Specific activity 228 INDEX

TABLE 12. Specific activity index (SAI) of tumour and of normal tissues of mice 12 hours after injection of 211At-BK 19.9108... 

Stone JH, Hoffinan GS, Merkel PA, et al. A disease-specific activity index for Wegener s granulomatosis modification of the Birmingham Vasculitis Activity Score. International Network for the Study of the Systemic Vasculitides (INSSYS). Arthritis Rheum 2001 44(4) 912-920. 

Enzymes are excellent catalysts for two reasons great specificity and high turnover rates. With but few exceptions, all reac tions in biological systems are catalyzed by enzymes, and each enzyme usually catalyzes only one reaction. For most of the important enzymes and other proteins, the amino-acid sequences and three-dimensional structures have been determined. When the molecular struc ture of an enzyme is known, a precise molecular weight could be used to state concentration in molar units. However, the amount is usually expressed in terms of catalytic activity because some of the enzyme may be denatured or otherwise inactive. An international unit (lU) of an enzyme is defined as the amount capable of producing one micromole of its reaction product in one minute under its optimal (or some defined) reaction conditions. Specific activity, the activity per unit mass, is an index of enzyme purity. 

Boiling-point at 11 mm. Specific gravity at 21 Refi active index. Optical rotation. ... 

Oxygen reduction specific activities of the low index planes of Pt and PtjNi in 0.1 M HCIO4 at 0.9 V versus RHE at 60°C. (From Science, 315, 493 (2007). Reproduced with permission from AAAS.)... 

The effect of zeolite porosity on the reaction rate was also well demonstrated in liquid-phase oxidation over titanium-containing molecular sieves. Indeed, the remarkable activity in many oxidations with aqueous H2O2 of titanium silicalite (TS-1) discovered by Enichem is claimed to be due to isolation of Ti(IV) active sites in the hydrophobic micropores of silicalite.[42,47,68 69] The hydrophobicity of this molecular sieve allows for the simultaneous adsorption within the micropores of both the hydrophobic substrate and the hydrophilic oxidant. The positive role of hydrophobicity in these oxidations, first demonstrated with titanium microporous glasses,[70] has been confirmed later with a series of titanium silicalites differing by their titanium content or their synthesis procedure.[71] The hydrophobicity index determined by the competitive adsorption of water and n-octane was shown to decrease linearly with the titanium content of the molecular sieve, hence with the content in polar Si-O-Ti bridges in the framework for Si/Al > 40.[71] This index can be correlated with the activity of the TS-1 samples in phenol hydroxylation with aqueous H2C>2.[71] The specific activity of Ti sites of Ti/Al-MOR[72] and BEA[73] molecular sieves in arene hydroxylation and olefin epoxidation, respectively, was also found to increase significantly with the Si/Al ratio and hence with the hydrophobicity of the framework. 

Ferrichrome iron transport in the enteric bacteria affords an experimentally feasible model for mechanistic studies. The ligand is rugged and can be labeled to high specific activity by microwave discharge activation of tritium gas. The labile ferric ion can be replaced with chromium to yield the kinetically stable isostructural chromic complex, chromichrome (61). Assuming this analog has the transport properties of the iron complex, its 3H counts would be an index of the behavior of... 

Friedel and Crafts themselves observed that aluminum chloride is by no means the only specific catalyst in the Friedel-Crafts reaction. A number of other acidic metal halides could also be employed however, these were less reactive. The strength or coordinating power of different Lewis acids can vary widely against different Lewis bases. Hence it is extremely difficult to establish a scale of strength of Lewis acids in a manner analogous to that used for Brpnsted acids. Despite the difficulties, a number of qualitative orders of reactivity have been proposed. A comparative study of the activity of various Friedel-Crafts catalysts was performed by Olah and coworkers. Thus the activity index (the lowest temperature at which reaction occurs) of a large number of Lewis acid halides was measured using the benzylation reaction as the probe. 

The activity holds major interest since it measures the content of the enzyme when the enzyme is to be used in a process. However, enzymes are usually marketed in terms of activity rather than weight. The specific activity (e.g., U kg") is a parameter of interest as an index of purity but otherwise is of less importance. There is a problem with the definitions of activity (the rather vague notion of standard conditions ). These are meant to refer to optimal conditions, especially with... 

Fig. 17.2 Comparison of specific activity of oxygen reduction on low index facets of Pd and Pt single crystals at 0.9 V [18]...

The activity index is calculated for each element in the model and it represents the portion of the total system energy that flows through a specific element. 

A series of reduced models are produced based on the activity index and MORA. More specifically, 19, 23, and 37% of the elements are eliminated to generate three reduced models. The accuracy of the reduced models degrades as more elements are eliminated however, even after removing 37% of the elements the reduced model retains only the most important elements to predict the system response with... 

Thirty minutes after intravenous administration of 5 jitCi of glycine, liver tissue was sampled. Adenine nucleotides extracted by acid were degraded to adenine and it was purified by silver nitrate precipitation and Dowex 50 column. The specific activity of adenine thus obtained served as the index of the rate of purine biosynthesis de novo. ... 

Tab 6 IMFL. UENCE OF 1-BUTEliE O. l THE SPECIFIC ACTIVITY SAl,POLYETHYLENE INTRINSIC /ISCOSITY AND MELT FLOM INDEX IMFI) (a)... 

Fig. 6.16 Specific activity of ORR measured at 0.9 V vs. RHE in HQO4 (0.1 M) at 333 K on three low-index facets of PtjNi, as compared with the corresponding facets of Pt. The specific activity of polycrystalline Pt is tdso marked by a horiTjontal dashed grey line. The values of the experimented d-band center position of each facet are also listed. Reprinted with permission from ref [6]...

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