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Related Concept Videos

Proton (¹H) NMR: Chemical Shift01:07

Proton (¹H) NMR: Chemical Shift

3.5K
Organic molecules primarily contain carbon and hydrogen atoms. While all the hydrogen isotopes are NMR-active, protium or hydrogen-1 is the most abundant. It has a significant energy separation between its nuclear spin states due to its large gyromagnetic ratio. As per Boltzmann's distribution, an increase in the energy separation implies a greater excess population of nuclei available for excitation, resulting in a strong NMR absorption signal.
Absorption signals of all the protium nuclei...
3.5K
NMR Spectroscopy: Chemical Shift Overview01:15

NMR Spectroscopy: Chemical Shift Overview

3.3K
The position of the absorption signal of a sample is reported relative to the position of the signal of tetramethylsilane (TMS), which is added as an internal reference while recording spectra. The difference between the absorption frequencies of the sample and TMS (in Hz) is divided by the spectrometer operating frequency (in MHz) to obtain a dimensionless quantity called the chemical shift. It is reported on the δ (delta) scale and expressed in parts per million.
For instance, the proton...
3.3K
Inductive Effects on Chemical Shift: Overview01:27

Inductive Effects on Chemical Shift: Overview

2.2K
The protons in unsubstituted alkanes are strongly shielded with chemical shifts below 1.8 ppm. Methine, methylene, and methyl protons appear at approximately 1.7, 1.2 and 0.7 ppm, while the proton signal from methane appears at 0.23 ppm. An electronegative substituent, such as chlorine, withdraws the electron density from the protons, increasing their chemical shift. Progressive substitution of the hydrogens in methane by chlorine shifts the proton signals increasingly downfield, to 3.05 ppm in...
2.2K
Chemical Shift: Internal References and Solvent Effects01:17

Chemical Shift: Internal References and Solvent Effects

1.4K
In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...
1.4K
π Electron Effects on Chemical Shift: Overview01:27

π Electron Effects on Chemical Shift: Overview

1.7K
An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0,...
1.7K
¹H NMR Chemical Shift Equivalence: Homotopic and Heterotopic Protons01:03

¹H NMR Chemical Shift Equivalence: Homotopic and Heterotopic Protons

4.2K
Protons in identical electronic environments within a molecule are chemically equivalent and have the same chemical shift. The replacement test is a useful tool to identify chemical equivalence and predict NMR spectra. A substituent replaces each of the protons being examined and the resulting molecules are compared. If the same molecule is obtained, the protons are equivalent or homotopic. Replacement of any hydrogens in ethane by chlorine yields chloroethane because all six protons are...
4.2K

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Assessment of Stress Effects on Cognitive Flexibility using an Operant Strategy Shifting Paradigm
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Paediatric extrapolation: A necessary paradigm shift.

Cécile Ollivier1, Yeruk Lily Mulugeta2, Lucia Ruggieri1

  • 1European Medicines Agency, 30 Churchill Place, Canary Wharf, London, E14 5EU, UK.

British Journal of Clinical Pharmacology
|November 8, 2018
PubMed
Summary
This summary is machine-generated.

Paediatric extrapolation strategies improve medicine availability for children. Understanding adult data and knowledge gaps is key to refining these approaches and reducing unnecessary pediatric trials.

Keywords:
clinical pharmacologydrug regulationevidence-based medicineoptimal design pharmacodynamicspaediatrics

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Area of Science:

  • Pharmacology
  • Paediatric Medicine
  • Regulatory Science

Background:

  • Legislative efforts have improved access to pediatric therapies.
  • Further measures are needed to expedite pediatric study completion.
  • International experts revised the ICH E11 guideline to harmonize paediatric extrapolation.

Purpose of the Study:

  • To update the ICH E11 guideline for global paediatric medicine development.
  • To harmonize approaches to paediatric extrapolation across regions.
  • To reduce regional differences in accepting paediatric data.

Main Methods:

  • Convening international experts over three years.
  • Revising the ICH E11 guideline on paediatric investigations.
  • Analyzing experiences in paediatric extrapolation for specific conditions.

Main Results:

  • Paediatric extrapolation has streamlined drug development in areas like HIV and seizures.
  • Successful application reduces the number of children needed in clinical trials.
  • Harmonized approaches improve global paediatric medicine development.

Conclusions:

  • Understanding adult data quality and quantity is crucial for effective paediatric extrapolation.
  • Identifying knowledge gaps in disease pathophysiology and drug development is essential.
  • Generating data to fill these gaps will enhance paediatric therapeutics development and protect children.