Investigation of resonance assisted hydrogen bond (RAHB) in some pyridine-based complexes: Intramolecular and intermolecular interactions

Investigation of resonance assisted hydrogen bond (RAHB) in some pyridine-based complexes: Intramolecular and intermolecular interactions

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Journal Pre-proof Investigation of resonance assisted hydrogen bond (RAHB) in some pyridine-based complexes: Intramolecular and intermolecular interactions Pouya Karimi, Mahmoud Sanchooli PII:

S0022-2860(19)31655-2

DOI:

https://doi.org/10.1016/j.molstruc.2019.127546

Reference:

MOLSTR 127546

To appear in:

Journal of Molecular Structure

Received Date: 4 October 2019 Revised Date:

15 November 2019

Accepted Date: 6 December 2019

Please cite this article as: P. Karimi, M. Sanchooli, Investigation of resonance assisted hydrogen bond (RAHB) in some pyridine-based complexes: Intramolecular and intermolecular interactions, Journal of Molecular Structure (2020), doi: https://doi.org/10.1016/j.molstruc.2019.127546. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.

There is intra- and intermolecular resonance assisted hydrogen bond (RAHB) in the pyridine- based complexes that highlight the role of R groups with π-conjugated system in overall stability of the complexes.

Investigation of resonance assisted hydrogen bond (RAHB) in some pyridine-based complexes: Intramolecular and intermolecular interactions

Pouya Karimi∗ and Mahmoud Sanchooli

Department of Chemistry, Faculty of Science, University of Zabol, P.O. Box 98615-538, Zabol, Iran

Abstract Intra- and intermolecular hydrogen bonding interactions in some pyridine-based complexes that have R groups without (H, −C2H5, and −C4H9) and with (−C2H3, −C4H5, −C6H7, and −C8H9) π-conjugated system were investigated using quantum mechanical calculations to know role of resonance on strength of interactions. Geometrical parameters and electronic properties based on atoms in molecules (AIM) analysis were studied to interpret the interactions. Also, aromaticity of the rings of the complexes was evaluated using aromatic fluctuation index (FLU) and para-delocalization index (PDI) to connect the mentioned benchmark to energy of the hydrogen bond interactions. Indeed, localized molecular orbital energy decomposition analysis (LMOEDA) was employed to realize contribution of components of energy in stability of the complexes.

Keywords: Hydrogen bond; RAHB; pyridine; AIM; LMO-EDA



Corresponding author ; E-mail: [email protected](P. Karimi) 1

Introduction Hydrogen bonds have constructive role on existence of protein’s secondary structure, DNA, and RNA [1-4]. Also, these interactions are important in biological systems [5], protein folding [6], and catalysis [7]. Indeed, hydrogen bonds play an imperative function in determining the specificity of the ligand-target binding [8]. Accordingly, hydrogen bonds influence many biological, physical, and chemical processes [9-11]. The resonance-assisted hydrogen bond (RAHB) refers to cooperative interplay between π-delocalization and hydrogen bond strength [12,13]. Formation of intramolecular hydrogen bonding has a main effect on molecular properties, geometries, and potency of drugs [14]. The role of RAHB in stability and strength of intramolecular hydrogen bond was evaluated for some enolizable structures [15]. Moreover, Gilli et al. investigated intramolecular N-H…O RAHB in some Heterodienes [16]. Also, formation of intramolecular hydrogen bonds in malonaldehyde and its saturated analogue 3-hydroxy propanal has been theoretically studies [17]. Results indicate reducing of the hydrogen bond distance that assisted by resonance in the π electron system. Indeed, the influence of π electron system on the polarizability of the intramolecular hydrogen bond in malonaldehyde has been explored [18]. Results confirmed effect of delocalization on unusual strength of the mentioned hydrogen bond. Mo and coworkers studied origin of nonadditivity in RAHB and showed that both σ-framework and π-resonance contribute to the nonadditivity in RAHB [19]. Also, RAHB was examined in some substituted conformers that have potential of formation of intramolecular hydrogen bonding [20]. Furthermore, a quantitative view of the role of π-electron delocalization on hydrogen bonding has been previously studied in systems with oxygen, nitrogen, and sulfur as acceptor atoms [21].

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Grabowski and coworkers introduce universal descriptors of the hydrogen bond strength based on atoms in molecules (AIM) and electron localization function (ELF) method [22]. Also, interplay between RAHB and aromaticity of the substituted o-hydoxybenzaldehydes has been recently probed [23] that results emphasize on resonance effect of the π-electrons within the hydrogen bond motif. Interestingly, Bernd Kuhn et al. explored intramolecular hydrogen bonding in five-to eight-member ring systems and revealed that changes in membrane permeability, water solubility, and lipophilicity depend on several factors, such as strength of hydrogen bond interactions, geometries, and relative energies [24]. Furthermore, cooperative intramolecular hydrogen bonding interactions in carbohydrates have been formerly studied [25,26] that highlight role of these interactions in life systems. Because of the important role of hydrogen bonds in biological systems, simultaneous intra- and intermolecular hydrogen bond interactions in some pyridine-based complexes that assisted through resonance are studied in the present work. Typical structures of the mentioned complexes together with R groups are presented in scheme 1. As can be observed, the R group has one, two, three, and four double bonds in complexes d, e, f, and g, respectively. Thus, effect of elongation of the R groups that have π-conjugated system and assist the hydrogen bond interactions can investigate in the current complexes as a case of cooperative RAHB. Also, energy data and structural parameters of the mentioned complexes are compared with a, b, and c ones that have R groups with no double bonds to verify supportive role of RAHB in the pyridinebased complexes.

Computational methods

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Geometry optimizations were executed at the PBEKCIS/6-311++G** level of theory using Gaussian09 program package [27]. The binding energies were calculated for all complexes with correction for the basis set superposition error (BSSE) using the Boys-Bernardi counterpoise technique [28]. The topological properties of electron charge densities have been calculated by the atoms in molecules (AIM) method on the wave functions achieved at the above mentioned level using AIM2000 [29] program. The population analyses were carried out by natural bond orbital (NBO) method [30] using NBO program implemented under Gaussian09 program package [31]. The localized molecular orbital energy decomposition analysis (LMO-EDA) was performed using Gamess software [32].

Results and Discussion Energy data Using strategically neighboring R groups is a way to change properties of intramolecular hydrogen bonding and can construct cooperative hydrogen bonding centers [33]. In the present study, geometry optimizations of the structures involving intra- and intermolecular and hydrogen bonding interactions that have different R groups (pyridine-based complexes) were performed using Gaussian09 program package. Typical structure of the mentioned complexes together with numbers of atoms is shown in Scheme 1.The R group in complexes a, b, and c is hydrogen, ethyl, and butyl, respectively. On the other hand, the R group in complexes d, e, f, and g is a π-conjugated system with one, two, three, and four double bonds, respectively. Binding energies of the binary complexes that were formed through intermolecular hydrogen bonding interactions of the water molecule with nitrogen atom of monomers were calculated at the PBEKCIS/6-

4

311++G** level of theory and are gathered in the Table 1. Also, the BSSE corrected binding energies are presented in this Table. Results indicate that complex g has the largest binding energy value. In addition, elongation of the R groups that have π-conjugated system leads to increase of binding energies. This result highlights the assistant role of resonance on intermolecular hydrogen bonding in the current pyridine-based complexes. Geometrical parameters were studied to find role of R groups on hydrogen bon lengths. Results presented in Table 1 show that increase of length of π-conjugated system in the R groups is accompanied by decrease of intramolecular hydrogen bond length (dO…H) in monomers. The dO…H values in the present work are relatively less than o-carbonyl hydroquinones [34] that indicate role of R groups with π-conjugated system on values of intramolecular hydrogen bond lengths. Moreover, complex formation is followed by decrease of dO…H values. As can be seen, increase of length of π-conjugated system leads to decrease of intermolecular hydrogen bond length (dN…H) values. These results show intramolecular and intermolecular RAHB in the mentioned system and verify supportive effect of intermolecular hydrogen bonding on intramolecular hydrogen bonding. Cooperative intra- and intermolecular hydrogen bonding interactions in biological systems have been previously investigated. For instance, some authors studied intramolecular C−H…O hydrogen bonding in ofloxacin that forms a cooperative hydrogen bonding system with neighboring O−H…O hydrogen bonding. They concluded that cooperative hydrogen bonding interactions regulate conformation of ofloxacin [35]. Also, formation of cooperative intra- and intermolecular hydrogen bonding interactions were studied in dimers of α–hydroxyesters with methanol [36]. Results reveal that increase of length of π-conjugated system in monomers is accompanied by decrease of energy gap (EG) values. Moreover, binary complexes have smaller

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EG values than corresponding monomers. Also, the chemical potentials (µ) were calculated using the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies as:

μ = − (I + A)/2

eq. 1

In the above equation, I and A are ionization potentials and electron affinities of the molecular systems, respectively. Chemical potential is used to predict chemical reactivity of molecules. Results indicate that monomer with R group that have longest π-conjugated system (−C8-H9) has largest chemical potential among other monomers and interacts with water molecule via intermolecular hydrogen bonding interaction to forms complex g with largest binding energy. Order of chemical potential of the monomers (in eV) based on R groups without π-conjugated system is: H (-4.916) <−C2H5 (-4.784) <−C4H9 (-4.762). The mentioned order for monomers with R groups that have π-conjugated system is: −C2H3 (-4.901) <−C4H5 (-4.808) <−C6H7 (-4.663) <−C8H9 (-4.549). As can be seen, nature of R groups and existence of π-conjugated system effect on chemical potential of the molecules.

AIM and NBO analysis AIM analysis was performed to find relationship between electron charge densities at bond and ring critical points (ρBCP and ρRCP) and energy data. Results indicate that values of electron charge densities at ring critical points (RCPs) of rings A (ρRCP(A)) of the complexes are larger than those for ring B (ρRCP(B)). As can be seen in Table 2, increase of length of π-conjugated system is accompanied by decrease/increase of ρRCP(A)/ρRCP(B).The order of ∇2ρBCP values at bond critical points of intramolecular hydrogen bonds (in au) based in complexes that

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have R groups without π-conjugated system is: a (-0.03161) < b (-0.03466) < c (-0.03468). The mentioned order for complexes with R groups that have π-conjugated system is: d (-0.03447) < e (-0.03484) < f (-0.03497) < g (-0.03505). As can be seen, all the ∇2ρBCP values are negative that indicate covalent nature of intramolecular hydrogen bonding interactions [37] in these complexes. Also, aromaticity of the rings A and B of the complexes based on aromatic fluctuation index (FLU) [38] were calculated. Results show that order of aromaticity at rings A and B of the complexes is in harmony with order of ρRCP(A) and ρRCP(B). Energies of intramolecular hydrogen bonding interactions in the pyridine-based complexes (E′HB) were estimated using properties of RCPs to connect strength of intramolecular hydrogen bonding interactions to aromaticity of the rings and thus to nature of the R groups. The values of E′HB in the mentioned complexes are more negative than recently reported for complexes involving 4-substituted-8-hydroxyquinolines [39]. This outcome emphasizes on supportive role of resonance on E′HB values in the pyridine-based complexes. As can be observed in Fig.1, raise of aromaticity at ring B of the complexes a-c and d-g, is followed by increase of strength of intramolecular hydrogen bonding interactions. Recently, mutual effects of aromaticity and strength of hydrogen bonding interactions have been also investigated [40]. Results showed that increase of aromaticity of the rings is in accord with increase of strength of hydrogen bonding interactions. Furthermore, electron-donating substituents can enhance strength of intramolecular hydrogen bonding interactions in some substituted o-hydroxybenzaldehyde [23]. On the other hand, decrease of aromaticity at ring A of the pyridine-based complexes is accompanied by decrease of dN…H values and also increase of binding energies of the complexes (see Fig 2). In addition, aromaticity of the rings A and B were evaluated using

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para-delocalization index (PDI) [41]. Results presented in Table 2 show that the order of FLU and PDI values in the complexes based on R groups is relatively alike. Therefore, aromaticity is a helpful factor that can influence on strength of the intra- and intermolecular hydrogen bonding interactions in the current pyridine-based complexes. Population analysis was executed using NBO method [29] on optimized geometries to find role of donor-acceptor interactions on the strength of the intra- and intermolecular hydrogen bonding interactions in the complexes. Results indicate that increase of donor-acceptor interaction energy (2E) values of LPO4

BD*O6-H5 interaction is followed by increase of

E′HB values. The order of 2E values (in kcal mol-1) in complexes that involve R groups without π-conjugated system is: a (25.15) < b (34.29) < c (34.43). The mentioned order for other complexes is: d (27.49) < e (34.98) < f (35.8) < g (36.00). These values are relatively larger than 2

E values for similar interactions in o-carbonyl hydroquinones [34]. This result shows effect of

resonance on 2E values of the intramolecular hydrogen bonding. Also as can be seen in Fig. 3, there is a linear relation between binding energies and 2E values of the LPN1

BD*O3-H2

interaction. Consequently, donor-acceptor interactions contribute in strength of intra- and intermolecular hydrogen bonding interactions in the present complexes and can be manipulated using resonance effect of R groups.

Energy decomposition analysis The localized molecular orbital energy decomposition analysis (LMO-EDA) was performed on the optimized complexes using Gamess software to realize contribution of various components of interaction energy on stability of complexes. Interaction energies of the complexes involve electrostatic, exchange, repulsion, polarization, and dispersion energy

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components that are denoted as Ees, Eex, Erep, Epol, and Edisp, respectively. Results presented in the Table 3 show that the most important components of interaction energy in the binary complexes are electrostatic and exchange energy, respectively. In fact, coexistence of intramolecular and intermolecular hydrogen bonding interactions leads to stability for the complexes thorough electrostatic and exchange effects. Also, elongation of the R groups that have π-conjugated system leads to increase of contribution of Ees and Eex in interaction energy. Therefore, electrostatic and exchange energies play supportive roles in the resonance-assisted hydrogen bonding interactions in these complexes.

Conclusions There is intramolecular and intermolecular RAHB in the current pyridine-based complexes. Elongation of the R groups that have π-conjugated system leads to increase of strength of intra- and intermolecular hydrogen bonding interactions. The molecule with R group that have longest π-conjugated system has largest chemical potential among other molecules and forms complex g with largest binding energy. Aromaticity is a supportive factor for increase of strength of intramolecular hydrogen bonding interactions in the complexes. Donor-acceptor interaction energies of the LPX

BD*Y-Z interaction (X= O4, N1; Y= O6, O3; Z= H5, H2)

have useful contributions to strength of intra- and intermolecular hydrogen bonding. Electrostatic and exchange energies are the most important components of the interaction energies and have helpful roles in the resonance-assisted hydrogen bonding interactions in the complexes.

Acknowledgments We thank the vice-chancellor of research and technology at university of Zabol.

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Table 1: The binding energies (in kcal mol1-1), energy gaps (in eV), and hydrogen bond lengths (in Å) of the optimized binary complexes calculated at the PBEKCIS/6-311++G** level.

a

Complex

-∆E

-a∆E

EG

dN…H

dO…H

a

7.10

6.51

2.451, 2.968

1.9637

1.7147, 1.7229

b

7.40

6.81

2.380, 2.859

1.9542

1.6406, 1.6473

c

7.42

6.80

2.385, 2.861

1.9542

1.6397, 1.6480

d

7.26

6.69

2.285, 2.757

1.9572

1.6455, 1.6547

e

7.44

6.86

2.199, 2.474

1.9517

1.6354, 1.6465

f

7.58

6.96

2.047, 2.093

1.9479

1.6314, 1.6402

g

7.64

7.04

1.760, 1.797

1.9454

1.6287, 1.6375

refers to the BSSE corrected binding energies. The Italic values belong to monomers.

Table 2: The electron charge density values at RCPs and aromaticity indices at rings A and B of the complexes (in au) calculated at the PBEKCIS/6-311++G** level.

FLUring

FLUring

PDIring

PDIring

2 A×10

2 B×10

2 A×10

2 B×10

1.948

0.829

1.221

8.150

3.075

2.353

2.070

1.037

1.144

7.619

3.361

c

2.351

2.071

1.038

1.147

7.618

3.362

d

2.336

2.061

1.102

1.189

7.375

3.260

e

2.326

2.079

1.169

1.164

7.112

3.278

f

2.321

2.087

1.207

1.149

6.957

3.282

g

2.319

2.092

1.228

1.139

4.576

3.285

Complex

ρring A×102

ρring B×102

a

2.374

b

Table 3: The components of interaction energies in the optimized binary complexes at the PBEKCIS/6-311++G** level. Complex

Eelect

Eexch

Erep

Epol

a

-13.03

-10.42

19.12

-3.99

b

-13.53

-10.75

19.77

-4.19

c

-13.55

-10.75

19.78

-4.20

d

-13.39

-10.64

19.54

-4.14

e

-13.65

-10.85

19.94

-4.26

f

-13.85

-11.01

20.24

-4.34

g

-13.99

-11.12

20.45

-4.40

Scheme 1: Typical structure of the binary complexes a-g together with R groups and atom numbering.

Figure 1: Relationship between aromaticity of the rings B in the complexes (a-c: ■ and d-g: ▲) and energies of intramolecular hydrogen bonding interactions.

Figure 2: Relationship between aromaticity of the rings A in the complexes (a-c: ■ and d-g: ▲) and binding energies of the complexes. Figure 3: Linear correlation between (a-c: ■ and d-g: ▲).

2

E values and binding energies of the complexes

Scheme 1

-5.60

E'HB/kcal mol-1

-5.50 -5.40 -5.30 -5.20 -5.10 -5.00 0.0124

0.012

0.0116

FLU ring B/au

Fig. 1

0.0112

7.800

-ΔE/kcal mol-1

7.600

7.400

7.200

7.000 0.008 0.009

0.01

0.011 0.012 0.013 0.014

FLU ring A/au

Fig. 2

7.10

-ΔE/kcal mol-1

6.90

6.70

6.50

6.30 9.00

9.50

10.00 2E

Fig. 3

/kcal mol-1

10.50

11.00



Aromaticity is a supportive factor for increase of strength of IHB



Electrostatic and exchange are most important components of interaction energy



Resonance assists intra- and intermolecular hydrogen bonding



Coexistence of intra- and intermolecular hydrogen bonding lead to stability of complexes



RAHB aid augmentation of donor-acceptor interaction energies of the complexes

Pouya Karimi: Investigation, Reviewing and Editing, Methodology, Software Mahmoud Sanchooli: Data Validation, Writing- Original draft preparation

Declaration of interests ☐The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: