Reply to the Comment on “Michael Addition Based Chemodosimeter

Oct 22, 2018 - A very simple chemodosimeter has been developed for creatinine biomolecules based on Michael addition reaction by using ...
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Reply to the Comment on Michael Addition Based Chemodosimeter for Serum Creatinine Detection Using (E)-3-(Pyren-2yl)-1-(3,4,5-trimethoxyphenyl)prop-2- en-1-one Chalcone Ellairaja Sundaram, Venkatesan Subramanian, Kumaravel Velayutham, Rohini Gomathinayagam, and Vairathevar Sivasamy Vasantha ACS Sens., Just Accepted Manuscript • DOI: 10.1021/acssensors.8b00818 • Publication Date (Web): 22 Oct 2018 Downloaded from http://pubs.acs.org on October 24, 2018

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Reply to the Comment on Michael Addition Based Chemodosimeter for Serum Creatinine Detection Using (E)‑3-(Pyren-2-yl)-1-(3,4,5-trimethoxyphenyl)prop-2- en-1-one Chalcone EllairajaSundaram, † VenkatesanSubramanian, ‡ KumaravelVelayutham,§RohiniGomathinayagam,§ and Vairathevar Sivasamy Vasantha*,† †Department

of Natural Products Chemistry, School of Chemistry, Madurai Kamaraj University, Madurai - 625 021, Tamilnadu, India. ‡Chemical Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai - 600 020, Tamilnadu, India. §Alpha Hospital and Research Center, Madurai - 625 009, Tamilnadu, India Abstract A very simple chemodosimeter has been developed for creatinine biomolecules based on Michael addition reaction by using (E)‑3-(Pyren-2-yl)-1-(3,4,5-trimethoxyphenyl)prop-2- en-1one Chalcone. The photophysical properties of the chalcone were thoroughly analyzed using UV-Vis and Emission techniques. The chalcone has exhibited two absorption maxima at 297 & 407 nm which are due n-π* and π-π* transactions, respectively. This property was further confirmed by repeating UV-Vis absorbance studies of the chalcones in different solvents having different polarity. The PTP chalcone has originally exhibited ICT mechanism and it is arrested while creatinine is added. However, a ratiometric response is observed due to the creatinine induced ICT mechanism and it is also clearly supported with DFT studies. In our original work, we have done DFT studies for only one isomer of the creatinine. Currently, we have extended our DFT studies for another isomer also. The relative quantum yield of the PTP chalcone was calculated in sensing and standard conditions as 0.85 and 0.45, respectively. This reply complements the comment of Krishnamoorthy et al on our recent work entitled, Michael Addition Based Chemodosimeter for Serum Creatinine Detection Using (E)‑3-(Pyren2-yl)-1-(3,4,5-trimethoxyphenyl)prop-2- en-1-one Chalcone: The creatinine exists in two isomeric forms. We have considered one of the isomers and now we have also performed calculations on another isomer. The results obtained from DFT calculations by Krishnamoorthy and group and our group are similar(Figure 1).The HOMO and LUMO of PTP-CRT are mainly located on pyrene group only, which indicates that intramolecular charge transfer is not feasible. The CRT induced ICT shown scheme is purely based on emission interpretations and which was confirmed by blue shift that is well-reported mechanism. The FMO results produced in the main manuscript also indicates the same. There is a slight interpretation misconception that in the PTP

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molecule the LUMO is predominantly located on α, β-unsaturated carbonyl. Moreover, significant contribution also found on pyrene as well as phenyl ring. That is why, we have written the contribution up to phenyl ring. This is the idea behind our interpretation. At this point, we agree with Krishnamoorthy et al., that the initial ICT was initiated from pyrene to α, βunsaturated carbonyl predominantly and then small contribution from phenyl ring. We are thankful to the explanation by Krishnamoorthy et al., regarding FMO analysis.

Figure 1. FMO images. PTP-CRT [PTP= (E)-3-(pyren-2-yl)-1-(3,4,5-trimethoxyphenyl)prop-2en-1-one, CRT= Creatinine done by our group(top) and Krishnamoorthy et al.,(bottom) The probe has initially adopted ICT mechanism, in which charge transfer occurs from pyrene to α, β-unsaturated carbonyl part and small contribution to phenyl ring. When CRT is added to α, βunsaturated carbonyl part, the delocalization is arrested and the initial ICT is inhibited and then CRT induces charge transfer which is confirmed by the emission analysis synthesized Michael adduct. Herein, DFT studies are only used to support the occurrence and inhibition of ICT mechanism before and after addition of CRT. CRT induced ICT was supported by purely based on the emission results only. Generally molar extinction coefficient for n-π* is less than that of π-π*. However, the transitions assigned for our chalcone are the characteristic absorption maxima for all chalcones.1-4This kind of behavior is mainly due to the presence of extended conjugation -C=C-C=O chromophore system in the chalcone structure which resulted in greater delocalization of 𝜋electrons along the molecule. In our case, it is well understood that π-π*occurred at lower the wavelength and n-π* occurred at higher energy and thus lower wavelength. To confirm this property, UV-Vis spectral studies for the chalcone in solvents having different polarity was carried out (Figure 2). The

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results indicate that π-π* shows red shift and n-π* shows blue shift with increasing polarity of the solvent(Table 1). Solvent PET n-hexane Ethylacetate Ethanol Methanol

π-π *(nm) 288 289 292 296 300

n- π*(nm) 378 377 365 364 370

Table 1. UV-vis transitions of PTP chalcone at various solvents.

Figure 2. UV vis spectra of PTP chalcone in various solvents The mechanism is proposed based on the UV-Vis and emission results. Initially, ICT was operated from donor pyrene to the acceptor part majorly at α-β, unsaturated carbonyl and then significantly at phenyl part. After binding of creatinine at α-β, unsaturated double bond, it is further enhance donating ability of pyrene, but conjugation between donor and acceptor part is disconnected after the binding of CRT and hence ICT from the pyrene moiety to acceptor is arrested. The CRT induced ICT is further supported by observing the ratiometric responses and blue shift in emission. But, after binding with creatinine the initial ICT is inhibited and thus results creatinine induced ICT via Michael adduct formation. The mechanism is further supported by DFT study.5 The ICT mechanism has been widely exploited for cation sensing. Generally, if the electron-donating character of the electron donating group is reduced, blue shifts in both the absorption and emission will occur. Conversely, if a cation promotes the electron-donating character of the electron donating group, the absorption and fluorescence spectra will be red-shifted.6-7In our case, CRT reduced the donating ability of pyrene to acceptor part through the conjugate addition at α-β, unsaturated double bond and hence blue shift is observed rather than red shift. Regarding Scheme 1, we have given a tentative and simplified form of ICT mechanism by showing only two electrons transfer from HOMO of donor to HOMO of the nearby acceptor for the clarity. This kind of representation is generally followed earlier in many reports.8-9 However,

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a two photon absorption in pyrene is already reported one.10 Moreover, we have proved the photophysical properties of Michael adduct by analyzing the synthesized Michael adduct using PTP and CRT under basic medium to support our mechanism. We have used the words “photophysical interaction” for the interaction between chalcone and creatinine in the abstract only.

Actually, since we have used a UV-Vis and Fluorimetry

techniques to analyze Michael Adduct formation, the statement has been used in the abstract. As Krishnamoorthy et al, corrected pointed out, it is not photophysical interaction; it is a well known photochemical reaction through Michael Addition. As per suggestion of Krishnamoorthy et al suggestion, the absorbance is given in % . Figure 3 shows the effect of pH on absorbance of the probe. There is negative absorption region at the both ends of the spectra. The experiment was repeated thrice also; the same trend was observed. But, the two absorbance peaks of the probe were appeared at middle of the spectra. The absorbance values at λmax of the probe were measured at middle region i.e in the positive region only. The negative absorbance may be due to on stray light radiation, molar absorption coefficient of the system analyzing, pH, temperature, solvent etc.11 The data obtained from figure 3 are not that much significant to this research work and also the emission data explain clearly about the effect of pH on photophysical property of the probe. Generally, during the development of sensor, the linear range of the sensor should be wide in the useful region so that it can apply for real field analysis. So, we have bothered about linear range not absorbance range. Therefore, in articles related to sensor, the basic concept is not strictly followed. For examples, the absorbance value of nanomaterials and quantum dots used in the development of sensors were kept more than one.12-15 Even Krishnamoorthy et al has also reported absorbance value greater than one for the basic study. Hence, we have also kept absorbance value greater than one for analytical purpose.

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Figure 3.pH studies based on the absorbance changes of PTP chalcone while adjusting the pH from 2 to 12.5. [Final concentration of PTP chalcone is 5 μM which was made from bulk (0.001 M of PTP) through dilution method using various buffer solutions of pH from 2 to 12.5.] Regarding the quantum yield, the excitation wavelength is the main criteria to choose our standard. Based on the excitation wavelength appeared in our unknown only we can fix the standard.17-18So in this aspect excitation wavelength plays vital role. Meanwhile, emission intensity is also independent of excitation wavelength. Suppose if you don’t want to consider excitation wavelength, we no need to bother about integrated area also. Actually, we have followed the standard articles related to sensor and calculated the quantum yield16. We have actually calculated the Q.E for our optimized experimental conditions during development of sensor by following earlier reports in ACS.19-22 Now, the quantum yield was calculated as per the suggestion of the Krishnamoorthy et al and found to be 0.45. We agreed that the quantum yield should be as 0.85 and it’s a typo error in our supplementary file. We have given calculated as up to 4 digits i.e 0.8500. Final Michael adducts should be beta product not alpha product (Scheme 1).

Scheme 1. Plausible Mechanism for the formation of PTP-CRT adducts (a) and energy level diagram for proposed biosensor (b).

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In summary, we have concluded that we have developed chemodosimeter for creatinine via ICT mechanism. Krishnamoorthy et al has commented to the editorial office about our work. The mechanisms proposed photo physical property of the probe and sensor are correct. We have done new experiments for proving our proposed mechanism. However, we have made some useful corrections then and there in our manuscript based on the commends i.e one e sentence has been rewritten in DFT part, absorption unit change, quantum yield representation in two digit (in supplementary file etc,. In our DFT studies, a small correction is made as per Krishnamoorthy et al. We have also done some addition DFT studies for another CRT isomer. We have a good agreement with Krishnamoorthy et al by using the same software. We thank Krishnamoorthy et al for spending their valuable time on our paper and indicating useful corrections.

■AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. ORCID Vairathevar Sivasamy Vasantha: 0000-0002-5991-5091 ■ACKNOWLEDGMENTS The first author thanks DST-INSPIRE Fellowship Scheme, New Delhi, India (grant no. DST/INSPIRE-Fellowship/2012/ 251) and UCG project (F.NO.41-352/2012 (SR)) for financial support. Authors thank to Krishnamoorthy et al for their valuable time. References 1. Dyer, J. R. Applications of Absorption Spectroscopy of Organic Compounds, PrenticeHall, New Delhi, India, 1971. 2. Si, Z. K.; Zhang, Q.; Xue, M.Z; Sheng, Q.R.; Liu, Y. G.. Novel UV-sensitive bischalcone derivatives: synthesis and photocrosslinking properties in solution and solid PMMA film. Research on Chemical Intermediates. 2011, 37, 635–646. 3. Meng, G.T.;Mee, H.T.; Ying, Y.; Suzie Hui, C.K.; Zhi-Qiang. L.; Way to Improve Luminescent Efficiency of Bis-Chalcone Derivatives” Journal of Chemistry.,2016, 2016, 1-8. 4. Sonia, E.; Blanco, Ferdinando H.; Ferretti.Determination of absorptivity and formation constant of a chalcone association complex Talanta.,1988, 45, 1103–1109. 5. Jiasheng, W.; Weimin, L.; Jiechao, G.; Hongyan, Z.; Pengfei, W.New sensing mechanisms for design of fluorescent chemosensors emerging in recent years.Chem. Soc. Rev.,2011, 40, 3483–3495. 6. de Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T.; Huxley, A. J. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T. E. Signaling Recognition Events with Fluorescent Sensors and Switches. Chem. ReV.1997, 97, 1515-1566. 7. Jong, S.K.; Duong, T.Q.Calixarene-Derived Fluorescent Probes.Chem. Rev.,2007, 107, 3780-3799. 8. Valeur, B.; Leray, I.Design principles of fluorescent molecular sensors for cation recognition.Coord. Chem. ReV.2000, 205, 3-40.

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