Ultrasonic relaxation method

This report has been written in order to demonstrate the nature of spin-state transitions and to review the studies of dynamical properties of spin transition compounds, both in solution and in the solid state. Spin-state transitions are usually rapid and thus relaxation methods for the microsecond and nanosecond range have been applied. The first application of relaxation techniques to the spin equilibrium of an iron(II) complex involved Raman laser temperature-jump measurements in 1973 [28]. The more accurate ultrasonic relaxation method was first applied in 1978 [29]. These studies dealt exclusively with the spin-state dynamics in solution and were recently reviewed by Beattie [30]. A recent addition to the study of spin-state transitions both in solution and the... 

Pulse ultrasonic relaxation method, 32 18 Pump-and-probe techniques, 46 137 Purification, of actinide metals, see Actinide, metals, purification XjPj Purified protein, 36 94 Purple acid phosphatases, 40 371, 376, 43 362, 395-398, 44 243-245 biological function, 43 395 homology, 43 397... 

Resonator ultrasonic relaxation method, 32 18 Respiratory chains, 45 351-354 aerobic growth, 45 354-357 anaerobic growth, 45 357-359 autotrophic growth, 45 359-362 complexes, proteins, 38 240-241 membrane-bound Fe—S enzymes, 38 302-303... 

Consideration of the thermodynamics of a representative reaction coordinate reveals a number of interesting aspects of the equilibrium (Fig. 5). Because the complex is in spin equilibrium, AG° x 0. Only complexes which fulfill this condition can be studied by the Raman laser temperature-jump or ultrasonic relaxation methods, because these methods require perturbation of an equilibrium with appreciable concentrations of both species present. The photoperturbation technique does not suffer from this limitation and can be used to examine complexes with a larger driving force, i.e., AG° 0. In such cases, however, AG° is difficult to measure and will generally be unknown. 

Effects of addition of n-tetradecyltrimethylammonium bromide (C14TAB) on the micelle-monomer exchange processes of /f-decyltrimethylammonium bromide (CioTAB) were investigated by the ultrasonic relaxation method. The relaxation frequency increased and the relaxation strength decreased with increasing amount of CuTAB added. The dependence of the relaxation frequency on the amount of CuTAB added was in fair agreement with the relaxation theory of Annianson for mixed micelle... 

There have been further kinetic investigations of the complexes formed between the alkali and alkaline earth cations and various neutral polycyclics. Eyring and coworkers have studied - the reaction of 18-crown-6 (3) with the aqueous cations Li, Na+, K+, Rb+, Cs+, T1+, Ag+, NH4+, and Ca + by means of the ultrasonic relaxation method. The data are analysed in terms of the two-step model proposed by Chock for the complexation of univalent ions by dibenzo-30-crown-10 (4) in methanol... 

Figure 6.16 Temperature dependence of the relaxation time associated with isomerization of the hpid alkyl chain in DODDMAB vesicles as measured by the ultrasonic relaxation method for small vesicles (o) and for large vesicles ( ). Reproduced from Reference 134 with permission of the American Chemical Society.

Rassing et al. [62] studied kinetics of sodium perfluorooctanoate micellar systems using the ultrasonic relaxation method. They observed a fast relaxation process attributed to a micelle formation. The ultrasonic relaxation times revealed that periodic fluctuations in temperature and pressure caused by the acoustic wave are several magnitudes less than the temperature or pressure perturbations of jump techniques. Rassing et al. [62] suggested that the ultrasonic and jump methods measure different modes of micelle formation whose relaxation times differ by several orders of magnitude. Ultrasonic absorption techniques [69-71 ] have also been used to measure relaxation spectra of sodium perfluorooctanoate and cesium perfluorooctanoate [72,73]. 

The kinetics of micelle formation have been investigated using the ultrasonic relaxation method for alkali metal salts of perfluorooctanoic acid [206]. The... 

The dynamics of the square-planar - octahedral isomerization of a nickel(II) complex with N-(2-piperidinoethyl)salicylaldiminato ligands has been studied by ultrasonic relaxation methods- O This rearrangement can be represented as follows. Scheme 11.8 ... 

The most significant results obtained for complexes of iron(II) are collected in Table 3. The data derive from laser Raman temperature-jump measurements, ultrasonic relaxation, and the application of the photoperturbation technique. Where the results of two or three methods are available, a gratifying agreement is found. The rate constants span the narrow range between 4 x 10 and 2 X 10 s which shows that the spin-state interconversion process for iron(II) complexes is less rapid than for complexes of iron(III) and cobalt(II). 

Studies on the dynamics of complexation for guests with cyclodextrins have been carried out using ultrasonic relaxation,40 151 168 temperature jump experiments,57 169 183 stopped-flow,170,178,184 197 flash photolysis,57 198 202 NMR,203 205 fluorescence correlation spectroscopy,65 phosphorescence measurements,56,206 and fluorescence methods.45,207 In contrast to the studies with DNA described above, there are only a few examples in which different techniques were employed to study the binding dynamics of the same guest with CDs. This probably reflects that the choice of technique was based on the properties of the guests. The examples below are grouped either by a type of guest or under the description of a technique. 

Several methods are successfully applicable in this field, e.g. dielectric relaxation methods 164>, IR investigations in the near, fundamental, and far IR regions 165>, RAMAN spectroscopy 166>, NMR spectroscopy 32-34-16 ), and ultrasonic absorption i 8-i70). 

Apart from the temperature-jump technique, other relaxation methods that have been used are those of ultrasonic absorption" " and electric-field pulse. Another technique that has been used for some of the more slowly included guest molecules is that of stopped-flow. ... 

The volume difference can be found without the use of high-pressure techniques in favorable cases from the amplitude of the sound absorption observed in ultrasonic relaxation of the spin equilibrium. This method will be described below in Section III,C. 

Methods E, electronic spectra G, Gouy N, NMR U, ultrasonic relaxation. 

Methods T, Raman laser temperature-jump U, ultrasonic relaxation P, photoperturbation. 

Relaxation methods can be classified as either transient or stationary (Bernasconi, 1986). The former include pressure and temperature jump (p-jump and t-jump, respectively), and electric field pulse. With these methods, the equilibrium is perturbed and the relaxation time is monitored using some physical measurement such as conductivity. Examples of stationary relaxation methods are ultrasonic and certain electric field methods. Here, the reaction system is perturbed using a sound wave, which creates temperature and pressure changes or an oscillating electric field. Chemical relaxation can then be determined by analyzing absorbed energy (acous-... 

Chemical relaxation methods are widely used to study the kinetics of fast chemical reactions in solution. In particular, ultrasonic absorption techniques have been used to investigate fast exchange processes with relaxation times in the range 0.3 xs to 0.3 ns. The longer end of this time range has become accessible in recent years through the use of cylindrical resonator methods [1] which have lowered the frequency range covered by fictional pulse echo methods. 

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. 

General discussion of intra- and intermolecular interactions 3 van der Waals interactions 3 Coulombic interactions 5 Medium effects on conformational equilibria 5 Quantum mechanical interpretations of intramolecular interactions 7 Methods of study 8 Introduction 8 Nmr and esr spectroscopy 8 Microwave spectroscopy (MW) 12 Gas-phase electron diffraction (ED) 12 X-ray crystallographic methods 13 Circular-dichroism spectroscopy and optical rotation 14 Infrared and Raman spectroscopy 18 Supersonic molecular jet technique 20 Ultrasonic relaxation 22 Dipole moments and Kerr constants 22 Molecular mechanic calculations 23 Quantum mechanical calculations 25 Conformations with respect to rotation about sp —sp bonds 27 Carbon-carbon and carbon-silicon bonds 28 Carbon-nitrogen and carbon-phosphorus bonds 42 Carbon-oxygen and carbon-sulphur bonds 48 Conformations with respect to rotation about sp —sp bonds Alkenes and carbonyl derivatives 53 Aromatic and heteroaromatic compounds 60 Amides, thioamides and analogues 75 Conclusions 83 References 84... 

In connexion with dielectric and other spectroscopic relaxation methods, e.g. NMR, the group of ultrasonic relaxation, temperature- and pressure-jump methods 340 - 342) jjg mentioned. These yield information on the processes in electrolyte solution and confirm the basic chemical model of free ions and ion pairs in the solution... 

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