Evaluation of Common Theoretical Methods for Predicting Infrared Multiphotonic Dissociation Vibrational Spectra of Intramolecular Hydrogen-Bonded Ions

Author(s)

Rodrigues-Oliveira, Andre F. ^[1] ; Ribeiro, Francisco W. M. ^[1] ; Cervi, Gustavo ^[1] ; Correra, Thiago C. ^[1]

Affiliation

^[1] Univ Sao Paulo, Inst Chem, Dept Fundamental Chem, Ave Prof Lineu Prestes 748, BR-05508000 Sao Paulo - Brazil

• Document type: Journal article
• Source: ACS OMEGA; v. 3, n. 8, p. 9075-9085, AUG 2018.
• Web of Science Citations: 4

Abstract

Infrared photodissociation analyses are supported by theoretical calculations that allow a trustworthy interpretation of experimental spectra of gaseous ions. B3LYP calculations are the most prominent method used to model IR spectra, as detailed in our bibliographic survey. However, this and other commonly used methods are known to provide inaccurate energy values and geometries, especially when it comes to long-range linteractions, such as intramolecular H-bonds, which show increased anharmorucity. Therefore, we evaluated some of the most commonly used density functional theory methods (B3LYP, CAM-B3LYP, and M06-2X) and basis sets (6-31+G(d,p), 6-311++G(d,p), 6-311++G(3df,2pd), aug-cc-pVDZ, and aug-cc-pVTZ), including anharmonicity and dispersion corrections. The results were compared to MP2 calculations and to experimental high-frequency (2000-4000 cm(-1)) IR multiphotonic dissociation (IRMPD) spectra of two protonated model molecules containing intramolecular hydrogen bonds: biotin and tryptophan. M06-2X/6-31+G(d,p) was shown to be the most cost-effective level of theory, whereas CAM B3LYP was the most efficient method to describe the van der Waals interactions. The use of the dispersion correction D3, proposed by Grimmer improved the descnpfion of O-H vibrations involved in H-bonding but worsened the description of N-H stretches. Anharmonic calculations were shown to be extremely expensive when compared to other approaches. The efficiencies of well-established scaling factors (SFs) in opposition to sample-dependent SFs were also discussed and the use of fitted SFs were shown to be the most cost-effective approach to predict IRMPD spectra. M06-2X/6-31+G(d,p) and CAM-B3LYP/aug-cc-pVDZ were also tested against the fingerprint region. Our results suggest that these methods can also be used for analysis in this lower frequency range and should be regarded as the methods of choice for cost-effective IRMPD simulations rather than the ubiquitous B3LYP method, especially when further molecular properties are needed. (AU)

• FAPESP's process: 14/15962-5 - Reaction mechanism of asymmetric catalysts by mass spectrometry and gas-phase vibrational ion spectroscopy
• Grantee: Thiago Carita Correra
• Support Opportunities: Research Grants - Young Investigators Grants
• FAPESP's process: 17/18485-1 - Mechanistic studies of haloamination reactions promoted by metallic and organic catalysts
• Grantee: Francisco Wanderson Moreira Ribeiro
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 16/19698-6 - Instrumental development for mechanistic studies
• Grantee: Gustavo Cervi
• Support Opportunities: Scholarships in Brazil - Master
• FAPESP's process: 15/08539-1 - Multi-User Equipment approved in grant 2014/15962-5: ion trap mass spectrometer modified to perform infrared vibrational spectroscopy (IRMPD)
• Grantee: Thiago Carita Correra
• Support Opportunities: Multi-user Equipment Program