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Factors Affecting Dissolution: Polymorphism, Amorphism and Pseudopolymorphism01:21

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Polymorphism refers to the existence of a drug substance in multiple crystalline forms, known as polymorphs. Recently, this term has been expanded to include solvates (forms containing a solvent), amorphous forms (non-crystalline forms), and desolvated solvates (forms from which the solvent has been removed).
Some polymorphic crystals possess lower aqueous solubility than their amorphous counterparts, leading to incomplete absorption. For instance, the oral suspension of Chloramphenicol, which...
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¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

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At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
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Mechanistic Models: Overview of Compartment Models01:21

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Mechanistic models, a category encompassing both physiological and compartmental modeling, differ from empirical models' approaches to incorporating known factors about the systems being modeled. Empirical models describe data with minimal assumptions, while mechanistic models aim to provide a robust description of available data by specifying assumptions and integrating known factors about the system. Compartmental analysis is a key example of a mechanistic model in pharmacokinetics and...
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¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

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The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
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¹H NMR: Complex Splitting01:13

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A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
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Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
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Quantum Chemical Study on Mefenamic Acid Polymorphic Forms.

Svitlana V Shishkina1, Yevhenii A Vaksler1, Irina S Konovalova1

  • 1SSI Institute for Single Crystals NAS of Ukraine, Department of X-ray Diffraction Study and Quantum Chemistry, 60 Nauky ave., Kharkiv 61001, Ukraine.

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Summary
This summary is machine-generated.

Mefenamic acid

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Area of Science:

  • Computational chemistry
  • Solid-state chemistry
  • Materials science

Background:

  • Mefenamic acid is a widely used nonsteroidal anti-inflammatory drug (NSAID).
  • Understanding its polymorphic structures is crucial for drug formulation and efficacy.
  • Polymorphism significantly impacts physicochemical properties like solubility and bioavailability.

Purpose of the Study:

  • To investigate the quantum chemical properties of three mefenamic acid polymorphic structures.
  • To elucidate the structural stability and deformation behavior of these polymorphs.
  • To correlate computational findings with experimental observations under pressure.

Main Methods:

  • Quantum chemical calculations
  • Analysis of pairwise interaction energies
  • Shear deformation modeling
  • Shift energy profile analysis

Main Results:

  • A centrosymmetric dimer formed by O-H···O hydrogen bonds is a key building unit in all polymorphs.
  • Polymorphs I and II are columnar-layered, while polymorph III exhibits a columnar structure.
  • Stability order (I > II > III) correlates with interaction energy anisotropy.
  • Crystal structures are resistant to shear deformation; high energy barriers prevent pressure-induced deformation.

Conclusions:

  • The study provides fundamental insights into the structural stability of mefenamic acid polymorphs.
  • Computational methods successfully explain experimental data, particularly for polymorph I under pressure.
  • Findings contribute to a deeper understanding of drug polymorphism and solid-state behavior.