Hydride-alkenylcarbyne to alkenylcarbene transformation in bisphosphine-osmium complexes

The elongated dihydrogen complex [formula: see text](1) reacts with 1,1-diphenyl-2-propyn-1-ol and 2-methyl-3-butyn-2-ol to give the hydride-hydroxyvinylidene-pi-alkynol derivatives [OsH{=C=CHC(OH)R2}{eta2-HC(triple bond)CC(OH)R2}(PiPr3)2]BF4 (R = Ph (2), Me (3)), where the pi-alkynols act as four-electron donor ligands. Treatment of 2 and 3 with HBF(4) and coordinating solvents leads to the dicationic hydride-alkenylcarbyne compounds [OsH((triple bond)CCH=CR2)S2(PiPr3)2][BF4]2 (R = Ph, S = H(2)O (4), CH(3)CN (5); R = Me, S = CH(3)CN (6)), which in acetonitrile evolve into the alkenylcarbene complexes [Os(=CHCH=CR2)(CH3CN)3(PiPr3)2][BF4](2) (R = Ph (7), Me (8)) by means of a concerted 1,2-hydrogen shift from the osmium to the carbyne carbon atom. Treatment of 2-propanol solutions of 5 with NaCl affords OsHCl2((triple bond)CCH=CPh2)(PiPr3)2 (10), which reacts with AgBF(4) and acetonitrile to give [OsHCl((triple bond)CCH=CPh2)(CH3CN)(PiPr3)2]BF(4) (11). In this solvent complex 11 is converted to [OsCl(=CHCH=CPh2)(CH3CN)2(PiPr3)2]BF(4) (12). Complex 5 reacts with CO to give [Os(=CHCH=CPh2)(CO)(CH3CN)2(PiPr3)2][BF(4)](2) (15). DFT calculations and kinetic studies for the hydride-alkenylcarbyne to alkenylcarbene transformation show that the difference of energy between the starting compounds and the transition states, which can be described as eta(2)-carbene species [formula: see text] increases with the basicity of the metallic center. The X-ray structures of 4 and 7 and the rotational barriers for the carbene ligands of 7, 8, and 12 are also reported.     

Modeling of adsorption and ultrasonic desorption of cadmium(II) and zinc(II) on local bentonite

The adsorption and ultrasonic desorption of toxic heavy metal cations (i.e., Cd(II) and Zn(II)) on natural bentonite have been modeled with the aid of a factorial design approach. The ability of untreated bentonite to remove Cd(II) and Zn(II) from aqueous and acidic solutions at different pH values has been studied for different metal concentrations by varying the amount of adsorbent, temperature, stirring speed, and contact time. The same factors, except stirring speed and metal concentration, were applied in desorption study. Ultrasound power was used for desorption instead of stirring speed. A flame atomic absorption spectrometer was used to measure the cadmium and zinc concentration before and after both experimental study. The highest adsorption for Zn and Cd was 99.85 and 96.84%, respectively, and the highest desorption for Zn and Cd obtained was 66.57 and 51.37%, respectively. It is believed that the models obtained for adsorption and desorption may provide a background for detailed mechanism searches and pilot and industrial scale applications.     

Student Interest in Engineering Design‐Based Science

Current reform efforts in science education around the world call on teachers to use integrated approaches to teach science. As a part of such reform efforts in the United States, engineering practices and engineering design have been identified in K–12 science education standards. However, there is relatively little is known about effective ways of teaching science through engineering design. The study explores the approaches or strategies used by a sixth grade science teacher to teach science and engineering in an integrative manner. Classroom observations, teacher interview, and student surveys were used to study the features of engineering integration implemented by the teacher and the changes in student interest in science and engineering by participating in an engineering design‐based science unit. Findings suggest that the teacher explicitly included practices and core ideas from engineering and science; used an engaging, motivating engineering challenge; and provided students with opportunities to be autonomous. Students engaged in the activities in the engineering unit and their interest level slightly increased. The results suggest that the three strategies that the teacher used to teach engineering and science are important foundations of integrated science and engineering education.     

Small-molecule fluorophores to detect cell-state switching in the context of high-throughput screening

A small molecule capable of distinguishing the distinct states resulting from cellular differentiation would be of enormous value, for example, in efforts aimed at regenerative medicine. We screened a collection of fluorescent small molecules for the ability to distinguish the differentiated state of a mouse skeletal muscle cell line. High-throughput fluorescence-based screening of C2C12 myoblasts and myotubes resulted in the identification of six compounds with the desired selectivity, which was confirmed by high-content screening in the same cell states. The compound that resulted in the greatest fluorescence intensity difference between the cell states was used as the screening agent in a pilot screen of 84 kinase inhibitors, each present in four doses, for inhibition of myogenesis. Of the kinase inhibitors, 17 resulted in reduction of fluorescence at one or more concentrations; among the "hits" included known inhibitors of myogenesis, confirming that this compound is capable of detecting the differentiated myotube state. We suggest that the strategy of screening for screening agents reported here may be extended more broadly in the future.     

Experimental device for study of the thermal stimulated direct current in the composite materials

Journal of Thermal Analysis and Calorimetry - Presents the device for analysis the thermally stimulated electrical conductivity of composites in the wide temperature range. The main advantage of...     

Synthesis of new fluorogenic cyanine dyes and incorporation into RNA fluoromodules

A new fluorogenic cyanine dye was synthesized and found to have low fluorescence quantum yield in fluid solution and in the presence of double-stranded DNA but 80-fold enhanced fluorescence in viscous glycerol solution. An RNA aptamer selected for binding to the new dye exhibits K(d) = 87 nM and 60-fold fluorescence enhancement. The dye-aptamer pair is a fluoromodule that can be incorporated into fluorescent sensors and labels.     

Thermolysis of ammonium nitrate/potential donor of active chlorine compositions

The thermal stability of the ammonium nitrate (AN)/sodium salt of 1,3-dichlor-2,4,6-trioxo-1,3,5-triazacyclohexane (DC) composition has been studied. The factors of influence on the rates of reactions in the composition, namely, a water content, composition wetting methods, a dispersion of composition components, sample mass values, have been examined. The water presence in the composition reduces its thermal stability. The mechanism includes the partial dissociation of AN to HNO₃ and NH₃ and the hydrolysis of DC with the formation of some unstable Cl-containing compounds (chloramines, nitrogen chloride). The reaction of ammonium cation with active chlorine has been found to give rise to the explosion of the AN/DC composition. Such a situation is typical for other ammonium salt/DC compositions.     

Intramolecular sensitization of photocleavage of the photolabile 2-(2-nitrophenyl)propoxycarbonyl (NPPOC) protecting group: photoproducts and photokinetics of the release of nucleosides

Novel photolabile protecting groups based on the 2-(2-nitrophenyl)propoxycarbonyl (NPPOC) group with a covalently linked thioxanthone as an intramolecular triplet sensitizer exhibit significantly enhanced light sensitivity under continuous illumination. Herein we present a detailed study of the photokinetics and photoproducts of nucleosides caged with these new protecting groups. Relative to the parent NPPOC group, the light sensitivity of the new photolabile protecting groups is enhanced by up to a factor of 21 at 366 nm and is still quite high at 405 nm, the wavelength at which the sensitivity of the parent compound is practically zero. A new pathway for deprotection of the NPPOC group proceeding through a nitroso benzylalcohol intermediate has been discovered to complement the main mechanism, which involves beta elimination. Under standard conditions of lithographic DNA-chip synthesis, some of the new compounds, while maintaining the same chip quality, react ten times faster than the unmodified NPPOC-protected nucleosides.     

An amperometric biosensor based on multiwalled carbon nanotube-poly(pyrrole)-horseradish peroxidase nanobiocomposite film for determination of phenol derivatives

An amperometric biosensor based on horseradish peroxidase (HRP) and carbon nanotube (CNT)/polypyrrole (PPy) nanobiocomposite film on a gold surface has been developed. The HRP was incorporated into the CNT/PPy nanocomposite matrix in one-step electropolymerization process without the aid of cross-linking agent. Amperometric response was measured as a function of concentration of phenol derivatives, at a fixed bias voltage of -50 mV. Optimization of the experimental parameters was performed with regard to pH and concentration of hydrogen peroxide. The linear range, sensitivity and detection limit of the biosensor were investigated for eighteen phenol derivatives. The sensitivity in the linear range increased in this order: 4-methoxyphenol>2-aminophenol>guaiacol=m-cresol>2-chlorophenol=4-chlorophenol=hydroquinone=pyrocatechol>2,6-dimethoxyphenol>3-chlorophenol>p-cresol>p-benzoquinone=4-acetamidophenol>catechol>phenol=pyrogallol=2,4-dimethylphenol. CNTs was shown to enhance the electron transfer as a mediator and capable to carry higher bioactivity owing to its intensified surface area. The biosensor exhibited low detection limits with a short response time (2s) for the tested phenolics compared to the reported working electrodes. It retained 70% of its initial activity after using for 700 measurements in 1 month.     

Preparation of ribavirin analogues by copper- and ruthenium-catalyzed azide-alkyne 1,3-dipolar cycloaddition

In this study, we described the synthesis of 1,4- and 1,5-disubstituted-1,2,3-triazolo-nucleosides from various alkynes with 1′-azido-2′,3′,5′-tri-O-acetylribose using either copper-catalyzed azide-alkyne cycloaddition (CuAAC) or ruthenium-catalyzed azide-alkyne cycloaddition (RuAAC), respectively. Optimized RuAAC conditions were realized with the commercially available [Cp^∗RuCl(PPh₃)₂] under microwave heating, which allows a significant acceleration of the reaction times (from 6 h to 5 min). This reaction can work under water-containing system. RuAAC and CuAAC are useful tools for the synthesis of 1,2,3-triazolyl-nucleosides small libraries.