Beena Varghese

Study on the spectral and inclusion properties of a sensitive dye, 3-naphthyl-1-phenyl-5-(5-fluoro-2-nitrophenyl)-2-pyrazoline, in solvents and β-cyclodextrin

3-Naphthyl-1-phenyl-5-(5-fluoro-2-nitrophenyl)-2-pyrazoline (NPFP), a fluorogenic probe and its derivative NPFP-Phenylephrine were synthesized and their absorption and fluorescence properties were recorded in solvents of varying polarity. Spectroscopic studies reveal that, the solvatochromic behavior of the compounds depend not only on the polarity but also on the hydrogen-bonding properties of the solvents. The effects of β-cyclodextrin on the fluorescence properties of both compounds were studied. It was found that there is an enhancement in the fluorescence intensity of labeled drug (NPFP-Phenylephrine) in the presence of β-cyclodextrin. In the present study, the molecular motions of NPFP-Phenylephrine embedded in a β-cyclodextrin cavity have been investigated by fluorescence techniques in steady-state and time resolved modes.

Tuning the constrained photophysics of a pyrazoline dye 3-naphthyl-1-phenyl-5-(4-carboxyphenyl)-2-pyrazoline inside the cyclodextrin nanocavities: A detailed insight via experimental and theoretical approach

The modulation in the photophysics of a pyrazoline dye 3-naphthyl-1-phenyl-5-(4-carboxyphenyl)-2-pyrazoline (NPCP), when it drifts from bulk water into the nanocages of aqueous cyclodextrin solutions was investigated. The intramolecular charge transfer (ICT) fluorescence band intensity was found to increase with a blue shift in the presence of cyclodextrins. The results from 1H NMR and 1HH COSY NMR spectral analysis clearly points out the position of pyrazoline ring inside the cavity and its role in complexation process. A quantitative assessment of the emission intensity data on Benesi-Hildebrand (B-H) equation along with ESI-MS spectra reveals the probable stoichiometry of NPCP-CD complexes. Molecular docking and molecular dynamics studies were conducted for β/γ cyclodextrin associated inclusion complexes of NPCP. The results obtained by computational studies are in good relation with the data obtained through experimental methods and both ascertain the encapsulation of NPCP into cyclodextrins.

3-Naphthyl-1-phenyl-5-(4-carboxyphenyl)-2-pyrazoline – a pyrazoline based heterocyclic dye as a fluorescent label for biomolecules containing an amino group and its evaluation using HPLC

The use of 3-naphthyl-1-phenyl-5-(4-carboxyphenyl)-2-pyrazoline as a pre-column derivatization agent for the HPLC analysis of biomolecules containing an –NH2 group is proposed in this article. The derivatization conditions to obtain quantitative reaction were optimized by considering different parameters (time, temperature, pH and reagent concentration) using seven amino acids as model analytes. The resulting derivatives were well separated on a reversed-phase column with an isocratic elution profile and detected fluorimetrically at excitation and emission wavelengths of 370 and 480 nm, respectively. The proposed method was validated for accuracy, precision, sample stability, linearity, and detection and quantification limits and were all found to be satisfactory. Through this study, we are forecasting the emergence of pyrazoline based heterocyclic dyes as organic fluorescent markers for the labelling of diagnostically important compounds, for their determination and quantification of practical interest.

3(2H)-Furanone as a promising scaffold for the synthesis of novel fluorescent organic dyes: an experimental and theoretical investigation

3(2H)-Furanones are a type of five-membered heterocyclic compounds of synthetic and biological importance. For exploring the utilities of this “sweet” aroma component for bio-analytical purposes we have prepared and characterized two novel fluorophores (2Z)-2-(5-fluoro-2-ntro benzylidene)-5-phenyl-3(2H)-furanone (FNPF) and (2Z)-2-(4-carboxy benzylidene)-5-phenyl-3-(2H)-furanone (CBPF) on a 3-furanone skeleton. In order to expand their application potential, the photophysical properties have been investigated using absorption and emission spectroscopy, in combination with quantum chemical calculations. As expected, both compounds showed efficient solvatochromic properties and the excited state dipole moments are larger than those of the ground state. Solvent dependent spectral data using TD-DFT calculations on the optimized ground and excited state structures of both compounds were found to correlate well with the experimental findings.

Spectral and theoretical study on complexation of sulfamethoxazole with β- and HPβ-cyclodextrins in binary and ternary systems

The inclusion complexes of sulfamethoxazole (SMX) with β-cyclodextrin (βCD) and (2-hydroxypropyl) β-cyclodextrin (HPβCD) were prepared. Fluorescence spectroscopy and electrospray mass spectrometry, ESI-MS, were used to investigate and characterize the inclusion complexation of SMX with cyclodextrins in solutions. Whereas in the solid state the complexes were characterized by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD) and Raman techniques. Enhanced twisted intramolecular charge transfer (TICT), emission as well as local excited (LE) bands were observed upon addition of HPβCD indicate that SMX enters deeper into the cyclodextrins cavity. The stoichiometries and association constants of these complexes have been determined by monitoring the fluorescence data. The effect of presence of ternary components like arginine and cysteine on the complexation efficiency of SMX with cyclodextrins was investigated. Molecular Dynamic simulations were also performed to shed an atomistic insight into the complexation mechanism. The results obtained showed that complexes of SMX with both cyclodextrins are stabilized in aqueous media by strong hydrogen bonding interactions.

Unveiling a versatile heterocycle: pyrazoline – a review

The design and synthesis of novel fluorescent heterocyclic dyes is a “hotspot” research area, due to their favourable photophysical properties and crucial role in charge transfer processes, which could allow huge advances in the fields of physics, chemistry and biology. One group of electron-rich nitrogen carriers, pyrazolines, are enjoying brisk growth, since they combine exciting electronic properties with the potential for dynamic applications. Concerning multi-functional applications, pyrazolines could provide a new range of applications that would revolutionize various fields. As reported in many studies, the potential applications of pyrazolines are vast and ever growing, but they have yet to make in-roads into real-life applications. This review provides an overview on the current status of pyrazoline derivatives in terms of synthesis, physico-chemical properties and various applications in order to realize their full potential for practical applications, and to trigger the synthesis and study of novel pyrazoline based compounds with much promise. We also present our conclusions and outlook for the future.

Spectrofluorimetric determination of Zn2+ ions in aqueous medium using 5-(4-flourophenyl)-quinolin-8-ol

Abstract A spectrofluorimetric method based on complex formation between Zn2+ ions and 5-(4-flourophenyl)-quinolin-8-ol has been developed for the rapid determination of trace levels of zinc ions. The method is sensitive and selective. The complex formed emit strongly at 535 nm with excitation wavelength at 394 nm. Complexation formation was optimized by studying the effect of pH, molar ratio of the metal to the ligand and the type of buffers. The study indicated that maximum complexation resulted when the pH of the mixture was maintained at 8.0 with 0.2 M carbonate buffer and metal to ligand was at a stoichiometric ratio of 1:2. Under the optimum conditions, the detection limit was 3 ppb. Appropriate validation of the method, yielded acceptable relative standard deviations of less than 2% (n = 5). The method was applied to the trace determination of Zn2+ ions in tap water, mineral water, fresh milk and cream samples successfully.