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Three new clip-like receptors (H2L1, H2L2, and H2L3) have been synthesized based on a biphenyl moiety consisting of two amide and Schiff base linkages, and used to prepare the corresponding copper(II) complexes, [Cu2(HL1)(py)2(H2O)](ClO4) (1), [Cu2(L2)(py)2] (2), and [Cu2(HL3)(py)2](ClO4) (3). Interestingly, upon complexation with Cu2+, the two arms of the biphenyl moiety of the ligands are forced to approach each other, thus considerably reducing the dihedral angle between the two phenyl rings with respect to the conformation assumed in the free ligands. The reason behind the formation of this type of sterically hindered structures has been explained using theoretical calculations. The solution state structures of the copper complexes were found to be almost the same as those detected in the solid state. Furthermore, the interaction between the complexes with calf-thymus DNA (ct-DNA) has been investigated. Among the three, complex 3 exhibits the strongest interaction with ct-DNA because of its structure and coordination environment, whereas complex 1 does not interact with ct-DNA. The binding mode of complex 3 with DNA was found to be mainly intercalative in nature and the interaction has been explored using optical melting and viscometric study. The binding process of 3 is forced mainly by electrostatic interactions, whereas for 2, non-electrostatic interactions appear to play a vital role. It is worth mentioning that the interaction between complex 3 and ct-DNA is governed by a high binding constant, a negative enthalpy change and a positive entropy change. CD measurements have also been performed to investigate the structural changes of ct-DNA.

Two compounds, namely 2-(1H-benzo[d]imidazol-2-yl)-6-methoxyphenol (BIMP) and (E)-ethyl 2-cyano-3-(pyren-3-yl)acrylate (ECPA), were synthesized and characterized. BIMP portrayed an interesting feature of aggregation promoted enhancement of excited state intramolecular proton transfer (ESIPT) in water. On the other hand, ECPA shows AIE emission in solution. Steady state spectroscopic studies revealed that the BIMP–ECPA ensemble in solution behaves as a white light emitter, where BIMP acts as a donor and ECPA as an acceptor. The mechanism operative behind the observed white light generation was revealed to be exciplex formation between BIMP and ECPA. The current report is the first example of white light generation from two synthesized AIEgens through exciplex formation and hence holds its own merit for a smart choice of synthesized compounds resulting in white light generation.

Photophysical properties of a synthesized asymmetric two-way proton transfer molecule 3-(benzo[d]thiazol-2-yl)-2-hydroxy-5-methoxybenzaldehyde (BTHMB) were studied in detail. BTHMB could undergo ex...

We report the crystal structure of 5, 7 –dihydroxy 4-methylcoumarin (HC) and its ratiometric sensing behavior towards F− and AcO− in aqueous DMSO. HC shows an outstanding feature in its crystal structure by forming a hexamer constituting of six O atoms via H-bonding, mimicking the chair form of cyclohexane. The detection limit for HC towards F− and AcO− are 1.12 × 10−8 (M) and 2.55 × 10−7(M) respectively. Interestingly, HC is selective towards F− in a mixture of anions. The mechanism of detection of anions by HC was established through 1H NMR titration. The practical utility has been explored by F− and AcO− detection in solid state.

The interaction of a cationic photosensitizer Safranin-O with liposome membranes having similar surface charge (negative) but differing in the presence of saturation on the lipid side-chain has been studied. To this end, dimyristoyl-l-R-phosphatidylglycerol (DMPG) and 1,2-dioleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DOPG) phospholipids were employed to prepare small unilamellar vesicles. The dye is found to bind in the headgroup region of both the liposome membranes with significantly higher affinity to DOPG lipid containing unsaturated side chain. The effects of various cyclodextrins (CDs) on the stability of the probe-bound liposome membranes have also been investigated using steady-state and picosecond-resolved fluorescence as well as dynamic light scattering techniques. The modulations of the fluorescence properties of the lipid-bound dye were exploited to rationalize the membrane destabilization following interaction with the cyclodextrins. Experimental results reveal the selective interaction of DMPG membrane with CDs leading to rupture of the integrated structure of the liposome units accompanying release of the bound probe to the bulk aqueous phase. On the contrary, no discernible interaction of the CDs was observed with DOPG liposome membrane. Our results also show the differential extents of interaction of various CDs (α-CD, β-CD, methyl-β-CD, and γ-CD) with DMPG leading to varying degrees of release of the bound-dye molecule.

We report the synthesis and photophysical properties of a coumarin based probe (1E)-1-(1-(7-(diethylamino)-2-oxo-2H-chromen-3-yl) ethylidene) thiosemicarbazide (DIDOT). DIDOT shows a polarity dependent change in the emission maxima in the solution phase. This is explained by the increased dipole moment in the excited state by an intramolecular charge transfer (ICT) process. DIDOT can successfully detect Zn(II) in aqueous methanol by a shift in the charge transfer emission maxima from approximately 506 to approximately 535 nm. This shift led to a change in the color of the emission from green to yellow under UV-light. The mechanism of Zn(II) detection has been delineated using electrospray ionization-mass spectrometry (ESI-MS), Fourier-transform infrared spectroscopy (FTIR) and fluorescence time resolved studies coupled with theoretical calculations. The increment in the charge transfer in the Zn(II) complex of DIDOT over the bare receptor as a consequence of conformational locking was determined to be the underlying cause of the cation detection phenomenon. The limit of detection and binding constant values of DIDOT towards Zn(II) were approximately 3 × 10−8 M and 2.35 × 105 M−1 respectively. Finally, the practical utility of DIDOT has been demonstrated by successful detection and quantification of Zn(II) in spiked water samples.

The -OH group protected 2-(hydroxyphenyl) benzothiazole (HBT) based ratiometric chemodosimeters have previously been reported to undergo regeneration of excited state intramolecular proton transfer (ESIPT) process upon deprotection. In the current work it is demonstrated for the first time that generation of anion of HBT leads to the optical changes in these types of chemodosimeters rather than regeneration of HBT by using a Hydrazine specific chemodosimeter based on substituted HBT.

Photophysical properties of 1-(2’-Hydroxy-5’-Chlorophenyl)-3-thio-5-oxo-1H-imidazo-[3,4-b] isoindol (HCHT) have been investigated thoroughly. Steady state and time resolved absorption and emission measurements in combination with theoretical calculation reveal that the synthesized molecule HCHT shows excited state thiolactim-thiolactum tautomerism through intramolecular hydrogen bonding between donor sulphur atom (-S-H) and acceptor nitrogen (N) atom. This is by far the first example where a sulfur atom is present as donor in an excited state proton transfer (ESIPT) process. Choice of sulfur atom in HCHT decelerates the irreversible ESIPT process compared to its oxygen atom donor analogue as evidence from excited state lifetime experiments.

We report the photophysical properties of a synthetic asymmetric azine-based compound (17Z,18E)-4′-((E)-3-phenylallylidene)-1′-(dimethylamino)-1-((pyren-8-yl)methylene)hydrazine (PYNC). The molecule PYNC shows an appreciable red shift in the emission maximum in a wide range of solvents. In water, PYNC shows the characteristic feature of excimer formation exclusively. However, in all other solvents, the excimer band is present alongside the charge transfer emission band. The assignment of charge transfer and excimer bands has been established by various steady-state emission spectral data. PYNC, owing to this novel excimer-coupled charge transfer phenomenon, can be a potential probe for studying various supramolecular assemblies of biological interest.

A methoxy substituted HBT derivative, namely 2-(benzo[d]thiazol-2-yl)-6-methoxyphenol (TMP), was synthesized and characterized. Detailed photophysical investigation of TMP indicated the coupling of excited state intramolecular proton transfer (ESIPT) and aggregation induced emission (AIE). Crystal structure analysis along with theoretical calculations on TMP showed equal preference of the proton to form hydrogen bonds with methoxy oxygen and the benzothiazole N atom, which is responsible for the observed AIE. TMP could be used as an efficient energy harvesting platform with rhodamine-B dye in aqueous solution, owing to Forster Resonance Energy Transfer (FRET) between the two. Finally, TMP can serve as an efficient probe for selective detection of sulfide in pure aqueous solution as well as in the solid state.

The present study depicts a spectroscopic investigation on the binding interaction of a phenazinium-based photosensitizer, phenosafranin (PSF) with a micelle forming surface active ionic liquid (SAIL), 1-butyl-3-methylimidazolium octyl sulfate (Bmim Os). The steady-state as well as time-resolved spectroscopic results reveals the binding of PSF with the micelles of the ionic liquid. The modulations of the spectral properties of PSF on interacting with Bmim Os micelles have been further employed to monitor the effect of various cyclodextrins, αCD, βCD and γCD (with varying dimensions of the hydrophobic cavity), on the Bmim Os micellar aggregates. The effective disruption of the Bmim Os micelles in presence of CDs is confirmed from the reduced size of Bmim Os micelles with added CD as observed from the DLS results.

The discrete effects of a series of structurally divergent monomeric viz. Sodium Chloride (NaCl), Tetra-butyl Ammonium Chloride (TBAC) and Sodium Benzoate (NaBz) and polymeric viz. Sodium Polystyrene Sulfonate (NaPSS) electrolytes towards the morphological and/or aggregation properties of Octadecyl-trimethyl Ammonium Bromide (OTAB) micelles have been quantified spectroscopically by means of the modulations of the absorption and emission spectral properties of an extrinsic anthracene-based probe 9-methyl anthroate (9-MA) within the concerned media. Further corroboration of the spectroscopic results was acquired from the non-invasive dynamic light scattering technique. The qualitatively similar mode of action of all the monomeric salts has been explained on the basis of the archetypal Israelachvili model whereas the corresponding extent of the morphological transition of the micelles, which is found to follow the order NaBz > NaCl > TBAC, has been explained invoking the co-sphere overlap model. Conversely, to explain the aggregation behaviour of the micelles in the presence of the polymeric electrolyte, a two-step model has been formulated. According to this model, at the low concentration regime, the polymeric salt is found to only neutralize the surface charge of the micelles inducing micellar growth; whereas further increment in the concentration of the polymer assists the hydrophobic association between the micelles leading to the formation of larger aggregates, eventually causing a phase separation.

The photophysical aspects of a synthesized coumarinyl chalcone derivative 3-((2E, 4E)-5-(4-(dimethylamino) phenyl) penta-2, 4-dienoyl)-4-hydroxy-2H-chromen-2-one (DPPHC) were explored. DPPHC shows excited state intramolecular proton transfer (ESIPT) suppressed excited state intramolecular charge transfer (ESICT) as evidenced from steady state and time resolved spectroscopic analysis. Interestingly, DPPHC behaves as a strong red emitter solely in chloroform and dichloromethane semi-polar solvents exclusively. Using this property, on-spot detection of these two solvents was achieved in paper strips coated with DPPHC as well as in spiked alcohol samples by emission ratiometry change.

Attempt has been made to explain why different aliphatic quaternary ammonium tribromides (QATBs) show different levels of efficiency in bromination reactions. For this study, tetrabutyl ammonium tribromide (TBATB, [N(C4H9)4]Br3), and cetyl trimethyl ammonium tribromide (CTMATB, [N(CH3)3C16H33]Br3) were used as representative examples. UV–Vis Spectroscopic method was employed to measure the thermodynamic parameters of the reactions. Influence of quaternary ammonium cation on tribromide (Br3−) performance was assessed with the aid of Density Functional Theory (B3LYP/6-311++G(d,p)) by determining the dissociation energy of the QATBs, energies of pairs of their frontier orbitals, which are HOMO and LUMO and calculation of dipole moments.

We present a detailed photophysical properties of a synthesized charge transfer (CT) molecule (2E, 4E)-ethyl 2-cyano-5-(4-(dimethylamino) phenyl) penta-2, 4-dienoate (ECDPPD) in bulk medium and its spectral modulation inside β-Cyclodextrin cavity. Enhancement of acceptor strength of 4-(dimethylamino) cinnamaldehyde by replacing the moderate acceptor in the form of a Formyl group by two acceptors known to display greater electron withdrawing ability along with extra conjugation which may be responsible for higher dipole moment both in ground as well as in excited state. The observed excited CT process and its solvent polarity dependent emissive properties is due to simply increasing the ‘end-to-end’ length between donor and acceptor along with introduction of two different acceptors in the same site. Low fluorescence quantum yield and shorter fluorescence lifetime is due to the operation of active non-radiative channels through flexible bonds supported by viscosity and temperature dependent spectral measurement. The molecule ECDPPD easily interacts with β-CD with the formation of inclusion complex with a definite stoichiometry where the photophysics are modulated and hence can be used as fluorescence microenvironment reporter for example to evaluate the polarity as well as the micro viscosity of various regions of protein and other bimolecular systems.

We report the synthesis of a novel hydrazine-bridged anthranilic acid–naphthalene conjugate (E)-2-(benzamido)-N′-((2-hydroxynaphthalen-1-yl) methylene) benzohydrazide (BBHAN) and its crystal structure. BBHAN can detect Al3+ by a sharp increment in fluorescence intensity (∼40 times) in aqueous methanolic medium. The limit of detection of BBHAN towards Al3+ is 1.68 × 10–9 M, and the former undergoes a 2:1 binding with Al3+ with a high binding constant of ∼1.15 × 1011 M2–. BBHAN detects Al3+ by the well-known mechanism of chelation-enhanced fluorescence (CHEF), established by fluorescence time-resolved measurement. The mode of interaction between BBHAN and Al3+ has been explored by 1H NMR and electrospray ionization mass spectrometry techniques. Paper strips coated with BBHAN can detect Al3+ under UV light observed through the naked eye. Lastly, BBHAN can detect Al3+ in MDA-MB-468 cells.

Encapsulation of a persuasive anticancer drug (Sanguinarine, SGR) within microheterogeneous environment of niosome has been investigated. Utilizing steady-state and time-resolved spectroscopic methods the effects of extrinsically added salts and temperature on the photophysical properties of niosome-bound bio-active drug have been explored thoroughly. The prototropic (alkanolamine⇌ iminium) equilibrium of SGR is found to be preferentially favored toward the neutral form inside the hydrophobic interior of niosome. With addition of salts and increment of temperature the reverse tendency of stabilization of the cationic species is observed which can be explained on the basis of degree of water penetration of water molecules to the hydration layer of niosome. Furthermore, drug sequestration has been investigated via disruption of niosome applying cyclodextrins (CDs). Exploration of the effect of CDs (β-CD and γ-CD) on the niosome aids to have knowledge of the effect of CDs on cell membrane. In addition, the differential rotational relaxation behavior of SGR at various environmental circumstances has been observed to substantiate with other experimental results.

The past few decades have witnessed significant advances in the development of functionalized gold nanoparticles (GNPs) for diverse applications in various fields such as chemistry, biology, pharma...

The present study demonstrates the interaction of potential chloride channel blocker drug, namely, 9-methylanthroate (9MA) with dimyristoylphosphatidylcholine (DMPC) lipid bilayer membrane in the solid gel (SG, at 15 °C) and liquid crystalline (LC, at 37 °C) phases of the lipid. Our spectroscopic results reveal a relatively greater degree of partitioning of the drug molecules into the DMPC lipid membrane at 37 °C (LC phase) compared to that at 15 °C (SG phase). Furthermore, the study is extended to explore the interaction of a bile salt (sodium deoxycholate, NaDC) with the DMPC lipid bilayer membrane in the SG as well as LC phase utilizing the environment-sensitive photophysical characteristics of the drug. Our steady-state and time-resolved spectroscopic results are invoked to critically analyze all the possibilities of bile salt-induced modulation of the photophysical behavior of the lipid-bound drug e.g., (i) expulsion of the lipid-bound drug molecules to the bulk aqueous phase upon addition of the bile salt, (ii) redistribution of population of the drug molecules within the lipid membrane and (iii) penetration of water molecules into the lipid bilayer membrane and thereby altering the hydration structure of the membrane. Cumulatively, our results appear to converge on the possibility of bile salt-induced hydration of the interfacial region of the lipid membrane as the actuating mechanism of the lipid-bile salt interaction. It is imperative to state that the present study emphasizes on the interaction of DMPC lipid membrane with the bile salt (NaDC) only in the submicellar concentration regime of NaDC which involves no significant perturbation of the lipid vesicle structure.

An asymmetric hydrazide, (12E, 13E)-2-((naphthalen-1-yl) methylene)-1-(1-(2-hydroxynaphthalen-6-yl) ethylidene) hydrazine (abbreviated as AH) is synthesized and characterized by standard techniques and crystal structure of AH has been obtained. The naked eye detection of F- in aqueous acetonitrile (acetonitrile: water=7:3/v:v) by AH has been investigated by UV-Visible titration and in presence of other anions, the limit of detection being 1.31×10-6(M). The mechanism of F- sensing has been explored by 1H NMR titration. AH undergoes hydrogen bonding with F- followed by deprotonation. The practical utility of AH has been explored by successful test kit response and color change in toothpaste solution.

Photophysical properties of a newly designed synthetic compound DYMDAP have been investigated in combination with computational calculations. DYMDAP shows a solvent dependent emissive behavior which in non-polar solvents shows two distinct peaks along with a shoulder but with increasing polarity as also proticity of the solvents the intensity of each band varies significantly. Along with the two bands, a new band is observed in polar protic solvent due to the proton transfer (PT) in the excited state of the compound. Only in polar protic solvents, intensity of the PT band increases significantly whereas in non-polar or polar aprotic medium intensity is sparse. By comparing the spectral observations of DYMDAP with two control compounds DYMP and DYMDAB the proton transfer process is assigned to be due to solvent mediated and the proton transfer process is enhanced by the presence of charge transfer moiety.

Two anthracene based receptors ADAMN and ANOPD were synthesized and characterized. The response of both towards F − ion has been monitored by UV–Vis and 1 H NMR spectroscopy as well as naked eye color change. Interestingly, change in acceptor unit endows ADAMN to behave as a INHIBIT logic gate with F − and H + as inputs whereas ANOPD remains totally silent towards F − . The reason for this differential behavior has been explored by DFT calculations. The practical utility of the logic gate response of ADAMN was explored by successful paper strip experiment.

We report the synthesis of a novel hydrazine based compound 1-[(2-Hydroxy-1, 2-diphenyl-ethyl)-hydrazonomethyl]-naphthalen-2-ol (2). Compound 2 is the first report of its kind. We utilized the aforesaid compound to detect Cu2+ and F− via emission enhancement and naked eye color change. The structural intricacies of 2 have been explored by its crytal structure. The mechanism of binding of 2 with F− has been established by 1H NMR titration. The limit of detection for Cu2+ and F− is ∼9.0 × 10−7 (M) and 1.0 × 10−6 (M), respectively. The practical performance of 2 is demonstrated by successful live cell imaging of Cu2+ and detection of F− in toothpaste.

Two amido-schiff bases (3-Hydroxy-naphthalene-2-carboxylic acid pyren-1-ylmethylene-hydrazide and Naphthalene-2-carboxylic acid pyren-1-ylmethylene-hydrazide) have been synthesized having a common structural unit and only differs by a -OH group in the naphthalene ring. Both of them can detect Cu2+ ion selectively in semi-aqueous medium in distinctly different output modes (one detects Cu2+ by naked-eye color change where as the other detects Cu2+ by fluorescence enhancement). The difference in the binding of Cu 2+ with the compounds is the reason for this observation. The detection limit is found to be micromolar region for compound which contains -OH group whereas the compound without -OH group detects copper in nano-molar region. DFT calculations have been performed in order to demonstrate the structure of the compounds and their copper complexes. Practical utility has been explored by successful paper strip response of both the compounds. The biological applications have been evaluated in RAW 264.7.

The present study demonstrates the binding interaction of a drug, berberine (BR) with DMPG liposome membrane as a function of the phase state of the lipid. Our results display an apparently contradicting interaction behavior of BR with DMPG lipid in the sense that the drug:lipid binding constant is found to be higher with the more ordered and compact solid gel (Lβ) phase at T = 288 K (lower permeability) of the lipid compared to the liquid crystalline (Lα) phase at T = 310 K (greater permeability). This result is rationalized on the basis of the probable location of the cationic drug molecules at the interfacial region of the lipid membrane having anionic headgroup. The excited-state relaxation dynamics of the lipid-bound drug coupled with rotational relaxation studies further substantiate a stronger binding of BR with the solid gel (Lβ) phase. The BR:DMPG binding interaction is meticulously quantified by calorimetric studies which reveal that the interaction phenomenon is enthalpically (ΔH 0) favorable, and is accompanied with marked modulation of the hydration structure surrounding the interacting species as rationalized on the basis of release of structured water molecules following the interaction. The calorimetric results also quantify the differential binding constants and binding stoichiometries of BR with DMPG; Ka = (2.32 ± 0.09) × 105 M− 1 and 2:1 stoichiometry in the solid gel (Lβ) phase (T = 288 K) versus Ka = (5.00 ± 0.2) × 104 M− 1 and 1:1 stoichiometry in the liquid crystalline (Lα) phase (T = 310 K). In addition, our results of nonionic surfactant (Triton X-100)-induced solubilization of DMPG lipid reveal differential degrees of release of lipid-bound drug depending on the phase state of the lipid. Fluorescence anisotropy and excited-state relaxation studies of the lipid-bound BR following interaction with TX100 display a greater degree of release of the drug molecules from the liquid crystalline (Lα) phase of the liposome membrane. These results are further corroborated from fluorescence correlation spectroscopic (FCS) results.

The present work reveals the binding interactions of a credible cancer cell photosensitizer, harmane (HM), with some selected bile salt aggregates of dissimilar hydrophobicity viz. sodium deoxycholate (NaDC), sodium cholate (NaC) and sodium taurocholate (NaTC). The explicit variation of the prototropic equilibrium of the photosensitizer both in the ground and excited state has been utilized to scrutinize the interaction phenomena. Differential modulation in the prototropic equilibrium of HM in the aforesaid aggregates has been explained on the basis of the structural dissimilarities of the bile salt monomers. The contrived hydrophobic surroundings provided by the aggregates have been reflected on the spectroscopic results, especially in the time-resolved fluorescence and the rotational dynamical behavior of the molecule of interest. Slow solvent reorientation time with regard to the lifetime of HM proliferated by the red-edge effect in two specific bile salts namely NaC and NaTC, whereas its absence in NaDC aggregates has also been elucidated on the basis of accessibility of the solvent molecules within the aggregates.

The interaction of Ribonuclease A (RNase A) with the bile salt, sodium deoxycholate (NaDC) is meticulously investigated using various spectroscopic techniques. The binding isotherm constructed from the modulation of intrinsic tyrosine fluorescence of the protein following interaction with NaDC conspicuously reveals an intrinsically complex stepwise interaction process which proceeds through the formation of distinct conformational states of the protein. The conformational transitions are found to occur at c 1 = 2.2 mM, and c 2 = 7.2 mM of NaDC. These results are subsequently corroborated from the studies of excited-state relaxation dynamics of the intrinsic tyrosine residues of RNase A, and the modulations in fluorescence behavior of an extrinsic probe (ANS) bound to the protein. The far-UV circular dichroism spectral analyses unveil only nominal influence on the secondary structural element of the protein up to [NaDC] = c 1 = 2.2 mM, which is then followed by marked disruption of the secondary structure of RNase A following further addition of NaDC. This clearly accounts for differential interaction behaviors of RNase A with the monomeric and micellar forms of NaDC (CMC of NaDC in aqueous buffer is estimated to be ∼3.0 mM). In Region-I (up to c 1 = 2.2 mM), the protein:surfactant interaction is argued to be predominantly governed by electrostatic/ionic interaction force. Subsequently, in Region-II (up to c 2 = 7.2 mM) the RNase A:NaDC interaction accompanies major denaturation of the protein (∼17% loss of the secondary structure of RNase A at c 2 = 7.2 mM) resulting in significant exposure of hydrophobic surfaces of the protein. However, the tertiary structure of the protein remains essentially unperturbed within the concentration regime of NaDC under study.

A computational analysis based on the “Atoms in Molecules” i.e. AIM formalism; of the molecular forces present within 3-Hydroxy-2-pyridin-2-yl-propenal (HPYP) has been undertaken in this contribution. The study presents a critical argument on the regulatory role(s) of hydrogen bonds (HBs) and other non-covalent interactions, viz. H···H and N···O/O···O; toward the structural features as well as global stabilization and/or destabilization of the aforesaid molecular system. Furthermore, to acquire a comprehensive account of the aromatic stabilization of the framework in the presence of the concerned non-covalent interactions; Nucleus Independent Chemical Shift (NICS) descriptor has been employed.

The modulations of the photophysics and dynamics of an archetypal anticancer β-carboline drug, namely, harmane (HM) within AOT reverse micelles (RMs) have been explored. To this end, particular focus is given on a pH-dependent study commensurate with the effect of increasing water content within the RM interior. Our results reveal markedly different photophysical behavior of the drug encapsulated within the RM compared to that in bulk aqueous medium. For example, our results show the presence (or absence) of the cationic (or neutral) emission of HM in RMs in pH values apparently much higher (or lower) than that of pure aqueous medium. The characteristic zwitterionic emission in strongly alkaline bulk aqueous solutions (e.g., pH 12.2 and 13.5) is also found to be lacking within the reverse micellar core, even in RMs with w 0 ≥ 10. These data are further substantiated from the study of the dynamical aspects of the interaction scenario, that is, modulation of the fluorescence decay and rotational relaxation behaviors of HM entrapped within the RMs. Cumulatively, our results indicate the presence of a proton gradient across the reverse micellar water pool in which the interfacial regime appears to be more acidic in comparison to the central core. The results with alkaline solutions (e.g., pH 10.0, 12.2 and 13.5) suggest selective compartmentalization of the hydroxide ions leaving the effective pH of the water pool lower than that of the bulk aqueous solution.

The present work is focused on exploring the interaction of two phenazinium-based biological photosensitizers, phenosafranin (PSF) and safranin-O (SO), with human serum albumin (HSA), with particular emphasis on the physiologically significant NB conformational transition of the protein on the dye:HSA interaction. In addition, the presence of methyl substitution on the planar phenazinium ring in SO paves way for looking into the effect of simple chemical manipulation (that is, methyl substitution on the dye nucleus) on the dye:protein interaction behavior as a function of various (pH-induced) isoforms of HSA. Our results reveal a significantly stronger binding interaction of SO with the B isoform of HSA (at pH9.0) compared to that with the N isoform (at pH7.4). On the contrary, the PSF:HSA interaction is found to be reasonably insensitive to the aforesaid conformational transition of HSA. However, the probable binding location of both the dye molecules (PSF and SO) is found to be within the protein scaffolds (domain IB). This is further quantified from the modulation of fluorescence decay behavior of the dyes within the protein scaffolds. It is important to note that the rotational relaxation behavior of the protein-bound dyes reveals an unusual 'dip-rise-dip', an observation not reported earlier. Such unusual anisotropy decay is meticulously analyzed by an associated (or multicomponent) exponential decay model which emphasizes on the fractional contributions from differential classes of fluorophore populations characterized by the fast (due to unbound or solvent exposed part of the fluorophore) and slow (due to embedded or bound part) motions, in combination with their different local mobilities. Furthermore, the translational diffusion of the dye molecules in the presence of the protein in different isoforms (N-form or B-form) at a single molecule level is also measured by Fluorescence Correlation Spectroscopy (FCS).

We report the synthesis and Zn2+ sensing of a novel coumarin-hydrazine conjugate 3-{1-[(4, 6-Dimethyl-pyrimidin-2-yl)-hydrazono]-ethyl}-chromen-2-one (3). Compound 3 can act as a neat fluorescent Zn2+ sensor by an increment in fluorescence intensity along with an appreciable red shift. Fluorescence enhancement is caused by complexation through cis-trans isomerization process in the presence of Zn2+ ion. The practical utility of 3 was demonstrated by successful test kit experiment to detect Zn2+ in water under UV-light.

The present work reveals the study of interaction of a promising chemotherapeutic drug ciprofloxacin (CFX) with a model transport protein bovine serum albumin (BSA). The occurrence of the drug-protein interaction is found to result in significant modulations of the fluorescence excitation and emission spectroscopic properties of CFX following interaction with BSA. However, the major focus of the study underlies a critical insight into the quantitation of the drug-protein interaction phenomenon. To this end, we have exploited the isothermal titration calorimetric (ITC) technique to quantify the affinity constant (K a ) and stoichiometry (n) of the CFX-BSA interaction with simultaneous revelation of the accompanying thermodynamics of the interaction process. In this context, our discussion also sheds light on the lacuna surrounding various experimental methodologies for evaluation of drug-protein binding parameters. Our endeavor also extends to elucidation of the kinetic parameters and energy of activation (E a ) of the CFX-BSA interaction. The present study also delineates the modulation of the dynamical aspects of CFX following interaction with BSA. The rotational relaxation dynamics of the protein-bound drug reveals the not-so-common “ dip-rise-dip ” anisotropy decay. Furthermore, the effect of drug binding on the native protein conformation has been evaluated from circular dichroism (CD) spectroscopy which reveals partial rupture of the protein secondary structure.

The spectral behaviour of a pharmaceutically important molecule, 1-(2-Hydroxy-5-bromo-phenyl)-3,5-dioxo-1 H -imidazo-[3,4- b ] isoindole (ADBR), has been reported. The photophysical properties of ADBR reveal the occurrence of excited state intramolecular proton transfer (ESIPT) phenomenon involving a four-membered system, resulting in a conversion from lactim to lactam form of ADBR in the excited state. Excitation at shorter wavelength resulted in dual emission from ADBR in water due to the presence of the proton transferred (lactam) form along with the excited local (lactim) form, although, only PT emission was observed in all other solvents of varying polarity used in this study. The ESIPT process was found to be hindered in water probably due to intermolecular hydrogen bonding between the water molecules and the functional groups of lactim form of ADBR involved in the ESIPT phenomenon. The time-resolved studies corroborated the steady state data and confirmed the operation of an ultrafast ESIPT process.

We report novel compound 4-nitro-2-((pyrimidin-2-ylamino) methyl) phenol (1) synthesized by the condensation of 5-nitro salicylaldehyde with 2-amino pyridine. Compound 1 serves as a dual signalling chromogenic receptor for F−/AcO− and Al3 + ions. The chromogenic response of 1 towards the aforementioned analytes is reversible with respect to either Al3 +/X (= F/AcO)− or X(F/AcO)−/Al3 +. The limit of detection of 1 for F− and AcO− are 1.0025 × 10− 7 M and 0.79 × 10− 7 M, respectively. The optical switching has been rationalized on the basis of UV–Vis titrations and 1H NMR titrations respectively. The optical switching has been successfully use by constructing reversible paper strips for detecting Al3 + as well as F−/AcO−.

Five new organotin(IV) complexes of compositions [Me 2 SnL 1 ] ( 1 ), [Me 2 SnL 2 ] n ( 2 ), [Me 2 SnL 3 ] ( 3 ), [Ph 3 SnL 1 H] n ( 4 ) and [Ph 3 SnL 3 H] ( 5 ) (where L 1 = (2 S )-2-(( E )-(( Z )-4-hydroxypent-3-en-2-ylidene)amino)-3-(1 H -indol-3-yl)propanoate, L 2 = (2 S )-( E )-2-((2-hydroxybenzylidene)amino)-3-(1 H -indol-3-yl)propanoate and L 3 = (2 S )-( E )-2-((1-(2-hydroxyphenyl)ethylidene)amino)-3-(1 H -indol-3-yl)propanoate were synthesized and spectroscopically characterized. The crystal structures of 1 – 4 were determined. For the dimethyltin derivative 2 , a polymeric chain structure was observed as a result of a long Sn∙∙∙O contact involving the exocyclic carbonyl oxygen-atom from the tridentate ligand of a neighboring Sn-complex unit. The tin atom in this complex has a distorted octahedral coordination geometry, in which the long Sn-O bond is almost trans to the tridentate ligand nitrogen-atom. In contrast, the dimethyltin(IV) complexes 1 and 3 displayed discrete monomeric structures where the tin atom has distorted trigonal-bipyramidal geometry with the two coordinating L oxygen atoms defining the axial positions. On the other hand, 4 is a chain polymer in the solid state. The ligand-bridged Sn atoms adopt a trans -Ph 3 SnO 2 trigonal-bipyramidal configuration with equatorial phenyl groups. A carboxylato oxygen atom from one and the hydroxyl oxygen of the successive ligand in the chain occupy the axial positions. The solution structures were predicted by the use of 119 Sn NMR chemical shifts. The photophysical properties of the complexes were investigated in the solid and in solution. The triphenyltin(IV) compound 4 was tested in detail ex vivo against A375 (human melanoma) cell line, exhibiting an IC 50 value of 261 nM to induce cell death as assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay without significant alteration of cytolysis as determined by lactate dehydrogenase (LDH) assay. Compound 4 -mediated potent cell death was also determined by Live and Dead assay and caspase-mediated cleavage of poly-ADP ribose polymerase (PARP). Potent cell death activity was not observed in primary cells, like blood-derived peripheral mononuclear cells (PBMC). Compound 4 inhibited the diphenyl hexatriene (DPH) binding to cells and decreased the micro viscosity in a dose-dependent manner. Additionally, the ability of 4 and cyclodextrin (CD) to interact was determined by molecular modelling.

Novel anthraimidazoledione-based compounds (1–3) are synthesized as selective colorimetric and fluorescent sensors for fluoride ion. The binding properties of the probes (1–3) are studied with different anions in acetonitrile solvent. Spectral red shifts in the absorption spectra and ‘turn-off’ emission are observed when fluoride is added to 1–3. The striking green to orange color change in the ambient light is thought to be due to the deprotonation of the N–H proton of the imidazole moiety of the probes by the basic F− ion. Interestingly, in all three cases the nonfluorescent probe-F− solutions, on treatment with copper perchlorate, show distinct color change from orange to golden yellow with resumption of fluorescence intensity. Furthermore, the reversibility of sensors (1–3) for the detection of F− ion is tested for four cycles indicating that “ON-OFF-ON” mechanism is operative. Test strip based on sensor 2 acts as a reusable cost-effective F− sensor.

A new FRET-based carbazole rhodamine hybrid (CRH) ratiometric fluorescent sensor is reported for the selective detection of Al3+. The design of the probe involved two parts: a carbazole hydrazone energy donor and a rhodamine spirolactone unit (potential rhodamine monoanion energy receptor). First, the emission of the carbazole chromophore (“donor” moiety) and next the absorption of the ring-opened rhodamine dye were measured, which clearly showed the overlap between these two spectra, indicating the FRET from the carbazole chromophore to the rhodamine moiety. FRET based ratiometric live-cell imaging for Al3+ has been rarely reported. Successful live cell imaging is demonstrated, where on addition of Al3+ solution (20 μL), the color of the CRH (20 μL) treated cells changed from blue to red.

We synthesized three cinnamaldehyde-based chalcone derivatives, (2E,4E)-1-(2-hydroxyphenyl)-5-phenylpenta-2,4-dien-1-one (HPD), (2E,4E)-5-(4-(dimethylamino)phenyl)-1-phenylpenta-2,4-dien-1-one (DPPD), and (2E,4E)-5-(4-(dimethylamino)phenyl)-1-(2-hydroxyphenyl)penta-2,4-dien-1-one (DPHPD). The molecule HPD was totally nonfluorescent. Exclusion of a phenolic -OH moiety from HPD along with the introduction of a dimethylamino moiety in DPPD resulted in excellent excited-state charge-transfer properties in the solution phase. Interestingly, introduction of phenolic -OH and dimethylamino moieties in DPHPD resulted in solvent selectivity in the excited state. DPHDP behaved as a strong fluorophore only in carbonyl- or thiocarbonyl-containing solvents, such as dimethylsulfoxide (DMSO), dimethylformamide (DMF) and dimethylacetamide (DMAC) and showed a prominent red color under UV light. However, no emission was observed in similar carbonylated solvents, such as acetone or formamide, or in viscous medium, such as glycerol. The difference in solvent response was probed by various spectroscopic techniques and analyzed using the crystal structure of the three chalcones along with theoretical calculations. The practical utility of DPHPD was explored by detecting the percentage of water in DMSO solvent.

Excited photophysics of a synthesized molecule namely 2-(benzo[d]thiazol-2-yl)-5-nitrophenol (BTNP) have been studied using steady state and time resolved techniques. BTNP exhibits ESIPT exclusively in non-polar media with exceptional Stokes’ shift. In polar solvents anion formation of BTNP hampers the ESIPT process. Solid state emission spectral pattern matches reasonably well with that in non-polar medium. Dynamic light scattering showed the increment of particle size in heptane in comparison to water, a trend reversed to conventional trait of Aggregation Induced Emission (AIE) active molecules. Nitro substituent in BTNP reverses the conventional definition of a ‘good solvent’ and ‘bad solvent’, thereby promoting ESIPT in non-polar medium via aggregation. As all reports on AIE active compounds claim water to be the solvent capable of producing the effect, we have reversed the effect by simple change in substitution. Reversal of AIE phenomenon would certainly open up new avenues in future research on AIE active fluorophores.

The present work demonstrates a detailed photophysics of bio-active drug-like acid viz., 2-hydroxynicotinic acid (2-HNA) and its interaction with a model plasma protein Bovine Serum Albumin (BSA). The drug which is in essence a vitamin-B3 derivative, is capable of exhibiting ultrafast lactim-lactam cross-over response and thereby the modulation of the lactam emission within the bio-environment of the protein has been depicted spectroscopically to reveal the drug-protein interaction. Apart from evaluating the binding constant, the probable location of the neutral drug molecule within the protein cavity (hydrophobic subdomain IIIA) has been explored by AutoDock-based blind docking simulation technique. In this microheterogeneous medium, slow solvent reorientation time with respect to the emissive lifetime of the drug explicate the Red Edge Effect (REE). To complement the findings about the binding process, chaotrope-induced protein denaturation has also been inspected. The probe also illustrates a perceptible difference in rotational relaxation time in confined medium than in aqueous medium which strengthen our verdict. Unfolding of the protein in the presence of the drug molecule has been probed by the decrease of the α-helical content, obtained via circular dichroism (CD) spectroscopy, which is also supported by the gradual slaughter of the esterase activity of the protein in the presence of the drug molecule.

The formation of a 1:1 hydrogen bonded complex of 1H-Pyrrolo[3,2-h]quinoline (1HPQ) with methanol has been characterized by quantum chemical calculations. To this end, we have resorted to the application of advanced quantum chemical tools e.g., Atoms-In-Molecule (AIM) and Natural Bond Orbital (NBO) analyses to characterize and elucidate the H-bond interactions present in 1HPQ:CH3OH complex. However, the major focus of the study underlies the exploration of the methanol-mediated excited-state double proton transfer (ESDPT) process in 1HPQ:CH3OH complex. Our computational results yield compelling evidence in favor of the feasibility of an ESDPT process while in contrary a corresponding ground-state process (GSDPT) is reasonably negated. The GSDPT process is inhibited by a high energy barrier (∼17.13 kcal mol−1) coupled with the lack of an energy minimum for the tautomer configuration at the ground-state. Conversely, the operation of an ESDPT process is argued on the basis of a distinct reversal of thermodynamic stabilities of the two geometries (1HPQ:CH3OH normal form and the tautomer) in the excited-state together with the remarkable lowering of the energy barrier of the process. The unique configuration of the transition state (TS) along the ESDPT potential energy surface is tested by IRC calculations. The presence of no ionic intermediate concludes in favor of a concerted mechanism.

In this paper, the binding interaction of a promising chloride channel blocker, 9-methyl anthroate (9-MA), with two different classes of molecular containers, β-cyclodextrins (β-CD and methyl-β-CD) and cucurbit[7]uril, having comparable cavity dimensions, has been thoroughly demonstrated via inspection of the modulation of the excited-state properties of the emissive molecule. Spectral data suggest that CB7 encapsulates the probe more efficiently in a 1:2 fashion, whereas the efficacies of β-CDs are relatively less and the corresponding stoichiometry is 1:1. Interestingly, despite being thermodynamically much more favorable than the probe-β-CD complexation equilibria, the fraction of probe-CB7 complex formed is appreciably smaller with respect to that of probe-β-CD complexes. This apparent inconsistency has been addressed via the proposition that since the formation of a 1:2 complex is entropically disadvantageous, it is anticipated that the activation barrier of the corresponding reaction is reasonably high, and thus only a small fraction of the reactants are able to surpass the energy barrier to form the products. This proposition has been thoroughly corroborated by fluorescence lifetime measurements at different temperatures.