TY - JOUR
T1 - Spectroscopic Characterization of the Divalent Metal Docking Motif to Isolated Cyanobenzoate
T2 - Direct Observation of Tridentate Binding to ortho-Cyanobenzoate and Implications for the CN Response
AU - Mohamed, Ahmed
AU - Edington, Sean C.
AU - Secor, Maxim
AU - Breton, James R.
AU - Hammes-Schiffer, Sharon
AU - Johnson, Mark A.
N1 - Publisher Copyright:
© 2023 American Chemical Society.
PY - 2023/2/16
Y1 - 2023/2/16
N2 - Cryogenic ion vibrational spectra of D2-tagged cyanobenzoate (CBA) derivatives are obtained and analyzed to characterize the intrinsic spectroscopic responses of the −CO2- headgroup to its location on the ring in both the isolated anions and the cationic complexes with divalent metal ions, M2+ (M = Mg, Ca, Sr). The benzonitrile functionality establishes the different ring isomers (para, meta, ortho) according to the location of the carboxylate and provides an additional reporter on the molecular response to the proximal charge center. The aromatic carboxylates display shifts slightly smaller than those observed for a related aliphatic system upon metal ion complexation. Although the CBA anions display very similar band patterns for all three ring positions, upon complexation with metal ions, the ortho isomer yields dramatically different spectral responses in both the −CO2- moiety and the CN group. This behavior is traced to the emergence of a tridentate binding motif unique to the ortho isomer in which the metal ions bind to both the oxygen atoms of the carboxylate group and the N atom of the cyano group. In that configuration, the −CO2- moiety is oriented perpendicular to the phenyl ring, and the CN stretching fundamental is both strong and red-shifted relative to its behavior in the isolated neutral. The behaviors of the metal-bound ortho complexes occur in contrast to the usual blue shifts associated with “Lewis” type binding of metal ions end-on to −CN. The origins of these spectroscopic features are analyzed with the aid of electronic structure calculations, which also explore differences expected for complexation of monovalent cations to the ortho carboxylate. The resulting insights have implications for understanding the balance between electrostatic and steric interactions at metal binding sites in chemical and biological systems.
AB - Cryogenic ion vibrational spectra of D2-tagged cyanobenzoate (CBA) derivatives are obtained and analyzed to characterize the intrinsic spectroscopic responses of the −CO2- headgroup to its location on the ring in both the isolated anions and the cationic complexes with divalent metal ions, M2+ (M = Mg, Ca, Sr). The benzonitrile functionality establishes the different ring isomers (para, meta, ortho) according to the location of the carboxylate and provides an additional reporter on the molecular response to the proximal charge center. The aromatic carboxylates display shifts slightly smaller than those observed for a related aliphatic system upon metal ion complexation. Although the CBA anions display very similar band patterns for all three ring positions, upon complexation with metal ions, the ortho isomer yields dramatically different spectral responses in both the −CO2- moiety and the CN group. This behavior is traced to the emergence of a tridentate binding motif unique to the ortho isomer in which the metal ions bind to both the oxygen atoms of the carboxylate group and the N atom of the cyano group. In that configuration, the −CO2- moiety is oriented perpendicular to the phenyl ring, and the CN stretching fundamental is both strong and red-shifted relative to its behavior in the isolated neutral. The behaviors of the metal-bound ortho complexes occur in contrast to the usual blue shifts associated with “Lewis” type binding of metal ions end-on to −CN. The origins of these spectroscopic features are analyzed with the aid of electronic structure calculations, which also explore differences expected for complexation of monovalent cations to the ortho carboxylate. The resulting insights have implications for understanding the balance between electrostatic and steric interactions at metal binding sites in chemical and biological systems.
UR - http://www.scopus.com/inward/record.url?scp=85147801115&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85147801115&partnerID=8YFLogxK
U2 - 10.1021/acs.jpca.2c07658
DO - 10.1021/acs.jpca.2c07658
M3 - Article
C2 - 36748882
AN - SCOPUS:85147801115
SN - 1089-5639
VL - 127
SP - 1413
EP - 1421
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 6
ER -