PubMed · 11636883
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S Lienhard. 1997. [Not Available].. https://pubmed.ncbi.nlm.nih.gov/11636883/
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The unusual charge transfer complexes formed between alkyl halide acceptors and hard Lewis base donors (amines and alcohols) in low dielectric solvent were examined using ultraviolet spectroscopy. The lambda(max) of the complex decreases with increasing ionization potential of the donor. The complex formation equilibria were probed by thermodynamic analysis and concentration variation. At ambient temperatures complex formation is generally slightly exergonic with a negative complexation entropy. The complex extinction coefficients are much lower (<10 l mol(-1) cm(-1)) than for typical charge transfer complexes. These complexes are extraordinary within a classical context since the halide acceptors have a negative electron affinity. They exhibited an atypical hypsochromic shift with increasing solvent dielectric constant.
Some nitrophenols are proposed as chromogenic reagents for the spectrophotometric determination of flucloxacillin. The reagent forms a greenish yellow 1:1 complex with flucloxacillin at pH 9.0. This complex is stable for at least 3.0 h after its formation. The greenish yellow charge transfer complex species has an absorption maximum at 446, 435, 442, 473 and 439 nm for p-nitrophenol (I), 2,4-dinitrophenol (II), 3,5-dinitrosalycilic acid (III), picramic acid (IV) and picric acid (V), respectively, with a molar absorptivity between 1.43 x 10(4) and 2.59 x 10(4) l mol(-1) cm(-1). Beer's low is valid over the concentration range 2.0-40 microg ml(-1) of flucloxacillin. The detection and quantitation limits as well as relative standard deviation were also calculated. The reagents have been successfully used for the spectrophotometric determination of flucloxacillin in pure form and in pharmaceutical preparations.