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Related Concept Videos

Mass Spectrometry: Isotope Effect01:13

Mass Spectrometry: Isotope Effect

Most elements exist in nature as a mixture of isotopes. The isotopes differ in weight due to their respective number of neutrons. The molecular weight of a molecule is different depending on the specific isotope of its elements involved. As a result, the mass spectrum of the molecule exhibits peaks from the same fragment at multiple positions. The positions of these mass signals depend on the mass differences between isotopes. Furthermore, the intensity of these signals is dependent on the...
Isotopes and Radioisotopes01:28

Isotopes and Radioisotopes

In the early 1900s, English chemist Frederick Soddy realized that an element could have atoms with different masses that were chemically indistinguishable. These different types are called isotopes — atoms of the same element that differ in mass. Isotopes differ in mass because they have different numbers of neutrons but are chemically identical because they have the same number of protons. Soddy was awarded the Nobel Prize in Chemistry in 1921 for this discovery.
An isotope containing more...
Isotopes01:12

Isotopes

Elements have a set number of protons that determines their atomic number (Z). For example, all atoms with eight protons are oxygen; however, the number of neutrons can vary for atoms of the same element. The sum of the number of protons and the number of neutrons is the mass number (A). Atoms with the same atomic number but different mass numbers are called isotopes. Elements can have multiple isotopes, for example, carbon-12, carbon-13, and carbon-14.
An element's atomic mass, or weight, is a...
Radioactivity and Nuclear Equations03:18

Radioactivity and Nuclear Equations

Nuclear chemistry is the study of reactions that involve changes in nuclear structure. The nucleus of an atom is composed of protons and, except for hydrogen, neutrons. The number of protons in the nucleus is called the atomic number (Z) of the element, and the sum of the number of protons and the number of neutrons is the mass number (A). Atoms with the same atomic number but different mass numbers are isotopes of the same element.
A nuclide of an element has a specific number of protons and...
Nuclear Overhauser Enhancement (NOE)01:06

Nuclear Overhauser Enhancement (NOE)

Irradiation of a spin-active nucleus causes an increase or decrease in the signal intensity of neighboring nuclei that are not necessarily chemically bonded or involved in J-coupling. This phenomenon, called the nuclear Overhauser enhancement (NOE), results from through-space interactions between the nuclear spins. The NOE effect decreases with increasing internuclear distance and is generally not observed beyond 4 angstroms. In NOE, dipole-dipole interactions between neighboring spin-active...
Multi-Step Reactions02:31

Multi-Step Reactions

Chemical reactions often occur in a stepwise fashion involving two or more distinct reactions taking place in a sequence. A balanced equation indicates the reacting species and the product species, but it reveals no details about how the reaction occurs at the molecular level. The reaction mechanism (or reaction path) provides details regarding the precise, step-by-step process by which a reaction occurs. Each of the steps in a reaction mechanism is called an elementary reaction. These...

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Related Experiment Video

Updated: May 27, 2026

Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method
05:51

Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method

Published on: July 19, 2019

Mechanism from isotope effects.

P F Cook1

  • 1a University of Oklahoma , Department of Chemistry and Biochemistry , Norman , Oklahoma , USA.

Isotopes in Environmental and Health Studies
|November 18, 2011
PubMed
Summary
This summary is machine-generated.

Isotope effects are versatile tools for determining reaction mechanisms in both organic and enzyme-catalyzed reactions. Analyzing these effects provides insights into rate-limiting steps and reaction pathways.

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Last Updated: May 27, 2026

Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method
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Area of Science:

  • Biochemistry
  • Chemical Kinetics
  • Enzymology

Background:

  • Isotope effects are powerful tools for elucidating reaction mechanisms.
  • Interpreting isotope effects in enzyme reactions is complex due to multiple rate-limiting steps.

Purpose of the Study:

  • To develop and apply simple theory for using isotope effects in determining reaction mechanisms.
  • To explore the application of isotope effects in both organic and enzyme-catalyzed reactions.

Main Methods:

  • Discussed techniques for measuring isotope effects, including competitive and noncompetitive methods.
  • Applied isotope effect theory to organic reactions and enzyme-catalyzed processes.
  • Utilized multiple isotope effects to differentiate between stepwise and concerted reactions.

Main Results:

  • Demonstrated how isotope effects provide information on rate-limiting steps in enzyme reactions.
  • Illustrated the use of isotope effects to determine reactant addition and product release order in specific enzyme reactions (6-phosphogluconate and alcohol dehydrogenase).
  • Showcased the application of multiple isotope effects in distinguishing between stepwise and concerted mechanisms for various enzymes (formate, glucose 6-phosphate dehydrogenase, and malic enzyme).

Conclusions:

  • Isotope effects offer valuable insights into complex reaction mechanisms, especially in enzymology.
  • Rate-limitation by multiple steps in enzyme catalysis can be leveraged to gain mechanistic information.
  • Multiple isotope effects are crucial for distinguishing between stepwise and concerted reaction pathways.