Long-lived intermediates

The term pseudosubstrate as used in this article will comprise sugar-related compounds that are chemically transformed by glycosidases, often forming long-lived intermediates and thereby acting as reversible inhibitors. Even in cases of weak inhibition, where the intermediate is too short-lived for chemical or physical characterization, the type of reaction catalyzed by the... 

The results are presented in Fig. 6, where the measured and calculated difference signals A5[r, x] are illustrated. The presence of a strong peak at r 2.7-3.0 A proves the existence of an I2 bond in different chemical environments this bond is present in CH2I—1 at times inferior to 10 nanoseconds, and in I3 at later times. This study proves, for the first time unambiguously, the presence of the long-living intermediate CH3I—1. 

The age equation. The Pa age equation, calculated assuming no chemical shifts in protactinium or uranium and an initial Pa/ U = 0, is analogous to the Th age equation (Eqn. 1), but simpler. There is no term analogous to the term because there is no long-lived intermediate daughter isotope between and Pa ... 

If the reaction has long lived intermediates, it is possible that the chain end could alternate between a chlorine ended and a sodium ended chain as a dichloride was added to give the chlorine end and then... 

In the absence of a long-lived intermediate, the time constants for product formation must be the same for the two branches of the parallel reactions giving triplet products or singlet products each appearance time is given by the reciprocal of the sum of the rates for the two parallel channels. As discussed above the appearance time for the production of the singlet... 

The anomalous plasma decay suggests that the deionization coefficient is larger at higher electron densities and higher H2 densities. The second interpretation proposes that electrons and H2 molecules can act as stabilizing third bodies and that this process involves the same long-lived intermediate complexes that are observed in merged beam experiments (see Section IV.B). 

The deposition of metals has also been studied by a large number of electrochemical techniques. For the deposition of Cu2+, for example, it is reasonable to ask whether both electrons are transported essentially simultaneously or whether an intermediate such as Cu+ is formed in solution. Such questions, like those of the ECE problem discussed above, have usually been investigated by forced convection techniques, since the rate of flow of reactant to and away from the electrode surface gives us an important additional kinetic handle. In addition, by using a second separate electrode placed downstream from the main working electrode, reasonably long-lived intermediates can be transported by the convection flow of the electrolyte to this second electrode and detected electrochemically. 

Only very few examples of alkene-]2-i-2] cycloadditions are known ]345, 347, 348]. By using a large excess of the moderate electron-rich alkene p-propenyl-anisol ]348] or even less electron-rich alkyl-subshtuted 1,3-butadienes [347] no thermal [2-1-2] cycloaddition occurs, but a photochemical cycloaddition can be enforced. The mechanism is proven to be stepwise via a biradical or dipolar intermediate ]347-351], comparable to the addition of the alkynes. During the addihon of cis- and trons-alkenes the existence of this relahvely long lived intermediate leads to a loss of stereochemical integrity. Addihon of ds-4-propenylanisol or trans-4-propenylanisol results in both cases exclusively in the trans-adduct (Scheme 4.61). 

Abramovitch and Takeuchi had explored the use of N-aminopyridinium ions as precursors to nitrenium ions in both photolysis and thermolysis reactions, but had not attempted to use these precursors under flash photolysis conditions. Moran and Falvey demonstrated that the LFP of 138 in CFI3CN (Scheme 57) generated a short-lived intermediate (1.5 jus) that had characteristics similar to the ions l31b-f. The transient was identified as the singlet ion 116. " Evidence from product analysis and spectrophotometric detection of the cation radical Ph2NH- as a long-lived intermediate was initially thought to indicate that there were parallel path-... 

If the oxidant is a double equivalent reactant like H2O2 or CI2, the oxidation of oxalate takes place without the formation of any long lived intermediate. This has been demonstrated in the oxidation of Co(NH3)5(C204)+ by H2O2, where C02 and... 

All ILs showed a rich photochemistry after UV photolysis leading to the buildup of various long-lived intermediate products as evidenced from the observation that ILs turn yellow upon continuous irradiation. On the other hand, exposing ILs to short excitation pulse (a rapid-scan method) significantly suppressed the formation of halides [22]. 

Fig. 6. The Nagra/PSI TDB 01/01 was used in this modelling chain for the performance assessment of a proposed Swiss repository for spent fuel, vitrified high-level waste, and long-lived intermediate-level waste.

The overall TOF of this reaction was unexpectedly low and may be due to deactivation by long lived intermediates blocking reactive sites on the bimetallic particles. We are currently attempting to determine the cause of this loss of activity. 

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