Silver ion complexes

Silver ion also catalyzes nucleophilic reactions of thiol esters, including reactions of acetylhomocysteine thiolactone (12) and diethylethylphosphonothiolate (52). In the first reaction, an insoluble complex of silver ion and the substrate was first produced at pH 7.5, which then reacted with the nucleophile, in this case an amino group of a protein. In the second reaction silver ion complexes of the substrate were also postulated, on the basis that silver ion complexes with sulfur are much more stable than those with oxygen (I). The complexes postulated were 1 1 and 2 1 silver ion-substrate complexes. These complexes were suggested to react with the nucleophiles, water and fluoride ion, giving as products phos-phonic acid and phosphonyl fluoride, respectively, and silver mercaptide. It is evident that the last reaction at least must involve only the direct interaction of a silver ion with the sulfur atom of the thiol ester without chelate formation. Therefore it appears the metal ion-catalyzed reactions of thiol esters are unique, in that they involve complex formation, but not chelate formation in their catalytic mechanism. 

There are factors other than olefin basicity and the steric effects of substituent groups on the olefin which can affect the stability of the silver ion complex. These include the energy required to displace solvate molecules from the coordination sphere of the metal ion and the degree of association between the cations and anions, especially in concentrated solutions or in solid salts. 

The marked difference between vc=c iid t for ethylene in the silver ion complex and in complexes with the other transition metals suggests either a much weaker coordinate bonding to silver or at least a smaller TT component in the coordinate bond. In this instance the t value is somewhat below that of free ethylene indicating a net transfer of charge from olefin to metal as opposed to the apparent net charge transfer from metal to olefin with the other metals. As has been suggested previously (152, 232, 403) the a component of the coordinate bond may predominate in... 

The nucleus or development center in physical development can be described as a dual electrode on which the reduction of silver ion to silver and the oxidation of developing agent take place simultaneously. Electrochemical measurements of silver physical development in a hydroquinone/Phenidone physical developer with silver ion complexed with thiocyanate proceed as a catalytic electrode process [39]. 

Figure 21. Chemical and physical development. In chemical development the silver ion source is solid silver halide. In physical development the silver ion source is a soluble silver ion complex,...

A minor shift in redox potential is caused by silver ion complexation of the diferrocenyl-monocryptand complex. In fact, the silver-free ferrocene ligand undergoes a single-step two-electron oxidation at E° = -1-0.39 V in MeCN. On incorporation of silver ion, the two-electron redox change occurs at ° = -1-0.50 V. 

Complexes. Silver tetrafluoroborate is insoluble in cyclohexane but very soluble in water, ether, toluene, and nitromethane, and moderately soluble in benzene and cyclohexene. - Solubility in the unsaturated hydrocarbons is attributed to n-bond formation between the unsaturated compound and silver ion. Complexes have been observed with both ir-electron donors and lone-pair donors thus Meerwein prepared stable complexes with benzene, mesitylene, cycloheptatriene, diethyl ether, dimethyl sulfoxide, and a series of acid nitriles. However, the silver tetrafluoroborate-benzene complex is reported variously as a 1 1 complex, a 1 2 complex, and as a 2 3 complex. ... 

The stability constants of silver ion complexes have been evaluated by classical partition techniques (130,131) and more recently by the measurement of dissociation pressures (132,133) and the methods of gas-solid (134) and gas-liquid chromatography (135,136). The use of supported solutions of silver nitrate as a stationary phase for the separation of olefins is now quite general. Enthalpies of formation have been recorded for olefin complexes of silver borofluoride (132), for silver nitrate complexes with cyclic olefins (131) and for silver nitrate-butadiene complexes (133) the results are summarized, together with some values for the ethylene-silver ion complex, in Table XXXVIII. 

The logs of the stability constants for the silver ion complexes of a number of olefins are linearly related to their heats of hydrogenation 139), although the explanation of this is probably not simple. 

A limitation of silver ion complexation chromatography is the low upper temperature limit of the columns, 65°C or 40°C, as variously reported. Metal camphorate complexes have been used for both isomeric and enantiomeric... 

Table 3. Thermodynamic data for silver-ion complex formation in aqueous solution...

In several papers silver-containing complexes were used as active components of selective stationary phases. Cook and Givand [60], for example, used silver ion complexes with different compounds as stationary phases. The best separation was obtained with the silver complex with pyridine. Complexes with 2,6-dimethylpyridine, quinoline, isoquinoline, 2,2-bipyrryl, etc., did not interact with olefins, which can probably be explained by steric factors [60]. 

Individual olefin isomers are generally much better separated on silver-impregnated adsorbents, and Table 7-2 provides several examples. Any factor which increases the stability of the olefin-silver ion complex will increase sample adsorption. For example cis olefins generally form much... 

Isomers of the unsaturated fatty acid esters (55) and uhsatnrated normal aldehydes (59) which differ only in the position of a double bond in the alkyl chain are surprisingly well separated on silver-impregnated silica but not on normal silica. The basis for these effects is somewhat more complicated than simple steric hindrance to silver ion complexation, however. TV"... 

Similar observations on the oxidation of the thallium atom or on the reduction of T1+ have been made by pulse radiolysis. They are in agreement, as for silver, with the value determined from the electrode potential and the sublimation energy of the bulk metal into atoms, i.e. °(T1 /T1 ) = —1.9 Vnhe-Silver ions complexed by cyanide, ammonia, or EDTA, Ag L, are not reduced by the radical (CH3)2C OH, even under basic conditions, and the redox potential of these complexed forms must be more negative than —2.1 According... 

The potential of a silver electrode in a solution containing an ion that forms a soluble complex with silver ion can be handled in a way analogous to the treatment above. For example, in a solution containing thiosulfate and silver ions, complex formation occurs ... 

The formation of the vinyl cation-silver ion complex in the slow step of the reaction is consistent with the observation of an inverse secondary deuterium kinetic isotope effect, because the terminal C—H bond undergoes a hybridization change from sp to sp in the rate-determining step of the reaction. 

The silver-carbon-bond vectors in 69a,b are oriented nearly perpendicular to the benzene ring planes, which primarily infers participation of their 7r-electron systems at the silver-carbon bond [62]. This kind of bonding is somewhat different to those found in silver ion complexes of other arenes [63]. 

Ruan Q et al (2009) Investigation of layer-by-layer assembled heparin and chitosan multilayer films via electrochemical spectroscopy. J Colloid Interface Sci 333 725-733 Fu J et al (2006) Construction of antibacterial multilayer films containing nanosilver via layer-by-layer assembly of heparin and chitosan-silver ions complex. J Biomed Mater Res A 79A 665-674... 

Asfari, Z. Vicens, J. Silver ion complexation by a calix[4]arene bis(crown ether). Ambivalence towards ether 26. and polyhapto coordinations. Supramol. Chem. 1999, 11. 

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