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Molecular Recognition, Conformational Behavior and Spectral Characteristics of Oxatub[4]arene Macrocycle Dipali N. Lande, and Shridhar P. Gejji J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.7b12472 • Publication Date (Web): 21 Dec 2017 Downloaded from http://pubs.acs.org on December 22, 2017

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The Journal of Physical Chemistry

Molecular Recognition, Conformational Behavior and Spectral Characteristics of Oxatub[4]arene Macrocycle Dipali N. Lande and Shridhar P. Gejji Department of Chemistry, Savitribai Phule Pune University, 411 007, India

Corresponding author: [email protected] Fax No.: +91-20-225691728 Telephone No.: +91-20 2560122

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Abstract In the present work we analyze molecular recognition behavior of synthetic hydroxylated oxatub[4]arene (TA4) receptor toward the methyl viologen in different redox states. The supramolecular binding of methyl viologen guest toward TA4 macrocyclic scaffold has been studied employing the dispersion corrected ωB97X-D based density functional theory (DFT). The methyl viologen in dicationic and neutral forms revealed distinct features in electronic, 1H NMR and infrared spectra. Quantum theory of atoms in molecules (QTAIM) in conjunction with the noncovalent interaction reduced density gradient (NCI-RDG) in real space, have been used as tools to characterize the underlying host-guest binding.


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Introduction Artificial molecular receptors endowed with the distinct structural characteristics and intriguing host-guest properties are the primary workhorses in the domain of supramolecular chemistry.1-4 The emergence of newer macrocyclic hosts have accelerated the expansion of this field with their potential applications in interdisciplinary areas including catalysis,5 molecular machines,6 supramolecular polymers,7 and drug delivery.8 During a past decade a variety of arene based molecular scaffolds for example, resorcinarenes,9 calixarenes,10 cyclotriveratrylenes,11 pillararenes12 and the modified cavitands incorporating pyrrole,13 pyridine14 or imidazolium15 heterocyclic groups instead of phenyl moieties in their architecture, have been obtained. A majority of these macrocyclic arenes are composed of mono-benzene or substituted benzene moieties. Extension from mono-arene to larger aromatic arenes including biphenyl, naphthols render resulting hosts with unique structural attributes such as deep and wider cavity, enhanced π-electron density etc., offer unquestionable advantages and make them fascinating.16,17 Interestingly the fluorescent characteristics of naphthalene endows the molecular container with natural affinity for sensing.18 The Li and coworkers19 synthesized methylene bridged biphenyl cyclo-oligomers (biphen[n]arene) using the reaction between 4,4’-biphenolether and paraformaldehyde in the presence of a Lewis acid catalyst. The hollow π-electron rich cavity of biphen[n]arene showed a large affinity toward multiple cationic as well as electron deficient neutral guests. As far as naphthalene monomer based macrocycles are concerned, calix[n]naphthalene scaffolds comprised of methylene bridge unit were derived from direct cyclocondensation reaction between 1-naphthol and formaldehyde under the basic conditions by Georghiou and coworkers.20 Further modifications at the bridging position of the macrocycle by amide or allyl functionalities was expected to



improve the guest binding ability and their potential applications as fluorescent sensors.21,22 However, majority of such naphthalene-based molecular cavitand suffered from difficult regioisomeric products with ill-defined and shallow cavities, and scarcely displayed satisfactory guest binding.23,24 To overcome these difficulties recently Jiang et.al.25-28 reported flexible naphthalene based macrocycles viz., oxatub[n]arene (n=4, 5 and 6) and synthesized by the one pot reaction under high dilution condition in which the repeating 2,6-dihydroxynaphthalene units are connected by ether (CH2-O-CH2) linkage at the 1,5-positions which minimize the potential isomerism and avoid the self-occupation of the cavity as well as helps in maintaining the deeper cavities. Additionally, the flexible naphthalene moieties lead to multiple conformers for effective guest binding. These oxatub[4]arene synthetic receptors can accommodate a variety of guests with varying size ranging from 1,4-diazabicyclo[2.2.2]octane, viologen derivatives to C60 or C70 fullerenes. In addition to this the guest binding and solid-state self-assemblies formation of zorb[4]arenes have been reported by the same group.29 It has been observed that the uncomplexed state, the such macrocycle assumes either collapsed or self-included conformations. In continuation to this Jiang et al. 30-34 reported a several molecular tubes based on the rigid bis-naphthalene cleft. Subsequently to mimic the biological functionalities these authors introduced converging functional groups such as urea and thiourea into the bis-napthalene cleft cavity which is referred as endo-functionalized bisurea/thiourea molecular tubes.35,36 On the theoretical front recently Gejji et al.37,38 studied structural features of inclusion complexes between the neutral guests and endofunctionalized urea/thiourea hosts. It has been shown that syn and anti configurational isomers of the macrocyle exhibit distinct selectivity toward guest binding and the complexation of centrosymmetric guest with the centrosymmetric anti isomer being energetically favored over the syn one.


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Viologens comprised of two pyridinium rings joined at para positions and have been known for electron relay in the photo- and electrochemical reactions. Their redox and electrochromic behavior garnered considerable interest across the scientific community.39-41 As a result of strong electron accepting and the one/two- electron reversible chemical and electrochemical reduction ability the viologen are known to exist as stable radical cation or in neutral forms.42 Its radical-cation finds potential applications in printing and display technologies.43 Besides this, the host-guest chemistry of viologens has attracted growing attention since the bipyridinium ions can be used for design of redox-active ionic liquid crystals;44-47 as building blocks in molecular machines to trigger the motion of a subunit following proper electrochemical stimulus.48-50 Remarkably, these guests exhibit characteristic charge transfer transition bands which can be used for anion recognition.51-53 In particular, the highly noxious methyl viologen cation (trade name paraquate i.e. N,N-dialkyl,4,4-bipyridinium), (MV2+) has widely been act as a probe for analyses interactions of DNA or zeolites.54,55 Moreover, MV2+ conduces stable inclusion host-guest

complexes

with

cyclodextrin,56

cucurbit[n]uril,57

calix[n]arene,58

pillar[n]arene59 and other macrocycles. Thus, it is of interest to investigate the complexation of viologen with recently reported naphthalene based supramolecular scaffold by mean of density functional theory protocol with the purpose of designing redox-switchable molecule. In this spirit, the present endeavor emphasis on the molecular insights for the inclusion of methyl viologen in its different redox state to the smart artificial hydroxylated oxatub[4]arene (TA4) receptor. We explore the distinct behavior of cationic and neutral guest upon encapsulation within such host-cavity. Theoretical investigations also enlightening on how cationic and neutral binding reflect in their spectral characteristics. A synopsis on the interplay of diverse non-covalent



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interactions underlying such host-guest binding has been presented using the NCI-RDG and QTAIM methods. The methodology adopted in this work is outlined below.

Computational Details Optimization of oxatub[4]arene (hosts) conformer, methyl viologen in its neutral and dicationic forms (guests) and their inclusion complexes were performed using the Gaussian 09 suit of program60 and Gauss View 5.0 utilized as graphic interface.61 The ωB97X-D hybrid exchange correlation functional proposed by Head-Gordon and coworkers62 was employed in conjunction with the internally stored 6-311+G(d,p) basis set. This level of theory is adequate for a faithful representation of underlying supramolecular interactions and describe well the electron distribution in host-guest chemistry.63-67 The tationary point structures of the host, guest and their complexes were confirmed to be the local minima on the multivariate potential energy surfaces from vibrational frequency calculations. The complexation of TA4 cavitands can be understood from the charge distribution within its cavity which can be characterized in terms of the molecular electrostatic potential (MESP) topography.68-70 To elucidate the nature and strength of underlying molecular interactions accompanying the guest encapsulation QTAIM analyses were carried out with the help of AIMAll-2000 software.71,72 Furthermore the non-localized dispersion and repulsive nonbonded interactions can be assured employing the NCI-RDG method as a tool.73 The RDG defined through s =

|∇ |

( )/ /

within the

QTAIM approach was calculated using the Multiwfn program74 and envisaged through the use of visual molecular dynamics software.75 Further the chemical shifts (δH) in 1H NMR spectra were derived by subtracting the nuclear magnetic shielding tensors of protons in the individual host, guest and their complexes from those in the tetramethylsilane used as the reference by the gauge-independent atomic orbital (GIAO) method.76 Effect of solvation (with the dichloromethane as solvent) on the structure and 1H NMR chemical 6 ACS Paragon Plus Environment

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shifts was simulated employing the self-consistent reaction field (SCRF) theory incorporating the polarization continuum model (PCM).77

Results and Discussion The naphthalene based TA4 supramolecular scaffold is made up of 2,6dihydroxynaphthalene units linked by ether bridges (CH2-O-CH2) at 1,5- position. The flipping of naphthalene monomer relative to linkages engenders different conformers with all the naphthalene monomers pointing along the same direction denoted as zigzag (I); one naphthalene ring flipped in a different direction referred as the disrupted zigzag (II); two neighboring naphthalene moieties flipped in different directions called as 1,2alternate (III) conformer and lastly two opposing naphthalene monomers flipped in different directions called as 1,3-alternate (IV) conformer. Stationary point structures thus derived were optimized in the framework of ωB97x-D/6-311+G(d,p) theory, which are displayed in Figure 1. All these conformers possess well defined cavities of tubular shape and varying dimensions. The cavity sizes are estimated by knowing the separation(s) of the radially opposite oxygens atoms in the naphthalene monomers. In an effort to understand the binding modes of hitherto conformers of TA4 the MESP topography was used. It has earlier been recognized that three dimensional (3D) MESP maps give a direct perspective of the segments in the molecular system along with its reactivity and affinity toward different guests. The MESP, V(r) generated by a molecule at a point r, is given by

V(r) =

ZA ρ(r ) − d r |r − R | |r − r |

The positive potential produced by N nuclei with nuclear charges (ZA), situated at (RA) has been signified by first term, whilst the second term denotes the negative potential engendered by continuous electron density, (r). MESP attains positive as well as 7 ACS Paragon Plus Environment


negative values with the complementary of the above terms and emerge with the effective electron rich regions in the molecular system. To examine the chemical reactivity V(r) was computed on the molecular surface. We consider 0.001 au ( ≡ !"# ) contour of the isoelectronic density that encloses more than 95% of the electronic charge and generally located 0.2–0.5 Å beyond the van der Waals radii of the atoms.78,79 Projection of these isosurfaces along the molecular plane for the TA4 conformers are displayed in Figure 2. The variation in MESP mapped are depicted using the coding scheme showing: red the most negative potential regions appropriate for the electrophilic attack whereas the blue signifying most positive electrostatic potential imply spatial regions which are more susceptible for nucleophilic attack. The prevalence of green further corresponds to potential halfway between the two extremes red and blue. As shown, the electrostatic potential intensifications follows the order red < orange < yellow < green < blue. As can be seen from Figure 2 MESP maps in zigzag, disrupted zigzag, 1,2 alternate and 1,3 alternate TA[4] conformers exhibit a trend which is qualitatively similar. The oxygen atoms from hydroxyl group and those from ether linkages are rendered with the relatively large negative electrostatic potential (dark red), accordingly the oxygen lone pairs are available for facilitate intermolecular interactions with the guest. In addition to this, the delocalized π-electron clouds of naphthalene rings renders large negative valued MESP (red) continuum within the inner surface of the conformer than the outer surface (reddish yellow). It may conjecture that the endo-binding of guest is more favored over the exo-binding. The most reactive protons from the hydroxyl functionalities endowed with the maximum brunt of positive charge and are largely electron deficient. Further the positive MESP was observed near the aromatic protons, the ortho position protons showing large electron deficient character than those at the meta position while ether linkage protons (-CH2) reveal a zero valued electrostatic potential. It can be speculated


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that all TA4 conformers are electron-rich and capable of accommodating cationic or electron deficient neutral guests in their cavities. In this digest, we choose methyl viologen as a proto type guest in its reduced (MV0) and oxidized (MV2+) which are portrayed in Figure 3. MESP mapped onto density isosurfaces are shown along with. The MV0 displays the negative potential near viologen core while the MV2+ reveals large positive potential (dark blue). In order to achieve allosteric binding of such guests with TA4 conformers, the closer contact of the complementary (highest positive and negative) regions in the MESP has been crucial to promotes strong electrostatic attractions. Taking cue from these considerations different host-guest complexes was generated by electrostatic docking of the electron deficient sites around the MESP critical points in the macrocycle. In simple words the lock and key mechanism based on the complimentary characteristics of electron distribution governs the complexation. Optimized structures of complexes between MV0 as well as MV2+ guest and I to IV conformers of TA4 host are illustrated in Figure S1 to S2 along with the relative stabilization energies given in parentheses. The interaction energies are calculated from the supramolecular approach, by subtracting the sum of energies of the isolated TA4 conformer and individual guest from that of the complex. The inclusion complexes of neutral and dicationic form of methyl viologen with 1,2-alternate (III) conformer of the TA4 reveals stronger binding than other conformers owing to matching of shape and size. These inferences are in consonance with the single crystal X-ray structure experiments on the MV2+ complexes of octabutyloxatub[4]arene reported by Jiang and coworkers.25 Hence it may be surmise that the substitution of the alkyl chain at -OH functionality does not affect the host-guest binding patterns. To scrutinize the thermodynamic parameters of the inclusion phenomenon Gibbs free energy (∆G) parameters were computed which turned out to be < 0, indicating formation of the inclusion complex is spontaneous and



exergonic. Noteworthy enough the complexation of 1,2-alternate conformer binds to the charged species more favorably (~2.5 times) than the reduced viologen which can be attributed to attractive cation···π interactions those stem from the polarization of the electronic cloud in TA4 macrocycle. Structural parameters of the host, guests and their energy minimal complexes from the ωB97x-D/6-311+G(d,p) theory are summarized in Table 1. The isolated cationic and neutral methyl viologen guests distinguished based on the number of electrons; the MV2+ has positive charged on two quaternary nitrogen atoms. Optimization of free MV0 reveal classical quinoid type structure where both intra-ring C1-C2 and inter-ring C3-C3’ bonds have double bond character with the pyridine rings being coplanar (dihedral ∠C2C3-C3’-C2’=180" ) to each other. The methyl (CH3) functionality shows deviation of 15+ from the molecular skeleton which suggests the nitrogen lone pair is not fully involved in π-conjugation. Since the hybridization of nitrogen centers are modified from sp2 to sp3 during reduction process (accommodation of two electron) which subsequently increase the pyramidal feature of nitrogen atom. On the other hand the central C3-C3’ bond joining bipyridinum rings turns to be 1.481 Å which is consistent with the single bond character between sp2 carbon atoms. Here two non-planar pyridine moieties deviate by 42" from the planarity as also observed in the earlier experiments. Encapsulation of viologen within the tubular TA4 cavity brings about structural perturbations and reflect in the structural parameters of individual host and guest. The double bonds in conjugated framework of encapsulated MV0 are elongated up to 0.003 Å contrary to the alternate C1N1 and C2-C3 single bonds which are shortened; the concomitant loss of p character relative to its free analogue was thus inferred. As may be noticed the two pyridine rings in the MV2+@TA4 complex tend to attain planarity (deviation up to 22" ). The penetration of


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MV2+ within the TA4 receptor brings about contraction of its cavity which explains its stronger binding than MV0 guest. In an attempt to shed some light on the supramolecular interactions between hostguest complexes Bader69 QTAIM methodology was used. Numerical data of the topological parameters viz., electron density (ρ), Laplacian of electron density (∇ ), kinetic and potential electron energy densities (G and V), and ellipticity parameters (.) for supramolecular interactions are collected in Table 3. The multiple C-H···π interactions are evident from the presence of the (3,-1) bond critical point (BCP) in between the bond path linking the methyl viologen hydrogen atoms with one or more carbon atoms of naphthalene moieties of the host, with the ρ being in the range 0.0049-0.0092 au for both complexes. The resultant ∇2ρ parameters for the same are positive evincing closed-shell type interactions. An appearance of BCP (ρ being in 0.0058 to 0.0074 au) for intermolecular C···C bond path between the viologen and naphthalene rings indicating attractive through-space interactions between the stacked π−π* orbitals in the complexes. Additionally the C-H···O, O-H···O contact are ascertained from the ρ values reported in the table.

Besides, the presence of intramolecular hydrogen-hydrogen

bonding interactions between the ortho-hydrogen atoms from adjacent pyridines in the MV0@TA4 complex explain its planar structure. The additional cation···/ interactions render large stability to the MV2+@TA4 complex. It has been observed here the total electron energy density (H) composed of counterbalancing kinetic (G > 0) and potential (V < 0) electron energy densities contributions. Furthermore, the ellipticity parameters (Ɛ=

0

0

− 1) at BCP were calculated which turn out be larger for C-H···π interactions owing

to the π-electrons serve as proton acceptors. NCI-RDG methods are utilized to capture details of the weak noncovalent interactions. Figure 3 displays graphical representation of the two dimensional (2D) 11 ACS Paragon Plus Environment


stiletto-heel shape scatter plots (s verses sign (1 )) and 3D spatial visualization of NCI isosurfaces and for the MV0@TA4 and MV2+@TA4 complexes. The sign (1 ) parameters are color-mapped onto the s-isosurfaces with two density-cutoffs being # and 2 and utilized to set the color scale.69 A red-green-blue scale color coding scheme has widely been preferred with the red representing 2 (repulsive) and blue for # (attractive). A direct visualization of 3D plot of MV0@TA4 complex impart the hydrogen bonding interactions which appear as round, localized, greenish blue NCI domain, in the region where hydrogen and oxygen atoms interact with each other and in the 2D plot shows a peak at sign (1 ) ≈ −0.03 au. The rest of weak intermolecular interactions for instance, C-H···π ones are represented by wider band around zero density (due to annihilation of the density gradient) region in 2D plot while a brownish green extended sheet like isosurfaces was observed in the 3D plots. The high ρ critical value (≈ 0.022 au) domain corresponds to destabilized steric clashes in closed shell ring interactions which emerge with the bright red cigar-shaped surfaces elongated along the direction of decreasing density up in the central region of aromatic moiety. Moreover the almond-shaped bicolored isosurfaces manifests between the hydrogen atoms of bipyridinium rings indicating dihydrogen interactions. The attractive component observed for these interactions are counterbalanced by destabilization arising from the induced ring closure. We find that the 2D scatter plot of cationic complex is not qualitatively different from the neutral complex. As demonstrated here the weak interactions between the host and guest shed light on unmistakable compatibility between QTAIM and NCI-RDG. To gain in-depth insights into the host-guest interactions with an emphasis on electronic spectra at molecular level, the time-dependent DFT (TDDFT) was adopted. Most representative molecular frontier orbitals are illustrated in Figure 6. The isolated MV0 and MV2+ guests show strong absorption bands near 345 nm (f= 1.00) and 279 nm


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(f=0.72) respectively, assigned to HOMO → LUMO transition whereas the TA4 scaffold reveal the corresponding band near ~312 nm. A new intermolecular charge transfer band was noticed in the visible region (625 nm) that arises from π (HOMO) → π∗ (LUMO) transition was observed for the MV0@TA4 complex. Noteworthy enough, such weak absorption band serve as an indicator of the host-guest binding. From the visual inspection of the frontier orbitals of the complex it become discernible that the interactions between MV0 and TA4 are of typical donor (guest) –acceptor (host) interactions. These inferences are significant and suggest the formation of complex is driven by intermolecular charge transfer interactions. A qualitatively different picture emerges for the charged (MV2+@TA4) complex in which the HOMO resides over the πorbitals of the host with polarization being induced from the guest. On the other hand the LUMO of the complex is rendered with large antibonding π-character and resides exclusively over the guest. Distinct binding behavior of cationic and neutral species toward molecular receptor can be monitored by the 1H NMR experiments. The GIAO derived δH values of isolated guest, molecular cavitand and their complexes were computed with the use of the dichloromethane as solvent which are compared in Table 3. The methyl viologen protons are broadly classified as: pyridine protons (H1 and H2) and methylene protons (H3) as displayed in Figure 3. The hierarchy of the calculated δH values turns out to be: H1> H2 > H3 for the isolated oxidized and reduced forms of methyl viologen. In comparison of MV2+ protons viz., H1 (9.94ppm), H2 (9.35 ppm) and H3 (5.49 ppm) are more de-shielded than those of MV0 guest. Upon complexation the protons exhibit upfield signals implying complete embedment of the guest within the host cavity. The host protons are nearly insensitive to complexation (cf. Table 3).



Encapsulation of the guest within the host cavity bring about the structural changes which reflect in the frequency shifts of their characteristic normal vibrations. The vibrational spectra of the free host, guest and their complex from theory in the form of the molar absorption coefficient (or molar absorptivity in units of 0.1 m2 mol−1) plotted versus the frequency (in cm−1) of neutral and charged complexes are illustrated in Figure S1 of the Supporting Information. The isolated MV0 shows a band near 3240 cm-1 arises from the –CH stretches of pyridine rings participating in C-H···π interactions. Upon complexation this vibration engenders the frequency up-shift to ~3250 cm-1 (blue shifted hydrogen bond) with a diminutive intensity. The C···C contacts between viologen and naphthalene moieties show signature in the C=C stretching of the MV0@TA4 complex and accordingly the wavenumber lowering of ~10 cm-1 is predicted. These arguments further can be extended to MV2+@TA4 complex as well. Moreover the direction of frequency shifts and intensity patterns of normal vibrations in their infrared spectra serve as a “fingerprint” for characterizing molecular interactions underlying the host-guest binding.

Conclusions In the present venture we report systematic analysis of hydroxylated oxatub[4]arene receptor employing the ωB97x-D based density functional theory. The by flipping of naphthalene monomers in the macrocyle yields zigzag, disrupted zigzag, 1,2alternate and 1,3-alternate conformers, which possess well-defined tubular shape cavities with varying dimensions. The oxidized and reduced forms of methyl viologen favors encapsulation within the 1,2-alternate conformer which is attributed to its perfect complementary size and shape, and stabilized via multiple non-covalent interactions of viologen protons with naphthalene rings and ether linked oxygens as well. It has been shown that MV2+ binds strongly to TA4 receptor which has been explained from the additional cation···π interactions. The MV0@TA[4] represents the donor-acceptor


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complex and accompanied by the intermolecular charge transfer interactions which manifests as the ~625 nm band in its electronic spectra. An encapsulation of the guest within host cavity further shows up-field perturbations of viologen (guest) protons in the 1H

NMR spectra. Besides the direction of shifts of -CH and -C=C characteristic stretchings

in the calculated vibrational spectra signify the formation of inclusion complex.

In conspectus, the molecular recognition of the methyl viologen guest by the oxatub[4]arene synthetic receptor discussed here should give impetus for design and modeling of supramolecular assemblies based on the naphthalene based receptors. Acknowledgements SPG acknowledges support from the Research Project (37(2)/14/11/2015-BRNS) from the Board of Research in Nuclear Sciences (BRNS), India. DNL is thankful to Savitribai Phule Pune University for the award of research fellowship through the University of Potential excellence scheme from the University Grants Commission, New Delhi, India. Authors thank the Center for Development of Advanced Computing (CDAC), Pune for providing National Param Supercomputing Facility.

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Page 24 of 33

Figures:

Top view

Side view

Zigzag (I)

Disrupted zigzag (II)

1,2-alternate (III)

1,3-alternate (IV)

Figure 1. Different conformers of parent hydroxylated oxatub[4]arene (TA4). 24 ACS Paragon Plus Environment

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Zigzag (I)

Disrupted zigzag (II)

1,2-alternate (III)

1,3-alternate (IV)

Figure 2. Electron density isosurfaces (0.001 au) overlaid with MESP (from +0.06 au to -0.06 au) in TA4 conformers.



Reduced methylviologen (MV0)

Oxidized methylviologen (MV2+) Figure 3. Optimized geometries and electron density mapped isosurfaces of methylviologen guests.


Page 26 of 33

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Top view

Side View

MV0@TA4

MV2+@TA4 Figure 4. Energy minimal optimized geometries of TA4 complexes.



MV0@TA4

MV2+@TA4

Figure 5. Two dimensional (2D) stiletto-heel shape scatter plots (s verses sign (1 )) and three dimensional (3D) spatial visualization of NCI isosurfaces and for MV0@TA4 and MV2+@TA4 complexes.


Page 28 of 33

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HOMO

LUMO

TA4

MV0

MV0@TA4

MV2+

MV2+@TA4

Figure 6. Most representative frontier molecular orbitals.



Page 30 of 33

Table 1. Selected structural parameters (bond-distances (R) in Å and dihedral angles (θ) in °) of MV0, MV2+ and their inclusion complexes. MV0

MV2+

MV0@TA4

MV2+@TA4

R(N-C1)

1.386

1.346

1.379

1.344

R(C1-C2)

1.342

1.375

1.343

1.375

R(C2-C3)

1.462

1.395

1.458

1.396

R(C3-C3’)

1.367

1.481

1.367

1.485

R(C4-N)

1.445

1.476

1.448

1.475

R(N-N)

7.124

7.011

7.081

6.973

0

42

0

22

165

179

176

179

θ(C2-C3-C3’-C2) θ (C1-C2-N-C4)


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Table 2. QTAIM parameters corresponding to noncovalent interactions present in TA4 inclusion complexes.

Complex MV0@TA4

MV2+@TA4

Non-covalent Interactions C2-H2···O C2’-H2’···O C1-H1···π C2-H2···π C1’-H1’···π C2’-H2’···π H2-H2’ π ···π C2-H2···O C2’-H2’···O C1-H1···π C2-H2···π C1’-H1’···π C2’-H2’···π π ···π cation···π

ρ

∇2ρ

G

V

Ɛ

0.0084 0.0091 0.0075 0.0092 0.0079 0.0070 0.0121 0.0074 0.0144 0.0073 0.0050 0.0077 0.0065 0.0088 0.0062 0.0061

0.0281 0.0280 0.0215 0.0282 0.0230 0.0222 0.0461 0.0213 0.0478 0.0233 0.0145 0.0214 0.0184 0.0270 0.0180 0.0235

0.0061 0.0062 0.0046 0.0060 0.0048 0.0047 0.0093 0.0044 0.0103 0.0050 0.0030 0.0044 0.0038 0.0056 0.0036 0.0049

-0.0053 -0.0055 -0.0037 -0.0049 -0.0039 -0.0037 -0.0071 -0.0032 -0.0087 -0.0042 -0.0025 -0.0036 -0.0030 -0.0046 -0.0027 -0.0041

1.1105 0.0681 0.2803 0.5106 2.2631 6.0888 0.8561 0.9668 0.1046 0.0239 0.9793 1.2646 1.4249 2.3528 0.0824 0.0049



Page 32 of 33

Table 3. 1H NMR chemical shifts (ppm) of host, guests and their complexes. δH

TA4

Ha Hb Hc Hd H1 H2 H3

8.08 9.32 5.19 6.24

MV0

6.85 6.45 3.69

MV2+

MV0@TA4

MV2+@TA4

9.94 9.35 5.49

8.12 9.35 5.38 6.27 4.50 3.63 2.79

8.09 9.24 5.53 6.33 6.53 7.71 4.64


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