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Mass Spectrometry: Molecular Fragmentation Overview01:20

Mass Spectrometry: Molecular Fragmentation Overview

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The ionization of a molecule into a molecular ion inside the mass spectrometer causes instability in the molecule's structure due to the loss of an electron. This eventually leads to the fragmentation or breaking of some bonds in the molecule. The fragmentation occurs predominantly at specific bonds to yield relatively stable fragments.
One type of fragmentation pattern is the cleavage of a single bond in the molecular ion. The cleavage leads to a radical and a cation. The cleavage can...
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Mass Spectrometry: Aromatic Compound Fragmentation01:23

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Upon ionization, aromatic compounds generate a molecular ion that is observed as a prominent peak in their mass spectra. For example, the molecular ion peak for benzene appears at a mass-to-charge ratio of 78, while toluene is observed at a mass-to-charge ratio of 92. The molecular ion benzene is highly stable and does not readily undergo further fragmentation due to the significant amount of energy required to disrupt the aromatic stability of the benzene ring. In contrast, the molecular ion...
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Mass Spectrometry: Amine Fragmentation00:55

Mass Spectrometry: Amine Fragmentation

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Amines can be identified using mass spectroscopy based on their characteristic fragmentation patterns. The molecular ions of amines undergo fragmentation via ⍺-cleavage. The ⍺-cleavage of the carbon-carbon bonds in amines generates an alkyl radical and resonance-stabilized nitrogen-containing cation.
In amines, the number of nitrogen atoms affects the mass of the molecular ion, which is described by the nitrogen rule of mass spectrometry. This rule states that a compound containing...
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Mass Spectrometry: Alkyne Fragmentation00:53

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The fragmentation of alkynes preferentially occurs at the carbon–carbon bond between the α and β carbon of the alkyne bond to generate a 3-propynyl cation (or propargyl cation). In terminal alkynes, there is the only type of fragmentation that yields the 3-propynyl cation. The unsubstituted 3-propynyl cation exhibits a peak at a mass-to-charge ratio of 39. In internal alkynes, the 3-propynyl cation is substituted. For example, 2-pentyne fragments into methyl-substituted...
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The resolution of a mass spectrometer depends on the efficiency of separating ions with different ion masses. The mass of an atom is approximated to the sum of the masses of protons and neutrons inside, considering the masses of protons and neutrons as equal. However, the masses of the proton (1.6726 × 10−24 g) and neutron (1.6749 × 10−24 g) are not truly equal. There is a minor error in the expression of atomic masses relative to the simplest atom of hydrogen. For...
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Mass Spectrometry: Alkene Fragmentation00:59

Mass Spectrometry: Alkene Fragmentation

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Alkenes lose one electron from the unsaturated π bond upon ionization and form stable molecular ions. Further fragmentation of alkenes occurs through three different reaction pathways. The most prominent fragmentation is the cleavage at the allylic position. The resultant allylic carbocation is resonance stabilized. In the mass spectra of terminal alkenes, this fragment appears at a mass-to-charge ratio of 41. In the internal alkenes, where there are two choices of allylic cleavage, the...
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Combining fragmentation method and high-performance computing: Geometry optimization and vibrational spectra of

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A novel fragment-based molecular tailoring approach (MTA) enables rapid and accurate quantum chemical calculations for protein geometry and infrared spectra. This method offers significant computational advantages for large biomolecules.

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Area of Science:

  • Computational chemistry
  • Quantum chemistry
  • Biophysics

Background:

  • Advanced quantum chemical methods are crucial for understanding protein structures and spectral features.
  • Calculating these properties for large proteins is computationally intensive and challenging.

Purpose of the Study:

  • To evaluate the fragment-based molecular tailoring approach (MTA) for protein geometry optimization and vibrational infrared (IR) spectra calculation.
  • To assess the accuracy, efficiency, and scalability of MTA for biomolecular computations.

Main Methods:

  • Employed MTA with CAM-B3LYP/aug-cc-pVDZ level of theory for geometry optimization and IR spectra of ten real proteins.
  • Utilized a polarizable continuum model with water as a solvent.
  • Compared MTA results with full calculation (FC) counterparts.

Main Results:

  • MTA achieved rapid and accurate IR spectra calculations for proteins up to 407 atoms.
  • Typical errors in total energy and IR frequencies were 5-10 millihartrees and 5 cm⁻¹, respectively, compared to FC.
  • MTA demonstrated significant advantages in computation time, memory, and disk space for larger systems.

Conclusions:

  • MTA is a viable and efficient approach for quantum chemical calculations of protein geometry and IR spectra.
  • The inherent parallelization of MTA allows for large-scale computations.
  • Future applications of MTA with high-performance computing (HPC) for biomolecules up to ~1000 atoms are feasible.