Metal‐Free Annulation of Arenes with 2‐Aminopyridine Derivatives: The Methyl Group as a Traceless Non‐Chelating Directing Group

A novel annulation reaction between 2‐aminopyridine derivatives and arenes under metal‐free conditions is described. The presented intermolecular transformation provided straightforward access to the important pyrido[1,2‐a]benzimidazole scaffold under mild reaction conditions. The unprecedented application of the methyl group of methylbenzenes as a traceless, non‐chelating, and highly regioselective directing group is reported.     

A colorimetric and ratiometric fluorescent turn-on fluoride chemodosimeter and application in live cell imaging: high selectivity via specific SiO cleavage in semi aqueous media and prompt recovery of ESIPT along with the X-ray structures

A ratiometric fluorescent turn-on probe for fluoride ion, based on modulation of the excited-state intramolecular proton transfer (ESIPT) process by chemodosimetric desilylation pathway is reported. The probe SNBT (silyl protected hydroxynaphthalene benzothiazole moiety) shows a significant increase of ratiometric absorption band at 440 nm and emission band at 477 nm by the deprotection of fluoride mediated silyl bond cleavage in CH₃CN–H₂O (8/2, v/v, 25 °C). The test strips based on SNBT and F⁻ are fabricated, which can act as a convenient and efficient F⁻ test kits. Furthermore, the biological application shows that it can be very useful as a selective fluoride probe in the fluorescence imaging of living cells.     

Copper‐Catalyzed (2+1) Annulation of Acetophenones with Maleimides: Direct Synthesis of Cyclopropanes

A practical copper‐catalyzed direct oxidative cyclopropanation of electron‐deficient alkenes with acetophenone derivatives is reported. The dehydrogenative annulation involves a double C? H bond functionalization at the α‐position of the ketone using di‐tert‐butyl peroxide as oxidant. The broad scope of the reaction and excellent functional‐group tolerance is demonstrated for the stereoselective synthesis of fused cyclopropanes. The developed transformation revealed an unprecedented reactivity for copper‐catalyzed processes.     

SH-type waves dispersion in an isotropic medium sandwiched between an initially stressed orthotropic and heterogeneous semi-infinite media

The present paper studies the propagation of shear waves (SH-type waves) in an homogeneous isotropic medium sandwiched between two semi infinite media. The upper half-space is considered as orthotropic medium under initial stress and lower half-space considered as heterogeneous medium. We have obtained the dispersion equation of phase velocity for SH-type waves. The propagation of SH-type waves are influenced by inhomogeneity parameters and initial stress parameter. The velocity of SH-type wave has been computed for different cases. We have also obtained the dispersion equation of phase velocity in homogeneous media in the absence of initial stress. The velocities of SH-type waves are calculated numerically as a function of kH (non-dimensional wave number) and presented in a number of graphs. To study the effect of inhomogeneity parameters and initial stress parameter we have plotted the velocity of SH-type wave in several figure. We have observed that the velocity of wave increases with the increase inhomogeneity parameters. We found that in both homogeneous and inhomogeneous media the velocity of SH-type wave increases with the increase of initial stress parameter. The results may be useful for the study of seismic waves propagation during any earthquake and artificial explosions.     

Crystallization and morphology of poly(ethylene‐2,6‐naphthalene dicarboxylate) in the presence of nucleating agents

The crystallization and morphology of poly(ethylene‐2,6‐naphthalene dicarboxylate) (PEN) containing, as nucleating agents, a sodium salt of a copolymer of ethylene and acrylic acid or a sodium salt of a copolymer of ethylene and methacrylic acid, were investigated with differential scanning calorimetry, polarized optical microscopy, and small‐angle light scattering. The nucleating agents accelerated the crystallization rate at high temperatures by decreasing the surface free energy barrier hindering nucleation. Meanwhile, the nucleating agents with flexible chains could also improve the mobility of the PEN chains and increase the crystallization rate at low temperatures. Hedrites were observed when PEN was crystallized at high temperatures, whereas crystallization at low temperatures led to the formation of spherulites. Similar but smaller morphologies were obtained in the presence of nucleating agents. With nucleating agents, the spherulites formed at low temperatures were less perfect, although the optical properties of the spherulites were not influenced. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2387–2394, 2002     

Self-organized critical earthquake model with moving boundary

A globally driven self-organized critical model of earthquakes with conservative dynamics has been studied. An open but moving boundary condition has been used so that the origin (epicenter) of every avalanche (earthquake) is at the center of the boundary. As a result, all avalanches grow in equivalent conditions and the avalanche size distribution obeys excellent finite size scaling. Though the recurrence time distribution of the time series of avalanche sizes obeys well both the scaling forms recently observed in analysis of the real data of earthquakes, it is found that the scaling function decays only exponentially in contrast to a generalized gamma distribution observed in the real data analysis. The non-conservative version of the model shows periodicity even with open boundary.     

N‐Linked Glycosyl Auxiliary‐Mediated Native Chemical Ligation on Aspartic Acid: Application towards N‐Glycopeptide Synthesis

A practical approach towards N‐glycopeptide synthesis using an auxiliary‐mediated dual native chemical ligation (NCL) has been developed. The first NCL connects an N‐linked glycosyl auxiliary to the thioester side chain of an N‐terminal aspartate oligopeptide. This intermediate undergoes a second NCL with a C‐terminal thioester oligopeptide. Mild cleavage provides the desired N‐glycopeptide.     

Spectacular Rate Enhancement of the Diels–Alder Reaction at the Ionic Liquid/n‐Hexane Interface

The use of the ionic liquid/n‐hexane interface as a new class of reaction medium for the Diels–Alder reaction gives large rate enhancements of the order of 10⁶ to 10⁸ times and high stereoselectivity, as compared to homogeneous media. The rate enhancement is attributed to the H‐bonding abilities and polarities of the ionic liquids, whereas the hydrophobicity of ionic liquids was considered to be the factor in controlling stereoselectivity.     

Stereodivergent Zweifel Olefination and its Mechanistic Dichotomy

Stereoselective Zweifel olefination using boronate complexes carrying two different reactive π-systems was achieved to synthesize vinyl heteroarenes and conjugated 1,3-dienes in good yield and up to 100 % stereoselectivity, which remains unexplored until now. Most importantly, we report the unprecedented formation of E vs. Z-vinyl heteroarenes for different heteroarenes under identical conditions. Density functional theory (DFT) investigations unveil the mechanistic dichotomy between olefin and heteroarene activation followed by 1,2-migration, leading to E or Z-vinyl heteroarenes respectively. We also report a previously unknown reversal of stereoselectivity by using 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as an electrophile. The Zweifel olefination using a boronate complex that carries two different olefins was previously unexplored due to significant challenges associated with the site-selective activation of olefins. We have solved this problem and reported the site-selective activation of olefins for the stereoselective synthesis of 1,3-dienes.     

Studies on the interaction of diacetylcurcumin with calf thymus-DNA

Ongoing research on curcumin and its structural derivatives are a subject of growing interest because of their demonstrated biological properties. Diacetylcurcumin (DAC), a synthetic derivative of natural non-toxic curcumin has been shown to affect a host of activities ranging from wound healing to life threatening diseases like AIDS, cancer etc. The interaction of diacetylcurcumin (DAC) with calf thymus-DNA (ct-DNA) has been investigated by spectroscopic and viscometric techniques. The fluorescence intensity of DAC was quenched by ct-DNA. The mean binding constant obtained from the spectroscopic techniques was 3.97 ± 0.31 × 10⁵ M⁻¹. Circular dichroism studies did not reveal any unwinding of the DNA helix on interaction with DAC, implying no conformational changes. The binding mode was analyzed by competitive binding between ethidium bromide (EB) and DAC for ct-DNA and also by viscometric studies. DAC was found to be a minor groove binder with a preference for the A-T region compared to the G-C region. This was substantiated by displacement studies with Hoechst 33258, a known minor groove binder. Docking studies were found to corroborate the experimental results.