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NMR Spin–Spin Coupling Constants in Polymethine Dyes as Polarity Indicators
Author(s) -
Murugan N. Arul,
Aidas Kestutis,
Kongsted Jacob,
Rinkevicius Zilvinas,
Ågren Hans
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201200270
Subject(s) - polarity (international relations) , merocyanine , chemical physics , dielectric , chemistry , chemical polarity , coupling constant , cyanine , polar , computational chemistry , spin (aerodynamics) , materials science , molecule , optoelectronics , physics , thermodynamics , organic chemistry , optics , quantum mechanics , biochemistry , cell , fluorescence
Herein, we explore the use of spin–spin coupling constants (SSCCs) in merocyanine (MCYNE) dyes as indicators of polarity. For this purpose, we use Car–Parrinello hybrid quantum mechanics/molecular mechanics (QM/MM) to determine the structures of MCYNE in solvents of different polarity, followed by computations of the SSCCs by using QM/MM linear‐response theory. The molecular geometry of MCYNE switches between neutral, cyanine‐like, and zwitterionic depending on the polarity of the solvent. This structural variation is clearly reflected in the proton SSCCs in the polymethine backbone, which are highly sensitive to the dielectric nature of the environment; this mechanism can be used as a “polarity indicator” for different microenvironments. This result is highlighted by computing the SSCCs of the MCYNE probe in the cavity of the beta‐lactoglobulin protein. The computed SSCCs clearly indicate a non‐polar hydrophobic dielectric nature of this cavity.