Aqueous solutions copper protein

FIGURE 10.6 Comparison of solid-state and liquid-state spectra from a copper protein. The figure illustrates shifts in apparent gz and Az-values of the S = 1/2 and I =3/2 spectrum from Cu11 in bovine superoxide dismutase as a function of the surrounding medium. Top trace frozen aqueous solution at 60 K middle trace frozen water/glycerol (90/10) solution at 60 K bottom trace aqueous solution at room temperature. (Modified from Hagen 1981.)... 

This section covers the practical considerations involved in reporting the concentration of a dissolved species in solution. The term species is a generic one, and can include anything from an element in aqueous solution (e.g., copper in solution), to a dissolved compound (e.g., dissolved nitrate), to neutral species in solution, to large complexes such as proteins in solution. 

Tab. 5 Potential values for copper(ll/l) proteins (principally cupredoxins) in aqueous solution (all values are presumed to be for 25 °C, p, 0.1 M)...

Copper in aqueous solution, and in proteins, is usually present in the Cu(I) or Cu(II) states. Cu(I) has 10 3d electrons, constituting a filled shell. All the electrons are paired and S = 0. Cu(II) has 9 3d electrons Cu(II) complexes are paramagnetic with S =. Because the 3d orbitals are more than half-filled, orbital angular momentum contributions from the d orbitals cause the average g value to be over 2. The EPR spectra are also affected by hyperfine coupling to the copper nucleus both of the common natural isotopes have I =. ... 

The adsorption of albumin from aqueous solution onto copper and nickel films and the adsorption of B-lactoglobulin, gum arabic, and alginic acid onto germanium were studied. Thin metallic films (3-4 nm) were deposited onto germanium internal reflection elements by physical vapor deposition. Transmission electron microscopy studies indicated that the deposits were full density. Substrate temperature strongly Influenced the surface structure of the metal deposits. Protein and/or polysaccharide were adsorbed onto the solid substrates from flowing... 

Quenching of excited-state [Ru(bipy)3] by reduced blue proteins involves electron transfer from the Cu with rate constants close to the diffusion limit for electron-transfer reactions in aqueous solution. It is suggested that the excited Ru complex binds close to the copper-histidine centre, and that outer-sphere electron transfer occurs from Cu through the imidazole groups to Ru. Estimated electron-transfer distances are about 3.3 A for plastocyanin and 3.8 A for azurin, suggesting that the hydrophobic bipy ligands of Ru " penetrate the residues that isolate the Cu-His unit from the solvent. ... 

The number of charges on a metal ion can be altered by addition or removal of an electron. Many transition metal ions found in humans can exist in a range of oxidation states. For example, copper has + 1 and + 2 (cuprous and cupric respectively), iron has + 2 and + 3 (ferrous and ferric respectively), but some of these states are not stable in aqueous solution at neutral pH without ligands being attached to the metal ion. Thus, the oxygen-carrying protein, haemoglobin, is able to maintain the... 

In contrast to other systems in which the mechanism (inner-sphere or outer-sphere electron transfer) may be a matter of debate, the reaction between the protein horse heart cytochrome c with anionic Cu" complexes was adjudged to proceed by an outer-sphere mechanism. [170] The copper(ll) complex bis(5,6-bis(4-suphonatophenyl)-3-(2-pyridyl)-l,2,4-triazine)Cu(ll), (the ligand is commonly known as ferrozine) possesses square pyramidal geometry with the two bidentate ligands in the equatorial plane, and the fifth axial position is occupied by a water molecule, in aqueous solution. 

In aqueous solution, the redox potential of the redox couple Cu2+/Cu+ is E° = +153 mV [6]. In contrast to this, the range of redox potentials found in copper proteins and enzymes extend from +183 mV in halocyanin [18] to + 785 mV in... 

The chemospecificity of the reaction suggested that it could be carried out using azides or alkynes attached to proteins if the reaction temperature could be lowered. This breakthrough was achieved by two groups who simultaneously reported that the reaction could be dramatically accelerated in the presence of Cu(I) salts [90, 91]. This allowed the reaction to take place in aqueous solution with temperatures from 4°C to RT. In the copper-catalyzed version of the reaction, terminal alkynes show high specificity for the antiproduct. 

The soluble proteins are precipitated from aqueous solutions by a large number of salts. These salts may be divided into two classes, namely, those, such as sodium chloride and ammonium sulphate, which precipitate (salt out) the protein in an unchanged condition, and those which form insoluble compounds with the protein, such as the salts of copper and silver. Salting out is an important means of separating proteins from complex mixtures obtained from animal and plant tissues and from one another, and has been the subject of much investigation. The salts which precipitate proteins unchanged differ in their action upon the various classes of these compounds. 

Blue (Type 1) copper proteins are found widely in nature. Typical examples are plasiocyaiiin (MW 10,500) and ascorbale oxidase (MW 150,000) which contain one and eight Cu atoms per protein, respectively. The former serves as a component of the electron transfer chain in plant photosynthesis while the latter is an enzyme involved in the oxidation of ascorbic acid. The oxidized form is characterized by intense blue color due to electronic absorption near 600 nm. In addition, blue copper proteins exhibit unusual properties such as extremely small hyperfine splitting constants (0.003 0.009 cm" ) in ESR spectra and rather high redox potential (4-0.2 0.8 V) compared to the Cu(ll)/Cu(I) couple in aqueous solution. 

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