Electric field jumps

Any reacting system occuring with a change in electric moment, AM, will show a dependence of the associated equilibrium constant K on the electric-field strength E 

There is a modest increase in the electrical conductance with an increase in the electric-field gradient, an effect that operates with both strong and weak electrolytes (the first Wien effect). More important in the present context is the marked increase in electrical conductance of weak electrolytes when a high-intensity electric field is applied (second Wien effect). The high field promotes an increase in the concentration of ion pairs and free ions in the equilibrium 

Commonly, a 10 volt/cm field will produce a 1% change in conductance of weak electrolytes. The measurement of very short relaxation times ( 50 ns) is possible by the electric-field jump method but the technique is generally complicated and mainly restricted to ionic equilibria.  

The five-coordinate Ni(L)Cl2 (L = Et2N(CH)2)2NH(CH2)2NEt2) acts as a moderately weak electrolyte in acetonitrile where equilibrium with a planar form is assumed 

Perturbation by an electric field jump (conductivity monitoring) produces a single relaxation. These data and other considerations give the rate constants shown in (3.11). Perturbation by a laser pulse of (3.11) using spectral monitoring (Sec. 3.5.1) gives reasonably concordant 

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Porschke D and Obst A 1991 An electric field jump apparatus with ns time resolution for electro-optical measurements at physiological salt concentrations Rev. Sc/. Instnim. 62 818-20... 

The electric field-jump method is applicable to reactions of ions and dipoles. Application of a powerful electric field to a solution will favor the production of ions from a neutral species, and it will orient dipoles with the direction of the applied field. The method has been used to study metal ion complex formation, the binding of ions to macromolecules, and acid-base reactions. 

The several experimental methods allow a wide range of relaxation times to be studied. T-Jump is capable of measurements over the time range 1 to 10 s P-jump, 10 to 5 X 10" s electric field jump, 10 to 10 s and ultrasonic absorption, 10 to 10 " s. The detection method in the jump techniques depends upon the systems being studied, with spectrophotometry, fluorimetry, and conductimetry being widely used. 

The electric-field-jump method with electric conductivity detecting system can be applied to reactions occuring on the order of milliseconds to microseconds. The rise time of the applied electric field is much faster than 0.1 ys. The strength of the electric field is 20 kV/cm. The details of the electric-field-jump apparatus can be found elsewhere (9). 

Methanol is one of the easy solvents to work with using the electric-field-jump technique. The preparation of the solvent is not nearly as arduous as is that of some other solvents such as acetonitrile. In methanol we observed that picric acid anion protonates at the diffusion controlled rate whereas dipicryl-amine sterically hinders the proton from recombining with it. 

Conventional, flow, temperature-jump, ultrasonic absorption, electric-field jump and nmr line broadening have all been used to measure the rates. UV-vis spectrophotometry and conductivity are the monitoring methods of choice. A variety of solvents have been used. The focus has been often on the dissociation since the dissociation rate constant appears in general to be the main controller of the overall stability. 

Pressure jump and electric field jump methods have also been used, as have methods depending upon periodic changes in some property. For example, absorption of ultrasonic sound causes a periodic change in the pressure of the system. 

Ehlers-Danlos syndrome 438 Eicosanoid 565 Eigen, Manfred 84 Elastase 66,609,610,611s cryoenzymology 616 P-cylinder in 78 Elastic fibers 436 Elastin 15,72,436 Electrical double layer 400 Electric field jump methods 468 Electrochemical gradient 410 Electrochemical transference 311 Electrode(s)... 

Small perturbations temperature, pressure and electric field jumps... 

Previous investigations of helix-coil transition kinetics, which used a variety of fast relaxation methods (electric field jump, ultrasonic absorption, dielectric relaxation and temperature jump), encountered many difficulties (12). The systems studied were long homopolymers (>200 residues) that often had hydrolyzable side chains. Controversial results have been reported, depending on the experimental technique employed, because unwanted side chain reactions or molecular reorientation were often difficult to distinguish from the helix-coil conformational change. However, as observed here, a maximum in the relaxation times was detected for these experiments ranging from 15 ps to 20 ns and was attributed to the helix-coil transition. 

Measurements of the relaxation times by relaxation methods (involving a temperature jump [T-jump], pressure jump, electric field jump, or a periodic disturbance of an external parameter, as in ultrasonic techniques) are commonly used to follow the kinetics of very fast reactions. 

An important turning point in reaction kinetics was the development of experimental techniques for studying fast reactions in solution. The first of these was based on flow techniques and extended the time range over which chemical changes could be observed from a few seconds down to a few milliseconds. This was followed by the development of a variety of relaxation techniques, including the temperature jump, pressure jump, and electrical field jump methods. In this way, the time for experimental observation was extended below the nanosecond range. Thus, relaxation techniques can be used to study processes whose half lives fall between the range available to classical experiments and that characteristic of spectroscopic techniques. 

The electrical field-jump method is applied to reactions involving ions and dipoles. The field induces a shift in the solution equilibrium in the direction of producing more ions, or in the orientation of dipoles. Thus, when a high electrical field is applied to a solution containing a weak eleetrolyte, the extent of dissociation increases. The method has been used to study metal ion complex formation reactions and acid-base reactions. 

The kinetics of hydrolysis of Fe(III) perchlorate in dilute solution have been investigated by means of an electric field jump relaxation method [155]. At 25°C and at a low ionic strength (<3 x 10 the hydrolysis step... 

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