Separation of Linear and Branched Alkanes Using Host–Guest Complexation of Cyclic and Branched Alkane Vapors by Crystal State Pillar[6]arene

Activated crystals of pillar[6]arene produced by removing the solvent upon heating were able to take up branched and cyclic alkane vapors as a consequence of their gate‐opening behavior. The uptake of branched and cyclic alkane vapors by the activated crystals of pillar[6]arene induced a crystal transformation to form one‐dimensional channel structures. However, the activated crystals of pillar[6]arene hardly took up linear alkane vapors because the cavity size of pillar[6]arene is too large to form stable complexes with linear alkanes. This shape‐selective uptake behavior of pillar[6]arene was further utilized for improving the research octane number of an alkane mixture of isooctane and n‐heptane: interestingly, the research octane number was dramatically improved from a low research octane number (17 %) to a high research octane number (>99 %) using the activated crystals of pillar[6]arene.     

Host–Guest Complexation Using Pillar[5]arene Crystals: Crystal-Structure Dependent Uptake,Release, and Molecular Dynamics of an Alkane Guest

Host–guest complexation has been mainly investigated in solution, and it is unclear how guest molecules access the assembled structures of host and dynamics of guest molecules in the crystal state. In this study, we studied the uptake, release, and molecular dynamics of n-hexane vapor in the crystal state of pillar[5]arenes bearing different substituents. Pillar[5]arene bearing 10 ethyl groups yielded a crystal structure of herringbone-type 1:1 complexes with n-hexane, whereas pillar[5]arene with 10 allyl groups formed 1:1 complexes featuring a one-dimensional (1D) channel structure. For pillar[5]arene bearing 10 benzyl groups, one molecule of n-hexane was located in the cavity of pillar[5]arene, and another n-hexane molecule was located outside of the cavity between two pillar[5]arenes. The substituent-dependent differences in molecular arrangement influenced the uptake, release, and molecular dynamics of the n-hexane guest. The substituent effects were not observed in host–guest chemistry in solution, and these features are unique for the crystal state host–guest chemistry of pillar[5]arenes.     

Copper‐Catalyzed Reaction of Trifluoromethylketones with Aldehydes via a Copper Difluoroenolate

A copper‐catalyzed reaction of easily accessible α,α,α‐trifluoromethylketones with various aldehydes affords difluoro‐methylene compounds in the presence of diboron and NaOtBu. The key process of the reaction is the formation of a copper difluoroenolate by 1,2‐addition of a borylcopper intermediate to α,α,α‐trifluoromethylketones and subsequent β‐fluoride elimination. Mechanistic studies including the isolation and characterization of a possible anionic copper alkoxide intermediate are also described.     

Intramolecular hydrogen bond in enol form of 3-substituted-2,4-pentanedione

The 3-substituent effect on the enolic ring of 2,4-pentanedione has been investigated. A linear relationship between the chemical shifts of the enolic proton and the chelated carbonyl stretching vibrations has been found for the various highly enolized 3-substituted-2,4-pentanediones. The stronger electron-withdrawing resonance effect of the substituent at 3-position results in the lower magnetic field shift of the enolic proton and the lower frequency shift of the chelated carbonyl stretching. Semi-empirical Hückel calculations have been performed to enable discussion of the electronic effect of the substituents.     

Structural Characterization of Chemical Species in Solution by a Theoretical Analysis of XANES Spectra

A theoretical analysis method using a discrete variational X (DV-X) molecular orbital (MO) calculation, based on electron transition from an inner orbital to an unoccupied orbital, is introduced to analyze X-ray absorption near-edge structure (XANES) spectra in a lower energy region below the X-ray absorption edge. The computational procedure is described in detail and the evaluation of an obtained result is also explained. Applications of this method are presented for Cu(II) ions in liquid ammonia, macrocyclic Cu(II) complex in aqueous solution, and Al(III) ions in aqueous solution.     

Non‐Covalent Interactions Enable the Length‐Controlled Generation of Discrete Tubes Capable of Guest Exchange

Supramolecular chemistry in confined spaces constructed from macrocyclic molecules has attracted much attention because it can utilize the specific binding properties of macrocyclic cavities. Herein we report the preparation of length‐controlled discrete tubular structures by homo‐/co‐assembly of rim‐differentiated and peralkylamino‐substituted pillar[5]arenes via hydrogen bonds and salt bridges. By dimerization and trimerization, the expanded tubes show a fivefold helical structure and stepwise binding, respectively. We found that the exchange speed of guest molecules in the tubes could be controlled by varying the tube length.     

Measurements of kineic parameters of inorganic pyrophosphatase by flow-injection procedures

Two flow-injection systems were designed for characterizing the enzymatic hydrolysis of pyrophosphate by inorganic pyrophosphatase (EC 3.6.1.1). By using a molybdenum(VI) reagent the selective determination of a product, orthophosphate, in the presence of pyrophosphate was made. An anion exchange column was employed for the simultaneous determination of both the substrate and the product with a molybdenum(V)/molybdenum(VI) reagent. The effects of magnesium concentration and reaction temperature on the enzyme activity were determined. The Michaelis constant and maximum velocity at 25°C and pH 7.2 were evaluated. K_m was ca. 3 μM.