Inactive complex

Simultaneous detenuination of Cu and Zn in the form of coloured PAR complexes is performed at pH 10 in the presence of pyrophosphate which binds the admixtures of Al, Fe and Mn into the inactive complexes. The measurements of the change in the optical density are made at 520 and 550 nm before and after the destmction of the complexes by EDTA, or at 530 nm before and after the destruction of the copper complexes by the thioglycolic acid and the destmction of the zinc complexes by EDTA. The detection limit for Cu is 2-5, for Zn - 3 p.g/diW. The application of these methodics at pH 8 enables one to determine simultaneously Cu and Zn at high excess of the latter. 

The simultaneous determination of Co and Ni is also made at pH 8 in the presence of pyrophosphate. The EDTA is added to the mixture of coloured complexes of these metals to bind the Cu and Zn admixtures into the inactive complexes. The optical density of the solution is measured at 530, 555 and 580 nm. The solution is heated to the boiling point to destmct the complex formed by Ni with PAR, and then is cooled. Again the measurements of optical density ai e performed at the same wavelengths. The Ni concentration is calculated from the variation in the optical density, and the Co concentration is calculated from the final values of optical density. The detection limits for these metals are 4 and 2 p.g/dm, respectively. 

In 1999, Kiindig and Bruin reported a closely related catalyst system 29a, in which a more readily accessible ligand has been employed [37]. Catalytic activity and stability are strongly dependent upon the nature of the neutral ligand L. While the acetonitrile complex 29b is stable, yet catalytically inactive, complex 29a with L = acrolein is stable only in the solid state, but decomposes as a solution in DCM... 

The effect of pH and cation concentration on pectinesterase (PE) activation and permeation on 30 kD MWCO ultrafiltration (UF) membrane was evaluated. In order of increasing effectiveness, PE activity was stimulated by monovalent and divalent cations, poly amines and trivalent cations. A similar trend was observed for permeation on UF membranes. Cation addition and higher pH releases PE from an inactive complex, increases activity, and increases permeation. Higher cation concentration decreases activity and permeation. These results suggest a common mechanism is involved in PE activation and permeation. 

MacDonnell et al. (15) first suggested competitive displacement for the stimulation of PE activity. An increase in activity was ascribed to competitive displacement of PE from an inactive complex followed by a decline in activity at higher concentrations due to competition for carboxylic acid binding sites between PE and cations. Competitive displacement of PE from pectic acid by cations was conclusively shown with Lineweaver-Burke plots (7). The effect was moderated by pH (7, 15). We have shown that other polyamines, including putrescine, a diamine, and spermine, a tetramine, "activate PE activity similarly to inorganic cations (13). 

Ultrafiltration of heterogenous colloidal suspensions such as citrus juice is complex and many factors other than molecular weight contribute to fouling and permeation. For example, low MW aroma compounds were unevenly distributed in the permeate and retentate in UF in 500 kd MWCO system (10). The authors observed that the 500 kd MWCO UF removed all suspended solids, including pectin and PE. If PE is complexed to pectate in an inactive complex, then it is conceivable that release of PE from pectin with cations will enhance permeation in UF. At optimum salt concentration, less PE activation was observed at lower pH values than at higher pH (15). In juice systems, it is difficult to separate the effect of juice particulates on PE activity. Model studies with PE extracts allows UF in the absence of large or insoluble particulates and control of composition of the ultrafilter. In... 

Inhibitors may act reversibly or irreversibly, but this classification is not particularly useful. It may even be misleading, because it suggests that reversible and irreversible inhibitors act in different ways when, in fact, both act by combining with the enzyme to give inactive complexes, but with quite different dissociation constants. The irreversible inhibitors give complexes that have very small dissociation constants the reversible inhibitors have significantly higher dissociation constants. 

Figure 8. The blocking effect (25 °C) of redox inactive complexes on the reaction of parsley plastocyanin PCu(I) + Co(phen)s3 Rate constants were determined at pH 7.5 (for U and m) and pH 5.8 (for A) [I = 0.10 M (NaCl)].

Other Studies. Experiments in which rate constant pH profiles, blocking effects of redox inactive complexes as well as the effect of Cr(III) modification should now be possible enabling sites on plastocyanin used by cytochrome f and P700 to be specified (25,26). 

Besides this, phosphite reacts with metal forming an inactive complex. Hence, the catalytic activity of the metal decreases with an increase in the phosphite concentration. The produced... 

The ability of MPO to catalyze the nitration of tyrosine and tyrosyl residues in proteins has been shown in several studies [241-243]. However, nitrite is a relatively poor nitrating agent, as evident from kinetic studies. Burner et al. [244] measured the rate constants for Reactions (24) and (25) (Table 22.2) and found out that although the oxidation of nitrite by Compound I (Reaction (24)) is a relatively rapid process at physiological pH, the oxidation by Compound II is too slow. Nitrite is a poor substrate for MPO, at the same time, is an efficient inhibitor of its chlorination activity by reducing MPO to inactive Complex II [245]. However, the efficiency of MPO-catalyzing nitration sharply increases in the presence of free tyrosine. It has been suggested [245] that in this case the relatively slow Reaction (26) (k26 = 3.2 x 105 1 mol-1 s 1 [246]) is replaced by rapid reactions of Compounds I and II with tyrosine, which accompanied by the rapid recombination of tyrosyl and N02 radicals with a k2i equal to 3 x 1091 mol-1 s-1 [246]. 

Direct free radical inhibitors suppress free radical formation by reacting with free radicals to form new inactive radicals (Reactions (1) and (2)) or chelating catalytically active transition metals to form inactive complexes ... 

Hydrogenation of butadiene with K3Co(CN)5, which is known to hydrogenate selectively conjugated dienes [75], was possible with 100% conversion and selectivity and a TOF up to 72 h-1 in the ionic liquid [BMIM][BF4], but the catalyst was deactivated after the first run and the inactive complex (BMIM)3Co(CN)5 was formed [69]. 

Fig. 8. Competitive inhibition of redox inactive complexes (I) on the [Co(phen)j] oxidation of parsley plastocyanin PCu(I) [98]. Second-order rate constants (25 °C), shown as relative values, were determined at pH 5.8 (Mes), 1=0.10 MfNaO) with [Pt(NH3)6] ( ), [(NH3)5CoNHj(NH3)5]s] [Co (III)4]a (A) and [CoflllUg ( ). Full formulae of the latter two complexes are as indicated above...

The metal surfaces are always covered with a monolayer of CO upon evacuation of the reactor and transfer to the UHV system. On both Pd and Ir the CO, which desorbs as CO2 when reacted with the oxide species, desorbs at a much higher temperature than CO from the clean surface. This result implies that the oxide species forms an inactive complex with CO upon adsorption of CO under reaction conditions. While the presence of the oxide species reduces the overall rate of reaction, the activation energy is unchanged, suggesting that oxygen serves as a simple site blocker on the surface. 

Ruthenium complexes B also undergo fast reaction with terminal alkenes, but only slow or no reaction with internal alkenes. Sterically demanding olefins such as, e.g., 3,3-dimethyl-l-butene, or conjugated or cumulated dienes cannot be metathesized with complexes B. These catalysts generally have a higher tendency to form cyclic oligomers from dienes than do molybdenum-based catalysts. With enol ethers and enamines irreversible formation of catalytically inactive complexes occurs [582] (see Section 2.1.9). Isomerization of allyl ethers to enol ethers has been observed with complexes B [582]. 

A serpin is a xerine proteinase inhibitor that forms cata-lytically inactive complexes which, after cleavage of the pi pif linkage, releases the inhibitor very slowly. O Malley et al. recently demonstrated that antichymo-trypsin (1) binds to chymotrypsin (E) to form an E I complex via a three-step mechanism ... 

Arsenic Dimercaprol Forms inactive complex with metal... 

Etanercept is a recombinant fusion protein produced in Chinese hamster ovary cells. It consists of the intracellular ligand-binding portion of the human p75 TNF receptor linked to the Fc portion of human immunoglobulin (Ig) Gi. Two p75 molecules are attached to each Fc molecule. Etanercept binds to soluble TNF-a and TNF-(3 and forms inactive complexes, effectively lowering circulating levels of these cytokines. It is administered subcutaneously, generally twice weekly. 

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