Turnover condition

Formic acid is stable under the reaction conditions. Optimization of the reaction conditions led to a system that afforded 30 turnovers of 1 after 5 h (Table 2). Based on both IR and UV-vis, the Ce-POM retains its structure under the turnover conditions. The formic acid product inhibits the reaction, so procedures to remove it during reaction are needed to increase CH20 conversions. 

Whatever the route to a rhodium dihydride alkene complex, the hydrogen must be transferred sequentially to the double bond. It had always been assumed that the first C-H bond is formed / to the amido-group, so that the more stable Rh-substrate chelate is formed. This is the alkylhydride isomer observed in stoichiometric NMR studies at low temperatures, and is supported by studies under catalytic turnover conditions, assuming a normal isotope effect... 

Hill, C. L. and Zhang, X. A smart catalyst that self-assembles under turnover conditions, Nature, 373 (1995), 324-326... 

Protein ALBP-PX was the first pyridoxamine-conjugated protein to be synthesized and structurally characterized. Under single-turnover conditions, this protein demonstrated amino acid production rates of only 56% of the free cofactor. However, depending on the nature of the a-keto acid, ALBP-PX did show a range of optical inductions for the amino acid product. Notably, enantiomeric excesses in the order of 94% were observed for the production of valine. Additionally, several trends were noted. All amino acid products that showed optical induction favored the 1-enantiomer, except alanine, which favored the d-enantiomer. Furthermore, a-keto acids with branched side chains... 

Fig. 6A,B Titration with ions. The hammerhead ribozyme reaction was examined on a background of ions A data obtained by Lott et al. [54]. The proposed binding of metal ions is illustrated B data obtained by Nakamatsu et al. [87]. An unmodified ribozyme (R34 gray curve) and a modified ribozyme (7-deaza-R34 black curve) were used. The rate constants were normalized by reference to the maximum rate constant ([La ]=3 (mol/1). Reactions were performed under single-turnover conditions in the presence of 80 nmol/1 ribozyme and 40 nmol/1 substrate at 37 °C...

Reaction conditions permitting a catalyst to pass through many catalytic rounds. Multiple-turnover conditions are usually obtained by maintaining the substrate concentration in excess over the concentration of active catalyst. This technique usually allows one the opportunity to evaluate the catalytic rate constant ka,t, which is the first-order decay rate constant for the rate-determining step for each cycle of catalysis, and one can evaluate the magnitude of other parameters such as the substrate s dissociation constant or Michaehs constant. 

Reaction conditions that only permit a catalyst to pass through a single round of catalysis. Single-turnover conditions are usually obtained by limiting the substrate concentration relative to the concentration of active catalyst. Occasionally, single-turnover conditions can also be achieved by limiting the period of reaction. 

RANDOM SCISSION KINETICS MULTIPLE DEAD-END INHIBITION MULTIPLE-TURNOVER CONDITIONS MULTIPLICATIVE MODEL MULTIPLICITY... 

OXYGEN, OXIDES 0X0 ANIONS SINGLET STATE JABLONSKI DIAGRAM SINGLET-TRIPLET ENERGY TRANSFER SINGLE-TURNOVER CONDITIONS Site-directed inhibitor,... 

Nuclear magnetic resonance (NMR) spectroscopy is the most widely used spectroscopic technique in synthetic chemistry [1], One main reason for the dominance of NMR is its versatility—by variation of only a few experimental parameters, a vast number of different NMR experiments can easily be performed, giving access to very different sets of information on the substance or the reaction under investigation. Today, NMR is dominant in structure elucidation, and in situ NMR spectroscopy can conveniently give insight into chemical reactions under real turnover conditions (in contrast to, e.g., x-ray crystallography, which can only provide a solid-state snapshot of a molecular conformation). 

Several other studies have dealt with NOS. Most of the work involves the organic radical part and is mentioned here without further detailed discussion. The role of tetrahydrobiopterin (BH4) as an essential cofactor in the oxygenase domain has been investigated under single turnover conditions using a potent... 

The spectral changes observed with (Cu",Co")- and (Cu ,Co")-BESOD respectively by reduction and oxidation with Oj" under turnover conditions were interpreted by a protonation and deprotonation of the bridging imidazolate anion. They were, moreover, shown to occur at the rate of the reduction and oxidation of the Cu center . 

The thematic approach to isolating the deacylation step is to generate the acylen-zyme in situ in the stopped-flow spectrophotometer by mixing a substrate that acylates very rapidly with an excess or stoichiometric amount of the enzyme. The acylenzyme is formed in a rapid step that consumes all the substrate. This is then followed by relatively slow hydrolysis under single-turnover conditions. For example, acetyl-L-phenylalanine p-nitrophenyl ester may be mixed with chy-motrypsin in a stopped-flow spectrophotometer in which the enzyme is acylated in the dead time. The subsequent deacylation may be monitored by the binding of proflavin to the free enzyme as it is produced in the reaction.8... 

Proof of formation of an intermediate from pre-steady state kinetics under single-turnover conditions... 

The step k2 is isolated by mixing an excess of ester substrate with the enzyme. Under this condition, the acylenzyme is formed it accumulates and then remains at a constant concentration over an extended period of time, as long as there is enough substrate present to ensure that the enzyme remains acylated (Chapter 4, equations 4.37 to 4.46). The process of the E-S complex giving the acylenzyme is thus isolated. The rate constant for this step is said to be measured under single-turnover conditions, since a single turnover of the enzyme from the E-S to the acylenzyme is measured, and not the recycling of enzyme as in the steady state. 

When 51V nuclear magnetic resonance (NMR) was used to follow the catalysis of trimethoxybenzene (tmb) bromination, the only vanadium species that were observed under conditions of 0.5 mM total vanadium(V) were oxodiper-oxovanadium(V) (V0(02)2 , -688 ppm), oxoperoxovanadium(V) (V0(02)+, -529 ppm), and cw-dioxovanadium(V) (-540 ppm). Within the experimental error of the integration, all of the vanadium was detected in the vanadium(V) oxidation state under turnover conditions, since the integrated signal intensity at various times throughout the reaction was equivalent to that of an equimolar solution of cis-V02+. 

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