Kinetic properties

Background. The phosphate minerals apatite, monazite and xenotime have strongly variable retention properties for Pb under crustal conditions. The mechanisms by which the daughter product can be lost include dissolution/reprecipitation reactions, recrystallization, and diffusive loss. The latter mechanism is likely a common source of discrepancy between a mineral date and the age of the rock from which it formed. 

At sufficiently high temperature, daughter Pb will tend to migrate out of a crystal rapidly by diffusion. Since diffusion is strongly temperature dependent, transport rates rapidly decrease as temperature drops, eventually becoming negligible. In certain cases, the apparent age recorded by a mineral corresponds to the temperature at which the daughter product ceased to be lost from the crystal. 

The diffusion equation. The general problem of unsteady-state diffusion within a solid involves the prediction of the concentration distribution C(x,y,z) within a solid as a function of the space coordinates and time, t. To derive an equation that can be solved for C(x,y,z,t), conservation of mass and Pick s first law (i.e., the rate of transfer of mass per unit area is proportional to the concentration gradient, see Pick 1855) are applied to a differential control volume. The resulting expression is the diffusion equation 

Using a coordinate transformation. Equation (3) can be modified to describe radial flow in a sphere (Crank 1975). The solution of this equation for the case of a sphere of radius r with an initially uniform concentration, Co, held in an infinite reservoir of zero concentration can then be translated into terms of fractional loss by integrating the mass 

In the case of short diffusion times (i.e., only near surface penetration), it can be useful to approximate a mineral with a planar boundary as a semi-infinite medium. For the case of diffusion from a well-stirred semi-infinite reservoir at concentration Co into a half space initially at zero concentration, the concentration distribution is given by 

Many complexes between metals and simple compounds associate and dissociate rapidly relative to environmental processes, e.g. algal uptake or particle sinking 

Different data interpretation models have been applied simple dissociation constants (Langford and Khan, 1975), discrete multi-component models (Lavigne et al., 1987 Plankey and Patterson, 1987 Sojo and de Haan, 1991 Langford and Gutzman, 1992), discrete kinetic spectra (Cabaniss, 1990), continuous kinetic spectra (Olson and Shuman, 1983 Nederlof et al., 1994) and log normal distribution (Rate et al., 1992 1993). It should be noted that for heterogeneous systems, analysis of rate constant distributions is a mathematically ill-posed problem and slight perturbations in the input experimental data can yield artefactual information (Stanley et al., 1994). 

Studies on addition of metals to NOM have shown evidence for slow transformation from labile to less labile complexes over time (Burba et al., 1994 Gamier et al., 1997). In general, Cu has been found to form less labile complexes with aquatic humic substances than do Zn, Pb, Cd or Mn, but there is some disparity in the lability order reported by different workers (Burba, 1994 Rocha etal, 1997). 

The specific activities of purified enzymes range from a low of 0.11 amole/minute/mg protein in He La cells (105) to a high of 20.7 /tmole/ minute/mg protein for the pig thymus enzyme. Purified synthetases absolutely require DNA for activity. Histones do not appear to be required for basal activity but, in the presence of DNA, further stimulate activity (43, 93,100,105,117,125,148,158,159,220,221,223). Thiol and Mg + are also believed to be required for maximal activity (43,59, 60, 93, 100, 105, 117, 125, 148, 158, 159, 220, 221, 233). The enzyme exhibits pH and temperature optima of approximately 8.0 (60, 105, 125, 148) and 25°C (43, 59, 60, 93, 100, 105, 117, 125, 148, 158, 159, 220,221, 233), respectively. The specificity for /8-NAD is absolute and neither NADH nor NADP+ is utilized as a substrate (84, 90, 171). Various NAD analogs with altered adenine moieties are incorporated into both monomer and oligomer but at greatly reduced rates (209). 

Kinetic parameters for the piuified enzyme have been obtained with synthetase alone or with added DNA and histone. With enzyme alone, theK , for NAD was in the range of 80 fiM and maximal velocity varied from 346 to 800 /imole/minute/mg protein (60, 125, 148, 159). In the presence of DNA and histones, values for NAD were in the range of 

25-100 ftM (100, 105, 159, 220, 221, 233) and were a function of the concentration of DNA (125, 148). Under these same conditions maximal velocity values were in the range of 1.4-1.9 /itmole/minute/mg protein (100,105,159,220,221,233) (refer to Table III for summary). 

Source Molec ular weight Sub- unit Spedfic activity (/imole/minAng) DNA re- quire- ment His- tone re- quire- ment for maxi- mal ac- tivity lliiol re- quire- ment for maxi- mal ac- tivity Diva- lent cation for maxi- mal ac- tivity Sedi- men- tation coef- ficient (S) 

Niedergang et al. (148) reported that their purified calf thymus enzyme [in the presence of 8mM Mg +] contained approximately 10% (hy weight) tightly bound DNA (20 base pairs). Activity of the enzyme was stimulated by histone HI when the ratio of DNA to histone was two. After digestion of bound DNA with DNase, synthetase activity was totally dependent on addition of DNA. The activity of the synthetase was affected by a wide variety of agents as demonstrated by recent studies with isolated nuclei and cultured cells (Table V) (3, 11, 14, 

---

Hidalgo-Alvarez R, Martin A, Fernandez A, Bastes D, Martinez F and de las Nieves F J 1996 Electro kinetic properties, colloidal stability and aggregation kinetics of polymer colloids Adv. Colloid Interface Sc/. 67 1-118... 

Transient, or time-resolved, techniques measure tire response of a substance after a rapid perturbation. A swift kick can be provided by any means tliat suddenly moves tire system away from equilibrium—a change in reactant concentration, for instance, or tire photodissociation of a chemical bond. Kinetic properties such as rate constants and amplitudes of chemical reactions or transfonnations of physical state taking place in a material are tlien detennined by measuring tire time course of relaxation to some, possibly new, equilibrium state. Detennining how tire kinetic rate constants vary witli temperature can further yield infonnation about tire tliennodynamic properties (activation entlialpies and entropies) of transition states, tire exceedingly ephemeral species tliat he between reactants, intennediates and products in a chemical reaction. 

Electrochemical systems are found in a number of industrial processes. In addition to the subsequent discussions of electrosynthesis, electrochemical techniques are used to measure transport and kinetic properties of systems (see Electroanalyticaltechniques) to provide energy (see Batteries Euel cells) and to produce materials (see Electroplating). Electrochemistry can also play a destmctive role (see Corrosion and corrosion control). The fundamentals necessary to analyze most electrochemical systems have been presented. More details of the fundamentals of electrochemistry are contained in the general references. 

The basic kinetic properties of this allosteric enzyme are clearly explained by combining Monod s theory and these structural results. The tetrameric enzyme exists in equilibrium between a catalytically active R state and an inactive T state. There is a difference in the tertiary structure of the subunits in these two states, which is closely linked to a difference in the quaternary structure of the molecule. The substrate F6P binds preferentially to the R state, thereby shifting the equilibrium to that state. Since the mechanism is concerted, binding of one F6P to the first subunit provides an additional three subunits in the R state, hence the cooperativity of F6P binding and catalysis. ATP binds to both states, so there is no shift in the equilibrium and hence there is no cooperativity of ATP binding. The inhibitor PEP preferentially binds to the effector binding site of molecules in the T state and as a result the equilibrium is shifted to the inactive state. By contrast the activator ADP preferentially binds to the effector site of molecules in the R state and as a result shifts the equilibrium to the R state with its four available, catalytically competent, active sites per molecule. 

The kinetic properties of chemical compounds include their absorption and distribution in the body, theit biotransformation to more soluble forms through metabolic processes in the liver and other metabolic organs, and the excretion of the metabolites in the urine, the bile, the exhaled air, and in the saliva. An important issue in toxicokinetics deals with the formation of reactive toxic intermediates during phase I metabolic reactions (see. Section 5.3.3). 

Electro-conductivity of molten salts is a kinetic property that depends on the nature of the mobile ions and ionic interactions. The interaction that leads to the formation of complex ions has a varying influence on the electroconductivity of the melts, depending on the nature of the initial components. When the initial components are purely ionic, forming of complexes leads to a decrease in conductivity, whereas associated initial compounds result in an increase in conductivity compared to the behavior of an ideal system. Since electro-conductivity is never an additive property, the calculation of the conductivity for an ideal system is performed using the well-known equation proposed by Markov and Shumina (Markov s Equation) [315]. 

In addition to the questions of the potentials and capacities of electrodes, which are essentially thermodynamic considerations, practical utilization of alloys as electrodes also requires attractive kinetic properties. 

In addition to this work on the / phase, both the thermodynamic and kinetic properties of the terminal solid-solution region, which extends to about 9 atom% lithium at 423 °C, were also investigated in detail [36]. 

One may conclude that the rate-determining step of the renaturation is at least partly influenced by the cis-trans isomerization of the peptide bond the secondary nitrogen atom of which arises from proline. Otherwise, only the entropy-controlled slow nuclea-tion should be observed kinetically. The covalent bridging through Lys-Lys, therefore, gives rise not only to thermodynamic stabilization of the triple helix but also to kinetic properties which have hitherto been observed in the case of type III procollagen146) and its aminoterminal fragment Col 1-3144). 

Figure 1 Is a flow sheet showing some significant aspects of the Iterative analysis. The first step In the program Is to Input data for about 50 physical, chemical and kinetic properties of the reactants. Each loop of this analysis Is conducted at a specified solution temperature T K. Some of the variables computed In each loop are the monomer conversion, polymer concentration, monomer and polymer volume fractions, effective polymer molecular weight, cumulative number average molecular weight, cumulative weight average molecular weight, solution viscosity, polymerization rate, ratio of polymerization rates between the current and previous steps, the total pressure and the partial pressures of the monomer, the solvent, and the nitrogen.

Physical, Chemical and Kinetic Properties of the Reaction System... 

Morgan, J. J. (1967). Chemical equilibria and kinetic properties of manganese in natural waters. In "Principles and Applications of Water Chemistry" (S. D. Faust and J. V. Himter, eds), pp. 561-623. Wiley, New York. 

Cyclobutadiene owes its observed instability much to the kinetic property. Cyclobutadiene dimerizes in the argon matrix above 35 K [69] and only exists for 2-10 ms under low pressure [70, 71], However, cyclobutadiene is stabilized by bulky substituents (Scheme 30). The ferf-butyl derivative was quantitatively prepared even at a high temperature (130 °C) [72]. Yellow crystals of the cyclobutadiene fused by two seven-membered rings did not decompose below 240 °C [73]. 

Gazaryan LA. Lagrimini L.M. (1996) Purification and unusual kinetic properties of a tobacco anionic peroxidases // Phytochemistry. V. 41. P. 1029-1034. 

Figure 37-14. Alternative promoter use in the liver and pancreatic B cell glucokinase genes. Differential regulation of the glucokinase GK) gene is accomplished by the use of tissue-specific promoters. The B cell GK gene promoter and exon 1B are located about 30 kbp upstream from the liver promoter and exon 1L. Each promoter has a unique structure and is regulated differently. Exons 2-10 are identical in the two genes, and the GK proteins encoded by the liver and B cell mRNAs have identical kinetic properties.

The multiple human variants of G-6-PD and the relationship of their kinetic properties to the presence of hemolytic anemia under conditions which closely simulate the erythrocyte internal environment have been elegantly studied by Yoshida (112). This author found that those enzyme variants with significantly reduced physiological activity are those associated with hemolytic anemia. 

---