Lewis acid-catalyzed stereospecific ring expansion of aziridine-2-carboxylates to imidazolidin-2-ones

Lewis acid-catalyzed ring expansion reaction of chiral aziridine-2-carboxylate proceeds regio- and stereospecifically to yield enantiomerically pure 4-functionalized imidazolidin-2-ones in high yields.     

Enzymatic synthesis of novel quercetin sialyllactoside derivatives

Quercetin and its derivatives are important flavonols that show diverse biological activity, such as antioxidant, anticarcinogenic, anti-inflammatory, and antiviral activities. Adding different substituents to quercetin may change the biochemical activity and bioavailability of molecules, when compared to the aglycone. Here, we have synthesised two novel derivatives of quercetin, quercetin-3-O-β-d-glucopyranosyl, 4′′-O-d-galactopyranosyl 3′′′-O-α-N-acetyl neuraminic acid i.e. 3′-sialyllactosyl quercetin (3′SL-Q) and quercetin-3-O-β-d-glucopyranosyl, 4′′-O-β-d-galactopyranosyl 6′′′-O-α-N-acetyl neuraminic acid i.e. 6′-sialyllactosyl quercetin (6′SL-Q) with the use of glycosyltransferases and sialyltransferases enzymes. These derivatives of quercetin were characterised by high-resolution quadrupole-time-of-flight electrospray ionisation mass spectrometry (HR-QTOF-ESI/MS) and ¹H and ¹³C nuclear magnetic resonance (NMR) analyses.     

High-temperature defect structure and electrical conduction in Ni1−xMgxO

The ionic transference number, the electrical conductivity, and Seebeck coefficient of Ni_1?xMg_xO (0.1 ≤ x ≤ 0.9) were measured as functions of temperature (900–1400°C) and oxygen partial pressure (10²–10⁵ Pa). The contribution of ionic conduction to the total conductivity of Ni_0.9Mg_0.1O was of the order of 10^?3?10^?2 at 900–1300°C, which led us to assume that the electronic conduction was predominating in Ni_1?xMg_xO (x ≤ 0.9). The electrical conductivities of both undoped and Al-doped Ni_1?xMg_xO depended on the $\text{1}\text{4}$ power of P_O2, which indicated a significant impurity effect on the defect equilibria and was interpreted as showing that doubly ionized cation vacancies were the dominant point defects at high temperatures. Analyses of the difference in the temperature dependences of conductivity and Seebeck coefficient showed that band-like conduction took place in the NiO-rich composition range (x ≤ 0.1), while thermally activated hopping of small polarons occurred in Ni_1?xMg_xO with x ≥ 0.3. The calculated drift mobility abruptly decreased in the composition region where the conduction mechanism changed.     

Synthesis of Ru(II) complexes of N-heterocyclic carbenes and their promising photoluminescence properties in water

Novel complexes 1 and 2 based on N-heterocyclic carbenes, which are analogous to Ru(bpy)(3)(2+) and Ru(terpy)(2)(2+), respectively, were synthesized. The complex, which is analogous to Ru(terpy)(2)(2+), exhibited promising photoluminescence properties with a long lifetime of 820 ns in acetonitrile and 3100 ns in water at room temperature, respectively. In addition, ab initio calculations were carried out.     

Excited-state tautomerization dynamics of 7-hydroxyquinoline in beta-cyclodextrin

The excited-state tautomerization dynamics of 7-hydroxyquinoline encapsulated in beta-cyclodextrin is compared with that in pure water by measuring isotope-dependent fluorescence kinetics as well as absorption and emission spectra. The normal species tautomerizes stepwise via forming anionic intermediate species in both systems. However, the enol-deprotonation time (40 ps in water) becomes as large as 170 ps whereas the imine-protonation time of the anionic intermediate (160 ps in water) becomes as short as 85 ps in beta-cyclodextrin. The slow formation and the fast decay of the anionic species are attributed to the unstability of the charged species in hydrophobic cages. Encapsulation can be utilized to enhance fluorescence enormously and to accelerate selective reactions by retarding other processes.     

Turning the [Ru(bpy)2dppz]2+ light-switch on and off with temperature

We report temperature-dependent excited-state lifetime measurements on [Ru(bpy)(2)dppz](2+) in both protic and aprotic solvents. These experiments yield a unifying picture of the excited-state photophysics that accounts for observations in both types of solvent. Our measurements support the notion of bpy-like and phz-like states associated with the dppz ligand and show that the ligand orbital associated with the bright state is similar in size to the corresponding orbital in the (3)MLCT state of [Ru(bpy)(3)](2+). In contrast to the current thinking, the experiments presented here indicate that the light-switch effect is not driven by a state reversal. Rather, they suggest that the dark state is always lowest in energy, even in aprotic solvents, and that the light-switch behavior is the result of a competition between energetic factors that favor the dark state and entropic factors that favor the bright (bpy) state.     

Syntheses of functionalized thieno[3,4-d]imidazoles and thieno[3,2-d]pyrimidines from chlorine-containing enamidonitriles

Enamidonitriles of the general formula Cl(X)C=C(CN)NHCOR readily react with methyl sulfanylacetate to give tri-or tetra-substituted thiophenes, which can be converted into new functional derivatives of thieno[3,2-d]pyrimidine and thieno[3,4-d]imidazole.     

Rhodium-catalyzed reductive cyclization of 1,6-diynes and 1,6-enynes mediated by hydrogen: catalytic C-C bond formation via capture of hydrogenation intermediates

Catalytic hydrogenation of carbon-, nitrogen- and oxygen-tethered 1,6-diynes 1a-9a and 1,6-enynes 10a-18a using cationic Rh(I) precatalysts at ambient temperature and pressure enables reductive carbocyclization to afford 1,2-dialkylidene cyclopentanes 1b-9b and monoalkylidene cyclopentanes 10b-18b, respectively, in good to excellent yields and as single alkene stereoisomers. Notably, the 1,3-diene and alkene containing cyclization products 1b-9b and 10b-18b are not subject to over-reduction under the conditions of catalytic hydrogenation in which they are formed. Reductive cyclization 1,6-diyne 1a and 1,6-enyne 10a performed under an atmosphere of D(2) provides the carbocyclization products deuterio-1b and deuterio-10b, respectively, which incorporate two deuterium atoms. The collective data are consistent with a catalytic mechanism involving heterolytic activation of elemental hydrogen (H(2) + Rh(+)X(-) --> Rh-H + HX) followed by Rh(I)-mediated oxidative cyclization of the 1,6-diyne or 1,6-enyne substrates to afford (hydrido)Rh(III)-based metallocyclopentadiene and metallocyclopentene intermediates, respectively. These transformations represent the first examples of metal-catalyzed reductive carbocyclization mediated by hydrogen.     

Photochemical modification of polymer surface by the pendant photobase generator containing oxime‐urethane groups and its application to an image‐recording material

Copolymers containing oxime‐urethane groups were prepared by the copolymerization of methyl methacrylate and benzophenoneoximinocarbonylaminoethyl methacrylate (BCM), and their photochemical properties were examined from the UV and IR absorption spectral changes. The decomposed fraction of oxime‐urethane groups in the copolymer increased with irradiation time, but it decreased with the content of BCM units in the copolymer. Changes of the surface properties of the copolymer film on irradiation were studied by measurements of the contact angle and dyeing with an acid dye. The surface of the copolymer film changed to become more hydrophilic upon irradiation with 254 nm of UV light. After the irradiated copolymer films were treated with HCl or methanol, changes of the contact angle of water on irradiation were compared. The copolymer film was dyed by acid dyes after treatment of the irradiated film with HCl. The degree of dyeing increased with irradiation time and BCM units in the copolymer, but it was unaffected by the film thickness. Various colors were developed on the irradiated area depending on the acid dye as the developer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1200–1207, 2002