REPRINT DOI: 10.1002/Slct.201902698 Full Papers

REPRINT DOI: 10.1002/slct.201902698 Full Papers

z Electro, Physical &Theoretical Chemistry Anti-Cancerous Brucine and Colchicine: Experimental and Theoretical Characterization Aboothahir Afzal,*[a, b] MohamedShahin Thayyil,[a] Mohammad Shariq,[c] YohannanSheena Mary,[d] Kaippallil Sundaresan Resmi,[d] Renjith Thomas,[e] Nasarul Islam,[f] and Ajithan Jyothi Abinu[b]

Brucine and colchicineare alkaloids, which are found abun- set. Relaxed energy scans on dihedral angles in brucine and dantly in Asian Countries, having medicinal values in Ayurveda colchicine were performed to generate potential energy and is used widely in China. But surprisingly, it is reported surfaces (PES) corresponding to rotational motions for con- recently in the literature that both brucineand colchicine formational analysis. Theoretical Light Harvesting Efficiency possess anti-cancerous effects. Acomprehensive quantum (LHE) parameter for different halogen substitutions for brucine computational study of brucineand colchicine to determine its and colchicine were determined by TD-DFT method. Molecular structural and electronic properties is lacking in the literature. electrostatic potential surfaces (MEP) of the title compounds The optimized molecular geometries, electronic and vibrational were generated to find the reactive molecular sites. Nonlinear spectral analysis, Frontier Molecular orbital analysis, natural optical properties (NLO) analysis showed that the first hyper bonding orbitals (NBO), non linear optical properties (NLO), polarizability values of brucine and colchicine are 25.56 and Vibrational circular dichroism (VCD) spectra were studied by 22.15 times than that of urea. The in-silica molecular docking Density Functional Theory (DFT) method by Computational analysis of brucine and colchicinewere done using the Maestro Chemistry tool Gaussian-09 with B3LYP/6-311++G(d, p) basis -Schrodinger suite 8.0 with cancer target proteins.

Introduction above alimited dose (narrow therapeutic window) which puts Brucine is an alkaloid, extracted from Nux-vomica tree, found alimitation to treat cancer. Colchicine, another alkaloid is abundantly in Asian countries, and is used as aconstituent of commonly used for treating gout,[7] pericarditis,[8] bechet‘s traditional medicines in Asian countries especially China for disease and familial Mediterranean fever[9] and is atubulin many years..[1–2] It is used to treat patients with arthritic and destabilizer first ever reported with amazing anti-mitotic traumatic pain by virtue of its anti-inflammatory, analgesic and activity and can treat cancer like chronic leukemia,[10] and also anti-rheumatic properties,[3] and also used for preparing drugs can treat cardiovascular problems.[11] Several studies on struc- used in Ayurveda and Homeopathy.[4] Surprisingly, Qin et.al,[5] tural variations in colchicine to increase its therapeutic in 2012 reported that, brucine is effective against hepatocel- efficiency were reported.[12] Brucine and colchicine are large lular carcinoma, while Serasanambati et.al,[6] in 2014 reported chiral molecules, as they can find good applications as chiral its potential activity against breast cancer, which may revolu- resolving agents by enantio selective recognition, brucine is tionize anticancer treatment. Unfortunately brucine is toxic used as chiral selector[13] in fractional distillation to resolve di- hydroxy fatty acids.[14] The chiral application potential of natural alkaloids is not explored to the maximum, but researchers have [a] A. Afzal, Dr. M. S. Thayyil Department of Physics, Calicut University, Malappuram district, Kerala found the possibility of applying optically pure alkaloids as E-mail: [email protected] chiral resolving agents.[15] Stereo-chemically relatedmolecules [b] A. Afzal,A.J.Abinu can be used for separation of acids of opposite configurations Department of Physics, Govt. Arts and Science college Calicut, Kerala by producing diastereomeric salts having different [c] Dr. M. Shariq [16,17] Department of Physics, Faculty of Science, Jazan University, Jazan, Saudi solubility. The chiral propertiesofbrucine and colchicine Arabia are determined by Vibrational circular dichroism (VCD) spectro- [d] Dr. Y. S. Mary, Dr. K. S. Resmi scopy. Department of Physics, Fatima Mata National College(Autonomous), The possible electrophilic and nucleophilic attacks on Kollam, Kerala, India [e] Dr. R. Thomas tertiary atoms of the title molecules and hyper molecular Department of Chemistry, St. Berchmans College (Autonomous), Changa- interaction were studied by NBO analysis. The distribution of nasserry, Kerala, India charges in the atoms of the molecule is calculated by natural [f] Dr. N. Islam bonding orbitals (NBO) analysis, which helps to understand the Department of Chemistry, Govt. Degree College, Sopore, J&K-193201, India electron density localization, hyper conjugation effects, and [15] Supporting information for this article is available on the WWW under intermolecular or intra molecular interaction. Both brucine https://doi.org/10.1002/slct.201902698 and colchicine are polar molecules, and have dielectric

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permittivity value around 3.[18] Non linear optical (NLO) proper- compounds were then used in NBO analysis using NBO 3.1 ties like electric dipole moment, the isotropic polarizability and Program.[13] UV-Visible spectra by TD-DFTmethod.[14,15] HOMO- the first hyperpolarizability can be theoretically calculated by LUMO energy levels and Molecular Electrostatic Potential (MEP) Density Functional Theory (DFT) method for understanding the were calculated using Gauss View 5.0. Light Harvesting NLO properties for possible applications in nonlinear optics.[15] Efficiency (LHE) of brucine and colchicine and also for its Organic solar cells are getting more popular, as organic solar different halogen substitutions were also determined by TD- cells with 13% power conversion efficiencywere developed.[19] DFT method using Gaussian-09 for its possible application in The light harvesting efficiency (LHE) is defined as the fraction organic solar cells. of light intensity absorbed by the solar cell at acertain In order to do the in-silica analysis for understanding of the wavelength to the incident light intensity .[20] anti-cancer effects ofbrucine and colchicine, the molecular Brucine and colchicine are significant to the pharmaceutical docking was carried out using Schrodinger suite using the industry due to its anticancerous effects, but acomplete Maestro version 18.4 packages such as receptor grid gener- quantum computational characterization of molecular proper- ation, Ligprep, and Glide XP docking. The pdb files of proteins ties is lacking in the literature. This motivated to perform were obtained from RCSB protein bank[39] whose PDBID’s are quantum computational calculations for characterizing struc- 1JNX[40],3U9 U[41],5NQR[42],1BHG[43],3S7 S[44],4AOW[45], tural, vibrational and electronic properties on brucine and 3U9U[41],5JM5[42],5NWH[42] and 5G3 N.[47] Each target protein colchicine. In this paper, analysis using IR, Raman, UV-Visible was prepared using the Protein preparation wizard in the spectroscopy, Vibrational circular dichroism spectral analysis Maestro 18–4 version.[48] Then, it was preprocessed, and the (VCD), natural bonding orbitals (NBO) analysis, Frontier molec- overlapped residues were removed, optimization and minimi- ular orbitals(FMO), Molecular electrostatic potential surfaces zation processes were done. The water moleculesifany present (MEP), LHE analysis by DFT method using Gaussian-09.[21] Non in the protein structure were removed from the protein linear optical properties like linear polarizability (α)and first structure before the minimization process since they were not order hyper-polarizability (β), and the molecular chemical suitable for molecular docking.[49] Asitemap can locate the stability due to charge delocalization and hyper-conjugative binding sites of proteins whose functionality size and solvent interactions were also calculated. exposure meet the user specification.[50] It also shows the Computational molecular docking is apowerful tool for regions in the binding sites which are suitable for Ligands structure based drug discovery.[22] In order to understand the hydrogen-bond donors, acceptors or hydrophobic groups to anticancer effects of the title compounds, the in-silica molec- occupy. The site scores obtained can be used to rank the ular docking of brucine and colchicine with cancer target possible binding sites accurately to eliminate those sites which proteins available in the literature were done. Quantum are not likely to be relevant. The ligand molecules, brucine, and computational techniques proved to be irreplaceable and colchicine were prepared using Ligprep, which generates inexpensive theoretical tools for characterization of energy minimized molecular structures in 3D. It eliminates the molecules,[23–26] identification of reactive areas of molecules, mistakes in the ligands and applies sophisticated methods to spectroscopic analysis[27] and is also used for the character- correct the Lewis structures to reduce the computational errors. ization and structural confirmations of new or yet to be Optimization using OPLS3e force field generated the low- synthesized molecules.[28–33] One of the biggest challenges in energy isomer of the ligands. Finally, these ligand molecules in drug discovery is screening of compounds to identify a the complex structure were docked with the target proteins. prospective drug which is along time consuming process, The ligand molecules were docked with the binding sites of where docking is proved to be very useful. If we dock anumber each of the corresponding cancer target proteins using the of compounds into target receptor structures virtually, only a Glide Grid ligand docking package[51] of the Schrodinger few number of compounds are needed to be experimentally software. Glide accurately finds the exact binding modes for a screened. The molecular docking software package Glide in large set of test cases. Glide does avirtual screening from HTVS Schrodinger suite[34,35] is found to be very effective for screening to SP to XP, modifying the data at each level such that only of drugs and is widely used by researchers especially in fewer compounds need to be studied at ahigher accuracy pharmaceutical industry. Quantum computational calculations level.[52] The ligands were docked to the active site of cancer of brucine and colchicine were done by DFT method[36] in the targets using Glide Extra precision (XP), which determine the ground state using Gaussian-09 with B3LYP/6-311++G(d,p) flexibility of ligands. Only those molecules, which are small and basis[21] with Gaussview-05 as interface.[37] The molecular active, would receive favorable docking scores with accurate structure of brucine and colchicinewere optimized at the hydrophobic contact with the ligand and protein. B3LYP/6-311++ basis set while natural bond orbital analysis (NBO) was done using NBO program in Gaussian-09.[38] Theoretical calculations on FTIR,FT-Raman, Vibrational Circular Results and Discussion Dichroism(VCD) spectra, NLO properties, NBO analysis and VCD Molecular geometry spectra of brucine,colchicine and its halogen substitutions were performed. The harmonic vibrational frequencies of FTIR The equilibrium molecular geometries of brucine and colchi- and FT-Raman spectra werecalculated and scaled by the cine were obtained by B3LYP/6-311++G(d,p) method are scaling factor 0.961.[12] The optimised structures of the title shown in figures 1and 2respectively. Bond length values

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Figure 1. Optimized structure of brucine

Figure 3. Graph showingvariation of potential energy with rotation of dihedral angle for relaxed scan of two selected dihedrals of brucine

The first scan was performed on brucine between the

dihedrals C27-O4-C29-H55 in the intervals of 10 degrees for 180 degrees using B3LYP/6-311++G(d,p). The second scan in

brucine molecule was done with the dihedral C26-O3-C28-H51. The variation of potential energy and dipole moment with dihedral angle are shown in figures 3and 4respectively. It is

Figure 2. Optimized structure of colchicine

(theoretical and experimental) of colchicine are shown in table 1.The optimized parameters of colchicineare in good agreement with the experimental data.

3. 2Potential Energy surfaces (PES) by Relaxed Dihedral Scan For conformational analysis of the brucine and colchicine molecules, relaxed potential energy scan[53] were performed by rotationofaside group in brucine and colchicine molecules separately at arbitrarily selected dihedral angles. We obtained the potential energy in the gas phase through relaxed geometry scans by selecting redundant coordinates using Gaussview-05 interface and Gaussian-09.[21,37] The dihedral angle in the optimized structure was changed continuously by aconstant step of 10° in the range of 180°.Ataparticular dihedral angle selected, the rest of the molecule was optimized Figure 4. Graph showingvariation of potential energy with rotation of and at this position the energy as well as molecular dipole dihedral angle for relaxed scan of aselected dihedral of colchicine moment werecalculated. The PES corresponding to the

rotationofthe CH3 group proved that conformational inter- conversions through stationary points are shown in figure 3. found that there are three global maxima and four global The molecular dipole moment as afunction of the torsional minima in the potential energy surface for both the con- dihedralangle is also studied which in-turn is linked to change formers. The conformational stabilization energy is determined in energy. to be 1.3544 kcal/mol. The global minima are observed in the

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Table 1. structural parameters of colchicine optimized by B3LYP/6-311 ++G(d,p)[52]

Bond length(Å) Theo-retical Bond Theore-ticalExperi-mental Dihedral Angle (°)Theoretical

O1-C15 1.3753 1.38 C15-O1-C26 115.4795 116 C26-O1-C-15-C13 -103.8572 O1-C26 1.4358 1.4 C19-O2-C27 114.5555 C26-O1-C15-C19 78.9639 O2-C19 1.3746 1.385 C20-O3-C28 116.5231 116.5 C15-O1-C26-H43 63.3324 O2-C27 1.4381 1.42 C24-O4-C29 122.0724 119.5 C15-O-1-C26-H44 -59.2438 O3-C20 1.3703 1.365 C8-N7-C22 122.0581 C15-O1-C26-H45 -178.3183 O3-C28 1.4355 1.445 C8-N7-H35 119.1324 C27-O2-C19-C15 82.183 O4-C24 1.3476 C22-N7-H35 118.7839 C27-O2-C19-C20 -99.0469 O4-C29 1.4425 1.42 N7-C8-C9 112.4517 C19-O2-C27-H46 179.5724 C21-O5 1.2357 1.26 N7-C8-C11 113.5122 113.5 C19-O2-C27-H47 -61.4302 C22-O6 1.2212 1.22 N7-C8-H30 103.5083 C19-O2-C27-H48 60.7883 C8-N7 1.4628 1.465 C9-C8-C11 111.8636 110 C28-O3-C20-C16 116.7071 N7-C22 1.3694 1.33 C9-C8-H30 107.82 C28-O3-C20-C19 -67.4166 N7-H35 1.007 C11-C8-H30 107.0233 C20-O3-C28-H49 -179.5134 C8-C9 1.5494 1.55 C8-C9-C10 114.7267 C20-O3-C28-H50 -61.394 C8-C11 1.5393 1.53 C8-C9-H31 107.75 C20-O3-C28-H51 61.014 C8-H30 1.0884 C8-C9-H32 108.3134 C29-O4-C24-C21 -30.4452 C9-C10 1.542 1.525 C10-C9-H31 110.3485 C29-O4-C24-C23 156.7068 C9-H31 1.0943 C10-C9-H32 108.4925 C24-O4-C29-H52 -44.6399 C9-H32 1.0941 H31-C9-H32 106.9171 C24-O4-C29-H53 77.3117 C12-C10 1.5098 1.5 C9-C10-C12 112.609 C24-O4-C29-H54 -162.5513 C10-H33 1.0946 C9-C10-H33 108.9554 C22-N7-C8-C9 128.1803 C10-H34 1.0925 C9-C10-H34 109.2413 C22-N7-C8-C11 -103.5617 C11-C14 1.4421 1.465 C12-C10-H33 109.2549 C22-N7-C8-H30 12.0881 C11-C17 1.3715 1.375 C12-C10-H34 109.9195 H35-N7-C8-C9 -49.9568 C12-C13 1.4125 1.395 H33-C10-H34 106.6808 H35-N7-C8-H11 78.3012 C16-C12 1.3935 1.335 C8-C11-C14 118.9748 117.5 H35-N7-C8-H30 -166.049 C13-C14 1.4995 1.475 C8-C11-C17 113.9129 113.5 C8-N7-C22-O6 1.6083 C13-C15 1.4099 1.435 C14-C11-C17 127.0369 128 C8-N7-C22-C25 -177.9381 C18-C14 1.3795 1.35 C10-C12-C13 119.5213 119.5 H35-N7-C22-O6 179.7517 C15-C19 1.4048 1.405 C10-C12-C16 120.3055 H35-N7-C22-C25 0.2052 C20-C16 1.3935 1.395 C13-C12-C16 120.1417 N7-C8-C9-C10 89.2384 C16-H36 1.0842 C12-C13-C14 120.6336 N7-C8-C9-H31 -34.0859 C17-C21 1.4556 1.455 C12-C13-C15 118.0748 118.5 N7-C8-C9-H32 -149.4127 C17-H37 1.0866 C14-C13-C15 121.2808 122.5 C11-C8-C9-C10 -39.8803 C23-C18 1.4109 1.395 C11-C14-C13 119.7152 C11-C8-C9-H31 -163.2046 C18-H38 1.0827 C11-C14-C18 124.0598 123 C11-C8-C9-H32 81.4686 C19-C20 1.4005 1.405 C13-C14-C18 116.2244 H30-C8-C9-C10 -157.2889 C21-C24 1.477 1.475 O1-C15-C13 120.6064 119.5 H30-C8-C9-H31 79.3868 C22-C25 1.5193 1.49 O1-C15-C19 117.9794 H30-C8-C9-H32 -35.94 C23-C24 1.3739 1.379 C13-C15-C19 121.3524 N7-C8-C11-C14 -56.3395 C23-H39 1.0862 C12-C16-C20 121.5396 121.5 N7-C8-C11-C17 126.5979 C25-H40 1.092 C12-C16-H36 120.4336 C9-C8-C11-C14 72.2206 C25-H41 1.0917 C20-C16-H36 118.0162 CÀC8-C11-C17 -104.8421 C25-H42 1.0921 C11-C17-C21 134.9745 135 H30-C8-C11-C14 -169.8936 C26-H43 1.0944 C11-C17-H37 115.8336 H30-C8-C11-C17 13.0437 C26-H44 1.0927 C21-C17-H37 108.9737 C8-C9-C10-C12 -45.8576 C26-H45 1.0894 C14-C18-C23 131.9261 132.5 C8-C9-C10-H33 75.524 C27-H46 1.0895 C14-C18-H38 115.025 C8-C9-C10-H34 -168.2868 C27-H47 1.0928 C23-C18-H38 112.99 H31-C9-C10-C12 76.0648 C27-H48 1.0939 O2-C19-C15 120.1209 119.5 H31-C9-C10-H33 -162.5535 C28-H49 1.0893 O2-C19-C20 120.1899 H31-C9-C10-H34 -46.3644 C28-H40 1.0955 C15-C19-C20 119.6778 120 H32-CÀC10-H12 -167.1085 C28-H51 1.0912 O3-C20-C16 118.8053 118.5 H32-CÀC10-H33 -45.7269 C29-H52 1.092 O3-C20-C19 121.8623 122.5 H32-C9-C10-H34 70.4623 C29-H53 1.0866 C16-C20-C19 119.2059 CÀC10-C12-C13 70.8992 C29-H54 1.0893 O5-C21-C17 119.3217 C9-C10-C12-C16 -107.0593 O5-C21-C24 119.9998 120 H33-C10-C12-C13 -50.3118 C17-C21-C24 120.6387 H33-C10-C12-C16 131.7297 O6-C22-N7 123.0857 H34-C10-C12-C13 -167.0542 O6-C22-C25 121.5572 H34-C10-C12-16 C14.9874 N7-C22-C25 115.3556 C8-C11-C14-C13 -3.722 C18-C23-C24 131.6341 130 C8-C11-C14-C18 176.573 C18-C23-H39 115.0139 C17-C11-C14-C13 172.9137 C24-C23-H39 113.3454 C17-C11-C14-C18 -6.7913 O4-C24-C21 119.9387 118 C8-C11-C17-C21 173.0421 O4-C24-C23 114.2895 110 C8-C11-C17-H37 -0.8625 C21-C24-C23 125.339 128 C14-C11-C17-C21 -3.7385

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Table 1. continued

Bond length(Å) Theo-retical Bond Theore-ticalExperi-mental Dihedral Angle(°)Theoretical

C22-C25-H40 113.8111 C14-C11-C17-H37 -177.6431 C22-C25-H41 108.6142 C10-C12-C13-C14 3.0761 C22-C25-H42 108.5252 C10-C12-C13-C15 -178.1027 H40-C25-H41 109.2603 C16-C12-C13-C14 -178.962 H40-C25-H42 109.05 C16-C12-C13-C15 -0.1409 H41-C25-H42 107.385 C10-C12-C16-C20 178.4411 O1-C26-H43 110.4104 C10-C12-C16-H36 -2.7665 O1-C26-H44 110.8281 C13-C12-C16-C20 0.4954 O1-C26-H45 106.1241 C13-C12-C16-H36 179.2877 H43-C26-H44 110.3432 C12-C13-C14-C11 -50.9067 H43-C26-H45 109.3098 C12-C13-C14-C18 128.8209 H44-C26-H45 109.7293 C15-C13-C14-C11 130.3104 O2-C27-H46 106.1707 C15-C13-C14-C18 -49.962 O2-C27-H47 110.5823 C12-C13-C15-O1 -177.7158 O2-C27-H48 110.4297 C12-C13-C15-C19 -0.6332 H46-C27-H47 109.7529 C14-C13-C15-O1 1.0973 H46-C27-H48 109.6431 C14-C13-C15-C19 178.1799 H47-C27-H48 110.1824 C11-C14-C18-C23 -2.4728 O3-C28-H49 105.9009 C11-C14-C18-H38 -179.4385 O3-C28-H50 110.2386 C13-C14-C18-C23 177.8128 O3-C28-H51 111.2198 C13-C14-C18-H38 0.847 H49-C28-H50 109.3001 O1-C15-C19-O2 -3.0069 H49-C28-H51 109.9948 O1-C15-C19-C20 178.2168 H50-C28-H51 110.0935 C13-C15-C19-O2 179.8364 O4-C29-H52 110.6629 C13-C15-C19-C20 1.0601 O4-C29-H53 111.1129 C12-C16-C20-O3 175.9155 O4-C29-H54 104.3562 C12-C16-C20-C19 -0.0723 H52-C29-H23 109.5614 H36-C16-C20-O3 -2.905 H52-C29-H54 109.6834 H36-C16-C20-C19 -178.8928 H53-C29-H54 111.3724 C11-C17-C17-O5 -159.4061 C11-C17-C21-C24 22.8885 H37-C17-C21-O5 14.7935 H37-C17-C21-C24 -162.9119 C14-C18-C23-C2 7.8231 C14-C18-C23-H39 -173.1913 H38-C18-C23-C24 -175.1635 H38-C18-C23-H39 3.8222 O2-C19-C20-O3 4.6691 O2-C19-C20-C16 -179.4706 O15-C19-C20-O3 -176.5554 O15-C19-C20-C16 -0.6951 O5-C21-C24-O4 -14.0661 O5-C21-C24-C23 157.9373 C17-C21-C24-O4 163.6238 C17-C21-C24-C23 -24.3728 O6-C22-C25-H40 177.8241 O6-C22-C25-H41 55.8807 O6-C22-C25-H42 -60.5666 N7-C22-C25-H40 -2.6218 N7-C22-C25-H41 -124.5653 N7-C22-C25-H42 118.9874 C18-C23-C24-O4 -179.6038 C18-C23-C24-C21 7.9963 H39-C23-C24-O4 1.3973 H39-C23-C24-C21 -171.0025

dihedralsofÀ180, À6-, + 60 and +180 degrees and the that energy change corresponds in the dipole moment change maxima are in the dihedrals of À120, 0and +120 degrees. also. Similarly the relaxed dihedral scan was performed on colchicine for dihedral angle H -C -C -N and obtained three global 41 25 22 7 Vibrational Assignments minima in the same range of rotation angles.The molecular dipole moment‘s variation of the torsional dihedral angle is FTIR and Raman spectra of brucine and colchicine are shown in shown in supporting information (figures SF1, SF2) and found figures 5–8 respectively. The assignments of skeletal vibrational

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Figure 5. FTIR spectrum of brucine- experimental and theoretical Figure 8. Theoretical and experimental FT-Raman spectrum of Colchicine

modes and functional group vibrations in the mid-IR region are summarized in Table S1 and S2 (Supporting information). The carbonyl stretching C=Ovibrations appear at 1665 cmÀ1 (IR), 1670 cmÀ1(DFT) for brucine and 1723, 1618 (IR), 1716, 1620 cmÀ1(DFT) for colchicine while C=Cstretching modes were assigned at 1660 (Raman), 1658 (DFT) for brucine and at 1584, 1560, 1488 (IR), 1590 (Raman), 1583, 1572, 1489 (DFT) for Colchicine. The CÀOmodes were seen in the range 1250– 1020 cmÀ1(IR), and at 1250, 1193 cmÀ1(Raman) for brucine and at 1086, 1050, 921 (IR), 1098, 1060, 926 (Raman) for colchicine.[54] Most of the ring modes are also in agreement with theoretically predicted wave numbers. In order to have a full understanding of the spectral and chiro-optic properties of these non linear oligo cyclic systems, we performed adetailed analysis of absorption behavior and vibrational circular dichro- Figure 6. Experimental and theoretical FTIR spectra of colchicine ism exhibited by these biologically active molecules.

Vibrational circular dichroism (VCD) Vibrational circular dichroism (VCD) is an extension of circular dichroism spectroscopy into the IR and near infrared region used to identify the absolute configuration and solution phase conformations.[55–57] The VCD spectra of brucine and colchicine are shown in figure 9. The CÀCstretching modes of the aromatic rings, CÀHand C=Ostretching modes atstereogenic centers generate VCD signals, and these are efficient identifiers of configuration identification of molecules, and also for optical purity and solution conformations that are primarily appliedto alkaloid like organic systems.[58] Chiral molecules show differential absorption of left versus right circularly polarized IR radiation by amolecular vibrational transition depends on the product of the electricdipole transition moment onto the magnetic dipole transition moment. All (3 N-6) vibrational modes of achiral molecule (N being the number of atoms in Figure 7. FT-Raman spectrum of brucine compared with theoretical FTIR spectrum the molecule) can give rise to circular dichroism. For biologically significant molecules, VCD analysis can help in finding

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ing to CH2 and CH3 groups are good markers of the configuration showing right polarization and left polarization respectively for colchicine. For colchicine,the carbonyl stretching mode shows the right polarization at 1629 cmÀ1 and CO stretching modes of 1004 cmÀ1 show left polarization. The VCD À1 spectral bands in the range 11400–1100 cm from CH2, and

CH3 groups are good markers of aconfiguration having right polarization and left polarization respectively for the halogen- substituted colchicine.

UV-VIS Spectroscopy The experimental and theoretical UV-VIS Spectroscopy were done to study the characteristics ofthe excited states of colchicine molecule by electronic absorption of radiation. The experimental UV-Visiblespectrum of colchicine was recorded in methanol and theoreticalUV-Visible spectrum was obtained in Figure 9. VCD spectra of brucine and colchicine gas phase by TD-DFT method (B3LYP/6-311++g(d,p). The band gap energy is calculated using E=hc/λ.[60] The excited electronic states, excitation energies, oscillator strengths, absorption wavelengths of colchicine were shown in table 2 selective applications of the bio-active enantiomers in the and comparative UV-Visible spectrumofcolchicine is shown in pharmaceutical industry and understandingtheir biochemical figure 10. The figure 10 shows three absorption bands at interactions.[59] Brucine has two enantiomeric forms, and their calculated VCD spectra containsome important information about their chirality characteristics.

The CH2 stretching modes of brucine (Fig.9) shows right polarization at 3004, 2950, 2940, 2895 cmÀ1 while modes at 3025, 2974, 2925 cmÀ1 in the VCD spectra show left polarization. The VCD bands at 1380, 1357, 1317, 1273, 1075, À1 À1 1025 cm and 1447, 1346, 1301, 1244, 1222 cm due to CH2

and CH3groups are configuration markers showing right polarization and left polarization respectivelyfor brucine. For brucine,the carbonyl stretching mode showing left polarization at 1678 cmÀ1.For brucine, CO stretching modes at 1149 cmÀ1 show left polarization. For halogen substituted brucine, the carbonyl stretching mode shows left polarization at 1669 (chlorine), 1667 (bromine) and 1668 cmÀ1 (fluorine). The VCD À1 bands in the range 11400–1100 cm correspond to CH2 and Figure 10. UV spectrum of colchicine–theoretical and experimental

CH3 groups are good markers of the configuration showing right polarization and left polarization for halogen substituted brucine.

The CH2 stretching modes of colchicine (Fig.9) showing 360 nm, 347 nm and 329 nm. The maximum absorbed peak right polarization at 2973, 2931 cmÀ1 while modes at 3095, appears at 360 nm with an oscillator strength f=0.2801, band 2939 cmÀ1 in the VCD spectra showing left polarization. VCD gap 3.4417 eV and HOMO-LUMO with 93% is responsible for spectral bands at 1595, 1527, 1493 cmÀ1 corresponding to C=C n!π*transition. The other two bands at 347 and 329 nm have stretching and 1466, 1432, 1370, 1269, 1224 cmÀ1 correspond- amaximum contribution from H-1 and aminor contribution

Table 2. Electronic properties of colchicine obtained by UV spectrum using TD-DFT method at B3LYP/6-311++G(d,p)

States Wavelength Oscillator strength Energy Composition(%) À1 λobs λcal (nm) (f) (cm ) (nm)

S1 351.2 360.24 0.28 27759.18 Singlet-A HOMO->LUMO (93%) HOMO->L+1(2%) S2 347.24 0.025 28798.02 Singlet-A H-1->LUMO (73%) H-3->LUMO (3%), H-1->L+1(8%), HOMO->LUMO (4%), HOMO->L+ 1(9%) S3 329.78 0.039 30322.41 Singlet-A H-1->L+1(51%), HOMO->L+ 1(41%)

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from HOMO. These two bands can be assigned to mixed colchicine than that of brucine. The entire data indicates that transitions including n!π*and π!π*. colchicine is more stable than brucine.

Frontier molecular orbital studies Molecular Electrostatic potential The charge transfer properties of molecules are usually The Molecular electrostatic potential surfaces (MEP) give ideas governedbythe pattern and energies of HOMO (electron about molecular shape, size, and also the neutral, negative,and donatingnucleophile) and LUMO (electron accepting electro- positive electrostatic potential areas of the molecules and are phile) in amolecule and Frontier molecular orbital studies expressed in the form of color coding. It also provides (FMO) studies give information about the stability of a information about the distribution of electronic and nuclear moleculefrom the energy gap between them.[61] If the energy charges in amolecule. When MEP values are mapped to the gap between HOMO and LUMO is higher, the stability and electron density surface one obtains descriptive illustration of chemical hardness of that molecule will be higher and vice molecule’s reactivity with respect to sensitivity towards the versa, i.e., for the lower value of the energy gap the molecule is electrophilic and nucleophilic attacks. In terms of electrophilic more chemically reactive and softer[62] .FMO diagram of attacks, molecule areas characterized by negative MEP values brucine is reported by N. Islam et al.[11] From the HOMO-LUMO are considered to be sensitive towards electrophilic, while diagram of colchicine shown in figure 11, the highest occupied molecule areas characterized by positive MEP values are considered to be sensitive towards nucleophilic attacks. To examine the chemical reactivity of the molecule, the MEP map is framed on the optimized geometry of the brucine and colchicine and are shown in Figure 12 and Figure 13

Figure 11. HOMO-LUMOdiagram of colchicine

molecular orbitals (EHOMO = À5.936 eV) and the lowest unoccu- Figure 12. Molecular electrostatic potential surface of brucine

pied molecular orbital (ELUMO = À2.287 eV) of colchicineare mainly concentrated over seven carbon ring including the contribution of carbonyl group as well as the methoxy substituent present on the seven-membered rings. In addition to it in case of HOMO,the electron density is uniformly distributed aromatic ring while as the LUMO have alittle contribution from the aromatic sextet. HOMO-LUMO energy gap for colchicine is calculated as 3.649 eV and 4.831 eV for brucine. The typical parameters that describe molecular chemical stabilityofbrucine and colchicine are shown in table S3 (supporting information). The energy band gap corresponding to the frontier molecular orbitals of brucine is greater than that of colchicine. From the electron affinityvalues, colchicine is more reactive than brucine, which is clear from the electro- negativity values of brucine and colchicine. Chemical hardness is more for brucine than that for colchicine. Electrophilicity (G) Figure 13. Molecular electrostatic potential surface of colchicine of colchicineismuch higher than that of brucine, which means the tendency to accept an electron pair is much higher for

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respectively. In an MEP surface map, red color indicates the n2(O1)!π*(C13-C15), C19-C20 from O2 of n2(O2)!π*(C19-C20), C19-C20 electrophilic attack, i.e., maximum negativepart and blue color from O3 of n2(O3)! π*(C19-C20), C23-C24 from O4 of n2(O4)!π* [63] indicates the nucleophilic, i.e., maximumpositive part. The (C23-C24), C21-C24 from O5 of n2(O5)!σ*(C20-C24), N7-C22 from O6 of potential reduces in the order of blue green-yellow orange-red. n2(O6)!σ*(N7-C22), O6-C22 from N7 of n1(N7)! σ*(O6-C22)having According to the results provided in figure 12, it can be seen stabilization energies, 7.09, 5.61, 13.79, 29.20, 16.83, 22.84 and that there are differences of maximal and minimal MEP values 49.51 KJ/mol. In the colchicine molecule, the natural hybrid between brucine and colchicinemolecules. While the differ- orbital with considerable p-characters, high energies, and low

ence between the minimal MEP values of brucine and occupation numbers aren2 (O1), n2(O2), n2(O3), n2(O4), n2(O5)and

colchicine molecules is 3kcal/mol, the difference between their n2(O6). The corresponding occupation numbers and energies maximal MEP values is large and is equal to ∼16 kcal/mol. are, respectively: 1.92209, 1.93090,1.89667, 1.80778, 1.90042, Thus, MEP surfaces indicate that sensitivity towards electro- 1.86973 and À0.38746, À0.38834, À0.36217, À0.31410, philic attacks of brucine and colchicine molecules is rather À0.23466, À0.23386 a.u. For colchicine molecule, the low

similar; however sensitivity towards nucleophilic attacks seems energy orbital with high occupation numbers is n1(O1), n1(O2),

to be quite different in favor of colchicine molecule. Locations n1(O3), n1(O4), n1(O5)and n1(O6). The energies of these orbital of red and purple color in MEP surfaces of brucine and are, À0.49383, À0.50040, À0.49701, À0.51961, À0.68094 and colchicine molecules indicate sensitivity of mainly oxygen À0.67065 a.u. with high occupation numbers, 1.95407, 1.95163, atoms towards the electrophilic attacks. The lowest MEP values 1.96058, 1.96552, 1.97829 and 1.97679. Thus, for colchicine, a indicate that locations of oxygen atoms could be sensitive pure p-type lone pair orbital participates in the electron

towards electrophilic attacks. donation to the n2(O1)!π*(C13-C15), n2(O2)!π*(C19-C20), n2(O3)!π*(C19-C20), n2(O4)!π*(C23-C24), n2(O5)!σ*(C20-C24), n (O )! *( N -C )and n (N )! *(O C )interaction. The Natural Bond Orbital (NBO)Analysis 2 6 σ 7 22 1 7 σ 6- 22 significant intra-molecular interaction between the molecules NBO analysis using NBO 3.1 program[65] for understanding the provides evidence that the molecules are highly stable due to hyper conjugation effects and its effect on the of inter and intra intra-molecular hyperconjugation interactions. The higher val- molecular interactionsasitprovides information on both ues of second order perturbationenergies of the title virtual and filled orbital spaces. Interaction between idealized compounds predict strong hyper conjugative interaction Lewis structure and empty non-Lewis orbital is due to second- between the orbital containing the lone pair of electrons and order perturbation, corresponding to the intra-molecular bonds the neighboring C= Oanti-bonding orbital. of brucine and colchicine. Second-order perturbation theory analysis of Fock matrix for the intra molecular bonds of brucine Nonlinear Optical properties and colchicine are shown in the tables S4 and S5 (supporting information), and the Lewis and non-Lewis orbitals are given in NLO properties of amolecule provide usefulinformationfor tables S6 and S7 (supporting information). their use in optoelectronic applications[11],and it is due to the The important hyper conjugative interactions (intra-molec- differential interaction of the light with the materials. These

ular) in the brucine molecule are: C10-C16 from O1 of n2(O1)!σ* properties are very important in various electronic devices like (C10-C16), C26-C27 from O3 of n2(O3)!π*(C26-C27), N6-C21 from O2 of television, light-emitting diodes, etc. Nowadays, organiccom- n2(O2)!σ*(N6-C21), C26-C27 from O4 of n2(O4)!π*(C26-C27), C17-C18 pounds are dominating conventional semiconductor elec- from N5 of n1(N5)! σ*(C17-C18)and O2-C21 from N6 of n1(N6)!π* tronics. The polarizability and hyperpolarizability data obtained

(O2-C21)with stabilization energies, 6.63, 25.26, 8.04, 8.16, 6.79 from the Raman frequency calculations can be used for this and 57.86 KJ/mol. The natural hybrid orbital with p-character, purpose. Dipole moment, the polarizability, first hyperpolariz-

higher energy, and low occupation number in brucine are n2 ability and second hyperpolarizability values are respectively, À23 À30 À37 (O1), n2 (O2), n2 (O3)and n2 (O4). The corresponding energy 4.239 Debye, 4.196 ×10 ,3.323 ×10 , À23.746 ×10 e.s.u values and low occupation numbers are respectively, À0.28906, for brucine and 6.094 Debye, 4.124 ×10À23,2.880 ×10À30, À0.24058, À0.35736, À0.36270 a.u. and 1.92992, 1.87338, À25.168 ×10À37e.s.u for colchicine. The organic material urea is

1.91741, 1.91634. The orbitals having low energies are n1 (O1), typically considered as astandard material to compare the NLO

n1 (O2), n1 (O3)and n1 (O4). Energies and high occupation properties of the compounds of interest. First hyperpolariz- numbers are respectively, À0.58858, À0.67171, À0.50175, ability values ofbrucine and colchicine are 25.56 and 22.15 À0.49211 a.u. and 1.96725, 1.97428, 1.96337, 1.96285. Thus, in times that of urea,[66] indicating that the title compounds are brucine,anearly pure p-type lone pair orbital participates in with potential to show very high NLO properties can be

the electron donation to the n2(O1)!σ*(C10-C16), n2(O2)!σ*(N6- developed to be used in organic electronics. C21), n2(O3)!π*(C26-C27), n2(O4)!π*(C26-C27), n1(N5)!σ*(C17-C18) and n (N )! *(O C )interactions. Greater the values of 1 6 π 2- 21 Light Harvesting Efficiency second order stabilization energy, greater the conjugation of the molecule from the interaction between electron acceptors Light Harvesting efficiency(LHE) is atheoretical parameter, and donors. which can be employed to predict the use of acompound as a The significant intra-molecular hyper conjugative interac- potential photosensitizer in dye sensitized solar cells (DSSC)’s [67] tions in the colchicine molecule are: C13-C15 from O1 of . The LHE values for brucine and colchicine for arbitrary

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halogen substitutions in the benzene ring and found that both LUMO+2(56%). The theoretically calculated LHE values are brominated brucine and colchicine have more LHE values than 0.4737, 0.683, and 0.1312, respectively. TD-DFT analysis again that for other halogen substitutions. To find the LHE of shows three oscillations λmax slightlylower than the fluori- halogenated substitution in brucine and colchicine, the methyl nated derivative (fig SF5 but higher than that of unsubstituted

group attached to the carbon atoms C27 and C24 of brucine and brucine (See table 3). In this derivative, the electronic tran- colchicine respectively are replaced by halogen atoms Fluorine, sitions occur at 258.34,247.644,and 243/24 nm of oscillator Bromine, and Chlorine respectively. The simulated UV spectra strength of 0.2388. 0.5064 NS 0.0632, respectively. The major of brucine and chlorinated brucine are shown in figures SF3 contributions to the electronic spectra is due to HOMO-1 to and SF4 (supporting information) LUMO (42%), HOMO-1 to LUMO+1(26%), HOMOOMO to TD-DFT calculations show three important electronic tran- LUMO (12%) for the first, HOMO-1 to LUMO (32%), HOMO-1 to sitions in 256.6,245.6, and 239.5 nm of oscillator strength of LUMO+1(38%), HOMO to LUMO+1(14%) for the second and 0.2831, 0.4221, and 0.0575, respectively. The first transition is HOMO to LUMO+2(64%), HOMO to LUMO+3(11%) for the between HOMO-1to LUMO (22%), HOMO to LUMO (34%), third. The LHE data provided in the table11 shows 0.423, HOMO to LUMO+1(11%). The second is due to HOMO-1 to 0.68884, and 0.1354, which is aclear indicator that the LUMO (16%), HOMO-1 to LUMO+1(17%), HOMO to LUMO efficiency of light harvesting is progressively increasing. (18%), HOMO to LUMO+ 1(24%) and third is due to H-1 to Brominated brucine shows ared shift from other halogen- LUMO+2(24%), HOMO to LUMO+1(11%), HOMO to LUMO+ ated compounds with electronic excitations at 268.86, 251.32 2(35%). For brucine, the LHE values for different transitions are and 244.66 nm having 0.2411. 0.6424 and 0.000, respectively 0.4789, 0.6216, and 0.1240,respectively.The LHE values of (See table10). The electrons participate in HOMO-1 to LUMO brucineand colchicine and its various halogen substitutions (33%), HOMO to LUMO (55%) for first transition, HOMO-1 to are shown in table 3. LUMO+1(34%), HOMO to LUMO+1(56%) for second and In the case of compounds with Fluorine in the side aromatic HOMO-1 to LUMO+2(27%), HOMO to LUMO+ 2(40%) for the ring, there are also three transitions corresponding to wave- third.TheLHE values also show an increase in the harvesting length 265.29, 248.00 and 243.69 nm with oscillating 0.2788, power of the compounds. The values are 0.4260, 0.7722, and 0.5002 and 0.0611 respectively (table 3). For the first transition, 0.0014 for the different transitions. Thus it can be concluded the major contribution is due to HOMO-1 to LUMO (42%) and that brominated brucine is having more LHE than the others. HOMO to LUMO (33%) and for the second HOMO-1 to LUMO The various electronic transitionsand LHE of the different (11%), HOMO-1 to LUMO+1(39%), HOMO to LUMO+1(32%) halogenated derivatives of this compound are also analyzed, and finally for the third, HOMO-1 to LUMO+2(18%), HOMO to and the results discussed as follows. Pure colchicine showed three major electronic transitions at 351.90, 325.75, and 307.60 nm with oscillator strength 0.5873, 0.323, and 0,0031, Table 3. Light Harvesting Efficiency of brucine, colchicine and halogen respectively. The first transition near visible range is HOMO to substitutions LUMO (94%), second HOMO to LUMO+1(86%) and third No. Compound Energy Wavelength Osc. LHE HOMO-3 to LUMO (31%), HOMO-3 to LUMO+1(45%). The À1 (cm ) (nm) Strength molecule shows good light harvesting efficiency, which is 1Brucine 38969.75 256.61 0.2831 0.4789 evident from the values 0.7414, 0.5248, and 0.008, respectively 40711.92 245.63 0.4221 0.6216 (See table 3). Fluorinated colchicine show wavelength 334.00, 41745.13 239.55 0.0575 0.1240 300.40 and 297.52 with oscillator strength 0.4841, 0.0444and 2Fluorinated bru- 37693.78 265.29580.2788 0.4737 cine 0.3402 respectively. The data indicates that there is ablue shift 40322.35 248.0 0.5002 0.6839 of wavelength on fluorination. The first transition is homo to 41034.55 243.69 0.0611 0.1312 lumo(90%), second HOMO-6 to LUMO (10%), HOMO-6 to 3Chlorinated bru- 38707.62 258.34 0.2388 0.4230 LUMO+1(33%), HOMO-3 to LUMO+1(14%), HOMO to cine 40380.43 247.64 0.5064 0.6884 LUMO+1(10%) and the third HOMO to LUMO+ 1(69%). The 41110.36 243.24 0.0632 0.1354 intensity of HOMO to LUMO transition decreased on fluorina- 4Colchicine 28416.72 351.90 0.5873 0.7414 tion. The light harvesting values are 0.4260, 0.7722, and 0.0014. 30697.67 325.75 0.3231 0.5248 When substitution with chlorine, afurther blue shift is 32509.21 307.60520.0039 0.0089 5Fluorinated col- 29939.51 334.00680.4841 0.6720 observed with values at258.34, 247.64, and 243.25 nm with chicine oscillator strength 0.2388, 0.5064,and 0.0632. The LHE values 33288.34 300.40 0.0444 0.0972 are 0.2388, 0.5064,and 0.0632, which is higher than the 33610.97 297.52 0.3402 0.5431 fluorinated analog (Table 10). The transitions are due to HOMO 6Chlorinated col- 38707.62 258.34710.2388 0.4230 to LUMO (90%), H-6 to LUMO (10%), HOMO-6 to LUMO+1 chicine (33%), HOMO-3 to LUMO+1(14%), HOMO to LUMO+1(10%) 40380.43 247.64470.5064 0.6884 &HOMO to LUMO+ 1(69%) respectively .In the case of 41110.36 243.24770.0632 0.1354 brominated analog, the excitations are at 268.86,251.32, and 7Brominated col- 37193.71 268.86270.2411 0.4260 chicine 244.67 nm with oscillator strength 0.2411, 0.6424 and 0.0006 39789.22 251.32440.6424 0.7722 with corresponding LHE values 0.4260, 0.7722, and 0.0014. 40871.62 244.66850.0006 0.0014

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Table 4. Binding affinity, nature of interaction of docked ligands (brucine and colchicine) with selected proteins by molecular docking

Ligand PDBID of Protein Binding affinity kcal/mol Nature of Interaction Length of interaction (A) Interacted Amino-acid

Brucine 5JM5 -8.218 HBOND 1.9 TRY55 HBOND 2.63 GLN222 3U9U -3.809 HBOND 1.97 SER43 HBOND 2.06 THR94 4AOW -2.895 HBOND 1.79 ARG155 HBOND 2.3 GLN20 5NWH -2.469 HBOND 2.25 ARG51

Colchicine 3S7S -5.298 HBOND 2.11 ALA438 5NQR -4.5 HBOND 2.12 ALA195 HBOND 1.77 ARG196 HBOND 2.63 ARG51 3U9U -4.24 HBOND 1.98 THR94 HBOND 2.36 SER43 1BHJ -4.2 HBOND 2.24 THR599 1JNX -2.387 H-BOND 2HIE1822 Colchicine (Cardiovascular) 5G3 N-4.684 HBOND 2.03 VAL30

Thus among the colchicine analogs, the brominated system has more LHE (Table 3)

Molecular docking The docking calculations were performed by using quantum computational software Maestro (V18.4) in Schrodinger suite.[68–69] The ligand binds at the substrate’s active sites by weak non-covalent interactions. The binding affinity, nature and distance of interaction of docked ligands (brucine and colchicine) with amino acids of the selected proteins are tabulatedintable 4. The docked ligand and ligand interaction diagram for brucine and colchicine for various cancer proteins are shown figures 14–19. Brucine showed alowest binding

Figure 15. Ligand interaction diagram of brucine with 5JM5

Figure 14. Molecular docking of brucine (yellow dotted lines) showing the residue-hydrogen bond interactions with 5JM5.

affinity of À8.218 kcal/mol with cancer protein (PDBID 5JMJ) interacting with amino acid TRY55 through hydrogen bond at a Figure 16. Molecular docking of Colchicine (yellow dotted line) showing the distance of 1.9 A, while colchicine showed alowest binding residue-hydrogen bond interactions with 3S7S. affinity of À5.298 kcal/mol with cancer protein (PDBID 3S7S) and interaction with aminoacid ALA438 through hydrogen bond at 2.11 A.Colchicine showed abinding affinity of

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À4.68 kcal/mol with cardiovascular protein (5G3 N) and interacted with amino acid VAL30 through hydrogen bond at distance of 2.03 A.

Conclusions Molecular structure, vibrational spectra, UV, NBO, NLO, HOMO- LUMO and molecular docking studies of anticancerous alkaloids brucine and colchicinewere done using Density Functional Theory(DFT) method at the B3LYP/6-311G++(d, p) level using Gaussian-09 software and were supported by experiments. The results obtained from the quantum computational DFT method agrees well with the experimental results. Conformational analysis of the each of the title molecules were done by relaxed potential energy scans at two arbitrary selected dihedrals. The vibrational assignments of the title molecules were obtained Figure 17. Ligand interaction diagram of Colchicine with 3S7S from FT-IR and FT-Raman spectra by theoretical and experimental methods. From the MEP surfaces obtained by DFT method, the difference between the minimal MEP values of brucine and colchicine molecules is 3kcal/mol, the difference between their maximal MEP values is largeand is equal to ∼16 kcal/mol. The sensitivity towards electrophilic attacks of brucine and colchicine molecules is rather similar, however sensitivity towards nucleophilic attacks seems to be quite different in favor of colchicine molecule. The TD-DFT theory calculations of the electronic structures and electronic absorption spectra of colchicinewere studied and observed in UV-VIS spectrum of colchicine, that the maximum absorbed peak appear at 360 nm and band gap 3.4417 eV corresponding to transition HOMO-LUMO with 93% cause n!π*transition. Figure 18. Molecular docking of Colchicine (yellow dotted line) showing the HOMO-LUMO energy gap for colchicine is calculated as residue-hydrogen bond interactions with cardiovascularprotein 5G3 N. 3.649 eV and 4.831 eV for brucine, while colchicineisfound to be more chemically reactive than brucine, while chemical hardness is more for brucine than that for colchicine. Electro- philicity (G)ofcolchicine is much higher than that of brucine, which means the tendency to accept an electron pair is much higher for colchicine than that of brucine. NBO analysis on title molecules were performed and avery strong intra molecular hyper-conjugative interaction was observed with greater stabi- lizationenergy in both brucine and colchicine. The significant intra-molecular interaction between the moleculesprovides evidence that the molecules are highly stable due to intra- molecular hyper conjugation interactions. The NBOs analysis predicts strong hyper conjugative interaction between the lone pair electron orbital of nitrogen and the C=Oanti-bonding

orbital in brucine. From the VCD spectra, CH2 and CH3 groups were found to act as markers of aconfiguration having right polarization and left polarization respectively for the halogen substitutions of the title molecules. The stretching modes of aromatic rings and carbonyl stretching modes in combination

with CH2 and CH3 groups stretching modes at stereogenic centers generate VCD bands in the range 11400–1100 cmÀ1 are Figure 19. Ligand interaction diagram of colchicine with cardiovascular good markersofthe configuration showing right polarization protein 5G3 N. and left polarization for halogen substituted brucine which are remarkably efficient configuration markers for these chiral molecular systems enabling them for chiral applications. The first order hyper polarizability values are greater than that of

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urea molecule by 25.56 and 22.15 times for brucine and [12] H. Alkad, M. J. Khubeiz, J. Rajwa, Drug Targets 2018, 18,105–121. colchicinerespectively, thereby enabling the title molecules for [13] R. Bhushan,D.Gupta, Biomed. Chromatogr. 2004, 18,838–40. [14] N. Malkar, V. Kumar, J. Am. Oil Chem. Soc. 1998, 75,1461–1463. NLO applications. From LHE calculations of brucine and [15] N. Islam,S.Niaz, T. Manzoor, A. H. Pandith, Spectrochim. Acta. 2014, 131, colchicinewith halogen substitutions, the brominated system 461–470. was found to possess higher values of LHE. Molecular docking [16] A. Białonska, Z. Ciunik, Cryst.Eng.Comm. 2004, 6,276–279. shows that brucine showed alowest binding affinity of [17] H. J. Schneider, Angew.Chem. Int. Ed. Engl. 1991, 30,1417–1436. [18] A. Afzal, M. S. Thayyil, P. A. Sivaramakrishnan, M. K. Sulaiman, K. P. À8.218 kcal/mol with cancer protein with PDBID 5JMJ, while Safna Hussan, C. Yohannan Panicker, K. L. Ngai, J. Non-Crystalline Solids. colchicineshowed alowest binding affinity of À5.298 kcal/mol 2019, 508,33–45. with cancer protein with PDBID 3S7S and also showed a [19] S. Kim, J. KLee, S. OKang, J. H. Yum, S. Fantacci, FDAngelis, D. DCenso, binding affinity of À4.68 kcal/mol with cardiovascular protein Md. K. Nazeeruddin, M. Grätzel, J. Am. Chem. Soc. 2006, 128,16701– 16707. 5G3 N. Thus the molecular docking results points out that the [20] G. J. Hedley, A. Ruseckas, I. D. W. Samuel, Chem. Rev. 2016, 117,796–837. reported facts that brucine and colchicine have anti-cancer [21] Gaussian-09, Revision D.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. effects. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, Supporting Information Summary K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery Jr., J. E. Peralta,F.Ogliaro, The details of the title molecules, various experimental and M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, T. Keith, quantum computational methods used are provided in the R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi,M.Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, supporting information.Moreover, simulated UV spectra of the J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. title molecules, dipole moment –angle graph by relaxed Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, dihedralscan, NBO results showing the formation of Lewis and R. L. Martin, K. Morokuma,V.G.Zakrzewski, G. A. Voth, P. Salvador, J. J. non-Lewis orbitals, vibrational assignments,IR, Raman spectra Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas,J.B.Foresman, J. V. Ortiz, J. Cioslowski, D. J. 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