Other Donor Systems

Other Donor Systems. The tetrathiocyanato-complexes MHg(SCN)4L2 (M = Cu or Fe L = PPh3, AsPhj, 2-aminopyridine, or nicotinamide) have structures (146) or (R7). Tl2PbCu(N02) contains Cu(N02)6 ions with M3 symmetry and Cu—N = 

Cu(N03)2, and Cu(C104)2 shows the formation of mixed complexes superhyperfine splitting of is observed in the e.p.r. of Cu(dtc)X 

2-one bis(thiosemicarbanazato)copper(ii) (148) is due to S — Cu charge transfer. The charge transfer spectrum of a novel Cui4[SCMe2CH2NH2] 12CI cluster has been 

A study of the imine hydrolysis of copper(ii) complexes containing the ligands iViV -ethylenebis-(thiophen-2-carbaldimine) (149), and -(pyridine-2-carbaldimine (150), shows two distinct reactions for first ligand involving each imine group in 

Copper(m)—A copper(iii) complex of the enzyme galactose oxidase has been postulated as the active intermediate in the oxidation of D-galactose. Autoxidation of copper(ii)-peptide complexes leads to relatively long-lived copper(iii)-peptide species.  

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Other donor systems. Although not as common as all-nitrogen donor rings, macrocycles incorporating sulfur donor atoms have been widely reported. Structures (42)-(45) illustrate four representative examples of this type. 

Some aspects of the Lowe-Thomeley mechanism for nitrogenase action, which has served us well over the past 15 years, are being called into question. In particular, the necessity for protein-protein dissociation after each electron transfer, the rate-determining step with dithionite as reductant, is being questioned when the natural electron donor flavodoxin or other artificial systems are used. Some aspects of the mechanism should be reinvestigated. 

All characterized BVMOs contain a flavin cofactor that is crucial for catalysis while NADH or NADPH is needed as electron donor. An interesting observation is the fact that most reported BVMOs are soluble proteins. This is in contrast to many other monooxygenase systems that often are found to be membrane-bound or membrane-associated. In 1997, Willetts concluded from careful inspection of... 

In addition to the backbone donor system the amino acid residues can contain a variety of donor centers (679E). The most important of these are the imidazole N atoms of His, the S atom of Cys, and to some extent the, 3-carboxylate O atom of Asp. Other side chain donors like the O atoms of Ser and phenolic O atoms of Tyr or amino N atoms of Lys are of minor importance for coordination of Ni11 ions. Also, thioether S-donors of Met play only a minor role in the interactions with Ni11 ions.1730... 

Heterocyclic nitrogen donors and their adducts with zinc chloride have been studied.623,624 A large number of other ligand systems have also been characterized, for example, zinc halide adducts of 2,2-dimethylpropane-1,3-diamine and hexamethylphosphoramide have been studied.625,626 The formation of mixed ligand complexes with chloride and substituted pyridines has been studied.627 The zinc tris(pyridyl) chloride anion has also been structurally characterized.628 Manganese(II) ions have been used to probe the stereochemistry in reactions of zinc halides with pyrazine.629... 

Lewis Bases. A variety of other ligands have been studied, but with only a few of the transition metals. There is still a lot of room for scoping work in this direction. Other reactant systems reported are ammoni a(2e), methanol (3h), and hydrogen sulfide(3b) with iron, and benzene with tungsten (Tf) and plati num(3a). In a qualitative sense all of these reactions appear to occur at, or near gas kinetic rates without distinct size selectivity. The ammonia chemisorbs on each collision with no size selective behavior. These complexes have lower ionization potential indicative of the donor type ligands. Saturation studies have indicated a variety of absorption sites on a single size cluster(51). 

In vivo, some other heterocyclic systems behave as NO-donors. Typical examples are the 3-amino-4-alkyl or arylalkyl derivatives of l,2,4-oxadiazol-5(4H)one 133 [169, 170]. These products can be synthesised following Scheme 6.25. 

The octanol-water partition coefficient, Kow, is the most widely used descriptor of hydrophobicity in quantitative structure activity relationships (QSAR), which are used to describe sorption to organic matter, soil, and sediments [15], bioaccumulation [104], and toxicity [105 107J. Octanol is an amphiphilic bulk solvent with a molar volume of 0.12 dm3 mol when saturated with water. In the octanol-water system, octanol contains 2.3 mol dm 3 of water (one molecule of water per four molecules of octanol) and water is saturated with 4.5 x 10-3 mol dm 3 octanol. Octanol is more suitable than any other solvent system (for) mimicking biological membranes and organic matter properties, because it contains an aliphatic alkyl chain for pure van der Waals interactions plus the alcohol group, which can act as a hydrogen donor and acceptor. 

Because of the expense, toxicity, and purification problems associated with use of stoichiometric amounts of tin hydrides, there has been interest in finding other hydrogen-atom donors. The trialkylboron-oxygen system for radical initiation has been used with tris(trimethylsily)silane or diphenylsilane as a hydrogen-donor system.133... 

Other structural features that have acceleratory influences in the base hydrolysis of Co(III) systems are (i) the incorporation of a pyridine ligand in the coordination sphere and (ii) the incorporation of a flat secondary nitrogen donor system in the polyamine ligand skeleton (5) (structures C and D in Fig. 17). 

On benzene and some other aromatic systems, the donor or acceptor nature of a substituent is critical for the MCD sign, whereas on others such as pyridine it is not, at least for weak substituents. Further, the MCD is helpful for the analysis of a wide field of chemical events such as conformational changes coupled with substitutions, proton tautomerism, proton dissociation on aromatics, or through-space interaction in bicyclic aromatic systems 299-318>. 

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