A Selective Cucurbit[8]uril-Peptide Beacon Ensemble for the Ratiometric Fluorescence Detection of Peptides

A convenient supramolecular strategy for constructing a ratiometric fluorescent chemosensing ensemble, consisting of a macrocyclic host (cucurbit[8]uril CB[8]), and a pyrene-tagged amphiphilic peptide beacon (AP 1), is reported. AP 1 unfolds upon encapsulation of the pyrene termini into the hydrophobic CB[8] cavity. This changes pyrene excimer to monomer emission. Substrates with higher affinity for the CB[8] cavity can displace AP 1 from the ensemble. The released AP 1 folds again to form a pyrene excimer, which allows for the ratiometric fluorescence monitoring of the substrate. In this report, the ensemble capacity for ratiometric fluorescence monitoring of biological substrates, such as amino acid derivatives, specific peptides, and proteins, in aqueous media is demonstrated.     

Contrasting Effect of Additives on Photoinduced Reactions of SmI2

The work described herein compares the effect of additives (HMPA, methanol, ethylene glycol, pinacol, N-methylethanolamine) on thermal and photochemical reactions of samarium diiodide (SmI₂). In thermal reactions, additives that coordinate to SmI₂ induce a significant increase in reaction rate. In photochemical reactions, the presence of an electronegative atom with a highly localized negative charge on the substrate leads to a rate deceleration. In order to benefit from the columbic interaction with the positively charged samarium cation, these substrates react preferentially by an inner sphere reduction mechanism. The addition of ligands prevents this close interaction causing rate retardation. Furthermore, studies demonstrate that excited state quenching of Sm^II by ethylene glycol and other additives indicate that it is unlikely to be the major cause for the observed rate retardation. This effect provides a simple diagnostic tool to distinguish between an inner and an outer sphere reduction mechanism.     

Impact of FRET between Molecular Aggregates and Quantum Dots

Energy transfer has been employed in third‐generation solar cells for the conversion of light into electrical energy. Long‐range nonradiative energy transfer from semiconductor quantum dots (QDs) to fluorophores has been demonstrated by using CdS QDs and thiophene?BODIPY (boron dipyrromethene, abbreviated as TG2). TG2 shows a broad photoluminescence (PL) spectrum, which varies with concentration. At very low concentrations, monomeric units are present; then, upon increasing the concentration, these monomers form a mixed (J‐/H‐)aggregated state. Energy transfer between the CdS QDs and TG2 was confirmed by separately investigating the interactions between CdS and the monomer of TG2 and between CdS and the aggregated states of TG2. Size‐dependent PL quenching confirmed that nonradiative Förster resonance energy transfer (FRET) from photoexcited CdS QDs to the J‐aggregate state of TG2 was the major energy‐relaxation channel, which occurred on the timescale of hundreds of fs. These results have broad applications in the field of light harvesting based on the assembly of molecular aggregates.     

Unprecedented Diastereoselective Arylogous Michael Addition of Unactivated Phthalides

The first highly enantioselective arylogous Michael reaction (AMR) of 3-unsubstituted phthalides has been described. This phase-transfer methodology, which uses catalytic amounts of KOH/18-crown-6 catalyst in mesitylene in the presence of N,O-bis(trimethylsilyl)acetamide (BSA), gives access to a broad range of 3-monosubstituted phthalides with high levels of syn diastereoselectivity and good yields, starting from 3-unsubstituted derivatives and diverse α,β-unsaturated carbonyl compounds. The reaction also applies to unactivated 3-alkyl phthalides to afford 3,3-dialkyl derivatives. A plausible mechanism has been suggested. DFT analysis of possible transition states gives a rationale of the high syn diastereoselectivity observed and its correlation with the solvent's dielectric constant.     

Isolation and characterization of 4-chlorophenol degrading bacterial strain from pharmaceutical xenobiotic compounds contaminated soil using enrichment technique

4- chlorophenol is available as the fundamental basic compound of numerous manufactured organics. It is produced from various sources like herbicides, wood additives, oil industries, pharmaceutical drugs and so on. It can be removed from the effluent by various ways but most effective method is bioremediation. In present study, aerobic bacterial strain was isolated from soil that was contaminated with pharmaceutical xenobiotic compounds using enrichment technique with 500 ppm of 4-chlorophenol as a sole source of carbon and energy. Colonies were isolated after 24 h of incubation on petri plate by media enrichment with 500 ppm of 4- chlorophenol and serial dilution method. 18 colonies were isolated and examined for their ability to degrade 500 ppm of 4-chlorophenol. The most potent strain, C17 was able to remove nearly ～99.93% of 4-chlorophenol in 24 h, 37 °C temperature and 6.8 pH. Based on morphological, biochemical, nucleotide homology and phylogenetic analysis the strain was found to have maximum similarity (98.98%) with Bacillus timonensis strain 10403023.     

Magnesium‐Catalyzed Hydroboration of Terminal and Internal Alkynes

A magnesium‐catalyzed hydroboration of alkynes providing good yields and selectivities for a wide range of terminal and symmetrical and unsymmetrical internal alkynes has been developed. The compatibility with many functional groups makes this magnesium catalyzed procedure attractive for late stage functionalization. Experimental mechanistic investigations and DFT calculations reveal insights into the reaction mechanism of the magnesium catalyzed protocol.     

Unveiling the binding interaction of zinc (II) complexes of homologous Schiff-base ligands on the surface of BSA protein: A combined experimental and theoretical approach

Four new zinc (II) complexes [Zn (HL¹H)Br₂] (1), [Zn (HL¹H)Cl₂] (2), [Zn₂(HL²)Br₃] (3), and [Zn (HL²)Cl] (4) have been synthesized by adopting template synthetic strategy and utilizing two homologous Schiff base ligands (H₂L¹ = 4-bromo-2-{[2-(2-hydroxyethylamino)-ethylimino]-methyl}-6-methoxyphenol, H₂L² = 4-bromo-2-{[3-(2-hydroxyethylamino)propylimino]methyl}-6-methoxyphenol), differing in one -CH₂- unit in the ligating backbone, by adopting template synthetic strategy. All the complexes have been characterized by single crystal X-ray diffraction analysis as well as by other routine physicochemical techniques. Ligand mediated structural variations have been observed and rationalized by density functional theoretical (DFT) calculations. Interaction of the complexes 1–4 with Bovine Serum Albumin protein (BSA) has been studied by different spectroscopic techniques. A complete thermodynamic profile (ΔH^o, ΔS^o and ΔG^o) was evaluated initially from the change in absorption and fluorescence spectra upon addition of BSA to the complexes. Appreciable binding constant values in the range ~ 0.94–4.51 × 10⁴ M⁻¹ indicate efficient binding tendency of the complexes to BSA with the sequence 1 ≅ 2 > 3 ≅ 4. Circular dichroism (CD), isothermal calorimetric titration experiments, molecular docking and molecular dynamics have been performed to gain deep insight into the binding regions of complex 1 to BSA. Experimental evidences suggest an interaction of zinc complexes at the surface of BSA protein and this particular binding has been exploited to determine unknown concentration of BSA protein. For this purpose complex 1 was explored as a BSA protein quantification tool.     

Development of the Vinylogous Pictet–Spengler Cyclization and Total Synthesis of (±)‐Lundurine A

A novel vinylogous Pictet–Spengler cyclization has been developed for the generation of indole‐annulated medium‐sized rings. The method enables the synthesis of tetrahydroazocinoindoles with a fully substituted carbon center, a prevalent structural motif in many biologically active alkaloids. The strategy has been applied to the total synthesis of (±)‐lundurine A.     

Synthesis and structure of 1,4-dipiperazino benzenes: chiral terphenyl-type peptide helix mimetics

The terphenyl structure has been proven to be an ideal scaffold mimicking side-chain functionalities of peptidic alpha-helices. The synthesis of 1,4-dipiperazino benzenes, using stepwise transition metal-catalyzed N-arylation of chiral piperazines to a central benzene core is reported. The structure determination by X-ray crystallography reveals a geometrical arrangement of the hydrophobic side chains resembling the orientation of key i, i + 3, and i + 7 positions in a peptidic alpha-helix or in terphenyl helix mimetics.