title: Conformational structures of jet-cooled acetaminophen-water clusters: a gas phase spectroscopic and computational study.
abstract: Jet-cooled acetaminophen (AAP)-water clusters, AAP-(H2O)1, were investigated by mass-selected resonant two-photon ionization (R2PI), ultraviolet-ultraviolet hole-burning (UV-UV HB), infrared-dip (IR-dip), and infrared-ultraviolet hole-burning (IR-UV HB) spectroscopy. Each syn- and anti-AAP rotamer has three distinctive binding sites (-OH, >CO, and >NH) for a water molecule, thus 6 different AAP-(H2O)1conformers are expected to exist in the molecular beam. The origin bands of the AAP(OH)-(H2O)1and AAP(CO)-(H2O)1conformers (including their syn- and anti-conformers) in the R2PI spectrum are shifted to red and blue compared to those of the AAP monomer, respectively. These frequency shifts upon complexation between a water molecule and a specific binding site of AAP are also predicted by theoretical calculations. The spectral assignments of the origin bands in the R2PI spectra and the IR vibrational bands in the IR-dip spectra of the four lowest-energy conformers of AAP-(H2O)1, [syn- and anti-AAP(OH)-(H2O)1and syn- and anti-AAP(CO)-(H2O)1], are aided by ab initio and time-dependent density functional theory (TDDFT) calculations. Further investigation of the IR-dip spectra has revealed a hydrogen-bonded NH stretching mode, supporting the presence of the syn-AAP(NH)-(H2O)1conformer. Moreover, by employing IR-UV HB spectroscopy, we have reconfirmed the existence of the syn-AAP(NH)-(H2O)1conformer, which happened to be buried underneath the broad background contributed by the AAP(OH)-(H2O)1conformers. These observations have led us to conclude that all of the possible conformers of AAP-(H2O)1have been found in this study.
authors.affiliation: Department of Chemistry (BK21+) and Research Institute of Natural Science, Gyeongsang National University, Jinju 52828, Republic of Korea. mychoi@gnu.ac.kr.
authors.forename: Ahreum
authors.initials: A
authors.lastname: Min
authors.affiliation: Department of Chemistry (BK21+) and Research Institute of Natural Science, Gyeongsang National University, Jinju 52828, Republic of Korea. mychoi@gnu.ac.kr.
authors.forename: Ahreum
authors.initials: A
authors.lastname: Ahn
authors.affiliation: Department of Chemistry (BK21+) and Research Institute of Natural Science, Gyeongsang National University, Jinju 52828, Republic of Korea. mychoi@gnu.ac.kr.
authors.forename: Cheol Joo
authors.initials: CJ
authors.lastname: Moon
authors.affiliation: Department of Chemistry (BK21+) and Research Institute of Natural Science, Gyeongsang National University, Jinju 52828, Republic of Korea. mychoi@gnu.ac.kr.
authors.forename: Ji Hoon
authors.initials: JH
authors.lastname: Lee
authors.affiliation: Department of Chemistry (BK21+) and Research Institute of Natural Science, Gyeongsang National University, Jinju 52828, Republic of Korea. mychoi@gnu.ac.kr.
authors.forename: Yeon Guk
authors.initials: YG
authors.lastname: Seong
authors.affiliation: Department of Chemistry, Seoul National University, Seoul 08826, Republic of Korea. seongkim@snu.ac.kr.
authors.forename: Seong Keun
authors.initials: SK
authors.lastname: Kim
authors.affiliation: Department of Chemistry (BK21+) and Research Institute of Natural Science, Gyeongsang National University, Jinju 52828, Republic of Korea. mychoi@gnu.ac.kr.
authors.forename: Myong Yong
authors.identifier: http://orcid.org/0000-0001-5729-5418
authors.initials: MY
authors.lastname: Choi
mesh_terms: D000082:Acetaminophen / Q000737:chemistry*; D005740:Gases / Q000737:chemistry; D008956:Models, Chemical; D008968:Molecular Conformation; D017550:Spectroscopy, Fourier Transform Infrared; D014867:Water / Q000737:chemistry*
chemical_list: D005740:Gases; D014867:Water; D000082:Acetaminophen