Search

The fluorescent property of the aqueous solution of a metal organic framework (MOF) of Mn(II), having a sedimentary rocks like microstructure in solid-state, has been investigated. The luminescent feature of the the aqueous solution of MOF has been employed for studying the interactions of MOF with different surfactants including neutral, cationic, and anionic types in water medium. Interestingly, the MOF can very selective sense Triton X-100 based micelle in water medium. During the sensing process the fluorescent monomer of the MOF gets accommodated at the palisade layer of Triton X-100 in water medium and this has also been justified by simple fluorescence spectral and FE-SEM microstructural analysis. Thus, a MOF of Mn(II) can act as a selective fluorescent sensor for Triton X-100 based organized medium in water.

A novel fluorescent probe and pharmaceutically significant: 3-pyrazolyl-2-pyrazoline derivative (PYZ) has been selected as an acceptor molecule for fluorescence resonance energy transfer (FRET) interaction with serum albumins. Steady state and time resolved fluorescence techniques were applied to elucidate the nature of interaction of PYZ with serum albumins (BSA and HSA). Negligible FRET mediated emission occurred in the case of HSA but an efficient FRET mediated emission resulted in case of BSA. To gain further insight into the FRET selectivity of PYZ with the proteins, FRET from L-tryptophan (donor; native tryptophan) to PYZ (acceptor) was performed with the aim of getting an idea about the steric restrictions imposed on PYZ by the other groups present in BSA and HSA. The studies revealed that the surface bound Trp-134 in BSA allows an efficient FRET process with PYZ while the buried Trp-214 in HSA does not. The unusual selectivity for FRET in case of PYZ and the serum albumins has also been attributed to the complex structure of PYZ due to the presence of bulkier phenyl moieties in it. The complex nature of the excited state photophysics of tryptophan (Trp) in proteins also accounts for this FRET selectivity of PYZ with BSA and HSA.

The synthesis and solvatochromic behavior of the compound, 7-oxy(5-selenocyanato-pentyl)-2H-1-benzopyran-2-one (PCM), a pervasive, bioactive coumarin derivative, which is expected to possess antioxidative properties and other important therapeutic activities of significant potency with low systematic toxicity, have been reported employing steady state and time resolved fluorescence techniques. Spectroscopic studies reveal that the solvatochromic behavior of the probe depends not only on the polarity of the medium but also on the hydrogen bonding properties of the solvents. Specific hydrogen bonding interaction of PCM in polar solvents modulated the order of the two close-lying lowest singlet states. The photophysical response of PCM in different solvents has been explained considering solute-solvent interactions. To corroborate these results, we performed the ground-state geometry, lowest energy transition and the UV–vis spectrum of PCM using the density functional theory (DFT) and the time-dependent density functional theory (TD–DFT) at B3LYP/6-31G ⁎ level. We found excellent correlation between the predicted and experimental spectral data, providing a useful tool in the design of new fluorogenic probes having potential therapeutic activity.

Interactions of luminescence, water soluble ZnS nanoparticles (NPs) with flavins and glucose oxidase have been thoroughly investigated through optical spectroscopy. The photoluminescence of ZnS nanoparticles was quenched severely (∼60%) by riboflavin while other flavins such as flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) show quenching to different extents under analogous conditions. However, interestingly no effect in luminescence intensity of ZnS NPs was observed with protein bound flavins such as in glucose oxidase. Fluorescence lifetime measurement confirmed the quenching to be static in nature. Scavenging of photo-generated electron of ZnS nanoparticles by the flavin molecules may be attributed to the decrease in luminescence intensity. Quenching of ZnS nanoparticles with flavins follows the linear Stern–Volmer plot. The Stern–Volmer constants decreased in the following order: K S−V (Riboflavin)> K S−V (FAD)> K S−V (FMN). This interaction study could generate useful protocol for the fluorimetric determination of riboflavin (vitamin B 2 ) content and also riboflavin status in biological systems.

This present investigation has revealed that steady state as well as time-resolved fluorescence techniques can serve as highly sensitive monitors for exploring the interaction of fluorescent probe 1-anthracene sulphonate (1-AS) with model transport proteins, bovine serum albumin (BSA) and human serum albumin (HSA).We have focused on fluorescence resonance energy transfer (FRET) between excited tryptophan in transport proteins to 1-AS, for the study of relaxation dynamics of biological molecules.

The solvatochromic behavior of 3-pyrazolyl 2-pyrazoline derivative (PYZ), a newly synthesized molecular probe having pharmaceutical importance, has been studied in various solvents of different polarity. The Kamlet and Taft solvatochromic comparison method was utilized to rationalize the solute–solvent interactions from absorption and emission measurements. Spectroscopic studies reveal that the solvatochromic behavior of the dye depends not only on the polarity of the medium but also on the hydrogen-bonding properties of the solvents. The non-radiative relaxation process is facilitated by an increase in the polarity of the media. The photophysical response of PYZ in different solvents has been explained considering solute–solvent interactions.

The association of a non-ionic surfactant of polyoxyethylene-p-(1,1,3,3-tetramethylbutyl)phenyl ether (Triton X) series with 2-AS in aqueous solution has been studied by means of steady-state, time-resolved fluorescence and fluorescence anisotropy techniques. The effect of the hydrophobic chain length on the structural dynamism of the fluorophore has been reported. Experimental results demonstrate that the equilibrium of this dynamism is sensitive to the environment. The association constant of the probe molecule with the non-ionic micelles of Triton X (TX), location of the probe in the micellar environment, have been determined from the change in emission characteristics of the probe as a function of surfactant concentration. The rate constant of quenching and mode of quenching of probe in micellar media have been ascertained. Quantitative estimates of the micropolarity at the binding sites of the probe molecule have been determined. Some of the environment-dependent relevant fluorescence parameters, fluorescence anisotropy (r), have been monitored for exploring the imposed motional restriction of the microenvironment around the probe. An attempt has been made to correlate the steady-state results with time resolved study.

The interaction of DNA bases and corresponding nucleotides with CdS nanoparticles (NPs), biofunctionalized by cysteine, has been investigated by absorption and fluorescence spectroscopy. Unique enhancement effect of adenine, in contrast to other nucleobases, on the luminescence of cysteine capped CdS (cys-CdS) NPs at both pH 7.5 and 10.5 was found, the extent of enhancement being much higher at pH 10.5. At the latter pH, the difference optical absorption spectra show development of new peak at 278 nm with corresponding decrease in the absorption of adenine at 260 nm, which is attributed to binding of adenine anion to the CdS surface through N7 of the purine ring. Appearance of a new band at 478 cm−1 and concomitant shift in the C8–N7 vibrations to 1610 cm−1 in the FTIR spectra of cys-CdS NPs with adenine also suggest Cd–N7 binding on the particle surface. Amongst various nucleotides, ATP exhibited maximum luminescence enhancement on CdS NPs for a given change in concentration in the micro-molar range at physiological pH. A quantitative correlation between ATP concentration and PL enhancement of CdS NPs has been established, a step which in future might assist in developing new protocols for fluorescence sensing of adenine nucleotides under certain pathological conditions.

Quenching of fluorescence of the dye 3,7-diamino-2,8-dimethyl-5-phenyl Phenazinium Chloride (Safranine T) has been investigated by AgCl nanoparticles in the W/O microemulsion medium at different [H 2 O]/[AOT] ratios ( ω ) and with Ag nanoparticles and Ag + in aqueous medium. A simple straightforward method has been introduced to prepare AgCl nanoparticles in well-characterized, monodispersed biomimicking nanocavities formed by sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in heptane. Experimental results reveal that the size of the AgCl nanoparticles increases with increase in hydration. The results of the quenching experiment were analysed in the light of Stern Volmer equation. Quenching of fluorescence of the dye has been found to decrease with decrease in the size of the nanoparticles of AgCl and the variation of Stern Volmer quenching constants ( K SV ) with particle size is different for two different size regimes.