Labile copper

Potentiometric stripping analysis has been applied by Sheffrin and Williams [320] to the measurement of copper in seawater at environmental pH. The advantage of this technique is that it can be used to specifically measure the biologically active labile copper species in seawater samples at desired pH values. The method was applied to seawater samples that had passed a 0.45 pm Millipore filter. Samples were studied both at high and at low pH values. 

The speciation of copper is different at high and low pH. At pH 1.0 most of the copper will be labile and a total copper concentration will be measured. At pH 7.7 there should be a smaller proportion of labile copper, as much will be complexed in various forms, depending on the constituents of the seawater. 

Figure 5.9. Measurements of labile copper at high pH. Source Author s own files... 

A kind of standard additions approach can also be used for the measurement of apparent complexing capacity. In this technique, labile copper is measured by differential pulse anodic stripping voltammetry after each of a number of spikes of ionic copper have been added to the sample [420]. 

Lahn B, Rehahn M. Coordination polymers from kinetically labile copper(I) and silver(I) complexes true macromolecules or solution aggregates Macromol Symp 2001 163 157-176. 

Although the halogenated chelates of chromium, cobalt, and rhodium would be difficult to prepare from the sensitive 3-halo-2,4-pentanediones, the copper (II) bromochelate was synthesized both from the bromodiketone and by direct bromination of copper acetylacetonate. The relatively labile copper chelates form much more rapidly than the kinetically stable chelates of chromium, cobalt, and rhodium. 

LABILE COPPER(I) CHLORIDE COMPLEXES PREPARATION AND HANDLING... 

Labile Copper(I) Chloride Complexes Preparation and Handling 223... 

The plot above has been produced with six identical distances from the centroid of the ligand (the metal center) to the amines. A non-spherical metal ion (e.g., a Jahn-Teller labile copper(II) ion) will induce different stresses to a symmetrical ligand. Alternatively, the ligand might be asymmetrical, i. e., the ligand itself might induce an asymmetry in the coordination sphere. Effects like these will be studied in Section 17.17. 

Ito, Kawakami and Sawamura recently described the borylation of al-lylic carbonates by B2pin2, catalyzed by bis(phosphine)copper(I) alkox-ides. It was proposed that bis(phosphine)copper(I) boryl species formed by alkoxide/boryl a-bond metathesis are key intermediates in the catalytic cycle [231]. Making use of related N-heterocyclic carbene stabilized precursors, Sadighi and co-workers have very recently isolated the thermally labile copper boryl complex (IPr)CuBpin (11.1) together with the products of oxygen atom, styrene and aldehyde insertion into the Cu-B bond (11.2-11.5 Scheme 24) [232,233,237]. The structure of 11.1 in the solid state reveals an approximately linear Cu(I) coordination geometry [ZB-Cu-C 168.1(2)°] and a Cu-B distance [2.002(3) A] which is somewhat shorter than the sum of the expected covalent radii [2.05 A] [106]. Yet further evidence for the... 

Further evidence for organometallic interactions was provided by complexation capacity measurements and pseudo stability constant determinations. Complexation capacity or the residual complexing ability of a natural water sample was determined by complexometric titration of the < 0.4-juLin filtrate with soluble copper (II) (18, 40, 44) followed by ASV measurement of free and labile copper. Plots of ASV peak current vs. the cumulative copper concentration as shown in Figure 9 were made, and the intersection of lines drawn from the intitial and final linear response regions was defined as the residual complexation capacity (43, 44,45). Complexation capacity measurements for fall 1978 are listed in Table VII. The average values for Sites 1-4 were 0.88, 0.99, 0.90, and 1.08 fiM, respectively. 

During the first hour, when the entire slug of copper is introduced, dispersion, dilution, and first-order kinetic reactions result in a two-dimensional pattern of labile copper of the shape illustrated in Figure 5. The pattern shows a distribution of concentration about the peak value as a result of initial mixing and subsequent dispersion. The peak is translated downcoast by the advective process and the distribution is skewed somewhat in this same direction as a result of the kinetic transformation of labile copper to bound and sorbed states. A peak value of 18.4 /xg/L is indicated which may be compared to a maximum possible value of about 40 /xg/L if the entire slug were simply mixed with the entire volume of the dispersion zone (the diamond-shaped area around the outfall). 

Figure 6 depicts the temporal history of labile copper in the first 3 hr after the slug is discharged as it is subjected to further translation, dispersion, and decay. This history may be contrasted with that of bound copper (C2) shown in Figure 7 where the same mechanisms are operative, but the mass transferred to this compartment increases as the... 

Figure 5, Dispersion of labile copper 1 hr after initial injection...

Figure 6. Advection and dispersion of labile copper during first 3 hr following discharge (contours show lines of equal concentration, figlL)...

Figure 3.4 illustrates how the replacement of H2O by NH3 in an aqueous solution depends on the concentration of NH3 in a labile copper complex. The concentration curves of the complexes in the graph indicate which mixed-ligand complexes of copper exist in the solution and in what concentrations. 

Kinetically labile copper(II) ions, in water, combine with an excess of L-alaninate ligands (LAla-0) to give a solution (at pH 8.3) that contains only the uncharged species [Cu(LAla-0)2]. This species, planar about the copper ion, may exist as cis (33) or trans (34) isomers. The equilibrium... 

Fig.12-12. Slow increase of the peak for labile copper in seawater from the eastern Atlantic due to the gradual release of copper from or nk complexes. Conditirms 25pmol/L oxine, borate pH buffer (pH 8.3), 90s adsorption at -0.15 V, scans initiated from -0.15 V. Data from the author (unpublished Challenger cruise, March 1991).

Without any work-up, the reaction mixture was then subjected to column chromatography and produced the [2]rotaxane 4T in high yield (62%). The compulsory use of a trace of hydrazine in degassed eluent has to be emphasized the function of hydrazine is to inhibit formation of extremely labile copper(II) complexes, which would be detrimental and lead to lower yields (28% with no additional hydrazine). The isolated yield of rotaxane 4T was 62%, which highlights the efficiency of the click strategy even for a double copper(I)-catalyzed 1,3-dipolar cycloaddition. This method proved to be at least equally efficient in the case of the [2]metallo-rotaxane 48" (Scheme 14.14), synthesized in 67% yield. High resolution ES-MS measurements and NMR spectroscopy confirmed the postulated structures of metallo-rotaxanes 47 and 48". ... 

Wang J, Foster N, Armalis S, Larson D, Zirino A, Olsen K (1995) Remote stripping electrode for in-situ monitoring of labile copper in the marine-environment. Anal Chim Acta 310 223-231... 

---