On the magnetic non-equivalence of methylene protons in some propane derivatives, and its variation with solvent and temperature

The magnetic non-equivalence, δ ab, of methylene protons in 1,2-disubstituted and 1,2,3-trisubstituted propanes (same substituent) shows a marked dependence on solvent and temperature that allows a correlation with conformational equilibrium. Results indicate that symmetry is a necessary, but not a sufficient, condition for observation of δ ab. Factors that affect rotamer population such as medium, temperature, and nature of substituents, contribute substantially to the magnitude of δ ab.     

Polymeric alkenoxy amino acid surfactants: II. Chiral separations of beta-blockers with multiple stereogenic centers

Two amino acid-based (leucine and isoleucine) alkenoxy micelle polymers were employed in this study for the separation of multichiral center-bearing beta-blockers, nadolol and labetalol. These polymers include polysodium N-undecenoxy carbonyl-L-leucinate (poly-L-SUCL) and polysodium N-undecenoxy carbonyl-L-isoleucinate (poly-L-SUCIL). Detailed synthesis and characterization were reported in our previous paper [26]. It was found that poly-L-SUCIL gives better chiral separation than poly-L-SUCL for both nadolol and labetalol isomers. The use of 50-100 mM poly-L-SUCIL as a single chiral selector provided separation of four and three isomers of labetalol and nadolol, respectively. Further optimization in separation of both enantiomeric pairs of nadolol and labetalol was achieved by evaluation of type and concentration of organic solvents, capillary temperature as well type and concentration of cyclodextrins. A synergistic approach, using a combination of poly-L-SUCIL and sulfated beta-CD (S-beta-CD) was evaluated and it showed dramatic separation for enantiomeric pairs of nadolol. On the other hand for labetalol enantiomers, separation was slightly decreased or remain unaffected using the dual chiral selector system. Finally, simultaneous separation of both nadolol and labetalol enantiomers was achieved in a single run using 25 mM poly-L-SUCIL and 5% w/v of S-beta-CD in less then 35 min highlighting the importance of high-throughput chiral analysis.     

Copper and nickel immobilized on cytosine@MCM-41: as highly efficient,reusable and organic–inorganic hybrid nanocatalysts for the homoselective synthesis of tetrazoles and pyranopyrazoles

In this work, a green approach is reported for efficient synthesis of biologically active tetrazole and pyranopyrazole derivatives in the presence of Cu-Cytosine@MCM-41 and Ni-Cytosine@MCM-41 (copper (II) and nickel (II) catalyst on the modified MCM-41 using cytosine). The synthesis of tetrazoles and pyranopyrazoles in the presence of these catalysts was performed in green solvents such as water or poly (ethylene glycol) (PEG). All products were obtained in high TOF (turnover frequency) numbers in the presence of these catalysts, which indicate the high efficiency of these catalysts in the synthesis of tetrazole and pyranopyrazole derivatives. The prepared catalysts were characterized by various techniques such as BET, TGA, XRD, FT-IR, SEM, EDS, WDX, TEM, and AAS. Mesoporous structure of these catalysts was confirmed by nitrogen adsorption–desorption isotherms. These catalysts can be recovered and reused for several runs without significant change in their catalytic activity or metal capacity. The recovered catalysts have been characterized by XRD, SEM, EDS, WDX, FT-IR and AAS techniques, by which their heterogeneous nature has been confirmed.