Silver complexes characteristics

In order to vary the electronic situation at the carbene carbon atom a number of carbo- and heterocycle-annulated imidazolin-2-ylidenes like the benzobis(imida-zolin-2-ylidenes) [58-60] and the singly or doubly pyrido-annulated A -heterocyclic carbenes [61-63] have been prepared and studied. Additional carbenes derived from a five-membered heterocycle like triazolin-5-ylidenes 10 [36], which reveals properties similar to the imidazolin-2-ylidenes 5 and thiazolin-2-ylidene 11 [37] exhibiting characteristic properties comparable to the saturated imidazolidin-2ylidenes 7 have also been prepared. Bertrand reported the 1,2,4-triazolium dication 12 [64]. Although all attempts to isolate the free dicarbene species from this dication have failed so far, silver complexes [65] as well as homo- and heterobimetallic iridium and rhodium complexes of the triazolin-3,5-diylidene have been prepared [66]. The 1,2,4-triazolium salts and the thiazolium salts have been used successfully as precatalysts for inter- [67] and intramolecular benzoin condensations [68]. 

Silver forms monovalent ion in solution, which is colourless. Silver(II) compounds are unstable, but play an important role in silver-catalysed oxidation-reduction processes. Silver nitrate is readily soluble in water, silver acetate, nitrite and sulphate are less soluble, while all the other silver compounds are practically insoluble. Silver complexes are however soluble. Silver halides are sensitive to light these characteristics are widely utilized in photography. 

MEH/GUB] Mehra, M. C., Gubeli, A. O., Complexing characteristics of insoluble selenites 1. Silver selenite, Radiochem. Radioanal. Lett., 2, (1969), 61-68. Cited on pages 303, 304, 514. 

In coated-wire electrodes (CWE) the membrane is placed directly on the electrode. The electrode can be a wire of noble metal, graphite wire, silver paste or Ag/AgCl electrode, which is the most popular solution. The role of the inner solution of ISE-s can be played in CWE-s by poli(hydroxyethyl methacrylate), polyvinyl alcohol or a hydrogel saturated with NaCl solution, placed between the electrode and the membrane. The membrane stability can be improved through addition of silver complexes to the membrane. The advantage of CWE-s over ISE-s is the possibility of cheap, mass production. The disadvantage of CWE-s is that the membrane can easily unstick from the electrode. Moreover, due to the high contact surface between the membrane and the solution, the membrane contents, i.e., the plasticizer and the ionophore, can be easily washed out into the membrane, which deteriorates the characteristics of the sensor in time. 

Since its introduction by Morris and others in 1962, TLC on silica gel impregnated with silver nitrate has been of enormous value to the lipid analyst. It is sometimes termed "argentation" chromatography. The basis of the separation is the facility with which the double bonds in the alkyl chains of fatty acids form polar complexes reversibly with silver compounds. Fatty acids can be separated according to both the number and the configuration of their double bonds and sometimes, with care, according to the position of the double bonds in the alkyl chain. HPLC has been slow to make a mark in this area, because of problems in preparing stable columns, but many of the major difficulties now appear to have been resolved. However, most of the data on the elution characteristics of silver complexes of unsaturated fatty acids has been obtained by TLC. 

Anhydrous silver hexafluorophosphate [26042-63-7] AgPF, as well as other silver fluorosalts, is unusual in that it is soluble in ben2ene, toluene, and xylene and forms 1 2 molecular crystalline complexes with these solvents (91). Olefins form complexes with AgPF and this characteristic has been used in the separation of olefins from paraffins (92). AgPF also is used as a catalyst. Lithium hexafluorophosphate [21324-40-3] LiPF, as well as KPF and other PF g salts, is used as electrolytes in lithium anode batteries (qv). 

The second step in 2D electrophoresis is to separate proteins based on molecular weight using SDS-PAGE. Individual proteins are then visualized by Coomassie or silver staining techniques or by autoradiography. Because 2D gel electrophoresis separate proteins based on independent physical characteristics, it is a powerful means to resolve complex mixtures proteins (Fig. 2.1). Modem large-gel formats are reproducible and are the most common method for protein separation in proteomic studies. 

Trost exploited the annulation of electron rich phenols and alkynoates to obtain coumarins in the presence of transition metal complexes. Ethyl propiolate and 3,4,5-trimethoxyphenol were coupled in formic acid in the presence of a palladium complex and sodium acetate to give 5,6,7-trimethoxycoumarin via a net C-H insertion in acceptable yield (4.42.). The coupling, characteristic of electron rich phenols, was also catalyzed by other transition metals, such as platinum or silver.56... 

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