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Atomic mass, stable isotopes

If an essential amino acid such as leucine is used to study protein turnover, the only sources are from dietary intake (I) or protein breakdown (B). Amino adds like leudne can be removed from the plasma, either for protein synthesis (S), oxidation (O), or incorporation into other metaboUc pathways after transamination/deamina-tion. In the case of leucine, this amino acid can also be completely oxidized in the human body to COj, allowing for the measurement of O as well. A simple model in the measurement of protein tumover/flux therefore takes into consideration the above factors so that flux (Q) is equal to I + B, which is in turn equal to S + O (i.e., Q = I + B = S-i- O). Isotope studies are used to derive these variables of protein turnover, since amino acid tracers can be used to measure Q and O, and if intake equals zero, then Q = B, and by subtraction, S = Q - Isotopes are molecules that share the same atomic number (protons), yet have different numbers of neutrons (atomic mass). Stable isotopes occur naturally and do not emit ionizing radiation, whereas radioactive isotopes undergo spontaneous decay. For these reasons, stable isotopes have become very popular in exercise research.Although useful, this model is very simplistic in that there are multiple amino acid pools mining over at very different rates. [Pg.113]

To this point, our discussion has concentrated only on substitution with isotopes of hydrogen. We can also look at rate effects that occur on substitution with isotopes of heavier atoms, including the stable isotopes %for Nfor and Ofor 0. Studies have been performed on heavy-atom isotope effects, both in chemical reactions (Jencks, 1%9) and in enzyme-catalyzed reactions (Cleland, 1977 O Leary Kleutz, 1972 O Leary, 1980 Huskey, 1991). One immediate problem is that the expected rate differences in heavy-atom isotope effects are much smaller because of the much smaller percentage change in atomic mass on isotopic substitution. [Pg.383]

Natural titanium consists of five isotopes with atomic masses from 46 to 50. All are stable. Eight other unstable isotopes are known. [Pg.76]

Terbium is reasonably stable in air. It is a silver-gray metal, and is malleable, ductile, and soft enough to be cut with a knife. Two crystal modifications exist, with a transformation temperature of 1289oC. Twenty one isotopes with atomic masses ranging from 145 to 165 are recognized. The oxide is a chocolate or dark maroon color. [Pg.189]

Each element that has neither a stable isotope nor a characteristic natural isotopic composition is represented in this table by one of that element s commonly known radioisotopes identified by mass number and relative atomic mass. [Pg.224]

Atoms with the same number of protons but a different number of neutrons are called isotopes. To identify an isotope we use the symbol E, where E is the element s atomic symbol, Z is the element s atomic number (which is the number of protons), and A is the element s atomic mass number (which is the sum of the number of protons and neutrons). Although isotopes of a given element have the same chemical properties, their nuclear properties are different. The most important difference between isotopes is their stability. The nuclear configuration of a stable isotope remains constant with time. Unstable isotopes, however, spontaneously disintegrate, emitting radioactive particles as they transform into a more stable form. [Pg.642]

Iodine [7553-56-2] I, atomic number 53, atomic weight 126.9044, is a nonmetaUic element belonging to the halogen family in Group 17 (VIIA) of the Periodic Table. The only stable isotope has a mass number of 127. There are 22 other iodine isotopes having masses between 117 and 139 14 of these isotopes yield significant radiation. [Pg.358]

Lead, atomic number 82, is a member of Group 14 (IVA) of the Periodic Table. Ordinary lead is bluish grey and is a mixture of isotopes of mass number 204 (15%), 206 (23.6%), 207 (22.6%), and 208 (52.3%). The average atomic weight of lead from different origins may vary as much as 0.04 units. The stable isotopes are products of decay of three naturally radioactive elements (see Radioactivity, natural) comes from the uranium series (see Uraniumand... [Pg.32]

Decay The spontaneous disintegration of an unstable atomic nucleus to form another more stable element or isotope of a lower atomic mass. [Pg.1427]

Accurate atomic weight values do not automatically follow from precise measurements of relative atomic masses, however, since the relative abundance of the various isotopes must also be determined. That this can be a limiting factor is readily seen from Table 1.3 the value for praseodymium (which has only 1 stable naturally occurring isotope) has two more significant figures than the value for the neighbouring element cerium which has 4 such isotopes. In the twelve years since the first edition of this book was published the atomic weight values of no fewer than 55 elements have been improved, sometimes spectacularly, e.g. Ni from 58.69( 1) to 58.6934(2). [Pg.16]

Atomic weights are known most accurately for elements which have only 1 stable isotope the relative atomic mass of this isotope can be determined to at least 1 ppm and there is no possibility of variability in nature. There are 20 such elements Be, F, Na, Al, P, Sc, Mn, Co, As, Y, Nb, Rh, I, Cs, Pr, Tb, Ho, Tm, Au and Bi. (Note that all of these elements except beryllium have odd atomic numbers — why )... [Pg.17]

Nitrogen has two stable isotopes N (relative atomic mass 14.003 07, abundance 99.634%) and (15.000 11, 0.366%) their relative abundance (272 1) is almost invariant in terrestrial sources and corresponds to an atomic weight of 14.00674(7). Both isotopes have a nuclear spin and can be used in nmr experiments. though... [Pg.411]

Oxygen has 3 stable isotopes of which 0 (relative atomic mass 15.994 915) is by far the most abundant (99.762 atom%). Of the others, O (16.999 134) has an abundance of only 0.038% and 0 (17.999 160) is 0.200% abundant. These values vary slightly in differing natural sources (the ranges being... [Pg.604]

Element has no stable nuclides the value given in parentheses is the atomic mass number of the isotope of longest known half-life. However, three such elements (Th, Pa and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated. [Pg.1342]

Fortunately, isotopic abundances as well as isotopic masses can be determined by mass spectrometry. The situation with chlorine, which has two stable isotopes, 0-35 and 0-37, is shown in Figure 3.2. The atomic masses of the two isotopes are determined in the usual way. The relative abundances of these isotopes are proportional to the heights of the recorder peaks or, more accurately, to the areas under these peaks. For chlorine, the data obtained from the mass spectrometer are... [Pg.52]

If the atomic mass of an element is known and if it has only two stable isotopes, their abundances can be calculated from the general equation cited above. [Pg.53]

Most of the chemical elements consist of mixtures of isotopes. Oxygen, atomic number 8, has three stable isotopes. The kind having mass number 16 is most abundant. About 99.76% of the oxygen atoms consist of this isotope. Only 0.04%... [Pg.90]

The nuclear charge and the electrons it attracts primarily determine the ways in which atoms behave toward other atoms. Mass differences cause only minor chemical effects. Since the isotopes of an element have the same nuclear charge and the same number of electrons per neutral atom, they react in the same ways. Thus we can speak of the chemistry of oxygen without specifying which one of the three stable isotopes is reacting. Only the most precise measurements will indicate the very slight chemical differences among them. [Pg.90]

Escherichia coli Adenine and adenosine are inhibitory74 and the synthesis of thiamine can be derepressed by culture in their presence.13,75 adth- Mutants are known.76 [l4C]Formate incorporates at C-2 of pyramine without dilution of molar activity. Glycine labeled with stable isotopes was fed to E. coli and the pyramine was analyzed by mass spectrometry. The two carbon atoms of glycine separated during the biosynthesis. The carboxyl was found12 at C-4, and the C-N fragment was the precursor of C-6-N-1. In conclusion, it is beyond doubt that pyramine synthesis follows the AIR pathway in E. coli. [Pg.305]

Numbers in parentheses are atomic mass numbers of most stable isotopes. [Pg.110]

The element exists as an intermediate in uranium and thorium minerals through their decay. There is no stable isotope. The longest-living isotope has a half-life of 8.3 hours. In the crust of the Earth, the total steady-state mass is estimated at a few tens of grams. Thus astatine is the rarest element (record ). A few atoms of this relative of iodine can be found in all uranium ore. It exhibits certain metallic properties. [Pg.153]

Fig. 3. Mass spectra of 1014 atoms of "Tc and of the stable isotopes of Mo. (a) Laser off, (b) laser on for "Tc and (c) with laser beams and gated detection [12a]... Fig. 3. Mass spectra of 1014 atoms of "Tc and of the stable isotopes of Mo. (a) Laser off, (b) laser on for "Tc and (c) with laser beams and gated detection [12a]...
Mykytiuk et al. [184] have described a stable isotope dilution sparksource mass spectrometric method for the determination of cadmium, zinc, copper, nickel, lead, uranium, and iron in seawater, and have compared results with those obtained by graphite furnace atomic absorption spectrometry and inductively coupled plasma emission spectrometry. These workers found that to achieve the required sensitivity it was necessary to preconcentrate elements in the seawater using Chelex 100 [121] followed by evaporation of the desorbed metal concentrate onto a graphite or silver electrode for isotope dilution mass spectrometry. [Pg.287]


See other pages where Atomic mass, stable isotopes is mentioned: [Pg.20]    [Pg.2]    [Pg.2]    [Pg.175]    [Pg.195]    [Pg.158]    [Pg.377]    [Pg.73]    [Pg.2]    [Pg.170]    [Pg.15]    [Pg.1284]    [Pg.243]    [Pg.243]    [Pg.1029]    [Pg.141]    [Pg.833]    [Pg.76]    [Pg.307]    [Pg.106]    [Pg.64]    [Pg.468]    [Pg.650]    [Pg.651]    [Pg.434]   
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Atom , atomic mass

Atom , atomic mass isotopes

Atomic mass

Atomic mass isotopes

Atoms isotopic

Atoms stable

Isotope stable isotopes

Isotopes atomic

Isotopes masses

Isotopic masses

Stable isotope

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