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QuantumMechanicalStudyofComplexationofDopamineandEpinephrinewithbeta-CyclodextrinUsingPM6,ONIOMandNBOAnalysis

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Copyright © 2012 American Scientific PublishersAll rights reservedPrinted in the United States of America

Journal ofComputational and Theoretical Nanoscience

Vol. 9, 1–6, 2012

Quantum Mechanical Study of Complexation ofDopamine and Epinephrine with �-Cyclodextrin

Using PM6, ONIOM and NBO Analysis

Rayenne Djemil∗ and Djameleddine KhatmiFaculty of Mathematics, Department of Chemistry, Informatics and Material Sciences,

BP, 401 Guelma’s University, Algeria

The structural aspects for complexation of dopamine (DA) and epinephrine (EP) to � CD wereexplored by using PM6, HF and ONIOM methods. The most stable structure was obtained at theoptimum position and angle. The complex orientation in which the catechol ring of the guest pene-trates into � CD cavity near primary hydroxyls is preferred in energy. The inclusion complex of DAwith � CD is more stable than that of EP. The structures show the presence of several intermolecu-lar hydrogen bond interactions that were studied on the basis of NBO analysis employed to quantifythe donor-acceptor interactions between the guest molecules and �-CD.

Keywords: Dopamine, Epinephrine, �-Cyclodextrin, Inclusion Complexes, Quantum Mechanics.

1. INTRODUCTION

Dopamine (DA 3, 4-dihydroxyphenethylamine DA) is animportant neurotransmitter molecule of catecholamines.It plays a very important role in the functioning of cen-tral nervous, renal, hormonal and cardiovascular systems.Its deficiency will lead to brain disorder such as Parkinson’sdisease and schizophrenia.1–5

Quantitative determination of DA is therefore impor-tant and has attracted much of interest of neuroscientistsand chemists. Electrochemical detection is a viable methodbecause DA is electrochemically active and electrochemi-cal methods have advantages such as simplicity speed andsensivity.6�7

However, in assay of DA his oxidation potential, thesemethods suffer from less selectivity due to the presenceof other species such as epinephrine (EP), or adrenalinewhich is structurally similar to DA and frequently existtogether in physiological fluids. Their oxidation potentialsare very close to each other on most solid electrodes.8�9

Therefore, it is a significant attempt to separatethe peak potentials of oxidation between DA and EPMany electrochemical approaches have been developedusing the pretreated electrodes, polymer-modified elec-trodes and monolayer-modified electrodes to solve theseproblems.10–13

∗Author to whom correspondence should be addressed.

Among these methods the type and attractive electrodemodifiers belongs to the cyclodextrin family.14–19 Natu-rally occurring cyclodextrins (CDs) have been widely stud-ied due to their ability to form inclusion complexes witha large variety of organic molecules. The �-, �- and�-cyclodextrin rings contain six, seven and eight glucoseunits respectively and exhibit conical with a hydrophobicinternal cavity and a hydrophilic exterior due to the pres-ence of hydroxyl groups. They are �-1, 4-linked cyclicoligomers of D-glucopyranose. Their well-known abilityto form supramolecular complexes with suitable organicand inorganic, neutral, and ionic substances has resultedin the design of selective electrodes.20–22

Cyclodextrin modified electrode, used to determine DAdisplayed excellent selectivity and sensitivity which couldseparate the DA and the other species oxidation peakpotentials and could detect DA at low concentration.20–22

Therefore, it is important to clarify the structures of theinclusion complexes from a viewpoint of molecular recog-nition within the hydrophobic cavities of CDs. The driv-ing forces for the complex formation have been attributedto hydrophobic interactions, van der Waals interactions,hydrogen bonding, and release of ring strain in the CDcavity.23

Computer modeling studies of cyclodextrin complexesare an important avenue in particular to understandingthe mechanism of complex formation, for interpretationthe experiments data and for elucidate structures.24 Thus,

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Quantum Mechanical Study of Complexation of Dopamine and Epinephrine with �-Cyclodextrin Djemil and Khatmi

in spite of its experimental detection, the geometry of the� CD-DA complex was not elucidated for technical diffi-culties related to its low solubility not making it possibleto carry out observations in NMR.25

We propose in this article a theoretical approach withthe aim to have some structural insights on the geome-tries of � CD-DA and � CD-EP complexes, to make acomparison between them and to evaluate the principalintermolecular interactions between guest molecules and� CD.In this paper, firstly we describe the formation of the

host-guest complexes between �-CD and catecholamineusing Parametric Model 6 (PM6)26 semi empirical methodimplemented in MOPAC 2009 program27 in order tolocalize the minimum energy structures as which is usedas starting structure for a subsequent optimization.After that, the structure is subjected to higher level cal-

culations, such Hartree-Fock/3-21G∗ level and ONIOM(our own N -layered integrated molecular orbital molecularmechanics) method, in order to approach the ideal geome-try and provide further insight into the different complex-ation properties of the guest molecule.Within the ONIOM procedure, two levels are defined:

density functional theory with B3LYP functional the6-31G∗ basis set were performed on the guest moleculeand Hartree-Fock method with 3-21G∗ basis set was usedfor the �-CD.The NBO population analysis procedure is employed to

quantify the donor–acceptor interactions between host andguest.

1.1. Computational Method

All the calculations were performed using the GAUSSIAN03 and MOPAC 2009 software packages. The startingstructures of � CD, dopamine and epinephrine wereconstructed with the help of the Cambridge chemBio3D Ultra (version 11.0, Cambridge software). Dopamineand epinephrine were optimized with B3LYP method at6-31G∗ level and the � CD was used without optimization.The method used by Liu and Guo was referred.28 The

glycosidic oxygen atoms of the � CD were onto theXY -plane, and their center was defined as the center ofthe coordination system. Then the guest was placed alongthe Z axis of the coordination system. The guest moleculeis allowed to enter and then pass through the � CDmolecule by steps with the ring to chain bond was coin-cident with Z axis. The relative position between the hostand the guest was measured by the Z-coordinate of thecommon carbon atom between cyclic part (catechol ring)and the chain of catecholamine.For the complexation process, the � CD molecule keeps

a fixed position while guest structure approached along theZ-axis toward the wide edge of the � CD torus.29�30

In order to find an even more stable structure of thecomplex, we rotate guest molecule to find the optimal

angle at each step, by scanning � circling around theZ-axis, at 20� intervals from 0� to 360� and scanningZ-coordinate at 1 Å intervals, � is the angles circlingaround Z-axis of the system and the bond of DA is coin-cident with Z-axis.Several energy expressions were used to characterize the

inclusion complexes. In addition to the absolute energyof the complex (the HF value as reported by Gaussian),the binding energy (�Ebinding) is defined as the differencebetween the energy of the complex and the energy ofthe individual components in their optimized geometry(Eopt�guest or Eopt�CD� from the complex

Ebinding = Ecomplex− Eopt��-CD+Eopt�guest�

The stabilization (complexation) energy upon complex-ation between guest and � CD was calculated for the min-imum energy structure as follows:

Ecomplexation = Ecomplex− E�-CD+Eguest�

Where: Ecomplex, E�CD and Eguest represent the ener-gies of the complex, the free guest and the free �-CD,respectively.The gas phase full optimizations were carried out at

PM6 and HF/3-21G∗. To improve the precision of the the-oretical results, ONIOM31–33 calculation was used to opti-mize the cyclodextrin molecule with HF at 3-21G∗ level,while treating the guest molecule using the three functionalof Lee et al. (B3LYP) with the split-valence 6-31G(d) basisset. The ONIOM energy is described as:33�35

EONIOM = Ehighmodel�+Elow real�−Elowmodel�

where E(high, model) is the energy of the guest (DAand EP) at B3LYP/6-31gd� level, E(low, real) is theenergy of the complex at the HF/3-21G∗ level, and E(low,model) is the energy of � CD at the HF/3-21G∗ level.The interaction between guest and � CD structures is

quantified on the basis of the NBO population analy-sis. The natural bonding orbitals (NBO) calculations wereperformed using NBO 3.1 program as implemented inthe Gaussian 03 package in order to understand varioussecond order interactions between the filled orbitals ofone subsystem and vacant orbitals of another subsystem,which is a measure of the intermolecular delocalization onhyperconjugation.36

2. RESULTS AND DISCUSSION

The inclusion complexes DA/� CD have two types of ori-entations Figure 1 which will be denoted head and tailorientations, respectively. Aromatic ring orientated to thecenter of mass of � CD, namely head orientation; aliphaticring orientated to the center of mass of � CD, namely tailorientation.

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Djemil and Khatmi Quantum Mechanical Study of Complexation of Dopamine and Epinephrine with �-Cyclodextrin

OHHNHO

HO

HO

HONH2

Fig. 1. Structures of: (a) epinephrine (b) dopamine.

The inclusion complex � CD/DA was carried out usingPM6 method to obtain the minimum energy structures.Considering the negative values of all complexation ener-gies we can say that the complexation process is energet-ically favorable. The most stable structure of DA/� CD isreached at Z = 6 Å for head orientation and at this pointthe binding energy BE is −20�79 kcal/mol. For tail orien-tation, the optimum position was found at −5 Å with BEis −21�38 kcal/mol figure.The energies of dopamine, � CD and the complexation

energies of their inclusion complexes obtained with PM6,HF/3-21G∗ and B3LYP/6-31G(d) methods are shown inTable I. The most stable structure can be obtained by com-paring energies of the two orientations of complexes aslisted in Table I. Thus, the complexation energies fromHF/3-21G∗ for head and tail orientations are −39�49 and−28�48 kcal/mol. These values show that the inclusioncomplex head orientation is more stable than tail orienta-tion. ONIOM (B3LYP/6-31G(d): HF/3-21G∗) results fol-low the same trend as the HF data. The complexationenergies from ONIOM calculations for head and tail orien-tations are −38�71 and −29�68 kcal/mol, respectively. Thecomplexation energies differences for two complexes fromHF/3-21G∗ and ONIOM (B3LYP/6-31G(d): HF/3-21G∗)are −11 and −9�04 kcal/mol, respectively.The energies of epinephrine, � CD and the complexa-

tion energies of their inclusion complexes are summarizedin Table II. The complexation energies differences fortwo complexes from HF/3-21G∗ and ONIOM (B3LYP/6-31G(d): HF/3-21G∗) are −20�68 and −20�99 kcal/mol,respectively. The energy gap between the two orientationsis more important than that of DA.These values obtained with HF and ONIOM (B3LYP/6-

31G(d): HF/3-21G∗) show that the head orientation is more

Table I. The HF/3-21G∗ and the ONIOM (B3LYP/6-31G(d): HF/3-21G∗) complexation energies of the inclusion complexes � CD/DA.

Orientation Ecplx (a.u) ECD (a.u) EDA (a.u) Ecomp kcal/mol

PM6Head −2�6418 −2.4990 −0�1096 −20�79Tail −2�6427 −2.4990 −0�1096 −21�38

HF/3-21G∗

Head −4738�563 −4227�8443 −510�6553 −39�49Tail −4738�545 −4227�8443 −510�6553 −28�48

ONIOMHead −4744�5587 −4227�8443 −516�6527 −38�71Tail −4744�5443 −4227�8443 −516�6527 −29�68

Table II. The HF/3-21G∗ and the ONIOM (B3LYP/6-31G(d): HF/3-21G∗) complexation energies of the inclusion complexes � CD/ EP.

Orientation Ecplx (a.u) ECD (a.u) EEP (a.u) Ecomp kcal/mol

PM6Head −2�7110 −2�4990 −0�1768 −22�05Tail −2�7105 −2�4990 −0�1768 −21�69

HF/3-21G∗

Head −4851�812 −4227�8443 −623�9111 −35�51Tail −4851�779 -4227�8443 −623�9111 −14�83

ONIOMHead −4859�076 −4227�8443 −631�1744 −35�79Tail −4859�042 −4227�8443 −631�1744 −14�79

stable than tail orientation. The inclusion complex of DAwith the � CD is more stable than that of EP.

2.1. NBO Analysis

In order to obtain additional insight into the nature of inter-action between guest and � CD, we undertook a popula-tion analysis using the NBO method. The advantages ofthis approach are that it concentrates almost the molecularenergy and molecular change within structures that mimicthe traditional lewis molecular of strictly localized bonds.The very small residual energetic and charge contributionsin saturated systems are largely due to delocalized, non-covalent interactions between bonding and antibondingorbitals of the NBO approach. This non-covalent bonding-antibonding interaction gives the quantitative descriptionof hyperconjugation.37

In terms of NBO approach this is expressed by meansthe second order perturbation interaction energy E2�

involving neighboring orbitals. The selected electron donororbitals, electron acceptor orbitals and their correspondingsecond-order interaction energies of the E2� indicate theintensity of the interaction between the electron donor andelectron acceptor orbitals. Thus, more great value of theE2� more the tendency of donor orbital is bigger.38

The electron donor orbitals, electron acceptor orbitalsand corresponding E2� energies, bond distances andangles between the hydrogen bonding are also shown inTables III and IV.The structures of the energy minimum obtained with

ONIOM calculations show the presence of several inter-molecular hydrogen bond interactions as shown inFigures 3 and 4. In the present study the hydrogen bondanalysis is carried out using NBO approach.In head orientation, the catechol ring of both complexes

is included deeply in � CD cavity from the wide secondaryhydroxyl group so that the hydroxyl groups was close to6-OH of � CD. This disposition allows forming two hydro-gen bonds between the hydroxyls catechol and oxygens ofthe narrow edge of the � CD, as donor or as acceptor: forDA, (O47 · · ·H162 O154 and O47 H129 · · ·O155) andfor EP (O47 · · ·H161 O148 and O55 · · ·H162 O149).At the wide secondary face, two hydrogen bonds type of

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Table III. The electron donor orbitals, electron acceptor orbitals and corresponding E2� energies, distances and angles for head and tail orientations(DA/�-CD).

B3lyp/6-31 G∗ mpw1pw91/6-31 G∗ ONIOM

Donor Acceptor d (Å) Angle (�) E2� (kcal/mol) d (Å) Angle (�� E2� (kcal/mol)

HeadLpO47 BD∗O154-H162 1�646 167�4 1�65 1�70 1�646 167�4 1�51LpO69 N158-H169 2�162 166�7 3�33 3�1 2�162 166�7 2�75LpO155 O47-H129 1�907 135�4 0�44 0�53 1�907 135�4 0�47LpO54 C150-H160 2�570 144�9 0�70 0�69 2�570 144�9 1�05LpO59 C157-H167 2�766 132�9 0�44 0�43 2�766 132�9 0�47LpO154 C41-H124 2�326 167 1�42 1�43 2�326 167 1�97

TailLpO75 O155-H163 1�699 169�7 5�43 5�53 1�704 168�6 1�35O154 C23-H103 2�540 173�2 1�46 1�45 2�524 173�5 2�02O155 C35-H103 2�360 147�1 1�34 1�34 2�315 148�4 2�13

Table IV. The electron donor orbitals, electron acceptor orbitals and corresponding E2� energies, distances and angles for head and tail orientations(EP/�-CD)

b3lyp/6-31G∗ mpw1pw91/6-31G∗ ONIOM

Donor Acceptor d (Å) Angle (�) E2� (kcal/mol) d (Å) Angle (�� E2� (kcal/mol)

HeadLpO47 BD∗O148-H161 1�751 153�9 1�71 1�751 153�9 1�50

1�81LpO54 BD∗O152-H167 2�363 111�6 1�43 2�363 111�6 2�20

1�43LpO55 BD∗O149-H162 2�367 162�3 2�54 2�367 162�3 4�01

2�51LpO152 BD∗O53-H133 1�847 161�6 2�08 1�847 161�6 1�71

2�22Tail

LpO54 BD∗O152-H167 1�780 166�2 1�06 1�780 166�2 0�631�08

LpN151 BD∗C15-H94 2�726 162�9 1�28 2�726 162�9 1�551�30

LPN151 BD∗C21-H101 2�527 160�8 1�6 2�527 160�8 2�151�70

(a) (b)

Fig. 2. The two approaches of DA from the wide secondary cyclodextrin cavity: (a) head orientation and (b) tail orientation.

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–6 –4 –2 0 2 4 6–26

–24

–22

–20

–18

–16

–14

–12

Com

plex

atio

n en

ergy

(K

cal/m

ol)

Z (A)

Head orientation Tail orientation

Fig. 3. Binding energies of dopamine/� CD inclusion complexes at dif-ferent position Z (Å) for both orientations head and tail using PM6method.

Fig. 4. Structures numbered of: (a) epinephrine (b) dopamine.

(a)

(b)

Fig. 5. Geometrical structures optimized with ONIOM method forDA/� CD complexes: (a) head orientation (b) tail orientation.

(a)

(b)

Fig. 6. Geometrical structures optimized with ONIOM method for EP/�CD Complexes: (a) head orientation (b) tail orientation.

interaction between the third hydroxyl of EP O152 withsecondary hydroxyls O54 and O53 of � CD as donor and asacceptor (O54 · · ·H167 O152 and O152 · · ·H133 O53)are observed to keep catechol ring inside the cavity, for DA,one hydrogen bond is established between oxygen atom(O69) of � CD and hydrogen atom (H169) of H169 N158bond and that allows to keep the chain group inside thecavity.For the tail orientation, the guest was partially incorpo-

rated in cavity, for EP, the chain establish two H-bondsN · · ·C H with the large face of the cavity (N151 asacceptor), the third hydroxyl catechol O152 maintainedthis position by an hydrogen bond (O152 H152 · · ·O54)with the OH wide edge of cavity. For DA, the part of cate-chol penetrates in the cavity near the secondary hydroxylsand the chain left out from narrow primary face. In thisstructure, one strong O · · ·H O hydrogen bond was estab-lished (O75 · · ·O155 H163).A number of type hydrogen bonds C H · · ·O stabi-

lize these structures, with energy values typically those ofweak.

3. CONCLUSION

The inclusion process for dopamine and epinephrine with� CD was studied according two orientations using quan-tum mechanics PM6, HF level theory with 3-21G∗ basisset and ONIOM (B3LYP/6-31G(d): HF/3-21G∗) hybrid

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calculations. The minimum energy structure for each ori-entation was localized with PM6 method. The affinity ofthese minimum energies structures was carried out withHF and ONIOM methods. The HF and ONIOM resultsshow that the head orientation is preferred according tocomplexation energy, in which the catechol ring is deeplyincluded into the hydrophobic cavity of � CD. However,the ONIOM method allowed bettering understanding thetype of host-guest interactions. The NBO population anal-ysis show that the driving forces for the complexes for-mation was due to the intermolecular hydrogen bonds inaddition to the hydrophobic interactions. This study showsthat the DA form inclusion complex with � CD more sta-ble than EP.

Acknowledgment: This paper was supported by Alge-rian Ministry of Higher Education and ScientificResearch and General Direction of Scientific andtechnologic research as a part of projects CNEPRU(No: E01520080026 and No: D01520100004) and PNR(8/u24/4814). We acknowledge the department of chem-istry at Guelma’s university in which this work wasperformed.

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