Molecular structure analysis and spectroscopic characterization of 9-methoxy-2H-furo[3,2-g]chromen-2-one with experimental (FT-IR and FT-Raman) techniques and quantum chemical calculations

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Highlights

  • FT-IR and FT-Raman spectra of 9M2HFC in the solid phase were recorded and analyzed.

  • The PED calculation provides a strong support for the frequency assignment.

  • The NBO analysis explains the intra molecular hydrogen bonding.

  • The first order hyperpolarizability and HOMO, LUMO energy gap were theoretically predicted.

Abstract

Experimental and theoretical investigations on the molecular structure, electronic and vibrational characteristics of 9-methoxy-2H-furo[3,2-g]chromen-2-one (9M2HFC) were presented. The vibrational frequencies were obtained by DFT/B3LYP calculations employing 6-311++G(d,p) basis set, were compared with experimental FT-IR and FT-Raman spectral data. The FT-IR spectrum (4000–400 cm−1) and FT-Raman spectrum (4000–100 cm−1) in solid phase were recorded for 9M2HFC. The geometry of the title compound was fully optimized. Quantum chemical calculations of the equilibrium geometry, the complete vibrational assignments of wavenumbers using potential energy distribution (PED) calculated with scaled quantum mechanics infrared intensities, Raman activities of the title molecule was reported. HOMO–LUMO energies, molecular electrostatic potential, Mulliken population analysis on atomic charges, natural bond orbital (NBO) analysis, non linear optical behavior in terms of first order hyperpolarizability, and thermodynamic properties of the title molecule were carried out. Finally, simulated FT-IR and FT-Raman spectra showed good agreement with the observed spectra.

Graphical abstract

In this work, the vibrational spectral analysis was carried out using FT-IR and FT-Raman spectroscopy for 9-methoxy-2H-furo[3,2-g]chromen-2-one. The computations were performed at DFT theory to get optimized geometry and vibrational wave numbers of the normal modes of the title compound. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The HOMO and LUMO energies, NBO analysis, were carried out.

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Introduction

A naturally occurring furocoumarin compound found in several species of plants including psoralea corylifolia [1]. 9M2HFC is white to cream colored drug, having a bitter taste producing a tingling sensation, and odorless. It is insoluble in cold water, sparingly soluble in boiling water. It is soluble in boiling alcohol, acetone and acetic acid and chloroform. Also it is soluble in aqueous alkalis with ring cleavage, reconstitution occurs upon neutralization [2]. It is a photoactive substance that forms DNA adducts in the presence of ultraviolet A irradiation. It has acquired a place in the treatment of psoriasis and other dermatoses. Psoriasis is a immunological disorder manifesting as localized or widespread erythematous scaling lesions or plaques. It sensitizes the skin to sunlight which induces erythema, inflammation and pigmentation. It is used along with ultraviolet light that is found in sunlight and some special lamps in a treatment called PUVA (Psoralen Ultraviolet A) to treat vitiligo, a disease in which skin color is lost and psoriasis, a skin condition associated with red and scaly patches. It is also used with ultraviolet light in the treatment of white blood cells. This treatment is called photopheresis and is used to treat the skin problems associated with mycosis. Molecular formula of 9M2HFC is C12H8O4. It belongs to C1 point group symmetry. An investigation on automated liquid – liquid extraction based on 96-well plate format in conjunction with ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) for the quantitation of 9M2HFC in human plasma was carried at by Manish Yadava et al. [3]. They analyzed include calorimetry, spectrophotometry, fluorimetry, thin-layer chromatography (TLC), time-resolved phosphorimetry, electrophoresis, chromatography/mass spectrometry and NMR studies was carried out by Gray L. Lehr et al. [4]. Pharmacological properties of 9M2HFC were also investigated [5]. Literature survey reveals that so far there is no complete theoretical study was carried out for 9M2HFC. Recently, among the computational methods calculating the electronic structure of the molecular systems, DFT calculations have been favorite one due to it’s great accuracy in reproducing the experimental values of molecular geometry, vibrational frequencies, atomic charges, dipole moment and thermo dynamical properties, etc. [6], [7], [8], [9], [10]. Advancements in DFT studies have reached a point were predicted properties of reasonable to high quality. The DFT methods are increasingly used by spectroscopists for elucidating the molecular properties. Therefore, the present aim is to give a complete description of the molecular geometry, molecular vibrations and electronic features of the present molecule. In this study, we set out experimental and theoretical investigations of 9M2HFC. The initial structures of the molecule under consideration was optimized, while intramolecular forces are brought to zero. In the ground state theoretical geometrical parameters, simulated FT-IR and FT-Raman spectra, interpretations of the vibrational spectra on the basis of potential energy distribution, HOMO–LUMO-energies, Mulliken population analysis, NBO analysis, molecular electrostatic potential (MEP), nonlinear optical (NLO) properties and thermodynamic properties have been calculated.

Section snippets

Experimental details

The compound 9M2HFC in the solid form was procured from Sigma Aldrich Company (USA) with a stated purity of 98% and used as such without further purification. The FT-Raman spectrum of the 9M2HFC was recorded in the region 4000–100 cm−1 in pure mode using Nd: YAG Laser of 100 mW with 2 cm−1 resolution on a BRUCKER RFS 27 at SAIF, IIT, Chennai, India. The FT-IR spectrum of the sample was recorded in the region 4000–400 cm−1 in evacuation mode using KBr pellet technique with 1.0 cm−1 resolution on a

Computational details

The optimized structure of the title compound, corresponding energy and vibrational harmonic frequencies were calculated by using DFT (B3LYP) with 6-311++G(d,p) basis set using GAUSSIAN 03W program package [11]. Without any constraint on the geometry the energy of the title molecule was minimized, whole intra molecular forces were brought to zero. The geometry was optimized at B3LYP level by using 6-311++G(d,p) basis set. The frequency calculation delivered the fundamental vibrational

Prediction of Raman intensities

The Raman activities (Si) calculated by Gaussian 03 program have been suitably adjusted by the scaling procedure and subsequently converted to relative Raman intensities (Ii) using the following relationship derived from the basic theory of Raman scattering [18].Ii=f(υ0-υi)4Siυi1-exp(hcυi/kbT)where υ0 is the exciting frequency (in cm−1), υi is the vibrational wave number of the ith normal mode, h, c and kb are universal constants, and f is the suitably chosen common scaling factor for all the

Structural analysis

The molecular structure along with numbering of atoms of 9M2HFC was obtained from Gaussian 03 and GAUSSVIEW programs as shown in Fig. 1. The most optimized structural parameters (bond length and bond angle) calculated by DFT (B3LYP) with 6-311++G(d,p) basis set. The theoretical values of bond length and bond angle for the title compound are compared with those of experimental values [20]. By considering the relaxation of all geometries, which correspond to true energy minima as revealed by the

Conclusion

The spectral studies such as FT-IR, FT-Raman for 9M2HFC was carried out with quantum chemical computations. A complete vibrational and molecular structure analysis has been performed based on the quantum mechanical approach by B3LYP calculations with 6-311++G(d,p) basis set. The difference between the observed and scaled wave number values of the most of the fundamental is very small. The complete vibrational assignment with PED was calculated. Mulliken population analysis was carried out. NBO

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