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Fermi resonance as a means to determine the hydrogen-bonding status of two infrared probes.

ABSTRACT: The C[double bond, length as m-dash]O/C[triple bond, length as m-dash]N stretching vibration arising from a carbonyl/nitrile functional group in various molecular systems has been frequently used to assess, for example, local hydrogen-bonding interactions, among other applications. However, in practice it is not always easy to ascertain whether the carbonyl or nitrile group in question is engaged in such interactions. Herein, we use 4-cyanoindole and cyclopentanone as models to show that, when a fundamental C[double bond, length as m-dash]O or C[triple bond, length as m-dash]N stretching mode is involved in Fermi resonance, the underlying vibrational coupling constant (W) is a convenient reporter of the hydrogen-bonding status of the corresponding carbonyl or nitrile group. Specifically, we find that for both groups a W value of 7.7 cm-1 or greater is indicative of their involvement in hydrogen-bonding interactions. Furthermore, we find that, as observed in similar studies, the Fermi resonance coupling leads to quantum beats in the two-dimensional infrared spectra of 4-cyanoindole in isopropanol, with a period of about 1.9 ps.

SUBMITTER: Rodgers JM

PROVIDER: S-EPMC5538721 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature

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Fermi resonance as a means to determine the hydrogen-bonding status of two infrared probes.

Rodgers Jeffrey M JM Abaskharon Rachel M RM Ding Bei B Chen Jianxin J Zhang Wenkai W Gai Feng F

Physical chemistry chemical physics : PCCP 20170601 24

The C[double bond, length as m-dash]O/C[triple bond, length as m-dash]N stretching vibration arising from a carbonyl/nitrile functional group in various molecular systems has been frequently used to assess, for example, local hydrogen-bonding interactions, among other applications. However, in practice it is not always easy to ascertain whether the carbonyl or nitrile group in question is engaged in such interactions. Herein, we use 4-cyanoindole and cyclopentanone as models to show that, when a ...[more]

PMID: 28604875

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Project description:1. 2-(N'-Acetyl-L-phenylalanylamino)ethyl 2'-pyridyl disulphide [compound (III)] and 2-(acetamido)ethyl 2'-pyridyl disulphide [compound (IV)] were synthesized by acylation of the common intermediate, 2-aminoethyl 2'-pyridyl disulphide, to provide examples of chromogenic thiol-specific substrate-derived two-protonic-state electrophilic probe reagents. These two reagents, together with n-propyl 2-pyridyl disulphide [compound (II)], provide structural variation in the non-pyridyl part of the molecule from a simple hydrocarbon side chain in compound (II) to a P1-P2 amide bond in compound (IV) and further to both a P1-P2 amide bond and a hydrophobic side chain (of phenylalanine) at P2 as a potential occupant of S2 subsites. 2. These disulphides were used as reactivity probes to investigate specificity and binding-site-catalytic-site signalling in a number of cysteine proteinases by determining (a) the reactivity at pH 6.0 at 25 degrees C at I 0.1 of compound (III) (a close analogue of a good papain substrate) towards 2-mercaptoethanol, benzimidazol-2-ylmethanethiol [compound (V), as a minimal catalytic-site model], chymopapains B1-B3, chymopapain A, papaya proteinase omega, actinidin, cathepsin B and papain, (b) the effect of changing the structure of the probe as indicated above on the reactivities of compound (V) and of the last five of these enzymes, and (c) the forms of pH-dependence of the reactivities of papain and actinidin towards compound (III). 3. The kinetic data suggest that reagents of the type investigated may be sensitive probes of molecular recognition features in this family of enzymes and are capable not only of detecting differences in binding ability of the various enzymes but also of identifying enzyme-ligand contacts that provide for binding-site-catalytic-site signalling mechanisms. 4. The particular value of this class of probe appears to derive from the possibility of activating the 2-mercaptopyridine leaving group not only by formal protonation, as was recognized previously [see Brocklehurst (1982) Methods Enzymol. 87C, 427-469], but also by hydrogen-bonding to the pyridyl nitrogen atom when the appropriate geometry in the catalytic site is provided by enzyme-ligand contacts involving the non-pyridyl part of the molecule.(ABSTRACT TRUNCATED AT 400 WORDS)

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Fermi resonance as a means to determine the hydrogen-bonding status of two infrared probes.

Publications

Fermi resonance as a means to determine the hydrogen-bonding status of two infrared probes.

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