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Related Concept Videos

¹H NMR Signal Multiplicity: Splitting Patterns01:13

¹H NMR Signal Multiplicity: Splitting Patterns

When protons A and X are coupled, their nuclear spin energy levels are slightly modified. This is because the energy required to excite proton A to a spin state parallel to proton X is slightly different from the energy required for it to become anti-parallel to spin X. Consequently, there are two possible excitation frequencies for A (A1 and A2), depending on the spin state of X, and vice versa. The mutual nature of coupling implies that the difference between frequencies A1 and A2, indicated...
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
Distribution of Molecular Speeds01:27

Distribution of Molecular Speeds

The motion of molecules in a gas is random in magnitude and direction for individual molecules, but a gas of many molecules has a predictable distribution of molecular speeds. This predictable distribution of molecular speeds is known as the Maxwell-Boltzmann distribution. The distribution of molecular speeds in liquids is comparable to that of gases but not identical and can help to understand the phenomenon of the boiling and vapor pressure of a liquid. Consider that a molecule requires a...
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

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...
Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.

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Related Experiment Video

Updated: Jul 8, 2026

Practical Aspects of Sample Preparation and Setup of 1H R1ρ Relaxation Dispersion Experiments of RNA
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Practical Aspects of Sample Preparation and Setup of 1H R1ρ Relaxation Dispersion Experiments of RNA

Published on: July 9, 2021

Exchange frequency in replica exchange molecular dynamics.

Daniel Sindhikara1, Yilin Meng, Adrian E Roitberg

  • 1Department of Physics, University of Florida, Gainesville, Florida 32611-8435, USA.

The Journal of Chemical Physics
|January 22, 2008
PubMed
Summary

Higher exchange-attempt frequency in replica exchange molecular dynamics (REMD) simulations improves sampling efficiency. This finding challenges conventional wisdom in REMD, demonstrating faster convergence with increased exchange rates.

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Spin Saturation Transfer Difference NMR (SSTD NMR): A New Tool to Obtain Kinetic Parameters of Chemical Exchange Processes
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Spin Saturation Transfer Difference NMR (SSTD NMR): A New Tool to Obtain Kinetic Parameters of Chemical Exchange Processes

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Last Updated: Jul 8, 2026

Practical Aspects of Sample Preparation and Setup of 1H R1ρ Relaxation Dispersion Experiments of RNA
08:17

Practical Aspects of Sample Preparation and Setup of 1H R1ρ Relaxation Dispersion Experiments of RNA

Published on: July 9, 2021

15N CPMG Relaxation Dispersion for the Investigation of Protein Conformational Dynamics on the µs-ms Timescale
08:09

15N CPMG Relaxation Dispersion for the Investigation of Protein Conformational Dynamics on the µs-ms Timescale

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Spin Saturation Transfer Difference NMR (SSTD NMR): A New Tool to Obtain Kinetic Parameters of Chemical Exchange Processes
11:44

Spin Saturation Transfer Difference NMR (SSTD NMR): A New Tool to Obtain Kinetic Parameters of Chemical Exchange Processes

Published on: November 12, 2016

Area of Science:

  • Computational Chemistry
  • Molecular Dynamics Simulations
  • Biophysics

Background:

  • Replica Exchange Molecular Dynamics (REMD) is a powerful technique for enhancing sampling in molecular simulations.
  • The relationship between exchange-attempt frequency and sampling efficiency in REMD is not fully understood.
  • Existing views often suggest a trade-off or diminishing returns with higher exchange frequencies.

Purpose of the Study:

  • To investigate the impact of exchange-attempt frequency on the sampling efficiency of REMD.
  • To challenge the conventional understanding of exchange frequency optimization in REMD.
  • To provide a clear correlation between exchange frequency and simulation convergence.

Main Methods:

  • Studied five peptides of varying lengths (1-21 residues).
  • Employed a range of exchange-attempt rates in REMD simulations.
  • Assessed convergence rates by comparing ensemble properties against longer reference simulations.
  • Developed a simplified model to illustrate the fundamental correlation.

Main Results:

  • Sampling efficiency demonstrably increases with higher exchange-attempt frequencies.
  • Convergence rates improve as exchange-attempt frequency is raised.
  • The observed behavior in complex systems is mirrored in a simpler, fundamental model.

Conclusions:

  • Increasing exchange-attempt frequency is beneficial for REMD sampling efficiency.
  • This finding contradicts common assumptions within the REMD community.
  • Optimizing exchange frequency by increasing it can lead to faster and more efficient molecular simulations.