Download Zinc isotopes in biology Oral tracers of enriched Zn and

Stable
isotope
64
Zn
66
Zn
67
Zn
68
Zn
70
Zn
Relative
atomic mass
63.929 142
65.926 034
66.927 128
67.924 845
69.925 32
Mole
fraction
0.4917
0.2773
0.0404
0.1845
0.0061
Zinc isotopes in biology
Oral tracers of enriched 67Zn and intravenously injected stable isotopic tracers with enriched
70
Zn are used simultaneously to determine the fraction of dietary zinc absorbed (FZA) in
humans. FZA is used in studies of zinc metabolism and homeostasis (the tendency of a body to
maintain relatively stable state, e.g., maintaining human body temperature at 37 °C). For
example, zinc isotopic tracers can be administered to patients to determine if zinc absorption in
their bodies may be impaired by ingestion of certain dietary supplements. One such study
conducted with Peruvian women showed that prenatal iron supplements affected the absorption
of zinc during pregnancy. Another isotope tracer study investigated zinc deficiency in children
with Crohn’s disease (an inflammatory disease of the intestines, especially the colon and ileum)
[32, 238-240].
Zinc radioisotopes (e.g. 65Zn) can also be used for determining zinc absorption in humans, but
they are now used rarely because of radiation hazards [32, 241-243]. ZnO nanoparticles enriched
with 67Zn are being studied for use as biological/environmental nanotoxicity tracers [32, 244].
Zinc isotopes in Earth/planetary science
Molecules, atoms, and ions of the stable isotopes of zinc possess slightly different physical,
chemical, and biological properties, and they commonly will be isotopically fractionated during
physical, chemical, and biological processes, giving rise to variations in isotopic abundances
and in atomic weights. There are measureable variations in the isotopic abundances of zinc in
natural terrestrial materials (Figure 1). Stable zinc isotopes can be used as tracers to investigate
biogeochemical and chemical processes in environmental contamination sites [245-248]. The
isotope-amount ratio n(66 Zn)/n(64Zn) can be used as an environmental tracer for detecting the
pathways of anthropogenic zinc [245-248].
Fig. 1: Variation in isotopic composition of selected zinc-bearing materials (modified from
[249]).
Zinc isotopes used as a source of radioactive isotope(s)
The 68Zn (p, 2p) 67Cu reaction in which targets with zinc enriched in 68Zn are irradiated and the
neutron induced reaction 67Zn (n, p) 67Cu are both processes for producing 67Cu for
radiotherapy [32, 250]. Irradiation of 64 Zn with a deuteron (the nucleus of 2 H, consisting of a
proton and a neutron) in a cyclotron will produce the radioisotope 64Cu, which can be used for
therapeutic applications and diagnosis with positron emission tomography (PET) via the 64Zn
(d, 2p) 64 Cu reaction [32, 251].
Glossary
anthropogenic – resulting from human activity. [return]
atomic number (Z) – The number of protons in the nucleus of an atom.
atomic weight (relative mean atomic mass) – the sum of the products of the relative atomic
mass and the mole fraction of each stable and long-lived radioactive isotope of that element in
the sample. The symbol of the atomic weight of element E is A r(E), and the symbol of the atomic
weight of an atom (isotope) of element E having mass number A is Ar( AE). Because relative
atomic masses are scaled (expressed relative) to one-twelfth the mass of a carbon-12 atom,
atomic weights are dimensionless. [return]
CT scan (X-ray computed tomography or X-ray CT, computerized axial tomography scan
or CAT scan) – a computerized tomography (CT) scan combines a series of X-ray images taken
from different angles and uses computer processing to create cross-sectional images, or slices, of
the bones, blood vessels and soft tissues inside your body [702].
cyclotron – an apparatus in which charged atomic and subatomic particles are accelerated by a
rapidly varying (radio frequency) electric field while following an outward spiral path in a
constant magnetic field. [return]
electron – elementary particle of matter with a negative electric charge and a rest mass of about
9.109 × 10–31 kg.
element (chemical element) – a species of atoms; all atoms with the same number of protons in
the atomic nucleus. A pure chemical substance composed of atoms with the same number of
protons in the atomic nucleus [703].
gamma rays (gamma radiation) – a stream of high-energy electromagnetic radiation given off
by an atomic nucleus undergoing radioactive decay. The energies of gamma rays are higher
than those of X-rays; thus, gamma rays have greater penetrating power.
half-life (radioactive) – the time interval that it takes for the total number of atoms of any
radioactive isotope to decay and leave only one-half of the original number of atoms.
intravenous (IV) – administered into a vein. [return]
isotope – one of two or more species of atoms of a given element (having the same number of
protons in the nucleus) with different atomic masses (different number of neutrons in the
nucleus). The atom can either be a stable isotope or a radioactive isotope.
isotopic abundance (mole fraction or amount fraction) – the amount (symbol n) of a given
isotope (atom) in a sample divided by the total amount of all stable and long-lived radioactive
isotopes of the chemical element in the sample. [return]
isotope-amount ratio (r) – amount (symbol n) of an isotope divided by the amount of another
isotope of the chemical element in the same system [706]. [return]
isotopic composition – number and abundance of the isotopes of a chemical element that are
naturally occurring [706]. [return]
isotopic fractionation (stable-isotope fractionation) – preferential enrichment of one isotope
of an element over another, owing to slight variations in their physical, chemical, or biological
properties [706]. [return]
metabolism – the chemical processes that occur within a living organism in order to maintain
life [708]. [return]
neutron – an elementary particle with no net charge and a rest mass of about 1.675 × 10–27 kg,
slightly more than that of the proton. All atoms contain neutrons in their nucleus except for
protium (1H). [return]
positron – the antimatter counterpart of the electron, with a mass identical to that of the electron
and an equal but opposite (positive) charge.
positron emission tomography (PET) scan – an imaging technique that is used to observe
metabolic activity within the body. The system detects pairs of gamma rays emitted indirectly
by a radioactive isotope used as a tracer, which emits positrons and which is introduced into the
body on a biologically-active molecule. Three-dimensional images of the concentration of the
radioactive isotope within the body are then constructed by computer analysis. The imaging
often is performed with an X-ray CT scan in the same instrument. [return]
proton – an elementary particle having a rest mass of about 1.673 × 10–27 kg, slightly less than
that of a neutron, and a positive electric charge equal and opposite to that of the electron. The
number of protons in the nucleus of an atom is the atomic number. [return]
radioactive decay – the process by which unstable (or radioactive) isotopes lose energy by
emitting alpha particles (helium nuclei), beta particles (positive or negative electrons), gamma
radiation, neutrons or protons to reach a final stable energy state.
radioactive isotope (radioisotope) – an atom for which radioactive decay has been
experimentally measured (also see half-life).
radiotherapy (radiation therapy) – the treatment of disease by means of radiation from
radioactive substances or X-rays.
stable isotope – an atom for which no radioactive decay has ever been experimentally measured.
tracer - substance used for tracking purposes. [return]
X-rays – electromagnetic radiation with a wavelength ranging from 0.01 to 10 nanometers—
shorter than those of UV rays and typically longer than those of gamma rays.
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