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Mass Spectrometry: Isotope Effect01:13

Mass Spectrometry: Isotope Effect

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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 difference between the molecular mass. Furthermore, the intensity of these signals is dependent on the...
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Enzymes speed up reactions by lowering the activation energy of the reactants. The speed at which the enzyme turns reactants into products is called the rate of reaction. Several factors impact the rate of reaction, including the number of available reactants. Enzyme kinetics is the study of how an enzyme changes the rate of a reaction.
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Enzyme kinetics studies the rates of biochemical reactions. Scientists monitor the reaction rates for a particular enzymatic reaction at various substrate concentrations. Additional trials with inhibitors or other molecules that affect the reaction rate may also be performed.
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Isotopes01:12

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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.
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Polarimetry finds application in chemical kinetics to measure the concentration and reaction kinetics of optically active substances during a chemical reaction. Optically active substances have the capability of rotating the plane of polarization of linearly polarized light passing through them—a feature called optical rotation. Optical activity is attributed to the molecular structure of substances. Normal monochromatic light is unpolarized and possesses oscillations of the electrical...
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Accurate Single-Molecule Kinetic Isotope Effects.

Yilin Guo1, Chen Yang1, Huiping Li2

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Single-molecule kinetic isotope effects (sm-KIE) using graphene junctions precisely track chemical reactions. This method reveals transition state structures and reaction dynamics, advancing chemical understanding and optimization.

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Area of Science:

  • Chemical Dynamics
  • Single-Molecule Studies
  • Surface Science

Background:

  • Conventional kinetic isotope effect (KIE) methods are limited by ensemble averaging.
  • Single-molecule techniques offer higher resolution for studying reaction mechanisms.
  • Graphene-based junctions provide a platform for precise molecular manipulation and observation.

Purpose of the Study:

  • To develop and apply an accurate single-molecule kinetic isotope effect (sm-KIE) method.
  • To overcome limitations of conventional ensemble KIE measurements.
  • To probe chemical reaction dynamics and transition state (TS) structures at the single-molecule level.

Main Methods:

  • Fabrication of graphene-molecule-graphene single-molecule junctions.
  • In situ real-time monitoring of single-molecule reaction trajectories.
  • Application of sm-KIE to study the Claisen rearrangement.

Main Results:

  • Observed C-O bond cleavage and C-C bond formation in the transition state of the Claisen rearrangement.
  • Demonstrated high detection sensitivity and accuracy of the sm-KIE method.
  • Determined transition state structures under varying electric fields, revealing multidimensional regulation.

Conclusions:

  • sm-KIE is a powerful tool for characterizing reaction dynamics and transition states.
  • This method provides deeper insights than conventional ensemble KIE.
  • Detection and manipulation of transition states offer new avenues for optimizing chemical reactions and biomimetic processes.