Isotope effects INDEX

It was concluded that while kinetic isotope effects are much more sensitive than Bronsted exponents to variations in pKa, the use of either quantity as an index of transition state symmetry may be doubtful. 

In the equation s is the measured dielectric constant and e0 the permittivity of the vacuum, M is the molar mass and p the molecular density, while Aa and A (po2) are the isotope effects on the polarizability and the square of the permanent dipole moment respectively. Unfortunately, because the isotope effects under discussion are small, and high precision in measurements of bulk phase polarization is difficult to achieve, this approach has fallen into disfavor and now is only rarely used. Polarizability isotope effects, Aa, are better determined by measuring the frequency dependence of the refractive index (see below), and isotope effects on permanent dipole moments with spectroscopic experiments. 

Here, A and v 2 are fitting parameters amenable to physical interpretation using Equation 12.11. The point of present concern is that the isotope effect on polarizability can now be expressed in terms of isotopic differences in refractive index. It follows from Equation 12.14 that a plot of AR/R = [6n2/((n2—l)(n2 + 2))][An/n] vs. v2 gives an approximately straight line,... 

Using Equation 12.12 one obtains (AA/A — Av /v 2) = (Aao/ao). We see that precise refractive index differences measured over a reasonable range of wavelengths allow the recovery of the polarizability isotope effect (i.e. the isotope effect on the electric field induced dipole moment), provided the molar volume and its isotope effect are available. 

CONTENTS Preface, C. Allen Bush. Thermodynamic Solvent Isotope Effects and Molecular Hydrophobicity, Terrence G. Oas and Eric J. Toone. Membrane Interactions of Hemolytic and Antibacterial Peptides, Karl Lohner and Richard M. Epand. Spin-Labeled Metabolite Analogs as Probes of Enzyme Structure, Chakravarthy Narasimhan and Henry M. Miziorko. Current Perspectives on the Mechanism of Catalysis by the Enzyme Enolase, John M. Brewer and Lukasz Leb-ioda. Protein-DNA Interactions The Papillomavirus E2 Proteins as a Model System, Rashmi S. Hedge. NMR-Based Structure Determination for Unlabeled RNA and DNA, Philip N. Borer, Lucia Pappalardo, Deborah J. Kenwood, and Istvan Pelczer. Evolution of Mononuclear to Binuclear CuA An EPR Study, William E. Antholine. Index. 

Adsorption on a clean surface shows a strong kinetic isotope effect, implying that the initial chemisorption process involves C-H bond scission. Adsorption appears to be facilitated by the presence of step-edge sites, since adsorbed intermediates are seen at low potentials on both polycrystalline Pt and on high-index Pt(335) surfaces. 

Their unique relation to water systems favors the inclusion of acid-base reactions in deuterium oxide with aqueous acid-base equilibria, even though some aspects of the chemistry suggest inclusion with nonaqueous solvents. In studies such as those of deuterium isotope effects, it is desirable to be able to measure pD as an index of acidity in heavy water. Glass electrodes respond in a nemstian way to changes in deuterium ion concentration, and therefore the usual combination of glass and calomel electrodes can form the basis of an operational definition of pD ... 

Many isotope effects in beam studies are only artifacts of the LAB-to-CM transformation and disappear when only the CM system is used. Beyond this, as has been shown for reactions (2)-(4), constraints imposed by energy and angular momentum considerations can cause isotopic effects which provide valuable clues as to mechanism. Other types of effects will be a consequence, and an indication of the importance of inertial mass. This field is clearly in its infancy and the shortness of the discussion here is not to be taken as an index of its future importance. 

Hj Dj exchange on, 26 39-43 heteropolyanion-supported, 41 230-231 high MiUer index, 26 12-15,35,36 -H-USY zeoUte, 39 186-187 hydrocarbons adsorption, 38 229-230 reactions of cyclopropane, cyclohexane, and n-heptane, 26 51-53 structural effects, 30 25-26 hydrogen adsorption on, 23 15 hydrogenation, 30 281-282 olefins, in ethanol, 30 352-353 in hydrogenation reaction, 33 101 -iron alloys, 26 75 isomerization, 30 2-3 isotope, NMR properties, 33 213,274 kinetic oscillations, 37 220-228 ball models of densely packed surfaces, 37 221-222... 

Analysis. There are five important methods for measuring the ratios of isotopes, making use respectively of—the spectrograph, the mass spectrograph, density measurements, atomic weight measurements and refractive index measurements. Any of these methods must be pushed to the present limits of accuracy or beyond in order to meet the requirements for tracer experiments. If, for example, an increase in concentration of C13 is effected from 1 per cent to 1.1 per cent and an accuracy of five per cent in the increase is required the determination must be accurate to one part in 20,000. 

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