The simplest mechanism

The analysis follows a similar pattern for all types of pre-equilibrium reaction, and this will be illustrated below with each step in the argument being listed. 

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The simplest mechanism to explain the much faster rate of dissociation of actomyosin-S-1 by ATP than that of ATP cleavage is that actin activates the myosin ATPase by accelerating the rate at which ADP and Pj are released. That is when ATP is added to actomyosin-S-1, ATP rapidly binds and dissociates actomyosin, myosin ATPase then hydrolyzes ATP to form myosin-ADP.Pj, this state then reattaches to actin and phosphate is released much faster from actomyosin. ADP.Pj than it is from myosin.ADP.Pj, as shown in the scheme below ... 

Leaving aside very simple inorganic single electron transfer steps, such as those discussed above, the simplest mechanism conceivable would consist of two processes, one chemical and the other electrochemical, denoted CE or EC. A simple example of a CE process would be the reduction of a weak acid, such as acetic acid ... 

Repeating the calculation at 170 K gives K2 = 32.41, which is considerably larger. At the colder temperature the reaction is strongly in favour of the reactants. This suggest that any source of oxygen atoms from water photolysis of cometary material would not form at the surface but the higher altitude layers with different chemistry may indeed form. Unfortunately, as we have seen, the formation of O2 from water photolysis is too slow by the simplest mechanisms. 

The simplest mechanism includes stages of catalyst oxidation to its highest valence state, the formation of a complex with ROOH, and the reaction (bimolecular) of this complex with olefin [240]. 

Thus, the mechanism of MT antioxidant activity might be connected with the possible antioxidant effect of zinc. Zinc is a nontransition metal and therefore, its participation in redox processes is not really expected. The simplest mechanism of zinc antioxidant activity is the competition with transition metal ions capable of initiating free radical-mediated processes. For example, it has recently been shown [342] that zinc inhibited copper- and iron-initiated liposomal peroxidation but had no effect on peroxidative processes initiated by free radicals and peroxynitrite. These findings contradict the earlier results obtained by Coassin et al. [343] who found no inhibitory effects of zinc on microsomal lipid peroxidation in contrast to the inhibitory effects of manganese and cobalt. Yeomans et al. [344] showed that the zinc-histidine complex is able to inhibit copper-induced LDL oxidation, but the antioxidant effect of this complex obviously depended on histidine and not zinc because zinc sulfate was ineffective. We proposed another mode of possible antioxidant effect of zinc [345], It has been found that Zn and Mg aspartates inhibited oxygen radical production by xanthine oxidase, NADPH oxidase, and human blood leukocytes. The antioxidant effect of these salts supposedly was a consequence of the acceleration of spontaneous superoxide dismutation due to increasing medium acidity. 

Specify the simplest mechanical interlock capable of achieving the following functions ... 

The simplest mechanism postulated for transfer between phases is that a concentration gradient exists only across a stagnant film between phases. Then the rate of transfer is proportional to the interfacial area and a difference of concentrations across the film. For a power law chemical rate, at steady state,... 

The simplest mechanism of enzyme action is formation of a temporary compound ES of enzyme E and substrate S followed by decomposition of ES into E and a product P. When ES is assumed to attain equilibrium, the corresponding... 

Collection Techniques. The simplest mechanical method for normal liquid droplets is the slide collection slide sampling) or impression method. This method was extensively used three decades ago, and has been rarely employed since then. In this method, when the slide is exposed to a spray, droplets impinging on it make impressions. The impressions are then observed and measured usually using a Quantimet image analyzer, although a microscope fitted with a traversing scale may be used for the measurement. The measured data are subsequently converted to actual droplet sizes based on a correction factor proposed by May.[659]... 

When dash pot and spring elements are connected in parallel they simulate the simplest mechanical representation of a viscoelastic solid. The element is referred to as a Voigt or Kelvin solid, and it is shown in Fig. 3.10(c). The strain as a function of time for an applied force for this element is shown in Fig. 3.11. After a force (or stress) elongates or compresses a Voigt solid, releasing the force causes a delay in the recovery due to the viscous drag represented by the dash pot. Due to this time-dependent response the Voigt model is often used to model recoverable creep in solid polymers. Creep is a constant stress phenomenon where the strain is monitored as a function of time. The function that is usually calculated is the creep compliance/(f) /(f) is the instantaneous time-dependent strain e(t) divided by the initial and constant stress o. ... 

When a spring and a dash pot are connected in series the resulting structure is the simplest mechanical representation of a viscoelastic fluid or Maxwell fluid, as shown in Fig. 3.10(d). When this fluid is stressed due to a strain rate it will elongate as long as the stress is applied. Combining both the Maxwell fluid and Voigt solid models in series gives a better approximation for a polymeric fluid. This model is often referred to as the four-parameter viscoelastic model and is shown in Fig. 3.10(e). Atypical strain response as a function of time for an applied stress for the four-parameter model is found in Fig. 3.12. 

In searching for the simplest mechanism to explain these observations and this rate form, Michaelis and Menten (1913) came up with the two-step elementary reaction mechanism... 

One of the simplest mechanisms that has been considered for Cu(II/I) electrochemistry involves the dissociation of either the Cu L or Cu L complex species to the solvated species (designated in Scheme 2 as Cu and Cu ), preceding or following the electron-transfer step [117]. 

Among chain-breaking antioxidants the stable dialkyl nitroxides such as di-f erf-butyl nitroxide (I) and 2,2,6,6-tetramethyl-4-pyridone nitroxide (II) inhibit oxidation by the simplest mechanism and therefore exhibit... 

The simplest mechanism, often assumed to be the operative one in general, is commonly called the ion-by-ion mechanism, since it occurs by sequential ionic reactions. The basis of this mechanism, illustrated for CdS, is given by... 

Analytic solution of the Michaelis-Menten kinetic equation The simplest mechanism of enzyme reactions is of the form... 

Accordingly, the simplest mechanism that accounts for the enhanced ethanolysis rates in the presence of metal ions is shown in IV, where a metal-bound ethanol molecule, made acidic by metal coordination, serves as a general acid catalyst for C—N bond cleavage. Here again enhanced reactivity is exhibited by the 18C6-complexed metal ethoxide species [13]. 

In all cases, to achieve a proper regulation of the flow, a pulsation damper is used. It operates on the principle of a mechanical ballast or can be electronically controlled. The simplest mechanical ballasting device is a coil with a low cross-section, several metres in length, placed between the pump and the injector. Under the influence of a wave of solvent, the tube uncoils slightly which increases its internal volume and dampens the variation in pressure. 

The simplest mechanism for transfer of the carboxyl group of carboxyphosphate to biotin would appear to be nucleophilic displacement of the phosphate leaving group by NT of biotin. The enzyme could presumably first catalyze removal of the NT hydrogen to form a ureido anion.59 Another reasonable possibility would be for the terminal phospho group of ATP to be transferred to biotin to form an O-phosphate60/61... 

To reach an understanding of why methane and chlorine do not react in the dark, we must consider the details of how the reaction occurs—that is, the reaction mechanism. The simplest mechanism would be for a chlorine molecule to collide with a methane molecule in such a way as to have chloromethane and hydrogen chloride formed directly as the result of a concerted breaking of the Cl-Cl and C-H bonds and making of the C-Cl and H-Cl bonds (see Figure 4-5). The failure to react indicates that there must be an energy barrier too high for this mechanism to operate. Why should this be so ... 

Macroscopic and microscopic rate constants Except in the simplest mechanisms, the observed rate constant for the reaction as a whole will not correspond to any one of the microscopic rate constants k characterizing the individual steps. The term observed rate constant, kobs, is used for the overall rate constant for the complete reaction. 

The maximal concentration of a putative intermediate in the simplest mechanism (Scheme 11.15) may be obtained from estimates of the rate constants using linear free energy relationships. This concentration of the intermediate could then be assessed by a suitable analytical method and, provided there is confidence in the estimated rate constants, the non-observation of an intermediate would be good evidence for excluding a stepwise process. As far as we are aware, this direct procedure has not been achieved but it is relevant to studies of concertedness [11]. 

Why do these exchange reactions occur The reaction almost certainly proceeds by deprotonation of the co-ordinated bpy ligand to generate a co-ordinated pyridyl anion. The simplest mechanism involves a simple deprotonation of the ligand, with the hydroxide ion acting as a base (Fig. 8-27). The difficulty with this mechanism is that it is not... 

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