Osmium tetroxide adducts

FIb.1. ORTEP drawing (50% ellipsoids) of the one-to-one CM-osmium tetroxide adduct Cgo(( 04)(4-tM-butylpyridine)2 showing the relationship of the m unit with the carbon duster. 

Osmium tetroxide, 183, 184, 189, 221, 224 Oxetane photochemical adducts, 294 Oxidative degradation of 19-substituted steroids, 275... 

Reaction with fluoride ion forms the adduct oxofluoro ion, [0s04F2]2. For example, osmium tetroxide reacts with sodium fluoride to form an oxofluoro salt of sodium ... 

Figure 10. Adduct of C60 with osmium tetroxide. Figure 11. Adduct of C70 with Ir(CO)Cl(PPh3)2.

The distortions induced in the DNA double helix by the interstrand cross-links have been characterized by several techniques. As judged by chemical probes (diethyl pyrocarbonate, hydroxylamine, osmium tetroxide), antibodies to cisplatin-modified poly(dG-dC)-poly(dG-dC), natural (DNase I) and artificial (1,10-phenanthroline-copper complex) nucleases, the cytosine residues are accessible to the solvent, and the distortions are located at the level of the adduct [48-50]. From the electrophoretic mobility of the multimers of double-stranded oligonucleotides containing a single interstrand cross-link [50] it is deduced that the DNA double helix is unwound (79°) and its axis is bent (45°). 

Osmium tetroxide forms very stable, five-coordinate adducts with several nitrogen donors, e.g., quinuclidine or hexamethylenetetramine1-5. 

A THC and other active constituents are believed to be metabolically converted to substances oxidized at C(7), and this oxidation has been carried out by osmium tetroxide hydroxylation of A THC (333) and subsequent removal of the tertiary hydroxy-group (Scheme 20). The isomerization of the double bond to A THC is most conveniently carried out by photo-isomerization in propan-2-ol and xylene for 14 days, " although a second method is available that depends on an El elimination reaction of the hydrogen chloride adduct of A THC, using a sterically hindered base (after blocking the phenolic hydroxy-group). ... 

Addition has also been shown to occur when the pyridinlum iodide (139) is irradiated. The product Is assigned the structure (140) and the relevance of this reaction to the photoreactivity of Kosower solvent polarity probes has been discussed. The use of osmium tetroxide to hydroxylate alkenes is a well known procedure which is often carried out in aromatic solvents. These arene solvents form charge transfer complexes with the osmium tetroxide and the photochemistry of these has now been examined. It is shown that with benzene and alkyl benzenes isolable adducts are formed that from benzene Is assigned structure (141). 

Studies of redox-active metallointercalation agents in the presence of dsDNA have been done with solutions containing the redox complexes of cobalt, iron and osmium [64,68,72,95]. Osmium tetroxide complexes with tertiary amines (Os, L) have been used as a chemical probe of DNA structure. The simultaneous determination, based on a sufficient peak separation on the potential scale of (Os, L)-DNA adducts and free (Os, L), was obtained by Fojta et al. [96] using a p5Tolytic graphite electrode. 

A successful X-ray analysis of pure C o could only be performed as late as 1991, but the cage-Uke structure and the extraordinary symmetry of the molecule had already been demonstrated before by measuring several crystalline derivatives of the fullerene. The first fuUerene compound characterized by X-ray analysis was the adduct with osmium tetroxide (Figure 2.31). 

Osmylation and Epoxidation With osmium tetroxide, carbon nanotubes react as expected for a compound containing double bonds. The osmylation adduct with the respective double bond being replaced by two C-O-bonds is formed as shown in Figure 3.78. However, the process is normally conducted in a photochemical way here. The intermediates thus obtained can be transformed into hydroxylated nanotubes by hydrolysis. In doing so, it is advisable to effect a reoxidation of the resultant osmium(Vl) by hydrogen peroxide in order to minimize the consumption of osmium. The osmylation of carbon nanotubes is reversible so the process may also be employed for purification or separation steps. Contrary to an ozonoly-sis with subsequent reductive work-up, the osmylation does not give rise to holes in the side wall. Hence the electronic structure is less affected. 

The first pure fullerene derivative to be prepared was C5o(0s04)(4-t-butylpyridine)2. The X-ray crystal structure of this compound provided direct evidence that the proposed structure for C o was correct. Osmium tetroxide, a powerful oxidizing agent, can add across the double bonds of many compounds, including polycyclic aromatic hydrocarbons. When OSO4 was reacted with C50 and 4-ferf-butylpyridine, 1 1 and 2 1 adducts were formed. The 1 1 adduct has been characterized by X-ray crystallography, and has the structure shown in Figure 13.37. 

Fig. 14 DNA modified with osmium tetroxide, 2, 2 -bipyridine (Os, bipy). (A), structure of the Os,bipy adduct with T residue. (B), AdTS DP voltammograms of (1), Os,bipy-modified DNA and (2), unmodified ssDNA Os, catalytic peak yielded by the DNA adduct III, peak due to reduction of A and C. Inset, cyclic voltammogram of the (1). modified and (2), unmodified DNA showing reversible faradaic peaks of the DNA-Os,bipy adduct. Background electrolyte 0.3 M ammonium formate, 50 mM sodium phosphate, pH 6.9. [242, 359] R. Kizek, L Havran, M. Fojta, and E. Paletek, Bioelectrochemistry, in press).

Covalent adducts and/or noncovalent complexes of DNA with some chemicals, including carcinogens or cytostatics, produce specific electrochemical signals. Appearance of specific peaks was observed on DNA interactions with mitomycin C, osmium tetroxide complexes, DM, aromatic amines, and a variety of other DNA binders (Sect. 12.7). 

C36H22CU2F12 208, Bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato(N-pheny 1-2-hydroxybenzyIideniminato-/Li 0)copper (II)), 42B, 863 C3gH24N2O4OS, Osmium tetroxide - 9-methylbenzanthracene - bis(pyridine) adduct (toluene solvate), 43B, 1378 C36H2gF9N2Nd07S3, Tris(thenoyltrifluoroacetonato)-1,2-di(4-pyridyl)-ethaneaquoneodymiumdll), 42B, 924... 

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