Hydroxy-Porphyrin as an Effective,Endogenous Molecular Clamp during Early Stages of Amyloid Fibrillization

Amyloid fibril formation of proteins is of great concern in neurodegenerative disease and can be detrimental to the storage and stability of biologics. Recent evidence suggests that insulin fibril formation reduces the efficacy of type II diabetes management and may lead to several complications. To develop anti-amyloidogenic compounds of endogenous origin, we have utilized the hydrogen bond anchoring, π stacking ability of porphyrin, and investigated its role on the inhibition of insulin amyloid formation. We report that hydroxylation and metal removal from the heme moiety yields an excellent inhibitor of insulin fibril formation. Thioflavin T, tyrosine fluorescence, Circular Dichorism (CD) spectroscopy, Field emission scanning electron microscopy (FESEM) and molecular dynamics (MD) simulation studies suggest that hematoporphyrin (HP) having hydrogen bonding ability on both sides is a superior inhibitor compared to hemin and protoporphyrin (PP). Experiments with hen egg white lysozyme (HEWL) amyloid fibril formation also validated the efficacy of endogenous porphyrin based small molecules. Our results will help to decipher a general therapeutic strategy to counter amyloidogenesis.     

The convolution for zero-order Mehler–Fock transform and pseudo-differential operator

The main aim of this paper is to find out the estimates of convolution for zero-order Mehler–Fock transform with various approaches. Pseudo-differential operator in terms of zero-order Mehler–Fock transform is defined and obtained its another integral representation. Further, its estimate in Lebesgue space has been studied. At the end some applications of zero-order Mehler–Fock transform and of convolution are discussed.     

An NHC-Stabilised Phosphinidene for Catalytic Formylation: A DFT-Guided Approach

In recent years, the applications of low-valent main group compounds have gained momentum in the field of catalysis. Owing to the accessibility of two lone pairs of electrons, NHC-stabilised phosphinidenes have been found to be excellent Lewis bases; however, they cannot yet be used as catalysts. Herein, an NHC-stabilised phosphinidene, 1,3-dimethyl-2-(phenylphosphanylidene)-2,3-dihydro-1H imidazole (1), for the activation of CO₂ is reported.A closer inspection of the CO₂ activation process by DFT calculations along with intrinsic bond orbital analysis shows that phosphinidene is associated with phenylsilane through a noncovalent π-π interaction between two phenyl rings which activates the Si−H bond facilitating hydride transfer to the CO₂ molecule. Detailed DFT studies along with spectroscopic experiments were combined to understand the mechanism of CO₂ activation and its catalytic reductive functionalisation leading to the formylation of a range of chemically inert primary amides under mild reaction conditions.     

Naphthalenediimides with High Fluorescence Quantum Yield: Bright-Red,Stable, and Responsive Fluorescent Dyes

The naphthalenediimide (NDI) scaffold in contrast to its higher congeners possess low-fluorescence. In spite of elegant synthetic developments, a highly emissive NDI is quite rare to find, as well as, a green-light-emitting NDI is yet to be explored. Herein, we report a novel class of symmetric and asymmetric NH₂-substituted core-NDIs ( 1 – 5 ) with tunable fluorescence in the visible region and extending to the NIR frontier. Importantly, the bis-NH₂-substituted NDI 2 revealed quantum yield, of ≈81 and ≈68 % in toluene and DMSO, respectively, suggesting versatility of the fluorophore in a wide range of solvent polarity. The dye 1 is shown to be the first NDI-based green-light emitter. The donor piperidine group in 5 diminish the by 40-fold providing a lever to modulate the excited-state intramolecular proton transfer (ESIPT) process. Our synthetic protocol applies a Pd catalyst and a benign hydride source simplifying the non-trivial −NH₂ group integration at the NDI-core. TD-DFT calculations predicted strong intramolecular hydrogen bonds in the excited state in the bulk nonpolar medium and responsiveness to solvent polarity. The maximization of the NDI emission outlined here would further boost the burgeoning repertoire of applications of the NDI scaffold.     

Interplay of Anion-π+ and π+-π+ Interactions in Novel Pyrido[2,1-a]isoquinolinium-Based AIEgens - Substituent- and Counterion-Dependent Fluorescence Modulation and Applications in Live Cell Mitochondrial Imaging**

Recently, the concept of anion-π⁺ interactions has witnessed unique applications in the field of AIEgen development. In this contribution, we disclose a consolidated study of a library of N-doped ionic AIEgens accessed through silver-mediated cyclization of pyridino-alkynes. A thorough photophysical, computational and crystallographic study has been conducted to rationalize the observed substituent- and counterion-dependent fluorescence properties of these luminogens. We further elucidate the prominent role of anion-π⁺ interactions, π⁺-π⁺ interactions and other non-covalent interactions, in inhibiting the undesired ACQ effect. Finally, we have also demonstrated the application of selected AIEgens for imaging of mitochondria in live cells.     

Generalizing the Aromatic δ-Amino Acid Foldamer Helix

A series of aromatic oligoamide foldamer sequences containing different proportions of three δ-amino acids derived from quinoline, pyridine, and benzene and possessing varying flexibility, for example due to methylene bridges, were synthesized. Crystallographic structures of two key sequences and ¹H NMR data in water concur to show that a canonical aromatic helix fold prevails in almost all cases and that helix stability critically depends on the ratio between rigid and flexible units. Notwithstanding subtle variations of curvature, i. e. the numbers of units per turn, the aromatic δ-peptide helix is therefore shown to be general and tolerant of a great number of sp³ centers. We also demonstrate canonical helical folding upon alternating two monomers that do not promote folding when taken separately: folding occurs with two methylenes between every other unit, not with one methylene between every unit. These findings highlight that a fine-tuning of helix handedness inversion kinetics, curvature, and side chain positioning in aromatic δ-peptidic foldamers can be realized by systematically combining different yet compatible δ-amino acids.     

Atom Transfer Oxidative Radical Cascade of Aryl Alkynoates towards 1,1‐Dichalcogenide Olefins

An oxidative trifunctionalization of aryl alkynoates has been devised via the chalcogenide radical triggered intramolecular 1,4‐aryl migration/decarboxylation cascade to prepare 1,1‐dichalcogenide tetrasubstituted alkenes in high yields (up to 98 %). This operationally simple reaction proceeds under metal‐free conditions, can be executed on gram scale, and highlights formal 1,1‐difunctionalization of alkynes. Synthetic potential of this protocol was demonstrated through a twofold cascade rearrangement to access highly conjugated tetra‐selenylated alkenes along with a cross‐dehydrogenative annulation to prepare fluorene derivative.     

Synthesis,characterization, crystal structure and catalytic activity of amido azo palladium(II) complex

Transition Metal Chemistry - The newly designed tridentate ligand, 2-((2-aminophenyl)diazenyl)-N-benzylaniline, 1 has been synthesized by the reaction between 2,2′-diaminoazobenzene and...     

Water wave scattering by three thin vertical barriers with middle one partially immersed and outer two submerged

Meccanica - The problem of oblique water wave scattering by three thin vertical barriers in deep water is investigated here assuming linear theory. The geometrical configurations of the three...     

Comparative Study of Nitro- and Azide-Functionalized ZnII-Based Coordination Polymers (CPs) as Fluorescent Turn-On Probes for Rapid and Selective Detection of H2S in Living Cells

Selective detection of H₂S in the cellular systems using fluorescent CPs/MOFs is of great scientific interest due to their outstanding aqueous stability, biocompatibility and real-time detection ability. Fabrication of such materials using complete biologically essential elements and applying them as an efficient biosensor is still quite challenging. In this context, two newly synthesized CPs containing biologically essential metal ion (Zn) and nitro/azido functional groups into the framework to sense extracellular and intracellular H₂S by reducing into respective amines are presented. The CP- 1 containing the azide group acted as an efficient fluorescent turn-on probe with the lowest detection limit (7.2 μM) and shortest response time (30 s) among the Zn-based probes reported till date. Moreover, CP- 1 exhibited green luminescence in live cells after imaging a very low concentration of H₂S, whereas the nitro analogue CP- 2 could not detect the target analyte due to its framework disruption.