁ for dendritic substituents of n generations and „dendriagent”︁ which stands for dendritic reagents. Moreover we give a short outlook on future developments.
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