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Related Concept Videos

IR Spectrum Peak Intensity: Amount of IR-Active Bonds00:55

IR Spectrum Peak Intensity: Amount of IR-Active Bonds

When infrared radiation is passed through a molecule, absorption occurs if the molecule's vibration leads to a substantial change in its bond dipole moment. Transitions between vibrational energy levels, typically corresponding to infrared frequencies (4000–400 cm−1), allow absorption if the vibration significantly alters the dipole moment, making the molecule infrared active. The molecular bonds have different stretching and bending vibrations, resulting in various peaks with varying...
IR Frequency Region: X–H Stretching01:24

IR Frequency Region: X–H Stretching

In IR spectroscopy, signals produced by the X−H bonds (such as C−H, O−H, or N−H) can be observed in the frequency range of  2700–4000 cm–1. The C−H stretching vibration forms sharp bands in the region 2850–3000 cm–1. The presence of the O−H stretching vibration leads to the forming of an absorption band in the frequency range 3650–3200 cm−1. At the same time, N−H stretching can be confirmed by absorption bands in the 3500–3100 cm−1 range. Even though both O−H and N−H bonds vibrate at a similar...
IR Spectrum Peak Broadening: Hydrogen Bonding01:23

IR Spectrum Peak Broadening: Hydrogen Bonding

The vibrational frequency of a bond is directly proportional to its bond strength. As a result, stronger bonds vibrate at higher frequencies, while weaker bonds vibrate at lower frequencies. The stretching vibration of the strong O–H bond in alcohols and phenols (very dilute solution or gas phase) appears as a sharp peak at 3600–3650 cm−1.
However, the extent of hydrogen bonding influences the observed stretching frequency and band broadening. Intermolecular or intramolecular hydrogen bonding...
IR and UV–Vis Spectroscopy of Aldehydes and Ketones01:29

IR and UV–Vis Spectroscopy of Aldehydes and Ketones

Infrared spectroscopy, also known as vibrational spectroscopy, is mainly used to determine the types of bonds and functional groups in molecules. In aldehydes and ketones, the carbonyl (C=O) bond shows an absorption around 1710 cm-1. The C=O bond vibration of an aldehyde occurs at lower frequencies than that of a ketone. In addition to the C=O absorption in an aldehyde, the aldehydic C–H bond also gives two peaks in the 2700–2800 cm-1 range. This absorption, coupled with the C=O stretching, is...
Infrared (IR) Spectroscopy: Overview01:09

Infrared (IR) Spectroscopy: Overview

When electromagnetic radiation passes through a material, atoms or molecules transition from a lower to a higher energy state by absorbing radiation corresponding to the energy difference between the two states. The absorption of infrared (IR) radiation causes transitions between vibrational energy levels in a molecule. Therefore, IR spectroscopy is a useful analytical tool for determining the molecular structure of molecules.
Different compounds display unique properties due to their...
Oxygen Transport in the Blood01:27

Oxygen Transport in the Blood

Hemoglobin (Hb) is a crucial molecule in the human body, consisting of four polypeptide chains, each bound to an iron-containing heme group. This unique structure enables hemoglobin to bind to oxygen, with each molecule capable of combining with four molecules of oxygen, leading to rapid and reversible oxygen loading. When fully loaded with oxygen, it is called oxyhemoglobin, while hemoglobin that has released oxygen is called reduced hemoglobin or deoxyhemoglobin. As hemoglobin binds oxygen,...

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Characterization of Biological Absorption Spectra Spanning the Visible to the Short-Wave Infrared
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Published on: January 10, 2025

Hydration-induced far-infrared absorption increase in myoglobin.

Chenfeng Zhang1, Stephen M Durbin

  • 1Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA.

The Journal of Physical Chemistry. B
|November 17, 2006
PubMed
Summary

Biological water near proteins enhances terahertz (THz) absorption, increasing protein polarizability. This finding challenges previous models of protein-water interactions at THz frequencies.

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Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase

Published on: December 4, 2017

Area of Science:

  • Biophysics
  • Physical Chemistry
  • Spectroscopy

Background:

  • Protein-water interactions create a "biological water" layer with distinct properties.
  • Biological water exhibits reduced far-infrared absorption due to hindered molecular motion.
  • Previous models did not fully account for biological water's influence on protein absorption.

Purpose of the Study:

  • To investigate the effect of biological water on the terahertz (THz) absorption of proteins.
  • To quantify the THz absorption of myoglobin across varying hydration levels.
  • To determine if biological water enhances or reduces protein absorption at THz frequencies.

Main Methods:

  • THz time-domain spectroscopy was employed to measure absorption.
  • Heme protein myoglobin was studied with water concentrations ranging from 3.6 to 98 wt %.
  • Absorption measurements were conducted in the 0.1-1.2 THz frequency range.

Main Results:

  • THz absorption per protein molecule increased with the presence of biological water.
  • Experimental results showed greater THz absorption than predicted by a non-interacting model.
  • A hydration-dependent increase in absorption per protein molecule was observed across frequencies.

Conclusions:

  • Biological water significantly enhances the THz absorption of proteins.
  • Water increases the polarizability of proteins at THz frequencies.
  • These findings necessitate revised models for protein-water interactions in the THz domain.