Probe Kinetics

The tip current depends on the rate of the interfacial IT reaction, which can be extracted from the tip current vs. distance curves. One should notice that the interface between the top and the bottom layers is nonpolarizable, and the potential drop is determined by the ratio of concentrations of the common ion (i.e., M ) in two phases. Probing kinetics of IT at a nonpolarized ITIES under steady-state conditions should minimize resistive potential drop and double-layer charging effects, which greatly complicate vol-tammetric studies of IT kinetics. 

Many reactions have also been carried out in water. The mechanisms of the reactions of acetone and 1,3-dihydroxyacetone using zinc-proline and related catalysts have been probed kinetically.98 The former exhibits an enamine route, whereas the latter involves rate-limiting deprotonation of the -carbon and formation of an enolate. An umbelliferyl ether of dihydroxyacetone (37) has been used as a fluorogenic probe for enolization, which may prove useful in screening of aldolases in water. 

Chemical environment of tethered probes kinetic heterogeneity and solvation sphere... 

The decrease in the rate constant with increasing cTEA+,w/cTEA+.o ratio may allow probing faster IT reactions with no complications associated with slow diffusion in the bottom phase. One should also notice that, unlike previously studied ET processes at the ITIES, the rate of the reverse reaction cannot be neglected. The difference is that in the former experiments no ET equilibrium existed at the interface because only one (reduced) form of redox species was initially present in each liquid phase (15,25). In contrast, reaction (29) is initially at equilibrium and has to be treated as a quasi-reversible process (56c). Probing kinetics of IT reactions at a nonpolarizable ITIES under steady-state conditions should be as advantageous as analogous ET measurements (25). The theory required for probing simple IT reactions with the pipet tips has not been published to date. ... 

B. S. Baines, K. Brocklehurst, P. R. Carey, M. Jarvis, E. Salih, and A. C. Storer. Chymopapain A. Purification and investigation by covalent chromatography and characterization by two-protonic-state reactivity probe kinetics, steady state kinetics and resonance raman spectroscopy of some dithioacyl derivatives. Biochem. J. 233 119(1986). 

Although equilibrium properties can be obtained, no dynamical information is given from the RCMC method. This is because the various bonding or reaction states are sampled directly, without going through the transition states. The RCMC method is therefore not useful for probing kinetic effects. 

The study of the 1-naphthylcarbene system is an example of the use of probe kinetics, first employed in great detail by Scaiano and coworkers in the study of radicals and biradicals. [23]... 

The probe kinetic methodology developed by Scaiano [23] to study radicals and biradicals by laser flash photolysis (LFP) methodology is readily extended to carbenes. LFP (308, 337, 351, or 355 nm) of diazirine or diazo compounds in the presence of pyridine produces carbenes, which generally react rapidly lO M sec" ) to form ylides. [28,29] Ylides are much easier to monitor than the carbenes because they have intense UV-Vis absorption and microsecond lifetimes. Pyridine ylide methodology has enabled LFP studies of alkyl, dialkyl, alkylhalo, dihalo and carbonylcarbenes. It is now a standard tool and will be used as long as LFP studies of simple carbenes are performed. 

A versatile and classical method for studying kinetic reactions and other kinetic phenomena on short time scales is the use of a stopped-flow apparatus (SFA) for fast reproducible mixing and then to apply, e.g., spectroscopic methods for detection. In this technique, the reactants are rapidly mixed in a mixing chamber, usually under full turbulent flow that ensures fast homogenization on length scales down to nanometers [99]. Provided that short, synchronized acquisitions can be made. X-ray or neutron scattering can be used to probe kinetic transitions and other processes directly by measuring the temporal evolution of the intensity of the (mixed) sample. 

Guo, S. X. Unwin, P. R. Whitworth, A. L. Zhang, T. 2004. Microelectrochemical techniques for probing kinetics at liquid/liquid interfaces. Prog. React. Kinet. Mech, 29, 125. 

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