Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
An experimental and theoretical investigation of Acenaphthene-5-boronic acid: Conformational study, NBO and NLO analysis, molecular structure and FT-IR, FT-Raman, NMR and UV spectra
Graphical abstract
Introduction
Boronic acids and their derivatives are among the most valuable classes of organoboron molecules. Unlike many organometallic derivatives and most organoboranes, boronic acids are usually stable in air and moisture, and are of relatively low toxicity and environmental impact. Due to their low toxicity and their ultimate degradation into the environmentally friendly end products boronic acid and its derivatives, are regarded as “green” compounds. In recent years, impressive advances have been made in the use of boronic acids in molecular recognition, materials science, and catalysis. The approval of the anticancer agent Velcade, the first boronic acid containing drug, further confirms the growing status of boronic acids as an important class of compounds in chemistry and medicine. Due to its high affinity for diols [1], [2], [3], there has been a great deal of progress made in the fabrication of boronic acid–based sensors for carbohydrates and other diol-containing compounds [4], [5], [6], [7], [8], [9], [10], during the last decade.
In this communication, we presented the results from DFT calculations of the molecular structure, electronic properties and vibrational, UV and NMR spectra of monomer and hydrogen bonded dimer of AN-5-BA. The FT-IR and FT-Raman spectra of the title compound have been recorded. To make an explicit assignment of the experimental spectra, precise normal coordinate analysis has been performed. Rigorous attention has been focused on the effect of intermolecular O–H⋯O hydrogen bonding, modeled at the DFT/B3LYP level, on the bond distances, calculated frequencies and the infrared and Raman intensities. The work also encompasses calculation of HOMO, LUMO, NLO, 2D molecular electrostatic potential (MESP) contour map and 3D MESP surface map. NBO analysis of AN-5-BA has been performed to reveal the information regarding charge transfer within the molecule. UV spectra of the title molecule has also been calculated and compared with the experimental spectra. The energy and oscillator strength calculated by Configuration Interaction Singles (CIS) method and time-dependent density functional theory (TD-DFT) results complement with the experimental findings.
Section snippets
Experimental
The compound AN-5-BA in the solid state was purchased from Sigma–Aldrich Chemical Company (USA) with a stated purity of 99% and it was used as such without further purification. The FT-IR spectrum of the compound was recorded using the Perkin Elmer FT-IR BX spectrometer in the range of 4000–400 cm−1. The spectrum was recorded with a scanning speed of 10 cm−1 min−1 and the spectral resolution of 4.0 cm−1. The FT-Raman spectrum of the compound was also recorded in the Bruker FRA 106/S instrument
Quantum chemical calculation
The final optimized geometry of monomeric molecule and its hydrogen-bonded dimer are shown in Fig. 1. All calculations were accomplished with the Gaussian 09 package of programs [11] and the full molecular geometry optimizations in the ground state (in vacuo) was studied by the DFT [12] with the three-parameter hybrid functional (B3) for the exchange part and the Lee–Yang–Parr (LYP) [13], [14], [15] correlation function, using 6-311++G(d,p) basis set. To circumvent the artificially lowered
Molecular geometry
For AN-5-BA, a number of minimum energy conformations are expected. These conformers differ from one another by the arrangements of two hydroxyl groups at the boron atom site. The four possible conformations of AN-5-BA corresponding to different relative spatial orientations of the two hydroxyl groups have been analyzed and compared. The analysis of each of the possible four conformers was carried out using the DFT and employing the 6-311++G(d,p) basis set. The geometries and ground state
Conclusions
In this study, we have carried out the experimental and theoretical vibrational analysis of AN-5-BA for the first time. In general, a good agreement between experimental and calculated normal modes of vibrations has been observed. The hydrogen bonded interaction between the two monomeric units of AN-5-BA molecule and consequently the counterpoise corrected interaction energy has also been calculated. Further the short d(O–H---O) of the hydrogen bonds (1.870 Å) indicates strong hydrogen bonding
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