atiormoetho

, R. Hfor Wom

Department of Chemistry, King Fahd University of Petr

h i g h l i g h t s

The complete vibrational assignmentand PED calculations have been done.

Thermodynamic properties weredetermined at different temperatures.

Received 8 November 2014

DFTNBONLO

ed in the treatmentof Capsaicin in theonal frequencies ofoying the spectrum. Cotle compoun

carried out. The vibrational harmonic frequencies were scaled using scale factor, yieldingagreement between the experimentally recorded and the theoretically calculated values. Stabthe molecule arising from hyper conjugative interactions, charge delocalization and intra mhydrogen bond-like weak interaction has been analyzed using Natural bond orbital (NBO) analysis byusing B3LYP/6-311++G(d,p) method. The results show that electron density (ED) in the r and p

antibonding orbitals and second-order delocalization energies E (2) conrm the occurrence of intramolecular charge transfer (ICT) within the molecule. The dipole moment (l), polarizability (a) and the

Corresponding author. Tel.: +91 9443690138.E-mail addresses: mutgee@gmail.com, muthu@svce.ac.in (S. Muthu).

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 146 (2015) 177186

Contents lists available at ScienceDirect

Spectrochimica Acta Part A: Molecular and

jouReceived in revised form 23 January 2015Accepted 1 March 2015Available online 9 March 2015

Keywords:FT-IR

vanillyl-6-nonenamide) is the active component in chili peppers, which is currently usof osteoarthritis, psoriasis and cancer. Fourier transform infrared (FT-IR) spectrumsolid phase were recorded in the region 4000400 cm1 and analyzed. The vibratithe title compound were obtained theoretically by DFT/B3LYP calculations empl6-311++G(d,p) basis set and were compared with Fourier transform infrared svibrational assignment analysis and correlation of the fundamental modes for the tihttp://dx.doi.org/10.1016/j.saa.2015.03.0271386-1425/ 2015 Elsevier B.V. All rights reserved.tandardmpleted werea goodility ofoleculara r t i c l e i n f o

Article history:

a b s t r a c t

Capsicum a hill grown vegetable is also known as red pepper or chili pepper. Capsaicin(8-Methyl-N- HOMOLUMO energies, MEPdistribution of the molecule werecalculated.

NLO and NBO analysis of themolecule were calculated.gineering, Sriperumpudur 602105, Tamilnadu, Indiaoleum & Minerals, Dhahran 31261, Saudi Arabia

g r a p h i c a l a b s t r a c t

In this work, the complete vibrational assignment with PED of 8-Methyl-N-vanillyl-6-nonenamide werecalculated using density functional theory (DFT) based on scaled quantum chemical approach. The calcu-lated HOMO and LUMO energies show that charge transfer occur within the molecule. Comparison ofsimulated spectra with the experimental spectra provides important information about the ability ofthe computational method to describe the vibrational modes.b PG & Research Department of Physics, Queen Marys College, Tamilnadu, IndiacDepartment of Physics, Sri Venkateswara College of EndSpectroscopic investigenergies, NLO and thenonenamideby DFT m

J. Sherin Percy Prema Leela a

aDepartment of Electronic Science, JBAS Collegen (FTIR spectrum), NBO, HOMOLUMOdynamic properties of 8-Methyl-N-vanillyl-6-ds

emamalini b, S. Muthu c,, Abdulaziz A. Al-Saadi den, Tamilnadu, India

Biomolecular Spectroscopyrnal homepage: www.elsevier .com/locate /saa

uesalp

This inadequacy observed in the literature encouraged us to carryout theoretical and experimental vibresearch on the molecule to give a corrfundamental bands in experimental FT-IRof calculated Potential energy distributionpresent study aims to give a complete descgeometry, molecular vibrations and elecpresent molecule. The redistribution of e

Results and discussion

: Morational spectroscopicect assignment of thespectrum on the basis(PED). Therefore, the

Vibrational analysis

The title compound consists of 49 atoms and has 141 normaledge no HF/DFT wave number and structural parameter calculationof 8-Methyl-N-vanillyl-6-nonenamide has been reported so far.

calculations.hyperpolarizability (b) valcapacity, entropy and enth

Introduction

Capsicum is the name of a group of annual plants in theSolanaceae family. They are native to Mexico and CentralAmerica but are cultivated for food in many warmer regions ofthe world. Capsicum varieties include the cayenne pepper,jalapeno pepper, other hot peppers, and paprika. Capsaicin is themost-studied active ingredient in the plant and has been approvedby the U.S. Food and Drug Administration (FDA) for use on theskin. Capsaicin (8-Methyl-N-vanillyl-6-nonenamide) is an activecomponent [1] of chili peppers, which are plants belonging to thegenus Capsicum. It is an irritant for mammals, including humanbeings, and produces a sensation of burning in any tissue withwhich it comes into contact. Pure capsaicin is a volatile, hydropho-bic, colorless, odourless, waxy compound. The molecular formulafor 8-Methyl-N-vanillyl-6-nonenamide is C18H27NO3 and itsmolecular mass is 305.41 g mol1. The compound [2] was rstextracted in 1816 by Christian Friedrich Bucholz. Capsaicin ispresent in large quantities in the placental tissue which holds theseeds, the internal membranes and, to a lesser extent, the othereshy parts of the fruits of plants in the genus Capsicum. The seedsthemselves do not produce any capsaicin, although the highestconcentration of capsaicin can be found in the white pith of theinner wall, where the seeds are attached [2]. Capsaicin hasanalgesic and anti-inammatory activities and is used currentlyin creams and gels (e.g., Axsain and Zostrix) to mitigate neurogenicpain. The drug purportedly reduces pain caused by osteoarthritis[3], joint and/or muscle pain from bromyalgia and from othercauses. One study with human subjects indicates that capsaicinmay be used to help regulate blood sugar levels by affectingcarbohydrate breakdown after a meal [4]. Capsaicin creams areused to treat psoriasis and reduce itching and inammation [5].Medical researchers are now looking at the use of capsaicin as apotential for cancer treatment. Capsaicin has been shown to slowthe growth of prostate cancer cells in laboratory studies androdents. Researchers are looking into the use of capsaicin forprostate cancer in humans. Even though a treatment may lookpromising in animal and laboratory studies, further studies arerequired to nd out whether the results apply to humans. Due tothe above biological importance of our compound, we haveevinced keen interest to report a conclusive conformational andvibrational study with the help of Density functional theorycalculations as well as infrared techniques.

In recent years, among the computational methods calculatingthe electronic structure of molecular systems, DFT methods hasbeen a favorite one due to its great accuracy in reproducing theexperimental values of molecular geometry, vibrational frequen-cies, atomic charges, dipole moment, thermo dynamical properties,etc [613]. A literature survey reveals that to the best of our knowl-

178 J. Sherin Percy Prema Leela et al. / Spectrochimica Acta Part Aription of the moleculartronic features of thelectron density (ED) inof the molecule has been computed. Thermodynamic properties (heaty) of the title compound at different temperatures were calculated.

2015 Elsevier B.V. All rights reserved.

various bonding, anti bonding orbital and E2 energies have beencalculated by natural bond orbital (NBO) analysis to give clearevidence of stabilization originating from the hyper conjugationof various intramolecular interactions. The HOMO, LUMO analysishas been used to elucidate information regarding charge transferwithin the molecule. In addition, MEP (Molecular electrostaticpotential) and thermodynamic properties were also calculated.The rst order hyperpolarizability (btotal) of this molecular systemand related properties (b, l, and Da) are calculated using B3LYP/6-311++G(d,p)methods based on the nite-eld approach. All thecalculations were performed using the Gaussian 03 program [14].

Computational details

In the present paper, density functional theory was adopted byemploying B3LYP/6-311++G(d,p) basis set level to calculate theproperties of the title molecule. The calculations were performedwith the Gaussian 03W program package, invoking gradientgeometry optimization [15] using Pentium IV personal computer.The vibrational frequencies for this molecule were calculated withthe B3LYP method with 6-311++G(d,p) basis set and then scaled[16] by 0.967. The vibrational wave number assignments andPED calculation have been carried out by combining the resultsof the Gauss View and the VEDA program [17,18] with symmetryconsiderations. The Natural Bonding Orbital (NBO) calculationwas performed using NBO 3.1 program [15] and was carried outin the Gaussian 03W package at the DFT/B3LYP level. The hyperconjugative interaction energy was deducted from the secondorder perturbation approach [1921]. HOMO and LUMO analysishave been used to elucidate the information regarding chargetransfer within the molecule and Molecular electrostatic potentialanalysis has been used to nd the reactive sites of the compound inthe Gaussian 03W package at the DFT/B3LYP level.

Experimental

The placental tissue of the capsicum was dried, powdered andtaken in a lter paper. This was placed inside the condenser of asterile round ask containing ethanol which acts as a solvent.The contents were heated and maintained at a constant tempera-ture of 5560 C for 35 h. The evaporated capsaicin was collectedon the walls of the tube. The process was repeated three to fourtimes and the extract was collected and dried. The FT-IR spectrumof the freshly prepared capsaicin (8-Methyl-N-vanillyl-6-none-namide) belonging to C1 point group symmetry was recorded inthe region 4000400 cm1, using Bruker IFS 66V Spectrometer.Fig. 1 shows the recorded FTIR spectrum and the theoretically pre-dicted FTIR spectrum obtained from B3LYP/6-311++G(d,p) level

lecular and Biomolecular Spectroscopy 146 (2015) 177186modes of vibration. The observed and theoretically scaled frequen-cies along with their PED are presented in Table 1. The functionalgroups present in the molecule were identied and a satisfactory

pec

: Movibrational band assignment has been made for the fundamentalmodes of vibration by observing the position, shape and intensityof the bands.

NH stretchThe vibrations belonging to NH stretching [22] always occur in

the region 34503250 cm1. In this study, the FTIR NH stretchingband is observed experimentally at 3309 cm1. The theoreticallycalculated values by B3LYP/6-311++G(d,p) method at 3628 cm1

is assigned to NH stretching vibrations. The PED contribution ofthese modes is 100%. When proceeding to lower energy, theobserved band at 1513 cm1 are partially coupled to CN andNH bending deformation and the theoretical value is at1451 cm1 with poor PED contribution.

Fig. 1. Experimental and theoretical FTIR s

J. Sherin Percy Prema Leela et al. / Spectrochimica Acta Part ACH stretchingThe Aromatic CH ring stretching vibrations are normally found

in the region 31003000 cm1 [23]. However these bands arerarely useful because they overlap with one another resultingin stronger absorption in this region. In the FTIR spectrum thebands observed at 2927 cm1 and 2857 cm1 are assigned to CHstretching vibrations. Scaled vibrations assigned to the aromaticCH stretching are 2928 cm1 and 2874 cm1 with the PEDcontribution of 89% and 99% showing good agreement with therecorded FTIR spectrum. The CH out of plane bending vibrationsoccur in the region 1000750 cm1 in aromatic compound[24,25]. The experimental band at 967 cm1 and 938 cm1 areassigned as CH out of plane bending and have good matchingwith theoretical wave number.

CH2 bending vibrationsThe CH2 bending modes follow the general order of wave num-

bers, CH2 deformation > CH2 wagging > CH2 twisting > CH2 rocking.The bending modes involving Hydrogen atom attached to thecentral Carbon falls in the 1450875 cm1 range [26,27]. It isnotable that both CH2 scissoring and CH2 rocking are sensitive tothe molecular conrmation. The scaled vibrational frequencies inthe range from 1431 to 1284 cm1 (mode No. 9882), 1267 cm1

(mode No. 79) and 1071 cm1 (mode No. 63) are assigned to CH2bending modes. The scaled vibrational frequencies at 1419 cm1

(mode No. 94) and 1346 cm1 (mode No. 88) are assigned to CH2scissoring and CH2 wagging vibration are in close agreementwith recorded FT-IR peaks at 1417 cm1 and 1341 cm1 with agood PED.

CO vibrationThe IR absorption is sensitive for both the Carbon and Oxygen

atoms of the carbonyl group. Normally the CO stretching vibra-tions occur in the region 12601000 cm1 [28]. In the presentstudy, the CO stretching vibration is assigned at 1186 cm1and1085 cm1 for the title compound which shows good agreementwith calculated frequencies 1181 cm1and 1088 cm1. The PEDcontributions are 11% and 11% respectively.

CC vibration

tra of 8-Methyl-N-vanillyl-6-nonenamide.

lecular and Biomolecular Spectroscopy 146 (2015) 177186 179The CarbonCarbon stretching modes are expected in the rangefrom 16001400 cm1 [29]. The observed frequency 1626, 1596,1553, 1528 cm1 of FTIR spectrum are assigned as CC stretchingvibrations. Silverstein et al. [30] assigned CN stretching vibrationsin the region 13821266 cm1 for aromatic amines. The CNstretching bands observed at 1239 cm1 and the theoreticallycalculated vibration at 1229 cm1 have good agreement withPED. The CCC trigonal bending vibrations exhibit the characteristicfrequencies at 995 cm1 and 1010 cm1 respectively [31]. Theexperimental frequencies 896 and 806 cm1 are assigned as CCCin plane bending and the scaled frequencies are 894 and875 cm1 with PED 29% and 32%. The experimental frequencies758,715 and 645 cm1 are assigned as CCC out of plane bendingwith 26%, 11% and 10% PED contributions.

NBO analysis

The natural bond orbital analysis provides an efcient methodfor studying intra and inter molecular bonding and interactionamong bonds and also provides convenient basis to investigatecharge transfer or conjugative interaction in molecular systems.NBO analysis has been performed on 8-Methyl-N-vanillyl-6-none-namide using NBO 3.1 program [32] in the Gaussian 03w packageat the B3LYP/6-311++G(d,p) level. Natural bond orbital (NBO)method of weinhold et al. [33] provides a scheme appropriate tothe analysis of lewis acid/base interactions [33,34]. Since theseinteractions lead to loss of occupancy from the localized NBOS of

Table 1Experimental and calculated DFT-B3LYP/6-311++G(d,p) levels of vibrational frequencies (cm1) of 8-Methyl-N-vanillyl-6-nonenamide.

ModeNos.

Experimental wave numbers(cm)1

Calculated wavenumbers B3LYP/6311++G(d,p) cm1

FT-IR Assignments PED

Relativea Absoluteb

137 3620w 3628 105 37 cOH(100)136 3309vs 3490 20 7 cNH(100)135 3073vw 3077 4 1 cCH(97)134 3068w 3068 7 2 cCH(100)133 3028s 3038 12 4 cCH(99)132 3013vw 3016 20 7 cCH(97)131 2987vw 2986 3 1 cCH(100)130 2979 59 21 cCH(100)129 2970w 2974 35 12 cCH(98)128 2970 21 8 cCH(100)127 2966vw 2969 24 9 cCH(86)126 2961 28 10 cCH(85)125 2954vw 2959 60 21 cCH(78)124 2958 46 17 cCH(99)123 2948 ms 2952 1 0 cCH(90)122 2936vw 2937 34 12 cCH(94)121 2933 0 0 cCH(98)120 2927s 2928 28 10 cCH(89)119 2912 29 10 cCH(92)118 2902 33 12 cCH(96)117 2901 37 13 cCH(100)116 2900 44 16 cCH(84)115 2899vw 2896 28 10 cCH(86)114 2893 8 3 cCH(93)113 2892 8 3 cCH(85)112 2883 21 8 cCH(90)111 2857 ms 2874 18 6 cCH(99)110 1651s 1657 193 69 cOC(88)109 1626vs 1656 5 2 cCC(82)108 1596s 1584 22 8 cCC(46), bCCC(34)107 1553w 1579 16 6 cCC(60)106 1528vw 1483 197 70 cCC(16), cOC(39)105 1473 280 100 cCC(47), cOC(13)104 1513vs 1451 19 7 cNC(57), bHNC(29)103 1451 ms 1451 2 1 cCC(48), cOC(15), bHOC(20)102 1446 51 18 cCC(12), cOC(30), bHOC(29)101 1443 7 2 cCC(57)100 1434 1 0 cCC(22), bHOC(17), bHCH(51)99 1433 10 3 cCC(11), sHCCC(23)98 1431 3 1 bHCH(88)97 1430 0 0 cNC(23), cCC(12)96 1427 5 2 bHCH(92)95 1424 1 0 cCC(28), cOC(22), bHCH(12)94 1419s 1417 16 6 cNC(18), bHNC(24), bHCHsci (12)93 1415 7 2 bHNC(17), bHCH(43)92 1407 31 11 bHCH(58)91 1362 3 1 bHCH (71)90 1352 30 11 bHCHwag (57)89 1341 9 3 bHCH(66)88 1346w 1341 3 1 bHCH(84)87 1337 5 2 bHCH(83)86 1331 11 4 bHCH(87)85 1319 21 8 bHCH(62)84 1292 23 8 cCC(15)83 1282vs 1285 4 2 bHCH(74)82 1284 1 0 bHCH(11), sHCCN(33)81 1282 11 4 cCC(57), sHCCC(22)80 1269 3 1 cCC(17), bHCC(13)79 1258vw 1267 1 0 bHCH(67), sHCOC(12)78 1246 196 70 cOC(68), bHCC(58)77 1240 13 5 bHCC(35), sHCCC(14)76 1239s 1229 50 18 cNCC(22), sHCCC(40)75 1219 50 18 bHCC(43)74 1201 ms 1214 114 41 bHCC(42), bHCC(12)73 1197 5 2 cCC(24), bHCC(19)72 1181 62 22 bHCC(52), sHCOC(11)71 1174w 1176 121 43 cCC(17)70 1160 23 8 cCC(11), bHCC(21)69 1153 17 6 cCC(41), bHCC(10)68 1139 1 0 bHCC(23)67 1123vw 1129 48 17 cCC(31), sHCCC(53)66 1123 1 0 bHCC(30)65 1097 32 11 bHCC(33), bHCCC(15)

180 J. Sherin Percy Prema Leela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 146 (2015) 177186

Table 1 (continued)

ModeNos.

Experimental wave numbers(cm)1

Calculated wavenumbers B3LYP/6311++G(d,p) cm1

FT-IR Assignments PED

Relativea Absoluteb

64 1088 12 4 bHCC(47), sHCOC(11)63 1071 5 2 bHCH(26), sHCOC(72)62 1060 2 1 bHCC(25)61 1029w 1034 4 2 bHCC(38)60 1020 2 1 cCC(16), bHCC(10)59 1016 44 16 bHCC(23)58 1001 2 1 bHCC(22)57 997 15 5 cCC(34), sHCCC(34)56 985 2 1 sHCCC(69)55 967vw 963 37 13 cCC(18), sHCCC(20)54 938vw 955 4 2 sHCCC(38)53 923 0 0 sHCCC(59), sCCCC(24)52 914 5 2 cCC(11), sHCCC(10)51 909 4 1 sHCCC(45)50 902 2 1 bCCC(11), sHCCC(17)49 896vw 894 0 0 cOC(10), binbCCC(29)48 879vw 875 0 0 sHCCC(55), sCCCC(30)47 859 25 9 sHCCC(41)46 841vw 841 3 1 sHCCC(84)45 813 1 0 sHCCC(25)44 806 ms 808 0 0 cCC(11), binCCC(32)43 800 17 6 bHCC(16), sHCCC(38)42 758vw 778 26 9 sHCCC(22), bopOCCC(26)41 754 3 1 bop OCNC(47)40 724 19 7 bNCC(15), bop OCCC(10), CCCC(14)39 715w 712 4 1 bOCC(12), bopOCCC(11)38 701 7 2 bOCN(32), bCNC(11)37 693 0 0 bCCC(42), bopCCCC(10)36 645w 645 9 3 bCCC(13), bopCCCC(10)35 598 17 6 bCCC(44), bopCCCC(19)34 542 21 7 bCCC(10), bopOCC(32)33 532 2 1 bOCN(11), bCCN(35)32 515 1 1 bCOC(12), bopOCCC(37)31 496 6 2 bOCN(12), sHNCC(65)30 467 30 11 bCCC(55)29 456 18 6 bCCC(48)28 446 22 8 bCCC(42)OPCCCC(20)27 437 33 12 bCCC(11), bOCC(19), bCOC(29)26 434 4 1 sCCCC(22), bopOCCC(14)25 419 97 35 bOCC(10), bCCC(23), bCCN(10)24 374 3 1 bCCC(25)23 360 1 0 bOCC(31)22 351 3 1 bNCC(18)21 328 2 1 bCCC(51)20 306 6 2 sHOCC(81)19 286 3 1 bCCC(26)18 263 1 1 sHOCC(10), sHCOC(30)17 252 2 1 bCNC(16), bOCC(10), bCCC(22)16 232 1 0 bCNC(11), bCCC(10), sCCCC(15)15 226 0 0 sHCCC(81)14 217 0 0 sCCCC(20), bop OCCC(21) bop

CCCC(12)13 196 0 0 sHCCC(94)12 194 0 0 sCCCC(53), sCCNC(12)11 179 0 0 sCCCC(24)10 167 4 2 sCCC(50)9 138 4 2 sCNCC(23), sCCCC(11)8 129 0 0 sCCCC(62)7 105 3 1 sCNCC(28), sCOCC(28)6 97 2 1 sCOCC(48)5 92 0 0 sCCCC(43)4 76 4 1 sNCCC(20), sCCNC(29)3 56 8 3 sCCCC(18), sNCCC(17), sCCNC(23)2 48 2 1 sCCCC(26), sNCCC(25), sCCCC(13)1 41 2 1 sCCCC(45), sCCCN(31)

Abbreviations: s strong; vs verystrong; m medium; ms mediumstrong; w weak; vw veryweak; c stretching; b bending; s Torsion, inp plane bending,opb out of plane bending.

a Absolute absorption intensity.b Relative absorption intensities normalized with highest peak absorption equal to 100.

J. Sherin Percy Prema Leela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 146 (2015) 177186 181

nena

: MoTable 2Second order perturbation theory analysis of fock matrix of 8-Methyl-N-vanillyl-6-no

Donor (i) Type ED/e Acceptor (j) Type

C1C2 r 1.96891 C1C6 r

C2C3 r

C6O8 r

C1C6 r 1.97578 C1C2 r

C2C10 r

C5C6 r

1.97578 C5O7 r

C1C6 p 1.69482 C2C3 p

C4C5 p

C1H26 r 1.97446 C2C3 r

182 J. Sherin Percy Prema Leela et al. / Spectrochimica Acta Part Athe idealized lewis structure into the empty non lewis orbitals,they are referred to as delocalization correction to the ZerothOrder natural Lewis structure. For each donor (i) and acceptor (j),the stabilization energy E(2) associated with the delocalizationi? j is estimated as:

E2 DEij qiFij2

ej ei

where qi is the donor orbital occupancy, ej and ei are diagonalelements and Fij is the off diagonal NBO Fock matrix element. Thelarger E(2) value, the more intensive is the interaction between elec-tron donors and acceptors, i.e., the more donation tendency fromelectron donors to electron acceptors and the greater the extent

C5C6 r

C2C3 r 1.97377 C1C2 r

C3C4 r

C2C3 p 1.69197 C1C6 p

C4C5 p

C10N11 r

C3C4 r 1.97398 C2C3 r

C2C10 r

C5O7 r

C3H27 r 1.97954 C1C2 r

C4C5 r

C4C5 r 1.97405 C5C6 r

C4C5 p 1.66814 C1C6 p

C2C3 p

C4H28 r 1.97809 C2C3 r

C5C6 r

C5C6 r 1.97085 C1C6 r

C4C5 r

O8C9 r

O7H29 r 1.98651 C4C5 r

C9H33 r 1.99125 C6O8 r

C10H36 r N11C12 r

C10H37 r 1.98073 C2C3 r

N11H40 r 1.98608 C12O13 r

C12O13 p

C12C14 r 1.97763 C10N11 r

C14H38 r 1.9794 C12O13 r

C14H39 r 1.96508 C12O13 p

C17C18 r 1.97952 C19C20 r

C17H45 r 1.97882 C18H47 r

C17H46 r 1.96942 C18C19 p

C17H46 r

C19C20 r 1.97415 C17C18 r

C18C19 r

C19H48 r 1.97273 C18H47 r

C20H49 r 1.96824 C19H48 r

C20H49 r 1.96824 C21H32 r

C20H49 r 1.96824 C22H25 r

O7 LP(2) 1.87397 C4C5 p

O8 LP(2) 1.86269 C1C6 p

N11 LP(1) 1.70607 C12C13 p

O13 LP(2) 1.70607 N11C12 r

O13 LP(2) 1.70607 C12C14 r

a E(2) means energy of hyper conjugative interaction (stabilization energy).b Energy difference between donor and acceptor i and j NBO orbitals.c F(i, j) is the Fock matrix element between i and j NBO orbitals.mide in NBO basis B3LYP/6-311++G(d,p) method.

ED/e aE(2) (kJ/mol) bE(j) E(i) (a.u) cF(i,j) (a.u)0.02481 3.39 1.26 0.0590.02386 3.58 1.28 0.0610.02862 4.78 1.03 0.0630.02236 3.61 1.3 0.0610.02989 3.27 1.13 0.0540.03630 4.36 1.26 0.0660.02009 3.11 1.07 0.0520.37525 18.8 0.3 0.0690.37907 19.17 0.29 0.0680.02386 4.51 1.11 0.063

lecular and Biomolecular Spectroscopy 146 (2015) 177186of conjugation of the whole system. The intra molecular hyperconjugative interactions are formed by orbital overlaps between rand p (CC, CN, C@O, CH, NH) bond orbitals which resultsintra-molecular charge transfer (ICT) causing stabilization of thesystem. These interactions are observed as increase in electrondensity (ED) in CC, CH, CO and NH antibonding orbital thatweakens the respective bonds. Delocalization of electron densitybetween occupied Lewis-type (bond or lone pair) NBO orbital andformally unoccupied (antibond or Rydgberg) non-Lewis NBO orbitalcorrespond to a stabilizing donoracceptor interaction. The strongintramolecular hyper conjugative interaction of the r and pelectrons of CC to the antibond CC bond in the ring leads tostabilization of some part of the ring as evident from Table 2. Forexample the intramolecular hyper conjugative interaction of

0.03630 3.89 1.06 0.0580.02236 3.55 1.28 0.060.01227 3.13 1.28 0.0570.38685 19.49 0.28 0.0670.37907 19.05 0.28 0.0660.03227 4.67 0.58 0.050.02386 3.48 1.28 0.060.02989 3.79 1.1 0.0580.02009 4.17 1.05 0.0590.02236 4.79 1.1 0.0650.02132 3.16 1.09 0.0520.03630 3.79 1.25 0.0620.38685 18.88 0.29 0.0660.37525 20.32 0.3 0.070.02386 3.47 1.1 0.0550.03630 3.99 1.06 0.0580.02481 4.14 1.28 0.0650.02132 3.89 1.28 0.0630.00967 3.36 0.98 0.0520.02132 4.73 1.31 0.070.02862 3.33 0.88 0.0490.07379 3.29 0.98 0.0520.02386 4.03 1.1 0.060.03371 4.2 1.24 0.0650.26947 0.51 0.73 0.0180.03227 4.28 0.97 0.0580.03371 4.11 1.07 0.0590.26947 4.64 0.56 0.0480.02335 3.73 1.06 0.0560.02317 4.25 0.92 0.0560.05091 3.85 0.55 0.0410.01912 3.02 0.66 0.040.01461 3.67 1.05 0.0560.01262 3.06 1.31 0.0570.02317 5.78 0.94 0.0660.02419 4.63 0.91 0.0580.00867 2.96 0.88 0.0460.00867 2.97 0.88 0.0460.37907 27.39 0.35 0.0930.38685 25.43 0.36 0.0910.26947 51.64 0.32 0.1150.07379 24.25 0.72 0.1190.06053 19.03 0.63 0.1

(C1C6) distribute to r (C1C2), r (C2C10), r (C5C6), r (C5O7)leading to stabilization of 4.36 kJ/mol. This enhanced conjugationwith bonding orbital of p (C1C6) distribute to p (C2C3), p (C4C5)which leads to strong delocalization of 18.8 and 19.17 kJ/molrespectively. In case of the orbitalr (N11H40) distribute to r

(C12O13), p (C12O13), with the stabilization energy of4.2 kJ/mol. The most important interaction energy in this moleculeis electron donating from N11 LP(1) to the antibonding acceptor p

(C12C13) resulting high stabilization energy of 51.64 kJ/mol.Therefore, the maximum energy delocalization takes place in thepp transition.

Potential energy surface (PES) scan

From the MEP it is evident that the negative potential sites are onelectronegative Oxygen atoms and the positive potential sites arearound the Hydrogen atoms.

Frontier molecular orbitals (FMOs)

The (HOMO) highest occupied molecular orbital and the(LUMO) lowest unoccupied molecular orbital are named as frontiermolecular orbitals (FMOs) as they lie at the outermost boundariesof the electrons of the molecules. The FMOs play an important rolein the optical and electric properties, as well as in quantumchemistry and UVVis spectrum [37]. The HOMO represents theability to donate an electron, LUMO as an electron acceptor repre-sents the ability to accept an electron. The energies of HOMO andLUMO orbitals of the compound in gas phase are 5.9365 and0.4893 eV respectively. The HOMO and LUMO orbital energy gapcalculated using B3LYP/6-311++G(d,p) method is +5.4472 eV. Thepositive and negative phase represented in red and blue colour,respectively are shown in Fig. 5. The Frontier orbital gap helpscharacterize the chemical reactivity and the kinetic stabilityof the molecule. A molecule with a small frontier orbital gap isgenerally associated with a high chemical reactivity, low kineticstability and is also termed as soft molecule. The lower value

J. Sherin Percy Prema Leela et al. / Spectrochimica Acta Part A: MoThe optimized conformers of the molecule 8-Methyl-N-vanillyl-6-nonenamide is obtained from Gaussian 03W program and isshown in Fig. 2, with calculated energies for C1 point groupsymmetry. The conformational prole of the title compound hasbeen investigated at the B3LYP/6-311++G(d,p) level. The multi-rotor nature of the compound and the absence of an experimentaldata that elucidate its chemical structure required us to carry out adetailed investigation of the conformationality and energetic tolocate the global minima. The E congurations were calculated tobe about 1.5 kcal/mol more stable than the Z congurations.Moreover, for the E conguration, the syn structure (the CH2groups at C15 is syn to the carbonyl group) was also calculated tobe 1 kcal/mol more stable than the anti structure. The deter-mination of the most stable E-syn form hasbeen conrmed byscreening the energy change when the phenyl group is rotatedabout the C10N11 bond. Again, two possible E-syn forms, I andII, are theoretically present are shown in the Fig. 3. Structure IIis 1 kcal/mol more stable and maintains a CC10N11C dihedralangle of 92 are shown in the Table S1. Structure I is shown bythe potential scan to have a at minima and expected to be easilystable. For the anti conguration, this at minima couldnt belocated. One feature of the stable structures is the intramolecularhydrogen bonding taking place between O8 and H29. The bonding,estimated to be 2.1 , is expected to provide an extra stability tothe molecule in the order of 5 kcal/mol [35,36].

Molecular electrostatic potential

The electrostatic potential V(r) that is created in the spacearound a molecule by its nuclei and electrons (treated as staticdistributions of charge) is a very useful property for analyzingand predicting molecular reactive behavior. It is rigorously denedand can be determined experimentally as well as computationally.The molecular electrostatic potential is related to electron densityFig. 2. The most stable conguration (E-syn) of 8-Methyl-N-vanillyl-6-nonenamideas predicted by the B3LYP/6-311++G(d,p) level.and a very useful descriptor for determining sites for electrophilicattack and nucleophilic reactions as well as hydrogen-bondinginteractions [35,36]. To predict reactive sites of electrophilicand nucleophilic attacks for the investigated molecule 8-Methyl-N-vanillyl-6-nonenamide, MEP at the B3LYP level optimizedgeometry with the basis set 6-311++G(d,p) was calculated andshown in the Fig. 4. The different values of the electrostatic poten-tial at the MEP surface are depicted by different colours red, blueand green representing the regions of most negative, most positiveand zero electrostatic potential respectively. The negative electro-static potential corresponds to an attraction of the proton by theaggregate electron density in the molecule (shades of red), whilethe positive electrostatic potential corresponds to the repulsionof the proton by the atomic nuclei (shade of blue). The negative(red and yellow) regions of MEP were related to electrophilicreactivity and the positive (blue) regions to nucleophilic reactivity.

Fig. 3. Potential energy scan for the internal rotation about the C10N11 bond in8-Methyl-N-vanillyl-6-nonenamide calculated at the B3LYP/6-311++G(d,p) level oftheory.

lecular and Biomolecular Spectroscopy 146 (2015) 177186 183of HOMO and LUMO energy gap explains the eventual chargetransfer interactions taking place within the 8-Methyl-N-vanillyl-6-nonenamide molecule.

: Mo184 J. Sherin Percy Prema Leela et al. / Spectrochimica Acta Part ANon linear optics

Non linear optical (NLO) [3840] effects are analyzed byconsidering the response of the dielectric material at the atomiclevel to the electric elds of an intense light beam. The propagation

Fig. 4. Electro static potential with contour (ESP), molecular electrostatic potentiB3LYP/6-31++G(d,p) method.

LUMO

HOMO

Fig. 5. Highest occupied and lowest unoccupied molecular orbitals of 8-Methyl-Nlecular and Biomolecular Spectroscopy 146 (2015) 177186of a wave through a material produces changes in the spatial andtemporal distribution of electrical charges as the electrons andatoms interact with the electromagnetic elds of the wave. Themain effect of the forces exerted by the eld on the chargedparticles is displacement of the valence electrons from their

al (MEP) and contour map of 8-Methyl-N-vanillyl-6-nonenamide obtained by

E(LUMO)= -0.4893 eV

LUMO PLOT

First exited

E(HUMO)= -5.9364eV

E = 5.4472 eV

HOMO PLOT

Ground state

-vanillyl-6-nonenamide compound obtained by B3LYP/6-31+G(d,p) method.

have been compared with the theoretical spectrum and have been

[5] W.P. Arnold, P.C. Van de Kerkhof, J. Am. Acad. Dermatol. (1993) 438442.

: Monormal orbits. This perturbation creates electric dipoles whosemacroscopic manifestation is the polarization [41]. Thus Nonlinearoptics (NLO) is the study of interaction of intense electromagneticeld with materials to produce modied elds that are differentfrom the input eld in phase, frequency or amplitude. Nonlinearoptics [42,43] is given increasing attention due to its wide applica-tion in the area of laser technology, optical communication anddata storage technology. The second-order polarizability or rsthyperpolarizability b, dipole moment l and polarizability Da ofthe Capsaicin compound are calculated using B3LYP 6-31G(d,p)basis set on the basis of the nite-eld approach. The completeequations for calculating the magnitude of total static dipolemoment l, the mean polarizability a, the anisotropy of thepolarizability Da and the mean rst polarizability b, using the x,y, z components from Gaussian 03 W output is as follows:

ltot l2x l2y l2z 1=2

a 1=3axx ayy azzDa 21=2axx ayy2 ayy azz2 azz axx26a2xx

1=2

bltot lx ly lz andbx bxxx bxyy bxzzby byyy bxxy byzzbz bzzz bxxz byyz

The calculated dipole moment, polarizability and rst orderhyperpolarizability values obtained from B3LYP/6-311++G(d,p)method are given in Table S2. Urea is one of the prototypicalmolecules used in the study of the NLO properties of molecularsystems and frequently used as a threshold value for comparativepurposes. The rst order hyperpolarizability of Capsaicin is3.4966 1030 esu which is nine times greater than the value ofurea (b0 = 0.372 1030 esu). So we conclude that the compoundis an attractive object for future studies of nonlinear opticalproperties.

4.7. Thermodynamic properties

The thermodynamic parameters namely heat capacity, entropyand enthalpy of the compounds have also been computed at theDFT-B3LYP level using 6-311++G(d,p) basis sets at 298.15 K inground state and listed in Table S3. The thermodynamic dataprovide helpful information for further study on the titlecompound. The standard thermodynamic functions can be usedas reference thermodynamic values to calculate the changes ofentropies (DS), changes of enthalpies (DH) and changes of Heatcapacity (DC) of the reaction. The dipole moment and its principalinertial axes strongly depend upon the molecular conformation.From Table S3, it can be observed that these thermodynamic func-tions are increasing with temperature ranging from 100 to 1000 Kdue to the fact that the molecular vibrational intensities increasewith temperature [4458].

The correlation equations between heat capacities, entropies,enthalpy changes and temperatures were tted by quadraticformulas, and the corresponding tting factors (R2) for thesethermodynamic properties are 0.99991, 0.99934 and 0.99991,respectively.

ENTROPYS = 315.66926 + 1.54034 T 3.43167 104 T2 (R2 = 0.99991)HEAT CAPACITYC = 36.10096 + 1.3561 T 5.01694 104 T2 (R2 = 0.99934)ENTHALPY

4 2 2

J. Sherin Percy Prema Leela et al. / Spectrochimica Acta Part AH = 13.70614 + 0.16083 T + 4.06098 10 T (R = 0.99991)The correlation graphs between heat capacities, entropies,

enthalpy changes and temperatures were shown in Fig. S1. All[6] V. Krishnakumar, N. Prabavathi, S. Muthunatesan, Spectrochim. Acta A 69(2008) 528533.

[7] R.G. Parr, W. Yang, Density Functional Theory of Atoms and Molecules, OxfordUniversity Press, New York, 1989.

[8] V. Krishnakumar, V. Balachandran, Spectrochim. Acta A 63 (2006) 464476.[9] A. Altun, K. Golcuk, M. Kumru, J. Mol. Struct. (Theochem) 625 (2003) 1724.found to be in very good agreement. In PES the most stableconformer is for 92 dihedral angle is conrmed. The stability ofthe molecule arising from hyper conjugative interactions, chargedelocalization has been analyzed using NBO analysis. HOMOand LUMO energy gaps explain the eventual charge transferinteractions taking place within the molecule. The rst orderhyperpolarizability of Capsaicin is 3.4966 1030 esu which isnine times greater than the value of urea (b0 = 0.372 1030 esu)and polarizability is 3.101 1023 esu.

The thermodynamic functions of capsaicin are increasingwith temperature ranging from 100 K to 1000 K due to the factthat the molecular vibrational intensities increase with tempera-ture. Other molecular properties like entropy, enthalpy and heatcapacity also calculated. The MEP map shows that the negativepotential sites are on oxygen and the positive potential sites arearound the hydrogen atoms. These sites may provide informationabout the possible reaction regions for the title structure. In con-clusion, all the calculated data and simulations not only showthe way to the characterization of the molecule but also help forthe fundamental researches in chemistry and biology in the future.

Acknowledgement

A.A. Al-Saadi thanks King Fahd University for Petroleum &Minerals (KFUPM) for providing the computing facility to supportthis work.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.saa.2015.03.027.

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The use of herbs as complementary and alternative medicinehas increased dramatically in the last 2025 years. Capsaicin themajor pungent ingredient in genus Capsicum, has long been usedin food additives and drugs. An infrared spectrum represents anger print of a sample with absorption peaks which correspondto the frequencies of vibrations between the bonds of the atomsmaking up the material. An attempt has been made in the presentwork for the proper wave number assignments from FT-IRspectrum. The vibrational band assignments of the recorded FTIRspectrum of the molecule (8-Methyl-N-vanillyl-6-nonenamide)

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186 J. Sherin Percy Prema Leela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 146 (2015) 177186

Spectroscopic investigation (FTIR spectrum), NBO, HOMOLUMO energies, NLO and thermodynamic properties of 8-Methyl-N-vanillyl-6-nonenamideby DFT methodsIntroductionComputational detailsExperimentalResults and discussionVibrational analysisNH stretchCH stretchingCH2 bending vibrationsCO vibrationCC vibration

NBO analysisPotential energy surface (PES) scanMolecular electrostatic potentialFrontier molecular orbitals (FMOs)Non linear optics4.7. Thermodynamic properties

ConclusionsAcknowledgementAppendix A Supplementary dataReferences