Multi-selective one dimensional proton NMR experiments for rapid screening and binding affinity measurements

High-throughput ligand-based proton NMR screening performed in the presence of a spy molecule and a control molecule is a valuable tool for identifying drug leads. A limitation of the technique is represented by the severe overlap encountered in the screening of large chemical mixtures. An approach for overcoming this overlap problem is the use of multi-selective R(1) filtered and COSY or TOCSY experiments. Application of this methodology to compounds binding to the Sudlow site I of human serum albumin is presented. The screening is performed by simply monitoring the intensity of two signals. The precise measurement of the relative intensity of the two resonances permits determination of the binding constant of the NMR-hit. For a simple competition binding mechanism, the rapidly-derived NMR binding constants are in good agreement with the values derived from full-titration ITC and fluorescence spectroscopy measurements.     

Enhanced thermal properties and flame retardancy from a thermosetting blend of a phosphorus‐containing bismaleimide and epoxy resins

Epoxy resins modified by an organosoluble phosphorus‐containing bismaleimide (3,3′‐bis(maleimidophenyl) ­phenylphosphine oxide; BMPPPO) were prepared by simultaneously curing epoxy/diaminodiphenylmethane (DDM), and BMPPPO. The resulted epoxy resins were found to exhibit glass transition temperatures as high as 212 °C, thermal stability at temperatures over 350 °C, and excellent flame retardancy with Limited oxygen index (LOI) values around 40. Incorporation of BMPPPO into epoxy resins via the thermosetting blend was demonstrated to be an effective way to enhance the thermal properties and flame retardancy simultaneously. Copyright © 2003 John Wiley & Sons, Ltd.     

n-Hexane dehydrocyclization over Pt?Ni supported on alumina catalysts

Pt–Ni/-Al₂O₃ catalysts have been prepared and studied in n-hexane dehydrocyclization. The selectivity for benzene and toluene, a chain lengthening product formation was improved by Ni and correlated with its content.

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Pt–Ni/-Al₂O₃ -. Ni . Ni , .

     

Theoretical investigation of the mechanisms of reaction of NCN with NO and NS

Quantum-chemical calculations were performed on the mechanisms of reaction of NCN with NO and NS. Possible mechanisms were classified according to four pathways yielding products in the following four possible groups: N2O/N2S + CN, N2 + NCO/NCS, N2 + CNO/CNS, and CNN + NO/NS, labeled in order from p1/p1s to p4/p4s. The local structures, transition structures, and potential-energy surfaces with respect to the reaction coordinates are calculated, and the barriers are compared. In the NCN + NO reaction, out of several adduct structures, only the nitroso adduct NCNNO lies lower in energy than the reactants, by 21.89 kcal/mol; that adduct undergoes rapid transformation into the products, in agreement with experimental observation. For the NS counterpart, both thionitroso NCNNS and thiazyl NCNSN adducts have energies much lower than those of the reactants, by 43 and 29 kcal/mol, respectively, and a five-membered-ring NCNNS (having an energy lower than those of the reactants by 36 kcal/mol) acts as a bridge in connecting these two adducts. The net energy barriers leading to product channels other than p4s are negative for the NS reaction, whereas those for the NO analogue are all positive. The channel leading to p1 (N2O + CN) has the lowest energy (3.81 kcal/mol), whereas the channels leading to p2 (N2 + NCO) and p2s (N2 + NCS) are the most exothermic (100.94 and 107.38 kcal/mol, respectively).     

Kinetically controlled Ag+-coordinated chiral supramolecular polymerization accompanying a helical inversion

We report kinetically controlled chiral supramolecular polymerization based on ligand–metal complex with a 3 : 2 (L : Ag⁺) stoichiometry accompanying a helical inversion in water. A new family of bipyridine-based ligands (d-L1, l-L1, d-L2, and d-L3) possessing hydrazine and d- or l-alanine moieties at the alkyl chain groups has been designed and synthesized. Interestingly, upon addition of AgNO₃ (0.5–1.3 equiv.) to the d-L1 solution, it generated the aggregate I composed of the d-L1AgNO₃ complex (d-L1 : Ag⁺ = 1 : 1) as the kinetic product with a spherical structure. Then, aggregate I (nanoparticle) was transformed into the aggregate II (supramolecular polymer) based on the (d-L1)₃Ag₂(NO₃)₂ complex as the thermodynamic product with a fiber structure, which led to the helical inversion from the left-handed (M-type) to the right-handed (P-type) helicity accompanying CD amplification. In contrast, the spherical aggregate I (nanoparticle) composed of the d-L1AgNO₃ complex with the left-handed (M-type) helicity formed in the presence of 2.0 equiv. of AgNO₃ and was not additionally changed, which indicated that it was the thermodynamic product. The chiral supramolecular polymer based on (d-L1)₃Ag₂(NO₃)₂ was produced via a nucleation–elongation mechanism with a cooperative pathway. In thermodynamic study, the standard ΔG° and ΔH_e values for the aggregates I and II were calculated using the van''t Hoff plot. The enhanced ΔG° value of the aggregate II compared to that of the formation of aggregate I confirms that aggregate II was thermodynamically more stable. In the kinetic study, the influence of concentration of AgNO₃ confirmed the initial formation of the aggregate I (nanoparticle), which then evolved to the aggregate II (supramolecular polymer). Thus, the concentration of the (d-L1)₃Ag₂(NO₃)₂ complex in the initial state plays a critical role in generating aggregate II (supramolecular polymer). In particular, NO₃⁻ acts as a critical linker and accelerator in the transformation from the aggregate I to the aggregate II. This is the first example of a system for a kinetically controlled chiral supramolecular polymer that is formed via multiple steps with coordination structural change.

The nanoparticles were transformed into the supramolecular polymer as the thermodynamic product, involving a helical inversion from left-handed to right-handed helicity.     

Sustainable biorefinery processes using renewable deep eutectic solvents

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Investigation of m-nitroaniline formation during the Zimmermann reaction

The Zimmermann reaction for the determination of 17-ketosteroids was tested under both room-temperature and steam-distillation reaction conditions. meta-Nitroaniline was isolated from the residue of the steam distillation by ether extraction and thin-layer chromatography. Conclusive identification was by infrared spectroscopy. In contrast, m-nitroaniline was not formed under room-temperature reaction conditions, even when allowed to react for 24 hr. Similar results were also obtained for the reaction between acetone and m-dinitrobenzene under alkaline conditions. In conclusion, the results indicate that m-nitroaniline formation cannot account for the conversion of structure I to structure II under room-temperature reaction conditions as investigated herein.     

Reactions of cobalt clusters with deuterium

The kinetics of chemical reactions of cobalt clusters Co_n with deuterium are described. Absolute rate constants have been measured in the size range n=7–68 at 293 K. The rate constants are found to be a strong function of cluster size, varying by a factor of 400. This size dependence is most prominent for n=7 to 25: Co₁₅ is the most reactive cluster, and Co_7–9 and Co_19–20 are particularly unreactive. Abrupt changes in the rate constants from one cluster size to the next are observed. For the clusters above n=25, the rate constants show several less prominent maxima and minima superimposed on a slow, nearly monotonic increase with cluster size.     

Role of tin in a PtSb alloy and a Pt-Sn/Al2O3 reforming catalyst

The conversion of n-hexane was studied on a Pt-Sn/Al₂O₃ catalyst, a PtSn alloy and on the corresponding Pt catalysts. The results indicate the same catalytic effect of tin in supported and unsupported catalysts. It is concluded that the role of tin is connected with alloy formation.

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- Pt-Sn/Al₂O₃, PtSn Pt-. . , .