Kinetic stability analytical methods

K. Thai, G. C. Visor, J. Duffy, W. C. Hsu, and L. C. Foster, Stability of interleukin ip (IL-ip) in aqueous solution Analytical methods, kinetics, products and solution formulation implications, Pharm. Res, 8, 485 (1992). 

This chapter will explore the relationship of thermodynamic and kinetic data as it pertains to characterizing the stability of various protein systems in the liquid state. Finally, from the wealth of information generated over the past few decades, it should be possible to assess the practical use of microcalorimetry for predicting stability. This technique used in combination with several other bio-analytical methods can serve as a powerful tool in the measurement of thermodynamic and kinetic phenomena.3-9 Attention will be given to limitations of the technique rendered from different applications as well as to areas where it is advantageous. Ultimately, the practical utility of this technique will rest with those familiar with the art. 

For these three materials, covalent bonding technologies cannot be used. With silanes, mixed anhydrides are formed lacking in hydrolytic stability. Coating with organic polymers [32] is the way to go. A bonded phase based on zirconia has been studied widely [43]. Method development strategies established with silica-based RP cannot be transferred to an RP bonded on zirconia. Selectivity is dependent, e.g., on the type of buffer used. Anions in the mobile phase influence retention. The kinetics of analyte interaction with the different active sites may lead to reduced efficiencies. 

Because of the small concentration of the 2 1 complex the last term can be ignored. From the extreme rate values in the absence of zinc and with an excess of zinc, 2i and 22 are determined as 2.4 X 104 min.-1 and 1.57 min.-1 respectively. These values can be combined with the trend in the rate constants to give the stability constant of the reactive complex, presumably Zn(OR)(OAc), as 3 X 107. For the simple zinc complex in water the literature values of the stability constant for the 1 1 complex vary from 2.5 X 108 to 6.3 X 108. The diazo coupling reaction of the complex indicates the smaller effect of coordination vis a vis protonation since this reaction is very sensitive to such effects and does not proceed with phenols. Unfortunately the choice of cations for such a reaction is restricted since the cation should not interfere with the analytical methods used to obtain the kinetic data nor should it introduce additional reactions such as occur with transition metal cations which can catalyze the decomposition of the diazonium salt via a redox process. 

Gu LC, Erdos EA, Chiang HS, Calderwood T, Isai K, Visor GC, Duffy J, Hsu WC, Foster LC. Stability of interleukin ip in aqueous solution analytical methods, kinetics, products, and solution formulation implications. Pharm Res 1991 8 485-490. 

Time-related variables are critical in GD work. One of the key features of any analytical method used in a production facility is the sample analysis time. Because GD is a kinetic-based system, the evolution of the plasma processes to, hopefully, an equilibrium situation, is of special concern. It is sufficient to say that any analysis (spectral acquisition) performed in a sequential mode requires that the plasma reach a steady state before analyses can be started — which is obviously arguable for simultaneous detection. Thus, for most analyses, the plasma stabilization time can be a substantial fraction of the overall sample analysis time. 

In Chapter 3, Busca summarizes the current state of knowledge of aluminas, the various polymorphs of which constitute some of the most commonly used catalyst components. The author starts with a discussion of the bulk structures of transition aluminas, which are the intermediate phases formed in the thermal transformation of aluminum oxyhydroxides into the thermodynamically most stable modification, a-alumina. Crucial are the definitions of the various phases, which are based on the methods of preparation rather than on the structural properties. The understanding of many alumina structures is incomplete, and progress, even with modem analytical methods and theory, is hampered by the defective and disordered nature of these materials. The stabilities of the various phases are governed by both thermodynamics and kinetics, either of which can be affected by impurities. The uncertainties in the surface stmctures are even greater than those of the bulk stmctures. Numerous models of alumina surface stmctures have been formulated over decades, but the tme stmctures seem to become even more elusive. Busca concludes his chapter with a list of research needs. 

In the spedes-specific method, the spike is usually an isotopically labeled analyte and supposed to simultaneously elute with the analyte in the entire separation procedure. The method is only possible when the composition and structure of the analyte are known in order to obtain the spike that is labeled with an enriched isotope. The premise of the method is that the labeled spikes have enough thermodynamic and kinetic stability and no isotopic exchange occurs between the spike and analyte. In this mode, the loss of the analyte after isotope dilution step has no influence on the analytical results. In fact, this... 

The main focus of the project was the elucidation of particle-stabilizer-solvent interactions as a function of the binding strength, the chain length, the concentration of the stabilizers, the polarity of the solvents, and the surface configuration as well as the size and morphology of the metal oxide nanoparticles. Therefore, to characterize the stabilization kinetics, a number of analytical methods, such as thermogravimetric analysis, isothermal titration calorimetry, and spectroscopic methods, were combined. 

Many transition metal complexes have been considered as synzymes for superoxide anion dismutation and activity as SOD mimics. The stability and toxicity of any metal complex intended for pharmaceutical application is of paramount concern, and the complex must also be determined to be truly catalytic for superoxide ion dismutation. Because the catalytic activity of SOD1, for instance, is essentially diffusion-controlled with rates of 2 x 1 () M 1 s 1, fast analytic techniques must be used to directly measure the decay of superoxide anion in testing complexes as SOD mimics. One needs to distinguish between the uncatalyzed stoichiometric decay of the superoxide anion (second-order kinetic behavior) and true catalytic SOD dismutation (first-order behavior with [O ] [synzyme] and many turnovers of SOD mimic catalytic behavior). Indirect detection methods such as those in which a steady-state concentration of superoxide anion is generated from a xanthine/xanthine oxidase system will not measure catalytic synzyme behavior but instead will evaluate the potential SOD mimic as a stoichiometric superoxide scavenger. Two methodologies, stopped-flow kinetic analysis and pulse radiolysis, are fast methods that will measure SOD mimic catalytic behavior. These methods are briefly described in reference 11 and in Section 3.7.2 of Chapter 3. 

In precolumn derivatization, the derivatization process alters the chemical nature of the analytes. Therefore, it may be necessary to develop new chromatographic methods. However, the separation can be optimized for the particular analytes, and any excess reagent can be removed so that it does not interfere with detection. The selection of precolumn derivatization reagents is therefore less restricted than is the choice of postcolumn derivatization reagents, and rapid kinetics are not particularly important. The stability of the derivative is important, however, as is the percent derivatization, which should be as near to 100% as possible. It is also important that the reaction yield only one derivative per analyte, so that coelutions of extra peaks does not occur, and so solute identification and quantitation are accurate. 

---