Charge transfer complexes, titration

An ethereal solution which was 1.38ilf in methyllithium was purchased from Foote Mineral Company. The concentration of methyllithium in ethereal solutions may be conveniently determined by a procedure described elsewhere in which the lithium reagent is titrated with 5ec-butyl alcohol, utilizing the charge transfer complex formed from bipyridyl or o-phenanthro-line and the lithium reagent as an indicator. 

The blue starch iodine complex has been used from time immemorial as an indicator in aqueous iodometric titrations water is required for development of the blue color. The color sensitivity is decreased with increasing temperature and also with increasing concentration of ethanol [134]. Although one might imagine this to be evidence for a charge-transfer complex,... 

An effective method for the titration of Grignard reagents is with menthol in the presence of 1,10-phenanthroline in THF. The endpoint of the titration is reached when a violet or burgundy color persists, which is indicative of a charge transfer complex formed beween the organomagnesium reagent and 1,10-phenanthroline. 

The pharmacological activity of charge transfer complexes has been reviewed. " The use of conductometric titration to study the charge transfer reactions of chlorpromazine is indicated in Section 1.4.2. 

For charge transfer complexes, if the permittivity of the solvent is high enough, the complex may dissociate, giving rise to ions capable of carrying current and thus affect the conductance of the solution. A conductance maximum is seen in the titration curve. In the absence of dissociation, com-plexation often may be ascertained from the formation of a spectroscopically observable new absorption band, either in the visible or in the uv, but this does not hold if the complex dissociates to any appreciable degree. Thus, conductimetric titration supplements spectroscopy in that formation of ions, usually not discernible spectroscopically, is readily followed conductimetrically. 

The formation of a charge transfer complex may also be indicated from potentiometry the electrode potential of an active electrode, usually Au or Pt, is measured against a reference electrode potential, say a saturated calomel electrode. Donor is then titrated against an acceptor solution, or vice versa, and a maximum or a minimum in the potential vs. tit rant concentration curve indicates the complex stochiometry. The technique has been applied to study the interactions between E. coli and antibiotics such as streptomycin and kanamycin, using a three-compartment cell. ... 

F. Gutmann and H. Keyzer, Conductivity Titrations of Charge-Transfer Complexes in Solution—II, Electrochim. Acta 11, 555-568, 1163-1169 (1966). 

The coulometric titration shown in Fig. 9(a) was performed at an HD-CoA concentration such that 95% of the MCAD was complexed. The titration consisted of two reductive events. The absorbance at 456 nm decreased sharply (AA = —0.20) during the first part of the titration because the reduction of flavin (see inset). An increase in absorbance at 570 nm accompanied flavin reduction, consistent with the formation of a charge transfer complex between the dienoyl-CoA hgand and the reduced enzyme. The ahsorhance at 570 nm reached a maximum between n = 2.6 and 3 reducing equivalents, with the majority of the 456 nm decrease in absorbance occurring during this part of the titration. From n = 3 to 11.8, the absorbance of... 

Beezer, A.E., Orban, M. and Tyrrell, J.V. (1979) Thermometric titration studies of association equUibiiums charge-transfer complexes between iodine and substituted pyridines in carbon tetrachloride. Acfa Chim. Acad. Sci. Hung., 99, 415 19. 

The detection of aromatic carboxylates via the formation of ternary complexes using lanthanide ion complexes of functionalised diaza-crown ethers 30 and 31 has been demonstrated [134]. Like the previous examples, these complexes contained vacant coordination sites but the use of carboxylic acid arms resulted in overall cationic 2+ or 1+ complexes. Furthermore, the formation of luminescent ternary complexes was possible with both Tb(III) and Eu(III). A number of antennae were tested including picolinate, phthalate benzoate and dibenzoylmethide. The formations of these ternary complexes were studied by both luminescence and mass spectroscopy. In the case of Eu-30 and Tb-30, the 1 1 ternary complexes were identified. When the Tb(III) and Eu(III) complexes of 30 were titrated with picolinic acid, luminescent enhancements of 250- and 170-fold, respectively, were recorded. The higher values obtained for Tb(III) was explained because there was a better match between the triplet energy of the antenna and a charge transfer deactivation pathway compared to the Eu(III) complex. 

Molecular tweezers such as 10 showed no affinity (Kassoc < 3M 1) for 7t-donor guests like naphthalene and anthracene. However, Tc-acceptors such as trinitrobenzene (TNB) and nitrated fluorenones were bound. The complexation experiments were performed by titrating a solution of the guest with the host and recording the upheld chemical shifts of the guest protons by XH NMR. Alternatively, the host could be titrated with guest and the increase in absorbance at the charge transfer band monitored. 

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