Platinum conformations

The most usual forms of platinum or, more frequently, of the platinum alloys containing 5 or 10% of rhodium, are thin protective sheaths contoured to conform with the shape of the underlying refractory. Sheaths of this type, generally 0-25 mm to 0-65 mm thick, are widely employed to protect tank lips, skimmer blocks, stirrers, thermocouple pockets, etc. More substantial —thicknesses-up to 2-5 mm thick —are used to protect orifices whose dimensional accuracy must be maintained to a high degree. 

The [Pt(Se4)2]2 complex (133) has been prepared by the reduction of the platinum(IV) species [Pt(Se4)3]2 with excess borohydride.328 The X-ray structure of the complex shows that each of the five-membered rings adopts a half-chair conformation, with the platinum coordination sphere exhibiting slight distortion from a square-planar geometry.329... 

Coleman, Kobylecki, and Utley studied the electrochemical reduction of the conformationally fixed ketones 4-tert-butylcyclohexanone and 3,3,5-tri-methylcyclohexanone 82>. Stereochemically, the cleanest reductions took place at a platinum cathode in a mixture of hexamethylphosphoramide and ethanol containing lithium chloride. Under these conditions the equatorial alcohol predominated heavily (95% from 4-fer/-butylcyclohexane and 91% from 3,3,5-trimethylcyclohexanone).In acidic media roughly equal quantities of axial and equatorial alcohol were produced. It was suggested that organo-lead intermediates are involved in the reductions in aqueous media. This is reasonable, based upon the probable mechanism of reduction in acid 83F Reductions in acid at mercury cathodes in fact do result in the formation of... 

Chiral bis-(binaphthophosphole) (bis(BNP)) ligands have been used in the asymmetric hydroformylation of styrene. In solution, the free diphospholes display fluxional behavior. Consistent with their structure, the reaction of the bis(BNP) compounds with platinum(II) derivatives gives either cis chelate mononuclear complexes or trans phosphorus-bridged polynuclear derivatives. Coordination to platinum enhances the conformational stability of bis(BNP)s and diastereomeric complexes can be detected in solution. In the presence of SnCl2, the platinum complexes give rise to catalysts that exhibit remarkable activity in the hydroformylation of styrene. Under optimum conditions, reaction takes place with high branched selectivity (80-85%) and moderate enantio-selectivity (up to 45% ee). 

The polynuclear platinum compounds stand in vivid contrast to mononuclear platinum complexes because the predominant DNA lesions are long-range inter- and intrastrand cross-links where the sites of platination may be separated by up to four base pairs. The consequent structural and conformational changes in DNA are also distinct. 

Kasparkova, J. Zehnulova, J. Farrell, N. Brabec, V. DNA interstrand crosslinks of novel antitumor trinuclear platinum complex BBR. Conformation, recognition by HMG-domain proteins and nucleotide excision repair. J Biol Chem 2002, 277, 48076-48086. 

Orpen, A.G., Pringle, P.G., Smith, M.B., and Worboys, K., Synthesis and properties of new tris(cyanoethyl)phosphine complexes of platinum(0,II), palladium, II), iridium(I) and rhodium(I). Conformational analysis of tris(cyanoethyl)phosphine ligands,. Organomet. Chem., 550, 255, 1998. 

Figure 3.31 Head-to-head and head-to-tail conformers of bis(purine)-platinum(II) units. (Adapted from Figure 12.4 of reference 38.)...

Cyclohexaamylose-N-methylacetohydroxamic acid, preparation of, 23 254 Cyclohexadienes, 20 293 reaction with HCN, 33 19, 20 on silica, reactions of, 34 54-56-34 64 cracking, 34 55, 72 vibrational spectra, 42 243 Cyclohexadienyl radicals, ESR of, 22 300 1,4-Cyclohexanediols, conversion of ethers, mechanism, 35 361-364 Cyclohexanes, 33 101, 102, 103 autoxidauon of, 25 303 conformational analysis of, 18 9-17 dehydrogenation, 31 14, 21-22 benzene accumulation over platinum, 36 18... 

Fig. II. (a) Schematic representation of hydrocarbons adsorbed on the [111] plane of platinum. Intersections of the lines of triangular net denote positions of the centers of platinum atoms. (1) Cyclohexane (2) all-cis conformation of cij-l,3,5-hexatriene (3) transoid conformations of cis- and trans-1,3,5-hexatriene (S4). (b) Adsorption configurations of acetylene and ethylene found most probable according to LEED studies 141).

The greatest research effort on radiation sensitizers has focused on organic compounds however, platinum complexes conform to the hypotheses for radiation sensitizers since they are electron affinic and react preferentially with the hydrated electron in aqueous solution. Early studies of cisplatin in combination with radiation therapy suggested a synergistic effect in antitumor activity (50,51). Much of the initial data were obtained using cells in tissue culture (52), these data indicated that the potential of cisplatin to inhibit repair of radiation-induced damage to DNA could be an important contributor to the enhanced tumor cell killing seen in vivo by the combination of these two modes of treatment. 

Antitumor drugs cisplatin as, history, 37 175-179 platinum compounds future studies, 37 206-208 resistance to, 37 192-193 second-generation, 37 178 Antiviral agents, 36 37-38 AOR, see Aldehyde oxidoreductase Aphanothece sacrum, ferredoxins, amino acid sequence, 38 225-227 Apo-calcylin, 46 455 Apo-caldodulin, 46 449-450 Apoenzyme, 22 424 Apoferritin biosynthesis, 36 457 cystalline iron core, 36 423 Fe(III)distribution, 36 458-459 Fe(II) sequestration, 36 463-464 ferroxidase centers, 36 457-458 iron core reconstruction in shell, 36 457 mineralization, 36 25 Mdssbauer spectra, 36 459-460 optical absorbance spectra, 36 418-419 subunit conformation and quaternary structure, 36 470-471... 

The data for carbon monoxide adsorbed on platinum were found not to obey this equation but to conform more closely to the equation of the type... 

The trans-platinum complex forms a 2 1 complex with [18]crown-6 and two centro-symmetrically related —NH3 groups bind 3 alternate oxygen atoms on each face, Fig. 23a. The crown adopts the normal D3d conformation, and the three independent N-0 distances range from 3.04 to 3.31 A. 

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