Microsoft Word - Bhawani Datta _38-49_.doc Bhawani Datt Joshi et al. / BIBECHANA 9 (2013) 38-49 : BMHSS, p.38 (Online Publication: Nov., 2012) BIBECHANA A Multidisciplinary Journal of Science, Technology and Mathematics ISSN 2091-0762 (online) Journal homepage: http://nepjol.info/index.php/BIBECHANA Structure, MESP and HOMO-LUMO study of 10-Acetyl- 10H-phenothiazine 5-oxide using vibrational spectroscopy and quantum chemical methods Bhawani Datt Joshi 1,2* , Poonam Tandon 1 , Sudha Jain 3 1Department of Physics, University of Lucknow, Lucknow-226007, UP, India 2Department of Physics, Siddhanath Sc. Campus, Mahendranagar, Tribhuvan University, Nepal 3Department of Chemistry, University of Lucknow, Lucknow-226007, UP, India *Corresponding author: E-mail: bdjoshi_007@yahoo.com Article history: Received 5 October, 2012; Accepted 7 November, 2012 Abstract In this communication, we have presented the geometry optimization, complete vibrational study with potential energy distribution (PED) and frontier orbital energy gap for the 10-Acetyl-10H-phenothiazine 5-oxide (APTZ) molecule using ab initio Hartree-Fock (HF) and density functional theory (DFT/B3LYP) method employing 6-311++G(d,p) basis set. The calculated IR and Raman spectra with their intensities, molecular electrostatic potential (MESP) surface and highest occupied molecular orbital (HOMO) - lowest unoccupied molecular orbital (LUMO) plot have been given. Keywords: APTZ; ab initio; DFT; IR; Raman; MESP; HOMO - LUMO. 1. Introduction Phenothiazines, the heterocyclic organic compounds in which sulphur and nitrogen are incorporated in the tricyclic system, exhibit a wide range of pharmacological / biological activities [1-10]. Their several derivatives have been found to possess clinical activities, such as: tranquilizers, antihistamines, diuretics, analgesics, neurolepitcs, anticancer activity [5,6] in vitro (cancer cell lines), antileukemic [5] antimutagenic [2], anti- trypanosomal, antileishmanial [3], and inhibition of the growth of autoimmune deficiency syndrome (AIDS)-related lymphoma cells [4]. Properties of 10-H-phenothiazine, such as: semiconductivity [11], electrical conductivities [12] and low thermal activation energies of charge transfer complexes [13], has opened new practical fields of investigation. Alconea Palafox et al. [14] had given a complete vibrational analysis of the Fourier transform (FT) infrared (IR) and FT-Raman spectra of both phenothiazine (PTZ) and N-methylphenothiazine molecules using ab initio method as well as quantum chemical calculations. Sharma et al. [15] found the better biological activity of 4-thiazolidinone derivatives of phenothiazine. Dixit et al. [2] had synthesized some 10H-phenothiazine sulphone derivatives and characterized them with selected bands of IR and 1H NMR spectroscopic methods. Bhawani Datt Joshi et al. / BIBECHANA 9 (2013) 38-49: BMHSS, p.39 (Online Publication: Nov., 2012) Fig. 1: Optimized structure of APTZ molecule. Literature survey reveals that neither the vibrational assignments nor the highest molecular orbital (HOMO) - lowest unoccupied molecular orbital (LUMO) study of APTZ derivative of phenothiazine has been studied so far. Thus, a complete vibrational study along with molecular electrostatic potential (MESP) surface and HOMO - LUMO analysis has been carried in the present study using ab initio Hartree-Fock (HF) and density functional theory (DFT) method. The vibrational spectroscopy, that deals the short range structure studies, has very keen applications in these days for the structure characterization of biologically active materials [16]. HOMO - LUMO analysis has been performed which helps elucidate charge transfer occurring in the molecule. 2. Methodology Computational Geometry optimization, an important issue in molecular mechanics, was performed as the first task of the computational work for the APTZ molecule taking the parameters from the X-ray diffraction data [17]. The optimized ground state molecular structure is shown in Fig. 1. The molecular structure, vibrational frequencies and energy of the optimized geometry of APTZ were computed employing the DFT [18] and HF methods using Gaussian 09 [19] program package employing 6-311++G(d,p) basis set based on Becke’s three parameters (local, non-local and Hartree-Fock) hybrid exchange functional with Lee-Yang- Parr correlation functional (B3LYP) [20,21]. The basis set 6-311++G(d,p) augmented by ‘d’ polarization functions on heavy atoms and ‘p’ polarization functions on hydrogen atoms as well as diffuse functions for both hydrogen and heavy atoms were used [22,23]. The absolute Raman intensities and IR absorption intensities were calculated in the harmonic approximation at the same level of theory as used for the optimized geometries associated with each normal mode, respectively. The normal mode analysis was performed and the PED was calculated along the internal coordinates using localized symmetry. For this purpose, a complete set of 84 internal coordinates were defined using Pulay’s recommendations [24,25]. The vibrational assignments of the normal modes were made on the basis of the PED calculated by using the program GAR2PED [26]. Raman and IR spectra were simulated using a pure Lorentzian band profile (fwhm = 8 cm-1) using indigenously developed software. Visualization and confirmation of calculated data were done by using the CHEMCRAFT program [27]. Bhawani Datt Joshi et al. / BIBECHANA 9 (2013) 38-49: BMHSS, p.40 (Online Publication: Nov., 2012) 3. Results and Discussion 3.1. Geometry optimization Initial geometry taken from X-ray diffraction data [17] of APTZ was minimized without any constraint to the potential energy surface and the optimized structural parameters were used in the vibrational frequency calculation to characterize all stationary points as minima. The molecular conformation from the crystalline structure, as well as yielded by geometry optimization, exhibits no special symmetries. Hence, APTZ molecule crystallizes in the monoclinic, P21/n form having lattice parameters a = 8.1244 (1) Å, b = 14.1787 (2) Å, c = 10.7576 (1) Å, β = 100.963 (1)o and z = 4 in a unit cell [17]. The sulphoxide Fig. 2: Comparison of the experimental (from single crystal X-ray diffraction) and optimized structure (purple) of APTZ (hydrogen atoms are excluded for clarity). oxygen atom is disordered over two sites with occupancies of 0.886 (4) and 0.114 (4), reflecting a partial inversion of the lone pair at the tetrahedral S-atom site. The optimized structure produced is very similar to the experimental one. Both the optimized and experimental structures of the title molecule were compared by superimposing them using a least-squares algorithm that minimizes the distances between the corresponding non-hydrogen atoms as shown in Fig. 2. 3.2. Molecular electrostatic potential surface In this study, the electrostatic potential (ESP), electron density (ED) and molecular electrostatic potential (MESP) maps for APTZ are as shown in Fig. 3. In ESP, the negative potential is localized near the oxygen atoms and reflects by the yellowish blobs, while the positive potential is localized on the rest surface. However, the ED plot of the title molecule shows uniform distribution. The molecular electrostatic potential (MESP), the force acting on a positive test charge located at point through the electrical charge cloud generated through the net charge of molecule (electrons and nuclei), has been a widely used entity in the chemical literature, generally employed as a tool for probing electron rich regions [28-31]. The MESP at a point ‘r’ in a molecular framework with nuclear charges ZA located at RA and electron density ρ(r) is given by a relation: Bhawani Datt Joshi et al./ BIBECHANA 9 (2013) 38-49: BMHSS, p.41 (Online Publication: Nov., 2012) where N is the total number of nuclei in the molecule. The first term on the right hand side of the above equation represent the contribution due to nucleus and second due to electrons, respectively. When the latter contribution overrides the former one, the net MESP attains a negative value, providing information about electron-rich sites. Fig. 3: (a) ESP (b) electron density (c) molecular electrostatic potential mapped on the isodensity surface in the range -6.521x10-2 (red) to +6.521x10-2 (blue) for APTZ. MESP correlates the total charge distribution with dipole moment, electronegativity, and partial charges and site of chemical reactivity of a molecule. The projection of molecular MESP of APTZ along the molecular plane is given in Fig. 3c. It provides a visual method to understand the relative polarity of a molecule and serves as a useful quantity to explain hydrogen bonding, reactivity and structure-activity relationship of molecules including biomolecules and drugs. It is the potential energy of a proton at a particular location near a molecule. Different values of the electrostatic potential at the surface of a molecule appear with the different colours. In general the attractive (or negative) potential appears in red coloured regions and those of repulsive (or positive) potential appear in blue. In the title molecule the regions near oxygen atoms are most attractive and the regions near hydrogen of methyl group are positive. 3.3. HOMO-LUMO analysis The HOMO is the outermost (highest energy) orbital containing electrons that could act as an electron donor. The LUMO is the innermost (lowest energy) orbital that has room to accept electrons and can act as the electron acceptor. According to the frontier molecular orbital theory, the formation of a transition state is due to an interaction between the frontier orbitals (HOMO and LUMO) of reactants [32]. The energy of the HOMO is directly related to the ionization potential and the energy of the LUMO is directly related to the electron affinity. High value of HOMO energy is likely to indicate a tendency of the molecule to donate electrons to appropriate acceptor molecule of low empty molecular orbital energy. The lower values of LUMO energy show more probability to accept electrons. So, the gap energy, i.e. the Bhawani Datt Joshi et al. / BIBECHANA 9 (2013) 38-49: BMHSS, p.42 (Online Publication: Nov., 2012) difference in energy between the HOMO and LUMO, is an important stability index. It is a critical parameter in determining molecular electrical transport properties because it is a measure of electron conductivity. Low gap value refers to the higher electronic transition and vice versa. The HOMO - LUMO plot with the frontier orbital energy gap for the title molecule is shown in Fig. 4. Fig. 4: HOMO-LUMO plot of APTZ molecule. In HOMO the main electronic transition is occurred at C=C bonds of all the rings, S atom of the rings R2 and carbonyl group (in small amounts), while in LUMO the charge density is mainly accumulated at CC bond in rings. Table 1. Electronic transitions, absorption wavelength λmax (nm), excitation energy (eV), oscillator strengths (f), frontier orbital energies (eV) and dipole moment (Debye) of APTZ. Calculated Gas Phase Benzene solution Excited States λmax (nm) Transitions E(ev) Oscillator strength (f) λmax (nm) Transitions E(ev) Oscillator strength (f) Transition type/ assignments 1 278 H→L 4.4594 0.0549 280 H→L 4.4249 0.0838 π→π * 2 256 H-1→L 4.8445 0.0152 251 H→L+1 4.9486 0.0983 3 252 H→L+1 4.9107 0.0537 246 H-3→L 5.0408 0.0271 4 244 H→L+2 5.0754 0.0283 244 H→L+2 5.0852 0.0489 π→π * 5 236 H-3→L 5.2463 0.0081 235 H-5→L 5.2858 0.0160 6 231 H-5→L 5.3783 0.0091 225 H→L+3 5.4995 0.0215 7 226 H-7→L 5.4730 0.0122 222 H→L+4 5.5930 0.0434 8 221 H-1→L+2 5.154 0.0152 221 H- 6→L 5.6169 0.0224 EHOMO (eV) ELUMO (eV) ∆E (eV) µ(D) Gas -6.9067143 -1.7289234 5.1777909 6.1429 Benzene -6.8639946 -1.7066112 5.1573834 7.0474 HOMO = 71, LUMO = 72 Bhawani Datt Joshi et al. / BIBECHANA 9 (2013) 38-49. : BMHSS, p.43 (Online Publication: Nov., 2012) The calculated frontier orbital energies, absorption wavelengths (λmax), oscillator strengths (f), excitation energies (E) and dipole moments (µ) for gas phase and benzene solvent environment (integral equation formalism-polarizable continuum model, IEF-PCM) using the TD-DFT/6-31G method are illustrated in Table 1. This electronic absorption corresponds to the transition from the ground to the first excited state and is mainly described by one electron excitation from the HOMO to the LUMO. The first allowed- dipole transition in the gas phase was calculated about 278 nm with oscillator strength 0.0549. The next transitions were calculated about 252, 244 and 221 nm with oscillator strengths 0.0537, 0.0283 and 0.0152, respectively. The transitions π→π* are the main observed transitions. 3.4. Vibrational assignment An APTZ molecule has 30 atoms and hence gives 84 (3N-6) fundamental modes of vibration. All of them are both the Raman and IR active. Since the vibrational wavenumbers calculated by DFT methods are higher than their precise values, so they were scaled down by the wavenumber linear scaling procedure (WLS) [νobs/νcal = (1.0087 – 0.0000163 x νcal) cm-1] of Yoshida et al. [33]. However, there are different scaling factors, but the vibrational wavenumbers calculated uniformly scaled with only one scaling factor [34,35] are often in good agreement to the observed ones. The Raman scattering cross sections, ∂σj/∂Ω, which are proportional to the Raman intensities, may be calculated from the Raman scattering amplitude and predicted wavenumbers for each normal modes using the relationship [36,37] j jj j j S c h kT hc                              − −       −       = Ω∂ ∂ νπν νν πσ 2 4 044 8 exp1 45 2 where Sj and υj are the calculated scattering activities and the predicted wavenumbers, respectively, of the jth normal mode, υo is the Raman excitation wavenumber and h, c and k are the universal constants. Assignments have been made on the basis of relative intensities, energies, line shape and potential energy distribution. All the vibrational bands have been assigned satisfactorily, together with the IR and the Raman intensities. The assigned wavenumbers of the vibrational modes calculated at the HF and B3LYP level with the basis set 6-311++G(d,p) along with their PED are given in Table 2. In the APTZ molecule, there are three rings with different functional groups as shown in Fig. 1. The vibrational assignments of these rings along with some functional groups have been discussed separately. The calculated IR and Raman spectra are given in the Figs. 5 and 6, respectively. 3.4.1. CH3 vibrations The title molecule has one methyl group associated with different types of vibrations: like symmetric and asymmetric stretching, deformations and rocking as listed in Table 2. Asymmetric stretching of CH3 is at 3039/3017 cm-1 in scaled DFT having intensities of 5.43/3.53 a.u in the IR and 258.68/292.55 a.u in the Raman spectra, respectively. The symmetric stretching is calculated at 2927 cm-1 (contribution 100%). This band is weak in IR band with intensity of 2.81 a.u. and strong intensity of 824.08 a.u. in the Raman spectra. The asymmetric bending modes of this group are calculated at 1461 and 1447 cm-1, while the symmetric bending mode is calculated around 1380 cm-1. The rocking vibration is calculated at 1043 and 1017 cm-1 in the scaled DFT, which is weaker in intensity in the IR spectrum in comparison to that in the Raman spectrum. Bhawani Datt Joshi et al. / BIBECHANA 9 (2013) 38-49: BMHSS, p.44 (Online Publication: Nov., 2012) Table 2. Calculated wavenumbers (in cm -1 ), IR and Raman intensities (in a.u.). Unscaled Scaled Intensity DFT HF DFT IR Raman PEDa (%) 3232 3228 3090 0.31 382.37 R1[υ(CH)](97) 3203 3213 3063 6.21 1517.81 R3[ υ(CH)](96) 3202 3212 3063 8.53 585.95 R1[υ(CH)](95) 3198 3205 3059 2.15 174.26 R3[υ(CH)](98) 3190 3197 3052 6.43 696.38 R1[υ(CH)](98) 3189 3196 3051 5.87 487.54 R3[υ(CH)](99) 3176 3182 3040 3.5 309.77 R1[υ(CH)](99) 3176 3181 3039 1.74 271.13 R3[υ(CH)](99) 3151 3152 3017 5.43 258.68 υa(CH3)(99) 3120 3123 2988 3.53 292.55 υa(CH3)(100) 3052 3061 2927 2.81 824.08 υs(CH3)(100) 1760 1906 1725 321.27 503.6 [υ(C=O)](78)+ρ[C=O](7)+[υ(CC)](5) 1636 1750 1607 18.47 370.17 R3[υ(CC)(32)+δin(CH)(6)]+R1[υ(CC)(22)+δa(5)] 1624 1742 1595 32.61 1411.67 R1[υ(CC)(35)+δin(CH)(11)+δa(6)]+R3[υ(CC)](27) 1619 1733 1591 13.48 527.92 R1[υ(CC)(35)+δ’a(5)]+R3[υ(CC)](27)+R2[υ(CC)]7) 1609 1719 1581 2.36 178.71 R1[υ(CC)](31)+R3[υ(CC)(27)+δin(CH)](8)]+R2[υ(CC)](9) 1507 1610 1483 52.39 7.75 R1[δin(CH)(25)+υ(CC)](11)]+R3[δin(CH)](24)+υ(CC)](6)+R2[υ(CC)] (8) 1492 1595 1468 90.55 105.5 R1[δin(CH)(25)+υ(CC)(19)]+R3[δin(CH)](20)+R2[υ(CC)(8)+υ(CN)(8 )] 1484 1578 1461 18.95 202.89 [δa(60)+δ’a(22)+ρ’(6)](CH3) 1481 1574 1458 13.74 21.16 R3[δin(CH)(33)+υ(CC)(21)]+R1[δin(CH)](14)+R2[δtrig](7) 1476 1572 1454 5.69 26.18 R1[δin(CH)(38)+υ(CC)(22)]+R3[δin(CH)](11)+υ(CC)(8)] 1469 1559 1447 7.43 128.29 [δ’a(61)+δa(19)+ρ(9)](CH3) 1399 1509 1380 40.71 79.17 δs[CH3](88)+[υ(CC)](7) 1340 1427 1323 12.27 376.6 R1[υ(CC)](49)+R3[υ(CC)](26)+R2[υ(CC)]6) 1332 1405 1315 62.21 319.78 R2[υ(CN)(26)+δin(NC21)(6)]+R3[υ(CC)(24)+δin(CH)(7)] 1326 1396 1309 10.69 307.35 R1[υ(CC)(36)+δin(CH)(8)]+R3[υ(CC)(25)+δin(CH)(9)]+R2[υ(CC)](9) 1309 1369 1293 61.86 190.42 R1[δin(CH)](25)+υ(NC21)(11)]+R3[δin(CH)(22)+υ(CC)(5)]+R2[δtrig]( 13) 1272 1345 1257 277.81 400.6 R2[υa(SO2)](85) 1257 1308 1243 97.12 1261.13 R2[υ(NC21)(16)+δin(CH)(18)+υ(CC)(8)+υ(CN)(22)] 1256 1300 1241 134.26 625.29 R3[δin(CH)](26)+υ(CC)(11)]+R2[υ(CN)](17)+R1[υ(NC21)](13) 1213 1294 1200 64.05 1000.42 R2[υ(CN)(15)+υ(CC)(12)+δin(CH)(11)+υ(NC21)(7)+δtrig(6)]+[υ(CC)] (11)+δ[C=O](9)+[ρ[CH3](5) 1187 1251 1174 0.46 62.57 R1[δin(CH)(55)+υ(CC)(9)]+R3[δin(CH)(19)+δin(CH)(9)] 1186 1233 1173 0.71 356.79 R3[δin(CH)(54)+υ(CC)(10)]+R1[δin(CH)](23) 1159 1213 1147 41.18 654.94 R1[δin(CH)(22)+υ(CC)(20)]+R3[δin(CH)(15)+υ(CC)(11)]+R2[υ(CS)]( 13) 1153 1188 1142 3.5 123.02 R3[δin(CH)(23)+υ(CC)(21)]+R1[υ(CC)(15)+δin(CH)(15)]+R2[υ(CS)](10) 1124 1185 1113 123.48 1162.02 R2[υs(SO2)(32)+υ(CS)(12)]+R1[δtrig](9)+R3[δtrig](9) 1083 1159 1073 26.3 29.9 R3[δtrig(18)+δin(CH)(8)+υ(CC)(7)]+R1[δtrig(19)+υ(CC)(6)]+R2[υ(CS)](1 3) 1058 1149 1049 37.24 1602.59 R1[υ(CC)](22)+δin(CH)(8)+[ρ’(13)+ρ(8)](CH3)+R2[υs(SO2)](14)+ω[ C=O](5)+[R3[υ(CC)(5)+δtrig(5)] 1057 1144 1048 0.46 248.47 R3[υ(CC)(37) +δin(CH)(10)+δtrig(7)] +R1[υ(CC)(21)+δtrig(9)] Bhawani Datt Joshi et al. / BIBECHANA 9 (2013) 38-49: BMHSS, p.45 (Online Publication: Nov., 2012) 1052 1115 1043 0.59 839.1 [ρ’(43)+ρ(7)+δa(5)](CH3)+ω[C=O](12)+R1[υ(CC)](6) 1048 1113 1039 42.63 1154.47 R2[υs(SO2)](31)+R3[δtrig(10)+υ(CC)(8)]+R1[δtrig(17)+υ(CC)(8)] 1026 1107 1017 32.89 197.49 [ρ(38)+ρ’(10)](CH3)+R1[δtrig(11)+υ(NC21)(7)]+ρ[C=O](5)+[υ(CC)]( 5)+δ’a[CH3](5) 1003 1106 996 0.05 6.51 R3[oop(CH)(81)+puck(12)] 1002 1103 994 0.09 6.74 R1[oop(CH)(83)+puck(11)] 991 1078 984 2.79 197.74 R3[δtrig](25)+R1[oop(CH)(12)]+R2[δtrig(6)+δin(NC21)(6)]+[υ(CC)](8) +ρ[C=O](6) 974 1076 967 0.87 13.73 R3[oop(CH)(88)+τ’(5)] 970 1057 963 0.85 43.24 R1[oop)CH)(84)+τ’(5)] 907 988 902 7.46 106.16 [υ(CC)](20)+R1[δtrig(15)+υ(CC)](7)+R3[oop(CH)](7)+R2[υ(CN)](6)+ ρ[CH3](5) 888 978 883 0.14 24.54 R3[oop(CH)(81)+puck(5)] 883 960 878 0.43 45.94 R1[oop(CH)(85)+puck(7)] 780 856 777 65.95 18.38 R3[oop(CH)(53)+puck(7)]+R1[oop(CH)](16)+R2[puck](6) 772 848 769 7.95 8.61 R1[oop(CH)](61)+R3[oop(CH)](22) 760 838 757 13.83 205.58 R3[puck(39)+oop(CH)(8)]+R1[puck](17)+R2[puck](17) 744 812 741 29.41 38.51 R1[puck(25)+oop(CH)(7)]+R3[δa(14)+puck(10)]+R2[υ(CS)]7) 740 808 737 2.75 49.1 R1[δa(16)+δ’a(5)+puck(12)+R3[δa(11)+δ’a(5)+puck(7)]+R2[υ(CS)(7) +υ(NC21)(5)] 732 795 730 41.02 52.37 R1[puck(24)+δ’a(6)]+R3[puck](21)+R2[ω(SO2)(8)+υ(CS)(10)+τ(6)] 680 734 678 0.96 1560.6 R1[δ’a(24)+δa(5)]+R3[δ’a(17)+δa(10)+puck(5)]+R2[υ(CS)](8) 650 696 649 6.25 59.28 R3[δ’a](39)+R1[δa(15)+δ’a(8)]+ρ[C=O](7)+[υ(CC)](6) 618 667 618 24.55 111.18 [ω(29)+δ(10)](C=O)+R2[δtrig(11)+oop(NC21)(10)]+ρ[CH3](6)+R1[δa] (6) 592 646 591 26.66 239.37 [ω(13)+δ(9)](C=O)+R1[puck(12)+τ(7)]+R2[oop(NC21)(5)+puck(5)]+ ρ’[CH3](6) 581 638 581 45.4 58.91 R2[ω(SO2)](27)+R3[puck(16)+τ(10)+δa(6)]+R1[δ’a](9) 561 630 561 53.14 590.6 R2[δ(SO2)(26)+δtrig(8)+δ’a(7)]+R1[τ’](5)+R3[τ](5)+τ(C11C12)(5) 555 606 555 13.39 309.64 R2[puck(16)+δtrig(7)+ρ(SO2)(5)]+ω[C=O](16)+R3[τ](10)+R1[τ](7)+ρ ’[CH3](5) 516 567 516 11.61 34.39 R1[τ](29)+R3[τ](22)+R2[τ](15) 502 553 502 7.58 81.73 R3[τ’](18)+δ[C=O](14)+R2[ρ(SO2)(12)+τ’(6)]+τ(C1C10)(9)+R1[τ’(7 )+δa(6)]+τ(C11C12)(5) 464 519 464 8.81 249 R2[δ(SO2)(23)+oop(NC21)(9)+δtrig(8)+τ’(7)]+R3[τ](16)+τ(C1C10)(1 3)+δ[C=O] (5) 458 505 458 1.63 301.3 R1[τ’](30)+R3[τ’(10)+τ(10)]+τ(C11C12)(13)+τ(C1C10)(8)+R2[γ(SO 2)](6) 411 442 412 10.79 887.25 ρ[C=O](28)+R3[τ’(11)+τ(6)+δ’a(8)]+R2[υ(CN)](10) 397 436 398 8.74 409.44 R2[δa(36)+δ’a(16)+υ(CS)(10)]+R1[τ’](9) 381 414 382 2.12 727.17 R1[τ’](15)+[ρ(14)+δ(6)](C=O)+R2[ρ(SO2)(11)+τ’(7)+υ(CS)(5)]+R3[ τ](5) 353 387 354 1.29 2098.6 R3[τ’(18)+τ(6)]+R1[τ’](15)+R2[υ(CS)(6)+υ(CN)(5)] 319 356 320 1.12 867.18 R2[δ’a(29)+δa(13)+υ(NC21)(5)]+[δ(11)+ρ(5)](SO2)+R3[τ’](9) 312 347 313 4.36 268.87 R2[(γ(15)+ω(5))(SO2)+υ(CS)(11)+δin(NC21)(8)]+R1[τ’(11)+τ(9)]+R3 [τ’](6)+ρ[C=O](6) 280 306 281 1.99 197.05 R3[τ](19)+R1[τ](11)+R2[oop(NC21)(6)+(ρ(6)+δ(5)(SO2))+υ(CS)(7)+ δtrig(5)]+τ(C1C10)(10)+τ(C11C12)(5 ) Bhawani Datt Joshi et al. / BIBECHANA 9 (2013) 38-49: BMHSS, p.46 (Online Publication: Nov., 2012) 242 274 243 4.75 1023.84 R2[(ω(20)+γ(18))(SO2)+υ(CS)(16)+δa(11)]+R3[δa](5) 205 224 206 1.75 636.7 R2[γ(SO2)(23)+δin(NC21)(18)]+R3[τ](15)+τ(C1C10)(14)+R1[τ](6) 193 214 194 0.26 784.79 R2[oop(NC21)(13)+ρ(SO2)(10)+υ(CS)(10)+δtrig(5)+τ’(5)]+R1[τ](12)+ R3[δa](6) 150 168 151 2.18 3124.11 τ(C11C12)(28)+τ(C1C10)(25)+R2[γ(SO2)(14)+δin(NC21)(8)]+R3[τ’]( 5) 128 147 129 0.12 6552.24 τ(C21C22)(26)+R2[puck(25)+ρ(SO2)(5)]+τ(C11C12)(10)+τ(C1C10)( 8)+ρ’[CH3](6)+R3[τ](6) 115 131 116 0.2 5116.14 τ(C21C22)(29)+τ(C11C12)(22)+R2[puck(11)+R2τ’(7)]+ρ’[CH3](8) 97 114 98 0.94 1060.01 R2[τ](26)+R2[τ’(12)+δin(NC21)(7)]+τ(C11C12)(18)+τ(C21C22 )(10)+τ(C1C10)(7) 75 81 76 0.59 19405.86 R2[oop(NC21)(45)+τ’(5)]+τ(C1C10)(16)+τ(C21C22)(10)+τ(C11C12) (6) 71 76 71 4.07 1737.43 τ(C21C26)(63)+R2[δin(NC21)](5)+τ(C1C10)(5) 51 50 52 4.64 23135.09 R2[τ’](24)+oop(NC21)(14)+τ(5)]+τ(C21C26)(18)+τ(C21C22)(14) Proposed assignments and potential energy distribution (PED) for vibrational normal modes. Types of vibration: ν, stretching; δ, deformation (bending), scissoring; oop, out-of-plane bending; ω, wagging; γ, twisting; ρ, rocking; τ, torsion. aPotential energy distribution (contribution ≥ 5). 3.4.2. C= O vibrations A carbonyl (C=O) group is connected at the nitrogen atom of ring R2. Regarding to this group; stretching, bending, rocking and wagging modes of vibrations are observed. The stretching of C=O is calculated at 1725 cm-1 (contribution 78%). The deformation and wagging calculated at 618 and 591 cm-1 are the mixed modes. The rocking vibration is calculated at 412 cm-1 (contribution 28%) with the intensities of 10.79 a.u. in the IR spectrum and 887.25 a.u. in the Raman spectrum, respectively. 3.4.3. Ring R1 vibrations Ring R1 has four CH moieties; hence one can expect four stretching modes associated to this group. All these modes are pure in the range 3090-3040 cm-1 and have very weak in intensity in the IR spectrum. The mixed in-plane deformations are calculated at 183, 1468, 1454, 1293, 1174 and 1147 cm-1. The out- of-plane bending modes are calculated at 994, 963, 878 and 769 cm-1. Fig. 5. Theoretical IR spectra between the ranges 0-3100 cm-1. Bhawani Datt Joshi et al. / BIBECHANA 9 (2013) 38-49: BMHSS, p.47 (Online Publication: Nov., 2012) The C-C stretching is stronger in intensity in the Raman spectrum than in the IR spectrum. These modes are calculated below 1595 cm-1. Around 741/730 cm-1 and 737/678 cm-1 are the puckering and deformation of the ring, respectively. The ring torsion is calculated at 516, 458 and 382 cm-1 in the mixed modes. 3.4.4. Ring R2 vibrations Two important functional groups SO2 and –COCH3 are connected with this ring R2. The six fundamental modes of vibrations are assigned with SO2 group; namely symmetric, asymmetric stretch, deformation and rocking, which belong to polarized in-plane vibrations. In addition to that, SO2 wagging and twisting modes would be expected to be depolarized out-of-plane symmetry species. The SO2 asymmetric stretching having contribution of 85% in PED is calculated at 1257 cm-1. The symmetric stretching is calculated at 1113/1029 cm-1, which have strong Raman intensities of 1162.02/1154.47 units. The deformations are calculated at 561 and 464 cm-1. The wagging and twisting vibrations are calculated at 581/243 cm-1 and 313/206 cm-1, respectively. Highly mixed rocking mode with low contribution in PED is calculated below 555 cm-1. CN stretching is calculated at 1315 and 1200 cm-1. NC21 stretching is calculated at 1243 cm-1, which has weak IR and strong Raman intensities as listed in Table 2. Fig. 6. Theoretical Raman spectra between the ranges 20-3200 cm-1. 3.4.5. Ring R3 vibrations Ring R3 has also four CH moieties; hence four CH stretching modes are assigned between the range 3063-3039 cm-1. The CC stretching of the ring is calculated at 1607/1048 cm-1. The trigonal ring deformation is calculated at 1073 cm-1 with weak intensities both in the IR and the Raman spectra. The ring puckering, asymmetric deformation and the ring torsion are calculated at 757, 649 and 502 cm-1, respectively. 4. Conclusion The equilibrium geometries and harmonic vibrational wavenumbers of all the 84 normal modes of the APTZ molecule were determined and analyzed both at DFT (B3LYP) and HF levels of theory employing the 6-311++G(d,p) basis set. These theoretical vibrational assignments along with the electronic transitions are important to understand the molecular structure and biological activity of the title Bhawani Datt Joshi et al. / BIBECHANA 9 (2013): 38-49: BMHSS, p.48 (Online Publication: Nov., 2012) molecule. The IR and the Raman spectra were presented, and the vibrational bands were assigned on the basis of the PED obtained from the DFT calculations. 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