Compound labels examples

Isotopically labeled compounds may be described by inserting the italic symbol of the isotope in brackets into the name of the compound for example, H C1 is hydrogen chloride[ CZ] or hydrogen chloride-36, and H C1 is hydrogen H chloride[ CZ] or hydrogen-2 chloride-38. 

A few data exist on the oxidation by ferricyanide. This is simple second-order (in oxidant and neutral hydrazine), and leads to quantitative production of nitrogen in accordance with scheme (71)-(74) with A 4 k and A i. No scrambling occurs during oxidation of N-labelled N2H4 indicating that all N2 is formed via di-imine" Di-imine so prepared is capable of hydrogenating added unsaturated compounds, for example, phenylpropiolic acid gives m-cinnamic acid" " . 

Shifts due to either a- or (3-deuterium substitution are also quite significant, usually leading to well resolved fluorine signals for the deu-terated and undeuterated species, which can be useful in characterization of deuterium labeled fluorinated compounds. An example of the a-effect is shown in Figure 2.11, which depicts the fluorine NMR spectrum of F—CH2CH2CH2CH2CH2CD2—F, a molecule that has... 

Specific activity of a radiopharmaceutical may be defined as the amount of radioactivity per unit mass of a radioisotope or a labeled compound. For example, if 100 mg l3lI-labeled albumin contains 150 mCi l3lI radioactivity, its specific activity would be 150/100, i.e., 1.5 mCi/mg. Specific activity is usually expressed in units such as Ci/g, mCi/mg, or MBq/mg. It is also expressed in terms of the radioactivity per mole of a labeled compound, e.g., mCi/mole, MBq/mole, mCi/pmole, or MBq/p,mole. Specific activity is usually provided on the product label. 

We begin our analysis of excerpt 4F by examining its use of compound labels. You have seen compound labels before. The ubiquitous R group (R, R, R",... or Ri, R2, R3,...) in organic chemistry, used to connote radical or residue (e.g., CHj— or CH3CH2— in R—Br), is one example. Another example is when authors include a bolded number (or bolded number and letter) immediately after the name of a compound in the text or table. Consider the following example, where 1 and 2 are the compound labels ... 

Like other abbreviations, compound labels must be defined before they are used alone. In the text, the label is defined by placing it immediately after the fully named compound, usually without parentheses. (Some authors use parentheses, especially for compound labels in subheadings.) Compound labels may also be defined in graphical illustrations of the compound (e.g., equations, tables, figures, schemes). Once defined, the label may be used alone, without parentheses. Consider these examples ... 

Concept boxes and links Educators define concepts as "perceived regularities in events or objects." In our biochemical maps, concepts include abstractions (for example, free energy), processes (for example, oxidative phosphorylation), and compounds (for example, glucose 6-phosphate). These broadly defined concepts are prioritized with the central idea positioned at the top of the page. The concepts that follow from this central idea are then drawn in boxes (Figure 1.13A). The size of the box and type indicate the relative importance of each idea. Lines are drawn between concept boxes to show which are related. The label on... 

What evidence is available to support the mechanism shown for the E2 reaction The experimental rate law tells us that both the base and the alkyl halide are present in the transition state or in some step prior to the transition state. Many other experimental techniques can be used to test whether a mechanism that has been proposed for a reaction is the one that is most plausible. Several of these employ the substitution of a less common isotope for one or more of the atoms of the compound. For example, a normal hydrogen atom ( H) can be replaced with a deuterium atom (2H or D) or a tritium (j H orT) atom. Or a normal carbon ( 62C) atom can be replaced with a C or C atom. Because isotopic substitution has only a very small effect on the chemical behavior of a compound, the iso-topically modified compound undergoes the same reactions and follows the same mechanisms as its unmodified counterpart. In one type of experiment, the isotope is used to trace the fate of the labeled atom as the reactant is converted to the product. 

The results5,20,22,26-31 of the Wilzbach labeling of a representative number of heterocyclic compounds are shown in Table I. A significant feature of the data is the relatively high specific activity in the crude product immediately after exposure to tritium gas compared with the ultimate activity in the purified compound. For example, the specific activity of crude benzothiophene (777 pCi/mg) dropped to 155 pCi/mg in the purified compound. Comparable data for N-methylpyrrole and trimethylpyridine were 247, dropping to 110, and 423, dropping to... 

A relatively new technique that uses radioactivity to study body processes and diagnose malfunctions is commonly called positron emission tomography (PET). In this technique radionuclides that decay by positron emission are incorporated into compounds. For example, brain function can be studied by incorporating 1gC into glucose, which is the main source of energy for the brain. By studying how this labeled glucose is metabolized in the brain, doctors can discover abnormalities caused by diseases such as cancer, Parkinson s disease, and epilepsy. 

A particularly useful method for determining relaxation times involves the use of flow reactors and labeled compounds. For example, say that the following reaction was proceeding over a solid catalyst ... 

In most studies with radioactive compounds, it is assumed that there are no isotope effects, that is, it is assumed that the radioactive molecules are randomly distributed among the total molecules of the compound and behave identically to the nonradioactive molecules. This is a reasonable assumption for most of the isotopes used in biology. The one exception is which has a mass three times that of normal H. However, for most biologically important H -labeled compounds, the total molecular weight is not much different from that of the unlabeled compound. For example, H 0 has a molecular weight only 19% greater than that of HaO. 

The decomposition of a compound labeled with a radioactive isotope can be due to one or more of four effects, as follows. (1) A primary (internal) radiation effect, wherein the decomposition of the molecules arises as a result of the disintegration of their unstable atomic nuclei. (2) A primary (external) radiation effect, in which decomposition occurs hy interaction of the molecule with a nuclear particle. (3) A secondary radiation effect, where decomposition arises from reaction with a reactive species produced hy the radiation. An example would he that of free radicals produced hy the radiolysis of residual water in freeze-dried carbohydrate samples. (4) A chemical effect, whereby decomposition arises from chemical reactions which are not connected with radiation. 

Problem 4.12 Draw stereochemical formulas for all the possible stereoisomers of the following compounds. Label pairs of enantiomers, and meso compounds. Tell which isomers, if separated from all other stereoisomers, will be optically active. Pick out several examples of diastereomers. 

Another type of line broadening is caused by electron exchange reactions between the radical and its parent compound, for example between phenoxyl radical and phenolate ion263 (equation 31, where the labels 1 and 2 mark individual molecules). 

Hot atom reactions can be used for synthesis of labeled compounds. So far this technique has been used primarily for and labeling. For example, an organic gaseous conqx)und is mixed with He and the sample is irradiated with neutrons. The reaction He(n,p) H produces tritium as hot atoms (indicated by the small arrow) with kinetic ergies of approximately 0.2 MeV. These hot atoms react with the organic molecules to produce labeled compounds. An example is the formation of labeled butanol... 

In the presence of various organic compounds labeled molecides containing the CT3 group were obtained (52-54). Typical examples are as shown below ... 

The list of compoimds that have been labeled with carbon-11 and fluorine-18 is extensive. Several recent reviews (7-15) have outlined methods of synthesizing compounds labeled with carbon-11 and fluorine-18 and have discussed some of the problems associated with such syntheses. In this chapter we will not attempt to list these syntheses. Instead, by using C-palmitic acid as a specific example, we will... 

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