Autocatalytic product

NO, the monomer C is CO, and the products are A2 = N2 and CB = CO2. The adsorption probability of C species (Fc) is the parameter of the model. The slow rate-determining step in this sequence is the dissociation of NO which requires a neighboring site to proceed. Since product formation liberates more vacant sites than those necessary for the dissociation of NO, an autocatalytic production of vacant sites takes place. 

Equation 2.3. Initiation of the autocatalytic product decomposition cycle... 

All parameters (J, kp, kT) shall be positive. p(C,) describes an autocatalytic production function which is first-order at small C, and zeroth order at large C,. Formally, it looks like the Michaelis-Menten expression (Eq. 12-32), although it does not have the same mechanistic basis. 

The kinetics of the oxidation of l-phenyl-2-thiourea by chlorite, in aqueous acidic media, are strongly influenced by the pH and show a complex acid dependence. The proposed mechanism involves HOC1 as a major intermediate whose autocatalytic production determines the observed kinetics of the reaction. The oxidation involved the formation of two stable intermediates, the sulfinic acid and the sulfonic acid, on the pathway towards total desulfurization to form phenylurea. A comprehensive 29-reaction scheme has been proposed to describe the observed complex kinetics.96 The oxidation of trimethylthiourea (TMTU) by chlorite in slightly acidic media is very fast. The oxidation of TMTU proceeds through the formation of sulfinic acid then to the sulfoxylate anion. The direct reaction of chlorine dioxide and TMTU is autocatalytic and is also inhibited by acid. A series of 28 reactions have been proposed to describe the mechanism.97... 

When only the linearly autocatalytic production of chiral molecules is active (k > 0, ko = k2 = 0), the trajectory is obtained ... 

In Eq. (a), there is the autocatalytic production of X and its enzymatic consumption. The total amount of enzyme is constant and, we have... 

The Belousov-Zhabotinsky reaction scheme can also produce moving spatial inhomogeneties in unstirred solutions. Spatial waves develop as an oxidizing region advances into a region of low but finite bromide ion concentration that falls below a critical value. The autocatalytic production of bromous acid at the interface advances the wave faster than the diffusion of any other molecules proceeds (Field et al., 1972). Nagy-Ungvarai and Hess (1991) used the electrochemical method to produce experimental data on the two-dimensional concentration profile of three variables in distributed Belousov-Zhabotinsky solutions. 

The simple model of a thermal explosion which we examined in the last section was based on the view that, for an exothermic reaction, heat played the role of an autocatalytic product. It is now interesting to ask if it is possible for chemical species produced as intermediates, or even final... 

As the concentration of bromomalonic acid, BrCH(COOH)2 increases reaction (RIO) becomes important. The bromide ion, Br produced by (RIO) is destroyed by (R2) as long as the autocatalytic production of bromous acid, HBr02, by the sequence (R4) + 2(R5) is able to maintain bromous acid. The concentration of HBr02 at the value of the second-order destruction of HBr02 by (R6), which creates the steady state is given by... 

Equation (6.43a) describes an autocatalytic production of X from A, while (6.43b), (6.43c) represent an enzymatic degradation of X to F proceeding with a regeneration of the enzyme Y. The intermediate compound D is a complex, D = XY. Hence, the total enzyme concentration, e, is given by... 

This process corresponds to single-electron oxidation by Br02 and to the autocatalytic production of HBr02. At the same time, we have the oxidation of Ce " (colorless) to Ce (yellow) that provokes the periodic change of color. The last process will regenerate the bromide and reduce the ceric ions. It can be summarized by ... 

We recognize the disappearance of bromide (process A), the oxidation of Ce cerium concomitant to the autocatalytic production of HB1O2, and the regeneration process. 

The peroxidase reaction provides another prototype for periodic behaviour and chaos in an enzyme reaction. As noted by Steinmetz et al. (1993), in view of its mechanism based on free radical intermediates, this reaction represents an important bridge between chemical oscillations of the Belousov-Zhabotinsky type, and biological oscillators. In view of the above discussion, it is noteworthy that the model proposed by Olsen (1983), and further analysed by Steinmetz et al. (1993), also contains two parallel routes for the autocatalytic production of a key intermediate species in the reaction mechanism. As shown by experiments and accounted for by theoretical studies, the peroxidase reaction possesses a particularly rich repertoire of dynamic behaviour (Barter et al, 1993) ranging from bistability (Degn, 1968 Degn et al, 1979) to periodic oscillations (Yamazaki et al, 1965 Nakamura et al, 1969 ... 

Products of thermal degradation metal chlorides produced fiom thermal stabilizers, products of degradation of some antioxidants, hydrogen chloride (autocatalytic product of PVC degradation)... 

Step (R3) is rate-limiting for process (A). Step (R2) is important in switching control from process (A) to process (B). Reaction (G) represents the autocatalytic production of HBrO in process (B). It is not elementary the rates of reaction (G) and process (B) are limited by step (R5). ... 

As a first approximation to Eq. (2) with boundary conditions (3), consider only the diffusion, autocatalytic production, and disproportionation of HBrO ... 

ZZKK assume that the rate of autocatalytic production of "active intermediate" (presumably HBr02) is proportional to the concentration... 

Nosticzius et al. [29, 43] have suggested that for Racz s systems (0.6M malonic acid in 3NH2SO4), it is the autocatalytic production of BrO which is important and malonyl radical is the control intermediate, whereas in the original FKN mechanism, the autocatalytic production of HBr02 and the control intermediate is the bromide ion. The autocatalytic steps and two types of control mechanisms depend on the circumstances. 

In the case of type II, after a time pause sufficient amount of free radicals are produced via interaction of Ce with acids produced from the oxidation of glucose. At a certain stage, autocatalytic production of BrO can be balanced by the negative feedback, involving interaction of BrO and P and Q. In course of time, the production of P and Q goes on increasing and when this exceeds the critical concentration necessary for countering the autocatalysis production of BrO, the type II oscillation stops. Thus, two type II oscillations are free-radical controlled (non-Br controlled). 

It is assumed that the velocity of band propagation is controlled by the concentration of Br (B) and bromous acid (A) in the band front and that trailing band does not affect the velocity of band propagation. Wave is due to (i) autocatalytic production and destruction of HBr02 and (ii) diffusion of HBr02. 

B-Z reaction using ferroin as a catalyst has been used for pattern formation studies for such a system. According to FKN mechanism, HB1O2 is the autocatalytic species. On commencement of autocatalysis the [Br ] is depleted to a value lower than the critical value. The autocatalytic production of HBrOj is accompanied by oxidation of ferroin to firrin Fe(phen3) +. Br formation occurs due to reaction of Fe(phen3) with bromo-malonic acid. Thus, a differential flow between HBr02 and Br can be achieved. 

Philp et al. have recently reported a beautiful example of a kinetically controlled self-repHcating systems that feeds on a DCL, strongly biasing the final product distribution towards the autocatalytic product that had a concentration of zero at the start of the experiment [5]. The system was set up by mixing five ingredients building blocks 6-9 and dipolarophile 14 (Scheme 8.3). 

Wynbergl suggested that the enantiomeric form of the chiral autocatalytic products might be able to form semi-stable dimer complexes, resulting in enrichment of the uncomplexed catalytic product. Experimental proof was given l that enantiomerically... 

First of all we observe that the network (6.26) contains an A2-element as integrated circuit for the autocatalytic production of X. In addition to this autocatalytic loop there is a second loop formed by the reaction R2. From the topological point of view, there is a strikingly close resemblance between the Brusselator in (6.26) and our autocatalytic excitation model in (6.7). Despite this topological resemblance, the two networks behave fundamentally differently, namely multiple steady states in (6.7) and a limit cycle in (6.26). This shows that a purely network topological classification of types of models will find its limits or is at least a pretentious program. 

Two channels are open simultaneously for converting the reactant A into the (autocatalytic) product B, and we may expect to find reaction rates and wave speeds faster than when either channel is closed. The relative contributions of the two channels may be expressed in terms of a dimensionless quotient, y = k /k a. ... 

Although derived in the context of biomolecular handedness, this formula is generally valid for any system that breaks a two-fold symmetry, such as mirror inversion. Using this formula, it is possible to understand the extraordinary sensitivity of bifurcation to small systematic biases that favor one enantiomer by increasing its production rate. For example, it can be estimated that the chiral asymmetry of the electroweak interaction can create differences of the order of one part in 10 between the enantiomers. Application of the above theory shows that if the autocatalytic production rate of the chiral molecules is faster than the racemization rates, then for a period in the range 10" to 10 years, the enantiomer favored by the electroweak force will dominate [16]. For such a scenario, there is currently no experimental evidence to show us how chiral autocatalysis with the required properties can originate in prebiotic chiral molecules. 

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