Digambara Patra

Recent developments in multi-component synchronous fluorescence scan analysis

The ability to analyse complex multi-component mixtures without resorting to tedious separation procedures is extremely useful for routine analysis. Single-wavelength fluorescence measurement is limited in its ability to analyse complicated multi-component samples when they have severely overlapping emission and/or excitation spectra. This can be overcome by using synchronous fluorescence scan (SFS), where overlapping of spectra can be minimized. The selectivity of SFS can still be increased by taking derivative spectrum, applying different multivariate methods, selective fluorescence quenching, three-dimensional synchronous measurement or using some of these procedures in combination. Recent developments in various synchronous fluorescence methods for analysis of multi-component systems are discussed in this review.

Art and Artefacts of Fluorescence Correlation Spectroscopy

Fluorescence correlation spectroscopy (FCS) is an important technique for studying low concentrations of analyte molecules in solution. The core molecular characteristic that can be addressed by FCS is the translational diffusion coefficient of the analyte molecules, which can be used for i.e. studying molecular binding and reactions, or conformational changes of macromolecules. The present paper discusses several possible optical and photophysical effects that can influence the outcome of a FCS measurement and thus can bias the value of the derived diffusion coefficient.

Total synchronous fluorescence scan spectra of petroleum products

Extending the two-dimensional synchronous fluorescence scan to a three-dimensional total synchronous fluorescence scan (TSFS) spectral measurement gives the total synchronous fluorescence characteristics of a multifluorophoric sample at various possible wavelength intervals (Δλ), which could help to characterize multifluorophoric systems better. TSFS spectra of petroleum products such as diesel, kerosene, petrol, engine oil etc., available in the Indian market, are reported. Fluorescence in these samples is due to the presence of polycyclic aromatic hydrocarbons (PAHs) of various ring sizes. The TSFS contour plot profiles of the neat samples measured at right-angle geometry is a result of various energy-degrading photophysical processes such as inner filter effect, light attenuation, resonance energy transfer, collisional quenching etc. TSFS plots make it easy to obtain the optimized Δλ of an unknown sample of analytical interest. TSFS and the excitation-emission matrix (EEM) techniques are similar, but the contour profiles generated are different. The response of the TSFS contour profiles to dilution is different from that in the EEM contour profiles. Thus, TSFS can provide an alternative way of presenting the fluorescence response of concentrated multifluorophoric samples.

Concentration dependent red shift: qualitative and quantitative investigation of motor oils by synchronous fluorescence scan.

Synchronous fluorescence scan (SFS) has been described as a successful technique to characterize Motor oils like diesel, petrol, kerosene, 2T oil and Mobil. The concentration dependent investigation of Motor oils shows a red shift in lambda(SFS)(max). Using red shift of lambda(SFS)(max), a method has been developed to quantify Motor oil in the concentration range 5-100% v/v. The concentration dependent overall rate of energy transfer of Motor oil gives a unique behavioral change according to the oil type and SFS is a simpler spectroscopic method to qualitatively differentiate between heavy and light oil. The molecular interaction of polycyclic aromatic compounds (PACs) in fluorophoric mixtures like resonance energy transfer and self-quenching via solvent collision has been clearly explained by SFS method. Effect of solvent and external quencher molecule on Motor oils has also been studied. Nitrobenzene is found to be a selective quencher for PACs of Motor oils.

Investigation on simultaneous analysis of multicomponent polycyclic aromatic hydrocarbon mixtures in water samples: a simple synchronous fluorimetric method

Simultaneous analysis of multicomponent polycyclic aromatic hydrocarbons in mixture of micellar solution (CTAB) has been investigated. A simple synchronous fluorimetric method has been used, which does not require pretreatment of data, solving of large amount of data and large amount of solution preparation for internal calibration, thus making the analysis simple and fast. The method is fairly successful for analysis of 6,7 and 10 components in a mixture solution. Attempt for 18-component analysis, however, shows a poor recovery for PAHs with low fluorescence. The detection limits are generally between 0.055 and 12.97 ng ml(-1) except for benzo[b]anthracene with detection limit of 32.21 ng ml(-1).

Study on effect of lipophilic curcumin on sub-domain IIA site of human serum albumin during unfolded and refolded states: A synchronous fluorescence spectroscopic study

Curcumin having pharmaceutical application as anti-oxidant, anti-inflammatory and anti-carcinogenic drug necessitates studying interaction of this molecule with native, unfolded and refolded state of human serum albumin (HSA), carrier protein in the blood. We proposed a simultaneous static and dynamic fluorescence quenching mechanism operating in the complex formation between HSA and curcumin. Location of curcumin in the close proximity of tryptophan with respect to tyrosine was further evident from the observation of two fold increase in rate of depletion of SFS intensity for tryptophan with respect to tyrosine in HSA in SFS spectrum. Alteration of SFS spectral peak position, electronic absorbance, fluorescence intensity and lifetime suggested chemical denaturation by urea expectedly unfold the protein molecule in the absence and presence of curcumin. Denatured HSA had similar fluorescence peak position and lifetime to that of L-tryptophan in the polar environment. During unfolding of HSA the spectral change of tyrosine and tryptophan was resolved through synchronous fluorescence spectra at two different Δλ in absence and presence of curcumin. It is found that curcumin remained bound to unfolded state of HSA and facilitated the process by pushing tryptophan moiety to more polar environment in the unfolded state. Dilution of the denatured protein by phosphate buffer reversibly refolded the sub-domain IIA, by also recovering fluorescence lifetime loss, but it was slow in the presence of curcumin. k(q) values indicate that curcumin-HSA complex is formed in the unfolded and refolded states as observed for native state.

Effect of sample geometry on synchronous fluorimetric analysis of petrol, diesel, kerosene and their mixtures at higher concentration

A comparison of synchronous fluorescence scan (SFS) spectra of petrol, diesel and their mixtures with kerosene in front surface, 45° and 90° angle sample geometry as obtainable from a commercial fluorimeter reveals that 90° angle sample geometry provides certain distinct characteristics to SFS spectra. The presence of extensive inner filter effects and resonance energy transfer in petroleum products are the major causes of the distinctive characteristics of these spectra. These characteristics enable the development of calibration plots for mixture samples (petrol–kerosene and diesel–kerosene) based on the shift in λSFSmax and SFS intensity. This novel method shows promise in detecting and estimating the contamination of petrol and diesel by kerosene. Calibration graphs obtained from SFS intensity measurement are found to be efficacious in the whole range 0–90% v/v of kerosene, and give a good linearity in the adulteration range generally found in the field (0–50% v/v) for petrol and diesel. The method is simple, rapid and superior both in terms of sensitivity (0.1% v/v) and accuracy to other analytical methods used for petroleum product analysis.

Study of diesel fuel contamination by excitation emission matrix spectral subtraction fluorescence

Abstract Study on diesel fuel contamination by various common adulterants like kerosene, blue marked kerosene (PDS), crude hexane, cyclohexane, turpentine oil, etc. has been carried out by excitation emission matrix fluorescence (EEMF). Excitation emission matrix spectral subtraction (EEMSS) fluorescence can be obtained by subtracting the EEMF spectrum of the adulterated sample from the reference neat sample. It was observed that EEMSS fluorescence could help to distinguish between neat and contaminated sample of diesel despite the presence of energy transfer and inner filter effects. Calibration graph obtained from the spectral volume using EEMSS fluorescence is found to be efficacious in the whole range 0–90% v/v of various adulterants present in diesel.

Unique role of ionic liquid [bmin][BF4] during curcumin–surfactant association and micellization of cationic, anionic and non-ionic surfactant solutions

Hydrophilic ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroburate, modified the properties of aqueous surfactant solutions associated with curcumin. Because of potential pharmaceutical applications as an antioxidant, anti-inflammatory and anti-carcinogenic agent, curcumin has received ample attention as potential drug. The interaction of curcumin with various charged aqueous surfactant solutions showed it exists in deprotonated enol form in surfactant solutions. The nitro and hydroxyl groups of o-nitrophenol interact with the carbonyl and hydroxyl groups of the enol form of curcumin by forming ground state complex through hydrogen bonds and offered interesting information about the nature of the interactions between the aqueous surfactant solutions and curcumin depending on charge of head group of the surfactant. IL[bmin][BF4] encouraged early formation of micelle in case of cationic and anionic aqueous surfactant solutions, but slightly prolonged micelle formation in the case of neutral aqueous surfactant solution. However, for curcumin IL [bmin][BF4] favored strong association (7-fold increase) with neutral surfactant solution, marginally supported association with anionic surfactant solution and discouraged (∼2-fold decrease) association with cationic surfactant solution.

Effect of Curcumin on Liposome: Curcumin as a Molecular Probe for Monitoring Interaction of Ionic Liquids with 1,2-Dipalmitoyl-sn-Glycero-3-Phosphocholine Liposome

Recent increase and wider use of ionic liquids (ILs) for various applications has drawn attention to their toxicological consequence on human health. The present study explores effects of three different kinds of widely used ILs, such as 1‐methyl‐3‐octylimidazolium chloride, 1‐buytl‐3‐methyl imadazolium tetrafluoroborate and 1‐benzyl‐3‐methyl imidazolium tetrafluoroborate, on liposome properties of 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine (DPPC) by applying curcumin as molecular probe. Fluorescence intensity of curcumin is reported as a novel rotor which is sensitive to viscosity and thus the fluidity of the solvent. It follows a linear relationship of log fluorescence vs viscosity as proposed by Förster–Hoffmann equation. Curcumin binds strongly to liposome. At low concentration, the lipophilic drug curcumin does not appreciably influence the phase transition temperature of DPPC but as concentration reaches high levels significantly depresses the phase transition temperature. ILs diminish membrane fluidity. 1‐methyl‐3‐octylimidazolium chloride disorders membrane properties by lowering the phase transition as is observed for higher concentration of curcumin, but 1‐buytl‐3‐methyl imidazolium tetrafluoroborate and 1‐benzyl‐3‐methyl imidazolium tetrafluoroborate do not modify phase transition temperature perceptibly; rather they broaden the phase transition at low molar concentration ratio. The three different kinds of ILs under study behave similarly at a high IL:DPPC ratio (1:2), while they behave differently at lower ratios (1:10–1:5).