Structural Geometry , Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density functional theory calculation

In the present investigation we investigate the structural, spectral and Molecular Orbitals (MO’s) properties of Naringin compound. It is a bioflavonoid, present in the fruits; it is responsible for bitter taste in fruits. The Naringin has a flavanone-7-O-glycoside between the flavanone naringenin and the disaccharide neohesperidose. It consists of naringenin (ring A-C), D-glucose (ring D) and L-rhamnose (ring E). Our aim is to predict the molecular structure and investigate the insights of the Naringin molecule. Besides that to study the vibrational behavior of Naringin, the FT-IR and FT-Raman spectra were recorded in the ranges of 4000-400cm-1 and 3500-50cm-1 respectively, and to study the frontier molecular orbitals, the UVVisible spectrum was recorded in the range of 500-200nm. In addition to that the geometry of Naringin molecular structure was optimized by Density Functional Theory (DFT/B3LYP) calculation using 6-31g (d, p) level of basis set. For the optimized structure, vibrational spectral calculation was performed by the same level of theory calculation, furthermore, interpreted the calculated spectra of Naringin in terms of TED analysis. Moreover, to explain the inter and intra molecular charge transfer within the molecule the Natural Bond Orbital analysis (NBO) was performed, NBO analysis gave us a clear picture about hyperconjugative interaction energy between the donor (i) and acceptor(j) bond orbitals. In addition to that, the first order hyperpolarizability (β0), polarizability (α) and dipole moment (μ) of Naringin was computed. The frontier MO’s (HOMO-LUMO) of Naringin was analyzed by TD-B3LYP/6-31g (d, p) level of basis set. Finally, the experimentally recorded results were compared with computed values, the agreement and discrepancies were studied carefully.


Introduction
Flavonoids are naturally occurring phenolic compounds with a diverse range of bioactivities [1].Among flavonoids, Naringin has great potential especially in the food and pharmaceutical industries due to their recognized antioxidant, anti-inflammatory, anti-ulcer, and hypocholesterolemic effects, whereas the Naringenin has also shown anti-mutagenic and neuroprotective activities [2].Naringin is a 'flavanone glycoside found in grape and citrus fruits.It has the distinct bitter taste of grapefruit juice.Its molecular formula is C27H32O14 and molecular weight is about 580.4g/mol, it consists of L-rhamnose and D-glucose with Naringenin at the 7-carbon portion [3].It is moderately soluble in water [4].It has been reported to protect against oxygen free radical-stimulated K_ permeability [5], metal chelating, antioxidant and free radical scavenging properties [6], Naringin, a major bioflavonoid in grapefruit, it has been shown to reduce radiation-induced damage to DNA [7].It also acts as the inhibitor of VEGF (Vascular Endothelial Growth Factor) release, which causes angiogenesis and has been proven to be effective against ethanol injury in rats [8,9].
Since the Naringin flavonoid having a wide application in above-mentioned fields, we investigate the structure geometry, vibrational spectra, Frontier Molecular Orbitals (FMOs), inter and intramolecular interactions by experimental and computation methods such as FT-IR, FT-Raman, UV-Visible spectra, DFT and Time dependent-DFT calculations.To the best of our knowledge, there is no such an article being published till now.

Experimental Details
FT-Raman and FT-IR Spectra using the KBr pellet technique.The spectrum was recorded at room temperature, with a scanning speed of 10 cm -1 per minute and at the spectral resolution of 2.0 cm -1 in CSIL Laboratory, Annamalai University, and Tamilnadu, India.The ultraviolet absorption spectrum of Naringin was recorded in the range of 200-500 nm using a shimadzu UV-2401PC, UV-Visible recording spectrometer.The UV pattern is taken from a 10 -5 molar solution of Naringin dissolved in methanol.

Computational Details
The entire calculations were performed at DFT level on a Pentium 1V/3.02GHz personal computer using Gaussian 03W Program package [10], invoking gradient geometry optimization [11].In this study, the DFT/B3LYP/6-31G (d, p) method has been utilized for the computation of molecular structure, vibrational frequencies and energies of optimized structures.By combining the results of the GAUSSVIEW program with symmetry considerations, vibrational frequency assignments were made with a high degree of accuracy and also the scaled quantum mechanics calculation was used to identify the vibrations [12,13].
It should be noted that Gaussian 03W package able to calculate the Raman activity.The Raman activities were transformed into Raman intensities using Raint program by the expression [14]: Where Ii is the Raman intensity, RA i is the Raman scattering activities, νi is the wavenumber of the normal modes and ν0 denotes the wavenumber of the excitation laser [15].

Molecular Geometry
Molecular structure of the Naringin was optimized by using DFT/B3LYP level of theory calculation using 6-31G (d, p) basis set.The optimized molecular structure along with numbering scheme is given in Figure 1.It is belongs to C 1 point group symmetry.To the best of our literature survey, the crystal data of this molecule is not available till date [16].So that, the optimized geometric parameters of Naringin is compared with Naringenin, quercetin and some flavones.It consists of L-rhamnose and D-glucose with naringenin at the 7-carbon, Naringin structure has 8 hydroxyl groups; it leads the molecule more inter-molecular hydrogen bonding interactions.The carbonyl present in naringenin forms intra-molecular hydrogen bonding interaction between carbonyl and hydroxyl groups.Due to this, the bond lengths of C

Vibrational Assignments
The Naringin molecule contains 73 atoms (including 8 -OH group, one methylene and methyl groups); hence it can have 213 normal modes of vibrations.To the best of our knowledge, there is no complete vibrational spectroscopic study carried out on Naringin.In the present investigation the FT-IR and FT-Raman spectra were recorded in the region of 4000-400cm -1 and 3500-50cm -1 , respectively.Stimulated IR and Raman spectra were constructed and compared with experimental spectra.The combined spectrum of FT-IR showed in Figure 2 and the FT-Raman spectrum showed in Figure 3. Similarly, Observed frequencies and calculated wave numbers are compared and listed in Table 1, also provided a detail results in Table S2 (Supporting information).The frequency calculation was performed by using B3LYP level of theory using 6-31G (d, p) basis set.The TED for all fundamental vibrations is calculated using SQM method.

C-H Vibrations
The heteroaromatic structure shows the presence of C-H vibration in the region 3100-3000 cm -1 , which is the characteristic region for the ready identification of C-H stretching vibration [18].In this region, the bands are not affected appreciably by nature of the substituent.In the present work, the C-H aromatic stretching frequency observed at 3071 cm -1 as a weak band in FT-Raman and its corresponding calculated wavenumber is 3083 cm -1 (mode numbers: 202).For the same mode five more harmonic vibrations are also appeared (mode numbers: 200, 201, 203-205).As expected these modes are pure stretching modes as it evident from the TED column (their contribution ~95%).The FT-IR bands 2890-2970 cm -1 (weak) and FT-Raman bands 2939, 2958, 2976 cm -1 (weak) are assigned to C-H stretching in ring B and ring D respectively.These assignments are comparable with harmonic frequencies 2888, 2939, 2943, 2952, 2965 and 2985 cm -1 (mode numbers: 185,191,[193][194][195][196] and also find support from TED.The mode numbers: 183, 184, 186, 188 and 192 are  assigned to ν C-H in ring E. The in-plane bending of C-H is observed at 1089, 1178 and 1296 (strong) in FT-IR and 1002 cm -1 in FT-Raman spectra.The calculated wavenumbers in the range 990-1312 cm -1 (mode numbers: 101, 117, 125-128, 140, 143, 145-147) are assigned to δ C-H with considerable TED value.The Outof-plane bending of τ C-H mode is observed at 896, 812, 607 cm -1 in FT-Raman and 919 and 608 cm -1 in FT-IR spectra, whereas the harmonic values are in the range of 605-922 cm -1 (mode nos: 67, 68, 80-82, 86, 94, 95).These assignments are in agreement with literature values [18][19].

Methyl Group (CH 3 ) Vibrations
The C-H stretching mode in CH 3 occurs at lower wavenumber than those of the aromatic ring (3000-3100 cm -1 ).The asymmetric stretching mode of the CH 3 group is expected to occur in the region of 2980 cm -1 and the symmetric one is at 2870 cm -1 [20][21].The methyl group (CH 3 ) has three stretching vibrations, namely one symmetric and two asymmetric modes [22].In this study, the computed wavenumbers for the CH 3 (asy) stretching and CH 3 (sym) stretching are 3021, 3008 cm -1 (mode numbers: 199, 198) and 2938 cm -1 /mode no: 190, respectively.These modes are supported by TED and above literature.These modes are 100% (TED) pure for CH 3 stretching vibration.
Two asymmetric CH 3 bending, one symmetric CH 3 bending, two CH 3 rocking and one CH 3 torsional vibrations are possible [22].The methyl group symmetric deformation absorbs moderately to strong in the range 1365±25 cm -1 and asymmetric methyl deformations in the region 1390-1480 cm -1 [23].Based on the above conclusion the observed bands 1453/1456 (FT-IR/ Raman) and 1363 cm -1 /FT-IR are attributed to δCH 3 (asym) and δCH 3 (sym), respectively.The methyl rocking generally appears in the region 1050±30 and 975+45 cm -1 [24], as a weak moderate or sometimes strong band, the wavenumber of which is coupled to the C-C stretching vibrations, which occur in the neighborhood of 900 cm -1 .The FT-Raman band 1122 cm -1 (medium strong) and
In this molecule, there are two CH 2 groups (ring B & D).The general order of CH 2 deformation is: CH 2 scissoring > CH 2 wagging > CH 2 twisting > CH 2 rocking.In the present study, the CH 2 bending modes follow the same trend.Since the bending modes involving hydrogen atom attached to the central carbon fall into the range 1450-875 cm -1 there are extensive vibrational coupling of these modes with CH 2 deformations particularly with the CH 2 twist [26].It is notable that both CH 2 scissoring and CH 2 rocking were sensitive to the molecular conformation.The mode numbers: 167, 174 are belonging to the δCH 2 mode.The frequencies observed at 1185 cm -1 (FT-Raman) and at 1136 cm -1 (FT-IR) are assigned to CH 2 wagging and CH 2 twisting, respectively.The other fundamental mode of CH 2 (rocking: mode number: 97) is observed in the expected region and also presented in Table 1.These assignments are found to be satisfactorily in agreement with the reported values [27].

O-H Vibrations
The broad, intense -OH stretching absorption from 3300 to 2500 cm -1 suggests the presence of carboxylic group in the Naringin extracted from kinnow peel.The strong and broad hydrogen bonded O-H stretching bands centering 3300 and 3400 cm -1 are for alcohols and phenols, respectively [28].The hydroxyl group vibrations are appeared in the higher range than other vibrations.In our study, the O-H group stretching vibration of A, B, C, D and E rings are lies at different frequencies.In this molecule, the mode numbers: 213, 208, 207 and 211, 209, 206 are assigned to the ν(OH) for ring D and ring E, respectively.The harmonic values 3653 cm -1 (mode number: 210/ring A) and 3672 cm -1 (mode number: 212/ring C) are belong to the core molecule of Naringin.The experimental νOH group vibration has observed at 3427 cm -1 as a shoulder band in FT-IR spectrum, which is exactly matches with the literature value 3433 cm -1 [29].

C=O and C-O Vibrations
Normal esters are characterized by strong IR absorption due to the carbonyl (C=O) stretching vibration in the range 1750-1735 cm -1 [32].The FT-IR and FT-Raman spectra show the vibrational frequency for C=O at 1646 cm -1 and 1633 cm -1 respectively [33,29].The presence of carbonyl group on Naringin can be confirmed from peak situated at 1634 cm -1 [34].The carbonyl stretching vibration observed as an intense band at 1603 cm -1 for 6-aminoflavone in FT-IR.The observed wavenumber of the carbonyl stretching vibration is lower due to π-electron being localized [22].In the present study the C 4 =O 14 stretching vibrations is appeared at 1646 (strong) and 1643 cm -1 (very strong) band in FT-IR and FT-Raman spectra respectively, while the harmonic value is 1710 cm -1 (mode number: 181).

NBO Analysis
The hyperconjugation may be given as stabilizing effect that arises from an overlap between an occupied orbital with another neighboring electron deficient orbital, when these orbitals are properly orientated.This non-covalent bonding-antibonding interaction can be quantitatively described in terms of the NBO analysis, which is expressed by means of the second-order perturbation interaction energy (E( 2)) [37-40][46-49].This energy represents the estimate of the off-diagonal NBO Fock matrix elements.It can be deduced from the second-order perturbation approach [41] where q i is the donor orbital occupancy, ε i and ε j are diagonal elements (orbital energies) and F (i, j) is the off diagonal NBO Fock matrix elements.
The NBO analysis has been carried out to elucidate the intra-molecular interaction among natural bond orbitals, the results of NBO analysis are presented in Table 2.In the present investigation, the π-π* interaction are mainly interested.Here the electron densities of conjugated π bonds are lower than the σ bond.Whereas, the delocalization is more while the transition from π bond to π* bond.The larger E (2) value, denotes that the more delocalization takes place into a particular bond, it mainly occurs during π-π* transition.Moreover, as mentioned above the electron densities in donor (i) π bonds decreases, at the same time electron density increases in acceptor (j) π* bonds.It is evident from the Table 2

Hyperpolarizability calculations
The first hyperpolarizabilities (β0) polarizability (α0) and dipole moment (μ) of Naringin molecule has calculated by B3LYP level of theory using 6-31G (d, p) basis set, based on the finite-field approach.In the presence of an applied electric field, the energy of a system is a function of the electric field.First hyperpolarizability is a third rank tensor that can be described by a 3x3x3 matrix.The 27 components of the 3D matrix can be reduced to 10 components due to Kleinman symmetry [42].It can be given in the lower tetrahedral format.It is obvious that the lower part of the 3x3x3matrix is a tetrahedral.The components of β are defined as the coefficients in the Taylor series expansion of the energy in the external electric field.When the external electric field is weak and homogeneous, this expansion becomes: where E 0 is the energy of the unperturbed molecules, F α is the field at the origin, and is the components of the dipole moment, polarizability and the first hyperpolarizability, respectively.The total static dipole moment μ, the mean polarizability α 0 , the anisotropy of polarizability Δα and the mean first hyperpolarizability β 0 , using the x, y, z components are defined as Many organic molecules, containing conjugated π electrons are characterized by large values of molecular first hyper polarizabilities, were analyzed by means of vibrational spectroscopy [43][44][45][46].The intra molecular charge transfer from the donor to acceptor group through a single-double bond conjugated path can induce large variations of both the molecular dipole moment and the molecular polarizability, making IR and Raman activity strong at the same time [47].
Table 3 lists the computed dipole moment (μ), polarizability (α) and first order hyperpolarizability (β 0 ) as, 1.832 Debye, 0.840 x 10-30 esu and 6.477 x 10 -30 esu, respectively.The first hyperpolarizability (β 0 ) of the title molecule is fifteen times higher than that of urea; hence this molecule has considerable NLO activity.In this molecule, the π-π* interaction plays a major role in intra-molecular charge transfer and hence the hyperpolarizability of the molecule being increased.

UV-Visible Spectral Studies and HOMO-LUMO Analysis
The ultraviolet absorption spectrum was obtained in the range of 200-500 nm to study the electronic properties of Naringin.The UV pattern was taken from a 10-5 molar solution of Naringin dissolved in methanol.TD-DFT calculation was performed to examine the electronic excitations within the MOs Copyright: © 2018 Subashchandrabose S et al.

Structural Geometry, Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density Functional Calculations
Page 19 of 22  4 shows the absorption spectrum (in methanol) of Naringin.The frontier molecular orbitals are shown in Figure S1 (Supplementary information).The HOMO is located over the 2px orbitals of carbon and oxygen atom in ring D, E and LUMO states appears in ring A.
In addition to that the neighboring HOMO-1,-2,-3 and LUMO+1, +2+3 are also shown in Figure S1.The estimated HOMO energy is -5.869 eV, and LUMO energy is -1.034 eV and the HOMO-LUMO energy gap is -4.835 eV.

Summary and Conclusion
In the present investigation we investigate the structural, spectral and molecular orbitals (MO's) properties of naringin.Naringin consists of naringenin (ring A-C), D-glucose (ring D) and L-rhamnose (ring E).The molecular geometry was studied and found the intra molecular hydrogen bonding between carbonyl and hydroxyl group (C 4 =O 14 ...H 16 -O 15 ).Vibrational behavior of Naringin was studied by FT-IR and FT-Raman spectra, these spectral values were compared with computed vibrational wavenumbers, agreement is good and discussed the discrepancies among wavenumbers.Furthermore, inter and intra molecular charge transfers were measured by NBO analysis, it clear showed the maximum energy exchange occurs among π-π* interactions.The calculated first order hyperpolarizability (6.477x10 -30 esu) is fifteen times higher than that of urea; hence this molecule has a considerable nonlinear optical property.The obtained UV spectrum show excitations at 328.00, 282.60, 279.80 nm, it clearly denote the excitation lay among the conjugative bonds and calculated HOMO is located over the 2px orbitals of carbon and oxygen atom in ring D, E and LUMO states appears in ring A, whereas, the band gap energy is estimated at -4.835 eV.
3 -C 8 (1.424), C 8 -C 10 (1.398) in ring A and C 4 -C 5 (1.516 Å) in ring B are positively elongated with C-C bond lengths (~1.4 Å) in ring C as well as with literature values [16].Zhang et al. observed the C=O and C-O bond lengths are about 1.235 and 1.427 Å, respectively for 5, 6, 7, 4'-tetramethoxy isoflavone [17].These observed values are in line with the calculated values (C 4 =O 14 : 1.243 and C 8 -O 15 : 1.337Å) of Naringin molecule.Moreover, there is a shrink in bond length of C 8 -O 15 due to delocalization of π-electron from C 4 =O 14 .On comparing the C-C bond length in ring D, E with ring A, B and C are higher (~1.5 Å) due to the boat form of ring D and ring E. In ring A, the angle of C 8 -O 15 -H 16 and C 3 -C 8 -C 10 are about 106.52º and 120.74º respectively.These angles are negatively deviated from the angles of C 24 -O 27 -H 28 (109.21º)and C 22 -C 24 -C 20 (119.78º) is due to the electron localized in ring E. The calculated bond lengths, bond angles and dihedral angles are listed in TableS1(Supporting information).

Figure 2 :
Figure 2: The combined experimental and theoretical FT-IR spectra of Naringin.

Figure 3 :
Figure 3: The combined experimental and theoretical FT-Raman spectra of Naringin.

Figure 4 :
Figure 4: The UV-Visible spectrum is taken from a 10-5 molar solution of Naringin dissolved in methanol.

et al. Structural Geometry, Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density Functional Calculations
Citation: Subashchandrabose S, R.Suresh R, Balakumar R, et al. (2018) Structural Geometry, Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density Functional Calculations.Int J Mol Theor Phy 2(1): 1-22.

et al. Structural Geometry, Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density Functional Calculations
Citation: Subashchandrabose S, R.Suresh R, Balakumar R, et al. (2018) Structural Geometry, Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density Functional Calculations.Int J Mol Theor Phy 2(1): 1-22.

et al. Structural Geometry, Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density Functional Calculations
Citation: Subashchandrabose S, R.Suresh R, Balakumar R, et al. (2018) Structural Geometry, Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density Functional Calculations.Int J Mol Theor Phy 2(1): 1-22.

et al. Structural Geometry, Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density Functional Calculations
Citation: Subashchandrabose S, R.Suresh R, Balakumar R, et al. (2018) Structural Geometry, Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density Functional Calculations.Int J Mol Theor Phy 2(1): 1-22.

et al. Structural Geometry, Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density Functional Calculations
[25,26]etching, δ: In-plane-bending, γ: Out-of-plane bending, vw: Very week, w: Week, m: Medium, s: Strong, vs: Very strong, Scaling factor: 0.9608 (palafox, 2000), b Relative IR Absorption intensities normalized with highest peak absorption equal to 100, c Relative raman intensities calculated by equation (2.1) and normalized to 100.dTotal energy distribution calculated at B3LYP/6-31G(d,p) level.harmonicbands961,1116 cm -1 (mode numbers: 98, 122) are assigned as rocking modes of CH 3 .The torsion vibrations are not observed in the FT-IR spectrum because this appears at very low frequency.The FT-Raman experimental band observed at 220 cm -1 shows an excellent agreement with theoretical results.These assignments support from the work of Sundaraganesan et al. and are within the frequency intervals given by Varsanyi[25,26].

et al. Structural Geometry, Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density Functional Calculations
the donor (π) bonds have 1.678, 1.621, 1.667, 1.702 and 1.652e as electron densities for C 2 -C 7 , C 3 -C 8 , C 17 -C 18 , C 19 -C 22 & C 20 -C 24 bond, respectively.These electron densities are relatively lesser than the σ bonds.On the other hand, the strong delocalization occurs between donor (π: C 2 -C 7 , C 3 -C 8 , C 17 -C 18 , C 19 -C 22 and C 20 -C 24 bonds) and acceptor ( π*: C 3 -C 8 , C 2 -C 7 , C 19 -C 22 , C 17 -C 18 and C 17 -C 18 bonds) bonds, and the electron densities relatively increased in acceptor bonds and hence leading to more stabilization energies are obtained as 51.46, 126.44, 96.23, 75.02 and 94.73 kJ/mol, respectively.The NBO analysis explores the insights of intra molecular interactions among the intra bonds in Naringin molecule.

et al. Structural Geometry, Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density Functional Calculations Page
R.Suresh R, Balakumar R, et al. (2018) Structural Geometry, Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density Functional Calculations.Int J Mol Theor Phy 2(1): 1-22.

Table 2 :
Second order perturbation theory analysis of Fock matrix in NBO basis for Naringin using B3LYP/6-31G(d,p) basis set.

et al. Structural Geometry, Vibrational and Electronic Spectra Investigation on Naringin Molecule Using Experimental and Density Functional Calculations
a E(2)means energy of hyper conjugative interaction (stabilization energy, converted as 1kcal/mol=4.18kJ/mol),

Table 3 :
The electric dipole moments (μ), polarizability (α) and hyperpolarizability (β 0 ) values of Naringin.Standard value for urea (μ=1.3732Debye, β0=0.3728x10-30esu) of Naringin.The both experimental UV and computed results are listed in Table 4.In this work the observed band gaps are about 328.00, 282.60, 279.80 nm and computed band gap are about 344.74, 293.04, 279.63 nm.These values clearly denote that the excitation lay among the conjugative bonds.The Figure