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Journal of Inclusion Phenomena and Macrocyclic Chemistry https://doi.org/10.1007/s10847-018-0809-x

ORIGINAL ARTICLE

Investigation of the upper rim binding of triphenylpyrylium cation with p-sulfonatocalix[4]arene

Marimuthu Senthilkumaran1 · Ramesh Kumar Chitumalla2 · Ganesan Vigneshkumar1 · Eswaran Rajkumar3 · Paulpandian Muthu Mareeswaran1  · Joonkyung Jang2

Received: 11 January 2018 / Accepted: 3 May 2018 © Springer Science+Business Media B.V., part of Springer Nature 2018

AbstractThe interaction of 2,4,6-triphenylpyrylium cation with p-sulfonatocalix[4]arene is studied using absorption, emission, NMR and electrochemical techniques. The increase in the absorption is observed with the increase in the concentration of p-sulfonatocalix[4]arene. The emission intensity of 2,4,6-triphenylpyrylium cation is also enhanced in the presence of p-sulfonatocalix[4]arene. The electrochemical titration reveals the presence of host–guest interaction. The NMR analysis explains the upper rim interaction of 2,4,6-triphenypyrylium cation with p-sulfonatocalix[4]arene. The mode of binding is studied using computational methods. The quantum chemical simulations reveal the binding orientation of cationic TPP with p-SC4. The calculated complexation energy (− 33.19 kcal mol−1) indicates the strong binding nature of 2,4,6-triph-enylpyrylium cation with p-sulfonatocalix[4]arene.

Keywords Emission · Cyclic voltammetry · P-sulfonatocalix[4]arene · NMR analysis · DFT study

Introduction

The third generation supramolecular host molecules such as calix[n]arenes have interesting chemical interactions with incoming guest molecules [1–5]. The tert-butylcalix[n]arenes (CA) receive importance due to their facile synthe-sis by means of simple phenol–formaldehyde chemistry [6, 7]. The CAs are having a hydrophobic cavity, hydro-philic upper and lower rims [8, 9]. Upper rim modification involves ipso substitution of tert-butyl group [7, 10]. Variety

of substitutions are available at this position like halogena-tion [11], nitration [12], sulfonation [13, 14], acylation [15] etc. The para-sulfonatocalix[4]arene (p-SC4) is a water solu-ble macrocycle synthesized from the upper rim modifica-tion of tert-butylcalix[4]arene [16, 17]. The p-SC4 possess π-electron rich cavity (aromatic ring), upper rim with nega-tive charges (sulphanato group) and hydrophilic lower rim (–OH group), therefore it has the propensity to encapsulate neutral, cationic organic molecules and ions to form supra-molecular complexes [18–20]. The binding of cationic guest molecules with p-SC4 is preferable due to the π-electron rich cavity, hydrophilic anchoring groups like sufonato groups [21–23]. The biocompatible nature of p-SC4 renders various biological applications like ionic transport, protein binding, enzyme blocking and drug delivery [24, 25].

The 2,4,6-triphenylpyrylium cation (TPP) is one of the cationic organic molecules having trivalent oxygen atom [26]. It can be used as sensitizer, electron transfer agent and catalyst, due to the electron accepting nature [27, 28]. Therefore, TPP is used to design sensors for amino acids [29], and proteins [30, 31]. The hydrophilic nature as well as phenyl ring substituents made TPP to interact efficiently with host molecules [32, 33]. The interaction of TPP with cucurbiturils is studied by Thangavel et al. [34]. The mode of binding of guest molecules with host molecules can be

Electronic supplementary material The online version of this article (https ://doi.org/10.1007/s1084 7-018-0809-x) contains supplementary material, which is available to authorized users.

* Paulpandian Muthu Mareeswaran mareeswaran@alagappauniversity.ac.in;

muthumareeswaran@gmail.com

* Joonkyung Jang jkjang@pusan.ac.kr

1 Department of Industrial Chemistry, Alagappa University, Karaikudi, Tamil Nadu 630 003, India

2 Department of Nanoenergy Engineering, Pusan National University, Busan 609-735, Republic of Korea

3 Department of Chemistry, Madras Christian College (Autonomous), Chennai, Tamil Nadu 600 059, India

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studied using computational studies [35]. The reports on the host–guest interaction of different guest molecules with calixarenes using density functional theory (DFT) are availa-ble in the literature [36–38]. Herein we report the host–guest interaction of TPP with p-SC4 using absorption, emission, electrochemical and NMR techniques. Further, the binding of cationic TPP with p-SC4 has been studied by means of quantum chemical simulations. The DFT based theoretical simulations elucidated the binding orientation and binding strength of the cationic TPP with p-SC4.

Experimental section

Materials and instruments

2,4,6-Triphenylpyrylium tetrafluoroborate (97%) and t-butyl-calix[4]arene are procured from Alfa Aesar (Hyderabad, India) and Sigma-Aldrich (Bengaluru, India) respectively. Ultra-pure water (Millipore) and HPLC grade acetonitrile are used as solvent throughout the study. The p-SC4 is syn-thesized according to the reported procedure and character-ized using 1H NMR spectral technique (Fig. S1) [20, 39].

Instruments

UV–Visible absorption spectrometric measurements and emission measurements are performed by using SCHI-MADZU UV-2401PC and JASCO FP-8200 Spectrofluor-ometer respectively. Electrochemical studies are carried out using Auto lab electrochemical analyzer (GPES software). A classical three electrode cell setup is used for the electro-chemical measurements. Cyclic Voltammetry measurements carried out using glassy carbon electrode with diameter 3 mm as a working electrode at applied potential from − 1.3 to 1.2 V for each sample with single cycle. The reference electrode is saturated silver chloride and counter electrode is platinum electrode. All experiments are carried out at room temperature. The NMR spectral analyses are carried out using Bruker 500 MHz NMR Spectrometer. D2O and Acetonitrile-d6 are used as solvents for both 1H NMR and rotating frame nuclear Overhauser effect (ROESY) NMR techniques. The framework of density functional theory (DFT) study is performed by Gaussian 09 quantum chemi-cal program.

UV–Visible absorption titration studies

For binding constant calculation, the concentration of TPP is fixed as 1 × 10−5 M, the concentration of p-SC4 is varied from 1 × 10−5 to 9 × 10−5 M and the absorption measure-ments are recorded for each sample. The binding constant

value (Ka) of TPP with p-SC4 is evaluated with the aid of the Benesi–Hildebrand equation [40] (Eq. 1),

Here, ΔA is the change in absorbance of the TPP on the addition of p-SC4. Δε is the difference in the molar extinc-tion coefficient between the free TPP and p-SC4–TPP com-plex. The plot of 1/ΔA versus 1/[p-SC4] gives a straight line. By using the slope value of the line, the binding constant Ka is calculated in solution. The binding stoichiometry is evaluated by Job’s plot method. The concentration of TPP is varied from 1 × 10−5 to 9 × 10−5 M and the p-SC4 concentra-tion in the reverse order from 9 × 10−5 to 1 × 10−5 M. The plot of the mole fraction versus change in the absorbance gives Job’s plot. Binding constant is also calculated using nonlinear regression analysis. The following equation is used for 1:1 complex [41, 42] (Eq. 2).

Fluorescence titration studies

The concentration of TPP is fixed at 1 × 10−5 M, the concen-tration of p-SC4s is varied from 1 × 10−5 to 9 × 10−5 M and the fluorescence spectra of TPP are recorded in the absence and in the presence of various concentrations of p-SC4. The binding constant is estimated based on the enhancement of fluorescence intensity with the change of concentration of p-SC4. We have calculated binding constant using modified Benesi–Hildebrand equation [39, 43] (Eq. 3),

where I0 is the luminescence intensity of the guest in the absence of host, I is the luminescence intensity of the guest in the presence of the host, [H] is the concentration of the host, and Ka is the binding constant for the binding of the host with the guest. In Eq. (3), a and b are constants. The value of Ka can be determined by plotting I0/I − I0 against the inverse of the concentration of the host, (M−1).

The fee energy change, ΔG value is calculated from the binding constant value (Ka) using the Eq. (4),

where ∆G is the free energy change of the reaction, R is gas constant, T is temperature and Ka is binding constant.

Cyclic voltammetry studies

The concentration of p-SC4 is prepared 1 × 10−3 M made up with water and TPP, prepared 1 × 10−3 M madeup ace-tonitrile separately. The 10 ml of p-SC4 is taken in three electrode cell setup and CV is performed. Then incremental additions 2 ml of TPP is made and CV is recorded. This procedure is continued up to 10 ml of TPP so that the

(1)1∕ΔA = 1∕KaΔ�[

p-SC4]

+ 1∕Δ�[TPP]

(2)A =(

A0 + A∞Ka

[

p-SC4])

∕(

1 + Ka

[

p-SC4])

(3)I0∕(

I − I0)

= b∕(a − b) ×[

1∕Ka[H] + 1]

(4)ΔG = −RT ln Ka

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concentration will reach 1:1 ratio. The recorded CVs are used to calculate binding constant [44]. The binding constant is calculated using Eq. (5).

where IG is the oxidation peak current of TPP, and IHG is the oxidation peak current of inclusion complex of TPP with p-SC4. IHG–IG means the peak current difference between inclusion complex and guest molecule. ΔI is the difference between the molar peak current coefficient of the inclusion complex and TPP. The [TPP]0 and [p-SC4]0 are the initial concentration of TPP and p-SC4 respectively.

NMR studies

TPP and p-SC4 complexs (1:0.5, 1:1) are prepared. All these samples are dissolved in D2O/Acetonitrile-d6 (1:1) solvent mixture and studied using 1H NMR technique. The indivitual 1H NMR of p-SC4 shown in Fig. S1. This figure shows three peaks at 7.3, 3.5 and 1.7 ppm. These peaks are corresponds to aromatic protons (7.3 ppm), –OH protons (3.5 ppm) and methylene protons (1.7 ppm) of p-SC4 [45]. The sample having 1:1 is studied using rotating frame nuclear over-houser effect (ROESY) technique.

Computational details

We performed the theoretical calculations within the frame-work of density functional theory (DFT) using Gaussian 09 quantum chemical program [46]. The optimization of cationic TPP and p-SC4 are performed separately using a meta-hybrid exchange–correlation functional (M06-2X) along with the standard 6-31G (d) basis set [47, 48]. The vibrational frequency analysis is carried out on the opti-mized geometries to ensure the real minima on the poten-tial energy surface. The employed DFT functional has been widely used in dealing with H-bonding and non-covalent interactions [49, 50]. The method and basis set used in this study have been successfully employed in our earlier studies of p-SC4 [19]. We have modeled the p-SC4 as a neutral mol-ecule to avoid the spurious interactions between p-SC4 and cationic TPP and also for computational simplicity. All the simulations were carried out in vacuum and no symmetry constraints were imposed during the optimization.

Results and discussion

UV–Visible absorption titration study

The structures of p-SC4 and TPP are given in Fig. 1. The UV–Visible absorption spectrum of p-SC4 and TPP are

(5)1∕(

IHG − IG)

= 1∕ΔI + 1∕Ka[TPP]0ΔI[

p-SC4]

0

shown in Figs. S2 and S3 respectively. The absorption max-ima of TPP are around 270, 350 and 415 nm [51]. The con-centration of TPP is fixed and concentrations of p-SC4 are varied and UV–Visible absorption spectra are recorded for all these samples (Fig. 2). In this figure, all the peaks of TPP are increasing by the increasing the concentration of p-SC4. The binding constant value is calculated from Benesi–Hilde-brand method (Eq. 1). The Benesi–Hildebrand plot is shown in Fig. S4. From this plot the binding constant (Ka) value is calculated as 2.45 × 104 M−1 (Table 1). The binding constant value indicates the strong binding between TPP and p-SC4. The host–guest association ratio between the p-SC4 and TPP is calculated from Job’s method (Fig. S5). The intense peak at 0.5 mol fraction indicates the 1:1 ratio of p-SC4/TPP com-plex. The binding constant is also calculated using nonlinear regression method (1:1 interaction) (Eq. 2). The nonlinear fit is given in Fig. S6 and the binding constant value calculated is 1.48 × 104 M−1. The binding constant value of both linear and nonlinear method are similar. The free energy changes (ΔG) of host–gust interaction between TPP and p-SC4 are calculated by means of binding constant values using Eq. (4) and are − 25.4 KJ mol−1 (linear fit) and − 24.1 KJ mol−1 (nonlinear fit). These values confirm the spontaneous bind-ing of TPP with p-SC4.

Fluorescence titration study

The fluorescence spectrum of TPP, excited at 400  nm is shown in Fig. S7. The fluorescence maxima of TPP is 470 nm. p-SC4 has no emission properties, therefore the emission technique can be used to study the interaction between p-SC4 and TPP. The peak around 470 nm is the characteristic peak for TPP, therefore the change in emission intensity at this wavelength is considered for the interaction of TPP with p-SC4. The emission intensity of TPP increases with increasing concentration of p-SC4 (Fig. 3). It shows that there is binding between p-SC4 and TPP. Therefore, the change in emission intensities from the concentration variation is taken for binding constant calculation using Modified Benesi–Hildebrand method (Eq. 3). The Modified

Fig. 1 Structure of p-sulfonatocalix [4] arene (p-SC4) and 2,4,6 triph-enylpyrylium tetrafluoroborate (TPP)

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Benesi–Hildebrand plot is shown in Fig. S8 and the binding constant (Ka) value is 1.8 × 104 M−1 (Table 2). This value

indicates the strong binding between TPP and p-SC4. The free energy change (ΔG) value is calculated using Eq. (4) and value is − 24.8 KJ mol−1 which confirms the spontaneity of the binding.

Electrochemical study

The cyclic voltammogram of p-SC4 and TPP are shown in Figs. S9 and S10 respectively. The shoulder peak around 0.8 V of p-SC4 is due to the oxidation of –OH group [52]. The 10 ml of 1 × 10−3 M of p-SC4 is taken in the cell setup. CVs of p-SC4 in the presence of 2 ml (1 × 10−3 M) incremental additions of TPP up to 10 ml is recorded (Fig. 4). The oxidation peak around 0.8 V decreases by the addition of TPP. This observation is due to the inter-action of TPP with p-SC4. The redox current and poten-tial variation is collected in Table 2. The binding constant is calculated using Benesi–Hildebrand equation (Eq. 5). Benesi–Hildebrand plot is shown in Fig. S11, and the binding constant value (Ka) is 7.3 × 102 M−1 (Table 1). Free energy change (ΔG) value is − 16.6 KJ mol−1, this value also confirms inclusion complex (p-SC4-TPP) is a spontaneous process. The absorption and emission techniques have higher binding constant values around 104 M−1, but in CV technique the binding constant value is lesser than the values obtained from optical techniques. This is due to the sensitivity of the techniques. The opti-cal techniques especially fluorescence technique is very sensitive compared to CV techniques. Also, in CV tech-nique, the counter ion will play a competitive role with the guest molecule. Therefore, the binding constant is lesser in CV technique compared to optical techniques.

NMR studies

The 1NMR titration of TPP with p-SC4 is carried out by fixing TPP concentration and varying p-SC4 concentration from 1:0 to 1:1 ratio (Fig. 5). For the convenience, the pro-tons of TPP are labbled in alphapets (a–i) and the protons of p-SC4 are labbled as Sa, Sb and Sc representing methyl

Fig. 2 UV–Visible absorption spectrum of TPP (1 × 10−5  M) in the presence of p-SC4 (1 × 10−5–9 × 10−5 M)

Table 1 Binding constant and ΔG values of TPP with p-SC4 using absorption, fluorescence and cyclicvoltametric techniques

Technique Binding constant, Ka, M−1

Free energy, ΔG, KJ mol−1

Absorption Linear fit 2.45 × 104 − 25.4 Nonlinear fit 1.48 × 104 −24.1

Fluorescence 1.85 × 104 −24.8Cyclicvoltametry 7.29 × 102 −16.6

Fig. 3 Emission spectrum of TPP (1 × 10−5  M) in the presence of p-SC4 (1 × 10−5–9 × 10−5 M) (excitation at 400 nm)

Table 2 CV of p-SC4 (10 ml of 10−3 M) with increasing concentra-tion of TPP

Concentration of TPP (ml, 10−3 M)

Epa (V) Ipa (µA) Epc (V) Ipc (µA)

0 0.901 2.484 − 0.3650 − 1.44462 0.913 2.016 − 0.2468 − 1.01364 0.878 1.941 − 0.2287 − 9.03306 0.893 1.846 − 0.2281 − 8.23348 0.884 1.654 − 0.2175 − 7.034210 0.854 1.418 − 0.2320 − 6.2347

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bridge, benzene ring and –OH units respectively (Fig. S12). At the initial addition of p-SC4 (1:0.5 ratio), all the protons are shifted to downfield region. Upon the second addition of p-SC4 (1:1) all the peaks are furthur shifted to downfield region. This downdfield shift confirms the upper rim binding of TPP with p-SC4 [35]. The shift values are collected in Table 3. This observation is further confirmed using ROESY spectra. The 1:1 ratio is selected for the ROESY spectra. The recorded ROESY spectra is given Fig. 6. The ROESY spectra shows that the protons of TPP (a–g) have correla-tions with Sb of p-SC4 (Sa,g; Sa,e; Sa,bcd; Sa,ih). There is

no corelation of Sa of p-SC4 with any protons of TPP, which confirms the upper rim binding of TPP with p-SC4.

Computational studies

To get a deeper understanding about the binding orientation and binding strength of the cationic TPP with p-SC4 we have carried out quantum chemical DFT simulations. The opti-mized geometries of the cationic TPP and p-SC4 are given Fig. 7. In the same figure, the dihedral angles between each phenyl ring with the central pyrylium ring are given. The opti-mized cationic TPP is not planar and the three phenyl rings are in fan propeller shape. After the optimization, the cationic TPP was placed in the cavity of cup-shaped p-SC4 and optimized the host–guest complex to evaluate its binding strength. We have modeled the p-SC4-TPP complex in two possible ways (Fig. 8) by varying the orientation of TPP phenyl ring inside the cavity of p-SC4. In the first model, we have placed the phenyl ring para to the oxygen of TPP in cavity and in the lat-ter case, we have placed the phenyl ring ortho to the oxygen of TPP in cavity. The TPP phenyl ring placed inside the cavity of p-SC4 is approximately parallel to the two phenyl rings of p-SC4 and perpendicular to the other two phenyl rings. The distances between TPP phenyl ring and the four phenyl rings of p-SC4 ranges from 3.50 to 3.70 Å. For the first model, the calculated complexation energy is − 33.19 kcal mol−1 which indicates the strong binding of cationic TPP with p-SC4. The calculated complexation energy was subjected to counter-poise correction to eliminate the basis set superposition error (BSSE) [53]. The BSSE energy is 7.03 kcal mol−1 and the uncorrected (raw) complexation energy is − 40.22 kcal mol−1.

Fig. 4 CV spectra of p-SC4 (10 ml of 1 × 10−3 M) with various con-centration of TPP

Fig. 5 1H NMR titration of TPP with p-SC4

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For the other orientation of TPP, a lower complexation energy (− 31.60 kcal mol−1) has been observed with a BSSE energy of 7.26 kcal mol−1. The high binding energy observed for the first model can be attributed to the two H-bonds formed between TPP and p-SC4. The two H-bond distances are found to be 2.42 and 2.52 Å. Significant H-bonding interactions were not observed for the second model of p-SC4–TPP complex and the minimum distance between the hydrogen of TPP and oxy-gen of p-SC4 is found to be 2.98 Å. The H-bonding interac-tions observed in the two models of the host–guest complex are given in Supporting Information. We have calculated the molecular electrostatic potential (MEP) maps to understand the relative polarity of the host–guest complex. The calcu-lated MEP maps have been given in Supporting Information as

Fig. S14. The negative and positive electrostatic potentials are shown in red and blue colors, respectively, whereas the green color represents the region of zero electrostatic potential. The positive electrostatic potential (blue color) is observed near the TPP and four sulfonate groups which are susceptible for intermolecular hydrogen bonding interactions.

Conclusion

The binding constant calculated using absorption and emis-sion spectral techniques are around 104 M−1. These values indicate the strong binding between the TPP and p-SC4. The Job’s plot confirms the 1:1 ratio of the host–guest complex.

Table 3 Proton shift values of 1H NMR titration of TPP with p-SC4

Protons 1:0 shift in ppm 1:0.5 shift in ppm

Difference in shift (1:0) − (1:0.5)

1:1 shift in ppm Differ-ence in shift (1:0) − (1:1)

ae 8.47 8.71 − 0.24 8.84 − 0.37bd 8.34 8.59 − 0.25 8.71 − 0.37igh 7.90 8.15 − 0.25 8.27 − 0.37c 7.81 8.07 − 0.26 8.19 − 0.38f 8.75 9.06 − 0.31 9.17 − 0.42

Fig. 6 ROESY spectra of TPP with p-SC4 at 1:1 ratio

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The decrease in the peak potential of p-SC4 reveals the interaction of TPP with p-SC4. The upper rim binding of TPP with p-SC4 is established by 1H NMR and ROESY spectral studies. The interaction of TPP with p-SC4 is due to the cationic nature of TPP and the anionic nature of p-SC4. The π–π interaction is also envisaged to influence the bind-ing. The complexation between TPP and p-SC4 is further investigated and supported by DFT studies. The high com-plexation energy evaluated from the theoretical simulations

is attributed to the cationic nature of TPP. Therefore, p-SC4 can be used to make upper rim self-assemblies using TPP derivatives to explore more optical insights.

Acknowledgements We acknowledge the financial support of Depart-ment of Science and Technology, Ministry of Science and Technol-ogy (DST INSPIRE) (Project number—IFA14/CH-147), India and this work was supported by the Korea Research Fellowship Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (2016H1D3A1936765).

Fig. 7 The optimized geometries of p-SC4 (a) and 2,4,6-triphenylpyrylium cation (b) obtained at M06-2X/6-31G (d) level of the theory. The given dihedral angles are in degrees

Fig. 8 The optimized geome-tries of the complex p-SC4–TPP in two possible orientations

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References

1. Shinkai, S.: Calixarenes: the third generation of supramolecules. Tetrahedron 49, 8933–8968 (1993)

2. Shinkai, S.: Calixarenes as new functionalized host molecules. Pure Appl. Chem. 58, 1523–1528 (1986)

3. Nimse, S.B., Kim, T.: Biological applications of functionalized calixarenes. Chem. Soc. Rev. 42, 366–386 (2013)

4. Ikeda, A., Shinkai, S.: Novel cavity design using calix[n]arene skeletons: toward molecular recognition and metal binding. Chem. Rev. 97, 1713–1734 (1997)

5. Ukhatskaya, E.V., Kurkov, S.V., Matthews, S.E., Loftsson, T.: Encapsulation of drug molecules into calix[n]arene nanobaskets. Role of aminocalix[n]arenes in biopharmaceutical field. J. Pharm. Sci. 102, 3485–3512 (2013)

6. Rodik, R.V., Boyko, V.I., Kalchenko, V.I.: Calixarenes in bio-medical researches. Curr. Med. Chem. 16, 1630–1655 (2009)

7. Gutsche, C.D., Pagoria, P.F.: Calixarenes. 16. Functionalized calixarenes: the direct substitution route. J. Org. Chem. 50, 5795–5802 (1985)

8. Vicens, J., Böhmer, V.: Calixarenes: A Versatile Class of Macro-cyclic Compounds. Springer, Dordrecht (2012)

9. Creaven, B.S., Donlon, D.F., McGinley, J.: Coordination chemis-try of calix[4]arene derivatives with lower rim functionalisation and their applications. Coord. Chem. Rev. 253, 893–962 (2009)

10. Ohto, K.: Review of the extraction behavior of metal cations with calixarene derivatives. Solvent Extract Res. Dev. Jpn. 17, 1–18 (2010)

11. Conner, M., Janout, V., Regen, S.L.: Synthesis and alkali metal binding properties of “upper rim” functionalized calix[4]arenes. J. Org. Chem. 57, 3744–3746 (1992)

12. Kumar, S., Kurur, N., Chawla, H., Varadarajan, R.: A convenient one pot one step synthesis of p-nitrocalixarenes via ipsonitration. Synth. Commun. 31, 775–779 (2001)

13. Shinkai, S., Araki, K., Matsuda, T., Nishiyama, N., Ikeda, H., Takasu, I., Iwamoto, M.: NMR and crystallographic studies of a p-sulfonatocalix(4) arene-guest complex. J. Am. Chem. Soc. 112, 9053–9058 (1990)

14. Valand, N.N., Patel, M.B., Menon, S.K.: Curcumin-p-sulfonatoca-lix[4]resorcinarene (p-SC[4]R) interaction: thermo-physico chem-istry, stability and biological evaluation. RSC Adv. 5, 8739–8752 (2015)

15. Shinkai, S., Nagasaki, T., Iwamoto, K., Ikeda, A., He, G.-X., Mat-suda, T., Iwamoto, M.: New syntheses and physical properties of p-alkylcalix [n] arenes. Bull. Chem. Soc. Jpn. 64, 381–386 (1991)

16. Chao, J., Wang, H., Song, K., Wang, Y., Zuo, Y., Zhang, L., Zhang, B.: Host-guest inclusion system of ferulic acid with p-Sulfonatocalix[n]arenes: preparation, characterization and anti-oxidant activity. J. Mol. Struct. 130, 579–584 (2017)

17. Shinkai, S., Mori, S., Tsubaki, T., Sone, T., Manabe, O.: New water-soluble host molecules derived from calix [6] arene. Tetra-hedron Lett. 25, 5315–5318 (1984)

18. Danylyuk, O., Leśniewska, B., Suwinska, K., Matoussi, N., Cole-man, A.W.: Structural diversity in the crystalline complexes of para-sulfonato-calix[4]arene with bipyridinium derivatives. Cryst. Growth Des. 10, 4542–4549 (2010)

19. Senthilkumaran, M., Maruthanayagam, K., Vigneshkumar, G., Chitumalla, R.K., Jang, J., Muthu Mareeswaran, P.: Spectral, electrochemical and computational investigations of binding of n-(4-hydroxyphenyl)-imidazole with p-sulfonatocalix[4]arene. J. Fluoresc. 27, 2159–2168 (2017)

20. Ashwin, B.M., Saravanan, C., Senthilkumaran, M., Sumathi, R., Suresh, P., Muthu Mareeswaran, P.: Spectral and electrochemi-cal investigation of p-sulfonatocalix[4]arene-stabilized vitamin E aggregation. Supramol. Chem. 30, 32–41 (2017)

21. Guo, D.S., Liu, Y.: Supramolecular chemistry of p-sulfonatocalix[n]arenes and Its Biological applications. Acc. Chem. Res. 47, 1925–1934 (2014)

22. Saravanan, C., Senthilkumaran, M., Ashwin, B.M., Suresh, P., Muthu Mareeswaran, P.: Spectral and electrochemical investiga-tion of 1,8-diaminonaphthalene upon encapsulation of p-sulfona-tocalix[4]arene. J. Incl. Phenom. Macrocycl. Chem. 88, 239–246 (2014)

23. Madasamy, K., Gopi, S., Senthilkumaran, M., Radhakrishnan, S., Velayutham, D., Muthu Mareeswaran, P., Kathiresan, M.: A supramolecular investigation on the interactions between ethyl terminated bis-viologen derivatives with sulfonato calix[4]arenes. Chem. Select. 2, 1175–1182 (2017)

24. Shinde, M.N., Barooah, N., Bhasikuttan, A.C., Mohanty, J.: Inhi-bition and disintegration of insulin amyloid fibrils: a facile supra-molecular strategy with p-sulfonatocalixarenes. Chem. Commun. 52, 2992–2995 (2016)

25. Paclet, M.H., Rousseau, C.F., Yannick, C., Morel, F., Coleman, A.W.: An absence of non-specific immune response towards para-sulphonato-calix[n]arenes. J. Incl. Phenom. Macrocycl. Chem. 55, 353–357 (2006)

26. Manoj, N., Ajayakumar, G., Gopidas, K., Suresh, C.: Structure absorption spectra correlation in a series of 2,6-dimethyl-4-ar-ylpyrylium salts. J. Phys. Chem. A 110, 11338–11348 (2006)

27. Che, Y., Ma, W., Ji, H., Zhao, J., Zang, L.: Visible photooxida-tion of dibenzothiophenes sensitized by 2-(4-methoxyphenyl)-4, 6-diphenylpyrylium: an electron transfer mechanism without involvement of superoxide. J. Phys. Chem. B 110, 942–2948 (2006)

28. Amat, A.M., Arques, A., Bossmann, S.H., Braun, A.M., Miranda, M.A., Vercher, R.F.: Synthesis, loading control and preliminary tests of 2,4,6-triphenylpyrylium supported onto Y-zeolite as solar photocatalyst. Catal. Today 101, 383–388 (2005)

29. El-Roz, M., Awala, H., Thibault-Starzyk, F., Mintova, S.: Selec-tive response of pyrylium-functionalized nanozeolites in the vis-ible spectrum towards volatile organic compounds. Sens. Actuator B 249, 114–122 (2017)

30. Shariatgorji, M., Nilsson, A., Källback, P., Karlsson, O., Zhang, X., Svenningsson, P., Andren, P.E.: Pyrylium salts as reactive matrices for MALDI-MS imaging of biologically active primary amines. J. Am. Soc. Mass. Spectrom. 26, 934–939 (2015)

31. Bayer, M., König, S.: Pyrylium-based dye and charge tagging in proteomics. Electrophoresis 37, 2953–2958 (2016)

32. Manoj, N., Gopidas, K.: Inclusion complexation of a few pyrylium salts by [small beta]-cyclodextrin studied by fluorescence, NMR and laser flash photolysis. Phys. Chem. Chem. Phys. 1, 2743–2748 (1999)

33. Montes-Navajas, P., Teruel, L., Corma, A., Garcia, H.: Specific binding effects for Cucurbit[8]uril in 2,4,6-triphenylpyrylium–Cucurbit[8]uril host–guest complexes: observation of room-tem-perature phosphorescence and their application in electrolumines-cence. Chem. Eur. J. 14, 1762–1768 (2008)

34. Thangavel, A., Sotiriou-Leventis, C., Dawes, R., Leventis, N.: Orientation of pyrylium guests in cucurbituril hosts. J. Org. Chem. 77, 2263–2271 (2012)

35. Athar, M., Lone, M.Y., Jha, P.C.: Recognition of anions using urea and thiourea substituted calixarenes: a density functional theory study of non-covalent interactions. J. Chem. Phys. 501, 68–77 (2018)

36. Ashwin, B.M., Chitumalla, R.K., Herculin Arun Baby, A., Jang, J., Muthu Mareeswaran, P.: Spectral, electrochemical and com-putational investigations on the host–guest interaction of Cou-marin-460 with p-sulfonatocalix [4] arene. J. Incl. Phenom. Mac-rocycl. Chem. 90, 51–60 (2018)

37. Saravanan, C., Chitumalla, R.K., Ashwin, B.M., Senthilkumaran, M., Suresh, P., Jang, J., Muthu Mareeswaran, P.: Effectual binding

Journal of Inclusion Phenomena and Macrocyclic Chemistry

1 3

of gallic acid with p-sulfonatocalix[4]arene: an experimental and theoretical interpretation. J. Lumin. 196, 392–398 (2018)

38. Rathod, N.V., Joshi, K., Jadhav, A.S., Kalyani, V.S., Selvaraj, K., Malkhede, D.D.: A novel interaction study of Th(IV) and Zr(IV) with 4-sulfonatocalix[6]arene: experimental and theoretical inves-tigation. Polyhedron 137, 207–216 (2017)

39. Muthu Mareeswaran, P., Ethiraj, B., Veerasamy, S., Kim, B., Woo, S.I., Rajagopal, S.: p-Sulfonatocalix [4] arene as carrier for cur-cumin. New. J. Chem. 38, 1336–1345 (2014)

40. Muthu Mareeswaran, P., Prakash, M., Subramanian, V., Raja-gopal, S.: Recognition of aromatic amino acids and proteins with p-sulfonatocalix[4]arene: a luminescence and theoretical approach. J. Phys. Org. Chem. 25, 1217–1227 (2012)

41. Thordarson, P.: Determining association constants from titration experiments in supramolecular chemistry. Chem. Soc. Rev. 40, 1305–1323 (2011)

42. Ashwin, B.M., Arun Baby, H., Prakash, A., Hochlaf, M., Muthu Mareeswaran, P.: A combined experimental and theoretical study on p-sulfonatocalix[4]arene encapsulated 7-methoxycoumarin. J. Phys. Org. Chem. (2017) https ://doi.org/10.1002/poc.3788e 3788-n/a

43. Ackermann, T., Connors, K.A.: Binding Constants: The Measure-ment of Molecular Complex Stability. Wiley, New York (1987)

44. Srinivasan, K., Stalin, T., Sivakumar, K.: Spectral and electro-chemical study of host–guest inclusion complex between 2,4-dini-trophenol and β-cyclodextrin. Spectrochim. Acta. A 94, 89–100 (2012)

45. Ashwin, B.M., Vinothini, A., Stalin, T., Muthu Mareeswaran, P.: Synthesis of a safranin T-p-sulfonatocalix[4]arene complex by means of supramolecular complexation. Chem. Select. 2, 931–936 (2017)

46. Frisch, M.J., Trucks, G.W., Schlegel, H.B., Scuseria, G.E., Robb, M.A., Cheeseman, J.R., Scalmani, G., Barone, V., Mennucci, B., Petersson, G.A., Nakatsuji, H., Caricato, M., Li, X., Hratchian, H.P., Izmaylov, A.F., Bloino, J., Zheng, G., Sonnenberg, J.L., Hada, M., Ehara, M., Toyota, K., Fukuda, R., Hasegawa, J., Ishida, M., Nakajima, T., Honda, Y., Kitao, O., Nakai, H., Vreven,

T., Montgomery, J.A., Peralta, J.E., Ogliaro, F., Bearpark, M., Heyd, J.J., Brothers, E., Kudin, K.N., Staroverov, V.N., Kobayashi, R., Normand, J., Raghavachari, K., Rendell, A., Burant, J.C., Iyen-gar, S.S., Tomasi, J., Cossi, M., Rega, N., Millam, J.M., Klene, M., Knox, J.E., Cross, J.B., Bakken, V., Adamo, C., Jaramillo, J., Gomperts, R., Stratmann, R.E., Yazyev, O., Austin, A.J., Cammi, R., Pomelli, C., Ochterski, J.W., Martin, R.L., Morokuma, K., Zakrzewski, V.G., Voth, G.A., Salvador, P., Dannenberg, J.J., Dapprich, S., Daniels, A.D., Farkas, Foresman, J.B., Ortiz, J.V., Cioslowski, J., Fox, D.J.: Gaussian 09, Revision B.01. Gaussian, Inc., Wallingford (2009)

47. Zhao, Y., Truhlar, D.G.: The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncova-lent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functionals. Theor. Chem. Acc. 120, 215–241 (2008)

48. Hehre, W.J., Ditchfield, R., Pople, J.A.: Self—consistent molecu-lar orbital methods. Xii. Further extensions of Gaussian—type basis sets for use in molecular orbital studies of organic mol-ecules. J. Chem. Phys. 56, 2257–2261 (1972)

49. Chu, Y., Xue, N., Xu, B., Ding, Q., Feng, Z., Zheng, A., Deng, F.: Mechanism of alkane H/D exchange over zeolite H-ZSM-5 at low temperature: a combined computational and experimental study. Catal. Sci. Technol. 6, 5350–5363 (2016)

50. Liu, H., Lee, J.Y.: Electric field effects on the adsorption of CO on a graphene nanodot and the healing mechanism of a vacancy in a graphene nanodot. J. Phys. Chem. C 116, 3034–3041 (2012)

51. Jayanthi, S., Ramamurthy, P.: Photoinduced electron transfer reac-tions of 2,4,6-triphenylpyrylium: solvent effect and charge-shift type of systems. Phys. Chem. Chem. Phys. 1, 4751–4757 (1999)

52. Saravanan, C., Ashwin, B.M., Senthilkumaran, M., Muthu Mareeswaran, P.: Supramolecular complexation of biologically important thioflavin-T with p-sulfonatocalix[4]arene. Chem. Select. 3, 2528–2535 (2018)

53. Boys, S.F., Bernardi, F.D.: The calculation of small molecular interactions by the differences of separate total energies. Some procedures with reduced errors. Mol. Phys. 19, 553–566 (1970)