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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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Related Experiment Video

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Assessment of Stress Effects on Cognitive Flexibility using an Operant Strategy Shifting Paradigm
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Keratoprosthesis prophylaxis: is it time for a paradigm shift?

J S Pelletier1,2,3, S B Barone1, J A Capriotii1,2

  • 1Department of Ophthalmology, Veloce BioPharma LLC, Fort Lauderdale, FL, USA, jpelletier@yahoo.com.

Clinical Ophthalmology (Auckland, N.Z.)
|September 27, 2018
PubMed
Summary

Boston Type I Keratoprosthesis requires special care to prevent infections. Exploring povidone-iodine as an alternative to antibiotics may improve outcomes and reduce resistance risks.

Keywords:
antimicrobial resistancekeratoprosthesisocular surfacepovidone-iodine

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Area of Science:

  • Ophthalmology
  • Biomaterials Science

Background:

  • The Boston Type I Keratoprosthesis is an advanced artificial cornea implant.
  • Maintaining ocular surface health is crucial for long-term device function.
  • Infectious complications like keratitis and endophthalmitis are significant risks.

Purpose of the Study:

  • To evaluate the role of prophylaxis in preventing infectious complications after Boston Type I Keratoprosthesis implantation.
  • To explore alternative prophylactic agents to topical antibiotics, such as povidone-iodine.
  • To address concerns regarding antibiotic resistance associated with chronic topical antibiotic use.

Main Methods:

  • Review of current standard-of-care prophylaxis protocols for Boston Type I Keratoprosthesis.
  • Discussion of the limitations and potential adverse effects of chronic topical antibiotic use.
  • Exploration of povidone-iodine formulations as a potential prophylactic agent.

Main Results:

  • Current prophylactic strategies are primarily anecdotal and lack controlled clinical trial data.
  • Chronic topical antibiotic use raises concerns about antibiotic resistance and opportunistic infections.
  • Povidone-iodine presents a potential alternative for prophylaxis, possibly mitigating antibiotic resistance.

Conclusions:

  • Optimizing Boston Type I Keratoprosthesis maintenance requires careful attention to ocular surface health.
  • Alternative prophylactic agents like povidone-iodine warrant investigation to improve safety and combat antibiotic resistance.
  • Further research, including clinical trials, is needed to validate the efficacy of non-antibiotic prophylaxis.