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ISSN : 2153-2435
Pharmaceutica Analytica Acta
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Experimental and Theoretical Spectroscopic Analysis on N-((1-(phenylsulfonyl)- 1H-indol-3-Yl)methyl)acetamide

Srinivasaraghavan R1, Seshadri S2*, Gnanasambandan T3 and Srinivasan G4

1Department of Physics, SCSVMV University, Kanchipuram-631561, Tamil Nadu, India

2Department of Physics, Dr. Ambedkar Govt. Arts College, Chennai-39, Tamil Nadu, India

3Department of Physics, Pallavan College of Engineering, Kanchipuram-631502, Tamil Nadu, India

4Department of Physics, Government Arts College, Chennai-35, Tamil Nadu, India

*Corresponding Author:
Seshadri S
Department of Physics, Dr. Ambedkar Govt. Arts College
Vyasarpadi, Chennai-39, Tamil Nadu, India
Tel: 0866-2497299
E-mail: [email protected]

Received date: June 15, 2017; Accepted date: August 02, 2017; Published date: August 07, 2017

Citation: Srinivasaraghavan R, Seshadri S, Gnanasambandan T, Srinivasan G (2017) Experimental and Theoretical Spectroscopic Analysis on N-((1-(phenyl-sulfonyl)-1H-indol-3-Yl)methyl)acetamide. Pharmaceut Anal Acta S8:002 doi: 10.4172/2153-2435.S8-002

Copyright: © 2017 Srinivasaraghavan R, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

In this work, The structural characteristics and vibrational spectroscopic analysis were carried out by quantum chemical methods with the hybrid exchange-correlation functional B3LYP using 6-31G (d, p) and 6-311++G (d, p) basis sets in order to investigate the fundamental modes of vibrational analysis and electronic properties of phenyl substituted compound N-((1-(phenylsulfonyl)-1H-indol-3-yl)methyl)acetamide. Density Functional Theory (DFT) method, using B3LYP functional, with 6-31G (d, p) and 6-311++G (d, p) basis sets, which in turn creates a platform to study the structure of the chosen compound. The experimentally obtained FTIR and FT Raman spectrum supports the results of theoretically observed ones. Detailed interpretations of the experimental spectra of the molecule along with the theoretical ones are reported based on Potential Energy Distribution (PED).

The total dipole moment, static total and anisotropy of polarisability and static first hyperpolarisability values were calculated. The FMOs, molecular electrostatic potential, global reactivity descriptors were also calculated and discussed. Molecular electrostatic potential and frontier molecular orbitals were constructed to understand the electronic properties. The intramolecular contacts are interpreted using Natural Bond Orbital (NBO) analysis to ascertain the charge distribution. The thermodynamic properties at different temperatures were calculated revealing the correlations between standard heat capacities, entropy and enthalpy changes with temperatures.

Keywords

N1PS3MA; NBO/NLMO; MEP; PED

Introduction

N-((1-(phenylsulfonyl)-1H-indol-3-yl)methyl)acetamide is basically an indole derivative, otherwise called [N1PS3MA] having molecular formula C16H16N2O3S. The phenyl sulfonyl ring makes 66.5(7) dihedral angle with the indole unit. Some of the indole alkaloids extracted from plants possess interesting cytotoxic, antitumour or antiparasitic properties [1,2]. Pyrido[1,2-a] indole derivatives have been identified as potent inhibitors of human immunodeficiency virus type-1 [3], and 5-chloro-3-(phenylsulfonyl) indole-2-carboxamide is reported to be a highly potent non-nucleoside inhibitor of HIV-1 reverse transcriptase [4]. The interaction of phenylsulfonylindole with calf thymus DNA has also been studied by spectroscopic methods [5]. The Compound was synthesized one and the molecular parametric details are obtained from the similar compound synthesized by A. Thenmozhi et al. [6] and no further studies have been carried out for the title compound yet. Literature survey reveals that so far no spectroscopic and computational work was carried out on the title compound. Therefore in our present investigation, the spectroscopic properties of N-((1-(phenylsulfonyl)-1H-indol-3-yl)methyl)acetamide were studied by vibrational spectroscopy (FT-IR, FT-Raman) and additionally the structure, vibrational frequencies and other thermodynamical parameters of the title molecule were calculated by the DFT method. The redistribution of electron density (ED) in various bonding and antibonding orbitals and E(2) energies have been calculated by Natural Bond Orbital (NBO/NLMO) analysis using DFT method to give clear evidence of stabilization originating from the hyperconjugation of various intramolecular interactions. The HOMO and LUMO analysis have been used to elucidate the information regarding charge transfer occurs within the molecule. Moreover, the Mulliken population analyses of the title compound have been calculated and the calculated results have been reported.

Experimental

The compound N-((1-(phenylsulfonyl)-1H-indol-3-yl)methyl) acetamide [N1PS3MA] was a synthesized one and reported in Literature [6] and used as such without further purification to record FTIR and FT Raman spectra. The FTIR spectrum of the compounds is recorded in the region 4000- 400 cm−1 in evacuation mode on Bruker IFS 66V spectrophotometer using KBr pellet technique (solid phase) with 4.0 cm−1 resolutions. The FT-Raman spectra of these compounds are also recorded in the same instrument with FRA 106 Raman module equipped with Nd: YAG laser source operating at 1.064 μm line widths with 200 mW powers. The spectra are recorded in the range of 3500– 100 cm−1 with scanning speed of 30 cm−1 min−1 of spectral width 2 cm−1. The frequencies of all sharp bands are accurate to ± 1 cm−1. The spectral measurements were carried out at Sophisticated Analytical Instrumentation Facility, IIT, Chennai, Tamil Nadu, India.

Methods of Analysis

The optimized molecular geometrical orientation and the vibrational frequency calculations are carried out for N1PS3MA, with the Gaussian 03W software package [7]. Becke’s three parameter exchange functional (B3) [8] and combination with the correlation functional of Lee, Yang and Parr (LYP) [9] were adopted with standard 6-31G(d,p) and 6-311++G (d,p) basis sets. The optimized geometrical parameters namely, bond length and bond angles calculated by two basis sets are listed in Table 1 along with the experimental data on the geometric structure of the selected molecule. This molecule has fifteen C-H bond lengths, seventeen C-C bond lengths, four C-N bond lengths, two S-O bond lengths, one C-S and N-S bond length, and a C-O bond length. The C-C bond length value of the ring is found to be 1.337 Å at B3LYP/6-311++G (d,p) level. The C-O bond length value is found to be 1.208 Å. The C-H bond length value calculated at B3LYP/6-311++G (d,p) level vary from 1.096 to 1.101 Å and the N-H bond length value is 1.411 Å. Here the value of S-C bond length is found to be high compared to other bond length values. The calculated bond angles of C-C-H, C-C-C, O-C-H and H-C-H are found to be slightly on the higher side compared to experimental values of bond angle. The Cartesian representation of the theoretical force constants have been computed at the optimized geometry by assuming C1 point group symmetry. The vibrational wavenumbers are calculated with PED calculations at the optimized geometrical orientation. The atomic charges, electric dipole moment, polarizability, first hyperpolarizability, HOMO, LUMO and thermodynamic parameters are also calculated theoretically. The Natural Bonding Orbital (NBO) calculations are performed using NBO 3.1 program as implemented in the Gaussian 03W [7] package at DFT level in order to understand various second-order interactions between the filled orbital of subsystem and vacant of another subsystem, which is a measure of the intermolecular delocalization or hyperconjugation. Finally, the calculated normal mode of vibrational frequencies will provide the thermodynamic properties using the principle of statistical mechanics. The optimized structure of N1PS3MA is shown in Figure 1.

Molecular parameters/Bond lengths Experimental B3LYP/6-31G(d,p) B3LYP/6-311++G(d,p)
H(39)-C(23) 1.100 1.101 1.101
H(38)-C(22) 1.100 1.101 1.092
H(37)-C(21) 1.100 1.101 1.096
H(36)-C(20) 1.100 1.101 1.096
H(35)-C(19) 1.100 1.104 1.092
H(34)-C(13) 1.100 1.099 1.101
H(33)-C(12) 1.100 1.099 1.091
H(32)-C(11) 1.100 1.099 1.102
H(31)-C(10) 1.100 1.112 1.097
H(30)-C(7) 1.100 1.089 1.092
H(29)-C(5) 1.113 1.131 1.113
H(28)-C(5) 1.113 1.131 1.094
H(27)-N(4) 1.012 1.081 1.039
H(26)-C(2) 1.113 1.118 1.116
H(25)-C(2) 1.113 1.116 1.117
H(24)-C(2) 1.113 1.116 1.117
C(23)-C(18) 1.337 1.403 1.402
C(23)-C(22) 1.337 1.396 1.331
C(22)-C(21) 1.337 1.398 1.331
C(21)-C(20) 1.337 1.397 1.335
C(20)-C(19) 1.337 1.398 1.382
C(19)-C(18) 1.337 1.404 1.376
C(18)-S(15) 1.790 1.731 1.746
O(17)-S(15) 1.450 1.422 1.45
O(16)-S(15) 1.450 1.425 1.451
S(15)-N(6) 1.696 1.654 1.701
C(14)-N(6) 1.396 1.406 1.401
C(14)-C(13) 1.337 1.416 1.381
C(14)-C(9) 1.337 1.439 1.381
C(13)-C(12) 1.337 1.39 1.381
C(12)-C(11) 1.337 1.409 1.389
C(11)-C(10) 1.337 1.386 1.372
C(10)-C(9) 1.337 1.395 1.356
C(9)-C(8) 1.337 1.456 1.396
C(8)-C(7) 1.337 1.386 1.362
N(6)-C(7) 1.401 1.388 1.401
C(8)-C(5) 1.497 1.506 1.494
C(5)-N(4) 1.450 1.444 1.441
N(4)-C(1) 1.369 1.381 1.389
O(3)-C(1) 1.208 1.251 1.247
C(2)-C(1) 1.509 1.516 1.509
Bond angles (°)
H(39)-C(23)-C(18) 120.0 120.2 120.1
H(39)-C(23)-C(22) 120.0 118.8 119.9
C(18)-C(23)-C(22) 120.0 121.0 119.5
H(38)-C(22)-C(23) 120.0 120.1 120.0
H(38)-C(22)-C(21) 120.0 119.9 120.0
C(23)-C(22)-C(21) 120.0 120.0 120.0
H(37)-C(21)-C(22) 120.0 120.1 120.1
H(37)-C(21)-C(20) 120.0 120.2 120.0
C(22)-C(21)-C(20) 120.0 119.7 119.9
H(36)-C(20)-C(21) 120.0 119.8 119.9
H(36)-C(20)-C(19) 120.0 120.2 119.2
C(21)-C(20)-C(19) 120.0 120.0 120.9
H(35)-C(19)-C(20) 120.0 119.2 119.7
H(35)-C(19)-C(18) 120.0 119.8 120.3
C(20)-C(19)-C(18) 120.0 121.0 120.7
S(15)-C(18)-C(23) 120.0 121.1 119.1
S(15)-C(18)-C(19) 120.0 118.5 119.5
C(23)-C(18)-C(19) 120.0 118.3 119.1
O(16)-S(15)-O(17) 109.5 117.2 117.7
O(16)-S(15)-N(6) 109.4 110.3 108.8
O(16)-S(15)-C(18) 109.5 106.5 110.1
O(17)-S(15)-N(6) 109.4 108.8 109.0
O(17)-S(15)-C(18) 109.5 109.6 110.2
N(6)-S(15)-C(18) 109.5 108.6 110.2
N(6)-C(14)-C(13) 122.0 121.1 120.4
N(6)-C(14)-C(9) 120.0 109.3 119.3
C(13)-C(14)-C(9) 120.0 118.6 119.8
H(34)-C(13)-C(14) 120.0 120.9 119.7
H(34)-C(13)-C(12) 120.0 120.2 119.8
C(14)-C(13)-C(12) 120.0 119.0 121.7
H(33)-C(12)-C(13) 120.0 119.0 119.2
H(33)-C(12)-C(11) 120.0 118.9 119.6
C(13)-C(12)-C(11) 120.0 122.1 121.1
H(32)-C(11)-C(12) 120.0 121.2 120.9
H(32)-C(11)-C(10) 120.0 119.4 120.4
C(12)-C(11)-C(10) 120.0 119.4 120.3
H(31)-C(10)-C(11) 120.0 122.7 118.8
H(31)-C(10)-C(9) 120.0 115.1 118.3
C(11)-C(10)-C(9) 120.0 120.3 120.9
C(8)-C(9)-C(14) 111.0 106.0 109.3
C(8)-C(9)-C(10) 120.0 121.4 120.5
C(14)-C(9)-C(10) 120.0 120.6 120.1
C(5)-C(8)-C(7) 120.9 121.2 120.3
C(5)-C(8)-C(9) 124.5 124.8 124.5
C(7)-C(8)-C(9) 111.0 106.0 108.1
C(8)-C(7)-H(30) 129.5 129.5 129.4
C(14)-N(6)-S(15) 127.0 125.4 124.9
C(7)-N(6)-C(14) 121.9 121.3 121.6
C(7)-N(6)-S(15) 127.1 128.1 126.2
N(4)-C(5)-C(8) 109.5 113.9 109.0
N(4)-C(5)-H(28) 109.4 108.1 108.9
N(4)-C(5)-H(29) 109.5 108.2 110.8
C(8)-C(5)-H(28) 109.4 109.2 110.7
C(8)-C(5)-H(29) 109.5 109.4 109.6
H(28)-C(5)-H(29) 109.5 107.9 109.3
C(1)-N(4)-C(5) 120.0 126.0 121.4
C(1)-N(4)-H(27) 120.0 120.8 120.3
C(5)-N(4)-H(27) 120.0 121.2 120.6
C(1)-C(2)-H(24) 109.5 113.8 111.1
C(1)-C(2)-H(25) 109.4 108.5 110.5
C(1)-C(2)-H(26) 109.5 108.4 110.5
H(24)-C(2)-H(25) 109.4 108.5 110.6
H(24)-C(2)-H(26) 109.5 108.4 110.3
H(25)-C(2)-H(26) 109.5 109.1 109.1
C(2)-C(1)-O(3) 120.0 122.1 121.1
C(2)-C(1)-N(4) 120.0 115.6 121.4
O(3)-C(1)-N(4) 120.0 122.3 120.8
N(6)-C(7)-C(8) 123.1 121.4 121.3
N(6)-C(7)-H(30) 121.9 118.1 119.3

Table 1: Molecular geometrical parameters of N-((1-(phenylsulfonyl)-1H-indol- 3-yl)methyl)acetamide N1PS3MA.

pharmaceutica-analytica-acta-Optimised-structure

Figure 1: Optimised structure of N-((1-(phenylsulfonyl)-1H-indol-3-yl)methyl)acetamide.

Vibrational assignments

The title molecule consists of 39 atoms, hence (3N-6) gives 111 normal modes of vibrations, and all are active in infrared and Raman spectra. The detailed vibrational assignments of fundamental modes along with the calculated IR, Raman intensities and normal mode description (characterized by PED) are reported in Table 2. For comparison, the observed and simulated Raman and IR spectra are presented in Figures 2 and 3.

FTIR ν IR cm-1 FT Raman νR cm-1 B3LYP/6-31G(d,p) B3LYP/6-311++G(d,p) Assignments with PED % calculation
νcal cm-1 IR intensity Raman activity νcal cm-1 IR intensity Raman activity
    20 0.323 2.789 19 1.221 1.404 α ring scissoring (15)
    25 2.441 1.833 24 1.008 9.701 τ ring (12)
    32 0.707 10.770 32 0.586 5.473 β ring (16)+γSO2(wag) (28)
    48 0.240 6.500 47 1.763 5.022 α ring (10)
    56 5.021 6.753 56 1.432 1.70 γCH3(wag) (16)
    74 16.795 0.571 75 6.403 3.70 τCH3(10)+γSO2(wag) (19)
    85 0.089 0.293 83 1.38 8.479 γCH3(wag) (25)
  113 115 1.270 0.477 113 0.45 6.769 γCO(12)+γNH(16)
  141 138 1.836 2.153 139 1.582 4.843 τCH(10)+τSO2 (23)
  147 145 4.598 1.900 144 2.960 0.754 α C N (27)+γCH (16)
    164 1.945 1.407 164 1.807 2.190 τCH(12)+βCH3(34)
  179 178 0.576 2.023 178 0.948 0.56 τCH3 (24)
  226 222 2.027 3.754 221 1.600 0.857 β CN (27)+γCH (11)
    248 1.811 1.348 249 2.244 0.816  α CH(16)+α CH3(14)
  280 279 4.354 3.16 279 3.541 2.806 βNCC(13)
    285 0.132 6.045 286 3.89 0.685  α CH(14)+α CH2(25)+ α CH3(13)
  297 296 0.338 1.471 298 3.009 4.830 τCH2 (15)
  310 307 1.387 4.166 308 9.148 3.536 βCCC(37)+α NH(18)+α CH3(34)
    316 3.901 5.285 317 4.043 6.435 νCC(14)+βring(26)
  365 363 3.240 0.589 363 0.054 0.487 γ ring 1 (12)
  401 403 9.417 2.96 404 8.240 1.504 τCH3 (41)+α NH(10)
412   412 19.862 1.263 412 0.486 2.664 τring (19)+βCCC (24)
421 421 421 0.171 0.264 422 9.892 4.194  α SO2(20)+α CH3(32)
435   436 3.468 0.413 439 66.473 2.867  α CH(24)+α NH(14)+α CH2(36)
466 465 467 15.884 1.034 467 23.901 2.162 γCN (21)+βring (19)
489 487 485 4.964 5.145 486 83.144 13.301 γring 4 (53)+γCS  (26)
537   536 1.237 3.037 536 89.263 1.692 τ ring (25)+γCH(19)
  543 545 49.015 1.275 544 68.808 3.132 δNS (37), δring 4 (26)
565 565 564 83.825 2.191 565 18.708 0.329 τNC(22)+βCCO(20)
577   576 81.884 2.600 574 61.412 87.798  α CH(12)+α SO2(36)+α CH3(18)
594 593 594 16.396 0.647 597 12.41 39.439 νCS (58)
  607 607 17.129 4.404 607 38.552 1.29 γCO(27)+τNC(14)
615 616 616 80.291 11.37 618 65.291 1.815 γNH (52)
627 628 626 3.573 4.454 627 0.266 1.146  α CH(27)+α CH3(43)
655   657 7.028 2.179 658 1.45 1.244 γCC(23)+α NH(15)
688 687 685 2.507 6.313 683 89.358 5.227  α CH(27)+γCN(31)
700 701 699 38.888 1.520 700 89.053 1.994 βCCN(33)
721 723 723 42.540 4.078 722 118.28 4.008  α CH(10)+δCH(19)
738 739 740 36.885 3.722 741 9.108 12.968 βNCH(18)
764 762 763 50.370 2.216 763 96.184 11.369 νCS (68)+δCH(12)
767   766 10.311 5.73 767 3.718 5.694 γCC(17)
778 779 780 11.655 11.90 779 78.261 2.105 γCH(26)+νCS  (52)
793 791 791 34.742 0.755 792 79.704 29.146 γCH(86)+δCH(12)
840 841 843 9.146 11.338 843 62.076 32.832 γCN(8)+α CH2(18)
860 859 859 1.339 3.920 859 0.344 3.122 βring(27)
866   865 1.460 3.625 866 90.347 4.019  α CH(26)+γCH  (39)
877 876 875 1.483 3.326 875 8.131 1.873 γCN(10)
939 939 942 1.322 0.304 945 7.926 3.195 γCH(29)+νCC(75)
951 952 952 1.368 0.779 952 4.830 1.704 γCC(36)+τring(13)
960   961 54.017 5.533 962 8.460 2.998 γCH  (46)
982 982 983 0.662 0.124 981 0.136 0.975 γSO(35)+α CH3(32)
987   986 2.980 2.592 985 0.496 1.778 νCN(27)+νCC(51)
  988 987 0.223 0.781 989 11.544 7.389 γCN(25)
998 998 997 0.156 0.171 998 39.504 1.876  α  CH3(48)+α CH2(15)
1010 1011 1010 4.304 20.167 1011 19.105 0.880 γCH(31)+γCC(17)
1014   1013 5.019 1.482 1015 33.371 0.14  α CH(82)
1030 1030 1029 3.264 9.970 1031 27.248 0.308 γCH(27)+βNCH(15)
1045 1045 1047 9.149 30.487 1046 9.167 3.667  α CH3(48)
1053   1051 10.234 0.628 1051 5.30 16.682 νCC(58)+βCCH(11)
1059 1059 1058 14.259 4.277 1060 6.5058 3.047 γCO(16)+νCN(63)
1082 1082 1083 52.544 6.016 1084 41.659 7.828 CH3(48)+α NH(12)
1090 1090 1089 14.801 6.129 1090 0.877 36.190 βNCH(21)+βring(18)
1109 1110 1107 6.206 0.464 1107 47.77 27.369 δSO ­(42)
1114   1113 83.117 4.395 1112 1.974 20.088  α CH(65)
1139 1139 1138 76.828 38.985 1138 3.191 6.124 βCCH(16)
1154 1153 1153 41.620 7.384 1155 9.916 2.805  α CH(83)
1159 1159 1158 0.263 5.652 1160 19.235 2.443 βNCH(21)
  1190 1190 14.053 1.708 1189 0.814 5.201 ν CC(72)
1192   1191 0.237 5.448 1192 12.360 7.885 ν CN (79)
1211 1211 1210 29.888 8.555 1214 0.859 1.774  α CH2(27)+νCN (58)
1243 1243 1242 11.162 7.103 1245 35.552 8.144 ν CN (64)+δCH (53)+νsSO (67)
1260   1260 17.425 5.235 1261 6.130 12.543  α CH2(19)+α NH(38)+νSO2 (61)
1293 1294 1293 27.507 19.927 1293 0.838 52.282 νCN(70)+νSO2 (59)+τCH3(44)
1310   1307 7.081 20.766 1305 15.639 10.117 τCC (33)+νSO2 (58)
1319 1319 1319 1.161 0.433 1320 4.864 62.133  νCC (92)+νaSO(78)
1342 1342 1341 18.645 3.235 1342 9.981 55.413 νCC (88)+βCCO(11)
1351 1351 1351 15.587 1.280 1354 24.991 36.373 βCCH(28)+νCC(84)
1366 1365 1366 2.151 28.067 1368 15.263 10.439 νCC(76)+α CH3(42)
1381 1381 1381 22.095 17.860 1383 40.296 54.424 νCC(69)+sCH2(13)
1392   1392 3.276 25.830 1392 8.968 21.589 νCC(59)+βCCH(33)+sCH2(17)
1408 1408 1407 19.935 9.575 1405 29.521 28.042 νCN(61)+βCCH(33)
1410   1410 42.073 8.629 1409 31.733 5.515 νCC(62)+α CH3(18)+α CH2(52)
1446 1446 1445 12.640 12.889 1447 55.399 28.687 νCC(75)+βHCH(13)
1477 1479 1480 19.743 11.107 1480 11.536 8.412 νCN(57)+βCCC(34)
1485   1483 19.696 5.38 1484 78.601 0.981 νCC(54)+βCCH(33)
  1487 1486 12.449 13.759 1487 49.737 3.491 νCC(67)+α CH3(28)
1492 1492 1492 4.139 6.625 1489 7.808 2.323  α CH2(34)+βHCH(13)
1501 1502 1500 3.612 1.36 1501 97.904 3.351  α CH3(47)+νCC(86)
1518   1518 74.569 2.762 1517 15.040 13.780 γCH(31)
1522 1521 1521 5.562 56.675 1521 39.928 6.329 γCH(29)
1542   1542 5.502 25.20 1541 18.558 11.265 γNH(23)+βHCH(52)
1557 1557 1556 0.669 32.009 1559 96.708 3.386 δCH(42)+βCCH(23)
  1572 1573 0.141 13.810 1577 12.07 15.154 δCH(17)
1587   1587 6.954 22.434 1587 14.92 2.408 δCH(27)
1610 1610 1613 99.064 1.307 1612 99.446 10.575 νCO(85)
3059 3059 3057 6.659 109.15 3060 8.4751 18.816 νsCH2(90)
3073 3073 3074 35.228 116.72 3072 8.1967 2.557 νsCH3(85)
3097 3101 3098 14.246 38.912 3098 12.005 71.489 νsCH3 (90)
3142 3141 3140 4.773 54.682 3142 9.0904 55.287 νasCH3 (83)
3154 3152 3154 7.492 79.984 3154 50.940 0.863 νasCH3 (89)
3177 3175 3176 7.008 59.638 3175 35.050 4.392 νasCH2(90)
3187   3189 1.026 55.803 3187 9.3773 26.404 νasCH3(99)
3192 3193 3190 16.385 93.665 3193 39.086 24.708 νCH(94)
3200 3199 3202 13.180 100.49 3200 14.099 65.217 νCH(96)
3205   3205 25.436 231.40 3205 26.684 80.673 νCH(99)
3211 3210 3210 12.756 159.73 3211 63.223 29.248 νCH(92)
3222   3225 2.541 72.83 3225 76.555 28.021 νCH(95)
3229 3231 3231 3.190 75.885 3230 76.029 26.494 νCH(98)
3240   3239 1.540 77.343 3239 33.335 98.316 νCH(93)
3299 3300 3301 12.302 37.116 3300 37.822 66.944 νCH(99)
3461 3460 3457 17.427 48.729 3459 61.024 13.574 νNH(98)

Table 2: Vibrational assignments of N1PS3MA using B3LYP/6-31 G(d,p) and B3LYP/6-311++G(d,p).

pharmaceutica-analytica-acta-simulated-IR-spectra

Figure 2: (a) Experimental, and (b) Theoretically simulated IR spectra of N-((1-(phenylsulfonyl)-1H-indol-3-yl)methyl)acetamide.

pharmaceutica-analytica-acta-Raman-spectra

Figure 3: (a) Experimental, and (b) Theoretically simulated Raman spectra of N-((1-(phenylsulfonyl)-1H-indol-3-yl)methyl)acetamide.

CH2 and CH3 vibrations: There is one CH3 and a CH2 group in this compound. Earlier researchers [10,11] have reported infrared bands occurring in the range 3100-2900 cm−1 as due to C-H stretching in their study. The assignments of CH2 group frequency involve six fundamentals namely, CH2 symmetric stretch; CH2 asymmetric stretch; CH2 scissoring and CH2 rocking which belongs to in-plane vibration and out of plane vibration namely CH2 wagging and CH2 twisting modes. The fundamental CH2 vibrations due to scissoring, wagging, twisting and rocking appear in the region 1500–800 cm−1. The asymmetric CH2 stretching vibrations are generally observed in the region 3200 - 3050 cm−1, while the symmetric stretching will appear between 3050 and 2900 cm−1 [12-14]. In this compound the asymmetric stretching of CH2 vibration occurs at 3177 cm−1 in FTIR and 3175 cm−1 in FT Raman spectra. The symmetric stretching vibrations occur at 3059 cm−1 in FTIR and in FT Raman spectra. The results of symmetric and asymmetric CH2 vibrations agree well with the DFT method.

CH2 scissoring is assigned to 1492, 1410 cm−1 in experimental observation agrees the values at 1492, 1410 cm−1 in B3LYP method. CH2 wagging is attributed to 1392 cm−1, 1381 cm−1 in FTIR, and the corresponding values in FT-Raman are in good agreement B3LYP values. Emilio et al. have observed CH3 scissoring at 1513 cm−1 and based on this reference, in our compound the band at 1501 cm−1 is assigned to CH3 scissoring and CH2 wagging is assigned to the band at 1365 cm−1 in both FTIR and FT-Raman spectra [15].

The title compound has one CH3 group. The asymmetric CH3 is expected around 3187 cm−1 and CH3 symmetric stretching is expected at 3073 cm−1 [16,17]. In this study apart from CH2 and CH3 the other CH asymmetric and symmetric stretching vibrations are identified in their respective ranges and these results agree well with the values of DFT method.

N-H vibrations: Normally the vibrational bands due to the N-H stretching are sharp by virtue of which they can be easily identified. Tsuboi [18] reported the N-H stretching frequency at 3481 cm−1 in aniline. In our study the band appear at 3460 and 3461 cm−1 in the FTIR and FT Raman spectrum is assigned to N-H stretching vibrations. The theoretically calculated value by DFT method at 3459 cm−1 shows agreement with experimentally observed value. Though the identification of bands is difficult, with the help of the animation option of chemcraft graphical interface for Gaussian programs, the N-H vibration is identified.

C-N vibrations: The identification of C-N vibrations is a very difficult task, since mixing of several bands are possible in this region. The conjugated C-N linkage in amine group gives rise to medium to weak bands near 1350-1150 cm−1 because of C-N stretching vibration. Silverstein have assigned C-N stretching absorption in the region 1300- 800 cm−1. Gnanasambandan et al. have identified in m-nitromethyl benzoate 1290, 1400 and 1420 cm−1 as C-N stretching vibrations. C–N stretching absorption in the region 1382-1266 cm−1 for aromatic amines. In our present work 1408, 1294, 1243, 1211 cm−1 in FT-IR and 1408, 1293, 1243 and 1211 cm−1 in FT-Raman are assigned to C-N stretching. The B3LYP values 1242, 1210, 1191 cm−1 corresponds to C-N stretching vibration. Our assignment is in good agreement with the literature [19-24].

C=O vibrations: The carbonyl group shows a strong absorption band due to C=0 stretching vibrations and is observed in the region 1850-1550 cm−1. Because of its high intensity and relatively interference free region in which it occurs, this band is reasonably easy to recognize [25-29]. In the present work the bands observed at 1610 cm−1 in FTIR and FT Raman spectrum is assigned to C=O stretching mode of vibration, and it well agrees with the values of DFT method.

C-S vibrations: In general the assignment of the band due to C-S stretching vibration in a compound is difficult. Since it is of variable intensity and may be found over the wide region 1035–245 cm−1 both in aliphatic and aromatic sulfides have a weak to medium band due to C-S stretching vibration in the region 710–570 cm−1 [30]. In the present work the band observed at 764cm−1 in FTIR and 762 cm−1 in FT Raman are assigned to C-S stretching vibration. Theoretically computed values are found to be in good agreement with the experimental results.

SO2 vibrations: Seshadri et al. [31] have reported SO vibrations in 1338 cm−1, 1226 cm−1, and 1217 cm−1 in FTIR spectrum. The wavenumbers at 1310 cm−1 and 1293 cm−1 in FTIR spectrum is assigned to SO2 asymmetric stretching vibration. The corresponding B3LYP values are 1307 and 1293 cm−1. B3LYP values are in good agreement with the experimental values. The symmetric and asymmetric SO2 stretching vibrations occur in the region 1125–1260 cm−1 and 1260– 1330 cm−1 respectively. In the title molecule, SO2 symmetric stretching is observed at 1260 cm−1 in FTIR and in FT-Raman. The calculated B3LYP values are 1260 cm−1. The values are in good agreement with the literature.

NBO/NLMO analysis

NBO (natural bond orbital) analysis provides an efficient method for studying intra- and intermolecular bonding and interaction among bonds. It also provides a convenient basis for the investigation of charge transfer or conjugative interactions in molecular system [32]. Another useful aspect of NBO method is that it gives information about interactions in both filled and virtual orbital spaces that could enhance the analysis of intra and intermolecular interactions. The second order Fock matrix was carried out to evaluate the donor–acceptor interactions in the NBO analysis. For each donor NBO (i) and acceptor NBO (j), the stabilization energy associated with ij delocalization can be estimated as:

Equation

Where qi is the donor orbital occupancy, are εi and εj diagonal elements and F (i, j) is the off diagonal NBO Fock matrix element.

In Table 3, the perturbation energies of significant donor–acceptor interactions are presented. The larger the E(2) value, the intensive is the interaction between electron donors and electron acceptors. In N1PS3MA, the interactions between the anti bonding orbitals C18− C23→C21−C22 and C18−C23→C19C20 have the highest E(2) value around 200.25 and 186.87 kcal/mol. The other significant interactions gives stronger stabilization energy values of 171.92 kcal/mol to the structure are the interaction between anti bonding orbital of C7– C8→C9−C14.

Donor Acceptor E(2) kJ/mol % from parent NBO Hybrid atoms
σ(N4-H27) σ*(C10-H31) 25.97 97.30 H31, H32
π(C9-C14) π*(C7-C8) 26.81 96.96 H31, H34
σ(C10-H31) σ*(N4-H27) 94.11 93.31 N4, C9
LP(1)N4 π*(C1-O3) 64.08 86.00 C1, O3
LP(1)N6 π*(C9-C14) 50.68 81.47 C7, C8, C9, C14, S15
LP(1)O17 σ*(N6-S15) 28.09 89.96 S15, O16, C18
π*(C7-C8) π*(C9-C14) 171.92 98.62 C10, H32
π*(C18-C23) π*(C19-C20) 186.87 85.50 C12, H33
π*(C18-C23) π*(C21-C22) 200.25 93.31 C19, H35

Table 3: Occupancy, percentage of p character of significant natural atomic hybrid of the natural bond orbital, Significant of NLMO’s and second Perturbation theory analysis of N1PS3MA calculated at B3LYP/6-311++G(d,p).

The natural localized molecular orbital (NLMO) analysis has been carried out since they show how bonding in a molecule is composed from orbitals localized on different atoms. The derivation of NLMOs from NBOs give direct insight into the nature of the localized molecular orbital’s ‘‘delocalization tails’’ [33,34]. Table 3 shows significant NLMO’s percentage from parent NBO and atomic hybrid contributions of N1PS3MA calculated at B3LYP level using 6-311++G (d,p) basis set. The NLMO of first lone pair of nitrogen atom N6 is the most delocalized NLMO and has only 82% contribution from the localized LP(1) N6 parent NBO, and the delocalization tail (∼16%) consists of the hybrids of C14 and C9.

Electrostatic Potential (ESP)

Molecular Electrostatic Potential (ESP) at a point in the space around a molecule gives an indication of the net electrostatic effect produced at that point by the total charge distribution (electron+nuclei) of the molecule and correlates with dipole moments, electronegativity, partial charges and chemical reactivity of the molecules. It provides a visual method to understand the relative polarity of the molecules. An electron density isosurface mapped with electrostatic potential surface depicts the size, shape, charge density and site of chemical reactivity of the molecules. The different values of the electrostatic potential represented by different colors; red represents the regions of the most negative electrostatic potential, blue represents the regions of the most positive electrostatic potential and green represents the region of zero potential. Potential increases in the order red < orange < yellow < green < blue. Such mapped electrostatic potential surfaces have been plotted for title molecules in 6-311++G(d,p) basis set using the computer software Gauss view. Projections of these surfaces along the molecular plane and a perpendicular plane are given in Figure 4 for N1PS3MA. The Figure 4 provides a visual representation of the chemically active sites and comparative reactivity of atoms.

pharmaceutica-analytica-acta-electrostatic-potential

Figure 4: Molecular electrostatic potential diagram of N-((1-(phenylsulfonyl)-1H-indol-3-yl)methyl)acetamide.

It may see that, in the molecules, a region of zero potential envelopes the p-system of the aromatic rings, leaving a more electrophilic region in the plane of hydrogen atoms. The shapes of the electrostatic potential at sites close to the polar group in the two molecules. The nitrogen group in the molecules is influenced by the stereo structure and the charge density distribution. These sites show regions of most negative electrostatic potential and high activity of the nitrogen groups. In contrast, regions close to the other polar atomoxygen of the aromatic ring show regions of mildly negative and zero potential, respectively [35].

Mulliken analysis

The atomic charges at all the exocyclic atoms are in accordance with their electro-negativity whereas the charges at all the C atoms of the ring are in accordance with the net flow of p electrons(delocalization of electron density) [36]. The Mulliken atomic charges at each atomic site of N1PS3MA is collected in Table 4 and displayed in Figure 5 along with atom numbering.

Atoms Charges Atoms Charges Atoms Charges Atoms Charges
C1 0.577027 C11 -0.087666 C21 -0.072860 H31 0.072460
C2 -0.395454 C12 -0.110949 C22 -0.096736 H32 0.090540
O3 -0.524224 C13 -0.088301 C23 -0.076653 H33 0.094154
N4 -0.503771 C14 0.261516 H24 0.108536 H34 0.125605
C5 -0.124109 S15 1.253532 H25 0.145389 H35 0.136340
N6 -0.687428 O16 -0.533908 H26 0.147683 H36 0.111008
C7 0.065181 O17 -0.533867 H27 0.262419 H37 0.108324
C8 0.044685 C18 -0.177122 H28 0.135455 H38 0.108456
C9 0.066036 C19 -0.078796 H29 0.110786 H39 0.148693
C10 -0.152691 C20 -0.085473 H30 0.156182 - -

Table 4: Population analysis of N1PS3MA calculated by B3LYP/6-311++G(d,p) basis set.

pharmaceutica-analytica-acta-Mulliken-atomic

Figure 5: Mulliken atomic charges diagram of N-((1-(phenylsulfonyl)-1Hindol- 3-yl)methyl)acetamide.

According to our calculation the negative charge in an investigated molecule is delocalized between nitrogen and oxygen atoms. The charges calculated for nitrogen atoms are different but the oxygen atoms (O(16) and O(17)) are having same charges (−0.533respectively). The charge on the O16 and O17 atom are found to be equal as they experience the same environment. This depreciation of the negative charges on the oxygen atom may be due to delocalization through the p−electron system of the pyrazole. The positive charges are localized on the hydrogen atoms. The charges on hydrogen’s H24, H25and H26 are found to be 0.108, 0.145 and 0.147 respectively and the differences in calculated charges are relatively small. For better visualization, the charge and atom graph is plotted for each charged atom and is displayed in the Figure 6.

pharmaceutica-analytica-acta-atomic-charge

Figure 6: Mulliken atomic charge versus atom diagram of N-((1-(phenylsulfonyl)- 1H-indol-3-yl)methyl)acetamide.

Electron density analysis

An analysis of the electron density of highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) of N1PS3MA can give us some idea about the ground and excited state proton transfer processes. The energies corresponding to HOMO and LUMO levels of N1PS3MA are performed by density functional method. The HOMO–LUMO energy calculation reveals that, there are 86 occupied and 429 unoccupied molecular orbitals associated with N1PS3MA. The energies corresponding to the highest occupied and lowest unoccupied molecular orbitals of N1PS3MA are found to be -5.886 and -1.2547 eV respectively as shown in Table 5. The energy gap between occupied and unoccupied molecular orbitals of N1PS3MA calculated at B3LYP/6-311++G (d,p) level is given in Table 5 reflects the chemical reactivity of the molecule. LUMO as an electron acceptor represents the ability to obtain an electron. HOMO represents the ability to donate an electron.

Molecular properties B3LYP/6-311++G(d,p) B3LYP/6-31G(d,p) Molecular properties B3LYP/6-311++G(d,p) B3LYP/6-31G(d,p)
εHOMO(eV) -5.88668 -6.32696 Chemical hardness(η) 2.31598 2.5002
εLUMO(eV) -1.25472 -1.32656 Chemical potential(μ) -3.57071 -3.8267
ε(H-L) (eV) 4.63195 5.00042 Electronegativity(χ) 3.57071 3.8267
Ionization potential(I) 5.88668 6.32696 Electrophilicity index(ω) 6.37498 7.3218
Electron affinity(A) 1.25472 1.32656 Softness(S) 0.43178 0.3999

Table 5: Molecular properties of N1PS3MA.

HOMO orbital on the aromatic ring of N1PS3MA (Figure 7) is primarily of anti-bonding character type over C1, C7, C8 atoms, whereas C2, C5, C10 and N4, N6 show bonding character. Both the hydroxyl and carbonyl oxygen having bonding character type, with a larger electron density over hydroxyl oxygen [37-39]. By using the HOMO and LUMO energy values, the global chemical reactivity descriptors of molecules such as hardness (), chemical potential (μ), softness (S) and electrophilicity index (χ) are calculated using the standard formulas and are defined as follows.

pharmaceutica-analytica-acta-HOMO-LUMO-energy

Figure 7: HOMO-LUMO energy diagram of N-((1-(phenylsulfonyl)-1H-indol- 3-yl)methyl)acetamide.

Equation

The values obtained for those global reactivity descriptors are listed in Table 5. For visual comparison the HOMO and LUMO diagram of the compound is shown in Figure 7.

Thermodynamic parameters

The temperature dependence of the thermodynamic properties such as heat capacity at constant pressure (Cp), entropy (S) and enthalpy change (ΔH0 →T) [40] for N1PS3MA were also determined by B3LYP/6-311++G(d,p) method and listed in Table 6. The Figure 7 depicts the correlation of heat capacity at constant pressure (Cp), entropy (S) and enthalpy change (ΔH0 →T) with temperature and the corresponding fitting equations are as follows

T (K) S (J/mol.K) Cp (J/mol.K) ddH (kJ/mol)
6-31G(d,p) 6-311++G(d,p) 6-31G(d,p) 6-311++G(d,p) 6-31G(d,p) 6-311++G(d,p)
100 406.32 401.71 136.67 141.78 11.42 9.17
200 526.35 528.66 227.69 236.69 24.16 28.03
298.15 642.01 641.59 338.55 335.83 61.32 56.11
300 734.23 733.68 360.07 357.69 65.99 69.73
400 818.73 810.16 438.21 432.96 105.97 99.37
500 889.56 888.72 505.6 513.42 153.26 146.82
600 953.98 959.28 561.23 578.34 201.82 197.53
700 1051.25 1052.5 616.77 630.53 263.14 258.06
800 1141.3 1139.56 664.38 673.05 327.19 323.31
900 1224.85 1220.93 701.83 708.23 393.76 392.43
1000 1302.62 1297.12 732.4 737.72 462.11 464.77

Table 6: Thermodynamic parameters of N1PS3MA.

Sºm=240.03433+0.7328 T-1.79433 × 10-4 T2 (R2=0.9999)

Cºpm=15.26587+0.65639 T-2.82786 × 10-4 T2 (R2=0.9998)

Hºm=-7.65942+0.08696 T+1.73344 × 10-4 T2 (R2=0.9998)

The entropies, heat capacities, and enthalpy changes are increasing with temperature ranging from 100 to 1000 K due to the increase in vibrational intensities with temperature. For the title compound, all thermodynamic parameters have been increased steadily.

Conclusion

The vibrational FT-IR and FT-Raman spectra of N1PS3MA were recorded and computed vibrational wavenumbers and their PED were calculated. The molecular structural parameters like bond length, bond angles, thermodynamic properties and vibrational frequencies of the fundamental modes of the optimized geometry have been determined from DFT calculations using 6-31G (d,p) and 6-311++G(d,p) basis sets. NBO analysis was made it indicated the intra molecular charge transfer between the bonding and antibonding orbital’s. The calculated HOMO and LUMO energies were used to analyse the charge transfer within the molecule. With the help of HOMO, LUMO values, the global reactivity descriptors were calculated. The predicted MEP Figure 8 revealed the negative regions of the molecule was subjected to the electrophilic attack of this compound.

pharmaceutica-analytica-acta-Thermodynamical-parameters

Figure 8: Thermodynamical parameters of N-((1-(phenylsulfonyl)-1H-indol-3-yl)methyl)acetamide.

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