Infrared Spectrum and Sites of Action of Sanguinarine by Molecular Mechanics and ab initio Methods

Alkaloids occupy an important position in chemistry and pharmacology. Among the various alkaloids, berberine and coralyne of the protoberberine group, sanguinarine of the benzophenanthridine group, and aristololactam-b -d-glucoside of the aristolochia group have potential to form molecular complexes with nucleic acid structures and have attracted recent attention for their prospective clinical and pharmacological utility. Sanguinarine is an alkaloid studied in the treatment of cancer cell proliferation. Found in several plants, is used in traditional medicine from several countries with Mexico and India in the natural treatment of wounds, conjunctivitis and as hallucinogen. Is a toxic quaternary ammonium salt from the group of benzylisoquinoline alkaloids. It is extracted from some plants, including bloodroot (Sanguinaria canadensis), Mexican prickly poppy (Argemone mexicana Linn) Chelidonium majus and Macleaya cordata. It is also found in the root, stem and leaves of the opium poppy but not in the capsule. Sanguinarine is a toxin that kills animal cells through its action on the Na+-K+ATPase transmembrane protein. Due to the diverse properties of this alkaloid, via computational methods was made using quantum chemistry to try to clarify some molecular properties that characterize its main sites of action as a drug. A study was made on a molecular structure of the sanguinarine, by Molecular Mechanics, PM3, Hartree-Fock, Density Functional Theory and Møller-Plesset. For calculations a cluster of six computers was used with Prescott-256 Celeron© D processors. The first principles calculations have been performed to study the equilibrium configuration of Sanguinarine molecule. Several physical properties have been calculated, including formation enthalpies, entropies, dipole moments, and the infrared emission/absorption spectrum. The results showed that the main site of molecular interaction was determined to be the hydrogen atoms. This has a strong antioxidant potential in its structure. It probably interacts with free radicals reducing their carcinogenic effect on cells. A study of the infrared spectrum complemented the paper. Absorption peaks in the infrared spectrum at 1000 cm -1 , for calculation MP2/6-31G and, 1240 and 1450 cm -1 for B3LYP/6-311G ** were obtained. The MP2 and B3LYP methods showed good results for the infrared absorption spectrum. Although the base used in the MP2 method is less accurate, compared to the B3LYP whose base xxx has more accurate and broader functionalities, they are approximately equal for frequency peaks located in the 1060.6 cm -1 and 991.1 cm -1 range.


Introduction
Sanguinarine has been shown to inhibit proliferation of several types of human cancer cell including multidrugresistant cells, whereas it has minimal cytotoxicity against normal cells such as neutrophils and keratinocytes.Is an alkaloid studied in the treatment of cancer cell proliferation [1] Found in several plants with Argemone mexinana Linn, the plant is used in traditional medicine from several countries with Mexico and India in the natural treatment of wounds, conjunctivitis and as hallucinogen [2].
It was reported to inhibit proliferation of different types of cancer cell, including human prostate carcinoma cells (LNCaP, PC-3 and DU145), multidrug-resistant uterine cervical carcinoma cells, human epidermoid carcinoma A431 cells, human erythroleukemia K562 cells, and the premalignant cell-line HaCaT [8,9].However, sanguinarine was found to be less toxic towards normal cells such as normal human epidermal keratinocytes [5].
Alkaloids occupy an important position in chemistry and pharmacology.Among the various alkaloids, berberine and coralyne of the protoberberine group, sanguinarine of the benzophenanthridine group, and aristololactam-b -dglucoside of the aristolochia group have potential to form molecular complexes with nucleic acid structures and have attracted recent attention for their prospective clinical and pharmacological utility.[14] Dihydrosanguinarine (DHSA), a benzophenanthridines sanguinarine (SA) biosynthetic precursor and a less toxic benzophenanthridine, was also identified, based on chromatographic properties and further confirmed by gas chromatography coupled to mass spectrometry.The benzophenanthridines sanguinarine (SA) and dihydrosanguinarine (DHSA) display antimicrobiae and cytotoxic activities.These alkaloids are accumulated in roots and mature seeds, whereas berberine, a protoberberine alkaloid with antiviral properties, is accrued both in aerial and underground tissues.[15] The alkaloids Allocryptopine, Dihydrosanguinarine, Protopine and Sanguinarine have density similar negative and positive charges.Already the main local density of positive charges are the hydrogens atoms distributed by molecular contours, and the negative oxygens atoms in its longitudinal ends, and cross for Allocryptopine and Protopine.[2] Due to the diverse properties of this alkaloid, via computational methods was made using quantum chemistry to try to clarify some molecular properties that characterize its main sites of action as a drug.A study was made on a molecular structure of the sanguinarine, by Molecular Mechanics [16][17][18][19][20][21][22][23][24][25][26][27][28][29], PM3 [28], Hartree-Fock [28,30,31], Density Functional Theory [28] and Møller-Plesset [28].For calculations a cluster of six computers was used with Prescott-256 Celeron© D processors 1.The first principles calculations have been performed to study the equilibrium configuration of Sanguinarine molecule.Several physical properties have been calculated, including formation enthalpies, entropies, dipole moments, and the infrared emission/ absorption spectrum.A study of the infrared spectrum complemented the work.
The main software used for the ab initio calculationsapplying the quantum chemistry was the GAMMES [16][17][18][19][20][21][22][23][24][25][26][27][28][29].Others computational dynamics software, publishing, viewing molecules were used, such as Avogadro, ChemDraw, GaussView, HyperChem, Mercury, Molden.[28] Section 2 briefly describes the methods used in molecular and ab initio mechanics, as well as the equipment usedcomputers.The best computational methods available are briefly explained.Obviously, the greater the function used in the calculation, the greater the requirement of the equipment to be employed, as well as the computational computation time.
In section 3 it is presented how the initial optimization geometry of the sanguinarine molecule and some of its physicochemical properties found in the liperature were performed.
It then follows to the discussions section, conclusions, tables, figures and annex.It finally presents a file in.pdb format (protein date bank), for the verification of the readers.

Molecular Dynamics
The great computational speed of molecular mechanics allows for its use in procedures such as molecular dynamics, conformational energy searching, and docking.All the procedures require large numbers of energy evaluations.Molecular mechanics methods are based on the following principles: Nuclei and electrons are lumped into atom-like particles; Atom-like particles are spherical (radii obtained from measurements or theory) and have a net charge (obtained from theory); Interactions are based on springs and classical potentials; Interactions must be preassigned to specific sets of atoms; Interactions determine the spatial distribution of atom-like particles and their energies; Note how these principles differ from those of quantum mechanics.[30][31][32][33][34] In short the goal of molecular mechanics is to predict the detailed structure and physical properties of molecules.Examples of physical properties that can be calculated include enthalpies of formation, entropies, dipole moments, and strain energies.Molecular mechanics calculates the energy of a molecule and then adjusts the energy through changes in bond lengths and angles to obtain the minimum energy structure.[30,32,33,34] The steric energy, bond stretching, bending, stretch-bend, out of plane, and torsion interactions are called bonded interactions because the atoms involved must be directly bonded or bonded to a common atom.The Van der Waals and electrostatic (qq) interactions are between non-bonded atoms.[28,[32][33][34][35][36][37]

Hartree Fock
The Hartree-Fock self-consistent method is based on the one-electron approximation in which the motion of each electron in the effective field of all the other electrons is governed by a one-particle Schrodinger¨ equation.The Hartree-Fock approximation takes into account of the correlation arising due to the electrons of the same spin, however, the motion of the electrons of the opposite spin remains uncorrelated in this approximation.The methods beyond self-consistent field methods, which treat the phenomenon associated with the many-electron system properly, are known as the electron correlation methods.One of the approaches to electron correlation is the Møller-Plesset (MP) perturbation theory in which the Hartree-Fock energy is improved by obtaining a perturbation expansion for the correlation energy.[38] However, MP calculations are not variational and can produce an energy value below the true energy.[39,40] Another first principles approach to calculate the electronic structure for many-electron systems is the Density Functional Theory (DFT).[40] In this theory, the exchangecorrelation energy is expressed, at least formally, as a functional of the resulting electron density distribution, and the electronic states are solved for self-consistently as in the Hartree-Fock approximation.[39][40][41][42] The Density Functional Theory is, in principle, exact but, in practice, both exchange and dynamic correlation effects are treated approximately.[43] A hybrid exchange-correlation functional is usually constructed as a linear combination of the Hartree-Fock exact exchange functional, and any number of exchange and correlation explicit density functionals.The parameters determining the weight of each individual functional are typically specified by fitting the functional's predictions to experimental or accurately calculated thermochemical data, although in the case of the "adiabatic connection functionals" the weights can be set a priori.[28,44]

B3LYP
The B3LYP (Becke, three-parameter, Lee-Yang-Parr) [45,46] exchange-correlation functional is: Are generalized gradient approximations: the Becke 88 exchange functional [47] and the correlation functional of Lee, Yang and Parr [48] for B3LYP, and E c DA is the VWN localdensity approximation to the correlation functional.[49] The three parameters defining B3LYP have been taken without modification from Becke's original fitting of the analogous B3PW91 functional to a set of atomization energies, ionization potentials, proton affinities, and total atomic energies.[50] The first principles methods -ab initio (i.e.HF and DFT) discussed above can be implemented with the aid of the GAMESS set of programs to study the electronic structure and to determine the various physical properties of many-electron systems.[51] A basis set is the mathematical description of the orbitals within a system (which in turn combine to approximate the total electronic wavefunction) used to perform the theoretical calculation.[52] 3-21G, 3-21G*, 6-31G, 6-31G*, 6-31G**, 6-311G, 6-311G*, 6-311G** are the basis sets used in the calculations.The functional Becke-style one parameter functional using modified Perdew-Wang exchange and Perdew-Wang 91 correlation is used for DFT Calculations.[43,53] The SCF method and extensions to it are mathematically and physically considerably more complicated than the oneelectron methods already discussed.Thus, one normally does not perform such calculations with pencil and paper, but rather with complicated computer programs.Terms like "Hartree-Fock" or "correlation energy" have specific meanings and are pervasive in the literature.[54] The vast literature associated with these methods suggests that the following is a plausible hierarchy:
The first principles calculations have been performed to study the equilibrium configuration of Sanguinarine molecule using the Hyperchem 7.5 Evaluation [65], Gaussview v.5 a general molecular and electronic structure processing program, an advanced semantic chemical editor, visualization, and analysis platform [66] and GAMESS is a computational chemistry software program and stands for General Atomic and Molecular Electronic Structure System [51] set of programs.The first principles approaches can be classified into two main categories: the Hartree-Fock approach and the density functional approach.[39] 3. Fundamentals

Geometry Optimization
The dynamic was held in Molecular Mechanics Force Field (Mm+), Equation ( 1), computed geometry optimization molecular at algorithm Polak-Ribiere [63], conjugate gradient, at the termination condition: RMS gradient [64] of 0.1 kcal/A.mol or 405 maximum cycles in vacuum.Molecular properties: electrostatic potential 3D mapped isosurface, mapped function range, minimum 0.144 at maximum 0.734 and minimum -0.008 at maximum +0.216, Mm+ and PM3 methods, respectively.For display range legend, from positive color lime green to negative color pink, total charge density contour value of 0.05, gourand shaded surface.

Discussions
The Figures (1-b) and (1-d) show the distribution of charges in the sanguinarine molecule.The Figure (1-b) represents the molecular dynamics by the Mm+ method, according to Equation (1).The charges range from 0.144, in pink, to 0.734, in lime green, to the distribution of charges in the molecule.
The Figure (1-d) represents the molecular dynamics by the PM3 method.The load distribution in the molecule ranges from -0.008 negative, in pink, to +0.216 positive, in lime green, respectively.
By the Mm+ method, Figure (1-b), this indicates that the molecule has a positive potential, having a positive variation of charge distribution, ∆δ = +0.59,being strongly antioxidant.Likewise in Figure (1-d), by the PM3 method, a positive charge distribution variation, ∆δ = + 0.224, of lesser intensity, but more suitably distributed, occurs.This method represents the most appropriate displacement of charges in the molecule.As a result we have a better view of the action sites of the molecule.The Mm+ method is inappropriate for the representation of the displacements of charges in the molecule, but efficient in the deduction of an antioxidant molecule.
Table 1.Thermochemical parameters of the molecule Sanguinarine obtained by ab initio methods [28].In Figure (1-d) it can be verified that the sites of antioxidant action are localized and distributed in the hydrogen atoms throughout the length of the molecule, presenting a strong electric potential of interaction in these sites.The nitrogen atom at the center of the molecule exerts the potential for moderate interaction compared to the hydrogens.Already the four oxygen atoms, located at both ends of the molecule, distributed two by two, have a negative potential, -0.008, represented in pink, also providing an antioxidant interaction, free radicals.
Figure 3.The above figure represents the transmittance (%) in function with wavelength cm -1 for the infrared spectrum of the sanguinarine molecule, after optimization of the geometry with the method/base, MP2/6-31G [28,76,77] obtained using computer programs GAMESS [51].The image was generated using the Avogadro program.[76].

Conclusions
The main sites of interactions of the molecule was finded.This has a strong antioxidant potential in its structure.It probably interacts with free radicals reducing their carcinogenic effect on cells.
The sites of antioxidant action are localized and distributed in the hydrogen atoms throughout the length of the molecule, presenting a strong electric potential of interaction in these sites.The nitrogen atom at the center of the molecule exerts the potential for moderate interaction compared to the hydrogens.Already the four oxygen atoms, located at both ends of the molecule, distributed two by two, also providing an antioxidant interaction, free radicals.
The infrared spectrum for the method/base, MP2/6-31G has absorption peaks at the frequencies main 1060.6 cm -1 and for the method/base, B3LYP/6-311G** 1027.5 and 991.1 cm - 1 , being approximately equal in both methods.
The MP2 and B3LYP methods showed good results for the infrared absorption spectrum.Although the base used in the MP2 method is less accurate, compared to the B3LYP whose base 6-311G** has more accurate and broader functionalities, they are approximately equal for frequency peaks located in the 1060.6 cm -1 and 991.1 cm -1 range.