Probing the heterogeneity of molecular level organization of ionic liquids: a comparative study using neutral Nile red and cationic Nile blue sulfate as fluorescent probes for butyrolactam-based protic ionic liquids.

Ionic liquids (ILs) are liquid salts composed of cations and anions, known for their significant local heterogeneity at the molecular level. To understand the microheterogeneity with regard to their local polarity and local viscosity, we have used two structurally similar but chemically distinguishable fluorescent probes: Nile red (NR), a neutral molecule, and Nile blue sulfate (NBS), a charged molecule. A comparative study of the response of the two probes to the molecular level heterogeneity of ILs is expected to provide a better clarity of understanding regarding the charged polar domain and the uncharged hydrophobic domain of ILs. Towards this, we synthesized two butyrolactam-based protic ionic liquids (PILs), i.e., BTF and BTD, with the same ionic headgroup ([BT]+) and different alkyl tails ([RCOO]-), where {R = H, C11H23}. BTF has no significant hydrophobic domain, whereas BTD has a larger hydrophobic domain. Temperature-dependent fluorescence parameters such as fluorescence intensity, lifetime, and anisotropy were measured for both NR and NBS molecules. The use of a pair of structurally similar but ionically different probes enables differential estimation of parameters like the microviscosity of a domain using the fluorescence anisotropy parameter (r). The absorption and emission spectra of both probe molecules are observed to be blue shifted upon going from BTF to BTD. NR showed a significant blue shift in absorption and emission band maxima. Conversely, NBS exhibited a small wavelength shift, possibly influenced by the preferred location of their charged head group domain. Temperature-dependent rotational relaxation time (θ) of NR in BTD is smaller than that of NBS by 60-70%, indicating that stronger charge-charge interactions exist between the polar domain of BTD and NBS. Moreover, it is observed that the local viscosity of the BTF IL around both probes is similar, whereas there is a considerable difference for the BTD IL. These results are an indication that NBS being charged prefers to locate itself in the charged head group region of the IL, whereas NR being neutral tends to reside both in the hydrophobic domain and in the head group but is predominantly located in the hydrophobic domain.

Exploring the Physical Properties of Lipid Membranes with Polyhydroxy Oxanorbornane Head Group Using NBD-Conjugated and DPH Fluorescent Probes.

The present study focuses on exploring the physical properties of lipid membranes based on the polyhydroxy oxanorbornane (PH-ONB) headgroup, designed as synthetic analogues of naturally occurring archaeal lipid membranes. Specifically, we study two variants of PH-ONB headgroup-based lipids differing in the number of hydroxy groups present in the headgroup, with one having two hydroxy groups (ONB-2OH) and the other having three (ONB-3OH). These lipids form stable bilayer membranes. The study begins with a comprehensive analysis of the fluorescence characteristics of nitrobenzoxadiazole (NBD)-tagged ONB-based lipids in different solvent environments and within a model lipid membrane 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). Subsequently, the physical properties of the ONB-based membranes were examined by using an NBD-tagged ONB-based probe and a commonly used extrinsic 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescent probe. The steady-state and time-resolved fluorescence properties of the NBD-tagged ONB-based probe and DPH were used to compare the physical properties of the ONB-based membranes, including polarity, fluidity, phase transition, order, hydration, location, heterogeneity, and rotational diffusion. The solid gel to liquid crystalline phase transition temperatures of ONB-2OH and ONB-3OH lipid membranes are found to be (68 ± 1) °C and (74 ± 1) °C, respectively. The variation in organization (size), fluidity, and phase transition temperature of ONB-based lipid membranes is explained by the extent of hydrogen bonding interactions between lipid head groups. ONB-based membranes exhibit characteristics similar to those of phospholipid membranes and possess a notably high phase transition temperature. These properties make them a promising and cost-effective synthetic alternative to archaeal lipid membranes with a wide range of potential applications.

Effects of donor and acceptor substituents on the photophysics of 4-ethynyl-2,1,3-benzothiadiazole derivatives.

The present work explores the photophysical, electrochemical, and fluorescence polarization properties of a group of π-conjugated phenylethynyl-2,1,3-benzothiadiazole derivatives (BTDs) bearing different electron-donating (ED) or electron-withdrawing (EW) substituents at the para position of the phenylethynyl moiety. The BTDs were synthesized through the Sonogashira cross-coupling reaction between 4-bromo-2,1,3-benzothiadiazole and the respective para-substituted phenylethynyl derivatives. The BTDs with the EW-substituents show relatively weak solvatochromic behavior, while the BTDs with the strong ED-substituents like methoxy and N,N-dimethylamino-based substituents (BTDPhOMe and BTDPhNMe2) exhibit a pronounced solvatochromic behavior. The change in dipole moments in the excited states of the derivatives was calculated using Lippert-Mataga plots. The conclusions drawn on the spectral behavior of the molecules could be rationalized by TD-DFT calculations involving electron density difference (EDD) maps that correlate with the ICT characteristics of the molecules. The experimental and theoretical calculations reveal that the BTDs with the strong ED-substituents (strong push-pull type BTDs) have a strong ICT character in the excited state. These strong push-pull type BTDs show high fluorescence quantum yield (ΦF) in apolar solvents and low ΦF in polar solvents. In contrast, the BTDs with the weak ED-substituents (weak push-pull type BTDs) and EW-substituents (pull-pull type BTDs) have a weaker ICT character with low ΦF in apolar and high ΦF in polar solvent media. There is good a agreement among the HOMO-LUMO band gaps obtained from absorption spectroscopy and electrochemical studies and theoretical calculations. The fluorescence anisotropy measurement in the glycerol medium shows that the studied BTDs generally exhibit higher sensitivity towards microviscosity than the traditional DPH fluorescence anisotropy probe.

Interaction between dry and hot extremes at a global scale using a cascade modeling framework.

Climate change amplifies dry and hot extremes, yet the mechanism, extent, scope, and temporal scale of causal linkages between dry and hot extremes remain underexplored. Here using the concept of system dynamics, we investigate cross-scale interactions within dry-to-hot and hot-to-dry extreme event networks and quantify the magnitude, temporal-scale, and physical drivers of cascading effects (CEs) of drying-on-heating and vice-versa, across the globe. We find that locations exhibiting exceptionally strong CE (hotspots) for dry-to-hot and hot-to-dry extremes generally coincide. However, the CEs differ strongly in their timescale of interaction, hydroclimatic drivers, and sensitivity to changes in the soil-plant-atmosphere continuum and background aridity. The CE of drying-on-heating in the hotspot locations reaches its peak immediately driven by the compounding influence of vapor pressure deficit, potential evapotranspiration, and precipitation. In contrast, the CE of heating-on-drying peaks gradually dominated by concurrent changes in potential evapotranspiration, precipitation, and net-radiation with the effect of vapor pressure deficit being strongly controlled by ecosystem isohydricity and background aridity. Our results help improve our understanding of the causal linkages and the predictability of compound extremes and related impacts.

Phenylethynylanthracene based push-pull molecular systems: tuning the photophysics through para-substituents on the phenyl ring.

Organic push-pull molecules contain donor and acceptor moieties connected via π-linkages through which intramolecular electron charge transfer (ICT) can occur in the ground and excited states; giving these molecules interesting photophysical properties. The molecules chosen in this work are some basic phenylethynylanthracene derivatives to show that with just a change of substituents this class of small molecules can show dramatic changes in their photophysical properties. The emission properties and ICT abilities of these molecules are compared with regards to various electron donating and withdrawing substituents. Substituents such as cyano and methoxycarbonyl groups do not induce any ICT character whereas substituents like aldehyde, N,N-dimethylamino and nitro groups cause appreciable ICT character in this class of molecules and their emission spectra extend almost throughout the whole visible region. The comparative ICT character was correlated with the results of electron density difference calculations. Computational studies show that the molecules are planar in their ground as well as excited states; except the nitro group containing molecule, which has an orthogonally twisted structure in the excited state. The emission properties of this molecule led to its inclusion into a class of nitroaromatics which shows maximum emission intensity in moderately polar solvents and the emission is quenched drastically by either decreasing or increasing solvent polarity. Fluorescence anisotropy studies show very good sensitivity of these compounds towards microviscosity of their immediate molecular environment. A white light emitting (WLE) gel was prepared using 4-(anthracen-9-ylethynyl)benzonitrile (AnPCN) and 4-(anthracen-9-ylethynyl)-N,N-dimethylaniline (AnPNMe2) by taking polyvinyl alcohol (PVA) as the gelator and the resulting gel exhibited very good CIE (0.31, 0.33) with CCT (6598 K) and CRI (87). As an example, the use of the gel was also demonstrated by applying it to a commercial UV LED which showed satisfactory results. AnPNMe2 was used to sense polar solvent vapors in TLC plates and Whatman paper due to its good solvatochromic behavior.

Understanding the aggregation of excitation wavelength independent emission of amphiphilic carbon dots for bioimaging and organic acid sensing.

Herein, excitation wavelength-independent, tunable emissive and amphiphilic CDs with high quantum yield were synthesized by a low-temperature oxidation method employing banana peel waste as a carbon source. These CDs showed longer wavelength emissions (green to yellow) independent of the excitation wavelength when dispersed in different polar to non-polar solvents. The quantum yields of the same CDs were 9-32% in different solvent polarities for different emissions. On the other hand, a large stokes-shifted emission (∼9606 cm-1) was observed for CDs in the non-polar and weak polar solvents. The particle size of CDs increases from a hydrophobic to a hydrophilic environment with the change in emission colour from yellow to green. A polar and a non-polar host matrix were used to overcome the limitation of aggregation-caused quenching of CDs in the solid state to obtain bright emissions. These CDs were potentially used for naked-eye detection of trifluoroacetic acid (TFA) by changing the emission colour from yellow to orange under UV 365 nm. Sensing of TFA was also shown reversibly switch emission colour and average lifetime for multiple cycles. Additionally, the highly emissive CDs show negligible cytotoxicity in 3T3 fibroblast cells, indicating possible bioimaging applications in 3T3 cells.

Rapid and sensitive naked eye detection of faecal pigments using their enhanced solid-state green fluorescence on a zinc acetate substrate.

The identification of trace faecal pigments in real-time and on-site detection remains a challenge for water quality monitoring. Herein, a simple, low-cost and rapid fluorescence-based analytical method has been developed in a solid matrix for faecal pigments like stercobilin and urobilin detection. This was made possible due to significant enhancement of green solid-state fluorescence (520 nm) by zinc(II) complexation with faecal pigments embedded in the surface of zinc acetate crystals. It enables naked-eye detection of these pigments even at a 10 µM level when excited with 365 nm blue-UV. It was demonstrated that easily available white cellulose paper strips or TLC silica plates coated with zinc acetate can be used as substrates. A photophysical study of solid-state faecal pigments-zinc(II) complexes suggests that green fluorescence enhancement results from the complexation, which can be attributed to the substantial decrease of the non-radiative decay rate (knr) as well as more efficient use of excitation light. The observation of reduced interference of humic acid fluorescence makes faecal pigment detection more efficient by this proposed method.

Photophysical Behavior of Plant Flavonols Galangin, Kaempferol, Quercetin, and Myricetin in Homogeneous Media and the DMPC Model Membrane: Unveiling the Influence of the B-Ring Hydroxylation of Flavonols.

Flavonols have been studied extensively because of their interesting biological activities and excited-state intramolecular proton transfer (ESIPT) behavior. Galangin, kaempferol, quercetin, and myricetin are structurally related flavonols that differ only in the number of B-ring hydroxyl substituents. In this work, we have carried out a detailed study on the photophysical behavior of these structurally related flavonols in various solvents and a 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) small unilamellar vesicles (SUVs) model membrane. We observed that these flavonols exist in different forms in the ground and excited states depending on the nature of the solvent. The weak intrinsic fluorescence of these flavonols gets enhanced in hydrogen-bond-accepting and alcoholic solvents. The phototautomer fluorescence intensity of these flavonols increases significantly in the DMPC membrane compared to water, suggesting ESIPT activation via binding interaction between flavonols and the membrane. According to our findings, both the number of B-ring hydroxy groups and membrane fluidity affect the flavonol binding with the membrane. The steady-state fluorescence intensity, steady-state anisotropy, fluorescence lifetime, and fluorescence anisotropy decay of flavonols were sensitive towards the temperature-induced DMPC membrane phase change. A quenching study has been performed to investigate the location and distribution of flavonols in the DMPC SUVs. Moreover, the antioxidant potential of flavonols in DMPC SUVs has been examined using the DPPH scavenging method. Our results reveal that the B-ring hydroxy groups significantly affect the photophysics, binding affinity, location, distribution, and DPPH scavenging activity of polyhydroxy-flavonols in the DMPC SUVs.

Resolving fluorescence signatures of a photoconvertible fluorophore by fluorescence spectroscopy and MCR-ALS-based combinatorial approach.

Photoconvertible fluorophores are important for a myriad of applications in chemistry and biology. Here, we spectrally resolve and quantify individual photophysical information of a dual-emitting photoconvertible fluorophore by fluorescence spectroscopy and multivariate curve resolution-alternate least square techniques. We found that the reactant fluorophore, which shows a weak locally excited (LE) emission and a dominant intramolecular charge transfer (ICT) emission, also exhibits an intermolecular charge transfer emission. The ICT emission bands of both the reactant and product fluorophores are originated from their respective LE states. The reactant fluorophore is a mixture of its different ground state conformers. Higher yields of photoconversion of the yellow-emitting reactant fluorophore are achieved via a visible light photoreaction, leading to formation of pure white light at an intermediate photoreaction time. These findings together help us to glean new photophysical and photochemical insights into the photoreaction of a dual-emitting photoconvertible fluorophore.

Photophysics of faecal pigments stercobilin and urobilin in aliphatic alcohols: introduction of a sensitive method for their detection using solvent phase extraction and fluorometry.

Faecal pigments (FPs) are ubiquitous in the environment and are a primary contaminant in groundwater and surface water. This article presents a new analytical paradigm by a fluorescence coupled extraction-based method involving FP fluorescence enhancement and minimization of background fluorescence for high sensitivity detection. FPs show higher fluorescence intensity in aliphatic alcohols due to the breaking down of higher-order H-aggregates into lower-order H-aggregates (dimers). DFT studies using the B3LYP functional and LANL2DZ basis set show π-π stacking and hydrogen-bonding contributions towards forming H-aggregated dimers of FPs in the implicit and explicit solvent environments of 1-hexanol. This study is the first report on the extractability of FPs using 1-hexanol as an efficient extraction medium in comparison to higher-order aliphatic alcohols (1-butanol, 1-hexanol and 1-octanol). Furthermore, FP-Zn(II) complexes in 1-hexanol medium significantly enhance the fluorescence emission intensity (∼14-17 times), and the emission intensity remains stable over time. This further helps to increase the detection limit of FPs in the picomolar to sub-picomolar concentration range. This study proposes a protocol involving extraction of FPs by 1-hexanol followed by the complexation of FPs with Zn(II) in the alcohol media and subsequent fluorimetric detection of the FP-Zn(II) complex with a high level of sensitivity, enabled by reduced interference from the background fluorescence of humic acid. The complexation behaviour of FPs with various metal salts was also examined, which provided an understanding of the fluorescence behaviour of FPs with various other metal ions commonly present in natural environmental water. The proposed analytical method has been further validated using real water samples.

Interaction of Dopamine with Zwitterionic DMPC and Anionic DMPS Multilamellar Vesicle Membranes.

Dopamine (DA), a naturally occurring neurotransmitter, plays a crucial role in the function of the mammalian nervous system. DA-lipid-membrane interaction is inevitable during the neurotransmission process. In this report, we have studied the interaction of DA with anionic 1,2-dimyristoyl-sn-glycero-3-phospho-l-serine (DMPS), neutral (zwitterionic) 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and synaptic membrane-mimicking mixed DMPC/DMPS (3:1 molar ratio) model multilamellar vesicle (MLV) membranes. Differential scanning calorimetry (DSC) studies suggest a strong specific interaction of DA with the anionic DMPS membrane, a weak interaction with the zwitterionic DMPC membrane, and a moderate interaction with the mixed DMPC/DMPS (3:1) membrane. The intrinsic fluorescence of DA was used as a new approach to gain a molecular-level understanding of DA-lipid-membrane interaction. Toward this end, a detailed photophysical study of DA, including its steady-state fluorescence anisotropy and fluorescence lifetime, was undertaken for the first time. The partition coefficient, location, and distribution of DA in the DMPS and DMPC model membranes were studied by employing intrinsic fluorescence. The effect of DA on the phase transition of the model membranes was also examined using the intrinsic fluorescence of DA. Zeta potential studies suggest a strong electrostatic interaction of DA with the anionic DMPS membrane and a nonspecific, relatively weak interaction of DA with the zwitterionic DMPC membrane. In addition, we observed cholesterol-induced DA expulsion from both DMPS and DMPC membranes. We believe that this work will provide a more in-depth understanding of DA-membrane interaction at a molecular level.

Curcumin-Induced Membrane Property Changes in DMPC Multilamellar Vesicles and the Effects of Membrane-Destabilizing Molecules on Curcumin-Loaded Multilamellar Vesicles.

Curcumin (CUR) is the major bioactive component of turmeric (Curcuma longa), commonly used as a spice and traditional medicine in India. CUR possesses a wide range of pharmacological benefits, including antioxidant, anticarcinogenic, antimutagenic, anti-inflammatory, anti-Alzheimer, and anti-Parkinson effects. The CUR-membrane interaction is believed to be the reason for such biological activity of CUR. Several research groups have modeled the interaction of CUR with artificial model lipid membranes using various techniques such as nuclear magnetic resonance (NMR), small-angle X-ray scattering (SAXS), and differential scanning calorimetry (DSC). However, the mechanism of its action is still unclear. A fluorescent-probe-based technique could be advantageous to study the CUR-lipid membrane interaction due to its sensitivity toward the local environment and its multiparametric nature. In this work, we have used the intrinsic fluorescence properties of CUR to investigate CUR-induced physical property changes in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) multilamellar vesicles (MLVs) at various CUR concentrations. By rationalizing the results of steady-state fluorescence intensity, fluorescence anisotropy, temperature-dependent fluorescence intensity, temperature-dependent fluorescence anisotropy, and quenching experiments, we have proposed a model showing concentration-dependent effects of CUR on the DMPC bilayer membrane. We suggest that at low concentrations (≤1 mol %), CUR is homogeneously distributed in the DMPC bilayer membrane in both the solid gel (SG) and liquid crystalline (LC) phases. At high concentrations (>1 mol %), CUR molecules form segregated domains that fluidize both membrane phases. However, the CUR-induced fluidization is less pronounced in the LC phase as some CUR molecules from the domain partition into the bilayer core. Further, the effects of membrane-destabilizing molecules such as bile salts, capsaicin (CAP), and piperine (PIP) on CUR-loaded DMPC multilamellar vesicles were studied. Our work also shows that CUR has a stabilizing effect on the DMPC membrane at high concentrations.

Nature of Saccharide-Induced F127 Micellar Dehydration: An Insight with FDAPT (2-Formyl-5-(4'-N,N-dimethylaminophenyl)thiophene), a Multiparametric Fluorescent Probe.

FDAPT (2-formyl-5-(4'-N,N-dimethylaminophenyl)thiophene) is an efficient environment-sensitive fluorescent probe, which senses the alteration of its microenvironment with six different fluorescent parameters, namely, emission intensity, wavelength, fluorescence anisotropy, and corresponding three time-dependent parameters fluorescence lifetime, time-resolved emission spectrum, and anisotropy decay. In the present work, the nature of saccharide-induced dehydration of a F127 polymeric micelle is investigated in detail with FDAPT emission. Using a multiparametric fluorescence approach, it is observed that the saccharide molecules not only decrease the critical micellization temperature of the F127 solution but also strongly alter the physical properties inside the micellar structures. The local polarity and fluidity significantly decrease in the saccharide-induced micelle as compared to the normal F127 micelle. The probe solvation dynamics study reveals that the water content in the core as well as corona domain diminishes significantly in the saccharide-induced micelle as compared to the normal micelle. More precisely, dehydration occurs more in the core region than in the corona region. Also, the saccharide-induced dehydration alters the relative size of the core and corona regions. The extent of dehydration varies with different saccharide molecules. It is also found that the dehydration efficiency order is trisaccharide (raffinose) > disaccharide (sucrose) > monosaccharide (glucose and fructose).

Carbon Dot-NaCl Crystals for White-Light Generation and Fabry-Perot Lasing.

Phosphor materials with broad spectral range and an average emission lifetime (20 µs) have been achieved from carbon dots (CDs)-NaCl crystals. A one-pot synthesis pathway has been developed for CDs-NaCl crystals formation at room temperature. Precursor for CDs materials was screened at room temperature by oxidation methodology from different simple sugar molecules. CDs (size less than 10 nm) prepared from the fructose sugar exhibit most intense emission. Utilizing ripe banana peel (contains ∼27% of fructose) as a precursor for the carbon dot formation, white-light emission with a CIE index of (0.29, 0.34) has been achieved from the single source with CDs-NaCl crystals upon excitation at 430 nm. The crystals also function as Fabry-Perot (F-P) mode resonator for lasing, with a laser threshold value of 0.9 mW and a resonating Q-factor of 207. These results outline a new approach for realizing F-P lasing and white light emission from a non-toxic green source with a quick, facile and low-cost synthesis procedure.

Safety of Ashwagandha Root Extract: A Randomized, Placebo-Controlled, study in Healthy Volunteers.

BACKGROUND: Ashwagandha (Withania somnifera) is a well-established and reputed herb in Ayurvedic medicine. It has been used as a "Rasayana" (rejuvenator), nootropic, and as a powerful natural adaptogen. The herb extract is extensively used for general wellbeing and in specific ailments. However, only a few studies have investigated the safety and tolerability of Ashwagandha in humans. This study evaluated the safety of Ashwagandha root extract consumption in healthy adults. METHODS: In this randomized, double-blind, placebo-controlled, and parallel-group study, 80 healthy participants (40 males, 40 females) were randomized in a 1:1 ratio to receive either Ashwagandha 300 mg or a placebo of the same dosage, twice daily, orally for 8 weeks. The study was conducted at MV Hospital, and King George Medical University, Lucknow, India. The primary safety outcomes considered were laboratory assessment of hematological parameters, serum biochemistry analysis including hepatotoxicity evaluation, and thyroid function parameters. The secondary outcomes of this study were the clinical adverse events and the vital parameters. The within and between the groups' datasets were compared using the Wilcoxon signed-rank test and the Mann Whitney U test, respectively. RESULTS: A detailed evaluation of the vital signs such as body weight, body temperature, pulse rate, respiratory rate, systolic and diastolic blood pressure, and Body Mass Index (BMI) were conducted for each participant at the baseline and the end of the study for treatment and placebo groups. Similarly, hematological and biochemical parameters were evaluated at the baseline and at the end of study. The outcome did not indicate any untoward effects in any of the treated volunteers. No statistically significant change or abnormality was observed in the considered parameters including thyroid hormonal profile in both the groups. No adverse events were reported by any of the participants in this study. CONCLUSIONS: Ashwagandha is being consumed since time immemorial following the Ayurvedic medicine practices. Modern science requires evidence of the safety and efficacy of the Ashwagandha extract before mass consumption for various health issues and as a supplement. The present study revealed that the consumption of Ashwagandha root extract for 8 weeks was safe in both males and females volunteers. However, long term study and varying dosage ranges should be investigated in the future.

Understanding the photophysics of stercobilin-Zn(II) and urobilin-Zn(II) complexes towards faecal pigment analysis.

A detailed photophysical study of two faecal pigments (FPs), Urobilin (UB) and Stercobilin (SB), and their zinc complexes [FP-Zn(II)] was carried out. The enhancement of UB and SB fluorescence resulting from the formation of their Zn(II) complexes was attributed to the complexation-induced rigidity of the chromophoric units, and the corresponding decrease of nonradiative decay rate constants of the excited singlet states (knr). The effect of various physicochemical environments was also studied in detail in order to understand the fluorescence behaviour of the Zn(II) complexes. FP-Zn(II) complexes have a lower solubility in water that results in the formation of molecular aggregates. The aggregation-induced loss of fluorescence of FP-Zn(II) complexes could be overcome by using the appropriate mixture of ethanol and water (70:30). Molecular orbital calculations on the FP-Zn(II) complexes provided a good idea of the geometry of the complexes and helped rationalise the enhancement of fluorescence after complexation. This study could pave the way towards developing a convenient non-extraction aqueous phase analytical procedure for detection of FPs using Zn(II) complexation method.

Stercobilin and Urobilin in Aqueous Media: Existence of Specific H-Aggregates and Nonspecific Higher Aggregates at Different Concentrations.

Fecal matter is considered to be one of the primary sources of water pollution. Understanding the aggregation behavior of the fecal pigments (FPs) could play a critical role in their detection and analysis. This work shows that in aqueous media, the fluorescence of FPs indicates the presence of multiple emitting species, which have been assigned to monomers, lower-order H-aggregates (dimers), and higher-order H-aggregates. Steady-state absorbance, fluorescence and time-resolved fluorescence decay studies conclude that the emission of FPs in aqueous medium indicates H-type of aggregation, even up to nanomolar and sub-nanomolar concentrations. Four sets of independent experiments involving the variation of (i) concentration of FPs, (ii) temperature, (iii) pH, and (iv) ethanol/water composition as solvent media suggest the presence of monomer (540 nm), dimer (516 nm), and higher-order aggregates (500 nm) of FPs in aqueous solutions. The dimeric FP species appear to be present in the entire concentration range of 1 pM to 1 µM. Fluorescence lifetimes of H-aggregates are relatively longer as compared to the corresponding monomers. Hydrogen bonding appears to play an important role in forming H-aggregates in the aqueous phase of FPs as observed in the IR spectra of the FPs in dichloromethane. Density functional theory (DFT) calculations using the B3LYP functional and the LANL2DZ basis set show the contributions of π-π stacking and hydrogen-bonding interactions toward the formation of H-aggregated dimer of FPs in aqueous media.

Total Emission Time Resolved Decay: a Method for Measurement and Resolution of Broad-Band Emission.

This article reports a time-resolved fluorescence data acquisition technique termed as "Total Emission Time Resolved Decay" (TETRD). TETRD is recorded by using zero-order diffraction of emission grating in TCSPC instrument. TETRD decay curve has entire wavelength dependent decay information buried in it. Cut-off filters are used to avoid scattering contamination. Two existing approaches are used for analysing the interconnected TETRD data. (i) First, global analysis: for discretely decaying multiple components, TETRD dataset is analyzed using global analysis. The normalized pre-exponentials (αi) and relative amplitudes (fi) recovered from global analysis reflect the individual component emission more faithfully and resembles with steady-state spectral data as well. (ii) Second, stretched exponential fitting (StrEF): for continuous lifetime distribution systems, StrEF (I(t) = I0 exp[-(t/τ)1/h]) has been used to analyse TETRD data. The average lifetime (τ) of StrEF matches well with the average lifetime of multi-exponential fitting, the heterogeneity factor (h) of StrEF is an additional parameter, which informs about local heterogeneity in the system. It is shown that the lifetimes obtained with TETRD matches well with the lifetimes obtained using conventional time resolved emission spectra (TRES). TETRD holds advantage in rapid data acquisition and facilitates inclusion of another variable (like concentration, solvent composition, pH, excitation wavelength etc.) into experimental design. Further, with the use of an appropriate data analysis tool, the multi-component decay profiles can be resolved conveniently.

Simultaneous Quantification of Multiple Polycyclic Aromatic Hydrocarbons in Aqueous Media using Micelle Assisted White Light Excitation Fluorescence.

Qualitative and quantitative display of multiple fluorescent analytes is made simple and reliable in this micelle assisted methodology. The adopted method involves micelle assisted evincing of ppb level of PAHs in water; measurement of total fluorescence (white light excitation fluorescence, WLEF) and data deciphering using multivariate analysis. This protocol yields sensitive and accurate quantification of the cancerous pollutants (PAHs) in aqueous media with Limit of Quantification of the order 1-10 µg/L and accuracy of >98%. The use of WLEF enables the simultaneous acquisition of fluorescence signatures of all the PAHs. It has the additional advantage of being portable, layman-friendly and cost-effective. The optimized amount of surfactants for the simultaneous extraction of PAHs from real samples was estimated as 27.8 mg (19.3 mM) of SDS and 9.1 mg (5 mM) of CTAB. Also, the analytical fidelity of the quantification such as percentage recovery (98 ± 2%), linear dynamic range (2-250 µg/L), RMSEP (<0.5), etc. explains the veracity of methodology.

A Multiparametric Fluorescence Probe to Understand the Physicochemical Properties of Small Unilamellar Lipid Vesicles in Poly(ethylene glycol)-Water Medium.

FDAPT (2-formyl-5-(4'-N,N-dimethylaminophenyl)thiophene) efficiently senses the minimum alteration of lipid bilayer microenvironment with all six different fluorescence parameters namely emission wavelength, fluorescence intensity, steady-state anisotropy, and their corresponding time-dependent parameters (Sahu et al., J. Phys. Chem. B 2018, 122, 7308-7318). In the present work, the effect of poly(ethylene glycol) on the small unilamellar vesicle is demonstrated with the emission behavior of the FDAPT probe. A medium and a high molecular weight PEG were chosen to perturb the lipid vesicles. The alteration of the bilayer polarity, water content inside bilayer, lipid packing density in the perturbed vesicles reflect significant changes in different fluorescence parameters of FDAPT probe. The effect of PEG on the unilamellar vesicle was rationalized with the alteration of the emission behavior, fluorescence lifetime, steady-state anisotropy and anisotropy decay of the probe. The simple and convenient fluorescence measurements provide new insights into the effect of PEG on the packing density, water volume, micro polarity, and microviscosity of the small unilamellar vesicle. The physiological understanding was extended to rationalize the cryoprotecting behavior of PEG.