title: Coupling of complex aromatic ring vibrations to solvent through hydrogen bonds: effect of varied on-ring and off-ring hydrogen-bonding substitutions.
abstract: In this study, we examine the coupling of a complex ring vibration to solvent through hydrogen-bonding interactions. We compare phenylalanine, tyrosine, l-dopa, dopamine, norepinephrine, epinephrine, and hydroxyl-dl-dopa, a group of physiologically important small molecules that vary by single differences in H-bonding substitution. By examination of the temperature dependence of infrared absorptions of these molecules, we show that complex, many-atom vibrations can be coupled to solvent through hydrogen bonds and that the extent of that coupling is dependent on the degree of both on- and off-ring H-bonding substitution. The coupling is seen as a temperature-dependent frequency shift in infrared spectra, but the determination of the physical origin of that shift is based on additional data from temperature-dependent optical experiments and ab initio calculations. The optical experiments show that these small molecules are most sensitive to their immediate H-bonding environment rather than to bulk solvent properties. Ab initio calculations demonstrate H-bond-mediated vibrational coupling for the system of interest and also show that the overall small molecule solvent dependence is determined by a complex interplay of specific interactions and bulk solvation characteristics. Our findings indicate that a full understanding of biomolecule vibrational properties must include consideration of explicit hydrogen-bonding interactions with the surrounding microenvironment.
authors.affiliation: Department of Biochemistry and Biophysics, University of Pennsylvania, 422 Curie Boulevard, Philadelphia, Pennsylvania 19104, USA. nvnucci@mail.med.upenn.edu
authors.forename: Nathaniel V
authors.initials: NV
authors.lastname: Nucci
authors.forename: J Nathan
authors.initials: JN
authors.lastname: Scott
authors.forename: Jane M
authors.initials: JM
authors.lastname: Vanderkooi
mesh_terms: D024322:Amino Acids, Aromatic / Q000737:chemistry*; D001679:Biogenic Amines / Q000737:chemistry*; D004298:Dopamine / Q000737:chemistry; D004837:Epinephrine / Q000737:chemistry; D006860:Hydrogen Bonding; D007980:Levodopa / Q000031:analogs & derivatives / Q000737:chemistry; D008956:Models, Chemical; D009638:Norepinephrine / Q000737:chemistry; D010649:Phenylalanine / Q000737:chemistry; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry; D013055:Spectrophotometry, Infrared / Q000379:methods; D013696:Temperature; D014443:Tyrosine / Q000737:chemistry; D014732:Vibration
chemical_list: D024322:Amino Acids, Aromatic; D001679:Biogenic Amines; D012997:Solvents; D014443:Tyrosine; D007980:Levodopa; D010649:Phenylalanine; D004298:Dopamine; D009638:Norepinephrine; D004837:Epinephrine