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The covalently bound diazo group as an infrared probe for hydrogen bonding environments

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Abstract

Covalently bound diazo groups are frequently found in biomolecular substrates. The C[double bond, length as m-dash]N[double bond, length as m-dash]N asymmetric stretching vibration (νas) of the diazo group has a large extinction coefficient and appears in an uncongested spectral region. To evaluate the solvatochromism of the C[double bond, length as m-dash]N[double bond, length as m-dash]N νas band for studying biomolecules, we recorded the infrared (IR) spectra of a diazo model compound, 2-diazo-3-oxo-butyric acid ethyl ester, in different solvents. The width of the C[double bond, length as m-dash]N[double bond, length as m-dash]N νas band was linearly dependent on the Kamlet–Taft solvent parameter, which reflects the polarizability and hydrogen bond accepting ability of the solvent. Therefore, the width of the C[double bond, length as m-dash]N[double bond, length as m-dash]N νas band could be used to probe these properties for a solvent. We found that the position of the C[double bond, length as m-dash]N[double bond, length as m-dash]N νas band was linearly correlated with the density of hydrogen bond donor groups in the solvent. We studied the relaxation dynamics and spectral diffusion of the C[double bond, length as m-dash]N[double bond, length as m-dash]N νas band of a natural amino acid, 6-diazo-5-oxo-L-norleucine, in water using nonlinear IR spectroscopy. The relaxation and spectral diffusion time constants of the C[double bond, length as m-dash]N[double bond, length as m-dash]N νas band were similar to those of the N[double bond, length as m-dash]N[double bond, length as m-dash]N νas band. We concluded that the position and width of the C[double bond, length as m-dash]N[double bond, length as m-dash]N νas band of the diazo group could be used to probe the hydrogen bond donating and accepting ability of a solvent, respectively. These results suggest that the diazo group could be used as a site-specific IR probe for the local hydration environments.

Graphical abstract: The covalently bound diazo group as an infrared probe for hydrogen bonding environments

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Publication details

The article was received on 23 Mar 2017, accepted on 28 Jun 2017 and first published on 28 Jun 2017


Article type: Paper
DOI: 10.1039/C7CP01867C
Citation: Phys. Chem. Chem. Phys., 2017, Advance Article
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    The covalently bound diazo group as an infrared probe for hydrogen bonding environments

    M. You, L. Liu and W. Zhang, Phys. Chem. Chem. Phys., 2017, Advance Article , DOI: 10.1039/C7CP01867C

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