Activated H2O2 time

The kinetics of this reaction at pH 7 are highly complex but can be interpreted in terms of rate determining formation of a cobalt(IV) intermediate which oxidizes water to H2O2 followed by oxidation of H2O2 by [Ru(bipy)3] " (see equations 84-88). Unfortunately, reaction (89) causes loss of cobalt as an insoluble oxide and this accounts for the observed decrease of catalytic activity with time. 

The use of a PPy film as a convenient matrix for dispersing an oxygen reduction electrocatalyst is questionable since the PPy matrix can react itself with O2, leading to H2O2 by a two-electron transfer reaction [13,15]. Hydrogen peroxide can then oxidize the PPy film, leading to degradation of the polymer and to a decrease of the electrocatalytic activity with time. 

Four other Norit SXRO activated carbon catalysts that essentially differ only in their H2O2 activity time have been tested in the glyphosate process. As expected, the reaction rate increased with a decreasing H2O2 time (Figure 17.3a). 

Fig. 9.4 Time course of the chemiluminescence reaction of (NH SO t -activated panal at pH values 4.5, 5.0, 5.5, and 6.0, in 3 ml of 10 mM acetate buffer in the presence of lOmg of CTAB, 20 pi of 0.1 M FeSC>4, and 20 pi of 10% H2O2 and at pH 8.0, in 3 ml of 50 mM Tris-HCl buffer containing 0.18 mM EDTA, 10 mg of CTAB, lOmg of NaHCC>3, 20pi of 0.1 M FeSC>4, and 20pi of 10% H2O2. All at 25°C. From Shimomura, 1989, with permission from the American Society for Photobiology.

Jones (refs. 11,12) subsequently investigated the relative reactivities of the various cobalt(III) species with Br, Mn and H2O2. The active p-oxodimer, Co was two to four orders of magnitude more reactive than Co which was four to five times more reactive than (Fig. 13). Furthermore, it should be noted that the rate of conversion of Co to Co is much higher than the rate of reaction of Co with ArCH3. In other words, in the absence of Br or Mn the cobalt species that reacts with ArCH3 cannot be Co. ... 

Fig. 2. displays the TOC removal of 0.2 mM Indigo Carmine as a fimction of time under different initial solution pHs in the presence of 10 mM H2O2, 1.0 g Fe-B/L, and 8W UVC. As the initial solution pH increases from 3.0 to 7.0, the mineralization kinetics becomes slower, indicating that the Fe-B nanocompsoite showed a decreased photo catalytic activity. For example, the difference between the TOC removal at initial solution pH of 3.0 and 7.0 is about 25 /o, which agrees well with previous studies [1-3]. 

The addition of acetic acid (0.5 equiv. to the substrate) to the catalyst system led to increased activity (doubling of yield) by maintaining the selectivity with 1.2 equiv. H2O2 as terminal oxidant. Advantageously, the system is characterized by a certain tolerance towards functional groups such as amides, esters, ethers, and carbonates. An improvement in conversions and selectivities by a slow addition protocol was shown recently [102]. For the first time, a nonheme iron catalyst system is able to oxidize tertiary C-H bonds in a synthetic applicable and selective manner and therefore should allow for synthetic applications [103]. 

Chemo-enzymatic epoxidation of unsaturated fatty acids with aqueous H2O2 has been conducted with considerable success and here we have a remarkable situation that undesirable ring opening of the epoxide does not occur. Excellent activity and stability has been realized with Novozym 435, a Candida antartica lipase B immobilized on polyacryl. This enzyme is readily separable, can be used several times without loss of activity, and has a turnover of more than 2,00,000 moles of products per mole of catalyst (Bierman et al., 2000). 

A common observation has been that different times are needed for the activation of NFJCB by different stimuli in the case of proinflammatory cytokines the kinetics of the activation is fast, while in the case of H2O2 the kinetics of the activation are slow and sustained. This led to the realization that perhaps different target regions on the IKB were affected by the stimulant, or that other transcription factors were involved. NFJCB is frequently associated with other transcription factors so that they... 

The catalytic activity in relation to a given reaction occurring on the surface is characterized by the rate g of this reaction, i.e., by the amount of reaction products formed under the given external conditions per unit time on unit surface area. An expression for g has different forms for different reactions. For the reactions of hydrogen-deuterium exchange, oxidation of CO, and synthesis of H2O2, this expression will be derived in Sections III, IV, and V, respectively. 

Kharazipour etal. (1998) used a peroxidase enzyme in combination with H2O2 to activate the surface of TMP fibres for self-bonding. Fibres were activated in a wet system, then dewatered and fluffed out before pressing at 190 °C for 5 minutes. The best IBS recorded for boards of 5 mm thickness made from the activated fibres was 0.55 MPa. The IBS was found to be dependent upon the pH of the treatment solution, the time of treatment and the board density. The authors noted that phenoloxidase gave comparable results to laccase, which was unexpected, since it was thought that the phenoloxidase would lead only to depolymerization of the lignin. 

Figure 4. Oxidative stability of subtilisins. Purified wild type or variant subtilisin was mixed with 0.3% H2O2 in O.IM Tris buffer (pH 8.6). At the times indicated aliquots were removed and tested for remaining enzymatic activity (2).

To study the effect of hydrogen peroxide, the lignin peroxidase was incubated in buffer, either pH 3.0 or 5.0, at the temperature of either 0°C or 10°C. Protein concentration was 30/i,g/ml and the concentration of H2O2 was 0.2 -11.6 mM. The incubation time varied between 0 and 295 min. After incubation 0.4 ml of the enzyme sample was pipetted directly into the activity assay mixture. 

The catalyst remains in the fluorous phase, whilst the product is completely extracted, and secondary alcohol can be prepared by H2O2 oxidation. The catalyst solution can be recycled several time without loss of activity. 

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