Nanotechnology allows the design and development of new release systems controlled at nanometer scale by computational chemistry studies in which hydrogels based on chitosan are studied for the adsorption of drugs in order to provide a better quality of life for patients in various medical treatments. The computational models generate a punctual analysis of the affinity of a drug for its receptor in addition to the study of pharmacokinetic and physicochemical properties using various external factors such as pH, temperature, ionic properties, etc. In this research, the adsorption of diclofenac on chitosan hydrogels was studied using Quantum mechanics with the objective of using it in patients with skin cancer, caused by the increase of cases to worldwide. The calculated properties were Gibbs free energy, QSAR properties such as partition coefficient, surface area, volume, mass as well as molecular vibrations before and after adsorption using the FTIR technique and finally the MESP corroborated the process of adsorption.

Keywords: Quantum Mechanics; FTIR; MESP; Gibbs; Skin Cancer

Introduction

During the 1980s, controlled release technology emerged as an alternative to traditional release mechanisms, with the main objective being optimal transport of the active ingredient, i.e. adequate doses released at specific sites, reducing side effects in other areas of the organism and maintaining a prolonged effectiveness [1]. A successful methodology for controlled release systems has been the use of polymer systems based in hydrogels consisting of a three–dimensional network of flexible polymer chains that absorb considerable amounts of water [2,3]. These materials aroused great scientific interest because of their biocompatibility characteristics attributed to the physical properties of the organism making them like living tissues. They are also characterized by their soft and elastic consistency and their low surface tension [2]. Also, they are used in adsorption process of different molecules, representing one of the main forms where the high energy interfaces are modified to decrease the total energy of the system. In the adsorption process it is important to consider two relevant aspects, a) the thermodynamics present in the energy of the system in equilibrium and b) the kinetics of the system, that is, the speed of the adsorption process [4]. Hydrogels are used in the pharmaceutical industry for the treatment of various diseases, for example cancer because is one of the most important health problems in the world [5]. Cancer is the uncontrolled growth of cells in the body [6]. Skin cancer is one of the most common neoplastic diseases in humans [7]. The most common types of skin cancer are basal cell carcinomas, squamous cell carcinomas, melanomas, and actinic keratoses.

In 2016 the American Cancer Society detected approximately 5.4 million basal cell and squamous cell cancers [8]. 95,360 new cases were estimated in the United States in 2017 [5]. One of the major factors causing this type of cancer is prolonged exposure to ultraviolet (UV) radiation particularly in people with white skin [9]. Therefore, it is more frequent to appear in areas of the skin more exposed to the sun such as the head, face, neck, hands and arms, although it may appear in any area of the body [10]. The treatment for skin cancer depends essentially on the type and degree of progress in which it is detected, among the main treatments are surgery, radiotherapy, chemotherapy and topical chemotherapy, among others [6].

Diclofenac (C14H11C12NO2) is one of the non–steroidal anti– inflammatory drugs with antipyretic and analgesic actions [11-12]. According to recent studies diclofenac is used for the prevention and treatment of some types of skin cancer since it can prevent the formation of new blood vessels needed by the development cancer cells, as well as block substances that produce inflammation and pain [13]. In previous studies, its efficacy has been demonstrated in the treatment of actinic keratosis, where it was applied as a gel containing 3% diclofenac and 2.5% hyaluronic acid [14]. The use of this drug in some cases has some adverse effects such as dry skin and eruptions where it is applied, among others, these effects are usually less than those caused by 5–Fluororacil (a drug used to treat some types of cancer skin) [15].

New systems of controlled release using computational chemistry allow for the design, transformation and calculate properties of the molecules at nano scale due to the study of atoms, molecules and macromolecules to simulate the interactions between the atoms [16,17]. Molecular modeling has become an important tool to complement scientific research, and is a fundamental way to understand complex systems or phenomena. In addition, it provides accessibility to regions of the parameter space that are inaccessible experimentally. It is also possible to determine properties of materials that have not yet been synthesized. For this reason, computational chemistry is complementary to experimental techniques and vice versa [18].

The computational methods are based on the calculation of the surfaces of potential energies, which are described as the interaction of forces between their atoms, which is why they differ in the way of calculating [19]. This includes mathematical methods and computational algorithms combined with the fundamental laws of physics [16]. Computational methods are divided in molecular mechanics and quantum mechanics. The first is based on simple models of molecular structure applying the laws of classical physics [20]. On the other hand quantum mechanics is based on the Schrödinger equation to describe a molecule as a direct treatment of the electronic structure which is subdivided into two classes: semi–empirical methods and AB initio methods (from the beginning) [21].

AMBER (Assisted Model Building with Energy Refinement) is a model based on molecular mechanics and is parameterized for macromolecules such as nucleic acids and proteins [22]. Moreover, semi–empirical methods are derived from the AB initio methods, relating certain elements of the Fock matrix with empirical or semi–empirical parameters [23]. Some semi–empirical methods are based on the Dewar approximation, among which are MINDO, AM1 and PM3. These only treat the valence electrons and use a minimal base set Slater type for atomic orbital’s to expand molecular orbital’s [24]. Parameterization method 3 (PM3) is a semi–empirical model that works similarly to the AM1 method since it uses the same equations with an improved set of parameters, but unlike this, PM3 slightly improves the results in both normal and in hydrogen bonds treatments [19].

This method takes the monocentric electronic repulsion integrals as parameters to be optimized (rather than obtained by means of atomic spectral data) [25]. The objective of this research was to determine the molecular analysis using the AMBER/PM3 hybrid model in the adsorption of diclofenac on chitosan hydrogels.

Methodology

Geometry Optimization

The calculation of the optimization geometry was carried out on a DELL I5 computer. Using the Hyperchem software, the AMBER model of molecular mechanics was firstly selected using the gradient conjugated method with a Polak–Ribiere algorithm and an RMS of 0.001 Kcal/Å–mol, respectively. Later, the calculation was performed using the PM3 model of quantum mechanics under the same conditions.

QSAR Properties

Hyperchem has the QSAR properties module in the Compute menu, where properties related to biological activity can be obtained. In drug delivery systems, the partition coefficient parameter (Log P) shows the octanol/water ratio to determine whether the molecule is hydrophilic or hydrophobic, evaluating the similarity of the drug with a pharmacological or biological activity that could make it a possible active drug in the human body.

FTIR Spectrum

From the Compute menu, the Vibration and rotation analysis option was selected and once the calculation is completed through the Compute–Vibration spectrum option, the FTIR spectrum was selected and the vibration mode is chosen by observing the different vibration modes at different wavelengths.

MESP

Once the FTIR spectrum has been obtained, the three–dimensional contour diagram, where the electronic distribution of the molecule, was obtained from the Compute menu and the plot molecular graphs option, with the objective of observing the nucleophilic zones and electrophiles, in addition to the distribution of the electron density of the HOMO and LUMO molecular orbital’s.

Results and Discussions

Structural and Energy Parameters

Figure 1 shows the optimization geometry of the molecules of diclofenac, chitosan and the interaction between both, obtained by the application of the AMBER/PM3 hybrid model, from which the corresponding thermodynamic data set are shown in Table 1. The negative value of the Gibbs free energy in the molecules individually shows a high stability in them, whereas in the interaction between the drug and the hydrogel it reflects a highly negative value showing an energetically favorable union between the OH groups of the chitosan with the diclofenac causing spontaneity in the reaction and indicating favorable direction to the products at a temperature of 298.15 K with slightly less stable and strong bonds than the molecules per individual [3,26,27]. According to the dipole moment of 11.91 debyes, diclofenac/chitosan hydrogel is characterized by being a highly polar molecule. The QSAR methodology is an important tool used to describe the biological activity relationships and the physicochemical characteristics of the molecules, mainly the logarithm of the partition coefficient (Log P).

Figure 1: Geometry molecular: a) Diclofenac, b) Hydrogel and c) Adsorption diclofenac/hidrogel.
Table 1: Thermodynamic properties obtained by AMBER/PM3 hybrid model.

Properties

Units

Diclofenac

Chitosan

Diclofenac/chitosan

Bond energy

Kcal/mol

– 3,308.10

– 20,815.47

– 24,130

Formation heat

Kcal/mol

– 52.420

– 1,574.88

– 1,633

Gibbs free energy

Kcal/mol

– 74,052.6

– 500,510

– 574,569

Dipolar  moment

Debyes

2.15

6.95

11.91

Diclofenac/chitosan hydrogel with a Log P value of –15.11indicate a hydrophilic character molecule with a considerable capacity of adsorption of the drug. It was also possible to determine the physicochemical characteristics of the molecules as the volume, mass and surface area according to these it is verified the capacity of adsorption and swelling of the hydrogel (Table 2) [28].

Table 2: QSAR properties

Properties

Units

Diclofenac

Chitosan

Diclofenac/chitosan

Surface area

Å2

455.64

1,517.77

1,698.5

Volumen

Å3

758.8

3,341.68

3,903.58

Mass

Amu

296.15

1,585.54

1,881.69

Log P

–––––

– 0.21

– 14.1

– 15.11

FTIR

Tables 3–5 show the main theoretical assignments of the diclofenac, chitosan and the diclofenac/chitosan respectively, determined by the AMBER/PM3 hybrid model.

Table 3 shows the vibrations of diclofenac molecule where of the OH stretching was localized at 3851 cm-1. Stretching of the methyl aliphatic groups was observed in the range of 3076–3046, 629–555 cm-1 respectively. NH stretching of the secondary amine was observed 3574–3418 cm-1, at 1975 cm-1 was attributed at carbonyl group stretching and at 715–698 cm-1 because of C–Cl stretching [29].

Table 3: FTIR vibrations for the diclofenac molecule.

Bond

Frequencies (cm-1)

Vibration type

OH

3851

Stretching

NH

3574-3418

Stretching

CH

3076–3046, 629–555

Stretching

C=O

1975

Stretching

C=C

1789–1347

Stretching

CO

1447

Stretching

OH

1241, 555–514

Wagging

CH

1049–781

Torsion

CCl

715-698

Stretching

In the case of the chitosan molecule the table 4 shows that, the OH stretching was appreciated at 3485–3442 cm-1, at 1554–1507 cm-1 as a flexion [27]. The stretching of the carbonyl bond of the acetyl group and of the genipine was localized between 2001 and 1950 cm-1 while the symmetric and asymmetric stretching vibration of the primary amine bonds were appreciated at 2458 cm-1 and 3408– 3994 cm-1, respectively.

Table 5 shows the diclofenac/chitosan cross–linking, the vibrational stretching modes present in the OH, C=O and CN groups at 3893–3753, 2001 and 1476–1456 cm-1 respectively, as well as the adsorption signals corresponding to the CH groups showing a vibration mode of torsion at 2001 cm-1 while the adsorption of diclofenac was observed like a torsion of the OH at 819 cm-1, from these signals it was possible to determine the adsorption of the diclofenac in the hydrogel since these signals ensure the existence of the cross–linking [27, 30,31].

Table 4: FTIR vibrations of hydrogel.

Bond

Frequencies (cm-1)

Vibration

OH

3485–3442

Stretching

HNH

3458

Symmetric stretching

HNH

3993–3408

Asymmetric stretching

CH

3235–3111

Stretching

HCH

3095–3093

Symmetric stretching

C=O

2001–1950

Stretching

C=C

1850

Stretching

CN

1643–1603

Stretching

OH

1554–1507

Flexion

CC

1457

Flexion

CO

1435–945

Stretching

Table 5: Diclofenac/hydrogel vibrations

Bond

Frequencies (cm-1)

Vibration

OH

3893–3753

Stretching (Hydrogel)

NH

3515–3359

Stretching (Hydrogel)

CH

3064–3052

Stretching (Diclofenac/hydrogel)

C=O

1970–1822

Stretching

CN

1476–1456, 1279–1270, 988

Stretching (Hydrogel)

CCO

1450

Asymetric stretching (Diclofenac)

OH

1437–1378, 1237

Torsion (Hydrogel)

CH

1222–1180, 1028–1002, 999–997

Torsion (Hydrogel)

CH

1001

Torsion (Diclofenac/hydrogel)

CH

959, 925–924, 780

Torsion (Diclofenac)

OH

823–822, 809–808, 727–663, 592–215

Torsion (Hydrogel)

OH

819

Torsion (Diclofenac/hydrogel)

COH

32

Torsion (Diclofenac/hydrogel)

CCl

207–206

Torsion (Diclofenac)

Electrostatic Potential Map

Electrostatic potential map (MEPS) is related to electron density as a descriptor to determine the sites of electrophilic attacks and nucleophilic reactions and hydrogen bonding interactions [26]. The importance of MEP lies in the fact that it simultaneously presents molecular size, shape and regions of positive, negative and neutral electrostatic potential in terms of color classification and is very useful in the investigation of the molecular structure with its relation of physicochemical property [30,32]. Figure 2a shows the MEPS of the molecule of diclofenac in which a homogeneous distribution is observed in its charges, the neutral region is represented in green color observed in the carbon chains characteristic of them, on the other hand the negative regions identified with the red color are located mainly in the oxygen atoms and in blue color the positive zones present in the hydrogen atoms with average values of –0.094 eV and 0.28 eV respectively [26-28,32]. Figure 2b shows the result of the MEPS obtained from the hydrogel crosslinked with genipine itself showing a homogeneous electron distribution with negative density at the oxygen atoms, this region being prone to an electrophilic attack due to the absence of electrons with an average value of –0.151eV. Finally, Figure 3 shows the distribution of electrostatic adsorption of diclofenac in chitosan, also showing a neutral trend with a slight modification in the intensity of the zones compared to the molecules per individual.

Figure 2: MESP about a) diclofenac and b) hydrogel.
Figure 3: Diclofenac/hydrogel mesp.

Conclusions

The adsorption process of diclofenac in hydrogels (chitosan/ genipin) was first verified by the Gibbs free energy which indicated spontaneity in the process and was verified by the value of the coefficient of partition that indicated an affinity to the water contained in the hydrogel. In addition, the optimization geometry was determined with the most stable conformation in which the formation of hydrogen bonds for the adsorption of diclofenac was appreciated. By means of the QSAR properties it is verified that the surface area and volume of the hydrogel presents the space required for the diclofenac molecule to be adsorbed.

The MESPs showed the electronic distribution before and after the adsorption. FTIR vibrations also indicated a displacement that was attributed to the energy released during the adsorption of diclofenac.

  1. Escobar J, García D, Zaldivar D, Katime I (2002) Hidrogeles. Principales caracteizticas en el diseño de sistemas de liberacion controlada de fármacos. Revista Iberoamericana Polimeros 3(3): 1-25.
  2. Mendizabal ME (2008) El uso de hidrogeles en medicina. La gaceta, ciencia & seguido 545: 15.
  3. Katime AIA, Katime TO, Katime TD (2005) Materiales inteligentes: Hidrogeles macromoleculares. Algunas aplicaciones biomédicas. Anal Real Soc Española Quím 4: 35-50.
  4. Josefina Viades Trejo (2013) Physicochemistry of Food (514).
  5. Siegel RL, Miller KD, Jemal A (2017) Cancer Statistics 2017. CA Cancer Journal for Clinicians 67(1): 7-30.
  6. American Cancer Society (2015) Cánceres de piel de células basales y de células escamosas.
  7. Lacy K, Alwan W (2013) Skin cancer. Medicine 41(7): 402-405.
  8. Kleinsmith LJ (2006) Principles of cancer biology. Pearson.
  9. Simões MC, Sousa JJS, Pais AA (2015) Skin cancer and new treatment perspectives: A review. Cancer Lett 357(1): 8-42.
  10. Jarell AD, Mully TW (2012) Basal cell carcinoma on the ear is more likely to be of an aggressive phenotype in both men and women. J Am Acad Dermatol 66(5): 780-784.
  11. Gan TJ (2010) Diclofenac: an update on its mechanism of action and safety profile. Curr Med Res Opin 26(7): 1715-1731.
  12. Altman R, Bosch B, Brune K, Patrignani P, Young C (2015) Advances in NSAID development: evolution of diclofenac products using pharmaceutical technology. Drugs 75(8): 859-877.
  13. Instituto Nacional Del Cancer.
  14. Wolf JE, Taylor JR, Tschen E, Kang S (2001) Topical 3.0% diclofenac in 2.5% hyaluronan gel in the treatment of actinic keratoses. Int J Dermatol 40(141): 709-713.
  15. Ha JH, Hwang DY, Yu J, Park DH, Ryu SH (2011) Onset of Manic Episode during Chemotherapy with 5-Fluorouracil. Psychiatry Investigation 8(1): 71-73.
  16. Jensen F (2007) Introduction to Computational Chemistry. Wiley.
  17. Leyva E, Estrín D (2011) Quimica Computacional. Simulaciones matemáticas del comportamiento de átomos y moléculas. Ciencia Hoy 21(124): 46-50.
  18. Cuevas GB (2003) La revolucionaria química computacional. Gaceta UNAM 3: 13.
  19. Young D (2001) Computational chemistry: A Practical Guide for Applying Techniques to Real-World Problems. Wiley-Interscience.
  20. Adamo C, Barone V (2002) Physically motivated density functionals with improved performances: The modified Perdew–Burke–Ernzerhof model. Journal of Chemical Physics 116(14): 5933-5940.
  21. Montenegro HA, Ceron NM, Rodriguez PJA (2008) Use of chemical methods to synthesize SnO2 -TiO2 nanopartícles. Rev Fac Univ Antioquia 44: 43-51.
  22. Case DA,  Cheatham TE, Darden T, Gohlke H, Luo R, et al. (2005) The Amber Biomolecular Simulation Programs. J Comput Chem 26(16): 1668-1688.
  23. Simkovic F, Thomas JMH, Keegan RM, Winn MD, Mayans O, et al. (2016) Residue contacts predicted by evolutionary covariance extend the application of ab initiomolecular replacement to larger and more challenging protein folds. IUCrJ 3(4): 259-270.
  24. Stewart B, Hylton DJ, Ravi N (2013) A Systematic Approach for Understanding Slater–Gaussian Functions in Computational Chemistry. Journal of Chemical Education 90(5): 609-612.
  25. Stewart JJ (2004) Optimization of parameters for semiempirical methods IV: Extension of MNDO, AM1, and PM3 to more main group elements. J Mol Model 10(2): 155-164.
  26. Delgadillo-Armendariz NL, Rangel-Vázquez NA, García-Castañón AI (2014) Spectroscopy analysis of chitosan-glibenclamide hydrogels. Spectrochim Acta A Mol Biomol Spectrosc 120: 524-528.
  27. Wee LL, Annuar MSBM, Ibrahim S (2011) Energetics of glucoamylase-catalyzed hydrolysis of commercial sago starch. Asia-Pacific J Mol Biol Biotech 19(4): 117-120.
  28. Delgadillo-Armendariz NL (2007) Determinar las propiedades estructurales de los principales componentes de una matriz polimérica de liberación controlada a base de quitosano: Polímero, entrecruzante, fármaco y solvente. M Sc. Thesis. Mexico.
  29. Shivakumar HN,  Desai BG, Deshmukh G (2008) Design and Optimization of Diclofenac Sodium Controlled Release Solid Dispersions by Response Surface Methodology. Indian J Pharm Sci 70(1): 22-30.
  30. Gunasekaran S, Rajalakshmi K, Kumaresan S (2013) Vibrational analysis, electronic structure and nonlinear optical properties of Levofloxacin by density functional theory. Spectrochim Acta A Mol Biomol Spectrosc 112: 351-363.
  31. Muthu S, Paulraj EI (2013) Molecular structure and spectroscopic characterization of ethyl 4-aminobenzoate with experimental techniques and DFT quantum chemical calculations. Spectrochim Acta Mol Biomol Spectrosc 112: 169-181.
  32. Sheela NR, Sampathkrishnan S, Kumar MT, Muthu S (2013) Quantum mechanical study of the structure and spectroscopic, first order hyperpolarizability, Fukui function, NBO, normal coordinate analysis of Phenyl-N-(4-Methyl Phenyl) Nitrone. Spectrochim  Acta A Mol Biomol Spectrosc 112: 62-77.