Sulfated Tin Oxide: A Reusable and Highly Efficient Heterogeneous Catalyst for the Synthesis of 2,4,5-Triaryl-1H-imidazole Derivatives

One-pot, three-component condensation of benzil/benzoin, substituted aromatic aldehydes, and ammonium acetate in an ethanol–water (1:1, v/v) solvent system using sulfated tin oxide catalyst under reflux condition afforded corresponding 2,4,5-triaryl-1H-imidazoles in excellent yield. The remarkable advantages offered by this method include green and reusable catalyst, mild reaction conditions, fast reaction rate, and excellent yield of products. This novel methodology maintains atom economy and an environmentally friendly approach.     

KHSO4 · H2O/SiO2‐Catalyzed,One‐Pot,Solvent‐Free Synthesis of Pyrazolines,Tetrahydrocarbozoles and Indoles using Microwave Irradiation

A new high‐yielding, operationally simple, solvent‐free, and mild method for preparation of pyrazolines, tetrahydrocarbazoles, and indoles has been developed using KHSO₄ · H₂O impregnated on SiO₂. The reactions have been probed under microwave irradiation (MWI), and ultrasonic and thermal conditions, employing different solid supports. The data revealed that KHSO₄ · H₂O impregnated on SiO₂ under MWI provides the best yields in a shorter time under solvent‐free reaction conditions.     

Stretching liquid bridges with bubbles: the effect of air bubbles on liquid transfer

Liquid bridges containing bubbles are relevant to industrial printing and are also a topic of fundamental scientific interest. We use flow visualization to study the stretching of liquid bridges, both with and without bubbles, at low capillary numbers. We find that whereas the breakup of wetting fluids between two identical surfaces is symmetric about the bridge midpoint, contact line pinning breaks this symmetry at slow stretching speeds for nonwetting fluids. We exploit this observation to force air bubbles selectively toward the least hydrophilic plate confining the liquid bridge.     

Carba-LNA-5MeC/A/G/T modified oligos show nucleobase-specific modulation of 3'-exonuclease activity, thermodynamic stability, RNA selectivity, and RNase H elicitation: synthesis and biochemistry

Using the intramolecular 5-exo-5-hexenyl radical as a key cyclization step, we previously reported an unambiguous synthesis of carba-LNA thymine (cLNA-T), which we subsequently incorporated in antisense oligonucleotides (AON) and investigated their biochemical properties [J. Am. Chem. Soc.2007, 129 (26), 8362-8379]. These cLNA-T incorporated oligos showed specific RNA affinity of +3.5-5 °C/modification for AON:RNA heteroduplexes, which is comparable to what is found for those of LNAs (Locked Nucleic Acids). These modified oligos however showed significantly enhanced nuclease stability (ca. 100 times more) in the blood serum compared to those of the LNA modified counterparts without compromising any RNase H recruitment capability. We herein report the synthesis of 5-methylcytosine-1-yl ((Me)C), 9-adeninyl (A), and 9-guaninyl (G) derivatives of cLNA and their oligonucleotides and report their biochemical properties as potential RNA-directed inhibitors. In a series of isosequential carba-LNA modified AONs, we herein show that all the cLNA modified AONs are found to be RNA-selective, but the magnitude of RNA-selectivity of 7'-R-Me-cLNA-G (cLNA-G) (ΔT(m) = 2.9 °C/modification) and intractable isomeric mixtures of 7'-(S/R)-Me-cLNA-T (cLNA-T, ΔT(m) = 2.2 °C/modification) was found to be better than diastereomeric mixtures of 7'-(S/R)-Me-cLNA-(Me)C with trace of cENA-(Me)C (cLNA-(Me)C, ΔT(m) = 1.8 °C/modification) and 7'-R-Me-cLNA-A (cLNA-A, ΔT(m) = 0.9 °C/modification). cLNA-(Me)C modified AONs however exhibited the best nuclease stability, which is 4-, 7-, and 20-fold better, respectively, than cLNA-T, cLNA-A, and cLNA-G modified counterparts, which in turn was more than 100 times stable than that of the native. When the modification sites are appropriately chosen in the AONs, the cLNA-A, -G, and -(Me)C modified sites in the AON:RNA hybrids can be easily recognized by RNase H, and the RNA strand of the hybrid is degraded in a specific manner, which is important for the design of oligos for therapeutic purposes. The cLNA-(Me)C modified AON/RNA, however, has been found to be degraded 4 times faster than cLNA-A and G modified counterparts. By appropriately choosing the carba-LNA modification sites in AON strands, the digestion of AON:RNA can be either totally repressed or be limited to cleavage at specific sites or at a single site only (similar to that of catalytic RNAzyme or DNAzyme). Considering all physico- and biochemical aspects of cLNA modified oligos, the work suggests that the cLNA modified antisense oligos have the potential of being a promising therapeutic candidate due to their (i) higher nucleobase-specific RNA affinity and RNA selectivity, (ii) greatly improved nuclease stability, and (iii) efficient RNase H recruitment capability, which can induce target RNA cleavage in a very specific manner at multiple or at a single site, in a designed manner.     

Phosphotungstic Acid Nanoclusters Grafted onto High Surface Area Hydrous Zirconia as Efficient Heterogeneous Catalyst for Synthesis of Octahydroquinazolinones and β-Acetamido Ketones

Phostungstic acid (PWA) nanoclusters grafted onto high surface area polycrystalline hydrous zirconia powder (PWA/ZrO₂) was prepared by wet impregnation method. The zirconia particles were synthesized using a modified sol–gel route. The obtained material was characterized by X-ray diffraction (XRD), UV–Vis–diffuse reflectance spectroscopy (UV–Vis–NIR–DRS), infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and sorptometric techniques. XRD study revealed the presence of tetragonal phase of zirconia in the synthesized sample. TEM study indicates presence of small PWA clusters with size in the range of 5–15 nm well dispersed on the surface of the ZrO₂ particles. The characteristic UV and IR absorption feature of the PWA was retained in the PWA/ZrO₂ material. The PWA/ZrO₂ material was used as an efficient catalyst for the preparation of octahydroquinazolinones and β-acetamido ketones. The octahydroquinazolinones were synthesized by the multicomponent condensation of dimedones, urea and aryl aldehydes in ethanol. Similarly, β-acetamido ketones were synthesized with high yield and purity by four component condensation of aryl aldehydes, enolizable ketones, and acetyl chlorides in acetonitrile. The protocols developed in this investigation using the PWA/ZrO₂ catalyst is advantageous in terms of simple experimentation, high yield and purity of the products and recovery and reutilization of the heterogeneous catalyst.     

Shaping Polymer Particles by Carbon Nanotubes

We report the formation of poly(propylene) spherical and ellipsoidal particles templated by carbon nanotubes via solution crystallization. With an increase in nanotube loading, the particle shape changes from sphere to ellipsoid. In the intermediate concentration range, both spherical and ellipsoidal shapes coexist. The particle size decreases with an increase in nanotube loading.

     

Immobile Pore-Water Storage Enhancement and Retardation of Gas Transport in Fractured Rock

Wet tensile testing is a common method to assess the stability of bentonite-bonded moulding sands. For wet tensile testing, a specimen is first heated from above in order to simulate heat-driven moisture transport induced by the casting process. Then, tensile stress is applied until rupture. In this study, neutron radiography imaging was applied to moulding sands in situ during heating and wet tensile testing in order to investigate the effects of water kinematics on the tensile strength. Neutron radiography allowed the localization of the rupture plane and the quantitative determination of the local water content with sub-mm resolution. Quantification of the temperature at the rupture plane and of the heat kinematics within the specimen was accomplished by temperature measurements both in situ and ex situ. In this way, experimental data correlating the wet tensile strength with the specific conditions of moulding sands at the rupture plane were obtained for the first time. Series of experiments with different initial sand moisture contents were conducted. The results show that the weakest location within a sand profile can be pinpointed at the interface between evaporation and condensation zone (i.e. at the 100 \(^\circ \)C isotherm), where water vaporization starts and the water bridges connecting the sand grains collapse. This weakest location has maximum strength, if the local water content at the rupture plane is between 5 and 9 wt.%. Less water leads to a strong decrease of wet tensile strength. More water requires an initial water content above 5 wt.%, which leads to a decrease of the tensile strength of the unheated sand.     

Synthesis,Photoluminescence Behavior of Green Light Emitting Tb(III) Complexes and Mechanistic Investigation of Energy Transfer Process

A series of five new terbium(III) ion complexes with 4,4-difluoro-1-phenylbutane-1,3-dione (HDPBD) and anciliary ligands was synthesized. The composition and properties of complexes were analyzed by elemental analysis, IR, NMR, powder X-ray diffaraction, TG-DTG and photoluminescence spectroscopy. These complexes exhibited ligand sensitized green emission at 546 nm associated with ⁵D₄?→?⁷F₅ transitions of terbium ion in the emission spectra. The photoluminescence study manifested that the organic ligands act as antenna and facilitate the absorbed energy to emitting levels of Tb(III) ion efficiently. The enhanced luminescence intensity and decay time of ternary C2-C5 complexes observed due to synergistic effect of anciliary ligands. The CIE color coordinates of complexes came under the green region of chromaticity diagram. The mechanistic investigation of intramolecular energy transfer in the complexes was discussed in detail. These terbium(III) complexes can be thrivingly used as one of the green component in light emitting material and in display devices.

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Graphical Abstract Illustrate the sensitization process of the Tb ion and intramolecular energy transfer process in the Tb³⁺ complex.