Tetraphenyl-phosphonium ion

P-gp substrates are in general either neutral or cationic at physiological pH (weak bases). Weak bases can cross the lipid membrane in the uncharged form and reprotonate in the negatively charged cytosolic leaflet of the membrane. With a few exceptions (e.g., the tetraphenyl phosphonium ion, which can reach the cytosolic membrane leaflet due to charge delocalization [70]), permanently charged cations do not cross the cell membrane and therefore cannot interact with P-gp in intact cells. They can, however, insert into the cytosolic leaflet in inside-out cellular vesicles and are then transported by P-gp [42, 71]. 

The new complex anion [PtSi8]2- gave (31) a crystalline salt with the tetraphenyl-phosphonium ion. The anions were [Pt(S6)3]2 , with three seven-membered chelate rings the angles within the rings, 8-Pt-8, were much larger than 90 . These systems containing platinum ions complexed by polysulfides are thus chemically rather more complicated than expected. 

Reactions of Phosphonium Salts.- Interest continues in the effects of solvent on the rate of alkaline decomposition of phosphonium salts. It has now been shown that, in the respective reactions of hydroxide ion and methoxide ion with tetraphenyl-phosphonium bromide in mixtures of DMSO and methanol, the rates of the reactions increase as the proportion of the dipolar aprotic... 

The large difference in the hydrophobic binding of the cationic tetraphenyl-phosphonium and anionic tetraphenylborate is caused by the large changes in the enthalpy of the phase transfer. While the entropic contribution is similar for both ions, the AH is slightly positive (+ 14.6 kJmol-1) for tetraphenylpho-sphonium (TPP+), whereas it is negative (up to -15.1 kJmol-1) for tetraphenylborate (TPB ) [6]. 

To take advantage of both modified layered silicate and the substantial presence of phosphorus, the combined use of phosphorus-modified silicates and phosphorus compounds may represent an innovative solution to achieve high levels of flame retardancy. Phosphonium-modified layered silicates in epoxy resins were associated with organo-phosphorus FRs by Schartel et al.59 Ion exchange of Na-montmorillonite was carried out using tetraphenyl phosphonium bromide. Triphenyl phosphate and a reactive phosphorus compound were used as FR incorporated in the epoxy resin. 

Likewise, room-temperature Raman spectra of single crystals of tetraphenyl-phosphonium salts with all three halide ions [45] showed a broadening of lines which can be fitted with five oscillators. This indicates the lifting of the fivefold degeneracy, which is the case in C2h (or lower) symmetry. 

Phosphonium salts, which are generally stable in the form of iodide and tetraphenyl-borate crystalline solids, are frequently purified by recrystallization. Where this is not possible, thick-layer chromatography (0.2-1 mm Kieselguhr, silica) may afford a satisfactory method of purification12,13. In this manner, analysis using secondary ion mass spectrometry (SIMS) has a detection limit 10-50 ng per spot14. 

The stibonium compounds are the most difficult to prepare and are the least common. These quaternary salts, excepting the hydroxides, which are obtained as sirupy masses, are white crystalline compounds. The tetra-phenyl-phosphonium and -arsonium ions are useful for precipitating large anions such as ReO, CIO and complex anions of metals. Tetraphenyl-stibonium hydroxide has been shown55 to contain tbp molecules, with the OH group in an axial position. 

The ion-exchanger type ISEs can be readily converted to other forms, as illustrated by conversion of a nitrate ion-exchanger to the chlorate form, and assembly into a chlorate ISE (98). Much work continues to be done on anion liquid ion-exchangers for anion ISEs (see Recent Titles in each Volume of Ion-Selective Electrode Reviews). For these tetraalkylammonium and -phosphoniura, tetraphenyl-arsonium and -phosphonium, and dye salts are a popular basis (99). 

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