An evaluation of amide group planarity in 7-azabicyclo[2.2.1]heptane amides. Low amide bond rotation barrier in solution

Here we show that amides of bicyclic 7-azabicyclo[2.2.1]heptane are intrinsically nitrogen-pyramidal. Single-crystal X-ray diffraction structures of some relevant bicyclic amides, including the prototype N-benzoyl-7-azabicyclo[2.2.1]heptane, exhibited nitrogen-pyramidalization in the solid state. We evaluated the rotational barriers about the amide bonds of various N-benzoyl-7-azabicyclo[2.2.1]heptanes in solution. The observed reduction of the rotational barriers of the bicyclic amides, as compared with those of the monocyclic pyrrolidine amides, is consistent with a nitrogen-pyramidal structure of 7-azabicyclo[2.2.1]heptane amides in solution. A good correlation was found between the magnitudes of the rotational barrier of N-benzoyl-7-azabicyclo[2.2.1]heptanes bearing para-substituents on the benzoyl group and the Hammett's sigma(p)(+) constants, and this is consistent with the similarity of the solution structures. Calculations with the density functional theory reproduced the nitrogen-pyramidal structures of these bicyclic amides as energy minima. The calculated magnitudes of electron delocalization from the nitrogen nonbonding n(N) orbital to the carbonyl pi orbital of the amide group evaluated by application of the bond model theory correlated well with the rotational barriers of a variety of amides, including amides of 7-azabicyclo[2.2.1]heptane. The nonplanarity of the amide nitrogen of 7-azabicyclo[2.2.1]heptanes would be derived from nitrogen-pyramidalization due to the CNC angle strain and twisting of the amide bond due to the allylic strain.     

CO hydrogenation on a highly loaded Rh/TiO2 catalyst and the influence of strong metal-support interaction

The CO hydrogenation on a highly loaded (25 wt.%) Rh/TiO₂ catalyst was investigated after reduction at 573 K and 723 K. Chemisorption measurements show that the Rt/TiO₂ ratio is in the SMSI state after the high temperature reduction. The catalytic activity is significantly lower in the SMSI state than after reduction at low temperature. The selectivity of CO hydrogenation is changed in the SMSI state to higher hydrocarbons

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CO Rh/TiO₂ (25 .%) 573 723 . , Rh/TiO₂ . , , .

     

Synthesis of a new tetrazolium salt giving a water-soluble formazan and its application in the determination of lactate dehydrogenase activity

A pyridine analog of 3-(4-,5dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide was synthesized. The new reagent, 2-phenyl-3-(4,5-dimethyl-2-thiazolyl)-5-(4-pyridyl)tetrazolium bromide, gave a water-soluble formazan dye on enzymatic reduction and was applied in the spectrophotometric determination of lactate dehydrogenase (0–84 mU ml^?1) in blood serum. The sensitivity (? = 1.83 × 10⁴ l mol cm^?1 at 539 nm) was about 70% of that obtainable with nitrotetrazolium blue.     

Stereospecific Syntheses of 5-Alkyl-3-ethoxy-2-((phenylchalcogeno)methylene)tetrahydrofurans

2-Ethoxy-4-(phenylchalcogeno)but-3-ynyl ketones 1-10 were reduced with LiBH(4) in Et(2)O diastereoselectively to give 5-(phenylchalcogeno)pent-4-yn-1-ols 11-20. Treatment of the phenylchalcogen-substituted alkynyl alcohols 11-20 with t-BuOK in t-BuOH provided useful (Z)-2-((phenylchalcogeno)methylene)tetrahydrofurans 21-31 stereoselectively.     

Evaluation of the dynamic properties of polymer latex particles interacting with quartz interface by evanescent wave dynamic light scattering

The diffusion behavior of polymer latex particles in dispersion near the quartz interface has been estimated by evanescent wave dynamic light scattering (EVDLS) technique. The diffusion coefficient of the particles was measured as a function of the distance between the particle and interface. The apparent diffusion coefficient estimated by EVDLS was small for particles near the interface and increased upon increasing the distance from the interface, and then saturated at a certain value which is close to the value expected for free-motion. The range of the distance over which diffusion was affected by interaction with the interface depended on the added salt concentration. This means that the diffusion of the particle is influenced by an electrostatic interaction between the particle and quartz interface in addition to the hydrodynamic effect near the wall. This range was found to be more than 800?nm at 0?M salt condition but about 400?nm at 10^-4 and 10^-3?M salt conditions. Hence it is appropriate to say that the hydrodynamic effect reaches up to 400?nm and the electrostatic effect is longer ranged, more than 800?nm, for the system studied here. The EVDLS technique is a very powerful tool for quantitative estimations of the dynamic behavior of the particle near the interface and for estimation of the range where the wall effect is dominant. EVDLS will give us an answer to the question of “where is the ‘interface’ and where is the ‘bulk’?”.     

Synthesis of poly(vinyl alcohol)-based poly(crown ether)s and permeability of their polymeric membranes

Polymers that contain crown ether moieties at the side chain and are capable of forming rather tough film were synthesized by the polymer reaction of poly(vinyl alcohol) with formyl derivatives of aliphatic crown ethers such as 12-crown-4, 15-crown-5, and 18-crown-6. In the passive transport of alkali metal picrates across the poly(crown ether) membranes the permeation, particularly of alkali metals which tend to form intramolecular sandwich-type complexes with the crown ether rings, was retarded, compared with a poly(vinyl alcohol) membrane. The cation selectivities in the permeation of poly(crown ether) membranes differed significantly from those of poly(vinyl alcohol).     

Synthesis of aminocyclohexitol via carbon-carbon bond-forming radical cyclization of oxime ether

The stannyl radical mediated-cyclization of oxime ether, derived from D-glucose, gave the aminocyclohexitol derivative. Stereoselective C-C bond forming cyclization proceeded via favorable conformers minimizing A(1,3)-strain between the oxime ether group and alpha-substituents.     

Experimental and computational study of the electronic structural changes in LiTi2O4 spinel compounds upon electrochemical Li insertion reactions

Electronic structural changes in LiTi(2)O(4) spinel compounds upon electrochemical lithium insertions were investigated by X-ray absorption spectroscopy (XAS) measurements and first principles calculations based on spin-polarized density functional theory. Ti K-edge, O K-edge XAS spectra and theoretical calculations indicate that oxide ions as well as titanium ions are involved in electronic structural changes caused by electrochemical lithium ion insertions. The considerable effect of the oxide ions in the early 3d transition metal (titanium) oxide system is discussed in this article.     

A facile structural rearrangement to unprecedented mu 2-eta 6:eta 6-bis(cyclopentadienylidene)ethene diruthenium complexes in the oxidation of 1,2-bis(ruthenocenyl)ethynes

The two-electron oxidation of 1,2-bis(ruthenocenyl)ethynes and bis(1',2',3',4',5'-pentamethylruthenocenyl)ethynes, prepared from alkyne metathesis of the corresponding propynes, gave the unprecedented mu 2-eta 6:eta 6-bis(cyclopentadienylidene)ethene diruthenium complexes.