Rupam Dutta

Investigation of Fibril Forming Mechanisms of l-Phenylalanine and l-Tyrosine: Microscopic Insight toward Phenylketonuria and Tyrosinemia Type II

Phenylketonuria and tyrosinemia type II, the two metabolic disorders, are originated due to the complications in metabolism of phenylalanine (Phe) and tyrosine (Tyr), respectively. Several neurological injuries, involving microcephaly, mental retardation, epilepsy, motor disease, and skin problems etc., are the symptoms of these two diseases. It has been reported that toxic amyloid fibrils are formed at high concentrations of Phe and Tyr. Our study indicates that the fibril forming mechanisms of Phe and Tyr are completely different. In the case of Phe, -NH3+ and -COO- groups of neighboring molecules interact via hydrogen bonding and polar interactions. On the other hand, there is no role of - NH3+ group in the fibril forming mechanism of Tyr. In Tyr fibril, the two hydrogen bonding partners are -OH and -COO- groups. In addition, we have also investigated the effect of three lanthanide cations on the fibrillar assemblies of Phe. It has been observed that the efficiencies of three lanthanides to inhibit the fibrillar assemblies of Phe follow the order Tb3+< Sm3+< Eu3+.

A Comparative Study of the Influence of Sugars Sucrose, Trehalose, and Maltose on the Hydration and Diffusion of DMPC Lipid Bilayer at Complete Hydration: Investigation of Structural and Spectroscopic Aspect of Lipid–Sugar Interaction

It is well-known that sugars protect membrane structures against fusion and leakage. Here, we have investigated the interaction between different sugars (sucrose, trehalose, and maltose) and phospholipid membrane of 1,2-dimyristoyl-sn-glycero-3-phoshpocholine (DMPC) using dynamic light scattering (DLS), transmission electron microscopy (TEM), and other various spectroscopic techniques. DLS measurement reveals that the addition of sugar molecule results a significant increase of the average diameter of DMPC membrane. We have also noticed that in the presence of different sugars the rotational relaxation and solvation time of coumarin 480 (C480) and coumarin 153 (C153) surrounding DMPC membrane increases, suggesting a marked reduction of the hydration behavior at the surface of phospholipid membrane. In addition, we have also investigated the effect of sugar molecules on the lateral mobility of phospholipids. Interestingly, the relative increase in rotational, solvation and lateral diffusion is more prominent for C480 than that of C153 because of their different location in lipid bilayer. It is because of preferential location of comparatively hydrophilic probe C480 in the interfacial region of the lipid bilayer. Sugars intercalate with the phospholipid headgroup through hydrogen bonding and replace smaller sized water molecules from the membrane surface. Therefore, overall, we have monitored a comparative analysis regarding the interaction of different sugar molecules (sucrose, trehalose, and maltose) with the DMPC membrane through DLS, TEM, solvation dynamics, time-resolved anisotropy, and fluorescence correlation spectroscopy (FCS) measurements to explore the structural and spectroscopic aspect of lipid-sugar interaction.

Inhibition of Fibrillar Assemblies of l-Phenylalanine by Crown Ethers: A Potential Approach toward Phenylketonuria

In this article, our aim is to investigate the interaction of l-phenylalanine (l-Phe) fibrils with crown ethers (CEs). For this purpose, two different CEs (15-Crown-5 (15C5) and 18-Crown-6 (18C6)) were used. Interestingly, we have observed that both CEs have the ability to arrest fibril formation. However, 18C6 was found to be a better candidate compared to 15C5. Field emission scanning electron microscopy and fluorescence lifetime imaging microscopy were used to monitor the fibril-arresting kinetics of CEs. The arresting process was further confirmed by fluorescence correlation spectroscopy and nuclear magnetic resonance studies.

Sodium Chloride Triggered the Fusion of Vesicle Composed of Fatty Acid Modified Protic Ionic Liquid: A New Insight into the Membrane Fusion Monitored through Fluorescence Lifetime Imaging Microscopy

The development of stable vesicular assemblies and the understanding of their interaction and dynamics in aqueous solution are long-standing topics in the research of chemistry and biology. Fatty acids are known to form vesicle structure in aqueous solution depending on the pH of the medium. Protic ionic liquid of fatty acid with ethyl amine (oleate ethyl amine, OEA) as a component spontaneously forms a vesicle in aqueous solution. The general comparison of dynamics and interaction of these two vesicles have been drawn using fluorescence correlation spectroscopy (FCS) and fluorescence lifetime imaging microscopy (FLIM) measurements. Further, FLIM images of a single vesicle are taken at multiple wavelengths, and the solvation of the probe molecules has been observed from the multiwavelength FLIM images. The lifetime of the probe molecule in OEA vesicle is higher than that in simple fatty acid vesicles. Therefore, it suggests that the membrane of the OEA vesicle is more dehydrated compared to that of fatty acid vesicles, and it facilitates OEA vesicles to fuse themselves in the presence of electrolyte, sodium chloride (NaCl). However, under the same conditions, only fatty acid vesicles do not fuse. The fusion of OEA vesicles is successfully demonstrated by the time scan FLIM measurements. The different events in the fusion process are analyzed in the light of the reported model of vesicle fusion. Finally, the local viscosity of the water pool of the vesicle is determined using kiton red, as a molecular rotor. With addition of NaCl, the fluidity in the interior of the vesicle is increased which leads to disassembly of vesicle. The rich dynamic properties of this vesicular assembly and the FLIM based approach of vesicle fusion will provide better insight into the growth of a protocell membrane.

5-Methyl Salicylic Acid-Induced Thermo Responsive Reversible Transition in Surface Active Ionic Liquid Assemblies: A Spectroscopic Approach

This article describes the formation of stable unilamellar vesicles involving surface active ionic liquid (SAIL), 1-hexadecyl-3-methylimidazolium chloride (C16mimCl), and 5-methyl salicylic acid (5mS). Turbidity, dynamic light scattering (DLS), transmission electron microscopy (TEM), and viscosity measurements suggest that C16mimCl containing micellar aggregates are transformed to elongated micelle and finally into vesicular aggregates with the addition of 5mS. Besides, we have also investigated the photophysical aspects of a hydrophobic (coumarin 153, C153) and a hydrophilic molecule (rhodamine 6G (R6G) perchlorate) during 5mS-induced micelle to vesicle transition. The rotational motion of C153 becomes slower, whereas faster motion is observed for R6G during micelle to vesicle transition. Moreover, the fluorescence correlation spectroscopy (FCS) measurements suggest that the translational diffusion of hydrophobic probe becomes slower in C16mimCl-5mS aggregates in comparison to C16mimCl micelle. However, a reverse trend in translational diffusion motion of hydrophilic molecule has been observed in C16mimCl-5mS aggregates. Moreover, we have also found that the C16mimCl-5mS containing vesicles are transformed into micelles upon enhanced temperature, and it is further confirmed by turbidity, DLS measurements that this transition is a reversible one. Finally, temperature-induced rotational motion of C153 and R6G has been monitored in C16mimCl-5mS aggregates to get a complete scenario regarding the temperature-induced vesicle to micelle transition.

Micelle-vesicle-micelle transition in aqueous solution of anionic surfactant and cationic imidazolium surfactants: Alteration of the location of different fluorophores

The presence of different surfactants can alter the physicochemical behaviors of aqueous organized assemblies. In this article, we have investigated the location of hydrophobic molecule (Coumarin 153, C153) and hydrophilic molecule (Rhodamine 6G perchlorate, R6G) during micelle-vesicle-micelle transition in aqueous medium in presence of anionic surfactant, sodium dodecylbenzenesulfonate (SDBS) and cationic imidazolium-based surfactant, 1-alkyl-3-methylimidazolium chloride (CnmimCl; n=12, 16). Initially, the physicochemical properties of anionic micellar solution of SDBS has been investigated in presence of imidazolium-based surfactant, CnmimCl (n=12, 16) in aqueous medium by visual observation, turbidity measurement, zeta potential (ζ), dynamics light scattering (DLS), and transmission electron microscopy (TEM). Zeta potential (ζ) measurement clearly indicates that the incorporation efficiency of C16mimCl in SDBS micelle is better than the other one due to the involvement of strong hydrophobic as well as electrostatic interaction between the two associated molecules. Turbidity and DLS measurements clearly suggest the formation of vesicles over a wide range of concentration. Finally, the rotational motion of C153 and R6G has also been monitored at different mole fractions of CnmimCl in SDBS-CnmimCl (n=12, 16) solution mixtures. The hydrophobic C153 molecules preferentially located in the bilayer region of vesicle, whereas hydrophilic R6G can be solubilized at surface of the bilayer, inner water pool or outer surface of vesicles. It is observed that rotational motion of R6G is altered significantly in SDBS-CnmimCl solution mixtures in presence of different mole fractions of CnmimCl. Additionally, the translational diffusion motion of R6G is monitored using fluorescence correlation spectroscopy (FCS) techniques to get a complete scenario about the location and translational diffusion of R6G.

Translational and Rotational Diffusion of Two Differently Charged Solutes in Ethylammonium Nitrate-Methanol Mixture: Does the Nanostructure of the Amphiphiles Influence the Motion of the Solute?

In this Article, we have investigated the translational and rotational diffusion of two structurally similar but differently charged solutes (rhodamine 6G perchlorate and fluorescein sodium salt) in ethylammonium nitrate (EAN)-methanol (CH3OH) mixture to understand the effect of added ionic liquid on the motion of the solutes. EAN and CH3OH both are amphiphilic molecules and characterized by an extended hydrogen bonding network. Recently, Russina et al. found that a wide distribution of clusters exist in the CH3OH rich region (0.10 ≤ χEAN ≤ 0.15) and EAN molecules preserve their bulk-sponge-like morphology (Russina, O.; Sferrazza, A.; Caminiti, R.; Triolo, A. J. Phys. Chem. Lett. 2014, 5, 1738-1742). The effect of this microheterogeneous mixture on the solutes motion shows some interesting results compared to other PIL (protic ionic liquid)-cosolvent mixtures. Analysis of the time-resolved anisotropy data with the aid of Stokes-Einstein-Debye (SED) hydrodynamic theory predicts that the reorientation time of both of the solutes appears close to the stick hydrodynamic line in the methanol rich region. The hydrogen bond accepting solutes experience specific interaction with CH3OH, and with increasing concentration of EAN, the specific interaction between the solute and solvent molecules is decreased while the decrease is more prominent in the low mole fraction of EAN due to the large size of cluster formation. The temperature dependent anisotropy measurements show that the hydrogen bonding interaction between EAN and CH3OH is increased with increasing temperature. Moreover, fluorescence correlation spectroscopy (FCS) shows the dynamic heterogeneity of the mixture which is due to the segregation of the alkyl chain of the PIL. Formation of a large cluster at a low mole fraction of IL (0.10 ≤ χEAN ≤ 0.15) can be proved by the insensitivity of the translational diffusion and rotational activation energy of the solutes to the concentration of EAN. Thus, the result of the work suggests that the addition of EAN to the CH3OH affects the specific interaction between solute and solvent and, as a consequence, the translational motion as well as the rotational motion of the solutes are modulated.

Influence of bile salt on vitamin E derived vesicles involving a surface active ionic liquid and conventional cationic micelle

This study has been actually performed with the aim to develop vitamin E derived vesicles individually from a surface active ionic liquid (1-Hexadecyl-3-Methylimidazolium chloride ([C16mim]Cl)) and a common cationic amphiphile (benzyldimethylhexadecylammonium chloride (BHDC)) and also to investigate their consequent breakdown in presence of bile salt molecule. From this study, it is revealed that the rotational motion of coumarin 153 (C153) molecule is hindered as the vitamin E content is increased in the individual micellar solution of [C16mim]Cl and BHDC. The extent of enhancement in rotational relaxation time is more pronounced in case of [C16mim]Cl-vitamin E solutions than in the BHDC-vitamin E vesicular aggregates which confirms the greater rigidity of the former vesicular system than the later one. Moreover, the effect of bile salt in the vitamin E forming vesicular assemblies have also been unravelled. It is found that the large area occupancy by the steroidal backbone of the bile salt plays a crucial role towards the enlargement of the average surfactant head group area. This results in disintegration of the vesicles composed of vitamin E and consequently, vesicles are transformed into mixed micellar aggregates. From the anisotropy measurement it is found that the rotational motion of C153 is more hindered in the [C16mim]Cl/BHDC-NaCh mixed micelles compared to that inside the individual vesicles. The fluorescence correlation spectroscopic (FCS) study also confirms that the mixed micelles have a more compact structure than that of the [C16mim]Cl-vitamin E and BHDC-vitamin E vesicles. Altogether, the micelle to vesicle transition involving any vitamin and their disruption by bile salt would be an interesting investigation both from the view point of basic colloidal chemistry and towards the generation of new drug delivery vehicle due to their unique microenvironment. Therefore, in future, these systems can be utilised as vehicle for the transport and as well as delivery of drugs and as probable reactor in nanomaterial synthesis.

Concentration-Driven Fascinating Vesicle-Fibril Transition Employing Merocyanine 540 and 1-Octyl-3-methylimidazolium Chloride

In this article, anionic lipophilic dye merocyanine 540(MC540) and cationic surface-active ionic liquid (SAIL) 1-octyl-3-methylimidazolium chloride (C8mimCl) are employed to construct highly ordered fibrillar and vesicular aggregates exploiting an ionic self-assembly (ISA) strategy. It is noteworthy that the concentration of the counterions has exquisite control over the morphology, in which lowering the concentration of both the building blocks in a stoichiometric ratio of 1:1 provides a vesicle to fibril transition. Here, we have reported the concentration-controlled fibril-vesicle transition utilizing the emerging fluorescence lifetime imaging microscopy (FLIM) technique. Furthermore, we have detected this morphological transformation by means of other microscopic techniques such as field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and cryogenic-transmission electron microscopy (cryo-TEM) to gain additional support. Besides, multiwavelength FLIM (MW-FLIM) and atomic force microscopy (AFM) techniques assist us in knowing the microheterogeneity and the height profile of the vesicles, respectively. We have replaced the SAIL, C8mimCl, by an analogous traditional surfactant, n-octyltrimethylammonium bromide (OTAB), and it provides a discernible change in morphology similar to that of C8mimCl, whereas 1-octanol is unable to exhibit any structural aggregation and thus reveals the importance of electrostatic interaction in supramolecular aggregate formation. However, the SAILs having the same imidazolium headgroup with different chain lengths other than C8mimCl are unable to display any structural transition and determine the importance of the correct chain length for efficient packing of the counterions to form a specific self-assembly. Therefore, this study reveals the synergistic interplay of electrostatic, hydrophobic, and π-π stacking interactions to construct the self-assembly and their concentration-dependent morphological transition.

Effect of Microheterogeneity of Different Aqueous Binary Mixtures on the Proton Transfer Dynamics of [2,2′-Bipyridyl]-3,3′-diol: A Femtosecond Fluorescence Upconversion Study

In this article, we have investigated the excited-state intramolecular double proton transfer dynamics of [2,2′-bipyridyl]-3,3′-diol, BP(OH)2, in three alcohol–water binary mixtures, namely, ethanol (EtOH)–water, n-propanol (PrOH)–water, tert-butyl alcohol (TBA)–water, and dimethyl sulfoxide (DMSO)–water utilizing the femtosecond fluorescence upconversion technique. We have found that in alcohol–water binary mixtures the proton transfer (PT) pathway of BP(OH)2 is sequential and the anomalous slowdown in PT dynamics is observed in mole fraction (χ) ranges χEtOH = 0.04–0.07, χEtOH = 0.23–0.28, χPrOH = 0.17–0.30, χTBA = 0.12–0.21, and χTBA = 0.40–0.46. Our study sheds light on the involvement of water network in the PT dynamics. Reduction in water accessibility due to the involvement of water molecules in cluster formation results in hindered PT dynamics, and this retardation is more for the TBA–water binary mixture compared to that for the other two mixtures. Additionally, we have found two anomalous regions for the DMSO–water binary mixture in ranges χDMSO = 0.12–0.16 and χDMSO = 0.26–0.34. However, most interestingly, beyond χDMSO = 0.40, we do not find any growth component in the femtosecond fluorescence upconversion trace, which may be due to the change in the PT mechanism from a sequential water-mediated pathway to a concerted intramolecular pathway.