Zinc complexes dichroic

CLM method can also be combined with various kinds of spectroscopic methods. Fluorescence lifetime of an interfacially adsorbed zinc-tetra-phenylporphyrin complex was observed by a nanosecond time-resolved laser induced fluorescence method [25]. Microscopic resonance Raman spectrometry was also combined with the CLM. This combination was highly advantageous to measure the concentration profile at the interface and a bulk phase [14]. Furthermore, circular dichroic spectra of the liquid-liquid interface in the CLM could be measured [19]. 

The circular dichroic spectrum of the zinc azoenzyme in solution contains one positive and two negative ellipticity bands at 420, 335, and 510 nm, respectively (Figure 3). On removal of zinc, almost the entire visible CD spectrum is abolished. It is completely restored on the addition of one gram atom of zinc per mole of enzyme. This eflFect of zinc on both the absorption and CD spectra suggests that the red color of the enzyme in solution may be caused by the formation of a zinc-azophenol coordination complex. Closely similar color changes can be observed by adding zinc to a typical azophenol compound, tetrazolyl-N-benzyloxycar-... 

Based on a series of studies with model azophenol-metal complexes, these absorption- and circular dichroic-pH titration data indicate the formation of an intramolecular coordination complex between arsanilazo-tyrosine-248 and the active site zinc ion where the enzyme is in solution (62, 63). This means that in solution, the phenolic hydroxyl group of tyrosine-248 would have to be much closer to the zinc ion than the 17 A indicated by the crystallographic studies. Consequently, there must be... 

Figure 4. Absorption ("upper panel) and circular dichroic (lower panel) spectra of AA—CPA—Zn as a function of pH. Intermediate pH spectra are those associated with complexation of active site zinc by arsanilazotyrosine 248 (see text).

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