Molecular oxygen between

On the other hand, isomerization of sil-trans P-carotene was found to be comparatively faster in a model containing methyl fatty acid and chlorophyll heated at 60°C (Table 4.2.6), resulting in 13-cw-P-carotene as the predominant isomer. The first-order degradation rate of P-carotene significantly decreased with the increased number of double bonds in the methyl fatty acid, probably due to competition for molecular oxygen between P-carotene and the fatty acid. Since the systems were maintained in the dark, although in the presence of air, the addition of chlorophyll should not catalyze the isomerization reaction. 

The reaction with 8 only occurred in stoichiometric ratios, hence we searched for a way to use copper-based molecular clips as true oxygenation catalysts. To this end the host molecule was altered by changing the pyrazole ligands for pyridine to obtain a model system that could mimic dicopper proteins, which can bind molecular oxygen between the copper centers in a bridging fashion [16]. After the binding of two Cu ... 

Oxidation first produces soluble oxygenated compounds of molecular weights between 500 and 3000 that increase the viscosity of oil then they polymerize, precipitate, and form deposits. Oxidation also causes formation of low molecular weight organic acids which are very corrosive to metals. 

Phenolic compounds are commonplace natural products Figure 24 2 presents a sampling of some naturally occurring phenols Phenolic natural products can arise by a number of different biosynthetic pathways In animals aromatic rings are hydroxylated by way of arene oxide intermediates formed by the enzyme catalyzed reaction between an aromatic ring and molecular oxygen... 

Run a stability calculation on the true (triplet) ground state of molecular oxygen. What is the energy difference between the ground state and the singlet state ... 

Luciferase-catalyzed luminescence of luciferin. Odontosyllis luciferin emits light in the presence of Mg2+, molecular oxygen and luciferase. The relationship between the luminescence intensity and the pH of the medium shows a broad optimum (Fig. 7.2.8). The luminescence reaction requires a divalent alkaline earth ion, of which Mg2+ is most effective (optimum concentration 30 mM). Monovalent cations such as Na+, K+, and NH have little effect, and many heavy metal ions, such as Hg2+, Cu2+, Co2+ and Zn2+, are generally inhibitory. The activity of crude preparations of luciferase progressively decreases by repeated dialysis and also by concentrating the solutions under reduced pressure. However, the decreased luciferase activity can be completely restored to the original activity by the addition of 1 mM HCN (added as KCN). The relationship between the concentration of HCN and the luciferase activity is shown in Fig. 7.2.9. Low concentrations of h and K3Fe(CN)6 also enhance luminescence, but their effects are only transient. 

But one must not be too facile with sweeping generalizations concerning concentration dependences or their absence. For example, consider the reaction between the cobalt(II) complex known as Co(sep)2+ and molecular oxygen. With these reagents only, the two-step reaction in acidic, aqueous solution is5... 

Ozone absorbs ultraviolet radiation very efficiently in the wavelength range between 200 and 300 nm, where molecular oxygen and nitrogen are... 

After 28 years the perepoxide quasi-intermediate was supported by a two-step no intermediate mechanism [71, 72]. The minimum energy path on the potential energy surface of the reaction between singlet molecular oxygen ( A and dg-teramethylethylene reaches a vaUey-ridge inflection point and then bifurcates leading to the two final products [73]. 

The concept, quasi-intennediate [70], was introduced in 1975 to symbolize a boundary between concerted and stepwise mechanisms. Recent advances in computer chemistry are allowing us to investigate subtle problems more clearly in the years since 2000. Concerted/stepwise boundary mechanisms were proposed for other diverse reactions than those of singlet molecular oxygen ( A. ... 

A complementary approach has been reported very recently [43]. hi this case negative charges were introduced into the salen ligand Iq (Fig. 14) with the aim of exchanging it on cationic supports, such as a layered double (Zn, Al) hydroxide. The expansion in the basal spacing indicated intercalation, at least partially, of the Ig-Mn complex between the layers of [Zn2,i5Alo,86(OH)6,o2]- The complex was used in the epoxidation of (i )-limonene with molecular oxygen and pivalaldehyde. The use of N-... 

The exact epoxidation mechanism is still not quite clear. However, in all possible mechanisms, the interaction between Au and Ti02 is essential. According to a mechanism suggested by Hayashi et al [1], molecular oxygen adsorbed on Ti02 is activated, probably to a... 

Of these steps, the last three can be discounted (10.6) on the grounds that there is no significant V(II) dependence, (10.7) is considered unimportant since Tl(II) is present only in minute concentrations, (10.8) is slow by comparison with the other steps in the set (k 0.13 1.mole . sec in 1 M HCIO4 at 0 °C). Both rate and stoichiometric data infer that the reaction between Tl(III) and V(n) occurs essentially by a two-electron oxidation (step (10.1)). In the presence of chloride, less V(IV) is produced. It is interesting to note that oxidation of V(II) by molecular oxygen or hydrogen peroxide generates V(IV). However, the oxidation of V(III) by Tl(III) does not occur as a two-electron step (see p. 231). 

Abel has assumed that the reaction between arsenite and molecular oxygen is catalyzed by a chromium intermediate. He suggested that chromium(IV) is converted by oxygen into chromium(VI) which causes the excess oxidation of arsenic(III). However, this mechanism is also devoid of experimental support. 

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