B.K. Barik a, H.M. Mallya a, R.K. Sinha b, and S. Chidangil b

a Department of Biochemistry, Melaka Manipal Medical College (Manipal campus), Manipal Academy of Higher Education, Manipal-576104, Karnataka, India

b Department of Atomic and Molecular Physics, Manipal Academy of Higher Education, Manipal-576104, Karnataka, India


Received 3 August 2020; revised 16 November 2020; accepted 24 November 2020

In this work, experimental and theoretical studies on danthron and emodin are presented. Experimentally, Fou-rier transform infrared (FTIR), Raman and UV-Vis spectra of danthron and emodin were recorded. The structure and vibrational frequencies of the molecules were calculated using density functional theory (DFT) with the B3LYP functional using the triple zeta (TZVP) basis set. Among various possible structures of danthron and emodin, it was found that the most stable structures involve intramolecular hydrogen bonds between two OH and C=O groups. The theoretical IR spectra of the most stable conformations of danthron and emodin correlate well with their experimental FTIR. Detailed vibrational frequency analysis was done for all the vibrational modes obtained and were assigned to the ring vibrations along with the stretching and bending of specific bond vibrations. The bands obtained from the experimental FTIR and Raman spectra of both the molecules correlate well with their theoretical data.

Keywords: danthron, emodin, Fourier transform infrared (FTIR), density functional theory

1. Introduction

Since ancient times anthraquinone derivatives (anthraquinones) obtained from different plant sources have been extensively used as medicines because of their laxative property. Recent studies confirm that these molecules also have anti-inflammatory, analgesic, antimicrobial and an-titumor activities  [1]. Many traditional Chinese medicines (TCMs) are anthraquinone derivatives in nature. Because of the  diversity in their functions these medicines are becoming important sources for potential therapeutic agents. But these medicines generally contain thousands of components. So it becomes very essential to analyse them and find out the exact components that bring out different biological functions. According to their therapeutic potentials different methods have been used to explore the phytochemical and pharmacological effects of TCMs [2]. Reports suggest that the methanolic extract of rhubarb (traditional Chinese medicine) has phenolic compounds in high concentrations, and also exhibits free radical scavenging actions and shows strong antioxidant properties  [3, 4]. The  dihydroxy anthraquinones are the major biologically active molecules in rhubarb  [4, 5]. One of the  dihydroxy anthraquinone derivatives, which is naturally found in barks and roots of many plants and also in Chinese herbs like Rheum officinale and Polygonam cuspidatum, is emodin that has many therapeutic applications [6]. Many studies have reported about the  biological actions of dihydroxy anthraquinones like dan-thron, physcion, aloe-emodin and chrysophanol. Though there are many investigations done for the functional aspect of these dihydroxy derivatives of anthraquinones, there are only a few theoretical calculation studies for the  structural and spectral properties  [7-9]. There are reports that the  dihydroxy anthraquinones exhibit a  strong intramolecular hydrogen bond [7, 10]. Danthron is one of the simplest anthraquinone derivatives that shows the chromophore framework which is specific to many compounds of pharmaceutical and biological interest.

Theoretical studies such as the geometrical op-timization and vibrational spectra calculation of the drugs provide a very good insight for the changes in the conformation [11], reactive nature [12], relationship between the structures and the function [13], and the way in which the drugs interact with other molecules [14]. Previously the ground state geometry optimization used to be done by ab initio Hartree-Fock (HF) method. But since many years the density functional theory (DFT) method is the method of choice for the optimization of geometries. In the present study, the dihydroxy anth-raquinone derivatives danthron and emodin were optimized by ab initio HF and DFT using different basis sets.

To the  best of our knowledge, the  theoretical IR spectra calculation by DFT using a TZVP basis set, its correlation to experimental IR spectra and the assignments of the calculated vibrational modes of aromatic anthraquinone rings of danthron and emodin have not been reported so far.

The objective of this study is to do the assignments of the  vibrational modes obtained from the calculated IR spectra for both the molecules and correlate them with the experimental FTIR spectra. The experimental Raman spectra were also carried out for a  comparison purpose. The  study further focuses on the  calculations of HOMO-LUMO molecular orbitals of danthron and emodin. For knowing the assignments of IR spectra the vibrational frequency calculations are very helpful [15]. Therefore the study gives an insight to the different vibrational assignments of the calculated IR spectra of danthron and emodin.

2. Materials and methods

2.1. Computational details

The xyz coordinates of the dihydroxy anthraqui-none derivatives were obtained using the  ArgusLab software package [16]. The TmoleX quantum chemical calculation program was used to optimize the ground state geometries using the xyz coordinates [17]. Ground state geometric optimi-zations were performed at HF and DFT (B3LYP) levels. The def-SV(P) basis set was used for HF calculations, whereas the def-SV(P) as well as the triple zeta basis set (TZVP) were used for the DFT calculations for the  optimization of ground state geometries. The optimized geometries of danthron and emodin were used to calculate the vibrational spectra by the  DFT method. The  DFT (B3LYP) meth od with the  TZVP basis set was used for the vibrational (IR) spectra calculation, because IR frequencies are efficiently reproduced by the DFT method  [18]. The  calculated IR frequencies were corrected using a scaling factor of 0.9778. The assignments of the calculated vibrational frequencies of different vibrational modes along with ring vibrations were carried out based on visual observations using the software TmoleX which is a graphical user interface to the  TURBOMOLE quantum chemistry program package  [17]. The  visual observation provides an insight of the ring vibrations along with different vibrations of bonds. The soft-ware TmoleX was also used for visualizing the opti-mized geometry and the HOMO and LUMO orbitals of the optimized molecules.

2.2. Experimental methods

Danthron and emodin were procured from Sigma-Aldrich and used as such without any further purifi-cation. The infrared spectra of these molecules were recorded using an FTIR spectrometer (JASCO FT/ IR-6300). A resolution of 4 cm-1 was used by the FTIR spectrometer while recording the spectra. The powder samples of the molecules were mixed separately with KBr to prepare the pellets using the pellet maker (Technosearch Instruments). The pellets were kept in the sample holder of the spectrophotometer and the FTIR spectra were recorded.

The Raman spectra were recorded using a home-built micro-Raman spectrometer. For recording the Raman spectra of danthron and emodin, a laser beam of 785 nm wavelength (Starbright Diode Laser, Torsana Laser Tech, Denmark) was focused onto the  samples by the  microscope objective. The laser beam with this particular wavelength was utilized to avoid the laser induced photo-damage of the sample by shorter wavelengths than this one. Also a longer wavelength helps to reduce the fluorescence effect which can compete with weak Ra-man signals. But longer wavelengths than this one will reduce the  detection efficiency  [19, 20]. The spectra were recorded using a 60X microscope objective (Nikon, Plan Fluor) with a 0.85 numerical aperture (NA). The spectral resolution of the spectrometer was 5.7 cm-1 (with the spectrometer slit width kept at 100 µm) by measuring the FWHM of a 997 cm-1 Raman band of the polystyrene bead spectrum.

The UV-Vis spectrum was recorded using a UV-Visible spectrophotometer (JASCO). 1 mg of danthron and emodin samples was mixed with 10 ml methanol separately to produce the stock solution. Then 0.1 ml of these solutions was diluted separately with 2.9 ml of methanol before recording the UV-Vis spectra for both the samples.

3. Results and discussion

3.1. Theoretical calculations

3.1.1. Geometry of danthron and emodin

Different ground state optimized conformations obtained for danthron and emodin using HF and DFT (BP86 and B3LYP) methods show that the  conformations are similar in different methods and basis sets. It is also noticed that all the  converged optimized conformations of dan-thron and emodin are completely planar in nature. The geometric optimization of danthron (1,8-di-hydroxy anthraquinone) and emodin (1,3,8-tri-hydroxy-6-methyl anthraquinone) by the  DFT (B3LYP) method with the  def-TZVP basis set produced three and eight conformations, respectively (Appendix, Tables A1 and A2). Conformation 1 (Conf-1) of danthron and emodin with two intramolecular hydrogen bonds have the  lowest total energy and so the most stable conformers as shown in Fig. 1.

The lowest total energy was always shown by the  conformation having the  double intramolecu-lar hydrogen bonding by the hydroxyl groups of C1 and C8 with the oxo group of C9. This result correlates with the results of Markovic et al. and Ruifa Jin et al. [7, 10]. The total energies obtained by HF and DFT with different basis sets for danthron explains that the  lowest total energy is produced by the conformation 1 with double intramolecular hydrogen bonds. The relative energies by HF and DFT (BP86) with different basis sets clarify that the conformation 1 with one intramolecular hydrogen bond is more stable compared to the  conformation 3, which is without any intramolecular hydrogen bond. When the total energies obtained from DFT (BP86) with def-SV(P) and TZVP basis sets were compared, it was clearly evident that the TZVP basis set produces lower total energy as compared to the  def-SV(P) basis set for a particular conformation.

When emodin was geometrically optimized at HF and DFT (BP86) levels, eight different conformations were converged. These structures are shown in Appendix, Table A2. The conformations 1, 2, 3 and 4 are closely similar to the conformations 5, 6, 7 and 8, respectively, except the orientation of hydroxyl group on C3.

Fig. 1. (a) Conformation 1 of danthron and (b) of emodin having the lowest total energy calculated at DFT (B3LYP) level with def-TZVP basis set.

The total energies show that the lowest total energy is obtained by the conformation 1 using DFT (BP86) with def-SV(P) and TZVP basis sets. The relative energies obtained by using DFT (BP86) with def-SV(P) and TZVP basis sets for the conformation 5 are 0.26 and 0.32 kcal/mol, respectively. But the HF with the def-SV(P) basis set indicates that the conformation 5 has the lowest energy, and the relative energy for the  conformation 1 is 0.08  kcal/mol, which is very less when compared with the relative energies produced between the  conformations 1 and 5 by DFT. Both the conformations 1 and 5 have double intramolecular hydrogen bonds. The relative energies specify that the conformations 2, 4, 6 and 8 have a  similar stability with one intramolecular hydrogen bond and the conformations 3 and 7 are the most unstable conformations without any intra-molecular hydrogen bonding.

3.1.2. HOMO and LUMO orbitals in danthron and emodin

In all the conformations of danthron the Huckel's method generated 268 molecular orbitals, out of which 62 were occupied and the rest were unoccupied molecular orbitals. The HOMO and LUMO were calculated by TmoleX using a 3D visualizer. The HOMO and LUMO for the conformation 1 of danthron are shown in Fig. 2(a, b).

When the  ground state geometry of emodin was optimized, a  total of 300 molecular orbitals were calculated by Huckel's method, out of which only 70 were occupied. The HOMO-LUMO were calculated for emodin by using the 3D visualizer of TmoleX. The HOMO and LUMO for the conformation 1 of emodin are shown in Fig. 3(a, b).

3.2. Experimental investigation of danthron

3.2.1. UV-Vis spectrum

Theoretical UV-Vis spectrum calculation was done using the  DFT method with B3LYP and the def-SVP basis set. For the theoretical calculation the conformation with the lowest total energy was used. The  calculated UV-Vis spectrum and the  experimental UV-Vis spectrum of danthron are shown in Fig. 4(a, b).

Fig. 2. (a) HOMO and (b) LUMO of danthron calculated with DFT (B3LYP)-def-TZVP.
Fig. 3. (a) HOMO and (b) LUMO of emodin calculated with DFT (B3LYP)-def-TZVP.
Fig. 4. (a) Calculated UV-Vis spectrum of danthron using DFT (B3LYP) with def-SVP basis set and (b) the experimental UV-Vis spectrum of danthron solution in methanol.

The theoretical and experimental UV-Vis spectra of danthron correlate well with each other.

3.2.2. FTIR spectrum of danthron

The FTIR spectrum for danthron is shown in Fig. 5 along with the  calculated IR spectrum of the most stable optimized geometry for danthron. From the correlation between the theoretical and the  experimental IR spectra, we observed that the calculated IR spectra of the conformer 1 with double intra-molecular hydrogen bonding correlated well with the  experimental IR spectrum whereas the peaks of IR spectrum from the conformer-3 deviate mostly from the peaks of the experimental FTIR spectrum (Appendix, Figs.  A1 and A2). Earlier the  IR spectrum has been reported by Smulevich  et  al.  [21]. In their work Smulevich et al. have explained two forms of dan-thron and for the IR frequency assignments they have given the approximate descriptions. In this work after optimizing the geometries for three different conformations their respective IR calculations were done. In our FTIR spectrum a strong and a  medium peak were observed at 783 and 456 cm-1, respectively, which were not present in the previous study. The theoretical calculation correlates these bands with a peak at 782 and 460 cm-1. The frequency assignment from the theoretical calculation suggested out-of-plane ring deformations for both the bands (Table 1).

Fig. 5. (a) Theoretically calculated IR spectra of the conformation of danthron having the lowest total energy by DFT method using B3LYP with def-TZVP basis set and (b) the experimental FTIR spectrum of danthron for the correlation.

3.2.3. Raman spectrum of danthron

Previously the Raman spectrum of danthron was reported by Fabriciova et al. [22]. For the comparison purposes we have also recorded the Raman spectrum of danthron which is shown in Fig. 6. As compared to the  previous work by Fabricio-va et al., we have successfully obtained a greater number of bands than before, i.e. 25 bands vs 16 bands before  [22] in the  range 1800-400  cm-1. Among the  few new peaks which are present in this Raman spectrum of danthron, the  peaks at 1163 and 1341 cm-1 have a strong intensity. Similarly the new bands observed at 741 and 781 cm-1 show a medium intensity. One new weak peak at 1619 cm-1 is observed in this present study which corresponds to the key characteristic very strong FTIR band of danthron at 1626 cm-1.

3.2.4. Vibrational assignments

The theoretical IR calculations of danthron by the  DFT (B3LYP) method with the  basis set TZVP produced 72 different vibrational modes. Among the  72 vibrational modes, 24 were out-of-plane modes and the rest were in-plane ones. But in the previous work by Smulevich et al. only three vibrations were assigned as out-of-plane and many assignments were not defined. Here in this work we have mentioned the assignments about all the 72 theoretically obtained IR vibrational frequencies which are shown in Table 1. In Table 1, we have focused to present the theoretical IR vibrational modes with the  assignments and their correlation with the corresponding experimental wavenumbers. The  previous experimental works on Raman spectra and IR spectra are also mentioned along with the bands obtained in this present work in Table 1.

While visualizing the  vibrational modes by the  TmoleX program for assignments, we observed different vibrations of the  rings of dan-thron molecule such as stretching, breathing and deformation of rings. In the  previous studies, many assignments were mentioned as asymmetric deformity and skeletal deformity. But in our study we have given the complete assignment list with the specification of ring and different individual bond vibrations. Mixtures of both the  in-plane and out-of-plane vibrational modes were noticed in a  range of 973-45  cm-1. All the  other vibrational modes were in-plane in a  range of 3296- 1032 cm-1. Ring deformation was observed in vibrational modes of 208, 314, 335, 443, 447, 1080, 1213, 1270, 1361, 1450 and 1477 cm-1. In 19 vibrational modes ring breathing was observed, out of which six modes were symmetric ring breathing and thirteen were asymmetric ring breathing. The  stretching of both the  O-H bonds was noticed for only two vibrational modes of 3267 and 3296  cm-1. The  vibrational modes in a  range of 3109-3142 cm-1 show mild stretching of few C-H bonds. The vibrational modes that were in a range of 3296-1700 cm-1 produced mainly vibration involving either one single ring or specific bonds without involving any of the rings. The details of all the theoretical vibrational modes of danthron are mentioned in Appendix, Table A3.

Fig. 6. Raman spectra of danthron (acquisition time 20 s, accumulation 5 and laser power 60 mW).
Table 1. Danthron theoretical IR table with the assignments for the vibrational modes and the correlation of experimental danthron FTIR and Raman data.
Vibrational modes IR wave-numbers - B3LYP-def-TZVP (cm-1) [this work] Calculated Raman wavenum-bers and calculated assignments in square brackets [22] Calculated IR frequency assignments [this work] Experimental IR and its approx. assignment descriptions in square brackets [21] FTIR [this work] [This work] Ra-man frequency and in square brackets Raman by Fabriciova et al. [22]
1 33w γ (Ring deformation)
2 45w γ (Ring deformation)
3 71vw γ (Ring deformation)
4 137w γ (Ring deformation)
5 174vw γ (Ring deformation)
6 189vw γ (Ring deformation)
7 208vw 203vw [δ (asymmetric def.)] Ring deformation
8 216vw γ (Ring deformation)
9 280vw 268w [τ (asymmetric def.) + Ω(CCC)] γ (Ring deformation)
10 314vw Ring deformation
11 335w Ring deformation
12 364w Ring stretching
13 368vw γ (Ring deformation)
14 443w Ring stretching 428w
15 447w Ring deformation 445m [Skel. Def.] 447m
16 460w 458vw [δ (C-O) + δ (C=O) + δ (asymmetric def.)] γ (Ring deformation) 456m 455s [456vw]
469m [δ (asymmetric def.)]
17 474w 475vw τ (asymmetric def.) Ring stretching 473m [δ (C=O)] 477m 488vs [487s]
18 484vw Asy ring breathing
19 495vw γ (Ring deformation)
20 543w Asy ring breathing 522m [Skel. Def. op] 524m 522m
21 546w γ (Ring deformation) 547w [Skel. Def.] 546w
22 572vw γ (Ring deformation)
23 573w 574vw [γ (C-O) +  τ (asymmetric def.)] Sym ring breathing
24 575vw γ (Ring deformation) 581s [Skel. Def.] 583m 582vs [583m]
25 623w 632vw [γ (COH)] Asy ring breathing 625w [Skel. Def.] 626w 625vs [626w]
668m [Skel. Def]. 667m
26 700w Ring stretching 699w [218+480-3n] 700w 701w
27 720w γ (Ring deformation) 708w [γ (CH)] 720w 726w
28 769w γ (Ring deformation) 743vs [γ (CH)] 744vs 741m
29 779w Asy ring breathing [γ (OH), γ (OD)] 780s 781m
30 782vs γ (Ring deformation) 783s
31 797vw γ (Ring deformation)
32 813m γ (Ring deformation) 812m 816s
33 836m Asy ring breathing 839m [Skel. Def.] 839s 839w
849m [γ (CH)] 849s
868w [430×2+8] 867w
34 900vw γ (Ring deformation) 893w
35 903vw γ (Ring deformation) 910w [430+470+10] 913w
36 915w γ (Ring deformation) 920w [Skel. Def.] 921w
37 957vw γ (Ring deformation)
38 958vw 961m [ν (CC)] γ (Ring deformation)
39 973w γ (Ring deformation) 975m [δ (CH)] 976m 972s [976m]
990w 988w
40 1032w Asy ring breathing 1032m [δ (CH)] 1034m
41 1060w 1054w [ν (CC)] Asy ring breathing 1059m [δ (CH)] 1059m 1055vs [1059m]
42 1080w Ring deformation 1079m [Skel. Def.] 1080m
1095vw [545×2+5]
1139 m
43 1154w 1144m [δ (CH) +  δ (trigonal def.)] Ring stretching 1155sh [579×2-8] 1153m. sh 1154w [1153m]
44 1164vw Asy ring breathing 1159/1162m [δ (CH)] 1161s 1163 s
45 1166m 1179w [δ (CH)] Ring stretching
46 1209vw 1203vs [ν (CC)] Asy ring breathing 1205sh [δ (OH). δ (OD)] 1203sh
47 1213vs Ring deformation 1210s [Ring st.] 1212 1207vs [1209s]
48 1270vs 1261w [ν (CC)] Ring deformation 1270vs [Ring st.] 1272vs 1291s [1292vs]
49 1283vs Sym ring breathing 1279vs [ν (C-O)] 1279vs
50 1313w 1308w Asy ring breathing 1299m [Ring st.] 1301s 1302s [1302vs]
51 1318m 1321vs [ν (C-O)] Asy ring breathing 1345w [Ring st.] 1344m 1341/1345 s
52 1361w 1357m [ν (CC) + δ (C=O) +  δ (asymmetric def.)] Ring deformation 1358m [ν (C-O)] 1353m 1352 vs [1352m]
53 1368s Sym ring breathing
54 1376s Ring stretching 1380sh [Ring st.] 1383m
1420vw. sh [1210+214-4] 1418w. sh
55 1438w Ring stretching 1442s [Ring st.] 1444s 1444s [1445m]
56 1450m 1453vw [δ (CH)] Ring deformation 1452m [Ring st]. 1454s
57 1475vs Sym ring breathing 1465s [Ring st.] 1466s
58 1477w 1487 Ring deformation 1472m [318+1159-7] 1473s
59 1561w Sym ring breathing 1568w [Ring st.] 1568m 1567vs [1569vs]
60 1570m Ring stretching 1574w [Ring st.] 1576m
61 1588w 1590vw [ν (CC)] Ring stretching
62 1599w 1592vw [ν (CC)] Ring stretching 1599m [Ring st.] 1599s 1595m [1601m]
63 1624vs Sym ring breathing 1625vs [ν (C=O)] 1626vs 1619 w
64 1689s 1691vs [ν (C=O)] Asy ring breathing 1672m [ν (C=O)] 1675m 1670vs [1675vs]
1778vs [ν (C=O)]
3063vs [ν (CH)]
65 3109w Alternate stretching of [C2-H2 and C7-H7], [C3-H3 and C6-H6] and [C4-H4 and C5-H5]
66 3110w Simultaneous stretching of [C2-H2 and C7-H7], [C3-H3 and C6-H6] and [C4-H4 and C5-H5]
67 3130w Alternate stretching of [C2-H2 and C7-H7], [C3-H3 and C6-H6] and [C4-H4 and C5-H5]
68 3131vw Simultaneous stretching of [C2-H2 and C7-H7], [C3-H3and C6-H6] and [C4-H4 and C5-H5]
69 3141w Alternate stretching of [C2-H2 and C7-H7], [C3-H3 and C6-H6] and [C4-H4 and C5-H5]
70 3142vw Simultaneous all C-H stretching
71 3267vs Stretching of O1-H1, O8-H8 (Alternatively)
72 3296w Stretching of O1-H1, O8-H8 (Simultaneously)
3553vs [ν (OH)]

γ: out of plane vibrational mode, Sym: symmetric and Asy: asymmetric.

3.3. Experimental investigation of emodin

3.3.1. UV-Vis spectrum

Theoretical UV-Vis spectrum calculation was done using the DFT method with B3LYP and the def-SVP basis set. For the theoretical calculation the conformation with the lowest total energy was used. The calculated UV-Vis spectrum and the  experimental UV-Vis spectrum of emodin are shown in Fig. 7.

Fig. 7. (a) Calculated UV-Vis spectrum of emodin using the DFT method with B3LYP using def-SVP basis set and (b) the experimental UV-Vis spectrum of emodin solution in methanol.

The theoretical and experimental UV-Vis spectra of danthron correlate well with each other.

3.3.2. FTIR spectrum of emodin

From the  correlation between the  theoretical and the experimental IR spectra, we observed that the calculated IR spectrum of the conformer 1 with double intra-molecular hydrogen bonding correlated well with the experimental IR spectrum. The comparison graph is provided in Appendix, Figs. A3 and A4. The FTIR spectrum for emodin along with the calculated IR spectra of conformer 1 is shown in Fig. 8. The IR spectra of conformations 4 and 6 having one intra molecular hydrogen bond also correlate with the experimental IR spectrum. But when we compared the IR spectra along with the total energy of the  conformations, the  conformation 1 with two intra molecular hydrogen bonds has the most stable geometry and correlations to the experimental IR spectrum. Previously the IR and Raman spectra have been reported by Edwards et al. [23]. In their purely experimental work they have shown the IR and Raman spectra of emodin and mentioned the  peaks for both the  spectra with approximate vibrational assignments. In this present work after optimizing the  geometries for eight different conformations of emodin, their respective IR spectra calculations were done. We were able to observe a total of 38 peaks in the IR spectrum of emodin as compared to 22 peaks observed by the previous work in the 1800-400 cm-1 range. Two peaks out of the 16 new peaks at 1033 and 1594 cm-1 are found to have a strong intensity with out-of-plane ring deformation and a symmetric ring breathing type of vibrations, respectively. Similarly four new peaks at 418, 452, 546 and 648 cm-1 have medium intensity levels with ring deformation (γ mode), asymmetric ring breathing, asymmetric ring stretching and ring deformation (γ mode) types of vibrations, respectively.

Fig. 8. (a) Theoretically calculated IR spectra of the conformation of emodin having the lowest total energy by DFT method using B3LYP with def-TZVP basis set and (b) the experimental FTIR spectrum of emodin for the correlation.

3.3.3. Raman spectrum of emodin

Previously the Raman spectrum of emodin was reported by Edwards et al. [23]. For the comparison purposes we have also recorded the  Raman spectrum of emodin which is shown in Fig. 9. We have successfully obtained a greater number of bands, i.e. 39 bands as compared to 26 bands [23] in the range 1800-400 cm-1. Out of the 13 new bands one band, i.e. at 456 cm-1, has a very strong intensity and correlates with the FTIR band of danthron at 452 cm-1 with an asymmetric ring breathing type of vibration. Two other bands at 549 and 1590 cm-1 show medium intensity levels that correlate with the FTIR bands at 549 and 1587 cm-1 having the corresponding assignments of ring deformation (γ mode) and symmetric ring breathing, respectively.

3.3.4. Vibrational assignments

The theoretical IR calculation of the emodin molecule by DFT (B3LYP) method with the basis set TZVP produced a  total of 84 vibrational modes. The  frequency assignments were given for all the 84 vibrational modes, whereas in the previous work done by Edwards et al. [21] only 21 approximate frequency assignments were mentioned for the obtained IR spectrum. Out of the 84 vibrational modes obtained in the present work, the numbers of in-plane and out-of-plane vibrational modes are 43 and 41, respectively. This means that almost 50% of the vibrational modes are out-of-plane that were not found in the case of danthron. In the case of danthron one third of the total vibrational modes were out-of-plane. The increase in the number of out-of-plane vibrational modes may be attributed to the extra two functional groups (OH and CH3) present in emodin in comparison to danthron.

The  theoretical IR values with frequency assignments and the  experimental IR values are mentioned in Table 2. Correlation has been done between both the values obtained in the present work along with the previously done work in Table  2. The  vibrational modes for each frequency were visualized using the TmoleX for their assignments and that revealed that the ring structure of emodin molecule was exhibiting stretching, deformation, symmetric and asymmetric breathing types of vibrational modes. In a frequency range of 904-30  cm-1, both in-plane and out-of-plane types of vibrations were observed. But after that in a range of 3717-904 cm-1 mostly in-plane vibrational modes were observed except three vibrational modes at 1033, 1452 and 3014  cm-1. Ring deformation vibrational modes were both in-plane and out-of-plane. As compared to dan-thron, the number of asymmetric ring breathing vibrational modes in emodin is greater, i.e. 13 vs 27. The symmetric ring breathings are always in-plane vibrational modes both in danthron and emodin. The  two characteristic vibrational frequencies for danthron at 1624 and 1689 cm-1 correlate with the bands in emodin at 1628 and 1689  cm-1 having symmetric and asymmetric ring breathing, respectively. But the  FTIR spectra of danthron and emodin show that there is a  shift of the  band of 1675  cm-1 in danthron to the 1666 cm-1 band of emodin. This shift can be due to the  presence of the  extra two functional groups in emodin as compared to danthron. The stretching of mainly OH groups is observed at 3241, 3273 and 3717 cm-1. Like the vibrations of danthron, the vibrational assignments for emo-din in the  range 3717-1689  cm-1 also produce the vibrations either in one single ring or in some specific bonds only. The details of all the theoreti cal vibrational modes of emodin are given in Appendix, Table A4.

Fig. 9. Raman spectra of emodin (acquisition time 10 s, accumulation 5 and laser power 60 mW).
Table 2. Emodin theoretical IR calculation mentioning their vibrational assignments and the correlation of experimental FTIR and Raman frequencies of emodin.
Vibrational mode IR wavenum-bers - B3LYP-def-TZVP (cm-1) [this work] Approximate frequency assignment [23] Calculated IR frequency assignments [this work] Raman frequency [this work] along with Raman frequency by Edwards et al. [23] in square brackets FTIR frequency [this work] and IR frequency by Edwards et al. [23] in square brackets
1 30vw γ (Ring deformation)
2 34w γ (Ring deformation)
3 61vw γ (Ring deformation)
4 109w γ (Ring deformation)
5 130vw γ (Ring deformation)
6 153vw γ (Ring deformation)
7 167vw Ring deformation
8 209w γ (Ring deformation)
9 213vw γ (Ring deformation)
10 236vw γ (Ring deformation)
11 252vw γ (Ring deformation)
12 253w γ (Ring deformation)
13 276w γ (Ring deformation)
14 336w Ring deformation
15 364w Ring stretching
16 382s γ (One ring with OH group on 3rd carbon deformation)
17 383w γ (Ring deformation)
18 405w γ (Ring deformation)
19 423vw γ (Ring deformation) 421w 418m
20 430w γ (Ring deformation)
21 443w γ (Ring deformation) 456vs 452m
22 465vw γ (Ring deformation) 468vs [467s] 470m [469w]
23 513w γ (Ring deformation) 516w [519w]
24 540w γ (Ring deformation)
25 549w γ (Ring deformation) 549m 546m
26 553w γ (Ring deformation)
27 555w Skeletal breathing (565ms) γ (Ring deformation) 566vs [565ms] 560w
28 584vw γ (Ring deformation) 585w 583w
29 604w γ (Ring deformation)
30 606w Skeletal deformation (610w) γ (Ring deformation) 607w [] 610m [610w]
31 631w Ring stretch, in-plane (632mw, br) Sym ring breathing 632vs [] 631vw
32 656vw γ (Ring deformation) 649w 648m
33 717w δ (C-H) out-of-plane; δ (OH) phenyl, out-of-plane (720mw, br) γ (Ring deformation) 720m [723vw] 722m [720mw, br]
34 728w γ (Ring deformation) 730w 732w, sh
35 770w ν (=C-H) aromatic, out-of-plane (759ms) Ring deformation 766w 759vs [759ms]
36 788w γ (Ring deformation)
37 798m γ (Ring deformation)
38 822s γ (Ring deformation) 822w
39 836vw γ (Ring deformation)
40 852w γ (Ring deformation) 875w 874s [875mw]
41 903w γ (Ring deformation)
42 904w γ (Ring deformation) 902w [907vw] 906m [909mw]
43 930w δ (C-CH), out-of-plane (942m) Asy* ring breathing 937vs [942m] 942w
44 987w Asy ring breathing 993w 994w
45 1008w Asy ring breathing
46 1028w Sym ring breathing
47 1033w γ (One ring with CH3 group on C6 carbon deformation) 1035w 1033s
48 1096s δ (C-CH), in-plane (1101mw) Asy ring breathing 1099w [1100vw, br] 1100s [1101mw]
49 1127w δ (C-CH), in-plane (1130vw) Asy ring breathing 1133w [1134vw] 1131m [1130vw]
50 1152s Ring stretching
51 1167w δ (OH) phenyl, free, in-plane (1167ms) Asy ring breathing 1170m [1170w] 1165s [1167ms]
52 1182w Ring stretch, in-plane (1196vw) Sym ring breathing 1192m [1195vw] 1188vw, sh
53 1220vs ν (C-O); δ (OH) phe-nyl, in-plane (1217s) Ring deformation 1216s [1217s]
54 1224m Asy ring breathing
Ring stretch, in-plane (1249vw) 1247w [1249vw]
55 1264vs Ring stretch, in-plane (1271s) Asy ring breathing 1278vs [1281ms] 1271s [1271s]
56 1308s Ring stretch, in-plane (1300ms) Sym ring breathing 1297vs [1298ms] 1301s [1300ms]
57 1312w Asy ring breathing
58 1328vs Ring stretch, in-plane (1333m) Asy ring breathing 1324w [1325vw] 1332s [1333m]
59 1374s ν (C-O) phenyl (1367m) Asy ring breathing 1365s [1368mw] 1369s [1367m]
60 1384s ν (C-O) phenyl (1386m) Ring stretching 1385m [1380mw] 1383m [1386m]
61 1389w Asy ring breathing
62 1399m Asy ring breathing
63 1413m Ring stretch (1413m) Asy ring breathing 1415w [1417mw] 1416s [1413m]
64 1440m Ring stretch (1446mw) Ring stretching 1443w [1446mw] 1443w
65 1452w γ (One ring with CH3 group on C6 carbon deformation) 1457vw
66 1463w Asy ring breathing
67 1478vs Ring stretch, coupled with Sym ring breathing 1477w [1479mw] 1478s [1478m]
66 1463w (OH) (1478m) Asy ring breathing
68 1489w Ring stretching
69 1558s ν (C=C) aromatic (1561mw) Asy ring breathing 1553m [1557m] 1561s [1561mw]
70 1575m ν (C=C) aromatic (1577w) Sym ring breathing 1572m [1577m] 1578s [1577w]
71 1587m Sym ring breathing 1590m 1594s
72 1609s ν (C=C) aromatic; quadrant ring stretch ( Ring stretching 1603m [1607m] 1610vs, sh [1610ms, sh]
73 1628vs ν (C=O) conjugated, H-bonded (1628vs) Sym ring breathing 1622w [] 1623vs [1628vs]
74 1689m ν (C=O) conjugated, free (1663w) Asy ring breathing 1658vs [1659s] 1666m [1663w]
75 2965w ν (CH3) asymmetric (2928vw) Stretching of C6(CH3)-H6(1, 2, 3) and C6-C6(CH3)
76 3014w γ [C6(CH3)-H6(1, 2) deformation]
77 3047w ν (CH) aromatic (3054vw) Stretching of C6(CH3)-H6(1, 2, 3)
78 3112w ν (C=CH) aromatic (3080vw) C4-H4 stretching
79 3118w C7-H7 stretching
80 3124w C5-H5 stretching
81 3143vw C2-H2 stretching
82 3241vs Stretching of O1-H1, O8-H8 (Alternatively)
83 3273m Stretching of O1-H1, O8-H8 (Simultaneously)
ν (OH) (3389m, br)
84 3717s Stretching of O3-H3

γ: out-of-plane vibrational mode, Sym: symmetric and Asy: asymmetric.

4. Conclusions

Our theoretical IR calculation studies were performed using the  most stable conformations of danthron as well as emodin having the  double intramolecular hydrogen bonding. The IR spectra calculated using the DFT (B3LYP) with the def-TZVP basis set relate well with the respective experimental FTIR spectra. Theoretically frequency assignments were allocated for all the vibrational modes. It was observed that there was a clear correlation between the  FTIR and Raman spectra with the  corresponding theoretical IR spectrum of the  most stable conformer. The  experimental FTIR and Raman spectra of danthron and emo-din show more bands as compared to the previously reported literature data. Some of the newly obtained bands with strong intensity levels are of great importance for the future database. The frequency assignments of danthron and emodin clearly mention the vibrational modes whether in-plane or out-of-plane. Also there is clarity regarding the types of ring vibrations of the molecules. These detailed studies of frequency assignments on the molecules will be very helpful for the future studies.


The authors are thankful to the FIST program of the  Government of India (SR/FST/PSI-174/2012) and the Department of Biotechnology (DBT), Government of India (BT/PR6413/MED/14/802/2005), for the facilities used in the work.


Fig. A1. Theoretical and experimental IR comparison of danthron.
Fig. A2. Correlation graph between the experimental FTIR spectrum and the theoretical IR spectra of dan-thron by (a) DFT (B3LYP) using TZVP basis set and (b) DFT with BP86 and def-SV(P) basis set.
Fig. A3. Comparison of theoretical and experimental emodin IR spectra.
Fig. A4. Correlation graph between the experimental FTIR spectrum and the theoretical IR spectra of emodin by (a) DFT with BP86 and def-SV(P) basis set and (b) DFT with B3LYP and def-TZVP basis sets.
Table A1. Different conformations of danthron with their total energy (TE) and relative energy calculated at HF and DFT (BP86) level with def-SV(P) and TZVP basis set.
Method img img img
HF with def-SV(P) basis set TE (Hartree) -833.620029 -833.638059 -833.600770
Relative energy (kcal/mol) 11.31 0 23.39
DFT (BP86)with def-SV(P) basis set TE (Hartree) -838.656440 -838.678801 -838.629784
Relative energy (kcal/mol) 14.03 0 30.76
DFT (BP86) with TZVP basis set TE (Hartree) -839.566836 -839.587766 -839.541888
Relative energy (kcal/mol) 13.13 0 28.79
Table A2. Different conformations of emodin with total energy (TE) and relative energy calculated at HF and DFT (BP86) level with def-SV(P) and TZVP basis sets.
Method img img img img img img img img
HF with def-SV(P) basis set TE (Hartree) -947.439852 -947.420929 -947.400895 -947.421061 -947.439977 -947.421061 -947.398713 -947.419650
Relative energy (kcal/ mol) 0.08 11.95 24.52 11.87 0 11.87 25.89 12.75
DFT (BP86) with def-SV(P) basis set TE (Hartree) -953.137295 -953.114130 -953.087037 -953.113843 -953.136877 -953.113843 -953.084647 -953.112100
Relative energy (kcal/ mol) 0 14.54 31.54 14.72 0.26 14.72 33.04 15.81
DFT (BP86) with TZVP basis set TE (Hartree) -954.184127 -954.162526 -954.136982 -954.162130 -954.183612 -954.162130 -954.134635 -954.160383
Relative energy (kcal/ mol) 0 13.55 29.58 13.80 0.32 13.80 31.05 14.90
Table A3. Details of danthron IR assignments.
Vibrational modes IR wavenum-bers - B3L-YP-def-TZVP (cm-1) [this work] Calculated IR frequency assignments [this work]
1 33w γ (Ring deformation)
2 45w γ (Ring deformation) + γ (deformation of C=O, C-H and O-H)
3 71vw γ (Ring deformation)
4 137w γ (Ring deformation) + γ (C10=O10 deformation)
5 174vw γ (Ring deformation) + γ (C=O deformation)
6 189vw γ (Ring deformation)
7 208vw Ring deformation
8 216vw γ (Ring deformation) + γ (C4-H4, C5-H5 and C-O deformation)
9 280vw γ (Ring deformation) + γ (C9=O9 deformation ) + γ (C4-H4 and C5-H5 deformation) + γ (C1-O1 and C8-O8 deformation)
10 314vw Ring deformation + C10=O10 deformation
11 335w Ring deformation
12 364w Ring stretching + C10=O10 deformation
13 368vw γ (Ring deformation) + γ (C3-H3, C6-H6 and C-O deformation)
14 443w Ring stretching + [O-H and C-O stretching]
15 447w Ring deformation + C=O deformation + β (O-H) + β (C-O)
16 460w γ (Ring deformation) + γ (C9=O9 deformation) +  γ (C3-H3, C6-H6 and C-O deformation)
17 474w Ring stretching + C9=O9 deformation + β (O-H)
18 484vw Asy ring breathing + C9=O9 stretching + C-O stretching
19 495vw γ (Ring deformation) + γ (C-H deformation)
20 543w Asy ring breathing + C=O stretching + stretching of C-O + stretching of C2-H2, C3-H3, C6-H6 and C7-H7
21 546w γ (Ring deformation) + γ (C=O deformation ) + γ (C2-H2, C3-H3, C6-H6, C7-H7 deformation) + γ (O-H deformation) + γ (C-O deformation)
22 572vw γ (Ring deformation) + γ (C9=O9 deformation) + γ (C-H deformation) + γ (C-O deformation)
23 573w Sym ring breathing + stretching of C2-H2 and C7-H7 + stretching of O-H and C-O + β (C-O)
24 575vw γ (Ring deformation) + γ (C=O deformation) + γ (C2-H2, C7-H7 deformation) + γ (O-H deformation)
25 623w Asy ring breathing + β (C3-H3 and C6-H6) + stretching of C9=O9 and C-O
26 700w Ring stretching + C=O deformation + β (C4-H4 and C5-H5) + stretching of O-H
27 720w γ (Ring deformation) + γ (C=O deformation) + γ (C3-H3, C4-H4, C5-H5, C6-H6 deformation) +  γ (O-H deformation) + γ (C-O deformation)
28 769w γ (Ring deformation) + γ (C-H deformation) + γ (O-H deformation) + γ (C-O deformation)
29 779w Asy ring breathing + C9=O9 stretching + β (C4-H4 and C5-H5) + C-H and C-O stretching
30 782vs γ (Ring deformation) + γ (C10=O10 deformation) + γ (C-H deformation) + γ (O-H deformation)
31 797vw γ (Ring deformation) + γ (C-H deformation) + γ (O-H deformation)
32 813m γ (Ring deformation) + γ (C-H deformation) + γ (C=O deformation) + γ (O-H deformation)
33 836m Asy ring breathing + C=O deformation + β (C3-H3, C4-H4, C5-H5, C6-H6)
34 900vw γ (Ring deformation) + γ (C-H deformation) + γ (O-H and C-O deformation)
35 903vw γ (Ring deformation) + γ (C-H deformation) +  γ (C10=O10 deformation) + γ (O-H deformation)
36 915w γ (Ring deformation) + γ (C-H deformation) +  γ (C=O deformation) + γ (O-H deformation)
37 957vw γ (Ring deformation) + γ (C-H deformation)
38 958vw γ (Ring deformation) + γ (C-H deformation)
39 973w γ (Ring deformation) + γ [deformation of C=O and C-H]
40 1032w Asy ring breathing + C=O deformation + β (C-H)
41 1060w Asy ring breathing + stretching of C=O + β (C-H) + β (O-H)
42 1080w Ring deformation + C=O deformation + β (C-H) + β (O-H)
43 1154w Ring stretching + β (C-H) + β (O-H) + stretching of C9=O9
44 1164vw Asy ring breathing + β (C-H) + β (O-H) + stretching of C=O
45 1166m Ring stretching + β (C-H) + β (O-H) + C=O deformation
46 1209vw Asy ring breathing + β (C-H) + β (O-H) + stretching of C9=O9
47 1213vs Ring deformation + β (C-H) + β (O-H) + C9=O9 deformation
48 1270vs Ring deformation + β (C-H) + β (O-H) + C10=O10 stretching + C9=O9 deformation
49 1283vs Sym ring breathing + β (C-H) + β (O-H) + stretching of C9=O9
50 1313w Asy ring breathing + stretching of C9=O9 + β (C-H) + β (O-H)
51 1318m Asy ring breathing + stretching of C9=O9 + β (C-H) +β (O-H) + deformation of C10=O10
52 1361w Ring deformation + deformation of C=O + β (O-H) + β (C2-H2, C3-H3, C6-H6, C7-H7)
53 1368s Sym ring breathing + β (O-H) + stretching of C2-H2 and C7-H7 + stretching of C=O + β (C3-H3, C4-H4, C5-H5, C6-H6)
54 1376s Ring stretching + β (C3-H3, C4-H4, C5-H5, C6-H6) + C9=O9 deformation + β (O-H)
55 1438w Ring stretching + β (C-H) + β (O-H) + stretching of C9=O9
56 1450m Ring deformation + β (C2-H2, C3-H3, C6-H6, C7-H7) + β (O-H)
57 1475vs Sym ring breathing + β (C-H) + β (O-H) + stretching of C=O
58 1477w Ring deformation + β (C3-H4, C4-H4, C5-H5, C6-H6) + β (O-H)
59 1561w Sym ring breathing + β (C-H) + β (O-H) + stretching of C=O
60 1570m Ring stretching + β (O-H) + stretching of C3-H3 and C6-H6 + β (C2-H2, C4-H4, C5-H5, C7-H7)
61 1588w Ring stretching + β (O-H) + stretching of C3-H3, C4-H4, C5-H5 and C6-H6, stretching of C=O
62 1599w Ring stretching + β (O-H) + β (C2-H2, C4-H4, C5-H5, C7-H7)
63 1624vs Sym breathing of ring + β (O-H) + β (C2-H2, C7-H7) + stretching of C=O
64 1689s Asy ring breathing + stretching of C2-H2, C7-H7, C4-H4 and C5-H5 + β (O-H)+ stretching of C10=O10 + β (C3-H3, C6-H6)

β: in-plane bending.

Table A4. Details of emodin IR assignments.
Vibrational mode Wavenum-bers [this work] (cm-1) Calculated IR frequency assignments [this work]
1 30vw γ (Ring deformation) + γ [C6(CH3)-H6(1, 2, 3)] deformation
2 34w γ (Ring deformation) + γ (C10=O10 deformation) + γ [C6(CH3)-H6(1, 2, 3)] deformation
3 61vw γ (Ring deformation), γ [deformation of C6-C6 (CH3)]
4 109w γ (Ring deformation) + γ (deformation of C=O) + γ (deformation of C-H)
5 130vw γ (Ring deformation) + γ (deformation of C=O) + γ (deformation of C2-H2 and C7-H7) +  γ [deformation of C6-C6(CH3)] + γ [C6(CH3)-H6(1, 2, 3) deformation]
6 153vw γ (Ring deformation) + γ [C6-C6(CH3) deformation] + γ [C6(CH3)-H6(1, 2, 3) deformation] +  γ [C2-H2 and C7-H7 deformation]
7 167vw Ring deformation + stretching of [C6-C6(CH3) + O-H + C6(CH3)-H6(1, 2, 3) + C4-H4 and C5-H5]
8 209w γ (Ring deformation) + γ (O3-H3 deformation) + γ (C-H deformation)
9 213vw γ (Ring deformation) + γ (C4-H4 and C6-H6 deformation) + γ (O3-H3 deformation)
10 236vw γ (Ring deformation) + γ [deformation of C6-C6(CH3) + C=O+ C6(CH3)- H6(1, 2, 3) + O1-H1 + C4-H4, C5-H5 and C7-H7]
11 252vw γ (Ring deformation) + γ [deformation of C=O + C3-O3+ C6-C6(CH3) + C6(CH3)-H6(1, 2)]
12 253w γ (Ring deformation) + γ [deformation of C-O + C6-C6(CH3) + C=O + O3-H3 + C2-H2, C4-H4 and C7-H7]
13 276w γ (Ring deformation) + γ [deformation of C-O + C10=O10 + O-H]
14 336w Ring deformation) + [stretching of C1-O1 + C8-O8 + C6-C6(CH3) + C6(CH3)-H6(1)]
15 364w Ring stretching + β (C10=O10) + β (C8-O8) + stretching of (O8-H8), C6-C6(CH3) and C6(CH3)-H6(1, 2, 3)
16 382s γ (Asy one ring deformation) + γ ( deformation of O3-H3)
17 383w γ (Asy one ring deformation) + γ [deformation of O3-H3 + C10=O10 + C1-O1 + O1-H1 + C3-O3 and O3-H3]
18 405w γ (Ring deformation) + γ [deformation of C10=O10 + C2-H2 and C7-H7]
19 423vw γ (Ring deformation) + γ [deformation of C9=O9 + C2-H2 and C7-H7]
20 430w γ (Ring deformation) + γ [deformation of C=O + O1-H1 + O8-H8 + C3-O3]
21 443w γ (Ring deformation) + γ [deformation of O-H + C4-H4 + C5-H5 and C6-C6(CH3)]
22 465vw γ (Ring deformation) + γ [deformation of C2-H2 + C7-H7 + O1-H1 + O8-H8 + C6-C6(CH3)]
23 513w γ (Ring deformation) + γ [deformation of C-O + O-H + C9=O9 + C6-C6(CH3) + C2-H2 and C7-H7 + C6(CH3)-H6(1, 2, 3)]
24 540w γ (Ring deformation) + γ [deformation of C-O + C9=O9 + C2-H2 and C5-H5 + C6-C6(CH3) and C6(CH3)-H6(1, 2, 3)]
25 549w γ (Ring deformation) + γ [deformation of C-O + C2-H2 and C2-H5 + C6-C6(CH3) and C6(CH3)-H6(1, 2, 3)]
26 553w γ (Ring deformation) + γ [deformation of C2-H2 + C6(CH3)-H6(1, 2, 3) and C=O]
27 555w γ (Ring deformation) + γ [deformation of C9=O9 + O-H + C-O and C6-C6(CH3)]
28 584vw γ (Ring deformation) + γ [deformation of C7-H7 + C8-O8 and C9=O9]
29 604w γ (Ring deformation) + γ [deformation of C3-O3 + C9=O9 + C4-H4, O-H and C6-C6(CH3)]
30 606w γ (Ring deformation) + γ [deformation of C3-O3 + C6-C6(CH3) + C9=O9 + O1-H1 + O8-H8 + C4-H4 and C5-H5]
31 631w Sym ring breathing + stretching of O-H, C2-H2 + C7-H7 and C6-C6(CH3)
32 656vw γ (Ring deformation) + γ [deformation of C=O + C4-H4 and O-H]
33 717w γ (Ring deformation) + γ [deformation of C9=O9 + C3-O3 + C6-C6(CH3) + C4-H4 and C5-H5]
34 728w γ (Ring deformation) + γ [deformation of C=O + C4-H4 + C5-H5 + C2-H2 and C7-H7]
35 770w Ring deformation + [stretching of C=O + C5-H5 + C-O +  C6-C6(CH3) + O3-H3] + γ (stretching of C4-H4)
36 788w γ (Ring deformation) + γ [deformation of O1-H1 + O8-H8 + C2-H2, C4-H4, C5-H5 and C7-H7]
37 798m γ (Ring deformation) + γ [deformation of O1-H1, O8-H8, C2-H2, C4-H4, C5-H5 and C7-H7]
38 822s γ (Ring deformation) + γ [deformation of C2-H2 +  C5-H5 + C7-H7 + C4-H4 + O1-H1 + O8-H8 and C9=O9]
39 836vw γ (Ring deformation) + γ [deformation of C2-H2 + C5-H5 + C7-H7 + C4-H4 + O1-H1 + O8-H8 and C6(CH3)-H6(1, 2, 3)
40 852w γ (Ring deformation) + γ [deformation of C10=O10+ O1-H1+ O3-H3 + C2-H2 + C4-H4 and C7-H7]
41 903w γ (Ring deformation) + γ [deformation of C9=O9 + C1-O1 + C8-O8 + O-H + C2-H2 + C7-H7 + C5-H5 + C6(CH3)-H6(1, 2, 3) and C6-C6(CH3)]
42 904w γ (Ring deformation) + γ [deformation of C4-H4 + C5-H5 + C7-H7 and O8-H8]
43 930w Asy ring breathing + stretching of C6-C6(CH3), C-O and O1-H1
44 987w Asy ring breathing + stretching of C6(CH3)-H6(1, 2, 3), C6-C6(CH3), C-O, C5-H5 and β [C6(CH3)-H6(1, 2, 3)]
45 1008w Asy ring breathing + stretching of C2-H2, C4-H4, C7-H7, C6-C6(CH3), C6(CH3)-H6(1, 2, 3) and C-O
46 1028w Sym ring breathing + β (C-H) + β (O3-H3) +  C10=O10 deformation + stretching of C6-C6(CH3)
47 1033w γ (One ring deformation) + γ [deformation of C5-H5 +  C7-H7 + C6-C6(CH3) and C6(CH3)-H6(1, 2, 3)]
48 1096s Asy ring breathing + β (C4-H4, C5-H5 and C7-H7) + β (O3-H3) + β [C6(CH3)-H6(1, 2, 3)], C=O deformation, stretching of C1-O1, C8-O8 and C6-C6(CH3)
49 1127w Asy ring breathing + β (C5-H5, C7-H7 and C4-H4) +  β (O8-H8 and O3-H3) + β [C6(CH3)-H6(1)] + stretching of C6-C6(CH3) and C9=O9
50 1152s Asy ring stretching + β (O3-H3) + β (C2-H2 and C7-H7), stretching of C3-O3, C1-O1 and C6-C6(CH3)
51 1167w Asy ring breathing + β (O-H) + β (C2-H2, C4-H4, C5-H5 and C7-H7), C10=O10 deformation and stretching of C-O, C9=O9 and C6-C6(CH3)
52 1182w Sym ring breathing + β (C4-H4,C5-H5 and C7-H7) + C10=O10 deformation + β (O3-H3) + stretching of C-O and C9=O9
53 1220vs Ring deformation + β (C2-H2, C5-H5 and C7-H7) + β (O-H) + C=O deformation + β [C6(CH3)-H6(1, 2, 3)], β [C1-O1, C8-O8 and C6-C6(CH3)] + stretching of C3-O3
54 1224m Asy ring breathing + β (O-H) + β (C2-H2, C4-H4, C5-H5 and C7-H7), stretching of C-O, C6-C6(CH3) and C9=O9
55 1264vs Asy ring breathing + β (C2-H2, C4-H4, C5-H5 and C7-H7), β (O-H), C=O deformation, β [C6(CH3)-H6(1, 2)] + stretching of C-O and C6-C6(CH3)
56 1308s Sym ring breathing + β (O1-H1 and O8-H8) + β (C4-H4), β [C6-C6(CH3)], β [C6(CH3)-H6(1, 2, 3)] + stretching of C9=O9 and C-O + deformation of C10=O10
57 1312w Asy ring breathing + β (O-H) + β (C-H) + β [C6(CH3)-H6(1, 2, 3)] + β [C6-C6(CH3)] and stretching of C-O and C9=O9
58 1328vs Asy ring breathing + β (O-H) + deformation of C=O +  β [C6(CH3)-H6(1, 2, 3)] + β (C4-H4 and C5-H5) and stretching of C-O
59 1374s Asy ring breathing + β (O3-H3 and O8-H3) +  β [C6-C6(CH3)], β (C2-H2 and C7-H7), C=O deformation, β [C6(CH3)-H6(1, 2)]
60 1384s Ring stretching + β (O-H) + deformation of C9=O9 +  β (C2-H2) + β [(CH3)6-H6(1, 2)], β [C6-C6(CH3)] and stretching of C-O and C10=O10
61 1389w Asy one ring breathing + β [C6(CH3)-H6(1, 2, 3)] + β (C4-H4 and C7-H7), stretching of C6-C6(CH3), C8-O8 and C9=O9
62 1399m Asy ring breathing + β (C-H) + β (O1-H1 and O3-H3) + β [C6(CH3)-H6(1, 2, 3)] + β [C6-C6(CH3)] deformation of C9=O9 and stretching of C10=O10
63 1413m Asy ring breathing + β [(CH3)6-H6(1, 2, 3)] + β [O-H] +  β (C4-H4, C7-H7 and C5-H5) + deformation of C9=O9 + β [C6-C6(CH3)]
64 1440m Asy ring stretching + β (O1-H1 and O3-H3), β (C-H), C9=O9 deformation + β (C3-O3) + β [(CH3)6-H6(1, 2, 3)] + stretching of C1-O1, C8-O8 and C6-C6(CH3) and deformation of C10=O10
65 1452w γ (Mild one ring deformation) + γ [deformation of (CH3)6-H6(1, 2, 3)]
66 1463w Asy ring breathing + β (O-H) + β (C-H) + β [C6(CH3)-H6(1, 2, 3)], stretching of C9=O9, C-O and C6-C6(CH3)
67 1478vs Sym ring breathing + β (O-H) + β (C-H) + β [C6(CH3)-H6(1, 2, 3)] stretching of C-O, C=O and C6-C6(CH3)
68 1489w Ring stretching + β (C4-H4 and C5-H5) + β (O1-H1 and O8-H8), stretching of C-O, C6-C6(CH3) and C9=O9
69 1558s Asy ring breathing + β (O8-H8) + β (C4-H4 and C7-H7) +  β (O3-H3), stretching of C=O, C6(CH3)-H6(1, 2, 3) and C6-C6(CH3)
70 1575m Sym ring breathing + β (O-H) + β (C-H) and stretching of C=O and C6-C6(CH3)
71 1587m Sym ring breathing + β (O-H) + β (C4-H4 and C5-H5) +  β [C6-C6(CH3)], β [C6(CH3)-H6(1, 2, 3)] and stretching of C=O
72 1609s Ring stretching + β (C-H) + β (O-H) + β [C6(CH3)-H6(1, 2, 3)], C=O deformation and stretching of C6-C6(CH3)
73 1628vs Sym ring breathing + β (C-H) + β (OH) + β [C6(CH3)-H6(1, 2, 3)] + stretching of C6-C(CH3) and C=O
74 1689m Asy ring breathing + stretching of C10=O10, C6-C(CH3) + β (O-H) + β (C-H) + C6(CH3)-H6(1, 2, 3)


[1] D.S.  Alves, L.  Pérez-Fons, A.  Estepa, and V.  Micol, Membrane-related effects underlying the biological activity of the anthraquinones emodin and barbaloin, Biochem. Pharmacol. 68(3), 549-561 (2004).

[2] X. Huang, L. Kong, X. Li, X. Chen, M. Guo, and H. Zou, Strategy for analysis and screening of bi-oactive compounds in traditional Chinese medicines, J. Chromatogr. B 812(1-2), 71-84 (2004).

[3] H. Matsuda, T. Morikawa, I. Toguchida, J.-Y. Park, S. Harima, and M. Yoshikawa, Antioxidant constituents from rhubarb: structural requirements of stilbenes for the activity and structures of two new anthraquinone glucosides, Bioorg. Med. Chem. 9(1), 41-50 (2001).

[4] Y. Cai, Q. Luo, M. Sun, and H. Corke, Antioxidant activity and phenolic compounds of 112 traditional Chinese medicinal plants associated with anticancer, Life Sci. 74(17), 2157-2184 (2004).

[5] C.H.  Xiao, S.S.  Yang, and X.K.  Hong. The  Chemistry of Traditional Chinese Medicines (Shanghai Science and Technology Publishing Press, Shanghai, 2000).

[6] B.A.  Monisha, N.  Kumar, and A.B.  Tiku, in: Anti-inflammatory Nutraceuticals and Chronic Diseases (Springer, Cham, 2016) pp. 47-73.

[7] R. Jin and H. Bao, A DFT study on the radical scavenging activity of hydroxyanthraquinone derivatives in rhubarb, Int. J. Quantum Chem. 111(5), 1064-1071 (2011).

[8] S.Z. Marković and N.T. Manojlović, DFT study on the reactivity of OH groups in emodin: structural and electronic features of emodin radicals, Monatsh. Chem. 140(11), 1311 (2009).

[9] Z.  Marković, N.  Manojlović, and S.  Zlatanović, Electronic absorption spectra of substituted anth-raquinones and their simulation using ZINDO/S method, J. Serbian Soc. Comput. Mech. 2(2), 73- 79 (2008).

[10] Q. Zhang, X. Gong, H. Xiao, and X. Xu, Density functional theory study on anthraquinone and its hydroxyl derivatives, Acta Chim. Sinica 64(5), 381 (2006).

[11] I.M. Kenawi, DFT analysis of diclofenac activity and cation type influence on the theoretical parameters of some diclofenac complexes, J. Mol. Struct. Theochem 761(1-3), 151-157 (2006).

[12] H.N.  Flores and M.D.  Glossman, CHIH-DFT determination of the electrical, optical, and magnetic properties and NICS aromaticity of megazol, J. Mol. Struct. Theochem 717(1-3), 1-3 (2005).

[13] P.G.  De  Benedetti, G.  Pier, S.  Quartieri, and A. Rastelli, A theoretical study of the structure- activity relationship in sulpha drugs, J. Mol. Struct. Theochem 85(1-2), 45-51 (1981).

[14] Y.B. Shankar Rao, M.V.S. Prasad, N. Udaya Sri, and V. Veeraiah, Vibrational (FT-IR, FT-Raman) and UV-Visible spectroscopic studies, HOMO- LUMO, NBO, NLO and MEP analysis of benzyl (imino (1H-pyrazol-1-yl) methyl) carbamate using DFT calculations, J. Mol. Struct. 1108, 567- 582 (2016).

[15] A.M.  Mansour, Coordination behavior of sul-famethazine drug towards Ru  (III) and Pt  (II) ions: Synthesis, spectral, DFT, magnetic, electrochemical and biological activity studies, Inorg. Chim. Acta 394, 436-445 (2013).

[16] M.A. Thompson, in: Proceedings of ACS Meeting, Vol. 172 (Philadelphia, 2004) p. 42.

[17] TURBOMOLE V6.2010, a  development of University of Karlsruhe and Forschungszentrum Karlsruhe GmbH, 1989-2007 (TURBOMOLE GmbH, since 2007),

[18] M. Büschel, Ch. Stadler, Ch. Lambert, M. Beck, and J. Daub, Heterocyclic quinones as core units for redox switches: UV-vis/NIR, FTIR spectro-electrochemistry and DFT calculations on the vibrational and electronic structure of the  radical anions, J. Electroanal. Chem. 484(1), 24-32 (2000).

[19] A.  Bankapur, E.  Zachariah, S.  Chidangil, M.  Valiathan, and D.  Mathur, Raman tweezers spectroscopy of live, single red and white blood cells, PLoS One 5(4), e10427 (2010).

[20] R.D.  Snook, T.J.  Harvey, E.C.  Faria, and P. Gardner, Raman tweezers and their application to the  study of singly trapped eukaryotic cells, Integr. Biol. 1(1), 43-52 (2009).

[21] G. Smulevich and M.P. Marzocchi, Single crystal and polarized infrared spectra of two forms of 1,8-dihydroxyanthraquinone vibrational assignment and crystal structures, Chem. Phys. 94(1-2), 99-108 (1985).

[22] G. Fabriciova, J.V. Garciá-Ramos, P. Miskovsky, and S.  Sanchez-Cortes, Adsorption and acidic behavior of anthraquinone drugs quinizarin and danthron on Ag nanoparticles studied by Raman spectroscopy, Vib. Spectrosc. 34(2), 273-281 (2004).

[23] H.G.M.  Edwards, E.M.  Newton, D.D.  Wynn- Williams, and S.R. Coombes, Molecular spectroscopic studies of lichen substances 1: parietin and emodin, J. Mol. Struct. 648(1-2), 49-59 (2003).


B.K. Barik a, H.M. Mallya a, R.K. Sinha b, S. Chidangil b

a Manipalo aukstojo mokslo akademijos Melakos Manipalo medicinos kolegijos Biochemijos skyrius, Manipalas, Karnataka, Indija

b Manipalo aukstojo mokslo akademijos Atominės ir molekulinės fizikos skyrius, Manipalas, Karnataka, Indija