pH-induced Conformational Isomerization of Bovine Serum Albumin Studied by Extrinsic and Intrinsic Protein Fluorescence

Serum albumins are multi-domain all α-helical proteins that are present in the circulatory system and aid in the transport of a variety of metabolites, endogenous ligands, drugs etc. Earlier observations have indicated that serum albumins adopt a range of reversible conformational isomers depending on the pH of the solution. Herein, we report the concurrent changes in the protein conformation and size that are inherent to the pH-induced conformational isomers of bovine serum albumin (BSA). We have investigated the fluorescence properties of both intrinsic (tryptophan) and extrinsic (ANS, pyrene) fluorophores to shed light into the structural features of the pH-dependent conformers. We have been able to identify a number of conformational isomers using multiple fluorescence observables as a function of pH titration. Our results indicate that at pH 3, a partially-folded, ‘molten-globule-like’ state is populated. Moreover, equilibrium unfolding studies indicated that the ‘molten-globule-like’ state unfolds in a non-cooperative fashion and is thermodynamically less stable than the native state. The fluorescence-based approach described in the present work has implications in the study of pH-induced conformational plasticity of other physiologically relevant proteins.     

Coherent Solution‐phase Synthesis of a Germanium‐Graphitic Nanocomposite and Its Evaluation for Lithium‐Ion Battery Anodes: Non‐innocent Role of the Mashima Reagent

The organosilicon reagent 1,4‐bis‐(trimethylsilyl)‐1,4‐diaza‐2,5‐cyclohexadiene 2 plays the binary role of the simultaneous reduction of GeCl₂.dioxane 1 dissolved in oleylamine to Ge nanocrystals and the formation of graphitic sheets under hot‐injection conditions. This colloidal synthetic route to germanium nanocrystals embedded on N‐doped graphitic nanosheets Ge/NG is free of any template or catalyst and involves easy purification techniques. The Ge/NG/C obtained after carbonization has been explored for anode performance in lithium‐ion batteries. Both Ge/NG and Ge/NG/C can be obtained on a gram scale and are bottleable under argon for months.     

Possible structures for the lamellar-isotropic (Lam-I) and lamellar-nematic (Lam-N) liquid crystalline phases

The three refractive indices of a liquid crystal that exhibits lamellar analogues of the three-dimensional isotropic, nematic, and smectic A phases are reported as functions of temperature for the Lam-I and Lam-N phases. The data suggest a number of striking behaviour types. The orientational distribution of the mesogenic moieties becomes more highly peaked in two dimensions on cooling from the Lam-I to the Lam-N phase; the two-dimensional order associated with mesogenic director n in the Lam-N phase is weak; and conformational changes in the side chain result in an increase in the refractive index perpendicular to the lamellae with decreasing temperature in the Lam-N phase.     

Photovoltaic and Amplified Spontaneous Emission Studies of High‐Quality Formamidinium Lead Bromide Perovskite Films

This study demonstrates the formation of extremely smooth and uniform formamidinium lead bromide (CH(NH₂)₂PbBr₃ = FAPbBr₃) films using an optimum mixture of dimethyl sulfoxide and N,N‐dimethylformamide solvents. Surface morphology and phase purity of the FAPbBr₃ films are thoroughly examined by field emission scanning electron microscopy and powder X‐ray diffraction, respectively. To unravel the photophysical properties of these films, systematic investigation based on time‐integrated and time‐dependent photoluminescence studies are carried out which, respectively, bring out relatively lower nonradiative recombination rates and long lasting photogenerated charge carriers in FAPbBr₃ perovskite films. The devices based on FTO/TiO₂/FAPbBr₃/spiro‐OMeTAD/Au show highly reproducible open‐circuit voltage (V_oc) of 1.42 V, a record for FAPbBr₃‐based perovskite solar cells. V_oc as a function of illumination intensity indicates that the contacts are very selective and higher V_oc values are expected to be achieved when the quality of the FAPbBr₃ film is further improved. Overall, the devices based on these films reveal appreciable power conversion efficiency of 7% under standard illumination conditions with negligible hysteresis. Finally, the amplified spontaneous emission (ASE) behavior explored in a cavity‐free configuration for FAPbBr₃ perovskite films shows a sharp ASE threshold at a fluence of 190 μJ cm^?2 with high quantum efficiency further confirming the high quality of the films.     

Mechanoluminescence Study of Europium Doped CaZrO<Subscript>3</Subscript> Phosphor

Behaviour displayed by mechanoluminescence (ML) in CaZrO₃:Eu³⁺ doped phosphors with variable concentration of europium ions are described. When the ML is excited impulsively by the impact of a load on the phosphors the ML intensity increases with time, attains a maximum value and then it decreases. In the ML intensity versus time curve, the peak increases and shifts towards shorter time values with increasing impact velocities. Sample was synthesized by combustion synthesis method with variable concentration of Eu³⁺ ions (0.1, 0.2, 0.5, 1, 1.5 mol%) and characterized by X-ray diffraction technique. The total ML intensity I_T is defined as the area below the ML intensity versus time curve. Initially I_T increases with impact velocity V₀ of the load and then it attains a saturation value for higher values of impact velocities which follow the relation I_T = I_T ⁰ exp.(?V_c/V₀) where I_T ⁰ and V_c are constants. Total ML intensity increases linearly with the mass of the phosphors for higher impact velocities. The ML intensity I_m, corresponding to the peak of ML intensity versus time curve increases linearly with the impact velocities. The time t_m, is found to be linearly related to 1000/V₀. The mechanoluminescence induced by impulsive excitation in europium doped CaZrO₃ phosphors plays a significance role in the understanding of biological sensors and display device application.     

Polycatenar Mesogens with Various Degree of Flexibility of Molecular Structure

A series of newly synthesised rod‐like polycatenar mesogens forms columnar phases, with the number of molecules in the column cross section depending on the core rigidity. For non‐symmetric molecules, an additional density modulation, namely helical arrangement of molecules with a periodicity of approximately 10 molecular distances develops along the columns. For one of the compounds, a new type of columnar liquid crystal phase with 3D positional order is observed. Introducing a stilbene unit in the mesogenic core enhances the fluorescent properties of the compounds. In the hexagonal columnar phase, polarised light emission is observed.     

Phase behavior and self-organized structures of diglycerol monolaurate in different nonpolar organic solvents

Nonaqueous phase behavior and reverse micellar structures of diglycerol monolaurate (DGL) in different nonpolar organic solvents, such as n-decane, n-tetradecane, and n-hexadecane, have been studied over a wide range of compositions and temperatures. The equilibrium phases are identified by means of visual observation and small-angle X-ray scattering (SAXS). A solid phase present at lower temperature swells small amount of oils and transforms into a lamellar liquid crystalline structure at higher temperature. The melting temperature of the solid phase is virtually constant at all mixing ratios of the surfactant and oil. With the further increase of temperature, the liquid crystal transforms into an isotropic single-liquid phase near the surfactant axis, whereas there is a coexistence region of two isotropic phases near the solvent axis. The area of the two-liquid (II) phase region depends largely on the hydrocarbon chain length of the oils, the longer chain leading to the wider II area. Accordingly, the DGL surfactant is most miscible with decane, exhibiting a reduced miscibility with increasing solvent hydrocarbon chain length. Increasing temperature enhances the dissolution tendency of the surfactant in oil, where the two-liquid phase transforms into an isotropic single phase. SAXS analysis based on the GIFT technique is used to characterize the structure of the reverse micellar aggregates in the isotropic single-phase liquids. We have demonstrated that instead of changing polarity or a functional group of the solvent molecules, if we optimize the hydrophilic nature of the surfactant head group, the alkyl chain length of the solvent oils can serve as a tunable parameter of the micellar geometry. The hydrophilic surfactant DGL interestingly forms cylindrical micelles in nonpolar oils, decane, and tetradecane in the dilute region above the II phase region. The micellar size shows temperature dependence behavior, and the micellar length goes on increasing with decreasing temperature; eventually we found a signature of the onset of critical fluctuations in the deduced pair-distance distribution function near the phase separation line. The signature of the attractive interaction between the cylindrical reverse aggregates when a phase separation line is approached is likely to be a precursor of critical phenomenon. Doping with a trace of water results in a similar but more pronounced structural enhancement. The transfer free energy of diglycerol moiety from a hydrophilic environment to different hydrocarbon oils may account for these phenomena.     

Organic thin film formation using asymmetric surface-active viologens

In the present study, asymmetric surface-active viologens were applied successfully for the thin film formation of organic pigments using the immersion plating technique. The influences of the hydrophobicity of the surfactants and the pH of the plating solution on the film formation were investigated. In addition, the interfacial chemistry and electrochemistry of the surfactants were studied, and the mechanism of the film formation has been proposed and discussed.     

Chemical constituents of Nepalese propolis (II)

A novel flavanonol (1), three new isoflavones (2-4) and a new flavan-3-ol (5) were isolated along with ten other known flavonoids (6-15) from the methanolic extract of propolis collected from Chitwan, Nepal. Their structures were determined on the basis of spectral analysis.