Bioinspired,Size‐Tunable Self‐Assembly of Polymer–Lipid Bilayer Nanodiscs

Polymer‐based nanodiscs are valuable tools in biomedical research that can offer a detergent‐free solubilization of membrane proteins maintaining their native lipid environment. Herein, we introduce a novel ca. 1.6 kDa SMA‐based polymer with styrene:maleic acid moieties that can form nanodiscs containing a planar lipid bilayer which are useful to reconstitute membrane proteins for structural and functional studies. The physicochemical properties and the mechanism of formation of polymer‐based nanodiscs are characterized by light scattering, NMR, FT‐IR, and TEM. A remarkable feature is that nanodiscs of different sizes, from nanometer to sub‐micrometer diameter, can be produced by varying the lipid‐to‐polymer ratio. The small‐size nanodiscs (up to ca. 30 nm diameter) can be used for solution NMR spectroscopy studies whereas the magnetic‐alignment of macro‐nanodiscs (diameter of > ca. 40 nm) can be exploited for solid‐state NMR studies on membrane proteins.     

Pulsed laser excitation of phosphate stabilised silver nanoparticles

Laser flash photolysis studies were carried out on two types of silver nanoparticles prepared byγ-radiolysis of Ag⁺ solutions in the presence of polyphosphate as the stabiliser. Type I silver nanoparticles displayed a surface plasmon band at 390 nm. Type II silver nanoparticles showed a 390 nm surface plasmon band with a shoulder at 550 nm. On photoexcitation in the surface plasmon band region, using 35 picosecond laser pulses at 355 nm and 532 nm, the type II solutions showed transient bleaching and absorption signals in the 450–900 nm region, which did not decay appreciably up to 5 nanoseconds. These transient changes were found to get annealed in the intervalt where 5 ns<t< 100 ns. Extended photolysis of the nanoparticle solutions with repetitive laser pulses resulted in a decrease in the values of the average particle size which were measured by employing the dynamic light scattering technique.     

Dissolvable membranes as sensing elements for microfluidics based biological/chemical sensors

We demonstrate a chemical and biological sensing mechanism in microfluidics that transduces chemical and biological signals to electrical signals with large intrinsic amplification without need for complex electronics. The sensing mechanism involves a dissolvable membrane separating a liquid sample chamber from an interdigitated electrode. Dissolution of the membrane (here, a disulfide cross-linked poly(acrylamide) hydrogel) in the presence of a specific target (here, a reducing agent-dithiothreitol) allows the target solution to flow into contact with the electrode. The liquid movement displaces the air dielectric with a liquid, leading to a change (open circuit to approximately 1 kOmega) in the resistance between the electrodes. Thus, a biochemical event is transduced into an electrical signal via fluid movement. The concentration of the target is estimated by monitoring the difference in dissolution times of two juxtaposed sensing membranes having different dissolution characteristics. No dc power is consumed by the sensor until detection of the target. A range of targets could be sensed by defining membranes specific to the target. This sensing mechanism might find applications in sensing targets such as toxins, which exhibit enzymatic activity.     

Control of the Supramolecular Excimer Formation of Thioflavin T within a Cucurbit[8]uril Host: A Fluorescence On/Off Mechanism

On or off? A new excimer band at λ=570 nm was visualized during the noncovalent host–guest interaction between thioflavin T (ThT) and cucurbit[8]uril (CB8). Controlled dissociation of this assembly in the presence of Ca²⁺ was demonstrated as an on/off fluorescence switch (see picture).

     

Scope of a novel three-component synthesis of highly functionalized pyridines(dagger)

A mechanistically unique three-component synthesis provides a variety of functionalized pyridine derivatives in fair to excellent yields. The scope of this reaction was studied with respect to the alkoxyallene, the nitrile, and the carboxylic acid. Due to the 4-hydroxy group, these pyridine derivatives are suitable precursors for subsequent palladium-catalyzed reactions. Suzuki couplings of the corresponding pyridyl nonaflates lead to a variety of pyridine and bipyridine derivatives.     

Lead(IV) acetate: intriguing reactivity profile

LTA reaction of homoallyl alcohols derived from norbornyl alpha-diketones exclusively furnished the corresponding alpha-diketones via beta-fragmentation of the allyl group in refluxing benzene while changing the solvent to MeOH resulted in the formation of novel methoxy substituted spirocyclic tetrahydrofuran products.     

Molecular‐Recognition‐Assisted pKa Shifts and Metal‐Ion‐Induced Fluorescence Regeneration in p‐Sulfonatocalix[6]arene‐Encapsulated Acridine

The host–guest interactions of cationic (AcH⁺) and neutral (Ac) forms of the dye acridine with the macrocyclic host p‐sulfonatocalix[6]arene (SCX6) were investigated by using ground‐state absorption, steady‐state and time‐resolved fluorescence, and NMR measurements. The cationic form undergoes significant complexation with SCX6 (K_eq=2.5×10⁴ M ^?1), causing a sharp decrease in the fluorescence intensity and severe quenching in the excited‐state lifetime of the dye. The strong binding of the AcH⁺ form of the dye with SCX6 is attributed to ion–ion interactions involving the sulfonato groups (SO₃^?) of SCX6 and the positively charged AcH⁺ at pH of approximately 4.3. Whereas, the neutral Ac form of the dye undergoes weak complexation with SCX6 (K_eq=0.9×10³ M ^?1) and the binding constant is lowered by one order of magnitude compared with that of the SCX6–AcH⁺ system. The strong affinity of SCX6 to the protonated form leads to a large upward pK_a shift (≈2 units) in the dye. In contrast, strong emission quenching upon SCX6 interaction and the regeneration of fluorescence intensity of the dye in the presence of Gd³⁺ through competitive binding have also been demonstrated.     

Supramolecular Assembly Induced Emission of Thiazole Orange with Sulfobutylether β-cyclodextrin: A Stimuli-Responsive Fluorescence Sensor for Tyramine

Modulation and control of stimuli responsive features of molecular assemblies in organized assemblies/cavitand macrocycles have received immense attention in many areas. In this study, we have established the formation of a discrete molecular assembly of thiazole orange (TO) dyes at the portals of the sulfobutylether β-cyclodextrin (SBE₇βCD) macrocycle leading to the evolution of a strong and distinct emission band from aggregated TO. The supramolecular assembly promoted portal aggregation of TO in its 1 : 4 (SBE₇βCD : TO) composition, characterized by absorption, fluorescence, circular dichroism, ITC and ¹H NMR measurements, was probed to be selectively responsive to tyramine among other biogenic amines/neurotransmitters. For the first time, the different extent of emission quenching of SBE₇βCD : TO assembly in the presence of biogenic amines/neurotransmitters is translated to achieve a selective on-off fluorescence sensor for the detection of tyramine against other neurotransmitters with a limit-of-detection (LOD) as low as ∼575 nM (79 ppb). The emission features of the assembly with changes in temperature is found to be highly reproducible even after several temperature cycles and is promising to design an optical supramolecular thermometer in the ambient temperature range.     

Bioinspired,Size‐Tunable Self‐Assembly of Polymer–Lipid Bilayer Nanodiscs

Polymer‐based nanodiscs are valuable tools in biomedical research that can offer a detergent‐free solubilization of membrane proteins maintaining their native lipid environment. Herein, we introduce a novel ca. 1.6 kDa SMA‐based polymer with styrene:maleic acid moieties that can form nanodiscs containing a planar lipid bilayer which are useful to reconstitute membrane proteins for structural and functional studies. The physicochemical properties and the mechanism of formation of polymer‐based nanodiscs are characterized by light scattering, NMR, FT‐IR, and TEM. A remarkable feature is that nanodiscs of different sizes, from nanometer to sub‐micrometer diameter, can be produced by varying the lipid‐to‐polymer ratio. The small‐size nanodiscs (up to ca. 30 nm diameter) can be used for solution NMR spectroscopy studies whereas the magnetic‐alignment of macro‐nanodiscs (diameter of > ca. 40 nm) can be exploited for solid‐state NMR studies on membrane proteins.