title: NMR spin-spin coupling constants in polymethine dyes as polarity indicators.
abstract: 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.
authors.affiliation: Division of Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of Technology, 10691 Stockholm, Sweden. murugan@theochem.kth.se
authors.forename: N Arul
authors.initials: NA
authors.lastname: Murugan
authors.forename: Kestutis
authors.initials: K
authors.lastname: Aidas
authors.forename: Jacob
authors.initials: J
authors.lastname: Kongsted
authors.forename: Zilvinas
authors.initials: Z
authors.lastname: Rinkevicius
authors.forename: Hans
authors.initials: H
authors.lastname: Ågren
mesh_terms: D004396:Coloring Agents / Q000737:chemistry*; D018360:Crystallography, X-Ray; D007202:Indicators and Reagents / Q000737:chemistry; D007211:Indoles / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000592:standards; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory; D012015:Reference Standards
chemical_list: D004396:Coloring Agents; D007202:Indicators and Reagents; D007211:Indoles; C098209:VPM chloride