2 research outputs found
Electronic Circular Dichroism Spectroscopy of Jet-Cooled Phenylalanine and Its Hydrated Clusters
We obtained resonant two-photon ionization
circular dichroism (R2PICD)
spectra of jet-cooled phenylalanine (Phe) and its hydrated clusters
(PheÂ(H<sub>2</sub>O)<sub><i>n</i></sub>, <i>n</i> = 1–2) near the origin band of the S<sub>0</sub>–S<sub>1</sub> transition. The R2PICD spectra of Phe exhibit well-resolved
CD bands of six different conformers present in the jet, which vary
in sign and magnitude depending on their conformations. We revised
the previous structural assignments of the Phe conformers based on
the comparison between the experimental and theoretical CD signs,
infrared spectra, and rotational band contours. The R2PICD spectra
of PheÂ(H<sub>2</sub>O)<sub><i>n</i></sub> reveal that hydration
with one or two water molecule(s) does not affect the CD signs of
Phe conformers but significantly increases their CD magnitudes. Furthermore,
conformational selection by solvation alters relative populations
of Phe conformers, leading to a sign inversion in the CD spectra of
PheÂ(H<sub>2</sub>O)<sub><i>n</i></sub> compared with that
of Phe monomer
Isomer-Specific Induced Circular Dichroism Spectroscopy of Jet-Cooled Phenol Complexes with (−)-Methyl l‑Lactate
Induced circular
dichroism (ICD) is the CD observed in the absorption
of an achiral molecule bound to a transparent chiral molecule through
noncovalent interactions. ICD spectroscopy has been used to probe
the binding between molecules, such as protein–ligand interactions.
However, most ICD spectra have been measured in solution, which only
exhibit the averaged CD values of all conformational isomers in solution.
Here, we obtained the first isomer-selective ICD spectra by applying
resonant two-photon ionization CD spectroscopy to jet-cooled phenol
complexes with (−)-methyl l-lactate (PhOH-(−)ÂML).
The well-resolved CD bands in the spectra were assigned to two conformers,
which contained different types of hydrogen-bonding interactions between
PhOH and (−)ÂML. The ICD values of the two conformers have different
signs and magnitudes, which were explained by differences both in
the geometrical asymmetries of PhOH bound to (−)ÂML and in the
electronic coupling strengths between PhOH and (−)ÂML