Uncovering the physical origin of the difference between aliphatic chain and aromatic ring in the "hydrophobic" effects on partial molar volume

The partial molar volume changes in the transfer of several hydrophobic molecules, which are composed of aromatic rings and an aliphatic chain of different lengths, from carbon tetrachloride to water (DeltaV(hyd)) are calculated using the three-dimensional interaction site model theory of molecular solvation. The theory reproduces recent experimental observations: the addition of a methyl group decreases DeltaV(hyd); in contrast, the addition of an aromatic ring increases DeltaV(hyd). The discrepancy is found to originate from the difference between chain and ring structures rather than that between aliphaticity and aromaticity. Furthermore, a general rule of the variation in DeltaV(hyd) due to the addition of a hydrocarbon is found through the theoretical analysis. An outward addition at the trans position, which is to form chain structure, decreases DeltaV(hyd), while an inward addition at the cis position, which is to form ring structure, increases DeltaV(hyd). This is explained in terms of solvent packing rather than the so-called hydrophobic hydration. The present findings argue against the traditional idea that the hydrophobic hydration can be represented by the observed values of DeltaV(hyd).     

Enantioselective addition of terminal alkynes to aldehydes catalyzed by a Cu(I)-TRAP complex

The addition of terminal alkynes to aromatic aldehydes was carried out under mild conditions in the presence of a Cu-phosphine complex, which was prepared in situ from Cu(O-t-Bu) and TRAP chiral bisphosphine, to yield enantiomerically enriched propargyl alcohols with moderate enantioselectivities. Furthermore, according to stoichiometric reactions, the reaction presumably involves the addition of a TRAP-coordinated Cu(I) acetylide to an aldehyde.     

Preferential orientation of crystallites spatially confined in lamellar microdomains of polyethylene‐block‐[atactic poly(propylene)]

Synchrotron small angle X‐ray scattering (SAXS), wide angle X‐ray scattering (WAXS), and transmission electron microscopy were carried out for an oriented polyethylene‐block‐[atactic poly(propylene)] with a molecular weight of 1.13×10⁵ and a volume fraction of polyethylene of 0.5. Isothermal crystallization at 93°C did not destroy the pre‐formed microdomain, however, with a higher crystallization temperature, the microdomain was more heavily deformed and more crystalline lamella grew. In WAXS profiles, preferential orientation of (020) reflection peak was observed, indicating that the crystalline lamella grew in parallel with the micro domain interface.     

Efficient Method for the Elongation of the N‐Acetylglucosamine Unit by Combined Use of Chitinase and β‐Galactosidase

A novel strategy for the regio‐ and stereoselective synthesis by two enzymatic steps of oligosaccharides having an N‐acetylglucosamine unit at the nonreducing end was developed. The first step involves a chitinase‐catalyzed highly selective β‐N‐acetyllactosamination of an oligosaccharide acceptor with a 4,5‐dihydrooxazole derivative of N‐acetyllactosamine as the glycosyl donor. The usage of a transition‐state‐analogue substrate for the chitinase under basic conditions allows the reaction to proceed only in the synthetic direction while suppressing hydrolysis of the product in aqueous media. Several chitinase mutants also catalyzed the glycosylation efficiently under neutral conditions. The second step is a regioselective cleavage of the glycosidic bond between the terminal galactose unit and the adjacent N‐acetylglucosamine unit by the action of a β‐galactosidase. This constitutes a very useful method to add an N‐acetylglucosamine unit to the nonreducing end of chito‐ and cello‐oligosaccharide derivatives in a regio‐ and stereoselective manner.     

Using triethynylphosphine ligands bearing bulky end caps to create a holey catalytic environment: application to gold(I)-catalyzed alkyne cyclizations

The synthesis, properties and catalytic uses of phosphinoalkynes bearing bulky end caps at the alkyne termini, that is, tris[(triarylsilyl)ethynyl]phosphines are reported. The most salient feature of the new phosphines is the holey molecular shape possessing a deep and large-scale metal-binding cavity. The holey phosphines displayed remarkable rate enhancement in the gold(I)-catalyzed six- and seven-membered ring forming cyclizations of acetylenic keto esters and 1,7-enynes. It is proposed that the cavity in the ligand forces a nucleophilic center (enol or alkene) of the acetylenic compounds close to the gold-bound alkyne, making ring-closing anti attack feasible.