Venkatesan Srinivasadesikan

Novel pyrene containing monomeric and dimeric supramolecular AIEE active nano-probes utilized in selective “off–on” trivalent metal and highly acidic pH sensing with live cell applications

Two novel pyrene containing monomeric and dimeric Schiff base derivatives PCS1 and PCS2 have been synthesized via one-pot reaction and their nano-J-type aggregation induced emission enhancement (AIEE) was well demonstrated using UV-Vis/PL, transmission electron microscopy (TEM), dynamic light scattering (DLS), time resolved photoluminescence (TRPL), and live cell imaging studies. In contrast to PCS2, PCS1 in CH3CN exhibits fluorescence “off–on” sensor selectivity towards transition trivalent metal ions (Fe3+, Cr3+ and Al3+) among other metals, via PET inhibition with excimer PCS1–PCS1* formation. The 2 : 1 stoichiometry of PCS1⋯M3+ (M = Fe/Cr/Al) sensor complexes was calculated from Jobs plots based on their PL titrations. In addition, the binding sites of PCS1⋯M3+ sensor complexes were well recognised from the 1H NMR titrations and supported by ESI(+ve) mass and FTIR analysis. Additionally, fluorescence reversibilities of PCS1⋯M3+ were observed via consequent addition of M3+ ions and PMDTA, respectively. Furthermore, the detection limits (LODs) and the association constant (Ka) values of PCS1⋯M3+ complexes were calculated using standard deviation and linear fittings. Likewise, quantum yield (Φ) measurements, TEM analysis, determination of the effect of pH, density functional theory (DFT) and time resolved photoluminescence (TRPL) studies were performed for the PCS1⋯M3+ sensor complexes. More importantly, confocal fluorescence microscopy imaging of Raw264.7 cells showed that PCS1 could be used as an effective fluorescent probe for detecting transition trivalent metal ions (Fe3+, Cr3+, and Al3+) in living cells. Impressively, both PCS1 and PCS2 showed “off–on” sensing at highly acidic pH values (1–3) with live cell applications.

Acid/Base and H2PO4- Controllable High-Contrast Optical Molecular Switches with a Novel BODIPY Functionalized [2]Rotaxane

A novel multifunctional mechanically interlocked switchable [2]rotaxane R4 containing two molecular stations and rotaxane arms terminated with boron-dipyrromethene (BODIPY) fluorophores and its derivatives were synthesized for the first time by CuAAC click reaction. The shuttling motion of macrocycle between the dibenzylammonium and triazolium recognition sites and the distance dependent photoinduced electron transfer process of R4 is demonstrated by utilizing external chemical stimuli (acid/base). Interestingly, the reversible self-assembly process of R4 was recognized by the acid-base molecular switch strategy. Notably, two symmetrical triazolium groups acted as molecular stations, H2PO4(-) receptors, and H-bonded donors. Both [2]rotaxane R4 and thread R2 demonstrated excellent optical responses and high selectivity toward H2PO4(-) ion. The specific motion and guest-host interactions of mechanically interlocked machines (MIMs) were also further explored by quantum mechanical calculations. The thread R2 also demonstrated to enable the detection of H2PO4(-) in RAW 264.7 cells successfully.

A dihydrogen phosphate selective anion receptor based on acylhydrazone and pyrazole

A novel chromogenic anion receptor 1 based on acylhydrazone and pyrazole has been designed and synthesized. Chromogenic anion receptor 1 forms stable 1 : 1 complexes with dihydrogen phosphate (H2PO4−) and other halide (Cl−, Br−) anions in DMSO solution, as shown by UV-vis, fluorescence and 1H NMR spectroscopic experiments. The pyrazole containing host 1 in the optimized geometry of the complex has been noted as planar. The planarity of the host with the H2PO4− anion resulted from four strong N–H⋯O and two weak C–H⋯O types of H-bonding. In total six H-bonding and the planarity of the host in the complex are responsible for the high binding energy. The addition of an excess of more basic anions (F− and CH3COO−) induces stepwise deprotonation, an event signalled by the appearance of a bright yellow color. The intensity of the fluorescence spectrum increases when hydrogen bonding occurs and decreases when deprotonation occurs, which is evidenced by fluorescence titrations.

Novel anthracene- and pyridine-containing Schiff base probe for selective “off–on” fluorescent determination of Cu2+ ions towards live cell application

The novel anthracene- and pyridine-containing Schiff base derivative 2-(2-(anthracen-9-ylmethylene)hydrazinyl)pyridine (AP) has been synthesized via one-pot reaction and its fluorescent “off–on” detection of Cu2+ ions, via PET-based mechanism, is reported. The 1 : 1 stoichiometry of AP⋯Cu2+ sensor complex was calculated from Jobs plot based on PL titrations and supported by ESI (+Ve) mass spectral analysis. In addition, the binding sites of AP⋯Cu2+ sensor conjugate were supported by 1H NMR titration. The detection limit (LOD) and association constant (Ka) of AP⋯Cu2+ complex were obtained by standard deviation and linear fittings. Furthermore, quantum yield (Φf), SEM analysis, pH effect, FTIR interpretation and density functional theory (DFT) studies were conducted for the AP⋯Cu2+ sensing conjugate. More decisively, confocal fluorescence microscopy imaging from Raw264.7 cells indicated that AP could be used as an effective fluorescent probe for the analysis of Cu2+ ions in living cells.

Computational and experimental studies on the effect of hydrogenation of Ni-doped TiO2 anatase nanoparticles for the application of water splitting

We have studied theoretically and experimentally the effect of Ni-doping in TiO2 nanoparticles (NPs) on hydrogenation. The doped NPs can be hydrogenated readily in a much shorter time at T 80 kcal mol−1 increase in exothermicities.

Quantum mechanical calculations for the misincorporation of nucleotides opposite mutagenic 3,N4-ethenocytosine.

The ubiquitous nature and persistence of exocyclic DNA adducts suggest their involvement as initiators of carcinogenesis. We have investigated the misincorporation properties of the exocyclic DNA adduct, 3,N(4)-ethenocytosine, using DFT and DFT-D methods. Computational investigations have been carried out by using the B3LYP, M062X, and wB97XD methods with the 6-31+G* basis set to determine the hydrogen bonding strengths, binding energy, and physical parameters. The single point energy calculations have been carried out at MP2/6-311++G** on corresponding optimized geometries. The energies were compared among the 3,N(4)-ethenocytosine adduct with DNA bases to find the most stable conformer. The solvent phase calculations have also been carried out using the CPCM model. The computed reaction enthalpy values provide computational insights to the earlier experimental observation in in vitro, E.coli, and mammalian cells of a high level of substitution mutation in which C → A transversion results from εC-T pairing [εC-T3 and εC-T4] in the adduct containing DNA sequence.

Facile rhodamine-based colorimetric sensors for sequential detections of Cu(II) ions and pyrophosphate (P2O74−) anions

Two rhodamine hydrazine derivatives Rh1 and Rh2 with catechol and ether functionalities have been synthesized and utilized towards sequential colorimetric detections of Cu(II) and pyrophosphate (PPi) ions in CH3CN–H2O (v/v = 9 : 1, 5 mM Tris–HCl, pH 7.4) semi-aqueous medium. Notably, Rh1 and Rh2 are the first example of colorimetric rhodamine-based probes for the sequential detections of Cu2+ ion and PPi anion. Based on the significant colorimetric responses (from colorless to pink) of Rh1 and Rh2 to Cu2+ ions, the detection limits were estimated as low as 1.22 × 10−8 M and 8.0 × 10−7 M, respectively, which signified the utilities of designed probes towards facile detections of Cu2+ ions. Furthermore, upon the successive addition of PPi ion to Rh1–Cu2+ and Rh2–Cu2+ complexes, it has been altered and restored to its origin of Rh1 and Rh2 via re-coordination of PPi to Cu2+ ion, which was confirmed by color changes from pink to colorless. Moreover, computational DFT calculations provided more insights into HOMO–LUMO structures of rhodamine derivatives and their copper complexes. Additionally, the solid state strip-based colorimetric detections of Cu2+ ion were supplemented as a real time application.

Model Calculations for the Misincorporation of Nucleotides Opposite Five-Membered Exocyclic DNA Adduct: N2,3-Ethenoguanine

Five-membered exocyclic DNA adducts are biologically very significant because of their potential to block DNA replication and transcription. N(2),3-Ethenoguanine (N(2,3)-εG) has been identified in the liver DNA of vinyl chloride-exposed rats as a five-membered DNA adduct. Singer et al. ( Carcinogenesis 1987 , 8 , 745 - 747 ) reported that the misincorporation of thymine (T), with two hydrogen bonds to N(2,3)-εG, represents the mutagenic event. Although the base-pairing specificity and mode of misincorporation have been studied experimentally for the N(2),3-ethenoguanine adduct, molecular-level information is not yet clear. In this study, we have considered all four different DNA nucleotides paired with the N(2),3-ethenoguanine adduct for model calculations toward the determination of base-pairing specificity. To provide insight into the mutagenic process of DNA damage based on geometric characteristics and electronic properties, the B3LYP and M06 methods were employed for these model calculations. Single-point energy calculations at the MP2/6-311++G** level on the corresponding optimized geometries were also carried out to better estimate the hydrogen-bonding strengths. The polarizable conductor calculation model (CPCM), which accounts for the overall polarizability of the solvent, was also employed. The computed reaction enthalpy values lie in the order εG-G(2) (10.3 kcal/mol) > εG-G(4) (9.6 kcal/mol) > εG-T(4) (9.2 kcal/mol) > εG-G(1) (9.1 kcal/mol) > εG-A(5) (8.2 kcal/mol) > εG-C(2) (7.9 kcal/mol) at the M06 level, which indicates that guanine and thymine are most favorable for mispairing with the N(2),3-ethenoguanine adduct.

Quantum mechanistic insights on aryl propargyl ether Claisen rearrangement.

The mechanism of aryl propargyl ether Claisen rearrangement in gas and solvent phase was investigated using DFT methods. Solvent phase calculations are carried out using N,N-diethylaniline as a solvent in the PCM model. The most favorable pathways involve a [3,3]-sigmatropic reaction followed by proton transfer in the first two steps and then deprotonation or [1,5]-sigmatropic reaction. Finally, cyclization yields benzopyran or benzofuran derivatives. The [3,3]-sigmatropic reaction is the rate-determining step for benzopyran and benzofuran with ΔG(‡) value of 38.4 and 37.9 kcal mol(-1) at M06/6-31+G**//B3LYP/6-31+G* level in gas and solvent phase, respectively. The computed results are in good agreement with the experimental results. Moreover, it is found that the derivatives of aryl propargyl ether proceeded Claisen rearrangement and the rate-determining step may be shifted from the [3,3]-sigmatropic reaction to the tautomerization step. The NBO analysis revealed that substitution of the methyl groups on the aliphatic segment has decreased the stabilization energy E(2) and favors the aryl propargyl ether Claisen rearrangement.

Spectroscopic probe on N–H⋯N, N–H⋯O and controversial C–H⋯O contact in A–T base pair: A DFT study

DNA base pair A-T has been investigated by IR and NMR spectroscopy using DFT methods. The results have been analyzed in terms of infrared vibrational frequencies and (1)H NMR chemical shifts. Different types of interactions N-H⋯N, N-H⋯O and C-H⋯O types have been investigated in DNA base pairs. Although, previous reports argued about the third C-H⋯O type interaction in A-T base pair, such typical interaction has been analyzed thoroughly by IR and NMR spectroscopy using DFT methods. Our results show that the CH⋯O interaction in the A-T base pair is a weak interaction compared to normal hydrogen bond interactions.